Preserve comments on map keys

Allows more sophisticated functionality

.github/FUNDING.yml

@@ -0,0 +1 @@
+github: mikefarah

.github/workflows/release.yml

@@ -40,17 +40,7 @@ jobs:
       IMAGE_NAME: mikefarah/yq
     runs-on: ubuntu-latest
     steps:
-      - name: Get latest release tag      
-        uses: oprypin/find-latest-tag@v1
-        with:
-          repository: mikefarah/yq  # The repository to scan.
-          releases-only: true  # We know that all relevant tags have a GitHub release for them.
-        id: yq  
-        
-      - name: Clone source code
-        uses: actions/checkout@v2
-        with:
-          ref: ${{ steps.yq.outputs.tag }}
+      - uses: actions/checkout@v2
       
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v1

README.md

@@ -90,7 +90,7 @@ docker run --rm -v "${PWD}":/workdir mikefarah/yq <command> [flags] [expression
 #### Run commands interactively:
 
 ```bash
-docker run --rm -it -v "${PWD}":/workdir mikefarah/yq sh
+docker run --rm -it -v "${PWD}":/workdir --entrypoint sh mikefarah/yq
 ```
 
 It can be useful to have a bash function to avoid typing the whole docker command:
@@ -103,7 +103,7 @@ yq() {
 
 ### Go Get:
 ```
-GO111MODULE=on go get github.com/mikefarah/yq
+GO111MODULE=on go get github.com/mikefarah/yq/v4
 ```
 
 ## Community Supported Installation methods

cmd/version.go

@@ -11,7 +11,7 @@ var (
 	GitDescribe string
 
 	// Version is main version number that is being run at the moment.
-	Version = "4.3.1"
+	Version = "4.5.0"
 
 	// VersionPrerelease is a pre-release marker for the version. If this is "" (empty string)
 	// then it means that it is a final release. Otherwise, this is a pre-release

examples/data1.yaml

@@ -1,4 +1,6 @@
-a: simple # just the best
-b: [1, 2]
-c:
-  test: 1
+a:
+  key1: "value1"
+  key2: 2.6
+  ab:
+    key1: 6
+    key2: "h"

github-action/Dockerfile

@@ -1,4 +1,4 @@
-FROM mikefarah/yq:4.3.1
+FROM mikefarah/yq:4.5.0
 
 COPY entrypoint.sh /entrypoint.sh
 

go.mod

@@ -1,14 +1,14 @@
 module github.com/mikefarah/yq/v4
 
 require (
-	github.com/elliotchance/orderedmap v1.3.0
+	github.com/elliotchance/orderedmap v1.4.0
 	github.com/fatih/color v1.10.0
-	github.com/goccy/go-yaml v1.8.4
-	github.com/jinzhu/copier v0.1.0
+	github.com/goccy/go-yaml v1.8.8
+	github.com/jinzhu/copier v0.2.3
 	github.com/spf13/cobra v1.1.1
 	github.com/timtadh/data-structures v0.5.3 // indirect
 	github.com/timtadh/lexmachine v0.2.2
-	golang.org/x/sys v0.0.0-20210105210732-16f7687f5001 // indirect
+	golang.org/x/sys v0.0.0-20210124154548-22da62e12c0c // indirect
 	gopkg.in/op/go-logging.v1 v1.0.0-20160211212156-b2cb9fa56473
 	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b
 )

go.sum

@@ -36,8 +36,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=
 github.com/dgryski/go-sip13 v0.0.0-20181026042036-e10d5fee7954/go.mod h1:vAd38F8PWV+bWy6jNmig1y/TA+kYO4g3RSRF0IAv0no=
-github.com/elliotchance/orderedmap v1.3.0 h1:k6m77/d0zCXTjsk12nX40TkEBkSICq8T4s6R6bpCqU0=
-github.com/elliotchance/orderedmap v1.3.0/go.mod h1:8hdSl6jmveQw8ScByd3AaNHNk51RhbTazdqtTty+NFw=
+github.com/elliotchance/orderedmap v1.4.0 h1:wZtfeEONCbx6in1CZyE6bELEt/vFayMvsxqI5SgsR+A=
+github.com/elliotchance/orderedmap v1.4.0/go.mod h1:wsDwEaX5jEoyhbs7x93zk2H/qv0zwuhg4inXhDkYqys=
 github.com/fatih/color v1.7.0/go.mod h1:Zm6kSWBoL9eyXnKyktHP6abPY2pDugNf5KwzbycvMj4=
 github.com/fatih/color v1.10.0 h1:s36xzo75JdqLaaWoiEHk767eHiwo0598uUxyfiPkDsg=
 github.com/fatih/color v1.10.0/go.mod h1:ELkj/draVOlAH/xkhN6mQ50Qd0MPOk5AAr3maGEBuJM=
@@ -52,8 +52,8 @@ github.com/go-playground/locales v0.13.0/go.mod h1:taPMhCMXrRLJO55olJkUXHZBHCxTM
 github.com/go-playground/universal-translator v0.17.0/go.mod h1:UkSxE5sNxxRwHyU+Scu5vgOQjsIJAF8j9muTVoKLVtA=
 github.com/go-playground/validator/v10 v10.4.1/go.mod h1:nlOn6nFhuKACm19sB/8EGNn9GlaMV7XkbRSipzJ0Ii4=
 github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/melR3HDY=
-github.com/goccy/go-yaml v1.8.4 h1:AOEdR7aQgbgwHznGe3BLkDQVujxCPUpHOZZcQcp8Y3M=
-github.com/goccy/go-yaml v1.8.4/go.mod h1:U/jl18uSupI5rdI2jmuCswEA2htH9eXfferR3KfscvA=
+github.com/goccy/go-yaml v1.8.8 h1:MGfRB1GeSn/hWXYWS2Pt67iC2GJNnebdIro01ddyucA=
+github.com/goccy/go-yaml v1.8.8/go.mod h1:U/jl18uSupI5rdI2jmuCswEA2htH9eXfferR3KfscvA=
 github.com/gogo/protobuf v1.1.1/go.mod h1:r8qH/GZQm5c6nD/R0oafs1akxWv10x8SbQlK7atdtwQ=
 github.com/gogo/protobuf v1.2.1/go.mod h1:hp+jE20tsWTFYpLwKvXlhS1hjn+gTNwPg2I6zVXpSg4=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
@@ -101,8 +101,8 @@ github.com/hashicorp/memberlist v0.1.3/go.mod h1:ajVTdAv/9Im8oMAAj5G31PhhMCZJV2p
 github.com/hashicorp/serf v0.8.2/go.mod h1:6hOLApaqBFA1NXqRQAsxw9QxuDEvNxSQRwA/JwenrHc=
 github.com/inconshreveable/mousetrap v1.0.0 h1:Z8tu5sraLXCXIcARxBp/8cbvlwVa7Z1NHg9XEKhtSvM=
 github.com/inconshreveable/mousetrap v1.0.0/go.mod h1:PxqpIevigyE2G7u3NXJIT2ANytuPF1OarO4DADm73n8=
-github.com/jinzhu/copier v0.1.0 h1:Vh8xALtH3rrKGB/XIRe5d0yCTHPZFauWPLvdpDAbi88=
-github.com/jinzhu/copier v0.1.0/go.mod h1:24xnZezI2Yqac9J61UC6/dG/k76ttpq0DdJI3QmUvro=
+github.com/jinzhu/copier v0.2.3 h1:Oe09ju+9qft7TffZ7l/04AB2f8u1+V4ZMxmp/nnqeOs=
+github.com/jinzhu/copier v0.2.3/go.mod h1:24xnZezI2Yqac9J61UC6/dG/k76ttpq0DdJI3QmUvro=
 github.com/jonboulle/clockwork v0.1.0/go.mod h1:Ii8DK3G1RaLaWxj9trq07+26W01tbo22gdxWY5EU2bo=
 github.com/json-iterator/go v1.1.6/go.mod h1:+SdeFBvtyEkXs7REEP0seUULqWtbJapLOCVDaaPEHmU=
 github.com/jstemmer/go-junit-report v0.0.0-20190106144839-af01ea7f8024/go.mod h1:6v2b51hI/fHJwM22ozAgKL4VKDeJcHhJFhtBdhmNjmU=
@@ -182,6 +182,8 @@ github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXf
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/subosito/gotenv v1.2.0/go.mod h1:N0PQaV/YGNqwC0u51sEeR/aUtSLEXKX9iv69rRypqCw=
 github.com/timtadh/data-structures v0.5.3 h1:F2tEjoG9qWIyUjbvXVgJqEOGJPMIiYn7U5W5mE+i/vQ=
 github.com/timtadh/data-structures v0.5.3/go.mod h1:9R4XODhJ8JdWFEI8P/HJKqxuJctfBQw6fDibMQny2oU=
@@ -257,8 +259,8 @@ golang.org/x/sys v0.0.0-20190624142023-c5567b49c5d0/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20200116001909-b77594299b42/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200223170610-d5e6a3e2c0ae h1:/WDfKMnPU+m5M4xB+6x4kaepxRw6jWvR5iDRdvjHgy8=
 golang.org/x/sys v0.0.0-20200223170610-d5e6a3e2c0ae/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20210105210732-16f7687f5001 h1:/dSxr6gT0FNI1MO5WLJo8mTmItROeOKTkDn+7OwWBos=
-golang.org/x/sys v0.0.0-20210105210732-16f7687f5001/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210124154548-22da62e12c0c h1:VwygUrnw9jn88c4u8GD3rZQbqrP/tgas88tPUbBxQrk=
+golang.org/x/sys v0.0.0-20210124154548-22da62e12c0c/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.1-0.20180807135948-17ff2d5776d2/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
@@ -281,6 +283,7 @@ golang.org/x/tools v0.0.0-20190628153133-6cdbf07be9d0/go.mod h1:/rFqwRUd4F7ZHNgw
 golang.org/x/tools v0.0.0-20190816200558-6889da9d5479/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.0.0-20190911174233-4f2ddba30aff/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.0.0-20191012152004-8de300cfc20a/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/tools v0.0.0-20191112195655-aa38f8e97acc h1:NCy3Ohtk6Iny5V/reW2Ktypo4zIpWBdRJ1uFMjBxdg8=
 golang.org/x/tools v0.0.0-20191112195655-aa38f8e97acc/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 h1:go1bK/D/BFZV2I8cIQd1NKEZ+0owSTG1fDTci4IqFcE=
@@ -323,6 +326,7 @@ gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.2.4/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.2.8 h1:obN1ZagJSUGI0Ek/LBmuj4SNLPfIny3KsKFopxRdj10=
 gopkg.in/yaml.v2 v2.2.8/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b h1:h8qDotaEPuJATrMmW04NCwg7v22aHH28wwpauUhK9Oo=
 gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=

pkg/yqlib/all_at_once_evaluator.go

@@ -1,29 +1,54 @@
 package yqlib
 
-import "container/list"
+import (
+	"container/list"
 
-/**
-	Loads all yaml documents of all files given into memory, then runs the given expression once.
-**/
+	yaml "gopkg.in/yaml.v3"
+)
+
+// A yaml expression evaluator that runs the expression once against all files/nodes in memory.
 type Evaluator interface {
 	EvaluateFiles(expression string, filenames []string, printer Printer) error
+
+	// EvaluateNodes takes an expression and one or more yaml nodes, returning a list of matching candidate nodes
+	EvaluateNodes(expression string, nodes ...*yaml.Node) (*list.List, error)
+
+	// EvaluateCandidateNodes takes an expression and list of candidate nodes, returning a list of matching candidate nodes
+	EvaluateCandidateNodes(expression string, inputCandidateNodes *list.List) (*list.List, error)
 }
 
 type allAtOnceEvaluator struct {
 	treeNavigator DataTreeNavigator
-	treeCreator   PathTreeCreator
+	treeCreator   ExpressionParser
 }
 
 func NewAllAtOnceEvaluator() Evaluator {
-	return &allAtOnceEvaluator{treeNavigator: NewDataTreeNavigator(), treeCreator: NewPathTreeCreator()}
+	return &allAtOnceEvaluator{treeNavigator: NewDataTreeNavigator(), treeCreator: NewExpressionParser()}
+}
+
+func (e *allAtOnceEvaluator) EvaluateNodes(expression string, nodes ...*yaml.Node) (*list.List, error) {
+	inputCandidates := list.New()
+	for _, node := range nodes {
+		inputCandidates.PushBack(&CandidateNode{Node: node})
+	}
+	return e.EvaluateCandidateNodes(expression, inputCandidates)
+}
+
+func (e *allAtOnceEvaluator) EvaluateCandidateNodes(expression string, inputCandidates *list.List) (*list.List, error) {
+	node, err := e.treeCreator.ParseExpression(expression)
+	if err != nil {
+		return nil, err
+	}
+	context, err := e.treeNavigator.GetMatchingNodes(Context{MatchingNodes: inputCandidates}, node)
+	if err != nil {
+		return nil, err
+	}
+	return context.MatchingNodes, nil
 }
 
 func (e *allAtOnceEvaluator) EvaluateFiles(expression string, filenames []string, printer Printer) error {
 	fileIndex := 0
-	node, err := treeCreator.ParsePath(expression)
-	if err != nil {
-		return err
-	}
+
 	var allDocuments *list.List = list.New()
 	for _, filename := range filenames {
 		reader, err := readStream(filename)
@@ -37,7 +62,7 @@ func (e *allAtOnceEvaluator) EvaluateFiles(expression string, filenames []string
 		allDocuments.PushBackList(fileDocuments)
 		fileIndex = fileIndex + 1
 	}
-	matches, err := treeNavigator.GetMatchingNodes(allDocuments, node)
+	matches, err := e.EvaluateCandidateNodes(expression, allDocuments)
 	if err != nil {
 		return err
 	}

pkg/yqlib/all_at_once_evaluator_test.go

@@ -0,0 +1,40 @@
+package yqlib
+
+import (
+	"testing"
+
+	"github.com/mikefarah/yq/v4/test"
+)
+
+var evaluateNodesScenario = []expressionScenario{
+	{
+		document:   `a: hello`,
+		expression: `.a`,
+		expected: []string{
+			"D0, P[a], (!!str)::hello\n",
+		},
+	},
+	{
+		document:   `a: hello`,
+		expression: `.`,
+		expected: []string{
+			"D0, P[], (doc)::a: hello\n",
+		},
+	},
+	{
+		document:   `- a: "yes"`,
+		expression: `.[] | has("a")`,
+		expected: []string{
+			"D0, P[0], (!!bool)::true\n",
+		},
+	},
+}
+
+func TestAllAtOnceEvaluateNodes(t *testing.T) {
+	var evaluator = NewAllAtOnceEvaluator()
+	for _, tt := range evaluateNodesScenario {
+		node := test.ParseData(tt.document)
+		list, _ := evaluator.EvaluateNodes(tt.expression, &node)
+		test.AssertResultComplex(t, tt.expected, resultsToString(list))
+	}
+}

pkg/yqlib/candidate_node.go

@@ -2,8 +2,6 @@ package yqlib
 
 import (
 	"fmt"
-	"strconv"
-	"strings"
 
 	"github.com/jinzhu/copier"
 	yaml "gopkg.in/yaml.v3"
@@ -15,13 +13,37 @@ type CandidateNode struct {
 	Document  uint          // the document index of this node
 	Filename  string
 	FileIndex int
+	// when performing op against all nodes given, this will treat all the nodes as one
+	// (e.g. top level cross document merge). This property does not propegate to child nodes.
+	EvaluateTogether bool
+	IsMapKey         bool
 }
 
 func (n *CandidateNode) GetKey() string {
-	return fmt.Sprintf("%v - %v", n.Document, n.Path)
+	keyPrefix := ""
+	if n.IsMapKey {
+		keyPrefix = "key-"
+	}
+	return fmt.Sprintf("%v%v - %v", keyPrefix, n.Document, n.Path)
 }
 
-func (n *CandidateNode) CreateChildPath(path interface{}) []interface{} {
+func (n *CandidateNode) CreateChild(path interface{}, node *yaml.Node) *CandidateNode {
+	return &CandidateNode{
+		Node:      node,
+		Path:      n.createChildPath(path),
+		Document:  n.Document,
+		Filename:  n.Filename,
+		FileIndex: n.FileIndex,
+	}
+}
+
+func (n *CandidateNode) createChildPath(path interface{}) []interface{} {
+	if path == nil {
+		newPath := make([]interface{}, len(n.Path))
+		copy(newPath, n.Path)
+		return newPath
+	}
+
 	//don't use append as they may actually modify the path of the orignal node!
 	newPath := make([]interface{}, len(n.Path)+1)
 	copy(newPath, n.Path)
@@ -44,10 +66,10 @@ func (n *CandidateNode) UpdateFrom(other *CandidateNode) {
 	n.UpdateAttributesFrom(other)
 	n.Node.Content = other.Node.Content
 	n.Node.Value = other.Node.Value
-	n.Node.Alias = other.Node.Alias
 }
 
 func (n *CandidateNode) UpdateAttributesFrom(other *CandidateNode) {
+	log.Debug("UpdateAttributesFrom: n: %v other: %v", n.GetKey(), other.GetKey())
 	if n.Node.Kind != other.Node.Kind {
 		// clear out the contents when switching to a different type
 		// e.g. map to array
@@ -56,6 +78,8 @@ func (n *CandidateNode) UpdateAttributesFrom(other *CandidateNode) {
 	}
 	n.Node.Kind = other.Node.Kind
 	n.Node.Tag = other.Node.Tag
+	n.Node.Alias = other.Node.Alias
+	n.Node.Anchor = other.Node.Anchor
 
 	// merge will pickup the style of the new thing
 	// when autocreating nodes
@@ -66,46 +90,3 @@ func (n *CandidateNode) UpdateAttributesFrom(other *CandidateNode) {
 	n.Node.HeadComment = n.Node.HeadComment + other.Node.HeadComment
 	n.Node.LineComment = n.Node.LineComment + other.Node.LineComment
 }
-
-func (n *CandidateNode) PathStackToString() string {
-	return mergePathStackToString(n.Path)
-}
-
-func mergePathStackToString(pathStack []interface{}) string {
-	var sb strings.Builder
-	for index, path := range pathStack {
-		switch path.(type) {
-		case int, int64:
-			// if arrayMergeStrategy == AppendArrayMergeStrategy {
-			// sb.WriteString("[+]")
-			// } else {
-			sb.WriteString(fmt.Sprintf("[%v]", path))
-			// }
-
-		default:
-			s := fmt.Sprintf("%v", path)
-			var _, errParsingInt = strconv.ParseInt(s, 10, 64) // nolint
-
-			hasSpecial := strings.Contains(s, ".") || strings.Contains(s, "[") || strings.Contains(s, "]") || strings.Contains(s, "\"")
-			hasDoubleQuotes := strings.Contains(s, "\"")
-			wrappingCharacterStart := "\""
-			wrappingCharacterEnd := "\""
-			if hasDoubleQuotes {
-				wrappingCharacterStart = "("
-				wrappingCharacterEnd = ")"
-			}
-			if hasSpecial || errParsingInt == nil {
-				sb.WriteString(wrappingCharacterStart)
-			}
-			sb.WriteString(s)
-			if hasSpecial || errParsingInt == nil {
-				sb.WriteString(wrappingCharacterEnd)
-			}
-		}
-
-		if index < len(pathStack)-1 {
-			sb.WriteString(".")
-		}
-	}
-	return sb.String()
-}

pkg/yqlib/color_print.go

@@ -17,8 +17,8 @@ func format(attr color.Attribute) string {
 	return fmt.Sprintf("%s[%dm", escape, attr)
 }
 
-func ColorizeAndPrint(bytes []byte, writer io.Writer) error {
-	tokens := lexer.Tokenize(string(bytes))
+func colorizeAndPrint(yamlBytes []byte, writer io.Writer) error {
+	tokens := lexer.Tokenize(string(yamlBytes))
 	var p printer.Printer
 	p.Bool = func() *printer.Property {
 		return &printer.Property{

pkg/yqlib/context.go

@@ -0,0 +1,54 @@
+package yqlib
+
+import (
+	"container/list"
+
+	"github.com/jinzhu/copier"
+)
+
+type Context struct {
+	MatchingNodes  *list.List
+	Variables      map[string]*list.List
+	DontAutoCreate bool
+}
+
+func (n *Context) SingleChildContext(candidate *CandidateNode) Context {
+	list := list.New()
+	list.PushBack(candidate)
+	return n.ChildContext(list)
+}
+
+func (n *Context) GetVariable(name string) *list.List {
+	if n.Variables == nil {
+		return nil
+	}
+	return n.Variables[name]
+}
+
+func (n *Context) SetVariable(name string, value *list.List) {
+	if n.Variables == nil {
+		n.Variables = make(map[string]*list.List)
+	}
+	n.Variables[name] = value
+}
+
+func (n *Context) ChildContext(results *list.List) Context {
+	clone := Context{}
+	err := copier.Copy(&clone, n)
+	if err != nil {
+		log.Error("Error cloning context :(")
+		panic(err)
+	}
+	clone.MatchingNodes = results
+	return clone
+}
+
+func (n *Context) Clone() Context {
+	clone := Context{}
+	err := copier.Copy(&clone, n)
+	if err != nil {
+		log.Error("Error cloning context :(")
+		panic(err)
+	}
+	return clone
+}

pkg/yqlib/data_tree_navigator.go

@@ -3,16 +3,14 @@ package yqlib
 import (
 	"fmt"
 
-	"container/list"
-
 	logging "gopkg.in/op/go-logging.v1"
 )
 
 type DataTreeNavigator interface {
-	// given a list of CandidateEntities and a pathNode,
-	// this will process the list against the given pathNode and return
-	// a new list of matching candidates
-	GetMatchingNodes(matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error)
+	// given the context and a expressionNode,
+	// this will process the against the given expressionNode and return
+	// a new context of matching candidates
+	GetMatchingNodes(context Context, expressionNode *ExpressionNode) (Context, error)
 }
 
 type dataTreeNavigator struct {
@@ -22,22 +20,22 @@ func NewDataTreeNavigator() DataTreeNavigator {
 	return &dataTreeNavigator{}
 }
 
-func (d *dataTreeNavigator) GetMatchingNodes(matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	if pathNode == nil {
+func (d *dataTreeNavigator) GetMatchingNodes(context Context, expressionNode *ExpressionNode) (Context, error) {
+	if expressionNode == nil {
 		log.Debugf("getMatchingNodes - nothing to do")
-		return matchingNodes, nil
+		return context, nil
 	}
-	log.Debugf("Processing Op: %v", pathNode.Operation.toString())
+	log.Debugf("Processing Op: %v", expressionNode.Operation.toString())
 	if log.IsEnabledFor(logging.DEBUG) {
-		for el := matchingNodes.Front(); el != nil; el = el.Next() {
+		for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 			log.Debug(NodeToString(el.Value.(*CandidateNode)))
 		}
 	}
 	log.Debug(">>")
-	handler := pathNode.Operation.OperationType.Handler
+	handler := expressionNode.Operation.OperationType.Handler
 	if handler != nil {
-		return handler(d, matchingNodes, pathNode)
+		return handler(d, context, expressionNode)
 	}
-	return nil, fmt.Errorf("Unknown operator %v", pathNode.Operation.OperationType)
+	return Context{}, fmt.Errorf("Unknown operator %v", expressionNode.Operation.OperationType)
 
 }

pkg/yqlib/doc/Add.md

@@ -1,9 +1,9 @@
 Add behaves differently according to the type of the LHS:
 - arrays: concatenate
-- number scalars: arithmetic addition (soon)
-- string scalars: concatenate (soon)
+- number scalars: arithmetic addition
+- string scalars: concatenate
 
-Use `+=` as append assign for things like increment. `.a += .x` is equivalent to running `.a |= . + .x`.
+Use `+=` as append assign for things like increment. Note that `.a += .x` is equivalent to running `.a = .a + .x`.
 
 ## Concatenate and assign arrays
 Given a sample.yml file of:
@@ -67,23 +67,19 @@ will output
 - 2
 ```
 
-## Add object to array
+## Add new object to array
 Given a sample.yml file of:
 ```yaml
 a:
-  - 1
-  - 2
-c:
-  cat: meow
+  - dog: woof
 ```
 then
 ```bash
-yq eval '.a + .c' sample.yml
+yq eval '.a + {"cat": "meow"}' sample.yml
 ```
 will output
 ```yaml
-- 1
-- 2
+- dog: woof
 - cat: meow
 ```
 
@@ -131,3 +127,97 @@ b:
   - 4
 ```
 
+## String concatenation
+Given a sample.yml file of:
+```yaml
+a: cat
+b: meow
+```
+then
+```bash
+yq eval '.a = .a + .b' sample.yml
+```
+will output
+```yaml
+a: catmeow
+b: meow
+```
+
+## Relative string concatenation
+Given a sample.yml file of:
+```yaml
+a: cat
+b: meow
+```
+then
+```bash
+yq eval '.a += .b' sample.yml
+```
+will output
+```yaml
+a: catmeow
+b: meow
+```
+
+## Number addition - float
+If the lhs or rhs are floats then the expression will be calculated with floats.
+
+Given a sample.yml file of:
+```yaml
+a: 3
+b: 4.9
+```
+then
+```bash
+yq eval '.a = .a + .b' sample.yml
+```
+will output
+```yaml
+a: 7.9
+b: 4.9
+```
+
+## Number addition - int
+If both the lhs and rhs are ints then the expression will be calculated with ints.
+
+Given a sample.yml file of:
+```yaml
+a: 3
+b: 4
+```
+then
+```bash
+yq eval '.a = .a + .b' sample.yml
+```
+will output
+```yaml
+a: 7
+b: 4
+```
+
+## Increment number
+Given a sample.yml file of:
+```yaml
+a: 3
+```
+then
+```bash
+yq eval '.a += 1' sample.yml
+```
+will output
+```yaml
+a: 4
+```
+
+## Add to null
+Adding to null simply returns the rhs
+
+Running
+```bash
+yq eval --null-input 'null + "cat"'
+```
+will output
+```yaml
+cat
+```
+

pkg/yqlib/doc/Comment Operators.md

@@ -78,17 +78,22 @@ b: dog # leave this
 ```
 
 ## Remove all comments
+Note the use of `...` to ensure key nodes are included.
+
 Given a sample.yml file of:
 ```yaml
 a: cat # comment
+# great
+b: # key comment
 ```
 then
 ```bash
-yq eval '.. comments=""' sample.yml
+yq eval '... comments=""' sample.yml
 ```
 will output
 ```yaml
 a: cat
+b:
 ```
 
 ## Get line comment

pkg/yqlib/doc/Document Index.md

@@ -1,4 +1,4 @@
-Use the `documentIndex` operator to select nodes of a particular document.
+Use the `documentIndex` operator (or the `di` shorthand) to select nodes of a particular document.
 ## Retrieve a document index
 Given a sample.yml file of:
 ```yaml

pkg/yqlib/doc/Env Variable Operators.md

@@ -1,3 +1,5 @@
+This operator is used to handle environment variables usage in path expressions. While environment variables can, of course, be passed in via your CLI with string interpolation, this often comes with complex quote escaping and can be tricky to write and read. Note that there are two forms, `env` which will parse the environment variable as a yaml (be it a map, array, string, number of boolean) and `strenv` which will always parse the argument as a string.
+
 
 ## Read string environment variable
 Running

pkg/yqlib/doc/Equals.md

@@ -29,6 +29,24 @@ true
 false
 ```
 
+## Don't match string
+Given a sample.yml file of:
+```yaml
+- cat
+- goat
+- dog
+```
+then
+```bash
+yq eval '.[] | (. != "*at")' sample.yml
+```
+will output
+```yaml
+false
+false
+true
+```
+
 ## Match number
 Given a sample.yml file of:
 ```yaml
@@ -47,6 +65,24 @@ true
 false
 ```
 
+## Dont match number
+Given a sample.yml file of:
+```yaml
+- 3
+- 4
+- 5
+```
+then
+```bash
+yq eval '.[] | (. != 4)' sample.yml
+```
+will output
+```yaml
+true
+false
+true
+```
+
 ## Match nulls
 Running
 ```bash

pkg/yqlib/doc/Keys.md

@@ -0,0 +1,35 @@
+# Keys
+
+Use the `keys` operator to return map keys or array indices. 
+## Map keys
+Given a sample.yml file of:
+```yaml
+dog: woof
+cat: meow
+```
+then
+```bash
+yq eval 'keys' sample.yml
+```
+will output
+```yaml
+- dog
+- cat
+```
+
+## Array keys
+Given a sample.yml file of:
+```yaml
+- apple
+- banana
+```
+then
+```bash
+yq eval 'keys' sample.yml
+```
+will output
+```yaml
+- 0
+- 1
+```
+

pkg/yqlib/doc/Length.md

@@ -16,6 +16,20 @@ will output
 3
 ```
 
+## null length
+Given a sample.yml file of:
+```yaml
+a: null
+```
+then
+```bash
+yq eval '.a | length' sample.yml
+```
+will output
+```yaml
+0
+```
+
 ## Map length
 returns number of entries
 

pkg/yqlib/doc/Multiply.md

@@ -1,13 +1,14 @@
-Like the multiple operator in `jq`, depending on the operands, this multiply operator will do different things. Currently only objects are supported, which have the effect of merging the RHS into the LHS.
+Like the multiple operator in jq, depending on the operands, this multiply operator will do different things. Currently only objects are supported, which have the effect of merging the RHS into the LHS.
 
-Upcoming versions of `yq` will add support for other types of multiplication (numbers, strings).
-
-To concatenate when merging objects, use the `*+` form (see examples below). This will recursively merge objects, appending arrays when it encounters them.
+To concatenate arrays when merging objects, use the *+ form (see examples below). This will recursively merge objects, appending arrays when it encounters them.
 
+To merge only existing fields, use the *? form. Note that this can be used with the concatenate arrays too *+?.
 Note that when merging objects, this operator returns the merged object (not the parent). This will be clearer in the examples below.
 
+Multiplication of strings and numbers are not yet supported.
+
 ## Merging files
-Note the use of eval-all to ensure all documents are loaded into memory.
+Note the use of `eval-all` to ensure all documents are loaded into memory.
 
