Bump version

Fixes #716 #715

.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: actions/checkout@v2
-        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 }}
       
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v1

README.md

@@ -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/evaluate_all_command.go

@@ -42,14 +42,21 @@ func evaluateAll(cmd *cobra.Command, args []string) error {
 		colorsEnabled = true
 	}
 
-	if writeInplace && len(args) < 2 {
+	firstFileIndex := -1
+	if !nullInput && len(args) == 1 {
+		firstFileIndex = 0
+	} else if len(args) > 1 {
+		firstFileIndex = 1
+	}
+
+	if writeInplace && (firstFileIndex == -1) {
 		return fmt.Errorf("Write inplace flag only applicable when giving an expression and at least one file")
 	}
 
 	if writeInplace {
 		// only use colors if its forced
 		colorsEnabled = forceColor
-		writeInPlaceHandler := yqlib.NewWriteInPlaceHandler(args[1])
+		writeInPlaceHandler := yqlib.NewWriteInPlaceHandler(args[firstFileIndex])
 		out, err = writeInPlaceHandler.CreateTempFile()
 		if err != nil {
 			return err

cmd/evalute_sequence_command.go

@@ -62,14 +62,21 @@ func evaluateSequence(cmd *cobra.Command, args []string) error {
 		colorsEnabled = true
 	}
 
-	if writeInplace && len(args) < 2 {
+	firstFileIndex := -1
+	if !nullInput && len(args) == 1 {
+		firstFileIndex = 0
+	} else if len(args) > 1 {
+		firstFileIndex = 1
+	}
+
+	if writeInplace && (firstFileIndex == -1) {
 		return fmt.Errorf("Write inplace flag only applicable when giving an expression and at least one file")
 	}
 
 	if writeInplace {
 		// only use colors if its forced
 		colorsEnabled = forceColor
-		writeInPlaceHandler := yqlib.NewWriteInPlaceHandler(args[1])
+		writeInPlaceHandler := yqlib.NewWriteInPlaceHandler(args[firstFileIndex])
 		out, err = writeInPlaceHandler.CreateTempFile()
 		if err != nil {
 			return err
@@ -102,7 +109,7 @@ func evaluateSequence(cmd *cobra.Command, args []string) error {
 			err = streamEvaluator.EvaluateFiles(processExpression(""), []string{args[0]}, printer)
 		}
 	default:
-		err = streamEvaluator.EvaluateFiles(args[0], args[1:], printer)
+		err = streamEvaluator.EvaluateFiles(processExpression(args[0]), args[1:], printer)
 	}
 	completedSuccessfully = err == nil
 

cmd/version.go

@@ -11,7 +11,7 @@ var (
 	GitDescribe string
 
 	// Version is main version number that is being run at the moment.
-	Version = "4.4.0"
+	Version = "4.6.1"
 
 	// 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
+a:
-b: [1, 2]
+  key1: "value1"
-c:
+  key2: 2.6
-  test: 1
+  ab:
+    key1: 6
+    key2: "h"

github-action/Dockerfile

@@ -1,4 +1,4 @@
-FROM mikefarah/yq:4.4.0
+FROM mikefarah/yq:4.6.1
 
 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/goccy/go-yaml v1.8.8
-	github.com/jinzhu/copier v0.1.0
+	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 v1.4.0 h1:wZtfeEONCbx6in1CZyE6bELEt/vFayMvsxqI5SgsR+A=
-github.com/elliotchance/orderedmap v1.3.0/go.mod h1:8hdSl6jmveQw8ScByd3AaNHNk51RhbTazdqtTty+NFw=
+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 v1.8.8 h1:MGfRB1GeSn/hWXYWS2Pt67iC2GJNnebdIro01ddyucA=
-github.com/goccy/go-yaml v1.8.4/go.mod h1:U/jl18uSupI5rdI2jmuCswEA2htH9eXfferR3KfscvA=
+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 v0.2.3 h1:Oe09ju+9qft7TffZ7l/04AB2f8u1+V4ZMxmp/nnqeOs=
-github.com/jinzhu/copier v0.1.0/go.mod h1:24xnZezI2Yqac9J61UC6/dG/k76ttpq0DdJI3QmUvro=
+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 v0.0.0-20210124154548-22da62e12c0c h1:VwygUrnw9jn88c4u8GD3rZQbqrP/tgas88tPUbBxQrk=
-golang.org/x/sys v0.0.0-20210105210732-16f7687f5001/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+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=
@@ -324,6 +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

@@ -39,7 +39,11 @@ func (e *allAtOnceEvaluator) EvaluateCandidateNodes(expression string, inputCand
 	if err != nil {
 		return nil, err
 	}
-	return e.treeNavigator.GetMatchingNodes(inputCandidates, node)
+	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 {

pkg/yqlib/candidate_node.go

@@ -2,8 +2,6 @@ package yqlib
 
 import (
 	"fmt"
-	"strconv"
-	"strings"
 
 	"github.com/jinzhu/copier"
 	yaml "gopkg.in/yaml.v3"
@@ -18,10 +16,15 @@ type CandidateNode struct {
 	// 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) CreateChild(path interface{}, node *yaml.Node) *CandidateNode {
@@ -63,11 +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
-	n.Node.Anchor = other.Node.Anchor
 }
 