 ```bash
 yq eval-all 'select(fileIndex == 0) * select(fileIndex == 1)' file1.yaml file2.yaml
@@ -70,7 +71,6 @@ Given a sample.yml file of:
 a: {things: great}
 b:
   also: "me"
-
 ```
 then
 ```bash
@@ -111,6 +111,26 @@ b:
   - 5
 ```
 
+## Merge, only existing fields
+Given a sample.yml file of:
+```yaml
+a:
+  thing: one
+  cat: frog
+b:
+  missing: two
+  thing: two
+```
+then
+```bash
+yq eval '.a *? .b' sample.yml
+```
+will output
+```yaml
+thing: two
+cat: frog
+```
+
 ## Merge, appending arrays
 Given a sample.yml file of:
 ```yaml
@@ -143,6 +163,33 @@ array:
 value: banana
 ```
 
+## Merge, only existing fields, appending arrays
+Given a sample.yml file of:
+```yaml
+a:
+  thing:
+    - 1
+    - 2
+b:
+  thing:
+    - 3
+    - 4
+  another:
+    - 1
+```
+then
+```bash
+yq eval '.a *?+ .b' sample.yml
+```
+will output
+```yaml
+thing:
+  - 1
+  - 2
+  - 3
+  - 4
+```
+
 ## Merge to prefix an element
 Given a sample.yml file of:
 ```yaml
@@ -180,7 +227,7 @@ g: thongs
 f: *cat
 ```
 
-## Merge does not copy anchor names
+## Merge copies anchor names
 Given a sample.yml file of:
 ```yaml
 a:
@@ -197,7 +244,7 @@ yq eval '.c * .a' sample.yml
 will output
 ```yaml
 g: thongs
-c: frog
+c: &cat frog
 ```
 
 ## Merge with merge anchors

pkg/yqlib/doc/Recursive Descent (Glob).md

@@ -33,6 +33,8 @@ frog
 ```
 
 ## Recursively find nodes with keys
+Note that this example has wrapped the expression in `[]` to show that there are two matches returned. You do not have to wrap in `[]` in your path expression.
+
 Given a sample.yml file of:
 ```yaml
 a:
@@ -43,16 +45,16 @@ a:
 ```
 then
 ```bash
-yq eval '.. | select(has("name"))' sample.yml
+yq eval '[.. | select(has("name"))]' sample.yml
 ```
 will output
 ```yaml
-name: frog
-b:
-  name: blog
+- name: frog
+  b:
+    name: blog
+    age: 12
+- name: blog
   age: 12
-name: blog
-age: 12
 ```
 
 ## Recursively find nodes with values

pkg/yqlib/doc/Split into Documents.md

@@ -0,0 +1,31 @@
+# Split into Documents
+
+This operator splits all matches into separate documents
+
+## Split empty
+Running
+```bash
+yq eval --null-input 'splitDoc'
+```
+will output
+```yaml
+
+```
+
+## Split array
+Given a sample.yml file of:
+```yaml
+- a: cat
+- b: dog
+```
+then
+```bash
+yq eval '.[] | splitDoc' sample.yml
+```
+will output
+```yaml
+a: cat
+---
+b: dog
+```
+

pkg/yqlib/doc/String Operators.md

@@ -0,0 +1,52 @@
+# String Operators
+
+## Join strings
+Given a sample.yml file of:
+```yaml
+- cat
+- meow
+- 1
+- null
+- true
+```
+then
+```bash
+yq eval 'join("; ")' sample.yml
+```
+will output
+```yaml
+cat; meow; 1; ; true
+```
+
+## Split strings
+Given a sample.yml file of:
+```yaml
+cat; meow; 1; ; true
+```
+then
+```bash
+yq eval 'split("; ")' sample.yml
+```
+will output
+```yaml
+- cat
+- meow
+- "1"
+- ""
+- "true"
+```
+
+## Split strings one match
+Given a sample.yml file of:
+```yaml
+word
+```
+then
+```bash
+yq eval 'split("; ")' sample.yml
+```
+will output
+```yaml
+- word
+```
+

pkg/yqlib/doc/Traverse (Read).md

@@ -33,7 +33,7 @@ c: banana
 ```
 
 ## Special characters
-Use quotes around path elements with special characters
+Use quotes with brackets around path elements with special characters
 
 Given a sample.yml file of:
 ```yaml
@@ -41,7 +41,23 @@ Given a sample.yml file of:
 ```
 then
 ```bash
-yq eval '."{}"' sample.yml
+yq eval '.["{}"]' sample.yml
+```
+will output
+```yaml
+frog
+```
+
+## Keys with spaces
+Use quotes with brackets around path elements with special characters
+
+Given a sample.yml file of:
+```yaml
+"red rabbit": frog
+```
+then
+```bash
+yq eval '.["red rabbit"]' sample.yml
 ```
 will output
 ```yaml

pkg/yqlib/doc/Variable Operators.md

@@ -0,0 +1,58 @@
+For more complex scenarios, variables can be used to hold values of expression to be used in other expressions.
+
+## Single value variable
+Given a sample.yml file of:
+```yaml
+a: cat
+```
+then
+```bash
+yq eval '.a as $foo | $foo' sample.yml
+```
+will output
+```yaml
+cat
+```
+
+## Multi value variable
+Given a sample.yml file of:
+```yaml
+- cat
+- dog
+```
+then
+```bash
+yq eval '.[] as $foo | $foo' sample.yml
+```
+will output
+```yaml
+cat
+dog
+```
+
+## Using variables as a lookup
+Example taken from [jq](https://stedolan.github.io/jq/manual/#Variable/SymbolicBindingOperator:...as$identifier|...)
+
+Given a sample.yml file of:
+```yaml
+"posts":
+  - "title": Frist psot
+    "author": anon
+  - "title": A well-written article
+    "author": person1
+"realnames":
+  "anon": Anonymous Coward
+  "person1": Person McPherson
+```
+then
+```bash
+yq eval '.realnames as $names | .posts[] | {"title":.title, "author": $names[.author]}' sample.yml
+```
+will output
+```yaml
+title: Frist psot
+author: Anonymous Coward
+title: A well-written article
+author: Person McPherson
+```
+

pkg/yqlib/doc/aa.md

@@ -0,0 +1,12 @@
+# Operators
+
+In `yq` expressions are made up of operators. Operators have 0-2 arguments and run against the current 'matching' nodes in the expression tree.
+
+Lets look at a couple of examples.
+
+The `length` operator take no arguments, and will simply return the length of _each_ matching node. So if there were 2 nodes, one string and one array, length will update the 'matching' nodes context to be two new numeric scalar nodes representing the lengths of the orignal 'matching' nodes.
+
+The `=` operator takes two arguments, a `lhs` expression and `rhs` expression. It runs the 'matching' nodes context against the `lhs` expression to find the nodes to update, lets call it `lhsNodes`, and then runs the matching nodes against the `rhs` to find the new values, lets call that `rhsNodes`. It updates the `lhsNodes` values with the `rhsNodes` values and _returns the original matching nodes_. This is important, where length changed the matching nodes to be new nodes with the length values, `=` returns the original matching nodes, albeit with some of the nodes values updated. So `.a = 3` will still return the parent matching node, but with the matching child updated.
+
+Please see the individual operator docs for more information and examples.
+

pkg/yqlib/doc/headers/Add.md

@@ -1,6 +1,6 @@
 Add behaves differently according to the type of the LHS:
 - arrays: concatenate
-- number scalars: arithmetic addition (soon)
-- string scalars: concatenate (soon)
+- number scalars: arithmetic addition
+- string scalars: concatenate
 
-Use `+=` as append assign for things like increment. `.a += .x` is equivalent to running `.a |= . + .x`.
+Use `+=` as append assign for things like increment. Note that `.a += .x` is equivalent to running `.a = .a + .x`.

pkg/yqlib/doc/headers/Document Index.md

@@ -1 +1 @@
-Use the `documentIndex` operator to select nodes of a particular document.
+Use the `documentIndex` operator (or the `di` shorthand) to select nodes of a particular document.

pkg/yqlib/doc/headers/Env Variable Operators.md

@@ -0,0 +1,2 @@
+This operator is used to handle environment variables usage in path expressions. While environment variables can, of course, be passed in via your CLI with string interpolation, this often comes with complex quote escaping and can be tricky to write and read. Note that there are two forms, `env` which will parse the environment variable as a yaml (be it a map, array, string, number of boolean) and `strenv` which will always parse the argument as a string.
+

pkg/yqlib/doc/headers/Keys.md

@@ -0,0 +1,3 @@
+# Keys
+
+Use the `keys` operator to return map keys or array indices. 

pkg/yqlib/doc/headers/Multiply.md

@@ -1,13 +1,14 @@
-Like the multiple operator in `jq`, depending on the operands, this multiply operator will do different things. Currently only objects are supported, which have the effect of merging the RHS into the LHS.
+Like the multiple operator in jq, depending on the operands, this multiply operator will do different things. Currently only objects are supported, which have the effect of merging the RHS into the LHS.
 
-Upcoming versions of `yq` will add support for other types of multiplication (numbers, strings).
-
-To concatenate when merging objects, use the `*+` form (see examples below). This will recursively merge objects, appending arrays when it encounters them.
+To concatenate arrays when merging objects, use the *+ form (see examples below). This will recursively merge objects, appending arrays when it encounters them.
 
+To merge only existing fields, use the *? form. Note that this can be used with the concatenate arrays too *+?.
 Note that when merging objects, this operator returns the merged object (not the parent). This will be clearer in the examples below.
 
+Multiplication of strings and numbers are not yet supported.
+
 ## Merging files
-Note the use of eval-all to ensure all documents are loaded into memory.
+Note the use of `eval-all` to ensure all documents are loaded into memory.
 
 ```bash
 yq eval-all 'select(fileIndex == 0) * select(fileIndex == 1)' file1.yaml file2.yaml

pkg/yqlib/doc/headers/Split into Documents.md

@@ -0,0 +1,3 @@
+# Split into Documents
+
+This operator splits all matches into separate documents

pkg/yqlib/doc/headers/String Operators.md

@@ -0,0 +1 @@
+# String Operators

pkg/yqlib/doc/headers/Variable Operators.md

@@ -0,0 +1 @@
+For more complex scenarios, variables can be used to hold values of expression to be used in other expressions.

pkg/yqlib/encoder.go

@@ -50,7 +50,7 @@ func (ye *yamlEncoder) Encode(node *yaml.Node) error {
 	}
 
 	if ye.colorise {
-		return ColorizeAndPrint(tempBuffer.Bytes(), ye.destination)
+		return colorizeAndPrint(tempBuffer.Bytes(), ye.destination)
 	}
 	return nil
 }
@@ -76,6 +76,8 @@ func mapKeysToStrings(node *yaml.Node) {
 
 func NewJsonEncoder(destination io.Writer, indent int) Encoder {
 	var encoder = json.NewEncoder(destination)
+	encoder.SetEscapeHTML(false) // do not escape html chars e.g. &, <, >
+
 	var indentString = ""
 
 	for index := 0; index < indent; index++ {
@@ -153,11 +155,15 @@ func (o *orderedMap) UnmarshalJSON(data []byte) error {
 }
 
 func (o orderedMap) MarshalJSON() ([]byte, error) {
-	if o.kv == nil {
-		return json.Marshal(o.altVal)
-	}
 	buf := new(bytes.Buffer)
 	enc := json.NewEncoder(buf)
+	enc.SetEscapeHTML(false) // do not escape html chars e.g. &, <, >
+	if o.kv == nil {
+		if err := enc.Encode(o.altVal); err != nil {
+			return nil, err
+		}
+		return buf.Bytes(), nil
+	}
 	buf.WriteByte('{')
 	for idx, el := range o.kv {
 		if err := enc.Encode(el.K); err != nil {

pkg/yqlib/encoder_test.go

@@ -9,29 +9,11 @@ import (
 	"github.com/mikefarah/yq/v4/test"
 )
 
-var sampleYaml = `zabbix: winner
-apple: great
-banana:
-- {cobra: kai, angus: bob}
-`
-
-var expectedJson = `{
-  "zabbix": "winner",
-  "apple": "great",
-  "banana": [
-    {
-      "cobra": "kai",
-      "angus": "bob"
-    }
-  ]
-}
-`
-
-func TestJsonEncoderPreservesObjectOrder(t *testing.T) {
+func yamlToJson(sampleYaml string, indent int) string {
 	var output bytes.Buffer
 	writer := bufio.NewWriter(&output)
 
-	var jsonEncoder = NewJsonEncoder(writer, 2)
+	var jsonEncoder = NewJsonEncoder(writer, indent)
 	inputs, err := readDocuments(strings.NewReader(sampleYaml), "sample.yml", 0)
 	if err != nil {
 		panic(err)
@@ -42,6 +24,33 @@ func TestJsonEncoderPreservesObjectOrder(t *testing.T) {
 		panic(err)
 	}
 	writer.Flush()
-	test.AssertResult(t, expectedJson, output.String())
 
+	return strings.TrimSuffix(output.String(), "\n")
+}
+
+func TestJsonEncoderPreservesObjectOrder(t *testing.T) {
+	var sampleYaml = `zabbix: winner
+apple: great
+banana:
+- {cobra: kai, angus: bob}
+`
+	var expectedJson = `{
+  "zabbix": "winner",
+  "apple": "great",
+  "banana": [
+    {
+      "cobra": "kai",
+      "angus": "bob"
+    }
+  ]
+}`
+	var actualJson = yamlToJson(sampleYaml, 2)
+	test.AssertResult(t, expectedJson, actualJson)
+}
+
+func TestJsonEncoderDoesNotEscapeHTMLChars(t *testing.T) {
+	var sampleYaml = `build: "( ./lint && ./format && ./compile ) < src.code"`
+	var expectedJson = `{"build":"( ./lint && ./format && ./compile ) < src.code"}`
+	var actualJson = yamlToJson(sampleYaml, 0)
+	test.AssertResult(t, expectedJson, actualJson)
 }

pkg/yqlib/expression_parser.go

@@ -5,29 +5,28 @@ import (
 	"strings"
 )
 
-var myPathTokeniser = NewPathTokeniser()
-var myPathPostfixer = NewPathPostFixer()
+var myPathTokeniser = newExpressionTokeniser()
+var myPathPostfixer = newExpressionPostFixer()
 
-type PathTreeNode struct {
+type ExpressionNode struct {
 	Operation *Operation
-	Lhs       *PathTreeNode
-	Rhs       *PathTreeNode
+	Lhs       *ExpressionNode
+	Rhs       *ExpressionNode
 }
 
-type PathTreeCreator interface {
-	ParsePath(path string) (*PathTreeNode, error)
-	CreatePathTree(postFixPath []*Operation) (*PathTreeNode, error)
+type ExpressionParser interface {
+	ParseExpression(expression string) (*ExpressionNode, error)
 }
 
-type pathTreeCreator struct {
+type expressionParserImpl struct {
 }
 
-func NewPathTreeCreator() PathTreeCreator {
-	return &pathTreeCreator{}
+func NewExpressionParser() ExpressionParser {
+	return &expressionParserImpl{}
 }
 
-func (p *pathTreeCreator) ParsePath(path string) (*PathTreeNode, error) {
-	tokens, err := myPathTokeniser.Tokenise(path)
+func (p *expressionParserImpl) ParseExpression(expression string) (*ExpressionNode, error) {
+	tokens, err := myPathTokeniser.Tokenise(expression)
 	if err != nil {
 		return nil, err
 	}
@@ -36,18 +35,18 @@ func (p *pathTreeCreator) ParsePath(path string) (*PathTreeNode, error) {
 	if err != nil {
 		return nil, err
 	}
-	return p.CreatePathTree(Operations)
+	return p.createExpressionTree(Operations)
 }
 
-func (p *pathTreeCreator) CreatePathTree(postFixPath []*Operation) (*PathTreeNode, error) {
-	var stack = make([]*PathTreeNode, 0)
+func (p *expressionParserImpl) createExpressionTree(postFixPath []*Operation) (*ExpressionNode, error) {
+	var stack = make([]*ExpressionNode, 0)
 
 	if len(postFixPath) == 0 {
 		return nil, nil
 	}
 
 	for _, Operation := range postFixPath {
-		var newNode = PathTreeNode{Operation: Operation}
+		var newNode = ExpressionNode{Operation: Operation}
 		log.Debugf("pathTree %v ", Operation.toString())
 		if Operation.OperationType.NumArgs > 0 {
 			numArgs := Operation.OperationType.NumArgs
@@ -71,7 +70,7 @@ func (p *pathTreeCreator) CreatePathTree(postFixPath []*Operation) (*PathTreeNod
 		stack = append(stack, &newNode)
 	}
 	if len(stack) != 1 {
-		return nil, fmt.Errorf("expected end of expression but found '%v', please check expression syntax", strings.TrimSpace(stack[1].Operation.StringValue))
+		return nil, fmt.Errorf("Bad expression, please check expression syntax")
 	}
 	return stack[0], nil
 }

pkg/yqlib/expression_parser_test.go

@@ -7,36 +7,36 @@ import (
 )
 
 func TestPathTreeNoArgsForTwoArgOp(t *testing.T) {
-	_, err := treeCreator.ParsePath("=")
+	_, err := NewExpressionParser().ParseExpression("=")
 	test.AssertResultComplex(t, "'=' expects 2 args but there is 0", err.Error())
 }
 
 func TestPathTreeOneLhsArgsForTwoArgOp(t *testing.T) {
-	_, err := treeCreator.ParsePath(".a =")
+	_, err := NewExpressionParser().ParseExpression(".a =")
 	test.AssertResultComplex(t, "'=' expects 2 args but there is 1", err.Error())
 }
 
 func TestPathTreeOneRhsArgsForTwoArgOp(t *testing.T) {
-	_, err := treeCreator.ParsePath("= .a")
+	_, err := NewExpressionParser().ParseExpression("= .a")
 	test.AssertResultComplex(t, "'=' expects 2 args but there is 1", err.Error())
 }
 
 func TestPathTreeTwoArgsForTwoArgOp(t *testing.T) {
-	_, err := treeCreator.ParsePath(".a = .b")
+	_, err := NewExpressionParser().ParseExpression(".a = .b")
 	test.AssertResultComplex(t, nil, err)
 }
 
 func TestPathTreeNoArgsForOneArgOp(t *testing.T) {
-	_, err := treeCreator.ParsePath("explode")
+	_, err := NewExpressionParser().ParseExpression("explode")
 	test.AssertResultComplex(t, "'explode' expects 1 arg but received none", err.Error())
 }
 
 func TestPathTreeOneArgForOneArgOp(t *testing.T) {
-	_, err := treeCreator.ParsePath("explode(.)")
+	_, err := NewExpressionParser().ParseExpression("explode(.)")
 	test.AssertResultComplex(t, nil, err)
 }
 
 func TestPathTreeExtraArgs(t *testing.T) {
-	_, err := treeCreator.ParsePath("sortKeys(.) explode(.)")
-	test.AssertResultComplex(t, "expected end of expression but found 'explode', please check expression syntax", err.Error())
+	_, err := NewExpressionParser().ParseExpression("sortKeys(.) explode(.)")
+	test.AssertResultComplex(t, "Bad expression, please check expression syntax", err.Error())
 }

pkg/yqlib/expression_postfix.go

@@ -0,0 +1,95 @@
+package yqlib
+
+import (
+	"errors"
+
+	logging "gopkg.in/op/go-logging.v1"
+)
+
+type expressionPostFixer interface {
+	ConvertToPostfix([]*token) ([]*Operation, error)
+}
+
+type expressionPostFixerImpl struct {
+}
+
+func newExpressionPostFixer() expressionPostFixer {
+	return &expressionPostFixerImpl{}
+}
+
+func popOpToResult(opStack []*token, result []*Operation) ([]*token, []*Operation) {
+	var newOp *token
+	opStack, newOp = opStack[0:len(opStack)-1], opStack[len(opStack)-1]
+	log.Debugf("popped %v from opstack to results", newOp.toString(true))
+	return opStack, append(result, newOp.Operation)
+}
+
+func (p *expressionPostFixerImpl) ConvertToPostfix(infixTokens []*token) ([]*Operation, error) {
+	var result []*Operation
+	// surround the whole thing with brackets
+	var opStack = []*token{{TokenType: openBracket}}
+	var tokens = append(infixTokens, &token{TokenType: closeBracket})
+
+	for _, currentToken := range tokens {
+		log.Debugf("postfix processing currentToken %v", currentToken.toString(true))
+		switch currentToken.TokenType {
+		case openBracket, openCollect, openCollectObject:
+			opStack = append(opStack, currentToken)
+			log.Debugf("put %v onto the opstack", currentToken.toString(true))
+		case closeCollect, closeCollectObject:
+			var opener tokenType = openCollect
+			var collectOperator *operationType = collectOpType
+			if currentToken.TokenType == closeCollectObject {
+				opener = openCollectObject
+				collectOperator = collectObjectOpType
+			}
+
+			for len(opStack) > 0 && opStack[len(opStack)-1].TokenType != opener {
+				opStack, result = popOpToResult(opStack, result)
+			}
+			if len(opStack) == 0 {
+				return nil, errors.New("Bad path expression, got close collect brackets without matching opening bracket")
+			}
+			// now we should have [ as the last element on the opStack, get rid of it
+			opStack = opStack[0 : len(opStack)-1]
+			log.Debugf("deleteing open bracket from opstack")
+
+			//and append a collect to the opStack
+			result = append(result, &Operation{OperationType: collectOperator})
+			log.Debugf("put collect onto the result")
+			result = append(result, &Operation{OperationType: shortPipeOpType})
+			log.Debugf("put shortpipe onto the result")
+
+		case closeBracket:
+			for len(opStack) > 0 && opStack[len(opStack)-1].TokenType != openBracket {
+				opStack, result = popOpToResult(opStack, result)
+			}
+			if len(opStack) == 0 {
+				return nil, errors.New("Bad path expression, got close brackets without matching opening bracket")
+			}
+			// now we should have ( as the last element on the opStack, get rid of it
+			opStack = opStack[0 : len(opStack)-1]
+
+		default:
+			var currentPrecedence = currentToken.Operation.OperationType.Precedence
+			// pop off higher precedent operators onto the result
+			for len(opStack) > 0 &&
+				opStack[len(opStack)-1].TokenType == operationToken &&
+				opStack[len(opStack)-1].Operation.OperationType.Precedence > currentPrecedence {
+				opStack, result = popOpToResult(opStack, result)
+			}
+			// add this operator to the opStack
+			opStack = append(opStack, currentToken)
+			log.Debugf("put %v onto the opstack", currentToken.toString(true))
+		}
+	}
+
+	if log.IsEnabledFor(logging.DEBUG) {
+		log.Debugf("PostFix Result:")
+		for _, currentToken := range result {
+			log.Debugf("> %v", currentToken.toString())
+		}
+	}
+
+	return result, nil
+}

pkg/yqlib/expression_processing_test.go

@@ -12,40 +12,65 @@ var pathTests = []struct {
 	expectedTokens  []interface{}
 	expectedPostFix []interface{}
 }{
+	{
+		`.a | .b | .c`,
+		append(make([]interface{}, 0), "a", "PIPE", "b", "PIPE", "c"),
+		append(make([]interface{}, 0), "a", "b", "c", "PIPE", "PIPE"),
+	},
 	{
 		`[]`,
-		append(make([]interface{}, 0), "[", "]"),
+		append(make([]interface{}, 0), "[", "EMPTY", "]"),
 		append(make([]interface{}, 0), "EMPTY", "COLLECT", "SHORT_PIPE"),
 	},
+	{
+		`{}`,
+		append(make([]interface{}, 0), "{", "EMPTY", "}"),
+		append(make([]interface{}, 0), "EMPTY", "COLLECT_OBJECT", "SHORT_PIPE"),
+	},
+	{
+		`[{}]`,
+		append(make([]interface{}, 0), "[", "{", "EMPTY", "}", "]"),
+		append(make([]interface{}, 0), "EMPTY", "COLLECT_OBJECT", "SHORT_PIPE", "COLLECT", "SHORT_PIPE"),
+	},
+	{
+		`.realnames as $names | $names["anon"]`,
+		append(make([]interface{}, 0), "realnames", "ASSIGN_VARIABLE", "GET_VARIABLE", "PIPE", "GET_VARIABLE", "TRAVERSE_ARRAY", "[", "anon (string)", "]"),
+		append(make([]interface{}, 0), "realnames", "GET_VARIABLE", "ASSIGN_VARIABLE", "GET_VARIABLE", "anon (string)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "PIPE"),
+	},
+	{
+		`.b[.a]`,
+		append(make([]interface{}, 0), "b", "TRAVERSE_ARRAY", "[", "a", "]"),
+		append(make([]interface{}, 0), "b", "a", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+	},
 	{
 		`.[]`,
-		append(make([]interface{}, 0), "TRAVERSE_ARRAY", "[", "]"),
-		append(make([]interface{}, 0), "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+		append(make([]interface{}, 0), "SELF", "TRAVERSE_ARRAY", "[", "EMPTY", "]"),
+		append(make([]interface{}, 0), "SELF", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
 	},
 	{
 		`.a[]`,
-		append(make([]interface{}, 0), "a", "SHORT_PIPE", "TRAVERSE_ARRAY", "[", "]"),
-		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE"),
+		append(make([]interface{}, 0), "a", "TRAVERSE_ARRAY", "[", "EMPTY", "]"),
+		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
 	},
 	{
 		`.a.[]`,
-		append(make([]interface{}, 0), "a", "SHORT_PIPE", "TRAVERSE_ARRAY", "[", "]"),
-		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE"),
+		append(make([]interface{}, 0), "a", "TRAVERSE_ARRAY", "[", "EMPTY", "]"),
+		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
 	},
 	{
 		`.a[0]`,
-		append(make([]interface{}, 0), "a", "SHORT_PIPE", "TRAVERSE_ARRAY", "[", "0 (int64)", "]"),
-		append(make([]interface{}, 0), "a", "0 (int64)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE"),
+		append(make([]interface{}, 0), "a", "TRAVERSE_ARRAY", "[", "0 (int64)", "]"),
+		append(make([]interface{}, 0), "a", "0 (int64)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
 	},
 	{
 		`.a.[0]`,
-		append(make([]interface{}, 0), "a", "SHORT_PIPE", "TRAVERSE_ARRAY", "[", "0 (int64)", "]"),
-		append(make([]interface{}, 0), "a", "0 (int64)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE"),
+		append(make([]interface{}, 0), "a", "TRAVERSE_ARRAY", "[", "0 (int64)", "]"),
+		append(make([]interface{}, 0), "a", "0 (int64)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
 	},
 	{
 		`.a[].c`,
-		append(make([]interface{}, 0), "a", "SHORT_PIPE", "TRAVERSE_ARRAY", "[", "]", "SHORT_PIPE", "c"),
-		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE", "c", "SHORT_PIPE"),
+		append(make([]interface{}, 0), "a", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "SHORT_PIPE", "c"),
+		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "c", "SHORT_PIPE"),
 	},
 	{
 		`[3]`,
@@ -53,24 +78,34 @@ var pathTests = []struct {
 		append(make([]interface{}, 0), "3 (int64)", "COLLECT", "SHORT_PIPE"),
 	},
 	{
-		`d0.a`,
-		append(make([]interface{}, 0), "d0", "SHORT_PIPE", "a"),
-		append(make([]interface{}, 0), "d0", "a", "SHORT_PIPE"),
+		`.key.array + .key.array2`,
+		append(make([]interface{}, 0), "key", "SHORT_PIPE", "array", "ADD", "key", "SHORT_PIPE", "array2"),
+		append(make([]interface{}, 0), "key", "array", "SHORT_PIPE", "key", "array2", "SHORT_PIPE", "ADD"),
+	},
+	{
+		`.key.array * .key.array2`,
+		append(make([]interface{}, 0), "key", "SHORT_PIPE", "array", "MULTIPLY", "key", "SHORT_PIPE", "array2"),
+		append(make([]interface{}, 0), "key", "array", "SHORT_PIPE", "key", "array2", "SHORT_PIPE", "MULTIPLY"),
+	},
+	{
+		`.key.array // .key.array2`,
+		append(make([]interface{}, 0), "key", "SHORT_PIPE", "array", "ALTERNATIVE", "key", "SHORT_PIPE", "array2"),
+		append(make([]interface{}, 0), "key", "array", "SHORT_PIPE", "key", "array2", "SHORT_PIPE", "ALTERNATIVE"),
 	},
 	{
 		`.a | .[].b == "apple"`,
-		append(make([]interface{}, 0), "a", "PIPE", "TRAVERSE_ARRAY", "[", "]", "SHORT_PIPE", "b", "EQUALS", "apple (string)"),
-		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "b", "SHORT_PIPE", "apple (string)", "EQUALS", "PIPE"),
+		append(make([]interface{}, 0), "a", "PIPE", "SELF", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "SHORT_PIPE", "b", "EQUALS", "apple (string)"),
+		append(make([]interface{}, 0), "a", "SELF", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "b", "SHORT_PIPE", "apple (string)", "EQUALS", "PIPE"),
 	},
 	{
 		`(.a | .[].b) == "apple"`,
-		append(make([]interface{}, 0), "(", "a", "PIPE", "TRAVERSE_ARRAY", "[", "]", "SHORT_PIPE", "b", ")", "EQUALS", "apple (string)"),
-		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "b", "SHORT_PIPE", "PIPE", "apple (string)", "EQUALS"),
+		append(make([]interface{}, 0), "(", "a", "PIPE", "SELF", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "SHORT_PIPE", "b", ")", "EQUALS", "apple (string)"),
+		append(make([]interface{}, 0), "a", "SELF", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "b", "SHORT_PIPE", "PIPE", "apple (string)", "EQUALS"),
 	},
 	{
 		`.[] | select(. == "*at")`,
-		append(make([]interface{}, 0), "TRAVERSE_ARRAY", "[", "]", "PIPE", "SELECT", "(", "SELF", "EQUALS", "*at (string)", ")"),
-		append(make([]interface{}, 0), "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SELF", "*at (string)", "EQUALS", "SELECT", "PIPE"),
+		append(make([]interface{}, 0), "SELF", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "PIPE", "SELECT", "(", "SELF", "EQUALS", "*at (string)", ")"),
+		append(make([]interface{}, 0), "SELF", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SELF", "*at (string)", "EQUALS", "SELECT", "PIPE"),
 	},
 	{
 		`[true]`,
@@ -103,9 +138,9 @@ var pathTests = []struct {
 		append(make([]interface{}, 0), "a", "mike (string)", "CREATE_MAP", "COLLECT_OBJECT", "SHORT_PIPE"),
 	},
 	{
-		`{.a: .c, .b.[]: .f.g.[]}`,
-		append(make([]interface{}, 0), "{", "a", "CREATE_MAP", "c", "UNION", "b", "SHORT_PIPE", "TRAVERSE_ARRAY", "[", "]", "CREATE_MAP", "f", "SHORT_PIPE", "g", "SHORT_PIPE", "TRAVERSE_ARRAY", "[", "]", "}"),
-		append(make([]interface{}, 0), "a", "c", "CREATE_MAP", "b", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE", "f", "g", "SHORT_PIPE", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE", "CREATE_MAP", "UNION", "COLLECT_OBJECT", "SHORT_PIPE"),
+		`{.a: .c, .b.[]: .f.g[]}`,
+		append(make([]interface{}, 0), "{", "a", "CREATE_MAP", "c", "UNION", "b", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "CREATE_MAP", "f", "SHORT_PIPE", "g", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "}"),
+		append(make([]interface{}, 0), "a", "c", "CREATE_MAP", "b", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "f", "g", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE", "CREATE_MAP", "UNION", "COLLECT_OBJECT", "SHORT_PIPE"),
 	},
 	{
 		`explode(.a.b)`,
@@ -157,15 +192,10 @@ var pathTests = []struct {
 		append(make([]interface{}, 0), "foo*", "PIPE", "(", "SELF", "ASSIGN_STYLE", "flow (string)", ")"),
 		append(make([]interface{}, 0), "foo*", "SELF", "flow (string)", "ASSIGN_STYLE", "PIPE"),
 	},
-	{
-		`{}`,
-		append(make([]interface{}, 0), "{", "}"),
-		append(make([]interface{}, 0), "EMPTY", "COLLECT_OBJECT", "SHORT_PIPE"),
-	},
 }
 
-var tokeniser = NewPathTokeniser()
-var postFixer = NewPathPostFixer()
+var tokeniser = newExpressionTokeniser()
+var postFixer = newExpressionPostFixer()
 
 func TestPathParsing(t *testing.T) {
 	for _, tt := range pathTests {
@@ -175,7 +205,7 @@ func TestPathParsing(t *testing.T) {
 		}
 		var tokenValues []interface{}
 		for _, token := range tokens {
-			tokenValues = append(tokenValues, token.toString())
+			tokenValues = append(tokenValues, token.toString(false))
 		}
 		test.AssertResultComplexWithContext(t, tt.expectedTokens, tokenValues, fmt.Sprintf("tokenise: %v", tt.path))
 

pkg/yqlib/expression_tokeniser.go

@@ -0,0 +1,434 @@
+package yqlib
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	lex "github.com/timtadh/lexmachine"
+	"github.com/timtadh/lexmachine/machines"
+)
+
+func skip(*lex.Scanner, *machines.Match) (interface{}, error) {
+	return nil, nil
+}
+
+type tokenType uint32
+
+const (
+	operationToken = 1 << iota
+	openBracket
+	closeBracket
+	openCollect
+	closeCollect
+	openCollectObject
+	closeCollectObject
+	traverseArrayCollect
+)
+
+type token struct {
+	TokenType            tokenType
+	Operation            *Operation
+	AssignOperation      *Operation // e.g. tag (GetTag) op becomes AssignTag if '=' follows it
+	CheckForPostTraverse bool       // e.g. [1]cat should really be [1].cat
+
+}
+
+func (t *token) toString(detail bool) string {
+	if t.TokenType == operationToken {
+		if detail {
+			return fmt.Sprintf("%v (%v)", t.Operation.toString(), t.Operation.OperationType.Precedence)
+		}
+		return t.Operation.toString()
+	} else if t.TokenType == openBracket {
+		return "("
+	} else if t.TokenType == closeBracket {
+		return ")"
+	} else if t.TokenType == openCollect {
+		return "["
+	} else if t.TokenType == closeCollect {
+		return "]"
+	} else if t.TokenType == openCollectObject {
+		return "{"
+	} else if t.TokenType == closeCollectObject {
+		return "}"
+	} else if t.TokenType == traverseArrayCollect {
+		return ".["
+
+	} else {
+		return "NFI"
+	}
+}
+
+func pathToken(wrapped bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		value := string(m.Bytes)
+		value = value[1:]
+		if wrapped {
+			value = unwrap(value)
+		}
+		log.Debug("PathToken %v", value)
+		op := &Operation{OperationType: traversePathOpType, Value: value, StringValue: value, Preferences: traversePreferences{}}
+		return &token{TokenType: operationToken, Operation: op, CheckForPostTraverse: true}, nil
+	}
+}
+
+func opToken(op *operationType) lex.Action {
+	return opTokenWithPrefs(op, nil, nil)
+}
+
+func opAssignableToken(opType *operationType, assignOpType *operationType) lex.Action {
+	return opTokenWithPrefs(opType, assignOpType, nil)
+}
+
+func assignOpToken(updateAssign bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		log.Debug("assignOpToken %v", string(m.Bytes))
+		value := string(m.Bytes)
+		op := &Operation{OperationType: assignOpType, Value: assignOpType.Type, StringValue: value, UpdateAssign: updateAssign}
+		return &token{TokenType: operationToken, Operation: op}, nil
+	}
+}
+
+func multiplyWithPrefs() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		prefs := multiplyPreferences{}
+		options := string(m.Bytes)
+		if strings.Contains(options, "+") {
+			prefs.AppendArrays = true
+		}
+		if strings.Contains(options, "?") {
+			prefs.TraversePrefs = traversePreferences{DontAutoCreate: true}
+		}
+		op := &Operation{OperationType: multiplyOpType, Value: multiplyOpType.Type, StringValue: options, Preferences: prefs}
+		return &token{TokenType: operationToken, Operation: op}, nil
+	}
+}
+
+func opTokenWithPrefs(op *operationType, assignOpType *operationType, preferences interface{}) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		log.Debug("opTokenWithPrefs %v", string(m.Bytes))
+		value := string(m.Bytes)
+		op := &Operation{OperationType: op, Value: op.Type, StringValue: value, Preferences: preferences}
+		var assign *Operation
+		if assignOpType != nil {
+			assign = &Operation{OperationType: assignOpType, Value: assignOpType.Type, StringValue: value, Preferences: preferences}
+		}
+		return &token{TokenType: operationToken, Operation: op, AssignOperation: assign}, nil
+	}
+}
+
+func assignAllCommentsOp(updateAssign bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		log.Debug("assignAllCommentsOp %v", string(m.Bytes))
+		value := string(m.Bytes)
+		op := &Operation{
+			OperationType: assignCommentOpType,
+			Value:         assignCommentOpType.Type,
+			StringValue:   value,
+			UpdateAssign:  updateAssign,
+			Preferences:   commentOpPreferences{LineComment: true, HeadComment: true, FootComment: true},
+		}
+		return &token{TokenType: operationToken, Operation: op}, nil
+	}
+}
+
+func literalToken(pType tokenType, checkForPost bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		return &token{TokenType: pType, CheckForPostTraverse: checkForPost}, nil
+	}
+}
+
+func unwrap(value string) string {
+	return value[1 : len(value)-1]
+}
+
+func numberValue() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		var numberString = string(m.Bytes)
+		var number, errParsingInt = strconv.ParseInt(numberString, 10, 64) // nolint
+		if errParsingInt != nil {
+			return nil, errParsingInt
+		}
+
+		return &token{TokenType: operationToken, Operation: createValueOperation(number, numberString)}, nil
+	}
+}
+
+func floatValue() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		var numberString = string(m.Bytes)
+		var number, errParsingInt = strconv.ParseFloat(numberString, 64) // nolint
+		if errParsingInt != nil {
+			return nil, errParsingInt
+		}
+		return &token{TokenType: operationToken, Operation: createValueOperation(number, numberString)}, nil
+	}
+}
+
+func booleanValue(val bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		return &token{TokenType: operationToken, Operation: createValueOperation(val, string(m.Bytes))}, nil
+	}
+}
+
+func stringValue(wrapped bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		value := string(m.Bytes)
+		if wrapped {
+			value = unwrap(value)
+		}
+		return &token{TokenType: operationToken, Operation: createValueOperation(value, value)}, nil
+	}
+}
+
+func getVariableOpToken() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		value := string(m.Bytes)
+
+		value = value[1 : len(value)-1]
+
+		getVarOperation := createValueOperation(value, value)
+		getVarOperation.OperationType = getVariableOpType
+
+		return &token{TokenType: operationToken, Operation: getVarOperation, CheckForPostTraverse: true}, nil
+	}
+}
+
+func envOp(strenv bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		value := string(m.Bytes)
+		preferences := envOpPreferences{}
+
+		if strenv {
+			// strenv( )
+			value = value[7 : len(value)-1]
+			preferences.StringValue = true
+		} else {
+			//env( )
+			value = value[4 : len(value)-1]
+		}
+
+		envOperation := createValueOperation(value, value)
+		envOperation.OperationType = envOpType
+		envOperation.Preferences = preferences
+
+		return &token{TokenType: operationToken, Operation: envOperation}, nil
+	}
+}
+
+func nullValue() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		return &token{TokenType: operationToken, Operation: createValueOperation(nil, string(m.Bytes))}, nil
+	}
+}
+
+func selfToken() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		op := &Operation{OperationType: selfReferenceOpType}
+		return &token{TokenType: operationToken, Operation: op}, nil
+	}
+}
+
+func initLexer() (*lex.Lexer, error) {
+	lexer := lex.NewLexer()
+	lexer.Add([]byte(`\(`), literalToken(openBracket, false))
+	lexer.Add([]byte(`\)`), literalToken(closeBracket, true))
+
+	lexer.Add([]byte(`\.\[`), literalToken(traverseArrayCollect, false))
+	lexer.Add([]byte(`\.\.`), opTokenWithPrefs(recursiveDescentOpType, nil, recursiveDescentPreferences{RecurseArray: true,
+		TraversePreferences: traversePreferences{DontFollowAlias: true, IncludeMapKeys: false}}))
+
+	lexer.Add([]byte(`\.\.\.`), opTokenWithPrefs(recursiveDescentOpType, nil, recursiveDescentPreferences{RecurseArray: true,
+		TraversePreferences: traversePreferences{DontFollowAlias: true, IncludeMapKeys: true}}))
+
+	lexer.Add([]byte(`,`), opToken(unionOpType))
+	lexer.Add([]byte(`:\s*`), opToken(createMapOpType))
+	lexer.Add([]byte(`length`), opToken(lengthOpType))
+	lexer.Add([]byte(`sortKeys`), opToken(sortKeysOpType))
+	lexer.Add([]byte(`select`), opToken(selectOpType))
+	lexer.Add([]byte(`has`), opToken(hasOpType))
+	lexer.Add([]byte(`explode`), opToken(explodeOpType))
+	lexer.Add([]byte(`or`), opToken(orOpType))
+	lexer.Add([]byte(`and`), opToken(andOpType))
+	lexer.Add([]byte(`not`), opToken(notOpType))
+	lexer.Add([]byte(`\/\/`), opToken(alternativeOpType))
+
+	lexer.Add([]byte(`documentIndex`), opToken(getDocumentIndexOpType))
+	lexer.Add([]byte(`di`), opToken(getDocumentIndexOpType))
+	lexer.Add([]byte(`splitDoc`), opToken(splitDocumentOpType))
+
+	lexer.Add([]byte(`join`), opToken(joinStringOpType))
+	lexer.Add([]byte(`split`), opToken(splitStringOpType))
+	lexer.Add([]byte(`keys`), opToken(keysOpType))
+
+	lexer.Add([]byte(`style`), opAssignableToken(getStyleOpType, assignStyleOpType))
+
+	lexer.Add([]byte(`tag`), opAssignableToken(getTagOpType, assignTagOpType))
+	lexer.Add([]byte(`anchor`), opAssignableToken(getAnchorOpType, assignAnchorOpType))
+	lexer.Add([]byte(`alias`), opAssignableToken(getAliasOptype, assignAliasOpType))
+	lexer.Add([]byte(`filename`), opToken(getFilenameOpType))
+	lexer.Add([]byte(`fileIndex`), opToken(getFileIndexOpType))
+	lexer.Add([]byte(`fi`), opToken(getFileIndexOpType))
+	lexer.Add([]byte(`path`), opToken(getPathOpType))
+
+	lexer.Add([]byte(`lineComment`), opTokenWithPrefs(getCommentOpType, assignCommentOpType, commentOpPreferences{LineComment: true}))
+
+	lexer.Add([]byte(`headComment`), opTokenWithPrefs(getCommentOpType, assignCommentOpType, commentOpPreferences{HeadComment: true}))
+
+	lexer.Add([]byte(`footComment`), opTokenWithPrefs(getCommentOpType, assignCommentOpType, commentOpPreferences{FootComment: true}))
+
+	lexer.Add([]byte(`comments\s*=`), assignAllCommentsOp(false))
+	lexer.Add([]byte(`comments\s*\|=`), assignAllCommentsOp(true))
+
+	lexer.Add([]byte(`collect`), opToken(collectOpType))
+
+	lexer.Add([]byte(`\s*==\s*`), opToken(equalsOpType))
+	lexer.Add([]byte(`\s*!=\s*`), opToken(notEqualsOpType))
+	lexer.Add([]byte(`\s*=\s*`), assignOpToken(false))
+
+	lexer.Add([]byte(`del`), opToken(deleteChildOpType))
+
+	lexer.Add([]byte(`\s*\|=\s*`), assignOpToken(true))
+
+	lexer.Add([]byte("( |\t|\n|\r)+"), skip)
+
+	lexer.Add([]byte(`\."[^ "]+"`), pathToken(true))
+	lexer.Add([]byte(`\.[^ \}\{\:\[\],\|\.\[\(\)=]+`), pathToken(false))
+	lexer.Add([]byte(`\.`), selfToken())
+
+	lexer.Add([]byte(`\|`), opToken(pipeOpType))
+
+	lexer.Add([]byte(`-?\d+(\.\d+)`), floatValue())
+	lexer.Add([]byte(`-?[1-9](\.\d+)?[Ee][-+]?\d+`), floatValue())
+	lexer.Add([]byte(`-?\d+`), numberValue())
+
+	lexer.Add([]byte(`[Tt][Rr][Uu][Ee]`), booleanValue(true))
+	lexer.Add([]byte(`[Ff][Aa][Ll][Ss][Ee]`), booleanValue(false))
+
+	lexer.Add([]byte(`[Nn][Uu][Ll][Ll]`), nullValue())
+	lexer.Add([]byte(`~`), nullValue())
+
+	lexer.Add([]byte(`"[^"]*"`), stringValue(true))
+	lexer.Add([]byte(`strenv\([^\)]+\)`), envOp(true))
+	lexer.Add([]byte(`env\([^\)]+\)`), envOp(false))
+
+	lexer.Add([]byte(`\[`), literalToken(openCollect, false))
+	lexer.Add([]byte(`\]`), literalToken(closeCollect, true))
+	lexer.Add([]byte(`\{`), literalToken(openCollectObject, false))
+	lexer.Add([]byte(`\}`), literalToken(closeCollectObject, true))
+	lexer.Add([]byte(`\*[\+|\?]*`), multiplyWithPrefs())
+	lexer.Add([]byte(`\+`), opToken(addOpType))
+	lexer.Add([]byte(`\+=`), opToken(addAssignOpType))
+	lexer.Add([]byte(`\$[a-zA-Z_-0-9]+`), getVariableOpToken())
+	lexer.Add([]byte(`as`), opToken(assignVariableOpType))
+
+	err := lexer.Compile()
+	if err != nil {
+		return nil, err
+	}
+	return lexer, nil
+}
+
+type expressionTokeniser interface {
+	Tokenise(expression string) ([]*token, error)
+}
+
+type expressionTokeniserImpl struct {
+	lexer *lex.Lexer
+}
+
+func newExpressionTokeniser() expressionTokeniser {
+	var lexer, err = initLexer()
+	if err != nil {
+		panic(err)
+	}
+	return &expressionTokeniserImpl{lexer}
+}
+
+func (p *expressionTokeniserImpl) Tokenise(expression string) ([]*token, error) {
+	scanner, err := p.lexer.Scanner([]byte(expression))
+
+	if err != nil {
+		return nil, fmt.Errorf("Parsing expression: %v", err)
+	}
+	var tokens []*token
+	for tok, err, eof := scanner.Next(); !eof; tok, err, eof = scanner.Next() {
+
+		if tok != nil {
+			currentToken := tok.(*token)
+			log.Debugf("Tokenising %v", currentToken.toString(true))
+			tokens = append(tokens, currentToken)
+		}
+		if err != nil {
+			return nil, fmt.Errorf("Parsing expression: %v", err)
+		}
+	}
+	var postProcessedTokens = make([]*token, 0)
+
+	skipNextToken := false
+
+	for index := range tokens {
+		if skipNextToken {
+			skipNextToken = false
+		} else {
+			postProcessedTokens, skipNextToken = p.handleToken(tokens, index, postProcessedTokens)
+		}
+	}
+
+	return postProcessedTokens, nil
+}
+
+func (p *expressionTokeniserImpl) handleToken(tokens []*token, index int, postProcessedTokens []*token) (tokensAccum []*token, skipNextToken bool) {
+	skipNextToken = false
+	currentToken := tokens[index]
+
+	if currentToken.TokenType == traverseArrayCollect {
+		//need to put a traverse array then a collect currentToken
+		// do this by adding traverse then converting currentToken to collect
+
+		if index == 0 || tokens[index-1].TokenType != operationToken ||
+			tokens[index-1].Operation.OperationType != traversePathOpType {
+			op := &Operation{OperationType: selfReferenceOpType, StringValue: "SELF"}
+			postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
+		}
+
+		op := &Operation{OperationType: traverseArrayOpType, StringValue: "TRAVERSE_ARRAY"}
+		postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
+
+		currentToken = &token{TokenType: openCollect}
+
+	}
+
+	if index != len(tokens)-1 && currentToken.AssignOperation != nil &&
+		tokens[index+1].TokenType == operationToken &&
+		tokens[index+1].Operation.OperationType == assignOpType {
+		currentToken.Operation = currentToken.AssignOperation
+		currentToken.Operation.UpdateAssign = tokens[index+1].Operation.UpdateAssign
+		skipNextToken = true
+	}
+
+	postProcessedTokens = append(postProcessedTokens, currentToken)
+
+	if index != len(tokens)-1 &&
+		((currentToken.TokenType == openCollect && tokens[index+1].TokenType == closeCollect) ||
+			(currentToken.TokenType == openCollectObject && tokens[index+1].TokenType == closeCollectObject)) {
+
+		op := &Operation{OperationType: emptyOpType, StringValue: "EMPTY"}
+		postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
+	}
+
+	if index != len(tokens)-1 && currentToken.CheckForPostTraverse &&
+		tokens[index+1].TokenType == operationToken &&
+		tokens[index+1].Operation.OperationType == traversePathOpType {
+		op := &Operation{OperationType: shortPipeOpType, Value: "PIPE"}
+		postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
+	}
+	if index != len(tokens)-1 && currentToken.CheckForPostTraverse &&
+		tokens[index+1].TokenType == openCollect {
+
+		op := &Operation{OperationType: traverseArrayOpType}
+		postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
+	}
+	return postProcessedTokens, skipNextToken
+}

pkg/yqlib/lib.go

@@ -1,3 +1,5 @@
+// Use the top level Evaluator or StreamEvaluator to evaluate expressions and return matches.
+//
 package yqlib
 
 import (
@@ -11,86 +13,92 @@ import (
 
 var log = logging.MustGetLogger("yq-lib")
 
-type OperationType struct {
+type operationType struct {
 	Type       string
 	NumArgs    uint // number of arguments to the op
 	Precedence uint
-	Handler    OperatorHandler
+	Handler    operatorHandler
 }
 
 // operators TODO:
-// - keys operator for controlling key metadata (particularly anchors/aliases)
 // - mergeEmpty (sets only if the document is empty, do I do that now?)
 
-var Or = &OperationType{Type: "OR", NumArgs: 2, Precedence: 20, Handler: OrOperator}
-var And = &OperationType{Type: "AND", NumArgs: 2, Precedence: 20, Handler: AndOperator}
+var orOpType = &operationType{Type: "OR", NumArgs: 2, Precedence: 20, Handler: orOperator}
+var andOpType = &operationType{Type: "AND", NumArgs: 2, Precedence: 20, Handler: andOperator}
 
-var Union = &OperationType{Type: "UNION", NumArgs: 2, Precedence: 10, Handler: UnionOperator}
+var unionOpType = &operationType{Type: "UNION", NumArgs: 2, Precedence: 10, Handler: unionOperator}
 
-var Pipe = &OperationType{Type: "PIPE", NumArgs: 2, Precedence: 30, Handler: PipeOperator}
+var pipeOpType = &operationType{Type: "PIPE", NumArgs: 2, Precedence: 30, Handler: pipeOperator}
 
-var Assign = &OperationType{Type: "ASSIGN", NumArgs: 2, Precedence: 40, Handler: AssignUpdateOperator}
-var AddAssign = &OperationType{Type: "ADD_ASSIGN", NumArgs: 2, Precedence: 40, Handler: AddAssignOperator}
+var assignOpType = &operationType{Type: "ASSIGN", NumArgs: 2, Precedence: 40, Handler: assignUpdateOperator}
+var addAssignOpType = &operationType{Type: "ADD_ASSIGN", NumArgs: 2, Precedence: 40, Handler: addAssignOperator}
 
-var AssignAttributes = &OperationType{Type: "ASSIGN_ATTRIBUTES", NumArgs: 2, Precedence: 40, Handler: AssignAttributesOperator}
-var AssignStyle = &OperationType{Type: "ASSIGN_STYLE", NumArgs: 2, Precedence: 40, Handler: AssignStyleOperator}
-var AssignTag = &OperationType{Type: "ASSIGN_TAG", NumArgs: 2, Precedence: 40, Handler: AssignTagOperator}
-var AssignComment = &OperationType{Type: "ASSIGN_COMMENT", NumArgs: 2, Precedence: 40, Handler: AssignCommentsOperator}
-var AssignAnchor = &OperationType{Type: "ASSIGN_ANCHOR", NumArgs: 2, Precedence: 40, Handler: AssignAnchorOperator}
-var AssignAlias = &OperationType{Type: "ASSIGN_ALIAS", NumArgs: 2, Precedence: 40, Handler: AssignAliasOperator}
+var assignAttributesOpType = &operationType{Type: "ASSIGN_ATTRIBUTES", NumArgs: 2, Precedence: 40, Handler: assignAttributesOperator}
+var assignStyleOpType = &operationType{Type: "ASSIGN_STYLE", NumArgs: 2, Precedence: 40, Handler: assignStyleOperator}
+var assignVariableOpType = &operationType{Type: "ASSIGN_VARIABLE", NumArgs: 2, Precedence: 40, Handler: assignVariableOperator}
+var assignTagOpType = &operationType{Type: "ASSIGN_TAG", NumArgs: 2, Precedence: 40, Handler: assignTagOperator}
+var assignCommentOpType = &operationType{Type: "ASSIGN_COMMENT", NumArgs: 2, Precedence: 40, Handler: assignCommentsOperator}
+var assignAnchorOpType = &operationType{Type: "ASSIGN_ANCHOR", NumArgs: 2, Precedence: 40, Handler: assignAnchorOperator}
+var assignAliasOpType = &operationType{Type: "ASSIGN_ALIAS", NumArgs: 2, Precedence: 40, Handler: assignAliasOperator}
 
-var Multiply = &OperationType{Type: "MULTIPLY", NumArgs: 2, Precedence: 45, Handler: MultiplyOperator}
-var Add = &OperationType{Type: "ADD", NumArgs: 2, Precedence: 45, Handler: AddOperator}
-var Alternative = &OperationType{Type: "ALTERNATIVE", NumArgs: 2, Precedence: 45, Handler: AlternativeOperator}
+var multiplyOpType = &operationType{Type: "MULTIPLY", NumArgs: 2, Precedence: 42, Handler: multiplyOperator}
+var addOpType = &operationType{Type: "ADD", NumArgs: 2, Precedence: 42, Handler: addOperator}
+var alternativeOpType = &operationType{Type: "ALTERNATIVE", NumArgs: 2, Precedence: 42, Handler: alternativeOperator}
 
-var Equals = &OperationType{Type: "EQUALS", NumArgs: 2, Precedence: 40, Handler: EqualsOperator}
-var CreateMap = &OperationType{Type: "CREATE_MAP", NumArgs: 2, Precedence: 40, Handler: CreateMapOperator}
+var equalsOpType = &operationType{Type: "EQUALS", NumArgs: 2, Precedence: 40, Handler: equalsOperator}
+var notEqualsOpType = &operationType{Type: "EQUALS", NumArgs: 2, Precedence: 40, Handler: notEqualsOperator}
+var createMapOpType = &operationType{Type: "CREATE_MAP", NumArgs: 2, Precedence: 40, Handler: createMapOperator}
 
-var ShortPipe = &OperationType{Type: "SHORT_PIPE", NumArgs: 2, Precedence: 45, Handler: PipeOperator}
+var shortPipeOpType = &operationType{Type: "SHORT_PIPE", NumArgs: 2, Precedence: 45, Handler: pipeOperator}
 