 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
@@ -76,6 +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
@@ -86,46 +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/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 expressionNode,
+	// given the context and a expressionNode,
-	// this will process the list against the given expressionNode and return
+	// this will process the against the given expressionNode and return
-	// a new list of matching candidates
+	// a new context of matching candidates
-	GetMatchingNodes(matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error)
+	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, expressionNode *ExpressionNode) (*list.List, error) {
+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", 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 := expressionNode.Operation.OperationType.Handler
 	if handler != nil {
-		return handler(d, matchingNodes, expressionNode)
+		return handler(d, context, expressionNode)
 	}
-	return nil, fmt.Errorf("Unknown operator %v", expressionNode.Operation.OperationType)
+	return Context{}, fmt.Errorf("Unknown operator %v", expressionNode.Operation.OperationType)
 
 }

pkg/yqlib/doc/Add.md

@@ -209,3 +209,15 @@ will output
 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/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/File Operators.md

@@ -35,6 +35,26 @@ will output
 0
 ```
 
+## Get file indices of multiple documents
+Given a sample.yml file of:
+```yaml
+a: cat
+```
+And another sample another.yml file of:
+```yaml
+a: cat
+```
+then
+```bash
+yq eval-all 'fileIndex' sample.yml another.yml
+```
+will output
+```yaml
+0
+---
+1
+```
+
 ## Get file index alias
 Given a sample.yml file of:
 ```yaml

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

@@ -1,19 +1,34 @@
-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 numbers, arrays and objects are supported.
 
-To concatenate arrays when merging objects, use the *+ form (see examples below). This will recursively merge objects, appending arrays when it encounters them.
+## Objects and arrays - merging
+Objects are merged deeply matching on matching keys. By default, array values override and are not deeply merged.
 
-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.
+### Merge Flags
+You can control how objects are merged by using one or more of the following flags. Multiple flags can be used together, e.g. `.a *+? .b`.  See examples below
 
-## Merging files
+- `+` to append arrays
+- `?` to only merge existing fields
+- `d` to deeply merge arrays
+
+### Merging files
 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
 ```
 
+## Multiply integers
+Running
+```bash
+yq eval --null-input '3 * 4'
+```
+will output
+```yaml
+12
+```
+
 ## Merge objects together, returning merged result only
 Given a sample.yml file of:
 ```yaml
@@ -71,7 +86,6 @@ Given a sample.yml file of:
 a: {things: great}
 b:
   also: "me"
-
 ```
 then
 ```bash
@@ -191,6 +205,32 @@ thing:
   - 4
 ```
 
+## Merge, deeply merging arrays
+Merging arrays deeply means arrays are merge like objects, with indexes as their key. In this case, we merge the first item in the array, and do nothing with the second.
+
+Given a sample.yml file of:
+```yaml
+a:
+  - name: fred
+    age: 12
+  - name: bob
+    age: 32
+b:
+  - name: fred
+    age: 34
+```
+then
+```bash
+yq eval '.a *d .b' sample.yml
+```
+will output
+```yaml
+- name: fred
+  age: 34
+- name: bob
+  age: 32
+```
+
 ## Merge to prefix an element
 Given a sample.yml file of:
 ```yaml

pkg/yqlib/doc/Reduce.md

@@ -0,0 +1,76 @@
+Reduce is a powerful way to process a collection of data into a new form.
+
+```
+<exp> as $<name> ireduce (<init>; <block>)
+```
+
+e.g.
+
+```
+.[] as $item ireduce (0; . + $item)
+```
+
+On the LHS we are configuring the collection of items that will be reduced `<exp>` as well as what each element will be called `$<name>`. Note that the array has been splatted into its individual elements.
+
+On the RHS there is `<init>`, the starting value of the accumulator and `<block>`, the expression that will update the accumulator for each element in the collection. Note that within the block expression, `.` will evaluate to the current value of the accumulator. 
+
+## yq vs jq syntax
+Reduce syntax in `yq` is a little different from `jq` - as `yq` (currently) isn't as sophisticated as `jq` and its only supports infix notation (e.g. a + b, where the operator is in the middle of the two parameters) - where as `jq` uses a mix of infix notation with _prefix_ notation (e.g. `reduce a b` is like writing `+ a b`).
+
+To that end, the reduce operator is called `ireduce` for backwards compatability if a `jq` like prefix version of `reduce` is ever added.
+
+
+## Sum numbers
+Given a sample.yml file of:
+```yaml
+- 10
+- 2
+- 5
+- 3
+```
+then
+```bash
+yq eval '.[] as $item ireduce (0; . + $item)' sample.yml
+```
+will output
+```yaml
+20
+```
+
+## Merge all yaml files together
+Given a sample.yml file of:
+```yaml
+a: cat
+```
+And another sample another.yml file of:
+```yaml
+b: dog
+```
+then
+```bash
+yq eval-all '. as $item ireduce ({}; . * $item )' sample.yml another.yml
+```
+will output
+```yaml
+a: cat
+b: dog
+```
+
+## Convert an array to an object
+Given a sample.yml file of:
+```yaml
+- name: Cathy
+  has: apples
+- name: Bob
+  has: bananas
+```
+then
+```bash
+yq eval '.[] as $item ireduce ({}; .[$item | .name] = ($item | .has) )' sample.yml
+```
+will output
+```yaml
+Cathy: apples
+Bob: bananas
+```
+

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/headers/Multiply.md

@@ -1,13 +1,18 @@
-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 numbers, arrays and objects are supported.
 