-var Length = &OperationType{Type: "LENGTH", NumArgs: 0, Precedence: 50, Handler: LengthOperator}
-var Collect = &OperationType{Type: "COLLECT", NumArgs: 0, Precedence: 50, Handler: CollectOperator}
-var GetStyle = &OperationType{Type: "GET_STYLE", NumArgs: 0, Precedence: 50, Handler: GetStyleOperator}
-var GetTag = &OperationType{Type: "GET_TAG", NumArgs: 0, Precedence: 50, Handler: GetTagOperator}
-var GetComment = &OperationType{Type: "GET_COMMENT", NumArgs: 0, Precedence: 50, Handler: GetCommentsOperator}
-var GetAnchor = &OperationType{Type: "GET_ANCHOR", NumArgs: 0, Precedence: 50, Handler: GetAnchorOperator}
-var GetAlias = &OperationType{Type: "GET_ALIAS", NumArgs: 0, Precedence: 50, Handler: GetAliasOperator}
-var GetDocumentIndex = &OperationType{Type: "GET_DOCUMENT_INDEX", NumArgs: 0, Precedence: 50, Handler: GetDocumentIndexOperator}
-var GetFilename = &OperationType{Type: "GET_FILENAME", NumArgs: 0, Precedence: 50, Handler: GetFilenameOperator}
-var GetFileIndex = &OperationType{Type: "GET_FILE_INDEX", NumArgs: 0, Precedence: 50, Handler: GetFileIndexOperator}
-var GetPath = &OperationType{Type: "GET_PATH", NumArgs: 0, Precedence: 50, Handler: GetPathOperator}
+var lengthOpType = &operationType{Type: "LENGTH", NumArgs: 0, Precedence: 50, Handler: lengthOperator}
+var collectOpType = &operationType{Type: "COLLECT", NumArgs: 0, Precedence: 50, Handler: collectOperator}
+var splitDocumentOpType = &operationType{Type: "SPLIT_DOC", NumArgs: 0, Precedence: 50, Handler: splitDocumentOperator}
+var getVariableOpType = &operationType{Type: "GET_VARIABLE", NumArgs: 0, Precedence: 55, Handler: getVariableOperator}
+var getStyleOpType = &operationType{Type: "GET_STYLE", NumArgs: 0, Precedence: 50, Handler: getStyleOperator}
+var getTagOpType = &operationType{Type: "GET_TAG", NumArgs: 0, Precedence: 50, Handler: getTagOperator}
+var getCommentOpType = &operationType{Type: "GET_COMMENT", NumArgs: 0, Precedence: 50, Handler: getCommentsOperator}
+var getAnchorOpType = &operationType{Type: "GET_ANCHOR", NumArgs: 0, Precedence: 50, Handler: getAnchorOperator}
+var getAliasOptype = &operationType{Type: "GET_ALIAS", NumArgs: 0, Precedence: 50, Handler: getAliasOperator}
+var getDocumentIndexOpType = &operationType{Type: "GET_DOCUMENT_INDEX", NumArgs: 0, Precedence: 50, Handler: getDocumentIndexOperator}
+var getFilenameOpType = &operationType{Type: "GET_FILENAME", NumArgs: 0, Precedence: 50, Handler: getFilenameOperator}
+var getFileIndexOpType = &operationType{Type: "GET_FILE_INDEX", NumArgs: 0, Precedence: 50, Handler: getFileIndexOperator}
+var getPathOpType = &operationType{Type: "GET_PATH", NumArgs: 0, Precedence: 50, Handler: getPathOperator}
 
-var Explode = &OperationType{Type: "EXPLODE", NumArgs: 1, Precedence: 50, Handler: ExplodeOperator}
-var SortKeys = &OperationType{Type: "SORT_KEYS", NumArgs: 1, Precedence: 50, Handler: SortKeysOperator}
+var explodeOpType = &operationType{Type: "EXPLODE", NumArgs: 1, Precedence: 50, Handler: explodeOperator}
+var sortKeysOpType = &operationType{Type: "SORT_KEYS", NumArgs: 1, Precedence: 50, Handler: sortKeysOperator}
+var joinStringOpType = &operationType{Type: "JOIN", NumArgs: 1, Precedence: 50, Handler: joinStringOperator}
+var splitStringOpType = &operationType{Type: "SPLIT", NumArgs: 1, Precedence: 50, Handler: splitStringOperator}
 
-var CollectObject = &OperationType{Type: "COLLECT_OBJECT", NumArgs: 0, Precedence: 50, Handler: CollectObjectOperator}
-var TraversePath = &OperationType{Type: "TRAVERSE_PATH", NumArgs: 0, Precedence: 50, Handler: TraversePathOperator}
-var TraverseArray = &OperationType{Type: "TRAVERSE_ARRAY", NumArgs: 1, Precedence: 50, Handler: TraverseArrayOperator}
+var keysOpType = &operationType{Type: "KEYS", NumArgs: 0, Precedence: 50, Handler: keysOperator}
 
-var DocumentFilter = &OperationType{Type: "DOCUMENT_FILTER", NumArgs: 0, Precedence: 50, Handler: TraversePathOperator}
-var SelfReference = &OperationType{Type: "SELF", NumArgs: 0, Precedence: 50, Handler: SelfOperator}
-var ValueOp = &OperationType{Type: "VALUE", NumArgs: 0, Precedence: 50, Handler: ValueOperator}
-var EnvOp = &OperationType{Type: "ENV", NumArgs: 0, Precedence: 50, Handler: EnvOperator}
-var Not = &OperationType{Type: "NOT", NumArgs: 0, Precedence: 50, Handler: NotOperator}
-var Empty = &OperationType{Type: "EMPTY", NumArgs: 50, Handler: EmptyOperator}
+var collectObjectOpType = &operationType{Type: "COLLECT_OBJECT", NumArgs: 0, Precedence: 50, Handler: collectObjectOperator}
+var traversePathOpType = &operationType{Type: "TRAVERSE_PATH", NumArgs: 0, Precedence: 55, Handler: traversePathOperator}
+var traverseArrayOpType = &operationType{Type: "TRAVERSE_ARRAY", NumArgs: 2, Precedence: 50, Handler: traverseArrayOperator}
 
-var RecursiveDescent = &OperationType{Type: "RECURSIVE_DESCENT", NumArgs: 0, Precedence: 50, Handler: RecursiveDescentOperator}
+var selfReferenceOpType = &operationType{Type: "SELF", NumArgs: 0, Precedence: 55, Handler: selfOperator}
+var valueOpType = &operationType{Type: "VALUE", NumArgs: 0, Precedence: 50, Handler: valueOperator}
+var envOpType = &operationType{Type: "ENV", NumArgs: 0, Precedence: 50, Handler: envOperator}
+var notOpType = &operationType{Type: "NOT", NumArgs: 0, Precedence: 50, Handler: notOperator}
+var emptyOpType = &operationType{Type: "EMPTY", NumArgs: 50, Handler: emptyOperator}
 
-var Select = &OperationType{Type: "SELECT", NumArgs: 1, Precedence: 50, Handler: SelectOperator}
-var Has = &OperationType{Type: "HAS", NumArgs: 1, Precedence: 50, Handler: HasOperator}
-var DeleteChild = &OperationType{Type: "DELETE", NumArgs: 1, Precedence: 40, Handler: DeleteChildOperator}
-var DeleteImmediateChild = &OperationType{Type: "DELETE_IMMEDIATE_CHILD", NumArgs: 1, Precedence: 40, Handler: DeleteImmediateChildOperator}
+var recursiveDescentOpType = &operationType{Type: "RECURSIVE_DESCENT", NumArgs: 0, Precedence: 50, Handler: recursiveDescentOperator}
+
+var selectOpType = &operationType{Type: "SELECT", NumArgs: 1, Precedence: 50, Handler: selectOperator}
+var hasOpType = &operationType{Type: "HAS", NumArgs: 1, Precedence: 50, Handler: hasOperator}
+var deleteChildOpType = &operationType{Type: "DELETE", NumArgs: 1, Precedence: 40, Handler: deleteChildOperator}
+var deleteImmediateChildOpType = &operationType{Type: "DELETE_IMMEDIATE_CHILD", NumArgs: 1, Precedence: 40, Handler: deleteImmediateChildOperator}
 
 type Operation struct {
-	OperationType *OperationType
+	OperationType *operationType
 	Value         interface{}
 	StringValue   string
 	CandidateNode *CandidateNode // used for Value Path elements
 	Preferences   interface{}
-	UpdateAssign  bool // used for assign ops, when true it means we evaluate the rhs given the lhs (instead of matching nodes)
+	UpdateAssign  bool // used for assign ops, when true it means we evaluate the rhs given the lhs
 }
 
-func CreateValueOperation(value interface{}, stringValue string) *Operation {
+func createValueOperation(value interface{}, stringValue string) *Operation {
 	var node yaml.Node = yaml.Node{Kind: yaml.ScalarNode}
 	node.Value = stringValue
 
@@ -108,7 +116,7 @@ func CreateValueOperation(value interface{}, stringValue string) *Operation {
 	}
 
 	return &Operation{
-		OperationType: ValueOp,
+		OperationType: valueOpType,
 		Value:         value,
 		StringValue:   stringValue,
 		CandidateNode: &CandidateNode{Node: &node},
@@ -117,13 +125,11 @@ func CreateValueOperation(value interface{}, stringValue string) *Operation {
 
 // debugging purposes only
 func (p *Operation) toString() string {
-	if p.OperationType == TraversePath {
+	if p.OperationType == traversePathOpType {
 		return fmt.Sprintf("%v", p.Value)
-	} else if p.OperationType == DocumentFilter {
-		return fmt.Sprintf("d%v", p.Value)
-	} else if p.OperationType == SelfReference {
+	} else if p.OperationType == selfReferenceOpType {
 		return "SELF"
-	} else if p.OperationType == ValueOp {
+	} else if p.OperationType == valueOpType {
 		return fmt.Sprintf("%v (%T)", p.Value, p.Value)
 	} else {
 		return fmt.Sprintf("%v", p.OperationType.Type)

pkg/yqlib/matchKeyString.go

@@ -1,6 +1,6 @@
 package yqlib
 
-func Match(name string, pattern string) (matched bool) {
+func matchKey(name string, pattern string) (matched bool) {
 	if pattern == "" {
 		return name == pattern
 	}

pkg/yqlib/operator_add.go

@@ -3,23 +3,23 @@ package yqlib
 import (
 	"fmt"
 
-	"container/list"
+	"strconv"
 
 	yaml "gopkg.in/yaml.v3"
 )
 
-func createSelfAddOp(rhs *PathTreeNode) *PathTreeNode {
-	return &PathTreeNode{Operation: &Operation{OperationType: Add},
-		Lhs: &PathTreeNode{Operation: &Operation{OperationType: SelfReference}},
+func createAddOp(lhs *ExpressionNode, rhs *ExpressionNode) *ExpressionNode {
+	return &ExpressionNode{Operation: &Operation{OperationType: addOpType},
+		Lhs: lhs,
 		Rhs: rhs}
 }
 
-func AddAssignOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	assignmentOp := &Operation{OperationType: Assign}
-	assignmentOp.UpdateAssign = true
+func addAssignOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	assignmentOp := &Operation{OperationType: assignOpType}
+	assignmentOp.UpdateAssign = false
 
-	assignmentOpNode := &PathTreeNode{Operation: assignmentOp, Lhs: pathNode.Lhs, Rhs: createSelfAddOp(pathNode.Rhs)}
-	return d.GetMatchingNodes(matchingNodes, assignmentOpNode)
+	assignmentOpNode := &ExpressionNode{Operation: assignmentOp, Lhs: expressionNode.Lhs, Rhs: createAddOp(expressionNode.Lhs, expressionNode.Rhs)}
+	return d.GetMatchingNodes(context, assignmentOpNode)
 }
 
 func toNodes(candidate *CandidateNode) []*yaml.Node {
@@ -36,24 +36,24 @@ func toNodes(candidate *CandidateNode) []*yaml.Node {
 
 }
 
-func AddOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func addOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("Add operator")
 
-	return crossFunction(d, matchingNodes, pathNode, add)
+	return crossFunction(d, context, expressionNode, add)
 }
 
-func add(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
-	lhs.Node = UnwrapDoc(lhs.Node)
-	rhs.Node = UnwrapDoc(rhs.Node)
+func add(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+	lhs.Node = unwrapDoc(lhs.Node)
+	rhs.Node = unwrapDoc(rhs.Node)
 
-	target := &CandidateNode{
-		Path:     lhs.Path,
-		Document: lhs.Document,
-		Filename: lhs.Filename,
-		Node:     &yaml.Node{},
-	}
 	lhsNode := lhs.Node
 
+	if lhsNode.Tag == "!!null" {
+		return lhs.CreateChild(nil, rhs.Node), nil
+	}
+
+	target := lhs.CreateChild(nil, &yaml.Node{})
+
 	switch lhsNode.Kind {
 	case yaml.MappingNode:
 		return nil, fmt.Errorf("Maps not yet supported for addition")
@@ -63,7 +63,48 @@ func add(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*Candida
 		target.Node.Tag = "!!seq"
 		target.Node.Content = append(lhsNode.Content, toNodes(rhs)...)
 	case yaml.ScalarNode:
-		return nil, fmt.Errorf("Scalars not yet supported for addition")
+		if rhs.Node.Kind != yaml.ScalarNode {
+			return nil, fmt.Errorf("%v (%v) cannot be added to a %v", rhs.Node.Tag, rhs.Path, lhsNode.Tag)
+		}
+		target.Node.Kind = yaml.ScalarNode
+		target.Node.Style = lhsNode.Style
+		return addScalars(target, lhsNode, rhs.Node)
+	}
+
+	return target, nil
+}
+
+func addScalars(target *CandidateNode, lhs *yaml.Node, rhs *yaml.Node) (*CandidateNode, error) {
+
+	if lhs.Tag == "!!str" {
+		target.Node.Tag = "!!str"
+		target.Node.Value = lhs.Value + rhs.Value
+	} else if lhs.Tag == "!!int" && rhs.Tag == "!!int" {
+		lhsNum, err := strconv.Atoi(lhs.Value)
+		if err != nil {
+			return nil, err
+		}
+		rhsNum, err := strconv.Atoi(rhs.Value)
+		if err != nil {
+			return nil, err
+		}
+		sum := lhsNum + rhsNum
+		target.Node.Tag = "!!int"
+		target.Node.Value = fmt.Sprintf("%v", sum)
+	} else if (lhs.Tag == "!!int" || lhs.Tag == "!!float") && (rhs.Tag == "!!int" || rhs.Tag == "!!float") {
+		lhsNum, err := strconv.ParseFloat(lhs.Value, 64)
+		if err != nil {
+			return nil, err
+		}
+		rhsNum, err := strconv.ParseFloat(rhs.Value, 64)
+		if err != nil {
+			return nil, err
+		}
+		sum := lhsNum + rhsNum
+		target.Node.Tag = "!!float"
+		target.Node.Value = fmt.Sprintf("%v", sum)
+	} else {
+		return nil, fmt.Errorf("%v cannot be added to %v", lhs.Tag, rhs.Tag)
 	}
 
 	return target, nil

pkg/yqlib/operator_add_test.go

@@ -5,6 +5,15 @@ import (
 )
 
 var addOperatorScenarios = []expressionScenario{
+	{
+		skipDoc:    true,
+		document:   `[{a: foo, b: bar}, {a: 1, b: 2}]`,
+		expression: ".[] | .a + .b",
+		expected: []string{
+			"D0, P[0 a], (!!str)::foobar\n",
+			"D0, P[1 a], (!!int)::3\n",
+		},
+	},
 	{
 		description: "Concatenate and assign arrays",
 		document:    `{a: {val: thing, b: [cat,dog]}}`,
@@ -38,11 +47,11 @@ var addOperatorScenarios = []expressionScenario{
 		},
 	},
 	{
-		description: "Add object to array",
-		document:    `{a: [1,2], c: {cat: meow}}`,
-		expression:  `.a + .c`,
+		description: "Add new object to array",
+		document:    `a: [{dog: woof}]`,
+		expression:  `.a + {"cat": "meow"}`,
 		expected: []string{
-			"D0, P[a], (!!seq)::[1, 2, {cat: meow}]\n",
+			"D0, P[a], (!!seq)::[{dog: woof}, {cat: meow}]\n",
 		},
 	},
 	{
@@ -61,6 +70,56 @@ var addOperatorScenarios = []expressionScenario{
 			"D0, P[], (doc)::{a: [1, 2, 3, 4], b: [3, 4]}\n",
 		},
 	},
+	{
+		description: "String concatenation",
+		document:    `{a: cat, b: meow}`,
+		expression:  `.a = .a + .b`,
+		expected: []string{
+			"D0, P[], (doc)::{a: catmeow, b: meow}\n",
+		},
+	},
+	{
+		description: "Relative string concatenation",
+		document:    `{a: cat, b: meow}`,
+		expression:  `.a += .b`,
+		expected: []string{
+			"D0, P[], (doc)::{a: catmeow, b: meow}\n",
+		},
+	},
+	{
+		description:    "Number addition - float",
+		subdescription: "If the lhs or rhs are floats then the expression will be calculated with floats.",
+		document:       `{a: 3, b: 4.9}`,
+		expression:     `.a = .a + .b`,
+		expected: []string{
+			"D0, P[], (doc)::{a: 7.9, b: 4.9}\n",
+		},
+	},
+	{
+		description:    "Number addition - int",
+		subdescription: "If both the lhs and rhs are ints then the expression will be calculated with ints.",
+		document:       `{a: 3, b: 4}`,
+		expression:     `.a = .a + .b`,
+		expected: []string{
+			"D0, P[], (doc)::{a: 7, b: 4}\n",
+		},
+	},
+	{
+		description: "Increment number",
+		document:    `{a: 3}`,
+		expression:  `.a += 1`,
+		expected: []string{
+			"D0, P[], (doc)::{a: 4}\n",
+		},
+	},
+	{
+		description:    "Add to null",
+		subdescription: "Adding to null simply returns the rhs",
+		expression:     `null + "cat"`,
+		expected: []string{
+			"D0, P[], (!!str)::cat\n",
+		},
+	},
 }
 
 func TestAddOperatorScenarios(t *testing.T) {

pkg/yqlib/operator_alternative.go

@@ -1,20 +1,16 @@
 package yqlib
 
-import (
-	"container/list"
-)
-
 // corssFunction no matches
 // can boolean use crossfunction
 
-func AlternativeOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func alternativeOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- alternative")
-	return crossFunction(d, matchingNodes, pathNode, alternativeFunc)
+	return crossFunction(d, context, expressionNode, alternativeFunc)
 }
 
-func alternativeFunc(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
-	lhs.Node = UnwrapDoc(lhs.Node)
-	rhs.Node = UnwrapDoc(rhs.Node)
+func alternativeFunc(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+	lhs.Node = unwrapDoc(lhs.Node)
+	rhs.Node = unwrapDoc(rhs.Node)
 	log.Debugf("Alternative LHS: %v", lhs.Node.Tag)
 	log.Debugf("-          RHS: %v", rhs.Node.Tag)
 

pkg/yqlib/operator_anchors_aliases.go

@@ -6,146 +6,146 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-func AssignAliasOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func assignAliasOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
 	log.Debugf("AssignAlias operator!")
 
 	aliasName := ""
-	if !pathNode.Operation.UpdateAssign {
-		rhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
+	if !expressionNode.Operation.UpdateAssign {
+		rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
-		if rhs.Front() != nil {
-			aliasName = rhs.Front().Value.(*CandidateNode).Node.Value
+		if rhs.MatchingNodes.Front() != nil {
+			aliasName = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 		}
 	}
 
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
 
-	for el := lhs.Front(); el != nil; el = el.Next() {
+	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		log.Debugf("Setting aliasName : %v", candidate.GetKey())
 
-		if pathNode.Operation.UpdateAssign {
-			rhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		if expressionNode.Operation.UpdateAssign {
+			rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
-			if rhs.Front() != nil {
-				aliasName = rhs.Front().Value.(*CandidateNode).Node.Value
+			if rhs.MatchingNodes.Front() != nil {
+				aliasName = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 			}
 		}
 
 		candidate.Node.Kind = yaml.AliasNode
 		candidate.Node.Value = aliasName
 	}
-	return matchingNodes, nil
+	return context, nil
 }
 
-func GetAliasOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func getAliasOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("GetAlias operator!")
 	var results = list.New()
 
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		node := &yaml.Node{Kind: yaml.ScalarNode, Value: candidate.Node.Value, Tag: "!!str"}
-		lengthCand := &CandidateNode{Node: node, Document: candidate.Document, Path: candidate.Path}
-		results.PushBack(lengthCand)
+		result := candidate.CreateChild(nil, node)
+		results.PushBack(result)
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }
 
-func AssignAnchorOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func assignAnchorOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
 	log.Debugf("AssignAnchor operator!")
 
 	anchorName := ""
-	if !pathNode.Operation.UpdateAssign {
-		rhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
+	if !expressionNode.Operation.UpdateAssign {
+		rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
-		if rhs.Front() != nil {
-			anchorName = rhs.Front().Value.(*CandidateNode).Node.Value
+		if rhs.MatchingNodes.Front() != nil {
+			anchorName = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 		}
 	}
 
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
 
-	for el := lhs.Front(); el != nil; el = el.Next() {
+	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		log.Debugf("Setting anchorName of : %v", candidate.GetKey())
 
-		if pathNode.Operation.UpdateAssign {
-			rhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		if expressionNode.Operation.UpdateAssign {
+			rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 
-			if rhs.Front() != nil {
-				anchorName = rhs.Front().Value.(*CandidateNode).Node.Value
+			if rhs.MatchingNodes.Front() != nil {
+				anchorName = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 			}
 		}
 
 		candidate.Node.Anchor = anchorName
 	}
-	return matchingNodes, nil
+	return context, nil
 }
 
-func GetAnchorOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func getAnchorOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("GetAnchor operator!")
 	var results = list.New()
 
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		anchor := candidate.Node.Anchor
 		node := &yaml.Node{Kind: yaml.ScalarNode, Value: anchor, Tag: "!!str"}
-		lengthCand := &CandidateNode{Node: node, Document: candidate.Document, Path: candidate.Path}
-		results.PushBack(lengthCand)
+		result := candidate.CreateChild(nil, node)
+		results.PushBack(result)
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }
 
-func ExplodeOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func explodeOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- ExplodeOperation")
 
-	for el := matchMap.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 
-		rhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
-		for childEl := rhs.Front(); childEl != nil; childEl = childEl.Next() {
-			err = explodeNode(childEl.Value.(*CandidateNode).Node)
+		for childEl := rhs.MatchingNodes.Front(); childEl != nil; childEl = childEl.Next() {
+			err = explodeNode(childEl.Value.(*CandidateNode).Node, context)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 		}
 
 	}
 
-	return matchMap, nil
+	return context, nil
 }
 
-func explodeNode(node *yaml.Node) error {
+func explodeNode(node *yaml.Node, context Context) error {
 	node.Anchor = ""
 	switch node.Kind {
 	case yaml.SequenceNode, yaml.DocumentNode:
 		for index, contentNode := range node.Content {
 			log.Debugf("exploding index %v", index)
-			errorInContent := explodeNode(contentNode)
+			errorInContent := explodeNode(contentNode, context)
 			if errorInContent != nil {
 				return errorInContent
 			}
@@ -169,7 +169,7 @@ func explodeNode(node *yaml.Node) error {
 			valueNode := node.Content[index+1]
 			log.Debugf("traversing %v", keyNode.Value)
 			if keyNode.Value != "<<" {
-				err := overrideEntry(node, keyNode, valueNode, index, newContent)
+				err := overrideEntry(node, keyNode, valueNode, index, context.ChildContext(newContent))
 				if err != nil {
 					return err
 				}
@@ -178,14 +178,14 @@ func explodeNode(node *yaml.Node) error {
 					log.Debugf("an alias merge list!")
 					for index := 0; index < len(valueNode.Content); index = index + 1 {
 						aliasNode := valueNode.Content[index]
-						err := applyAlias(node, aliasNode.Alias, index, newContent)
+						err := applyAlias(node, aliasNode.Alias, index, context.ChildContext(newContent))
 						if err != nil {
 							return err
 						}
 					}
 				} else {
 					log.Debugf("an alias merge!")
-					err := applyAlias(node, valueNode.Alias, index, newContent)
+					err := applyAlias(node, valueNode.Alias, index, context.ChildContext(newContent))
 					if err != nil {
 						return err
 					}
@@ -205,7 +205,7 @@ func explodeNode(node *yaml.Node) error {
 	}
 }
 
-func applyAlias(node *yaml.Node, alias *yaml.Node, aliasIndex int, newContent *list.List) error {
+func applyAlias(node *yaml.Node, alias *yaml.Node, aliasIndex int, newContent Context) error {
 	if alias == nil {
 		return nil
 	}
@@ -221,15 +221,15 @@ func applyAlias(node *yaml.Node, alias *yaml.Node, aliasIndex int, newContent *l
 	return nil
 }
 
-func overrideEntry(node *yaml.Node, key *yaml.Node, value *yaml.Node, startIndex int, newContent *list.List) error {
+func overrideEntry(node *yaml.Node, key *yaml.Node, value *yaml.Node, startIndex int, newContent Context) error {
 
-	err := explodeNode(value)
+	err := explodeNode(value, newContent)
 
 	if err != nil {
 		return err
 	}
 
-	for newEl := newContent.Front(); newEl != nil; newEl = newEl.Next() {
+	for newEl := newContent.MatchingNodes.Front(); newEl != nil; newEl = newEl.Next() {
 		valueEl := newEl.Next() // move forward twice
 		keyNode := newEl.Value.(*yaml.Node)
 		log.Debugf("checking new content %v:%v", keyNode.Value, valueEl.Value.(*yaml.Node).Value)
@@ -250,12 +250,12 @@ func overrideEntry(node *yaml.Node, key *yaml.Node, value *yaml.Node, startIndex
 		}
 	}
 
-	err = explodeNode(key)
+	err = explodeNode(key, newContent)
 	if err != nil {
 		return err
 	}
 	log.Debugf("adding %v:%v", key.Value, value.Value)
-	newContent.PushBack(key)
-	newContent.PushBack(value)
+	newContent.MatchingNodes.PushBack(key)
+	newContent.MatchingNodes.PushBack(value)
 	return nil
 }

pkg/yqlib/operator_assign.go

@@ -1,66 +1,61 @@
 package yqlib
 
-import "container/list"
-
-func AssignUpdateOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
+func assignUpdateOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-	var rhs *list.List
-	if !pathNode.Operation.UpdateAssign {
-		rhs, err = d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
+	var rhs Context
+	if !expressionNode.Operation.UpdateAssign {
+		rhs, err = d.GetMatchingNodes(context, expressionNode.Rhs)
 	}
 
-	for el := lhs.Front(); el != nil; el = el.Next() {
+	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 
-		if pathNode.Operation.UpdateAssign {
-			rhs, err = d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		if expressionNode.Operation.UpdateAssign {
+			rhs, err = d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 		}
 
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
 		// grab the first value
-		first := rhs.Front()
+		first := rhs.MatchingNodes.Front()
 
 		if first != nil {
 			rhsCandidate := first.Value.(*CandidateNode)
-			rhsCandidate.Node = UnwrapDoc(rhsCandidate.Node)
+			rhsCandidate.Node = unwrapDoc(rhsCandidate.Node)
 			candidate.UpdateFrom(rhsCandidate)
 		}
 	}
-	// // if there was nothing given, perhaps we are creating a new yaml doc
-	// if matchingNodes.Len() == 0 {
-	// 	log.Debug("started with nothing, returning LHS, %v", lhs.Len())
-	// 	return lhs, nil
-	// }
-	return matchingNodes, nil
+
+	return context, nil
 }
 
 // does not update content or values
-func AssignAttributesOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
+func assignAttributesOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debug("getting lhs matching nodes for update")
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-	for el := lhs.Front(); el != nil; el = el.Next() {
+	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 
-		rhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
 		// grab the first value
-		first := rhs.Front()
+		first := rhs.MatchingNodes.Front()
 
 		if first != nil {
 			candidate.UpdateAttributesFrom(first.Value.(*CandidateNode))
 		}
 	}
-	return matchingNodes, nil
+	return context, nil
 }

pkg/yqlib/operator_booleans.go

@@ -7,7 +7,7 @@ import (
 )
 
 func isTruthy(c *CandidateNode) (bool, error) {
-	node := UnwrapDoc(c.Node)
+	node := unwrapDoc(c.Node)
 	value := true
 
 	if node.Tag == "!!null" {
@@ -25,10 +25,10 @@ func isTruthy(c *CandidateNode) (bool, error) {
 
 type boolOp func(bool, bool) bool
 
-func performBoolOp(op boolOp) func(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
-	return func(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
-		lhs.Node = UnwrapDoc(lhs.Node)
-		rhs.Node = UnwrapDoc(rhs.Node)
+func performBoolOp(op boolOp) func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+	return func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+		lhs.Node = unwrapDoc(lhs.Node)
+		rhs.Node = unwrapDoc(rhs.Node)
 
 		lhsTrue, errDecoding := isTruthy(lhs)
 		if errDecoding != nil {
@@ -44,35 +44,35 @@ func performBoolOp(op boolOp) func(d *dataTreeNavigator, lhs *CandidateNode, rhs
 	}
 }
 