-To concatenate arrays when merging objects, use the *+ form (see examples below). This will recursively merge objects, appending arrays when it encounters them.
+## Objects and arrays - merging
+Objects are merged deeply matching on matching keys. By default, array values override and are not deeply merged.
 
-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.
+### Merge Flags
+You can control how objects are merged by using one or more of the following flags. Multiple flags can be used together, e.g. `.a *+? .b`.  See examples below
 
-## Merging files
+- `+` to append arrays
+- `?` to only merge existing fields
+- `d` to deeply merge arrays
+
+### Merging files
 Note the use of `eval-all` to ensure all documents are loaded into memory.
 
 ```bash

pkg/yqlib/doc/headers/Reduce.md

@@ -0,0 +1,21 @@
+Reduce is a powerful way to process a collection of data into a new form.
+
+```
+<exp> as $<name> ireduce (<init>; <block>)
+```
+
+e.g.
+
+```
+.[] as $item ireduce (0; . + $item)
+```
+
+On the LHS we are configuring the collection of items that will be reduced `<exp>` as well as what each element will be called `$<name>`. Note that the array has been splatted into its individual elements.
+
+On the RHS there is `<init>`, the starting value of the accumulator and `<block>`, the expression that will update the accumulator for each element in the collection. Note that within the block expression, `.` will evaluate to the current value of the accumulator. 
+
+## yq vs jq syntax
+Reduce syntax in `yq` is a little different from `jq` - as `yq` (currently) isn't as sophisticated as `jq` and its only supports infix notation (e.g. a + b, where the operator is in the middle of the two parameters) - where as `jq` uses a mix of infix notation with _prefix_ notation (e.g. `reduce a b` is like writing `+ a b`).
+
+To that end, the reduce operator is called `ireduce` for backwards compatability if a `jq` like prefix version of `reduce` is ever added.
+

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

@@ -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
+func yamlToJson(sampleYaml string, indent int) string {
-apple: great
-banana:
-- {cobra: kai, angus: bob}
-`
-
-var expectedJson = `{
-  "zabbix": "winner",
-  "apple": "great",
-  "banana": [
-    {
-      "cobra": "kai",
-      "angus": "bob"
-    }
-  ]
-}
-`
-
-func TestJsonEncoderPreservesObjectOrder(t *testing.T) {
 	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

@@ -5,9 +5,6 @@ import (
 	"strings"
 )
 
-var myPathTokeniser = newExpressionTokeniser()
-var myPathPostfixer = newExpressionPostFixer()
-
 type ExpressionNode struct {
 	Operation *Operation
 	Lhs       *ExpressionNode
@@ -19,19 +16,21 @@ type ExpressionParser interface {
 }
 
 type expressionParserImpl struct {
+	pathTokeniser expressionTokeniser
+	pathPostFixer expressionPostFixer
 }
 
 func NewExpressionParser() ExpressionParser {
-	return &expressionParserImpl{}
+	return &expressionParserImpl{newExpressionTokeniser(), newExpressionPostFixer()}
 }
 
 func (p *expressionParserImpl) ParseExpression(expression string) (*ExpressionNode, error) {
-	tokens, err := myPathTokeniser.Tokenise(expression)
+	tokens, err := p.pathTokeniser.Tokenise(expression)
 	if err != nil {
 		return nil, err
 	}
 	var Operations []*Operation
-	Operations, err = myPathPostfixer.ConvertToPostfix(tokens)
+	Operations, err = p.pathPostFixer.ConvertToPostfix(tokens)
 	if err != nil {
 		return nil, err
 	}
@@ -70,7 +69,7 @@ func (p *expressionParserImpl) createExpressionTree(postFixPath []*Operation) (*
 		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

@@ -38,5 +38,5 @@ func TestPathTreeOneArgForOneArgOp(t *testing.T) {
 
 func TestPathTreeExtraArgs(t *testing.T) {
 	_, err := NewExpressionParser().ParseExpression("sortKeys(.) explode(.)")
-	test.AssertResultComplex(t, "expected end of expression but found 'explode', please check expression syntax", err.Error())
+	test.AssertResultComplex(t, "Bad expression, please check expression syntax", err.Error())
 }

pkg/yqlib/expression_postfix.go

@@ -20,20 +20,22 @@ func newExpressionPostFixer() expressionPostFixer {
 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 quotes
+	// surround the whole thing with brackets
-	var opStack = []*token{&token{TokenType: openBracket}}
+	var opStack = []*token{{TokenType: openBracket}}
 	var tokens = append(infixTokens, &token{TokenType: closeBracket})
 
 	for _, currentToken := range tokens {
-		log.Debugf("postfix processing currentToken %v, %v", currentToken.toString(), currentToken.Operation)
+		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
@@ -41,23 +43,23 @@ func (p *expressionPostFixerImpl) ConvertToPostfix(infixTokens []*token) ([]*Ope
 				opener = openCollectObject
 				collectOperator = collectObjectOpType
 			}
-			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: emptyOpType})
 			}
 			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
+			// 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
-			opStack = append(opStack, &token{TokenType: operationToken, Operation: &Operation{OperationType: shortPipeOpType}})
+			result = append(result, &Operation{OperationType: collectOperator})
-			opStack = append(opStack, &token{TokenType: operationToken, Operation: &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)
@@ -73,11 +75,12 @@ func (p *expressionPostFixerImpl) ConvertToPostfix(infixTokens []*token) ([]*Ope
 			// 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[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))
 		}
 	}
 

pkg/yqlib/expression_processing_test.go

@@ -12,40 +12,70 @@ var pathTests = []struct {
 	expectedTokens  []interface{}
 	expectedPostFix []interface{}
 }{
+	{
+		`.a as $item ireduce (0; . + $item)`, // note - add code to shuffle reduce to this position for postfix
+		append(make([]interface{}, 0), "a", "ASSIGN_VARIABLE", "GET_VARIABLE", "REDUCE", "(", "0 (int64)", "BLOCK", "SELF", "ADD", "GET_VARIABLE", ")"),
+		append(make([]interface{}, 0), "a", "GET_VARIABLE", "ASSIGN_VARIABLE", "0 (int64)", "SELF", "GET_VARIABLE", "ADD", "BLOCK", "REDUCE"),
+	},
+	{
+		`.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), "SELF", "TRAVERSE_ARRAY", "[", "EMPTY", "]"),
-		append(make([]interface{}, 0), "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+		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", "TRAVERSE_ARRAY", "[", "EMPTY", "]"),
-		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE"),
+		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", "TRAVERSE_ARRAY", "[", "EMPTY", "]"),
-		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE"),
+		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", "TRAVERSE_ARRAY", "[", "0 (int64)", "]"),
-		append(make([]interface{}, 0), "a", "0 (int64)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE"),
+		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", "TRAVERSE_ARRAY", "[", "0 (int64)", "]"),
-		append(make([]interface{}, 0), "a", "0 (int64)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE"),
+		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", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "SHORT_PIPE", "c"),
-		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE", "c", "SHORT_PIPE"),
+		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "c", "SHORT_PIPE"),
 	},
 	{
 		`[3]`,
@@ -69,18 +99,18 @@ var pathTests = []struct {
 	},
 	{
 		`.a | .[].b == "apple"`,
-		append(make([]interface{}, 0), "a", "PIPE", "TRAVERSE_ARRAY", "[", "]", "SHORT_PIPE", "b", "EQUALS", "apple (string)"),
+		append(make([]interface{}, 0), "a", "PIPE", "SELF", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "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", "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", "PIPE", "SELF", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "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", "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), "SELF", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "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", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SELF", "*at (string)", "EQUALS", "SELECT", "PIPE"),
 	},
 	{
 		`[true]`,
@@ -113,9 +143,9 @@ var pathTests = []struct {
 		append(make([]interface{}, 0), "a", "mike (string)", "CREATE_MAP", "COLLECT_OBJECT", "SHORT_PIPE"),
 	},
 	{
-		`{.a: .c, .b.[]: .f.g.[]}`,
+		`{.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", "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", "SHORT_PIPE", "f", "g", "SHORT_PIPE", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE", "CREATE_MAP", "UNION", "COLLECT_OBJECT", "SHORT_PIPE"),
+		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)`,
@@ -167,11 +197,6 @@ 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 = newExpressionTokeniser()
@@ -185,7 +210,7 @@ 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

@@ -34,9 +34,11 @@ type token struct {
 
 }
 
-func (t *token) toString() string {
+func (t *token) toString(detail bool) string {
 	if t.TokenType == operationToken {
-		log.Debug("toString, its an op")
+		if detail {
+			return fmt.Sprintf("%v (%v)", t.Operation.toString(), t.Operation.OperationType.Precedence)
+		}
 		return t.Operation.toString()
 	} else if t.TokenType == openBracket {
 		return "("
@@ -98,6 +100,9 @@ func multiplyWithPrefs() lex.Action {
 		if strings.Contains(options, "?") {
 			prefs.TraversePrefs = traversePreferences{DontAutoCreate: true}
 		}
+		if strings.Contains(options, "d") {
+			prefs.DeepMergeArrays = true
+		}
 		op := &Operation{OperationType: multiplyOpType, Value: multiplyOpType.Type, StringValue: options, Preferences: prefs}
 		return &token{TokenType: operationToken, Operation: op}, nil
 	}
@@ -180,6 +185,19 @@ func stringValue(wrapped bool) lex.Action {
 	}
 }
 
+func getVariableOpToken() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		value := string(m.Bytes)
+
+		value = 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)
@@ -237,6 +255,8 @@ func initLexer() (*lex.Lexer, error) {
 	lexer.Add([]byte(`or`), opToken(orOpType))
 	lexer.Add([]byte(`and`), opToken(andOpType))
 	lexer.Add([]byte(`not`), opToken(notOpType))
+	lexer.Add([]byte(`ireduce`), opToken(reduceOpType))
+	lexer.Add([]byte(`;`), opToken(blockOpType))
 	lexer.Add([]byte(`\/\/`), opToken(alternativeOpType))
 
 	lexer.Add([]byte(`documentIndex`), opToken(getDocumentIndexOpType))
@@ -269,6 +289,7 @@ func initLexer() (*lex.Lexer, error) {
 	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))
@@ -301,11 +322,13 @@ func initLexer() (*lex.Lexer, error) {
 	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(`\*[\+|\?d]*`), 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()
+	err := lexer.CompileNFA()
 	if err != nil {
 		return nil, err
 	}
@@ -339,7 +362,7 @@ func (p *expressionTokeniserImpl) Tokenise(expression string) ([]*token, error)
 
 		if tok != nil {
 			currentToken := tok.(*token)
-			log.Debugf("Tokenising %v", currentToken.toString())
+			log.Debugf("Tokenising %v", currentToken.toString(true))
 			tokens = append(tokens, currentToken)
 		}
 		if err != nil {
@@ -369,6 +392,12 @@ func (p *expressionTokeniserImpl) handleToken(tokens []*token, index int, postPr
 		//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})
 
@@ -386,6 +415,14 @@ func (p *expressionTokeniserImpl) handleToken(tokens []*token, index int, postPr
 