-func OrOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func orOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- orOp")
-	return crossFunction(d, matchingNodes, pathNode, performBoolOp(
+	return crossFunction(d, context, expressionNode, performBoolOp(
 		func(b1 bool, b2 bool) bool {
 			return b1 || b2
 		}))
 }
 
-func AndOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func andOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- AndOp")
-	return crossFunction(d, matchingNodes, pathNode, performBoolOp(
+	return crossFunction(d, context, expressionNode, performBoolOp(
 		func(b1 bool, b2 bool) bool {
 			return b1 && b2
 		}))
 }
 
-func NotOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func notOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- notOperation")
 	var results = list.New()
 
-	for el := matchMap.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		log.Debug("notOperation checking %v", candidate)
 		truthy, errDecoding := isTruthy(candidate)
 		if errDecoding != nil {
-			return nil, errDecoding
+			return Context{}, errDecoding
 		}
 		result := createBooleanCandidate(candidate, !truthy)
 		results.PushBack(result)
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_collect.go

@@ -6,34 +6,35 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-func CollectOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func collectOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- collectOperation")
 
-	if matchMap.Len() == 0 {
+	if context.MatchingNodes.Len() == 0 {
 		node := &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq", Value: "[]"}
 		candidate := &CandidateNode{Node: node}
-		return nodeToMap(candidate), nil
+		return context.SingleChildContext(candidate), nil
 	}
 
 	var results = list.New()
 
 	node := &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq"}
-
-	var document uint = 0
-	var path []interface{}
-
-	for el := matchMap.Front(); el != nil; el = el.Next() {
-		candidate := el.Value.(*CandidateNode)
-		log.Debugf("Collecting %v", NodeToString(candidate))
-		if path == nil && candidate.Path != nil && len(candidate.Path) > 1 {
-			path = candidate.Path[:len(candidate.Path)-1]
-			document = candidate.Document
+	var collectC *CandidateNode
+	if context.MatchingNodes.Front() != nil {
+		collectC = context.MatchingNodes.Front().Value.(*CandidateNode).CreateChild(nil, node)
+		if len(collectC.Path) > 0 {
+			collectC.Path = collectC.Path[:len(collectC.Path)-1]
 		}
-		node.Content = append(node.Content, candidate.Node)
+	} else {
+		collectC = &CandidateNode{Node: node}
+	}
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		log.Debugf("Collecting %v", NodeToString(candidate))
+		node.Content = append(node.Content, unwrapDoc(candidate.Node))
 	}
 
-	collectC := &CandidateNode{Node: node, Document: document, Path: path}
 	results.PushBack(collectC)
 
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_collect_object.go

@@ -17,92 +17,83 @@ import (
 ...
 */
 
-func CollectObjectOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func collectObjectOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- collectObjectOperation")
 
-	if matchMap.Len() == 0 {
+	if context.MatchingNodes.Len() == 0 {
 		node := &yaml.Node{Kind: yaml.MappingNode, Tag: "!!map", Value: "{}"}
 		candidate := &CandidateNode{Node: node}
-		return nodeToMap(candidate), nil
+		return context.SingleChildContext(candidate), nil
 	}
-	first := matchMap.Front().Value.(*CandidateNode)
+	first := context.MatchingNodes.Front().Value.(*CandidateNode)
 	var rotated []*list.List = make([]*list.List, len(first.Node.Content))
 
 	for i := 0; i < len(first.Node.Content); i++ {
 		rotated[i] = list.New()
 	}
 
-	for el := matchMap.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidateNode := el.Value.(*CandidateNode)
 		for i := 0; i < len(first.Node.Content); i++ {
-			rotated[i].PushBack(createChildCandidate(candidateNode, i))
+			rotated[i].PushBack(candidateNode.CreateChild(i, candidateNode.Node.Content[i]))
 		}
 	}
 
 	newObject := list.New()
 	for i := 0; i < len(first.Node.Content); i++ {
-		additions, err := collect(d, list.New(), rotated[i])
+		additions, err := collect(d, context.ChildContext(list.New()), rotated[i])
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
-		newObject.PushBackList(additions)
+		newObject.PushBackList(additions.MatchingNodes)
 	}
 
-	return newObject, nil
+	return context.ChildContext(newObject), nil
 
 }
 
-func createChildCandidate(candidate *CandidateNode, index int) *CandidateNode {
-	return &CandidateNode{
-		Document: candidate.Document,
-		Path:     candidate.CreateChildPath(index),
-		Filename: candidate.Filename,
-		Node:     candidate.Node.Content[index],
-	}
-}
-
-func collect(d *dataTreeNavigator, aggregate *list.List, remainingMatches *list.List) (*list.List, error) {
+func collect(d *dataTreeNavigator, context Context, remainingMatches *list.List) (Context, error) {
 	if remainingMatches.Len() == 0 {
-		return aggregate, nil
+		return context, nil
 	}
 
 	candidate := remainingMatches.Remove(remainingMatches.Front()).(*CandidateNode)
 
-	splatted, err := Splat(d, nodeToMap(candidate),
-		&TraversePreferences{FollowAlias: false, IncludeMapKeys: false})
+	splatted, err := splat(d, context.SingleChildContext(candidate),
+		traversePreferences{DontFollowAlias: true, IncludeMapKeys: false})
 
-	for splatEl := splatted.Front(); splatEl != nil; splatEl = splatEl.Next() {
+	for splatEl := splatted.MatchingNodes.Front(); splatEl != nil; splatEl = splatEl.Next() {
 		splatEl.Value.(*CandidateNode).Path = nil
 	}
 
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
 
-	if aggregate.Len() == 0 {
+	if context.MatchingNodes.Len() == 0 {
 		return collect(d, splatted, remainingMatches)
 	}
 
 	newAgg := list.New()
 
-	for el := aggregate.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		aggCandidate := el.Value.(*CandidateNode)
-		for splatEl := splatted.Front(); splatEl != nil; splatEl = splatEl.Next() {
+		for splatEl := splatted.MatchingNodes.Front(); splatEl != nil; splatEl = splatEl.Next() {
 			splatCandidate := splatEl.Value.(*CandidateNode)
 			newCandidate, err := aggCandidate.Copy()
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 
 			newCandidate.Path = nil
 
-			newCandidate, err = multiply(&MultiplyPreferences{AppendArrays: false})(d, newCandidate, splatCandidate)
+			newCandidate, err = multiply(multiplyPreferences{AppendArrays: false})(d, context, newCandidate, splatCandidate)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 			newAgg.PushBack(newCandidate)
 		}
 	}
-	return collect(d, newAgg, remainingMatches)
+	return collect(d, context.ChildContext(newAgg), remainingMatches)
 
 }

pkg/yqlib/operator_collect_test.go

@@ -13,6 +13,15 @@ var collectOperatorScenarios = []expressionScenario{
 			"D0, P[], (!!seq)::[]\n",
 		},
 	},
+	{
+		skipDoc:  true,
+		document: "{a: apple}\n---\n{b: frog}",
+
+		expression: `[.]`,
+		expected: []string{
+			"D0, P[], (!!seq)::- {a: apple}\n- {b: frog}\n",
+		},
+	},
 	{
 		skipDoc:    true,
 		document:   ``,

pkg/yqlib/operator_comments.go

@@ -7,47 +7,47 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-type CommentOpPreferences struct {
+type commentOpPreferences struct {
 	LineComment bool
 	HeadComment bool
 	FootComment bool
 }
 
-func AssignCommentsOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func assignCommentsOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
 	log.Debugf("AssignComments operator!")
 
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
 
-	preferences := pathNode.Operation.Preferences.(*CommentOpPreferences)
+	preferences := expressionNode.Operation.Preferences.(commentOpPreferences)
 
 	comment := ""
-	if !pathNode.Operation.UpdateAssign {
-		rhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
+	if !expressionNode.Operation.UpdateAssign {
+		rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
-		if rhs.Front() != nil {
-			comment = rhs.Front().Value.(*CandidateNode).Node.Value
+		if rhs.MatchingNodes.Front() != nil {
+			comment = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 		}
 	}
 
-	for el := lhs.Front(); el != nil; el = el.Next() {
+	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 
-		if pathNode.Operation.UpdateAssign {
-			rhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		if expressionNode.Operation.UpdateAssign {
+			rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 
-			if rhs.Front() != nil {
-				comment = rhs.Front().Value.(*CandidateNode).Node.Value
+			if rhs.MatchingNodes.Front() != nil {
+				comment = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 			}
 		}
 
@@ -63,15 +63,15 @@ func AssignCommentsOperator(d *dataTreeNavigator, matchingNodes *list.List, path
 		}
 
 	}
-	return matchingNodes, nil
+	return context, nil
 }
 
-func GetCommentsOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	preferences := pathNode.Operation.Preferences.(*CommentOpPreferences)
+func getCommentsOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	preferences := expressionNode.Operation.Preferences.(commentOpPreferences)
 	log.Debugf("GetComments operator!")
 	var results = list.New()
 
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		comment := ""
 		if preferences.LineComment {
@@ -84,8 +84,8 @@ func GetCommentsOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNod
 		comment = strings.Replace(comment, "# ", "", 1)
 
 		node := &yaml.Node{Kind: yaml.ScalarNode, Value: comment, Tag: "!!str"}
-		lengthCand := &CandidateNode{Node: node, Document: candidate.Document, Path: candidate.Path}
-		results.PushBack(lengthCand)
+		result := candidate.CreateChild(nil, node)
+		results.PushBack(result)
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_comments_test.go

@@ -71,11 +71,12 @@ var commentOperatorScenarios = []expressionScenario{
 		},
 	},
 	{
-		description: "Remove all comments",
-		document:    "# hi\n\na: cat # comment\n\n# great\n",
-		expression:  `.. comments=""`,
+		description:    "Remove all comments",
+		subdescription: "Note the use of `...` to ensure key nodes are included.",
+		document:       "# hi\n\na: cat # comment\n\n# great\n\nb: # key comment",
+		expression:     `... comments=""`,
 		expected: []string{
-			"D0, P[], (!!map)::a: cat\n",
+			"D0, P[], (!!map)::a: cat\nb:\n",
 		},
 	},
 	{

pkg/yqlib/operator_create_map.go

@@ -6,7 +6,7 @@ import (
 	"gopkg.in/yaml.v3"
 )
 
-func CreateMapOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func createMapOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- createMapOperation")
 
 	//each matchingNodes entry should turn into a sequence of keys to create.
@@ -18,29 +18,29 @@ func CreateMapOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode
 
 	sequences := list.New()
 
-	if matchingNodes.Len() > 0 {
+	if context.MatchingNodes.Len() > 0 {
 
-		for matchingNodeEl := matchingNodes.Front(); matchingNodeEl != nil; matchingNodeEl = matchingNodeEl.Next() {
+		for matchingNodeEl := context.MatchingNodes.Front(); matchingNodeEl != nil; matchingNodeEl = matchingNodeEl.Next() {
 			matchingNode := matchingNodeEl.Value.(*CandidateNode)
-			sequenceNode, err := sequenceFor(d, matchingNode, pathNode)
+			sequenceNode, err := sequenceFor(d, context, matchingNode, expressionNode)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 			sequences.PushBack(sequenceNode)
 		}
 	} else {
-		sequenceNode, err := sequenceFor(d, nil, pathNode)
+		sequenceNode, err := sequenceFor(d, context, nil, expressionNode)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 		sequences.PushBack(sequenceNode)
 	}
 
-	return nodeToMap(&CandidateNode{Node: listToNodeSeq(sequences), Document: document, Path: path}), nil
+	return context.SingleChildContext(&CandidateNode{Node: listToNodeSeq(sequences), Document: document, Path: path}), nil
 
 }
 
-func sequenceFor(d *dataTreeNavigator, matchingNode *CandidateNode, pathNode *PathTreeNode) (*CandidateNode, error) {
+func sequenceFor(d *dataTreeNavigator, context Context, matchingNode *CandidateNode, expressionNode *ExpressionNode) (*CandidateNode, error) {
 	var path []interface{}
 	var document uint = 0
 	var matches = list.New()
@@ -48,17 +48,17 @@ func sequenceFor(d *dataTreeNavigator, matchingNode *CandidateNode, pathNode *Pa
 	if matchingNode != nil {
 		path = matchingNode.Path
 		document = matchingNode.Document
-		matches = nodeToMap(matchingNode)
+		matches.PushBack(matchingNode)
 	}
 
-	mapPairs, err := crossFunction(d, matches, pathNode,
-		func(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+	mapPairs, err := crossFunction(d, context.ChildContext(matches), expressionNode,
+		func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
 			node := yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"}
 			log.Debugf("LHS:", NodeToString(lhs))
 			log.Debugf("RHS:", NodeToString(rhs))
 			node.Content = []*yaml.Node{
-				UnwrapDoc(lhs.Node),
-				UnwrapDoc(rhs.Node),
+				unwrapDoc(lhs.Node),
+				unwrapDoc(rhs.Node),
 			}
 
 			return &CandidateNode{Node: &node, Document: document, Path: path}, nil
@@ -67,7 +67,7 @@ func sequenceFor(d *dataTreeNavigator, matchingNode *CandidateNode, pathNode *Pa
 	if err != nil {
 		return nil, err
 	}
-	innerList := listToNodeSeq(mapPairs)
+	innerList := listToNodeSeq(mapPairs.MatchingNodes)
 	innerList.Style = yaml.FlowStyle
 	return &CandidateNode{Node: innerList, Document: document, Path: path}, nil
 }

pkg/yqlib/operator_delete.go

@@ -1,70 +1,72 @@
 package yqlib
 
 import (
-	"container/list"
 	"fmt"
 
 	yaml "gopkg.in/yaml.v3"
 )
 
-func DeleteChildOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-
-	nodesToDelete, err := d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
+func deleteChildOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	contextToUse := context.Clone()
+	contextToUse.DontAutoCreate = true
+	nodesToDelete, err := d.GetMatchingNodes(contextToUse, expressionNode.Rhs)
 
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-
-	for el := nodesToDelete.Front(); el != nil; el = el.Next() {
+	//need to iterate backwards to ensure correct indices when deleting multiple
+	for el := nodesToDelete.MatchingNodes.Back(); el != nil; el = el.Prev() {
 		candidate := el.Value.(*CandidateNode)
 
-		deleteImmediateChildOp := &Operation{
-			OperationType: DeleteImmediateChild,
-			Value:         candidate.Path[len(candidate.Path)-1],
-		}
+		if len(candidate.Path) > 0 {
+			deleteImmediateChildOp := &Operation{
+				OperationType: deleteImmediateChildOpType,
+				Value:         candidate.Path[len(candidate.Path)-1],
+			}
 
-		deleteImmediateChildOpNode := &PathTreeNode{
-			Operation: deleteImmediateChildOp,
-			Rhs:       createTraversalTree(candidate.Path[0 : len(candidate.Path)-1]),
-		}
+			deleteImmediateChildOpNode := &ExpressionNode{
+				Operation: deleteImmediateChildOp,
+				Rhs:       createTraversalTree(candidate.Path[0:len(candidate.Path)-1], traversePreferences{}, false),
+			}
 
-		_, err := d.GetMatchingNodes(matchingNodes, deleteImmediateChildOpNode)
-		if err != nil {
-			return nil, err
+			_, err := d.GetMatchingNodes(contextToUse, deleteImmediateChildOpNode)
+			if err != nil {
+				return Context{}, err
+			}
 		}
 	}
-	return matchingNodes, nil
+	return context, nil
 }
 
-func DeleteImmediateChildOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	parents, err := d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
+func deleteImmediateChildOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	parents, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
 
-	childPath := pathNode.Operation.Value
+	childPath := expressionNode.Operation.Value
 
 	log.Debug("childPath to remove %v", childPath)
 
-	for el := parents.Front(); el != nil; el = el.Next() {
+	for el := parents.MatchingNodes.Front(); el != nil; el = el.Next() {
 		parent := el.Value.(*CandidateNode)
-		parentNode := UnwrapDoc(parent.Node)
+		parentNode := unwrapDoc(parent.Node)
 		if parentNode.Kind == yaml.MappingNode {
 			deleteFromMap(parent, childPath)
 		} else if parentNode.Kind == yaml.SequenceNode {
 			deleteFromArray(parent, childPath)
 		} else {
-			return nil, fmt.Errorf("Cannot delete nodes from parent of tag %v", parentNode.Tag)
+			return Context{}, fmt.Errorf("Cannot delete nodes from parent of tag %v", parentNode.Tag)
 		}
 
 	}
-	return matchingNodes, nil
+	return context, nil
 }
 
 func deleteFromMap(candidate *CandidateNode, childPath interface{}) {
 	log.Debug("deleteFromMap")
-	node := UnwrapDoc(candidate.Node)
+	node := unwrapDoc(candidate.Node)
 	contents := node.Content
 	newContents := make([]*yaml.Node, 0)
 
@@ -72,11 +74,7 @@ func deleteFromMap(candidate *CandidateNode, childPath interface{}) {
 		key := contents[index]
 		value := contents[index+1]
 
-		childCandidate := &CandidateNode{
-			Node:     value,
-			Document: candidate.Document,
-			Path:     candidate.CreateChildPath(key.Value),
-		}
+		childCandidate := candidate.CreateChild(key.Value, value)
 
 		shouldDelete := key.Value == childPath
 
@@ -91,7 +89,7 @@ func deleteFromMap(candidate *CandidateNode, childPath interface{}) {
 
 func deleteFromArray(candidate *CandidateNode, childPath interface{}) {
 	log.Debug("deleteFromArray")
-	node := UnwrapDoc(candidate.Node)
+	node := unwrapDoc(candidate.Node)
 	contents := node.Content
 	newContents := make([]*yaml.Node, 0)
 

pkg/yqlib/operator_delete_test.go

@@ -37,6 +37,38 @@ var deleteOperatorScenarios = []expressionScenario{
 			"D0, P[], (doc)::[1, 3]\n",
 		},
 	},
+	{
+		skipDoc:    true,
+		document:   `a: [1,2,3]`,
+		expression: `del(.a[])`,
+		expected: []string{
+			"D0, P[], (doc)::a: []\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `a: [10,x,10, 10, x, 10]`,
+		expression: `del(.a[] | select(. == 10))`,
+		expected: []string{
+			"D0, P[], (doc)::a: [x, x]\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `a: {thing1: yep, thing2: cool, thing3: hi, b: {thing1: cool, great: huh}}`,
+		expression: `del(..)`,
+		expected: []string{
+			"D0, P[], (!!map)::{}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `a: {thing1: yep, thing2: cool, thing3: hi, b: {thing1: cool, great: huh}}`,
+		expression: `del(.. | select(tag == "!!map") | (.b.thing1,.thing2))`,
+		expected: []string{
+			"D0, P[], (!!map)::a: {thing1: yep, thing3: hi, b: {great: huh}}\n",
+		},
+	},
 	{
 		description: "Delete nested entry in array",
 		document:    `[{a: cat, b: dog}]`,

pkg/yqlib/operator_document_index.go

@@ -7,14 +7,14 @@ import (
 	"gopkg.in/yaml.v3"
 )
 
-func GetDocumentIndexOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func getDocumentIndexOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	var results = list.New()
 
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		node := &yaml.Node{Kind: yaml.ScalarNode, Value: fmt.Sprintf("%v", candidate.Document), Tag: "!!int"}
-		scalar := &CandidateNode{Node: node, Document: candidate.Document, Path: candidate.Path}
+		scalar := candidate.CreateChild(nil, node)
 		results.PushBack(scalar)
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_env.go

@@ -1,24 +1,24 @@
 package yqlib
 
 import (
-	"container/list"
+	"fmt"
 	"os"
 	"strings"
 
 	yaml "gopkg.in/yaml.v3"
 )
 
-type EnvOpPreferences struct {
+type envOpPreferences struct {
 	StringValue bool
 }
 
-func EnvOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	envName := pathNode.Operation.CandidateNode.Node.Value
+func envOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	envName := expressionNode.Operation.CandidateNode.Node.Value
 	log.Debug("EnvOperator, env name:", envName)
 
 	rawValue := os.Getenv(envName)
 
-	preferences := pathNode.Operation.Preferences.(*EnvOpPreferences)
+	preferences := expressionNode.Operation.Preferences.(envOpPreferences)
 
 	var node *yaml.Node
 	if preferences.StringValue {
@@ -27,26 +27,23 @@ func EnvOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNo
 			Tag:   "!!str",
 			Value: rawValue,
 		}
+	} else if rawValue == "" {
+		return Context{}, fmt.Errorf("Value for env variable '%v' not provided in env()", envName)
 	} else {
 		var dataBucket yaml.Node
 		decoder := yaml.NewDecoder(strings.NewReader(rawValue))
 		errorReading := decoder.Decode(&dataBucket)
 		if errorReading != nil {
-			return nil, errorReading
+			return Context{}, errorReading
 		}
 		//first node is a doc
-		node = UnwrapDoc(&dataBucket)
+		node = unwrapDoc(&dataBucket)
 	}
 	log.Debug("ENV tag", node.Tag)
 	log.Debug("ENV value", node.Value)
 	log.Debug("ENV Kind", node.Kind)
 
-	target := &CandidateNode{
-		Path:     make([]interface{}, 0),
-		Document: 0,
-		Filename: "",
-		Node:     node,
-	}
+	target := &CandidateNode{Node: node}
 
-	return nodeToMap(target), nil
+	return context.SingleChildContext(target), nil
 }

pkg/yqlib/operator_equals.go

@@ -1,22 +1,33 @@
 package yqlib
 
-import (
-	"container/list"
-)
+import "gopkg.in/yaml.v3"
 
-func EqualsOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func equalsOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- equalsOperation")
-	return crossFunction(d, matchingNodes, pathNode, isEquals)
+	return crossFunction(d, context, expressionNode, isEquals(false))
 }
 
-func isEquals(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
-	value := false
+func isEquals(flip bool) func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+	return func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+		value := false
 
-	if lhs.Node.Tag == "!!null" {
-		value = (rhs.Node.Tag == "!!null")
-	} else {
-		value = Match(lhs.Node.Value, rhs.Node.Value)
+		lhsNode := unwrapDoc(lhs.Node)
+		rhsNode := unwrapDoc(rhs.Node)
+
+		if lhsNode.Tag == "!!null" {
+			value = (rhsNode.Tag == "!!null")
+		} else if lhsNode.Kind == yaml.ScalarNode && rhsNode.Kind == yaml.ScalarNode {
+			value = matchKey(lhsNode.Value, rhsNode.Value)
+		}
+		log.Debugf("%v == %v ? %v", NodeToString(lhs), NodeToString(rhs), value)
+		if flip {
+			value = !value
+		}
+		return createBooleanCandidate(lhs, value), nil
 	}
-	log.Debugf("%v == %v ? %v", NodeToString(lhs), NodeToString(rhs), value)
-	return createBooleanCandidate(lhs, value), nil
+}
+
+func notEqualsOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("-- equalsOperation")
+	return crossFunction(d, context, expressionNode, isEquals(true))
 }

pkg/yqlib/operator_equals_test.go

@@ -5,6 +5,23 @@ import (
 )
 
 var equalsOperatorScenarios = []expressionScenario{
+	{
+		skipDoc:    true,
+		document:   "cat",
+		document2:  "dog",
+		expression: "select(fi==0) == select(fi==1)",
+		expected: []string{
+			"D0, P[], (!!bool)::false\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   "{a: { b: {things: \"\"}, f: [1], g: [] }}",
+		expression: ".. | select(. == \"\")",
+		expected: []string{
+			"D0, P[a b things], (!!str)::\"\"\n",
+		},
+	},
 	{
 		description: "Match string",
 		document:    `[cat,goat,dog]`,
@@ -14,7 +31,18 @@ var equalsOperatorScenarios = []expressionScenario{
 			"D0, P[1], (!!bool)::true\n",
 			"D0, P[2], (!!bool)::false\n",
 		},
-	}, {
+	},
+	{
+		description: "Don't match string",
+		document:    `[cat,goat,dog]`,
+		expression:  `.[] | (. != "*at")`,
+		expected: []string{
+			"D0, P[0], (!!bool)::false\n",
+			"D0, P[1], (!!bool)::false\n",
+			"D0, P[2], (!!bool)::true\n",
+		},
+	},
+	{
 		description: "Match number",
 		document:    `[3, 4, 5]`,
 		expression:  `.[] | (. == 4)`,
@@ -23,7 +51,18 @@ var equalsOperatorScenarios = []expressionScenario{
 			"D0, P[1], (!!bool)::true\n",
 			"D0, P[2], (!!bool)::false\n",
 		},
-	}, {
+	},
+	{
+		description: "Dont match number",
+		document:    `[3, 4, 5]`,
+		expression:  `.[] | (. != 4)`,
+		expected: []string{
+			"D0, P[0], (!!bool)::true\n",
+			"D0, P[1], (!!bool)::false\n",
+			"D0, P[2], (!!bool)::true\n",
+		},
+	},
+	{
 		skipDoc:    true,
 		document:   `a: { cat: {b: apple, c: whatever}, pat: {b: banana} }`,
 		expression: `.a | (.[].b == "apple")`,

pkg/yqlib/operator_file.go

@@ -7,32 +7,32 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-func GetFilenameOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func getFilenameOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("GetFilename")
 
 	var results = list.New()
 
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		node := &yaml.Node{Kind: yaml.ScalarNode, Value: candidate.Filename, Tag: "!!str"}
-		lengthCand := &CandidateNode{Node: node, Document: candidate.Document, Path: candidate.Path}
-		results.PushBack(lengthCand)
+		result := candidate.CreateChild(nil, node)
+		results.PushBack(result)
 	}
 
-	return results, nil
+	return context.ChildContext(results), nil
 }
 
-func GetFileIndexOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func getFileIndexOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("GetFileIndex")
 
 	var results = list.New()
 
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		node := &yaml.Node{Kind: yaml.ScalarNode, Value: fmt.Sprintf("%v", candidate.FileIndex), Tag: "!!int"}
-		lengthCand := &CandidateNode{Node: node, Document: candidate.Document, Path: candidate.Path}
-		results.PushBack(lengthCand)
+		result := candidate.CreateChild(nil, node)
+		results.PushBack(result)
 	}
 
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_file_test.go

@@ -29,6 +29,14 @@ var fileOperatorScenarios = []expressionScenario{
 			"D0, P[], (!!int)::0\n",
 		},
 	},
+	{
+		skipDoc:    true,
+		document:   "a: cat\nb: dog",
+		expression: `.. lineComment |= filename`,
+		expected: []string{
+			"D0, P[], (!!map)::a: cat # sample.yml\nb: dog # sample.yml\n",
+		},
+	},
 }
 
 func TestFileOperatorsScenarios(t *testing.T) {

pkg/yqlib/operator_has.go

@@ -7,25 +7,26 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-func HasOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func hasOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
 	log.Debugf("-- hasOperation")
 	var results = list.New()
 
-	rhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
-	wanted := rhs.Front().Value.(*CandidateNode).Node
+	rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
+	wanted := rhs.MatchingNodes.Front().Value.(*CandidateNode).Node
 	wantedKey := wanted.Value
 
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
 
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 
 		// grab the first value
-		var contents = candidate.Node.Content
-		switch candidate.Node.Kind {
+		candidateNode := unwrapDoc(candidate.Node)
+		var contents = candidateNode.Content
+		switch candidateNode.Kind {
 		case yaml.MappingNode:
 			candidateHasKey := false
 			for index := 0; index < len(contents) && !candidateHasKey; index = index + 2 {
@@ -40,7 +41,7 @@ func HasOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathT
 			if wanted.Tag == "!!int" {
 				var number, errParsingInt = strconv.ParseInt(wantedKey, 10, 64) // nolint
 				if errParsingInt != nil {
-					return nil, errParsingInt
+					return Context{}, errParsingInt
 				}
 				candidateHasKey = int64(len(contents)) > number
 			}
@@ -49,5 +50,5 @@ func HasOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathT
 			results.PushBack(createBooleanCandidate(candidate, false))
 		}
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_has_test.go