 	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 {
@@ -395,18 +432,8 @@ func (p *expressionTokeniserImpl) handleToken(tokens []*token, index int, postPr
 	if index != len(tokens)-1 && currentToken.CheckForPostTraverse &&
 		tokens[index+1].TokenType == openCollect {
 
-		op := &Operation{OperationType: shortPipeOpType, Value: "PIPE"}
+		op := &Operation{OperationType: traverseArrayOpType}
 		postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
-
-		op = &Operation{OperationType: traverseArrayOpType}
-		postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
-	}
-	if index != len(tokens)-1 && currentToken.CheckForPostTraverse &&
-		tokens[index+1].TokenType == traverseArrayCollect {
-
-		op := &Operation{OperationType: shortPipeOpType, Value: "PIPE"}
-		postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
-
 	}
 	return postProcessedTokens, skipNextToken
 }

pkg/yqlib/lib.go

@@ -25,6 +25,9 @@ type operationType struct {
 
 var orOpType = &operationType{Type: "OR", NumArgs: 2, Precedence: 20, Handler: orOperator}
 var andOpType = &operationType{Type: "AND", NumArgs: 2, Precedence: 20, Handler: andOperator}
+var reduceOpType = &operationType{Type: "REDUCE", NumArgs: 2, Precedence: 35, Handler: reduceOperator}
+
+var blockOpType = &operationType{Type: "BLOCK", Precedence: 10, NumArgs: 2, Handler: emptyOperator}
 
 var unionOpType = &operationType{Type: "UNION", NumArgs: 2, Precedence: 10, Handler: unionOperator}
 
@@ -35,6 +38,7 @@ var addAssignOpType = &operationType{Type: "ADD_ASSIGN", NumArgs: 2, Precedence:
 
 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}
@@ -45,6 +49,7 @@ var addOpType = &operationType{Type: "ADD", NumArgs: 2, Precedence: 42, Handler:
 var alternativeOpType = &operationType{Type: "ALTERNATIVE", NumArgs: 2, Precedence: 42, Handler: alternativeOperator}
 
 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 shortPipeOpType = &operationType{Type: "SHORT_PIPE", NumArgs: 2, Precedence: 45, Handler: pipeOperator}
@@ -52,6 +57,7 @@ var shortPipeOpType = &operationType{Type: "SHORT_PIPE", NumArgs: 2, Precedence:
 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}
@@ -70,14 +76,14 @@ var splitStringOpType = &operationType{Type: "SPLIT", NumArgs: 1, Precedence: 50
 var keysOpType = &operationType{Type: "KEYS", NumArgs: 0, Precedence: 50, Handler: keysOperator}
 
 var collectObjectOpType = &operationType{Type: "COLLECT_OBJECT", NumArgs: 0, Precedence: 50, Handler: collectObjectOperator}
-var traversePathOpType = &operationType{Type: "TRAVERSE_PATH", NumArgs: 0, Precedence: 50, Handler: traversePathOperator}
+var traversePathOpType = &operationType{Type: "TRAVERSE_PATH", NumArgs: 0, Precedence: 55, Handler: traversePathOperator}
-var traverseArrayOpType = &operationType{Type: "TRAVERSE_ARRAY", NumArgs: 1, Precedence: 50, Handler: traverseArrayOperator}
+var traverseArrayOpType = &operationType{Type: "TRAVERSE_ARRAY", NumArgs: 2, Precedence: 50, Handler: traverseArrayOperator}
 
-var selfReferenceOpType = &operationType{Type: "SELF", NumArgs: 0, Precedence: 50, Handler: selfOperator}
+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 emptyOpType = &operationType{Type: "EMPTY", Precedence: 50, Handler: emptyOperator}
 
 var recursiveDescentOpType = &operationType{Type: "RECURSIVE_DESCENT", NumArgs: 0, Precedence: 50, Handler: recursiveDescentOperator}
 

pkg/yqlib/operator_add.go

@@ -3,7 +3,6 @@ package yqlib
 import (
 	"fmt"
 
-	"container/list"
 	"strconv"
 
 	yaml "gopkg.in/yaml.v3"
@@ -15,12 +14,12 @@ func createAddOp(lhs *ExpressionNode, rhs *ExpressionNode) *ExpressionNode {
 		Rhs: rhs}
 }
 
-func addAssignOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func addAssignOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	assignmentOp := &Operation{OperationType: assignOpType}
 	assignmentOp.UpdateAssign = false
 
 	assignmentOpNode := &ExpressionNode{Operation: assignmentOp, Lhs: expressionNode.Lhs, Rhs: createAddOp(expressionNode.Lhs, expressionNode.Rhs)}
-	return d.GetMatchingNodes(matchingNodes, assignmentOpNode)
+	return d.GetMatchingNodes(context, assignmentOpNode)
 }
 
 func toNodes(candidate *CandidateNode) []*yaml.Node {
@@ -37,19 +36,24 @@ func toNodes(candidate *CandidateNode) []*yaml.Node {
 
 }
 
-func addOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func addOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("Add operator")
 
-	return crossFunction(d, matchingNodes, expressionNode, add)
+	return crossFunction(d, context, expressionNode, add)
 }
 
-func add(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+func add(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
 	lhs.Node = unwrapDoc(lhs.Node)
 	rhs.Node = unwrapDoc(rhs.Node)
 
-	target := lhs.CreateChild(nil, &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")

pkg/yqlib/operator_add_test.go

@@ -112,6 +112,14 @@ var addOperatorScenarios = []expressionScenario{
 			"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

@@ -1,18 +1,14 @@
 package yqlib
 
-import (
-	"container/list"
-)
-
 // corssFunction no matches
 // can boolean use crossfunction
 
-func alternativeOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func alternativeOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- alternative")
-	return crossFunction(d, matchingNodes, expressionNode, alternativeFunc)
+	return crossFunction(d, context, expressionNode, alternativeFunc)
 }
 
-func alternativeFunc(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+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)

pkg/yqlib/operator_anchors_aliases.go