@@ -5,6 +5,14 @@ import (
 )
 
 var hasOperatorScenarios = []expressionScenario{
+	{
+		skipDoc:    true,
+		document:   `a: hello`,
+		expression: `has("a")`,
+		expected: []string{
+			"D0, P[], (!!bool)::true\n",
+		},
+	},
 	{
 		description: "Has map key",
 		document: `- a: "yes"

pkg/yqlib/operator_keys.go

@@ -0,0 +1,54 @@
+package yqlib
+
+import (
+	"container/list"
+	"fmt"
+
+	"gopkg.in/yaml.v3"
+)
+
+func keysOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("-- keysOperator")
+
+	var results = list.New()
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		node := unwrapDoc(candidate.Node)
+		var targetNode *yaml.Node
+		if node.Kind == yaml.MappingNode {
+			targetNode = getMapKeys(node)
+		} else if node.Kind == yaml.SequenceNode {
+			targetNode = getIndicies(node)
+		} else {
+			return Context{}, fmt.Errorf("Cannot get keys of %v, keys only works for maps and arrays", node.Tag)
+		}
+
+		result := candidate.CreateChild(nil, targetNode)
+		results.PushBack(result)
+	}
+
+	return context.ChildContext(results), nil
+}
+
+func getMapKeys(node *yaml.Node) *yaml.Node {
+	contents := make([]*yaml.Node, 0)
+	for index := 0; index < len(node.Content); index = index + 2 {
+		contents = append(contents, node.Content[index])
+	}
+	return &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq", Content: contents}
+}
+
+func getIndicies(node *yaml.Node) *yaml.Node {
+	var contents = make([]*yaml.Node, len(node.Content))
+
+	for index := range node.Content {
+		contents[index] = &yaml.Node{
+			Kind:  yaml.ScalarNode,
+			Tag:   "!!int",
+			Value: fmt.Sprintf("%v", index),
+		}
+	}
+
+	return &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq", Content: contents}
+}

pkg/yqlib/operator_keys_test.go

@@ -0,0 +1,47 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var keysOperatorScenarios = []expressionScenario{
+	{
+		description: "Map keys",
+		document:    `{dog: woof, cat: meow}`,
+		expression:  `keys`,
+		expected: []string{
+			"D0, P[], (!!seq)::- dog\n- cat\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{}`,
+		expression: `keys`,
+		expected: []string{
+			"D0, P[], (!!seq)::[]\n",
+		},
+	},
+	{
+		description: "Array keys",
+		document:    `[apple, banana]`,
+		expression:  `keys`,
+		expected: []string{
+			"D0, P[], (!!seq)::- 0\n- 1\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `[]`,
+		expression: `keys`,
+		expected: []string{
+			"D0, P[], (!!seq)::[]\n",
+		},
+	},
+}
+
+func TestKeysOperatorScenarios(t *testing.T) {
+	for _, tt := range keysOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentScenarios(t, "Keys", keysOperatorScenarios)
+}

pkg/yqlib/operator_length.go

@@ -7,17 +7,21 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-func LengthOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func lengthOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- lengthOperation")
 	var results = list.New()
 
-	for el := matchMap.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
-		targetNode := UnwrapDoc(candidate.Node)
+		targetNode := unwrapDoc(candidate.Node)
 		var length int
 		switch targetNode.Kind {
 		case yaml.ScalarNode:
-			length = len(targetNode.Value)
+			if targetNode.Tag == "!!null" {
+				length = 0
+			} else {
+				length = len(targetNode.Value)
+			}
 		case yaml.MappingNode:
 			length = len(targetNode.Content) / 2
 		case yaml.SequenceNode:
@@ -27,9 +31,9 @@ func LengthOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTre
 		}
 
 		node := &yaml.Node{Kind: yaml.ScalarNode, Value: fmt.Sprintf("%v", length), Tag: "!!int"}
-		lengthCand := &CandidateNode{Node: node, Document: candidate.Document, Path: candidate.Path}
-		results.PushBack(lengthCand)
+		result := candidate.CreateChild(nil, node)
+		results.PushBack(result)
 	}
 
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_length_test.go

@@ -14,6 +14,30 @@ var lengthOperatorScenarios = []expressionScenario{
 			"D0, P[a], (!!int)::3\n",
 		},
 	},
+	{
+		description: "null length",
+		document:    `{a: null}`,
+		expression:  `.a | length`,
+		expected: []string{
+			"D0, P[a], (!!int)::0\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{a: ~}`,
+		expression: `.a | length`,
+		expected: []string{
+			"D0, P[a], (!!int)::0\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{a: key no exist}`,
+		expression: `.b | length`,
+		expected: []string{
+			"D0, P[b], (!!int)::0\n",
+		},
+	},
 	{
 		description:    "Map length",
 		subdescription: "returns number of entries",

pkg/yqlib/operator_multiply.go

@@ -2,92 +2,72 @@ package yqlib
 
 import (
 	"fmt"
+	"strconv"
 
 	"container/list"
 
 	yaml "gopkg.in/yaml.v3"
 )
 
-type CrossFunctionCalculation func(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error)
-
-func crossFunction(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode, calculation CrossFunctionCalculation) (*list.List, error) {
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
-	if err != nil {
-		return nil, err
-	}
-	log.Debugf("crossFunction LHS len: %v", lhs.Len())
-
-	rhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
-
-	if err != nil {
-		return nil, err
-	}
-	log.Debugf("crossFunction RHS len: %v", rhs.Len())
-
-	var results = list.New()
-
-	for el := lhs.Front(); el != nil; el = el.Next() {
-		lhsCandidate := el.Value.(*CandidateNode)
-
-		for rightEl := rhs.Front(); rightEl != nil; rightEl = rightEl.Next() {
-			log.Debugf("Applying calc")
-			rhsCandidate := rightEl.Value.(*CandidateNode)
-			resultCandidate, err := calculation(d, lhsCandidate, rhsCandidate)
-			if err != nil {
-				return nil, err
-			}
-			results.PushBack(resultCandidate)
-		}
-
-	}
-	return results, nil
+type multiplyPreferences struct {
+	AppendArrays  bool
+	TraversePrefs traversePreferences
 }
 
-type MultiplyPreferences struct {
-	AppendArrays bool
-}
-
-func MultiplyOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func multiplyOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- MultiplyOperator")
-	return crossFunction(d, matchingNodes, pathNode, multiply(pathNode.Operation.Preferences.(*MultiplyPreferences)))
+	return crossFunction(d, context, expressionNode, multiply(expressionNode.Operation.Preferences.(multiplyPreferences)))
 }
 
-func multiply(preferences *MultiplyPreferences) func(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
-	return func(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
-		lhs.Node = UnwrapDoc(lhs.Node)
-		rhs.Node = UnwrapDoc(rhs.Node)
+func multiply(preferences multiplyPreferences) func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+	return func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+		lhs.Node = unwrapDoc(lhs.Node)
+		rhs.Node = unwrapDoc(rhs.Node)
 		log.Debugf("Multipling LHS: %v", lhs.Node.Tag)
 		log.Debugf("-          RHS: %v", rhs.Node.Tag)
 
-		shouldAppendArrays := preferences.AppendArrays
-
 		if lhs.Node.Kind == yaml.MappingNode && rhs.Node.Kind == yaml.MappingNode ||
 			(lhs.Node.Kind == yaml.SequenceNode && rhs.Node.Kind == yaml.SequenceNode) {
 
-			var newBlank = &CandidateNode{
-				Path:     lhs.Path,
-				Document: lhs.Document,
-				Filename: lhs.Filename,
-				Node:     &yaml.Node{},
-			}
-			var newThing, err = mergeObjects(d, newBlank, lhs, false)
+			var newBlank = lhs.CreateChild(nil, &yaml.Node{})
+			var newThing, err = mergeObjects(d, context, newBlank, lhs, multiplyPreferences{})
 			if err != nil {
 				return nil, err
 			}
-			return mergeObjects(d, newThing, rhs, shouldAppendArrays)
-
+			return mergeObjects(d, context, newThing, rhs, preferences)
+		} else if lhs.Node.Tag == "!!int" && rhs.Node.Tag == "!!int" {
+			return multiplyIntegers(lhs, rhs)
 		}
 		return nil, fmt.Errorf("Cannot multiply %v with %v", lhs.Node.Tag, rhs.Node.Tag)
 	}
 }
 
-func mergeObjects(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode, shouldAppendArrays bool) (*CandidateNode, error) {
+func multiplyIntegers(lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+	target := lhs.CreateChild(nil, &yaml.Node{})
+	target.Node.Kind = yaml.ScalarNode
+	target.Node.Style = lhs.Node.Style
+	target.Node.Tag = "!!int"
+
+	lhsNum, err := strconv.Atoi(lhs.Node.Value)
+	if err != nil {
+		return nil, err
+	}
+	rhsNum, err := strconv.Atoi(rhs.Node.Value)
+	if err != nil {
+		return nil, err
+	}
+	target.Node.Value = fmt.Sprintf("%v", lhsNum*rhsNum)
+	return target, nil
+}
+
+func mergeObjects(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode, preferences multiplyPreferences) (*CandidateNode, error) {
+	shouldAppendArrays := preferences.AppendArrays
 	var results = list.New()
 
 	// shouldn't recurse arrays if appending
-	prefs := &RecursiveDescentPreferences{RecurseArray: !shouldAppendArrays,
-		TraversePreferences: &TraversePreferences{FollowAlias: false}}
-	err := recursiveDecent(d, results, nodeToMap(rhs), prefs)
+	prefs := recursiveDescentPreferences{RecurseArray: !shouldAppendArrays,
+		TraversePreferences: traversePreferences{DontFollowAlias: true, IncludeMapKeys: true}}
+	err := recursiveDecent(d, results, context.SingleChildContext(rhs), prefs)
 	if err != nil {
 		return nil, err
 	}
@@ -98,7 +78,12 @@ func mergeObjects(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode,
 	}
 
 	for el := results.Front(); el != nil; el = el.Next() {
-		err := applyAssignment(d, pathIndexToStartFrom, lhs, el.Value.(*CandidateNode), shouldAppendArrays)
+		candidate := el.Value.(*CandidateNode)
+		if candidate.Node.Tag == "!!merge" {
+			continue
+		}
+
+		err := applyAssignment(d, context, pathIndexToStartFrom, lhs, candidate, preferences)
 		if err != nil {
 			return nil, err
 		}
@@ -106,24 +91,24 @@ func mergeObjects(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode,
 	return lhs, nil
 }
 
-func applyAssignment(d *dataTreeNavigator, pathIndexToStartFrom int, lhs *CandidateNode, rhs *CandidateNode, shouldAppendArrays bool) error {
-
-	log.Debugf("merge - applyAssignment lhs %v, rhs: %v", NodeToString(lhs), NodeToString(rhs))
+func applyAssignment(d *dataTreeNavigator, context Context, pathIndexToStartFrom int, lhs *CandidateNode, rhs *CandidateNode, preferences multiplyPreferences) error {
+	shouldAppendArrays := preferences.AppendArrays
+	log.Debugf("merge - applyAssignment lhs %v, rhs: %v", lhs.GetKey(), rhs.GetKey())
 
 	lhsPath := rhs.Path[pathIndexToStartFrom:]
 
-	assignmentOp := &Operation{OperationType: AssignAttributes}
+	assignmentOp := &Operation{OperationType: assignAttributesOpType}
 	if rhs.Node.Kind == yaml.ScalarNode || rhs.Node.Kind == yaml.AliasNode {
-		assignmentOp.OperationType = Assign
+		assignmentOp.OperationType = assignOpType
 		assignmentOp.UpdateAssign = false
 	} else if shouldAppendArrays && rhs.Node.Kind == yaml.SequenceNode {
-		assignmentOp.OperationType = AddAssign
+		assignmentOp.OperationType = addAssignOpType
 	}
-	rhsOp := &Operation{OperationType: ValueOp, CandidateNode: rhs}
+	rhsOp := &Operation{OperationType: valueOpType, CandidateNode: rhs}
 
-	assignmentOpNode := &PathTreeNode{Operation: assignmentOp, Lhs: createTraversalTree(lhsPath), Rhs: &PathTreeNode{Operation: rhsOp}}
+	assignmentOpNode := &ExpressionNode{Operation: assignmentOp, Lhs: createTraversalTree(lhsPath, preferences.TraversePrefs, rhs.IsMapKey), Rhs: &ExpressionNode{Operation: rhsOp}}
 
-	_, err := d.GetMatchingNodes(nodeToMap(lhs), assignmentOpNode)
+	_, err := d.GetMatchingNodes(context.SingleChildContext(lhs), assignmentOpNode)
 
 	return err
 }

pkg/yqlib/operator_multiply_test.go

@@ -13,6 +13,51 @@ var multiplyOperatorScenarios = []expressionScenario{
 			"D0, P[], (!!map)::{a: {also: me}, b: {also: me}}\n",
 		},
 	},
+	{
+		skipDoc:    true,
+		document:   "# b\nb:\n  # a\n  a: cat",
+		expression: "{} * .",
+		expected: []string{
+			"D0, P[], (!!map)::# b\nb:\n    # a\n    a: cat\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   "# b\nb:\n  # a\n  a: cat",
+		expression: ". * {}",
+		expected: []string{
+			"D0, P[], (!!map)::# b\nb:\n    # a\n    a: cat\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{a: &a { b: &b { c: &c cat } } }`,
+		expression: `{} * .`,
+		expected: []string{
+			"D0, P[], (!!map)::{a: &a {b: &b {c: &c cat}}}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{a: 2, b: 5}`,
+		document2:  `{a: 3, b: 10}`,
+		expression: `.a * .b`,
+		expected: []string{
+			"D0, P[a], (!!int)::10\n",
+			"D0, P[a], (!!int)::20\n",
+			"D0, P[a], (!!int)::15\n",
+			"D0, P[a], (!!int)::30\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{a: 2}`,
+		document2:  `{b: 10}`,
+		expression: `select(fi ==0) * select(fi==1)`,
+		expected: []string{
+			"D0, P[], (!!map)::{a: 2, b: 10}\n",
+		},
+	},
 	{
 		skipDoc:    true,
 		expression: `{} * {"cat":"dog"}`,
@@ -71,7 +116,7 @@ var multiplyOperatorScenarios = []expressionScenario{
 	{
 		skipDoc:    true,
 		document:   `{a: {things: great}, b: {also: me}}`,
-		expression: `. * {"a":.b}`,
+		expression: `. * {"a": .b}`,
 		expected: []string{
 			"D0, P[], (!!map)::{a: {things: great, also: me}, b: {also: me}}\n",
 		},
@@ -79,16 +124,10 @@ var multiplyOperatorScenarios = []expressionScenario{
 	{
 		description:           "Merge keeps style of LHS",
 		dontFormatInputForDoc: true,
-		document: `a: {things: great}
-b:
-  also: "me"
-`,
-		expression: `. * {"a":.b}`,
+		document:              "a: {things: great}\nb:\n  also: \"me\"",
+		expression:            `. * {"a":.b}`,
 		expected: []string{
-			`D0, P[], (!!map)::a: {things: great, also: "me"}
-b:
-    also: "me"
-`,
+			"D0, P[], (!!map)::a: {things: great, also: \"me\"}\nb:\n    also: \"me\"\n",
 		},
 	},
 	{
@@ -107,6 +146,30 @@ b:
 			"D0, P[a], (!!seq)::[1, 2]\n",
 		},
 	},
+	{
+		description: "Merge, only existing fields",
+		document:    `{a: {thing: one, cat: frog}, b: {missing: two, thing: two}}`,
+		expression:  `.a *? .b`,
+		expected: []string{
+			"D0, P[a], (!!map)::{thing: two, cat: frog}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{a: [{thing: one}], b: [{missing: two, thing: two}]}`,
+		expression: `.a *? .b`,
+		expected: []string{
+			"D0, P[a], (!!seq)::[{thing: two}]\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{a: {array: [1]}, b: {}}`,
+		expression: `.b *+ .a`,
+		expected: []string{
+			"D0, P[b], (!!map)::{array: [1]}\n",
+		},
+	},
 	{
 		description: "Merge, appending arrays",
 		document:    `{a: {array: [1, 2, animal: dog], value: coconut}, b: {array: [3, 4, animal: cat], value: banana}}`,
@@ -115,6 +178,14 @@ b:
 			"D0, P[a], (!!map)::{array: [1, 2, {animal: dog}, 3, 4, {animal: cat}], value: banana}\n",
 		},
 	},
+	{
+		description: "Merge, only existing fields, appending arrays",
+		document:    `{a: {thing: [1,2]}, b: {thing: [3,4], another: [1]}}`,
+		expression:  `.a *?+ .b`,
+		expected: []string{
+			"D0, P[a], (!!map)::{thing: [1, 2, 3, 4]}\n",
+		},
+	},
 	{
 		description: "Merge to prefix an element",
 		document:    `{a: cat, b: dog}`,
@@ -132,11 +203,11 @@ b:
 		},
 	},
 	{
-		description: "Merge does not copy anchor names",
+		description: "Merge copies anchor names",
 		document:    `{a: {c: &cat frog}, b: {f: *cat}, c: {g: thongs}}`,
 		expression:  `.c * .a`,
 		expected: []string{
-			"D0, P[c], (!!map)::{g: thongs, c: frog}\n",
+			"D0, P[c], (!!map)::{g: thongs, c: &cat frog}\n",
 		},
 	},
 	{

pkg/yqlib/operator_path.go

@@ -16,12 +16,12 @@ func createPathNodeFor(pathElement interface{}) *yaml.Node {
 	}
 }
 
-func GetPathOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func getPathOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("GetPath")
 
 	var results = list.New()
 
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		node := &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq"}
 
@@ -31,9 +31,9 @@ func GetPathOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *P
 			content[pathIndex] = createPathNodeFor(path)
 		}
 		node.Content = content
-		lengthCand := &CandidateNode{Node: node, Document: candidate.Document, Path: candidate.Path}
-		results.PushBack(lengthCand)
+		result := candidate.CreateChild(nil, node)
+		results.PushBack(result)
 	}
 
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_pipe.go

@@ -1,11 +1,18 @@
 package yqlib
 
-import "container/list"
+func pipeOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
-func PipeOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
+	//lhs may update the variable context, we should pass that into the RHS
+	// BUT we still return the original context back (see jq)
+	// https://stedolan.github.io/jq/manual/#Variable/SymbolicBindingOperator:...as$identifier|...
+
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-	return d.GetMatchingNodes(lhs, pathNode.Rhs)
+	rhs, err := d.GetMatchingNodes(lhs, expressionNode.Rhs)
+	if err != nil {
+		return Context{}, err
+	}
+	return context.ChildContext(rhs.MatchingNodes), nil
 }

pkg/yqlib/operator_recursive_descent.go

@@ -6,28 +6,28 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-type RecursiveDescentPreferences struct {
-	TraversePreferences *TraversePreferences
+type recursiveDescentPreferences struct {
+	TraversePreferences traversePreferences
 	RecurseArray        bool
 }
 
-func RecursiveDescentOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func recursiveDescentOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	var results = list.New()
 
-	preferences := pathNode.Operation.Preferences.(*RecursiveDescentPreferences)
-	err := recursiveDecent(d, results, matchMap, preferences)
+	preferences := expressionNode.Operation.Preferences.(recursiveDescentPreferences)
+	err := recursiveDecent(d, results, context, preferences)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
 
-	return results, nil
+	return context.ChildContext(results), nil
 }
 
-func recursiveDecent(d *dataTreeNavigator, results *list.List, matchMap *list.List, preferences *RecursiveDescentPreferences) error {
-	for el := matchMap.Front(); el != nil; el = el.Next() {
+func recursiveDecent(d *dataTreeNavigator, results *list.List, context Context, preferences recursiveDescentPreferences) error {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 
-		candidate.Node = UnwrapDoc(candidate.Node)
+		candidate.Node = unwrapDoc(candidate.Node)
 
 		log.Debugf("Recursive Decent, added %v", NodeToString(candidate))
 		results.PushBack(candidate)
@@ -35,7 +35,7 @@ func recursiveDecent(d *dataTreeNavigator, results *list.List, matchMap *list.Li
 		if candidate.Node.Kind != yaml.AliasNode && len(candidate.Node.Content) > 0 &&
 			(preferences.RecurseArray || candidate.Node.Kind != yaml.SequenceNode) {
 
-			children, err := Splat(d, nodeToMap(candidate), preferences.TraversePreferences)
+			children, err := splat(d, context.SingleChildContext(candidate), preferences.TraversePreferences)
 
 			if err != nil {
 				return err

pkg/yqlib/operator_recursive_descent_test.go

@@ -63,12 +63,12 @@ var recursiveDescentOperatorScenarios = []expressionScenario{
 		},
 	},
 	{
-		description: "Recursively find nodes with keys",
-		document:    `{a: {name: frog, b: {name: blog, age: 12}}}`,
-		expression:  `.. | select(has("name"))`,
+		description:    "Recursively find nodes with keys",
+		subdescription: "Note that this example has wrapped the expression in `[]` to show that there are two matches returned. You do not have to wrap in `[]` in your path expression.",
+		document:       `{a: {name: frog, b: {name: blog, age: 12}}}`,
+		expression:     `[.. | select(has("name"))]`,
 		expected: []string{
-			"D0, P[a], (!!map)::{name: frog, b: {name: blog, age: 12}}\n",
-			"D0, P[a b], (!!map)::{name: blog, age: 12}\n",
+			"D0, P[], (!!seq)::- {name: frog, b: {name: blog, age: 12}}\n- {name: blog, age: 12}\n",
 		},
 	},
 	{
@@ -165,7 +165,7 @@ var recursiveDescentOperatorScenarios = []expressionScenario{
 		document:    `{a: &cat {c: frog}, b: *cat}`,
 		expression:  `[..]`,
 		expected: []string{
-			"D0, P[a], (!!seq)::- {a: &cat {c: frog}, b: *cat}\n- &cat {c: frog}\n- frog\n- *cat\n",
+			"D0, P[], (!!seq)::- {a: &cat {c: frog}, b: *cat}\n- &cat {c: frog}\n- frog\n- *cat\n",
 		},
 	},
 	{
@@ -187,7 +187,7 @@ var recursiveDescentOperatorScenarios = []expressionScenario{
 		document:    mergeDocSample,
 		expression:  `.foobar | [..]`,
 		expected: []string{
-			"D0, P[foobar], (!!seq)::- c: foobar_c\n  !!merge <<: *foo\n  thing: foobar_thing\n- foobar_c\n- *foo\n- foobar_thing\n",
+			"D0, P[], (!!seq)::- c: foobar_c\n  !!merge <<: *foo\n  thing: foobar_thing\n- foobar_c\n- *foo\n- foobar_thing\n",
 		},
 	},
 	{
@@ -195,7 +195,7 @@ var recursiveDescentOperatorScenarios = []expressionScenario{
 		document:   mergeDocSample,
 		expression: `.foobar | [...]`,
 		expected: []string{
-			"D0, P[foobar], (!!seq)::- c: foobar_c\n  !!merge <<: *foo\n  thing: foobar_thing\n- c\n- foobar_c\n- !!merge <<\n- *foo\n- thing\n- foobar_thing\n",
+			"D0, P[], (!!seq)::- c: foobar_c\n  !!merge <<: *foo\n  thing: foobar_thing\n- c\n- foobar_c\n- !!merge <<\n- *foo\n- thing\n- foobar_thing\n",
 		},
 	},
 	{
@@ -233,5 +233,5 @@ func TestRecursiveDescentOperatorScenarios(t *testing.T) {
 	for _, tt := range recursiveDescentOperatorScenarios {
 		testScenario(t, &tt)
 	}
-	documentScenarios(t, "Recursive Descent", recursiveDescentOperatorScenarios)
+	documentScenarios(t, "Recursive Descent (Glob)", recursiveDescentOperatorScenarios)
 }

pkg/yqlib/operator_select.go

@@ -4,28 +4,29 @@ import (
 	"container/list"
 )
 
-func SelectOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func selectOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
 	log.Debugf("-- selectOperation")
 	var results = list.New()
 
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
-
-		rhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		childContext := context.SingleChildContext(candidate)
+		childContext.DontAutoCreate = true
+		rhs, err := d.GetMatchingNodes(childContext, expressionNode.Rhs)
 
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
 		// grab the first value
-		first := rhs.Front()
+		first := rhs.MatchingNodes.Front()
 
 		if first != nil {
 			result := first.Value.(*CandidateNode)
 			includeResult, errDecoding := isTruthy(result)
 			if errDecoding != nil {
-				return nil, errDecoding
+				return Context{}, errDecoding
 			}
 
 			if includeResult {
@@ -33,5 +34,5 @@ func SelectOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *Pa
 			}
 		}
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_select_test.go

@@ -14,6 +14,14 @@ var selectOperatorScenarios = []expressionScenario{
 			"D0, P[1], (!!str)::goat\n",
 		},
 	},
+	{
+		skipDoc:    true,
+		document:   `[{animal: cat, legs: {cool: true}}, {animal: fish}]`,
+		expression: `(.[] | select(.legs.cool == true).canWalk) = true | (.[] | .alive.things) = "yes"`,
+		expected: []string{
+			"D0, P[], (doc)::[{animal: cat, legs: {cool: true}, canWalk: true, alive: {things: yes}}, {animal: fish, alive: {things: yes}}]\n",
+		},
+	},
 	{
 		skipDoc:    true,
 		document:   `[hot, fot, dog]`,

pkg/yqlib/operator_self.go

@@ -1,7 +1,5 @@
 package yqlib
 
-import "container/list"
-
-func SelfOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	return matchMap, nil
+func selfOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	return context, nil
 }

pkg/yqlib/operator_sort_keys.go

@@ -1,33 +1,32 @@
 package yqlib
 
 import (
-	"container/list"
 	"sort"
 
 	yaml "gopkg.in/yaml.v3"
 )
 
-func SortKeysOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func sortKeysOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
-		rhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
-		for childEl := rhs.Front(); childEl != nil; childEl = childEl.Next() {
-			node := UnwrapDoc(childEl.Value.(*CandidateNode).Node)
+		for childEl := rhs.MatchingNodes.Front(); childEl != nil; childEl = childEl.Next() {
+			node := unwrapDoc(childEl.Value.(*CandidateNode).Node)
 			if node.Kind == yaml.MappingNode {
 				sortKeys(node)
 			}
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 		}
 
 	}
-	return matchingNodes, nil
+	return context, nil
 }
 
 func sortKeys(node *yaml.Node) {

pkg/yqlib/operator_split_document.go

@@ -0,0 +1,14 @@
+package yqlib
+
+func splitDocumentOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("-- splitDocumentOperator")
+
+	var index uint = 0
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		candidate.Document = index
+		index = index + 1
+	}
+
+	return context, nil
+}

pkg/yqlib/operator_split_document_test.go

@@ -0,0 +1,32 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var splitDocOperatorScenarios = []expressionScenario{
+	{
+		description: "Split empty",
+		document:    ``,
+		expression:  `splitDoc`,
+		expected: []string{
+			"D0, P[], (!!null)::\n",
+		},
+	},
+	{
+		description: "Split array",
+		document:    `[{a: cat}, {b: dog}]`,
+		expression:  `.[] | splitDoc`,
+		expected: []string{
+			"D0, P[0], (!!map)::{a: cat}\n",
+			"D1, P[1], (!!map)::{b: dog}\n",
+		},
+	},
+}
+
+func TestSplitDocOperatorScenarios(t *testing.T) {
+	for _, tt := range splitDocOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentScenarios(t, "Split into Documents", splitDocOperatorScenarios)
+}

pkg/yqlib/operator_strings.go

@@ -0,0 +1,96 @@
+package yqlib
+
+import (
+	"container/list"
+	"fmt"
+	"strings"
+
+	"gopkg.in/yaml.v3"
+)
+
+func joinStringOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("-- joinStringOperator")
+	joinStr := ""
+
+	rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
+	if err != nil {
+		return Context{}, err
+	}
+	if rhs.MatchingNodes.Front() != nil {
+		joinStr = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
+	}
+
+	var results = list.New()
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		node := unwrapDoc(candidate.Node)
+		if node.Kind != yaml.SequenceNode {
+			return Context{}, fmt.Errorf("Cannot join with %v, can only join arrays of scalars", node.Tag)
+		}
+		targetNode := join(node.Content, joinStr)
+		result := candidate.CreateChild(nil, targetNode)
+		results.PushBack(result)
+	}
+
+	return context.ChildContext(results), nil
+}
+
+func join(content []*yaml.Node, joinStr string) *yaml.Node {
+	var stringsToJoin []string
+	for _, node := range content {
+		str := node.Value
+		if node.Tag == "!!null" {
+			str = ""
+		}
+		stringsToJoin = append(stringsToJoin, str)
+	}
+
+	return &yaml.Node{Kind: yaml.ScalarNode, Value: strings.Join(stringsToJoin, joinStr), Tag: "!!str"}
+}
+
+func splitStringOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("-- splitStringOperator")
+	splitStr := ""
+
+	rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
+	if err != nil {
+		return Context{}, err
+	}
+	if rhs.MatchingNodes.Front() != nil {
+		splitStr = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
+	}
+
+	var results = list.New()
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		node := unwrapDoc(candidate.Node)
+		if node.Tag == "!!null" {
+			continue
+		}
+		if node.Tag != "!!str" {
+			return Context{}, fmt.Errorf("Cannot split %v, can only split strings", node.Tag)
+		}
+		targetNode := split(node.Value, splitStr)
+		result := candidate.CreateChild(nil, targetNode)
+		results.PushBack(result)
+	}
+
+	return context.ChildContext(results), nil
+}
+
+func split(value string, spltStr string) *yaml.Node {
+	var contents []*yaml.Node
+
+	if value != "" {
+		var newStrings = strings.Split(value, spltStr)
+		contents = make([]*yaml.Node, len(newStrings))
+
+		for index, str := range newStrings {
+			contents[index] = &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: str}
+		}
+	}
+
+	return &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq", Content: contents}
+}

pkg/yqlib/operator_strings_test.go

@@ -0,0 +1,52 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var stringsOperatorScenarios = []expressionScenario{
+	{
+		description: "Join strings",
+		document:    `[cat, meow, 1, null, true]`,
+		expression:  `join("; ")`,
+		expected: []string{
+			"D0, P[], (!!str)::cat; meow; 1; ; true\n",
+		},
+	},
+	{
+		description: "Split strings",
+		document:    `"cat; meow; 1; ; true"`,
+		expression:  `split("; ")`,
+		expected: []string{
+			"D0, P[], (!!seq)::- cat\n- meow\n- \"1\"\n- \"\"\n- \"true\"\n",
+		},
+	},
+	{
+		description: "Split strings one match",
+		document:    `"word"`,
+		expression:  `split("; ")`,
+		expected: []string{
+			"D0, P[], (!!seq)::- word\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `""`,
+		expression: `split("; ")`,
+		expected: []string{
+			"D0, P[], (!!seq)::[]\n", // dont actually want this, just not to error
+		},
+	},
+	{
+		skipDoc:    true,
+		expression: `split("; ")`,
+		expected:   []string{},
+	},
+}
+
+func TestStringsOperatorScenarios(t *testing.T) {
+	for _, tt := range stringsOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentScenarios(t, "String Operators", stringsOperatorScenarios)
+}

pkg/yqlib/operator_style.go

@@ -26,43 +26,43 @@ func parseStyle(customStyle string) (yaml.Style, error) {
 	return 0, nil
 }
 
-func AssignStyleOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func assignStyleOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
 	log.Debugf("AssignStyleOperator: %v")
 	var style yaml.Style
-	if !pathNode.Operation.UpdateAssign {
-		rhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
+	if !expressionNode.Operation.UpdateAssign {
+		rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
-		if rhs.Front() != nil {
-			style, err = parseStyle(rhs.Front().Value.(*CandidateNode).Node.Value)
+		if rhs.MatchingNodes.Front() != nil {
+			style, err = parseStyle(rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 		}
 	}
 
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
 
-	for el := lhs.Front(); el != nil; el = el.Next() {
+	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		log.Debugf("Setting style of : %v", candidate.GetKey())
-		if pathNode.Operation.UpdateAssign {
-			rhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		if expressionNode.Operation.UpdateAssign {
+			rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 
-			if rhs.Front() != nil {
-				style, err = parseStyle(rhs.Front().Value.(*CandidateNode).Node.Value)
+			if rhs.MatchingNodes.Front() != nil {
+				style, err = parseStyle(rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value)
 				if err != nil {
-					return nil, err
+					return Context{}, err
 				}
 			}
 		}
@@ -70,15 +70,15 @@ func AssignStyleOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNod
 		candidate.Node.Style = style
 	}
 
-	return matchingNodes, nil
+	return context, nil
 }
 
-func GetStyleOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func getStyleOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("GetStyleOperator")
 
 	var results = list.New()
 
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		var style string
 		switch candidate.Node.Style {
@@ -100,9 +100,9 @@ func GetStyleOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *
 			style = "<unknown>"
 		}
 		node := &yaml.Node{Kind: yaml.ScalarNode, Value: style, Tag: "!!str"}
-		lengthCand := &CandidateNode{Node: node, Document: candidate.Document, Path: candidate.Path}
-		results.PushBack(lengthCand)
+		result := candidate.CreateChild(nil, node)
+		results.PushBack(result)
 	}
 
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_tag.go

@@ -6,58 +6,58 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-func AssignTagOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func assignTagOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
 	log.Debugf("AssignTagOperator: %v")
 	tag := ""
 
-	if !pathNode.Operation.UpdateAssign {
-		rhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
+	if !expressionNode.Operation.UpdateAssign {
+		rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
-		if rhs.Front() != nil {
-			tag = rhs.Front().Value.(*CandidateNode).Node.Value
+		if rhs.MatchingNodes.Front() != nil {
+			tag = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 		}
 	}
 
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
 
-	for el := lhs.Front(); el != nil; el = el.Next() {
+	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		log.Debugf("Setting tag of : %v", candidate.GetKey())
-		if pathNode.Operation.UpdateAssign {
-			rhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		if expressionNode.Operation.UpdateAssign {
+			rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 
-			if rhs.Front() != nil {
-				tag = rhs.Front().Value.(*CandidateNode).Node.Value
+			if rhs.MatchingNodes.Front() != nil {
+				tag = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 			}
 		}
-		candidate.Node.Tag = tag
+		unwrapDoc(candidate.Node).Tag = tag
 	}
 
-	return matchingNodes, nil
+	return context, nil
 }
 
-func GetTagOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func getTagOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("GetTagOperator")
 
 	var results = list.New()
 
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
-		node := &yaml.Node{Kind: yaml.ScalarNode, Value: UnwrapDoc(candidate.Node).Tag, Tag: "!!str"}
-		lengthCand := &CandidateNode{Node: node, Document: candidate.Document, Path: candidate.Path}
-		results.PushBack(lengthCand)
+		node := &yaml.Node{Kind: yaml.ScalarNode, Value: unwrapDoc(candidate.Node).Tag, Tag: "!!str"}
+		result := candidate.CreateChild(nil, node)
+		results.PushBack(result)
 	}
 
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_tag_test.go

@@ -26,6 +26,14 @@ var tagOperatorScenarios = []expressionScenario{
 			"D0, P[], (!!str)::'!!map'\n",
 		},
 	},
+	{
+		skipDoc:    true,
+		document:   `32`,
+		expression: `. tag= "!!str"`,
+		expected: []string{
+			"D0, P[], (doc)::\"32\"\n",
+		},
+	},
 	{
 		description: "Set custom tag",
 		document:    `{a: str}`,

pkg/yqlib/operator_traverse_path.go

@@ -9,31 +9,33 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-type TraversePreferences struct {
-	FollowAlias    bool
-	IncludeMapKeys bool
+type traversePreferences struct {
+	DontFollowAlias      bool
+	IncludeMapKeys       bool
+	DontAutoCreate       bool // by default, we automatically create entries on the fly.
+	DontIncludeMapValues bool
 }
 
-func Splat(d *dataTreeNavigator, matches *list.List, prefs *TraversePreferences) (*list.List, error) {
-	return traverseNodesWithArrayIndices(matches, make([]*yaml.Node, 0), prefs)
+func splat(d *dataTreeNavigator, context Context, prefs traversePreferences) (Context, error) {
+	return traverseNodesWithArrayIndices(context, make([]*yaml.Node, 0), prefs)
 }
 
-func TraversePathOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	log.Debugf("-- Traversing")
-	var matchingNodeMap = list.New()
+func traversePathOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("-- traversePathOperator")
+	var matches = list.New()
 
-	for el := matchMap.Front(); el != nil; el = el.Next() {
-		newNodes, err := traverse(d, el.Value.(*CandidateNode), pathNode.Operation)
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		newNodes, err := traverse(d, context, el.Value.(*CandidateNode), expressionNode.Operation)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
-		matchingNodeMap.PushBackList(newNodes)
+		matches.PushBackList(newNodes)
 	}
 
-	return matchingNodeMap, nil
+	return context.ChildContext(matches), nil
 }
 
-func traverse(d *dataTreeNavigator, matchingNode *CandidateNode, operation *Operation) (*list.List, error) {
+func traverse(d *dataTreeNavigator, context Context, matchingNode *CandidateNode, operation *Operation) (*list.List, error) {
 	log.Debug("Traversing %v", NodeToString(matchingNode))
 	value := matchingNode.Node
 
@@ -54,8 +56,7 @@ func traverse(d *dataTreeNavigator, matchingNode *CandidateNode, operation *Oper
 	switch value.Kind {
 	case yaml.MappingNode:
 		log.Debug("its a map with %v entries", len(value.Content)/2)
-		prefs := &TraversePreferences{FollowAlias: true}
-		return traverseMap(matchingNode, operation.StringValue, prefs, false)
+		return traverseMap(context, matchingNode, operation.StringValue, operation.Preferences.(traversePreferences), false)
 
 	case yaml.SequenceNode:
 		log.Debug("its a sequence of %v things!", len(value.Content))
@@ -64,47 +65,59 @@ func traverse(d *dataTreeNavigator, matchingNode *CandidateNode, operation *Oper
 	case yaml.AliasNode:
 		log.Debug("its an alias!")
 		matchingNode.Node = matchingNode.Node.Alias
-		return traverse(d, matchingNode, operation)
+		return traverse(d, context, matchingNode, operation)
 	case yaml.DocumentNode:
 		log.Debug("digging into doc node")
-		return traverse(d, &CandidateNode{
-			Node:      matchingNode.Node.Content[0],
-			Filename:  matchingNode.Filename,
-			FileIndex: matchingNode.FileIndex,
-			Document:  matchingNode.Document}, operation)
+
+		return traverse(d, context, matchingNode.CreateChild(nil, matchingNode.Node.Content[0]), operation)
 	default:
 		return list.New(), nil
 	}
 }
 
-func TraverseArrayOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	// rhs is a collect expression that will yield indexes to retreive of the arrays
+func traverseArrayOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
-	rhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
+	//lhs may update the variable context, we should pass that into the RHS
+	// BUT we still return the original context back (see jq)
+	// https://stedolan.github.io/jq/manual/#Variable/SymbolicBindingOperator:...as$identifier|...
+
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
 
-	var indicesToTraverse = rhs.Front().Value.(*CandidateNode).Node.Content
-	prefs := &TraversePreferences{FollowAlias: true}
-	return traverseNodesWithArrayIndices(matchingNodes, indicesToTraverse, prefs)
+	// rhs is a collect expression that will yield indexes to retreive of the arrays
+
+	rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
+	if err != nil {
+		return Context{}, err
+	}
+
+	var indicesToTraverse = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Content
+
+	//now we traverse the result of the lhs against the indices we found
+	result, err := traverseNodesWithArrayIndices(lhs, indicesToTraverse, traversePreferences{})
+	if err != nil {
+		return Context{}, err
+	}
+	return context.ChildContext(result.MatchingNodes), nil
 }
 
-func traverseNodesWithArrayIndices(matchingNodes *list.List, indicesToTraverse []*yaml.Node, prefs *TraversePreferences) (*list.List, error) {
+func traverseNodesWithArrayIndices(context Context, indicesToTraverse []*yaml.Node, prefs traversePreferences) (Context, error) {
 	var matchingNodeMap = list.New()
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
-		newNodes, err := traverseArrayIndices(candidate, indicesToTraverse, prefs)
+		newNodes, err := traverseArrayIndices(context, candidate, indicesToTraverse, prefs)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 		matchingNodeMap.PushBackList(newNodes)
 	}
 
-	return matchingNodeMap, nil
+	return context.ChildContext(matchingNodeMap), nil
 }
 
-func traverseArrayIndices(matchingNode *CandidateNode, indicesToTraverse []*yaml.Node, prefs *TraversePreferences) (*list.List, error) { // call this if doc / alias like the other traverse
+func traverseArrayIndices(context Context, matchingNode *CandidateNode, indicesToTraverse []*yaml.Node, prefs traversePreferences) (*list.List, error) { // call this if doc / alias like the other traverse
 	node := matchingNode.Node
 	if node.Tag == "!!null" {
 		log.Debugf("OperatorArrayTraverse got a null - turning it into an empty array")
@@ -115,32 +128,28 @@ func traverseArrayIndices(matchingNode *CandidateNode, indicesToTraverse []*yaml
 
 	if node.Kind == yaml.AliasNode {
 		matchingNode.Node = node.Alias
-		return traverseArrayIndices(matchingNode, indicesToTraverse, prefs)
+		return traverseArrayIndices(context, matchingNode, indicesToTraverse, prefs)
 	} else if node.Kind == yaml.SequenceNode {
 		return traverseArrayWithIndices(matchingNode, indicesToTraverse)
 	} else if node.Kind == yaml.MappingNode {
-		return traverseMapWithIndices(matchingNode, indicesToTraverse, prefs)
+		return traverseMapWithIndices(context, matchingNode, indicesToTraverse, prefs)
 	} else if node.Kind == yaml.DocumentNode {
-		return traverseArrayIndices(&CandidateNode{
-			Node:      matchingNode.Node.Content[0],
-			Filename:  matchingNode.Filename,
-			FileIndex: matchingNode.FileIndex,
-			Document:  matchingNode.Document}, indicesToTraverse, prefs)
+		return traverseArrayIndices(context, matchingNode.CreateChild(nil, matchingNode.Node.Content[0]), indicesToTraverse, prefs)
 	}
 	log.Debugf("OperatorArrayTraverse skipping %v as its a %v", matchingNode, node.Tag)
 	return list.New(), nil
 }
 
-func traverseMapWithIndices(candidate *CandidateNode, indices []*yaml.Node, prefs *TraversePreferences) (*list.List, error) {
+func traverseMapWithIndices(context Context, candidate *CandidateNode, indices []*yaml.Node, prefs traversePreferences) (*list.List, error) {
 	if len(indices) == 0 {
-		return traverseMap(candidate, "", prefs, true)
+		return traverseMap(context, candidate, "", prefs, true)
 	}
 
 	var matchingNodeMap = list.New()
 
 	for _, indexNode := range indices {
 		log.Debug("traverseMapWithIndices: %v", indexNode.Value)
-		newNodes, err := traverseMap(candidate, indexNode.Value, prefs, false)
+		newNodes, err := traverseMap(context, candidate, indexNode.Value, prefs, false)
 		if err != nil {
 			return nil, err
 		}
@@ -153,17 +162,13 @@ func traverseMapWithIndices(candidate *CandidateNode, indices []*yaml.Node, pref
 func traverseArrayWithIndices(candidate *CandidateNode, indices []*yaml.Node) (*list.List, error) {
 	log.Debug("traverseArrayWithIndices")
 	var newMatches = list.New()
-	node := UnwrapDoc(candidate.Node)
+	node := unwrapDoc(candidate.Node)
 	if len(indices) == 0 {
 		log.Debug("splatting")
 		var index int64
 		for index = 0; index < int64(len(node.Content)); index = index + 1 {
 
-			newMatches.PushBack(&CandidateNode{
-				Document: candidate.Document,
-				Path:     candidate.CreateChildPath(index),
-				Node:     node.Content[index],
-			})
+			newMatches.PushBack(candidate.CreateChild(index, node.Content[index]))
 		}
 		return newMatches, nil
 
@@ -190,20 +195,16 @@ func traverseArrayWithIndices(candidate *CandidateNode, indices []*yaml.Node) (*
 			return nil, fmt.Errorf("Index [%v] out of range, array size is %v", index, contentLength)
 		}
 
-		newMatches.PushBack(&CandidateNode{
-			Node:     node.Content[indexToUse],
-			Document: candidate.Document,
-			Path:     candidate.CreateChildPath(index),
-		})
+		newMatches.PushBack(candidate.CreateChild(index, node.Content[indexToUse]))
 	}
 	return newMatches, nil
 }
 
 func keyMatches(key *yaml.Node, wantedKey string) bool {
-	return Match(key.Value, wantedKey)
+	return matchKey(key.Value, wantedKey)
 }
 
-func traverseMap(matchingNode *CandidateNode, key string, prefs *TraversePreferences, splat bool) (*list.List, error) {
+func traverseMap(context Context, matchingNode *CandidateNode, key string, prefs traversePreferences, splat bool) (*list.List, error) {
 	var newMatches = orderedmap.NewOrderedMap()
 	err := doTraverseMap(newMatches, matchingNode, key, prefs, splat)
 
@@ -211,18 +212,24 @@ func traverseMap(matchingNode *CandidateNode, key string, prefs *TraversePrefere
 		return nil, err
 	}
 
-	if newMatches.Len() == 0 {
+	if !prefs.DontAutoCreate && !context.DontAutoCreate && newMatches.Len() == 0 {
 		//no matches, create one automagically
 		valueNode := &yaml.Node{Tag: "!!null", Kind: yaml.ScalarNode, Value: "null"}
+		keyNode := &yaml.Node{Kind: yaml.ScalarNode, Value: key}
 		node := matchingNode.Node
-		node.Content = append(node.Content, &yaml.Node{Kind: yaml.ScalarNode, Value: key}, valueNode)
-		candidateNode := &CandidateNode{
-			Node:     valueNode,
-			Path:     append(matchingNode.Path, key),
-			Document: matchingNode.Document,
-		}
-		newMatches.Set(candidateNode.GetKey(), candidateNode)
+		node.Content = append(node.Content, keyNode, valueNode)
 
+		if prefs.IncludeMapKeys {
+			log.Debug("including key")
+			candidateNode := matchingNode.CreateChild(key, keyNode)
+			candidateNode.IsMapKey = true
+			newMatches.Set(fmt.Sprintf("keyOf-%v", candidateNode.GetKey()), candidateNode)
+		}
+		if !prefs.DontIncludeMapValues {
+			log.Debug("including value")
+			candidateNode := matchingNode.CreateChild(key, valueNode)
+			newMatches.Set(candidateNode.GetKey(), candidateNode)
+		}
 	}
 
 	results := list.New()
@@ -234,7 +241,7 @@ func traverseMap(matchingNode *CandidateNode, key string, prefs *TraversePrefere
 	return results, nil
 }
 
-func doTraverseMap(newMatches *orderedmap.OrderedMap, candidate *CandidateNode, wantedKey string, prefs *TraversePreferences, splat bool) error {
+func doTraverseMap(newMatches *orderedmap.OrderedMap, candidate *CandidateNode, wantedKey string, prefs traversePreferences, splat bool) error {
 	// value.Content is a concatenated array of key, value,
 	// so keys are in the even indexes, values in odd.
 	// merge aliases are defined first, but we only want to traverse them
@@ -249,7 +256,7 @@ func doTraverseMap(newMatches *orderedmap.OrderedMap, candidate *CandidateNode,
 
 		log.Debug("checking %v (%v)", key.Value, key.Tag)
 		//skip the 'merge' tag, find a direct match first
-		if key.Tag == "!!merge" && prefs.FollowAlias {
+		if key.Tag == "!!merge" && !prefs.DontFollowAlias {
 			log.Debug("Merge anchor")
 			err := traverseMergeAnchor(newMatches, candidate, value, wantedKey, prefs, splat)
 			if err != nil {
@@ -258,33 +265,26 @@ func doTraverseMap(newMatches *orderedmap.OrderedMap, candidate *CandidateNode,
 		} else if splat || keyMatches(key, wantedKey) {
 			log.Debug("MATCHED")
 			if prefs.IncludeMapKeys {
-				candidateNode := &CandidateNode{
-					Node:     key,
-					Path:     candidate.CreateChildPath(key.Value),
-					Document: candidate.Document,
-				}
+				log.Debug("including key")
+				candidateNode := candidate.CreateChild(key.Value, key)
+				candidateNode.IsMapKey = true
 				newMatches.Set(fmt.Sprintf("keyOf-%v", candidateNode.GetKey()), candidateNode)
 			}
-			candidateNode := &CandidateNode{
-				Node:     value,
-				Path:     candidate.CreateChildPath(key.Value),
-				Document: candidate.Document,
+			if !prefs.DontIncludeMapValues {
+				log.Debug("including value")
+				candidateNode := candidate.CreateChild(key.Value, value)
+				newMatches.Set(candidateNode.GetKey(), candidateNode)
 			}
-			newMatches.Set(candidateNode.GetKey(), candidateNode)
 		}
 	}
 
 	return nil
 }
 
-func traverseMergeAnchor(newMatches *orderedmap.OrderedMap, originalCandidate *CandidateNode, value *yaml.Node, wantedKey string, prefs *TraversePreferences, splat bool) error {
+func traverseMergeAnchor(newMatches *orderedmap.OrderedMap, originalCandidate *CandidateNode, value *yaml.Node, wantedKey string, prefs traversePreferences, splat bool) error {
 	switch value.Kind {
 	case yaml.AliasNode:
-		candidateNode := &CandidateNode{
-			Node:     value.Alias,
-			Path:     originalCandidate.Path,
-			Document: originalCandidate.Document,
-		}
+		candidateNode := originalCandidate.CreateChild(nil, value.Alias)
 		return doTraverseMap(newMatches, candidateNode, wantedKey, prefs, splat)
 	case yaml.SequenceNode:
 		for _, childValue := range value.Content {

pkg/yqlib/operator_traverse_path_test.go

@@ -47,13 +47,30 @@ var traversePathOperatorScenarios = []expressionScenario{
 	},
 	{
 		description:    "Special characters",
-		subdescription: "Use quotes around path elements with special characters",
+		subdescription: "Use quotes with brackets around path elements with special characters",
 		document:       `{"{}": frog}`,
-		expression:     `."{}"`,
+		expression:     `.["{}"]`,
 		expected: []string{
 			"D0, P[{}], (!!str)::frog\n",
 		},
 	},
+	{
+		description:    "Keys with spaces",
+		subdescription: "Use quotes with brackets around path elements with special characters",
+		document:       `{"red rabbit": frog}`,
+		expression:     `.["red rabbit"]`,
+		expected: []string{
+			"D0, P[red rabbit], (!!str)::frog\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{"flying fox": frog}`,
+		expression: `.["flying fox"]`,
+		expected: []string{
+			"D0, P[flying fox], (!!str)::frog\n",
+		},
+	},
 	{
 		description:    "Dynamic keys",
 		subdescription: `Expressions within [] can be used to dynamically lookup / calculate keys`,
@@ -63,6 +80,14 @@ var traversePathOperatorScenarios = []expressionScenario{
 			"D0, P[apple], (!!str)::crispy yum\n",
 		},
 	},
+	{
+		skipDoc:    true,
+		document:   `{b: apple, fruit: {apple: yum, banana: smooth}}`,
+		expression: `.fruit[.b]`,
+		expected: []string{
+			"D0, P[fruit apple], (!!str)::yum\n",
+		},
+	},
 	{
 		description:    "Children don't exist",
 		subdescription: "Nodes are added dynamically while traversing",
@@ -83,7 +108,7 @@ var traversePathOperatorScenarios = []expressionScenario{
 	{
 		skipDoc:    true,
 		document:   `{}`,
-		expression: `.a.[1]`,
+		expression: `.a[1]`,
 		expected: []string{
 			"D0, P[a 1], (!!null)::null\n",
 		},
@@ -154,7 +179,7 @@ var traversePathOperatorScenarios = []expressionScenario{
 	{
 		skipDoc:    true,
 		document:   `{a: &cat {c: frog}, b: *cat}`,
-		expression: `.b.[]`,
+		expression: `.b[]`,
 		expected: []string{
 			"D0, P[b c], (!!str)::frog\n",
 		},
@@ -236,7 +261,7 @@ var traversePathOperatorScenarios = []expressionScenario{
 	{
 		skipDoc:    true,
 		document:   mergeDocSample,
-		expression: `.foobar.[]`,
+		expression: `.foobar[]`,
 		expected: []string{
 			"D0, P[foobar c], (!!str)::foo_c\n",
 			"D0, P[foobar a], (!!str)::foo_a\n",
@@ -298,7 +323,7 @@ var traversePathOperatorScenarios = []expressionScenario{
 	{
 		skipDoc:    true,
 		document:   mergeDocSample,
-		expression: `.foobarList.[]`,
+		expression: `.foobarList[]`,
 		expected: []string{
 			"D0, P[foobarList b], (!!str)::bar_b\n",
 			"D0, P[foobarList a], (!!str)::foo_a\n",
@@ -344,7 +369,7 @@ var traversePathOperatorScenarios = []expressionScenario{
 	{
 		skipDoc:    true,
 		document:   `{a: [a,b,c]}`,
-		expression: `.a.[0, 2]`,
+		expression: `.a[0, 2]`,
 		expected: []string{
 			"D0, P[a 0], (!!str)::a\n",
 			"D0, P[a 2], (!!str)::c\n",
@@ -361,7 +386,7 @@ var traversePathOperatorScenarios = []expressionScenario{
 	{
 		skipDoc:    true,
 		document:   `{a: [a,b,c]}`,
-		expression: `.a.[-1]`,
+		expression: `.a[-1]`,
 		expected: []string{
 			"D0, P[a -1], (!!str)::c\n",
 		},
@@ -377,7 +402,7 @@ var traversePathOperatorScenarios = []expressionScenario{
 	{
 		skipDoc:    true,
 		document:   `{a: [a,b,c]}`,
-		expression: `.a.[-2]`,
+		expression: `.a[-2]`,
 		expected: []string{
 			"D0, P[a -2], (!!str)::b\n",
 		},
@@ -395,7 +420,7 @@ var traversePathOperatorScenarios = []expressionScenario{
 	{
 		skipDoc:    true,
 		document:   `{a: [a,b,c]}`,
-		expression: `.a.[]`,
+		expression: `.a[]`,
 		expected: []string{
 			"D0, P[a 0], (!!str)::a\n",
 			"D0, P[a 1], (!!str)::b\n",
@@ -418,5 +443,5 @@ func TestTraversePathOperatorScenarios(t *testing.T) {
 	for _, tt := range traversePathOperatorScenarios {
 		testScenario(t, &tt)
 	}
-	documentScenarios(t, "Traverse", traversePathOperatorScenarios)
+	documentScenarios(t, "Traverse (Read)", traversePathOperatorScenarios)
 }

pkg/yqlib/operator_union.go

@@ -1,19 +1,17 @@
 package yqlib
 
-import "container/list"
-
-func UnionOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
+func unionOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-	rhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
+	rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-	for el := rhs.Front(); el != nil; el = el.Next() {
+	for el := rhs.MatchingNodes.Front(); el != nil; el = el.Next() {
 		node := el.Value.(*CandidateNode)
-		lhs.PushBack(node)
+		lhs.MatchingNodes.PushBack(node)
 	}
 	return lhs, nil
 }

pkg/yqlib/operator_value.go

@@ -1,8 +1,6 @@
 package yqlib
 
-import "container/list"
-
-func ValueOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	log.Debug("value = %v", pathNode.Operation.CandidateNode.Node.Value)
-	return nodeToMap(pathNode.Operation.CandidateNode), nil
+func valueOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debug("value = %v", expressionNode.Operation.CandidateNode.Node.Value)
+	return context.SingleChildContext(expressionNode.Operation.CandidateNode), nil
 }

pkg/yqlib/operator_variables.go

@@ -0,0 +1,29 @@
+package yqlib
+
+import (
+	"container/list"
+	"fmt"
+)
+
+func getVariableOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	variableName := expressionNode.Operation.StringValue
+	log.Debug("getVariableOperator %v", variableName)
+	result := context.GetVariable(variableName)
+	if result == nil {
+		result = list.New()
+	}
+	return context.ChildContext(result), nil
+}
+
+func assignVariableOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
+	if err != nil {
+		return Context{}, nil
+	}
+	if expressionNode.Rhs.Operation.OperationType.Type != "GET_VARIABLE" {
+		return Context{}, fmt.Errorf("RHS of 'as' operator must be a variable name e.g. $foo")
+	}
+	variableName := expressionNode.Rhs.Operation.StringValue
+	context.SetVariable(variableName, lhs.MatchingNodes)
+	return context, nil
+}

pkg/yqlib/operator_variables_test.go

@@ -0,0 +1,45 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var variableOperatorScenarios = []expressionScenario{
+	{
+		description: "Single value variable",
+		document:    `a: cat`,
+		expression:  `.a as $foo | $foo`,
+		expected: []string{
+			"D0, P[a], (!!str)::cat\n",
+		},
+	},
+	{
+		description: "Multi value variable",
+		document:    `[cat, dog]`,
+		expression:  `.[] as $foo | $foo`,
+		expected: []string{
+			"D0, P[0], (!!str)::cat\n",
+			"D0, P[1], (!!str)::dog\n",
+		},
+	},
+	{
+		description:    "Using variables as a lookup",
+		subdescription: "Example taken from [jq](https://stedolan.github.io/jq/manual/#Variable/SymbolicBindingOperator:...as$identifier|...)",
+		document: `{"posts": [{"title": "Frist psot", "author": "anon"},
+		{"title": "A well-written article", "author": "person1"}],
+"realnames": {"anon": "Anonymous Coward",
+				"person1": "Person McPherson"}}`,
+		expression: `.realnames as $names | .posts[] | {"title":.title, "author": $names[.author]}`,
+		expected: []string{
+			"D0, P[], (!!map)::title: \"Frist psot\"\nauthor: \"Anonymous Coward\"\n",
+			"D0, P[], (!!map)::title: \"A well-written article\"\nauthor: \"Person McPherson\"\n",
+		},
+	},
+}
+
+func TestVariableOperatorScenarios(t *testing.T) {
+	for _, tt := range variableOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentScenarios(t, "Variable Operators", variableOperatorScenarios)
+}

pkg/yqlib/operators.go

@@ -4,20 +4,80 @@ import (
 	"container/list"
 	"fmt"
 