@@ -6,146 +6,146 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-func assignAliasOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func assignAliasOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
 	log.Debugf("AssignAlias operator!")
 
 	aliasName := ""
 	if !expressionNode.Operation.UpdateAssign {
-		rhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.Rhs)
+		rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
-		if rhs.Front() != nil {
+		if rhs.MatchingNodes.Front() != nil {
-			aliasName = rhs.Front().Value.(*CandidateNode).Node.Value
+			aliasName = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 		}
 	}
 
-	lhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.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 expressionNode.Operation.UpdateAssign {
-			rhs, err := d.GetMatchingNodes(nodeToMap(candidate), expressionNode.Rhs)
+			rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
-			if rhs.Front() != nil {
+			if rhs.MatchingNodes.Front() != nil {
-				aliasName = rhs.Front().Value.(*CandidateNode).Node.Value
+				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, expressionNode *ExpressionNode) (*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"}
 		result := candidate.CreateChild(nil, node)
 		results.PushBack(result)
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }
 
-func assignAnchorOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func assignAnchorOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
 	log.Debugf("AssignAnchor operator!")
 
 	anchorName := ""
 	if !expressionNode.Operation.UpdateAssign {
-		rhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.Rhs)
+		rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
-		if rhs.Front() != nil {
+		if rhs.MatchingNodes.Front() != nil {
-			anchorName = rhs.Front().Value.(*CandidateNode).Node.Value
+			anchorName = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 		}
 	}
 
-	lhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.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 expressionNode.Operation.UpdateAssign {
-			rhs, err := d.GetMatchingNodes(nodeToMap(candidate), expressionNode.Rhs)
+			rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 
-			if rhs.Front() != nil {
+			if rhs.MatchingNodes.Front() != nil {
-				anchorName = rhs.Front().Value.(*CandidateNode).Node.Value
+				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, expressionNode *ExpressionNode) (*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"}
 		result := candidate.CreateChild(nil, node)
 		results.PushBack(result)
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }
 
-func explodeOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*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), expressionNode.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() {
+		for childEl := rhs.MatchingNodes.Front(); childEl != nil; childEl = childEl.Next() {
-			err = explodeNode(childEl.Value.(*CandidateNode).Node)
+			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.MatchingNodes.PushBack(key)
-	newContent.PushBack(value)
+	newContent.MatchingNodes.PushBack(value)
 	return nil
 }

pkg/yqlib/operator_assign.go

@@ -1,30 +1,28 @@
 package yqlib
 
-import "container/list"
+func assignUpdateOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
-
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
-func assignUpdateOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
-	lhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.Lhs)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-	var rhs *list.List
+	var rhs Context
 	if !expressionNode.Operation.UpdateAssign {
-		rhs, err = d.GetMatchingNodes(matchingNodes, expressionNode.Rhs)
+		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 expressionNode.Operation.UpdateAssign {
-			rhs, err = d.GetMatchingNodes(nodeToMap(candidate), expressionNode.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 {
 			rhsCandidate := first.Value.(*CandidateNode)
@@ -33,30 +31,31 @@ func assignUpdateOperator(d *dataTreeNavigator, matchingNodes *list.List, expres
 		}
 	}
 
-	return matchingNodes, nil
+	return context, nil
 }
 
 // does not update content or values
-func assignAttributesOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func assignAttributesOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
-	lhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.Lhs)
+	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), expressionNode.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

@@ -25,8 +25,8 @@ 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) {
+func performBoolOp(op boolOp) func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
-	return func(d *dataTreeNavigator, 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)
 
@@ -44,35 +44,35 @@ func performBoolOp(op boolOp) func(d *dataTreeNavigator, lhs *CandidateNode, rhs
 	}
 }
 
-func orOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func orOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- orOp")
-	return crossFunction(d, matchingNodes, expressionNode, performBoolOp(
+	return crossFunction(d, context, expressionNode, performBoolOp(
 		func(b1 bool, b2 bool) bool {
 			return b1 || b2
 		}))
 }
 
-func andOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func andOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- AndOp")
-	return crossFunction(d, matchingNodes, expressionNode, performBoolOp(
+	return crossFunction(d, context, expressionNode, performBoolOp(
 		func(b1 bool, b2 bool) bool {
 			return b1 && b2
 		}))
 }
 
-func notOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*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

@@ -6,21 +6,21 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-func collectOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*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 collectC *CandidateNode
-	if matchMap.Front() != nil {
+	if context.MatchingNodes.Front() != nil {
-		collectC = matchMap.Front().Value.(*CandidateNode).CreateChild(nil, node)
+		collectC = context.MatchingNodes.Front().Value.(*CandidateNode).CreateChild(nil, node)
 		if len(collectC.Path) > 0 {
 			collectC.Path = collectC.Path[:len(collectC.Path)-1]
 		}
@@ -28,7 +28,7 @@ func collectOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *
 		collectC = &CandidateNode{Node: node}
 	}
 
-	for el := matchMap.Front(); el != nil; el = el.Next() {
+	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))
@@ -36,5 +36,5 @@ func collectOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *
 
 	results.PushBack(collectC)
 
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_collect_object.go

@@ -17,22 +17,22 @@ import (
 ...
 */
 
-func collectObjectOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*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(candidateNode.CreateChild(i, candidateNode.Node.Content[i]))
@@ -41,59 +41,59 @@ func collectObjectOperator(d *dataTreeNavigator, matchMap *list.List, expression
 
 	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 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),
+	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_comments.go

@@ -13,41 +13,41 @@ type commentOpPreferences struct {
 	FootComment bool
 }
 
-func assignCommentsOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func assignCommentsOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
 	log.Debugf("AssignComments operator!")
 
-	lhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.Lhs)
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
 
 	preferences := expressionNode.Operation.Preferences.(commentOpPreferences)
 
 	comment := ""
 	if !expressionNode.Operation.UpdateAssign {
-		rhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.Rhs)
+		rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
-		if rhs.Front() != nil {
+		if rhs.MatchingNodes.Front() != nil {
-			comment = rhs.Front().Value.(*CandidateNode).Node.Value
+			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 expressionNode.Operation.UpdateAssign {
-			rhs, err := d.GetMatchingNodes(nodeToMap(candidate), expressionNode.Rhs)
+			rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 
-			if rhs.Front() != nil {
+			if rhs.MatchingNodes.Front() != nil {
-				comment = rhs.Front().Value.(*CandidateNode).Node.Value
+				comment = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 			}
 		}
 
@@ -63,15 +63,15 @@ func assignCommentsOperator(d *dataTreeNavigator, matchingNodes *list.List, expr
 		}
 
 	}
-	return matchingNodes, nil
+	return context, nil
 }
 
-func getCommentsOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+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 {
@@ -87,5 +87,5 @@ func getCommentsOperator(d *dataTreeNavigator, matchingNodes *list.List, express
 		result := candidate.CreateChild(nil, node)
 		results.PushBack(result)
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_create_map.go

@@ -6,7 +6,7 @@ import (
 	"gopkg.in/yaml.v3"
 )
 
-func createMapOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*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, expressio
 
 	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, expressionNode)
+			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, expressionNode)
+		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, expressionNode *ExpressionNode) (*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()
@@ -48,11 +48,11 @@ func sequenceFor(d *dataTreeNavigator, matchingNode *CandidateNode, expressionNo
 	if matchingNode != nil {
 		path = matchingNode.Path
 		document = matchingNode.Document
-		matches = nodeToMap(matchingNode)
+		matches.PushBack(matchingNode)
 	}
 
-	mapPairs, err := crossFunction(d, matches, expressionNode,
+	mapPairs, err := crossFunction(d, context.ChildContext(matches), expressionNode,
-		func(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+		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))
@@ -67,7 +67,7 @@ func sequenceFor(d *dataTreeNavigator, matchingNode *CandidateNode, expressionNo
 	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

@@ -1,53 +1,55 @@
 package yqlib
 
 import (
-	"container/list"
 	"fmt"
 
 	yaml "gopkg.in/yaml.v3"
 )
 
-func deleteChildOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func deleteChildOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
-
+	contextToUse := context.Clone()
-	nodesToDelete, err := d.GetMatchingNodes(matchingNodes, expressionNode.Rhs)
+	contextToUse.DontAutoCreate = true
+	nodesToDelete, err := d.GetMatchingNodes(contextToUse, expressionNode.Rhs)
 
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-
+	//need to iterate backwards to ensure correct indices when deleting multiple
-	for el := nodesToDelete.Front(); el != nil; el = el.Next() {
+	for el := nodesToDelete.MatchingNodes.Back(); el != nil; el = el.Prev() {
 		candidate := el.Value.(*CandidateNode)
 
-		deleteImmediateChildOp := &Operation{
+		if len(candidate.Path) > 0 {
-			OperationType: deleteImmediateChildOpType,
+			deleteImmediateChildOp := &Operation{
-			Value:         candidate.Path[len(candidate.Path)-1],
+				OperationType: deleteImmediateChildOpType,
-		}
+				Value:         candidate.Path[len(candidate.Path)-1],
+			}
 
-		deleteImmediateChildOpNode := &ExpressionNode{
+			deleteImmediateChildOpNode := &ExpressionNode{
-			Operation: deleteImmediateChildOp,
+				Operation: deleteImmediateChildOp,