+	"github.com/jinzhu/copier"
 	"gopkg.in/yaml.v3"
 )
 
-type OperatorHandler func(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error)
+type operatorHandler func(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error)
 
-func UnwrapDoc(node *yaml.Node) *yaml.Node {
+func unwrapDoc(node *yaml.Node) *yaml.Node {
 	if node.Kind == yaml.DocumentNode {
 		return node.Content[0]
 	}
 	return node
 }
 
-func EmptyOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	return list.New(), nil
+func emptyOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	context.MatchingNodes = list.New()
+	return context, nil
+}
+
+type crossFunctionCalculation func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error)
+
+func doCrossFunc(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode, calculation crossFunctionCalculation) (Context, error) {
+	var results = list.New()
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
+	if err != nil {
+		return Context{}, err
+	}
+	log.Debugf("crossFunction LHS len: %v", lhs.MatchingNodes.Len())
+
+	rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
+
+	if err != nil {
+		return Context{}, err
+	}
+
+	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
+		lhsCandidate := el.Value.(*CandidateNode)
+
+		for rightEl := rhs.MatchingNodes.Front(); rightEl != nil; rightEl = rightEl.Next() {
+			log.Debugf("Applying calc")
+			rhsCandidate := rightEl.Value.(*CandidateNode)
+			resultCandidate, err := calculation(d, context, lhsCandidate, rhsCandidate)
+			if err != nil {
+				return Context{}, err
+			}
+			results.PushBack(resultCandidate)
+		}
+
+	}
+	return context.ChildContext(results), nil
+}
+
+func crossFunction(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode, calculation crossFunctionCalculation) (Context, error) {
+	var results = list.New()
+
+	var evaluateAllTogether = true
+	for matchEl := context.MatchingNodes.Front(); matchEl != nil; matchEl = matchEl.Next() {
+		evaluateAllTogether = evaluateAllTogether && matchEl.Value.(*CandidateNode).EvaluateTogether
+		if !evaluateAllTogether {
+			break
+		}
+	}
+	if evaluateAllTogether {
+		return doCrossFunc(d, context, expressionNode, calculation)
+	}
+
+	for matchEl := context.MatchingNodes.Front(); matchEl != nil; matchEl = matchEl.Next() {
+		innerResults, err := doCrossFunc(d, context.SingleChildContext(matchEl.Value.(*CandidateNode)), expressionNode, calculation)
+		if err != nil {
+			return Context{}, err
+		}
+		results.PushBackList(innerResults.MatchingNodes)
+	}
+
+	return context.ChildContext(results), nil
 }
 
 func createBooleanCandidate(owner *CandidateNode, value bool) *CandidateNode {
@@ -26,23 +86,28 @@ func createBooleanCandidate(owner *CandidateNode, value bool) *CandidateNode {
 		valString = "false"
 	}
 	node := &yaml.Node{Kind: yaml.ScalarNode, Value: valString, Tag: "!!bool"}
-	return &CandidateNode{Node: node, Document: owner.Document, Path: owner.Path}
+	return owner.CreateChild(nil, node)
 }
 
-func nodeToMap(candidate *CandidateNode) *list.List {
-	elMap := list.New()
-	elMap.PushBack(candidate)
-	return elMap
-}
-
-func createTraversalTree(path []interface{}) *PathTreeNode {
+func createTraversalTree(path []interface{}, traversePrefs traversePreferences, targetKey bool) *ExpressionNode {
 	if len(path) == 0 {
-		return &PathTreeNode{Operation: &Operation{OperationType: SelfReference}}
+		return &ExpressionNode{Operation: &Operation{OperationType: selfReferenceOpType}}
 	} else if len(path) == 1 {
-		return &PathTreeNode{Operation: &Operation{OperationType: TraversePath, Value: path[0], StringValue: fmt.Sprintf("%v", path[0])}}
+		lastPrefs := traversePrefs
+		if targetKey {
+			err := copier.Copy(&lastPrefs, traversePrefs)
+			if err != nil {
+				panic(err)
+			}
+			lastPrefs.IncludeMapKeys = true
+			lastPrefs.DontIncludeMapValues = true
+		}
+		return &ExpressionNode{Operation: &Operation{OperationType: traversePathOpType, Preferences: lastPrefs, Value: path[0], StringValue: fmt.Sprintf("%v", path[0])}}
+	}
+
+	return &ExpressionNode{
+		Operation: &Operation{OperationType: shortPipeOpType},
+		Lhs:       createTraversalTree(path[0:1], traversePrefs, false),
+		Rhs:       createTraversalTree(path[1:], traversePrefs, targetKey),
 	}
-	return &PathTreeNode{
-		Operation: &Operation{OperationType: ShortPipe},
-		Lhs:       createTraversalTree(path[0:1]),
-		Rhs:       createTraversalTree(path[1:])}
 }

pkg/yqlib/operators_test.go

@@ -27,10 +27,9 @@ type expressionScenario struct {
 }
 
 func testScenario(t *testing.T, s *expressionScenario) {
-	var results *list.List
 	var err error
 
-	node, err := treeCreator.ParsePath(s.expression)
+	node, err := NewExpressionParser().ParseExpression(s.expression)
 	if err != nil {
 		t.Error(fmt.Errorf("Error parsing expression %v of %v: %v", s.expression, s.description, err))
 		return
@@ -55,7 +54,7 @@ func testScenario(t *testing.T, s *expressionScenario) {
 		candidateNode := &CandidateNode{
 			Document:  0,
 			Filename:  "",
-			Node:      &yaml.Node{Tag: "!!null"},
+			Node:      &yaml.Node{Tag: "!!null", Kind: yaml.ScalarNode},
 			FileIndex: 0,
 		}
 		inputs.PushBack(candidateNode)
@@ -66,13 +65,13 @@ func testScenario(t *testing.T, s *expressionScenario) {
 		os.Setenv("myenv", s.environmentVariable)
 	}
 
-	results, err = treeNavigator.GetMatchingNodes(inputs, node)
+	context, err := NewDataTreeNavigator().GetMatchingNodes(Context{MatchingNodes: inputs}, node)
 
 	if err != nil {
 		t.Error(fmt.Errorf("%v: %v", err, s.expression))
 		return
 	}
-	test.AssertResultComplexWithContext(t, s.expected, resultsToString(results), fmt.Sprintf("exp: %v\ndoc: %v", s.expression, s.document))
+	test.AssertResultComplexWithContext(t, s.expected, resultsToString(context.MatchingNodes), fmt.Sprintf("exp: %v\ndoc: %v", s.expression, s.document))
 }
 
 func resultsToString(results *list.List) []string {
@@ -110,7 +109,7 @@ func formatYaml(yaml string, filename string) string {
 	var output bytes.Buffer
 	printer := NewPrinter(bufio.NewWriter(&output), false, true, false, 2, true)
 
-	node, err := treeCreator.ParsePath(".. style= \"\"")
+	node, err := NewExpressionParser().ParseExpression(".. style= \"\"")
 	if err != nil {
 		panic(err)
 	}
@@ -219,7 +218,7 @@ func documentOutput(t *testing.T, w *bufio.Writer, s expressionScenario, formatt
 	var err error
 	printer := NewPrinter(bufio.NewWriter(&output), false, true, false, 2, true)
 
-	node, err := treeCreator.ParsePath(s.expression)
+	node, err := NewExpressionParser().ParseExpression(s.expression)
 	if err != nil {
 		t.Error(fmt.Errorf("Error parsing expression %v of %v: %v", s.expression, s.description, err))
 		return
@@ -245,19 +244,19 @@ func documentOutput(t *testing.T, w *bufio.Writer, s expressionScenario, formatt
 		candidateNode := &CandidateNode{
 			Document:  0,
 			Filename:  "",
-			Node:      &yaml.Node{Tag: "!!null"},
+			Node:      &yaml.Node{Tag: "!!null", Kind: yaml.ScalarNode},
 			FileIndex: 0,
 		}
 		inputs.PushBack(candidateNode)
 
 	}
 
-	results, err := treeNavigator.GetMatchingNodes(inputs, node)
+	context, err := NewDataTreeNavigator().GetMatchingNodes(Context{MatchingNodes: inputs}, node)
 	if err != nil {
 		t.Error(err, s.expression)
 	}
 
-	err = printer.PrintResults(results)
+	err = printer.PrintResults(context.MatchingNodes)
 	if err != nil {
 		t.Error(err, s.expression)
 	}

pkg/yqlib/path_postfix.go

@@ -1,92 +0,0 @@
-package yqlib
-
-import (
-	"errors"
-
-	logging "gopkg.in/op/go-logging.v1"
-)
-
-type PathPostFixer interface {
-	ConvertToPostfix([]*Token) ([]*Operation, error)
-}
-
-type pathPostFixer struct {
-}
-
-func NewPathPostFixer() PathPostFixer {
-	return &pathPostFixer{}
-}
-
-func popOpToResult(opStack []*Token, result []*Operation) ([]*Token, []*Operation) {
-	var newOp *Token
-	opStack, newOp = opStack[0:len(opStack)-1], opStack[len(opStack)-1]
-	return opStack, append(result, newOp.Operation)
-}
-
-func (p *pathPostFixer) ConvertToPostfix(infixTokens []*Token) ([]*Operation, error) {
-	var result []*Operation
-	// surround the whole thing with quotes
-	var opStack = []*Token{&Token{TokenType: OpenBracket}}
-	var tokens = append(infixTokens, &Token{TokenType: CloseBracket})
-
-	for _, token := range tokens {
-		log.Debugf("postfix processing token %v, %v", token.toString(), token.Operation)
-		switch token.TokenType {
-		case OpenBracket, OpenCollect, OpenCollectObject:
-			opStack = append(opStack, token)
-		case CloseCollect, CloseCollectObject:
-			var opener TokenType = OpenCollect
-			var collectOperator *OperationType = Collect
-			if token.TokenType == CloseCollectObject {
-				opener = OpenCollectObject
-				collectOperator = CollectObject
-			}
-			itemsInMiddle := false
-			for len(opStack) > 0 && opStack[len(opStack)-1].TokenType != opener {
-				opStack, result = popOpToResult(opStack, result)
-				itemsInMiddle = true
-			}
-			if !itemsInMiddle {
-				// must be an empty collection, add the empty object as a LHS parameter
-				result = append(result, &Operation{OperationType: Empty})
-			}
-			if len(opStack) == 0 {
-				return nil, errors.New("Bad path expression, got close collect brackets without matching opening bracket")
-			}
-			// now we should have [] as the last element on the opStack, get rid of it
-			opStack = opStack[0 : len(opStack)-1]
-			//and append a collect to the opStack
-			opStack = append(opStack, &Token{TokenType: OperationToken, Operation: &Operation{OperationType: ShortPipe}})
-			opStack = append(opStack, &Token{TokenType: OperationToken, Operation: &Operation{OperationType: collectOperator}})
-		case CloseBracket:
-			for len(opStack) > 0 && opStack[len(opStack)-1].TokenType != OpenBracket {
-				opStack, result = popOpToResult(opStack, result)
-			}
-			if len(opStack) == 0 {
-				return nil, errors.New("Bad path expression, got close brackets without matching opening bracket")
-			}
-			// now we should have ( as the last element on the opStack, get rid of it
-			opStack = opStack[0 : len(opStack)-1]
-
-		default:
-			var currentPrecedence = token.Operation.OperationType.Precedence
-			// pop off higher precedent operators onto the result
-			for len(opStack) > 0 &&
-				opStack[len(opStack)-1].TokenType == OperationToken &&
-				opStack[len(opStack)-1].Operation.OperationType.Precedence >= currentPrecedence {
-				opStack, result = popOpToResult(opStack, result)
-			}
-			// add this operator to the opStack
-			opStack = append(opStack, token)
-		}
-	}
-
-	if log.IsEnabledFor(logging.DEBUG) {
-		log.Debugf("PostFix Result:")
-		for _, token := range result {
-			log.Debugf("> %v", token.toString())
-		}
-	}
-
-	return result, nil
-}

pkg/yqlib/path_tokeniser.go

@@ -1,407 +0,0 @@
-package yqlib
-
-import (
-	"fmt"
-	"strconv"
-
-	lex "github.com/timtadh/lexmachine"
-	"github.com/timtadh/lexmachine/machines"
-)
-
-func skip(*lex.Scanner, *machines.Match) (interface{}, error) {
-	return nil, nil
-}
-
-type TokenType uint32
-
-const (
-	OperationToken = 1 << iota
-	OpenBracket
-	CloseBracket
-	OpenCollect
-	CloseCollect
-	OpenCollectObject
-	CloseCollectObject
-	TraverseArrayCollect
-)
-
-type Token struct {
-	TokenType            TokenType
-	Operation            *Operation
-	AssignOperation      *Operation // e.g. tag (GetTag) op becomes AssignTag if '=' follows it
-	CheckForPostTraverse bool       // e.g. [1]cat should really be [1].cat
-
-}
-
-func (t *Token) toString() string {
-	if t.TokenType == OperationToken {
-		log.Debug("toString, its an op")
-		return t.Operation.toString()
-	} else if t.TokenType == OpenBracket {
-		return "("
-	} else if t.TokenType == CloseBracket {
-		return ")"
-	} else if t.TokenType == OpenCollect {
-		return "["
-	} else if t.TokenType == CloseCollect {
-		return "]"
-	} else if t.TokenType == OpenCollectObject {
-		return "{"
-	} else if t.TokenType == CloseCollectObject {
-		return "}"
-	} else if t.TokenType == TraverseArrayCollect {
-		return ".["
-
-	} else {
-		return "NFI"
-	}
-}
-
-func pathToken(wrapped bool) lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		value := string(m.Bytes)
-		value = value[1:]
-		if wrapped {
-			value = unwrap(value)
-		}
-		log.Debug("PathToken %v", value)
-		op := &Operation{OperationType: TraversePath, Value: value, StringValue: value}
-		return &Token{TokenType: OperationToken, Operation: op, CheckForPostTraverse: true}, nil
-	}
-}
-
-func documentToken() lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		var numberString = string(m.Bytes)
-		numberString = numberString[1:]
-		var number, errParsingInt = strconv.ParseInt(numberString, 10, 64) // nolint
-		if errParsingInt != nil {
-			return nil, errParsingInt
-		}
-		log.Debug("documentToken %v", string(m.Bytes))
-		op := &Operation{OperationType: DocumentFilter, Value: number, StringValue: numberString}
-		return &Token{TokenType: OperationToken, Operation: op, CheckForPostTraverse: true}, nil
-	}
-}
-
-func opToken(op *OperationType) lex.Action {
-	return opTokenWithPrefs(op, nil, nil)
-}
-
-func opAssignableToken(opType *OperationType, assignOpType *OperationType) lex.Action {
-	return opTokenWithPrefs(opType, assignOpType, nil)
-}
-
-func assignOpToken(updateAssign bool) lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		log.Debug("assignOpToken %v", string(m.Bytes))
-		value := string(m.Bytes)
-		op := &Operation{OperationType: Assign, Value: Assign.Type, StringValue: value, UpdateAssign: updateAssign}
-		return &Token{TokenType: OperationToken, Operation: op}, nil
-	}
-}
-
-func opTokenWithPrefs(op *OperationType, assignOpType *OperationType, preferences interface{}) lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		log.Debug("opTokenWithPrefs %v", string(m.Bytes))
-		value := string(m.Bytes)
-		op := &Operation{OperationType: op, Value: op.Type, StringValue: value, Preferences: preferences}
-		var assign *Operation
-		if assignOpType != nil {
-			assign = &Operation{OperationType: assignOpType, Value: assignOpType.Type, StringValue: value, Preferences: preferences}
-		}
-		return &Token{TokenType: OperationToken, Operation: op, AssignOperation: assign}, nil
-	}
-}
-
-func assignAllCommentsOp(updateAssign bool) lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		log.Debug("assignAllCommentsOp %v", string(m.Bytes))
-		value := string(m.Bytes)
-		op := &Operation{
-			OperationType: AssignComment,
-			Value:         AssignComment.Type,
-			StringValue:   value,
-			UpdateAssign:  updateAssign,
-			Preferences:   &CommentOpPreferences{LineComment: true, HeadComment: true, FootComment: true},
-		}
-		return &Token{TokenType: OperationToken, Operation: op}, nil
-	}
-}
-
-func literalToken(pType TokenType, checkForPost bool) lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		return &Token{TokenType: pType, CheckForPostTraverse: checkForPost}, nil
-	}
-}
-
-func unwrap(value string) string {
-	return value[1 : len(value)-1]
-}
-
-func numberValue() lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		var numberString = string(m.Bytes)
-		var number, errParsingInt = strconv.ParseInt(numberString, 10, 64) // nolint
-		if errParsingInt != nil {
-			return nil, errParsingInt
-		}
-
-		return &Token{TokenType: OperationToken, Operation: CreateValueOperation(number, numberString)}, nil
-	}
-}
-
-func floatValue() lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		var numberString = string(m.Bytes)
-		var number, errParsingInt = strconv.ParseFloat(numberString, 64) // nolint
-		if errParsingInt != nil {
-			return nil, errParsingInt
-		}
-		return &Token{TokenType: OperationToken, Operation: CreateValueOperation(number, numberString)}, nil
-	}
-}
-
-func booleanValue(val bool) lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		return &Token{TokenType: OperationToken, Operation: CreateValueOperation(val, string(m.Bytes))}, nil
-	}
-}
-
-func stringValue(wrapped bool) lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		value := string(m.Bytes)
-		if wrapped {
-			value = unwrap(value)
-		}
-		return &Token{TokenType: OperationToken, Operation: CreateValueOperation(value, value)}, nil
-	}
-}
-
-func envOp(strenv bool) lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		value := string(m.Bytes)
-		preferences := &EnvOpPreferences{}
-
-		if strenv {
-			// strenv( )
-			value = value[7 : len(value)-1]
-			preferences.StringValue = true
-		} else {
-			//env( )
-			value = value[4 : len(value)-1]
-		}
-
-		envOperation := CreateValueOperation(value, value)
-		envOperation.OperationType = EnvOp
-		envOperation.Preferences = preferences
-
-		return &Token{TokenType: OperationToken, Operation: envOperation}, nil
-	}
-}
-
-func nullValue() lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		return &Token{TokenType: OperationToken, Operation: CreateValueOperation(nil, string(m.Bytes))}, nil
-	}
-}
-
-func selfToken() lex.Action {
-	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
-		op := &Operation{OperationType: SelfReference}
-		return &Token{TokenType: OperationToken, Operation: op}, nil
-	}
-}
-
-func initLexer() (*lex.Lexer, error) {
-	lexer := lex.NewLexer()
-	lexer.Add([]byte(`\(`), literalToken(OpenBracket, false))
-	lexer.Add([]byte(`\)`), literalToken(CloseBracket, true))
-
-	lexer.Add([]byte(`\.\[`), literalToken(TraverseArrayCollect, false))
-	lexer.Add([]byte(`\.\.`), opTokenWithPrefs(RecursiveDescent, nil, &RecursiveDescentPreferences{RecurseArray: true,
-		TraversePreferences: &TraversePreferences{FollowAlias: false, IncludeMapKeys: false}}))
-
-	lexer.Add([]byte(`\.\.\.`), opTokenWithPrefs(RecursiveDescent, nil, &RecursiveDescentPreferences{RecurseArray: true,
-		TraversePreferences: &TraversePreferences{FollowAlias: false, IncludeMapKeys: true}}))
-
-	lexer.Add([]byte(`,`), opToken(Union))
-	lexer.Add([]byte(`:\s*`), opToken(CreateMap))
-	lexer.Add([]byte(`length`), opToken(Length))
-	lexer.Add([]byte(`sortKeys`), opToken(SortKeys))
-	lexer.Add([]byte(`select`), opToken(Select))
-	lexer.Add([]byte(`has`), opToken(Has))
-	lexer.Add([]byte(`explode`), opToken(Explode))
-	lexer.Add([]byte(`or`), opToken(Or))
-	lexer.Add([]byte(`and`), opToken(And))
-	lexer.Add([]byte(`not`), opToken(Not))
-	lexer.Add([]byte(`\/\/`), opToken(Alternative))
-
-	lexer.Add([]byte(`documentIndex`), opToken(GetDocumentIndex))
-	lexer.Add([]byte(`di`), opToken(GetDocumentIndex))
-
-	lexer.Add([]byte(`style`), opAssignableToken(GetStyle, AssignStyle))
-
-	lexer.Add([]byte(`tag`), opAssignableToken(GetTag, AssignTag))
-	lexer.Add([]byte(`anchor`), opAssignableToken(GetAnchor, AssignAnchor))
-	lexer.Add([]byte(`alias`), opAssignableToken(GetAlias, AssignAlias))
-	lexer.Add([]byte(`filename`), opToken(GetFilename))
-	lexer.Add([]byte(`fileIndex`), opToken(GetFileIndex))
-	lexer.Add([]byte(`fi`), opToken(GetFileIndex))
-	lexer.Add([]byte(`path`), opToken(GetPath))
-
-	lexer.Add([]byte(`lineComment`), opTokenWithPrefs(GetComment, AssignComment, &CommentOpPreferences{LineComment: true}))
-
-	lexer.Add([]byte(`headComment`), opTokenWithPrefs(GetComment, AssignComment, &CommentOpPreferences{HeadComment: true}))
-
-	lexer.Add([]byte(`footComment`), opTokenWithPrefs(GetComment, AssignComment, &CommentOpPreferences{FootComment: true}))
-
-	lexer.Add([]byte(`comments\s*=`), assignAllCommentsOp(false))
-	lexer.Add([]byte(`comments\s*\|=`), assignAllCommentsOp(true))
-
-	lexer.Add([]byte(`collect`), opToken(Collect))
-
-	lexer.Add([]byte(`\s*==\s*`), opToken(Equals))
-	lexer.Add([]byte(`\s*=\s*`), assignOpToken(false))
-
-	lexer.Add([]byte(`del`), opToken(DeleteChild))
-
-	lexer.Add([]byte(`\s*\|=\s*`), assignOpToken(true))
-
-	lexer.Add([]byte("( |\t|\n|\r)+"), skip)
-
-	lexer.Add([]byte(`d[0-9]+`), documentToken())
-	lexer.Add([]byte(`\."[^ "]+"`), pathToken(true))
-	lexer.Add([]byte(`\.[^ \}\{\:\[\],\|\.\[\(\)=]+`), pathToken(false))
-	lexer.Add([]byte(`\.`), selfToken())
-
-	lexer.Add([]byte(`\|`), opToken(Pipe))
-
-	lexer.Add([]byte(`-?\d+(\.\d+)`), floatValue())
-	lexer.Add([]byte(`-?[1-9](\.\d+)?[Ee][-+]?\d+`), floatValue())
-	lexer.Add([]byte(`-?\d+`), numberValue())
-
-	lexer.Add([]byte(`[Tt][Rr][Uu][Ee]`), booleanValue(true))
-	lexer.Add([]byte(`[Ff][Aa][Ll][Ss][Ee]`), booleanValue(false))
-
-	lexer.Add([]byte(`[Nn][Uu][Ll][Ll]`), nullValue())
-	lexer.Add([]byte(`~`), nullValue())
-
-	lexer.Add([]byte(`"[^"]*"`), stringValue(true))
-	lexer.Add([]byte(`strenv\([^\)]+\)`), envOp(true))
-	lexer.Add([]byte(`env\([^\)]+\)`), envOp(false))
-
-	lexer.Add([]byte(`\[`), literalToken(OpenCollect, false))
-	lexer.Add([]byte(`\]`), literalToken(CloseCollect, true))
-	lexer.Add([]byte(`\{`), literalToken(OpenCollectObject, false))
-	lexer.Add([]byte(`\}`), literalToken(CloseCollectObject, true))
-	lexer.Add([]byte(`\*`), opTokenWithPrefs(Multiply, nil, &MultiplyPreferences{AppendArrays: false}))
-	lexer.Add([]byte(`\*\+`), opTokenWithPrefs(Multiply, nil, &MultiplyPreferences{AppendArrays: true}))
-	lexer.Add([]byte(`\+`), opToken(Add))
-	lexer.Add([]byte(`\+=`), opToken(AddAssign))
-
-	err := lexer.Compile()
-	if err != nil {
-		return nil, err
-	}
-	return lexer, nil
-}
-
-type PathTokeniser interface {
-	Tokenise(path string) ([]*Token, error)
-}
-
-type pathTokeniser struct {
-	lexer *lex.Lexer
-}
-
-func NewPathTokeniser() PathTokeniser {
-	var lexer, err = initLexer()
-	if err != nil {
-		panic(err)
-	}
-	return &pathTokeniser{lexer}
-}
-
-func (p *pathTokeniser) Tokenise(path string) ([]*Token, error) {
-	scanner, err := p.lexer.Scanner([]byte(path))
-
-	if err != nil {
-		return nil, fmt.Errorf("Parsing expression: %v", err)
-	}
-	var tokens []*Token
-	for tok, err, eof := scanner.Next(); !eof; tok, err, eof = scanner.Next() {
-
-		if tok != nil {
-			token := tok.(*Token)
-			log.Debugf("Tokenising %v", token.toString())
-			tokens = append(tokens, token)
-		}
-		if err != nil {
-			return nil, fmt.Errorf("Parsing expression: %v", err)
-		}
-	}
-	var postProcessedTokens = make([]*Token, 0)
-
-	skipNextToken := false
-
-	for index := range tokens {
-		if skipNextToken {
-			skipNextToken = false
-		} else {
-			postProcessedTokens, skipNextToken = p.handleToken(tokens, index, postProcessedTokens)
-		}
-	}
-
-	return postProcessedTokens, nil
-}
-
-func (p *pathTokeniser) handleToken(tokens []*Token, index int, postProcessedTokens []*Token) (tokensAccum []*Token, skipNextToken bool) {
-	skipNextToken = false
-	token := tokens[index]
-
-	if token.TokenType == TraverseArrayCollect {
-		//need to put a traverse array then a collect token
-		// do this by adding traverse then converting token to collect
-
-		op := &Operation{OperationType: TraverseArray, StringValue: "TRAVERSE_ARRAY"}
-		postProcessedTokens = append(postProcessedTokens, &Token{TokenType: OperationToken, Operation: op})
-
-		token = &Token{TokenType: OpenCollect}
-
-	}
-
-	if index != len(tokens)-1 && token.AssignOperation != nil &&
-		tokens[index+1].TokenType == OperationToken &&
-		tokens[index+1].Operation.OperationType == Assign {
-		token.Operation = token.AssignOperation
-		token.Operation.UpdateAssign = tokens[index+1].Operation.UpdateAssign
-		skipNextToken = true
-	}
-
-	postProcessedTokens = append(postProcessedTokens, token)
-
-	if index != len(tokens)-1 && token.CheckForPostTraverse &&
-		tokens[index+1].TokenType == OperationToken &&
-		tokens[index+1].Operation.OperationType == TraversePath {
-		op := &Operation{OperationType: ShortPipe, Value: "PIPE"}
-		postProcessedTokens = append(postProcessedTokens, &Token{TokenType: OperationToken, Operation: op})
-	}
-	if index != len(tokens)-1 && token.CheckForPostTraverse &&
-		tokens[index+1].TokenType == OpenCollect {
-
-		op := &Operation{OperationType: ShortPipe, Value: "PIPE"}
-		postProcessedTokens = append(postProcessedTokens, &Token{TokenType: OperationToken, Operation: op})
-
-		op = &Operation{OperationType: TraverseArray}
-		postProcessedTokens = append(postProcessedTokens, &Token{TokenType: OperationToken, Operation: op})
-	}
-	if index != len(tokens)-1 && token.CheckForPostTraverse &&
-		tokens[index+1].TokenType == TraverseArrayCollect {
-
-		op := &Operation{OperationType: ShortPipe, Value: "PIPE"}
-		postProcessedTokens = append(postProcessedTokens, &Token{TokenType: OperationToken, Operation: op})
-
-	}
-	return postProcessedTokens, skipNextToken
-}