-			Rhs:       createTraversalTree(candidate.Path[0:len(candidate.Path)-1], traversePreferences{}),
+				Rhs:       createTraversalTree(candidate.Path[0:len(candidate.Path)-1], traversePreferences{}, false),
-		}
+			}
 
-		_, err := d.GetMatchingNodes(matchingNodes, deleteImmediateChildOpNode)
+			_, err := d.GetMatchingNodes(contextToUse, deleteImmediateChildOpNode)
-		if err != nil {
+			if err != nil {
-			return nil, err
+				return Context{}, err
+			}
 		}
 	}
-	return matchingNodes, nil
+	return context, nil
 }
 
-func deleteImmediateChildOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func deleteImmediateChildOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
-	parents, err := d.GetMatchingNodes(matchingNodes, expressionNode.Rhs)
+	parents, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
 
 	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)
 		if parentNode.Kind == yaml.MappingNode {
@@ -55,11 +57,11 @@ func deleteImmediateChildOperator(d *dataTreeNavigator, matchingNodes *list.List
 		} 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{}) {

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, expressionNode *ExpressionNode) (*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 := candidate.CreateChild(nil, node)
 		results.PushBack(scalar)
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_env.go

@@ -1,7 +1,6 @@
 package yqlib
 
 import (
-	"container/list"
 	"fmt"
 	"os"
 	"strings"
@@ -13,7 +12,7 @@ type envOpPreferences struct {
 	StringValue bool
 }
 
-func envOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func envOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	envName := expressionNode.Operation.CandidateNode.Node.Value
 	log.Debug("EnvOperator, env name:", envName)
 
@@ -29,13 +28,13 @@ func envOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *Expr
 			Value: rawValue,
 		}
 	} else if rawValue == "" {
-		return nil, fmt.Errorf("Value for env variable '%v' not provided in env()", envName)
+		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)
@@ -46,5 +45,5 @@ func envOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *Expr
 
 	target := &CandidateNode{Node: node}
 
-	return nodeToMap(target), nil
+	return context.SingleChildContext(target), nil
 }

pkg/yqlib/operator_equals.go

@@ -1,25 +1,33 @@
 package yqlib
 
-import (
+import "gopkg.in/yaml.v3"
-	"container/list"
-)
 
-func equalsOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func equalsOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- equalsOperation")
-	return crossFunction(d, matchingNodes, expressionNode, isEquals)
+	return crossFunction(d, context, expressionNode, isEquals(false))
 }
 
-func isEquals(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+func isEquals(flip bool) func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
-	value := false
+	return func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+		value := false
 
-	lhsNode := unwrapDoc(lhs.Node)
+		lhsNode := unwrapDoc(lhs.Node)
-	rhsNode := unwrapDoc(rhs.Node)
+		rhsNode := unwrapDoc(rhs.Node)
 
-	if lhsNode.Tag == "!!null" {
+		if lhsNode.Tag == "!!null" {
-		value = (rhsNode.Tag == "!!null")
+			value = (rhsNode.Tag == "!!null")
-	} else {
+		} else if lhsNode.Kind == yaml.ScalarNode && rhsNode.Kind == yaml.ScalarNode {
-		value = matchKey(lhsNode.Value, rhsNode.Value)
+			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

@@ -14,6 +14,14 @@ var equalsOperatorScenarios = []expressionScenario{
 			"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]`,
@@ -23,7 +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)`,
@@ -32,7 +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, expressionNode *ExpressionNode) (*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"}
 		result := candidate.CreateChild(nil, node)
 		results.PushBack(result)
 	}
 
-	return results, nil
+	return context.ChildContext(results), nil
 }
 
-func getFileIndexOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*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"}
 		result := candidate.CreateChild(nil, node)
 		results.PushBack(result)
 	}
 
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_file_test.go

@@ -21,6 +21,16 @@ var fileOperatorScenarios = []expressionScenario{
 			"D0, P[], (!!int)::0\n",
 		},
 	},
+	{
+		description: "Get file indices of multiple documents",
+		document:    `{a: cat}`,
+		document2:   `{a: cat}`,
+		expression:  `fileIndex`,
+		expected: []string{
+			"D0, P[], (!!int)::0\n",
+			"D0, P[], (!!int)::1\n",
+		},
+	},
 	{
 		description: "Get file index alias",
 		document:    `{a: cat}`,

pkg/yqlib/operator_has.go

@@ -7,20 +7,20 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-func hasOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*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, expressionNode.Rhs)
+	rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
-	wanted := rhs.Front().Value.(*CandidateNode).Node
+	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
@@ -41,7 +41,7 @@ func hasOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode
 			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
 			}
@@ -50,5 +50,5 @@ func hasOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode
 			results.PushBack(createBooleanCandidate(candidate, false))
 		}
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_keys.go

@@ -7,12 +7,12 @@ import (
 	"gopkg.in/yaml.v3"
 )
 
-func keysOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func keysOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- keysOperator")
 
 	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)
 		node := unwrapDoc(candidate.Node)
 		var targetNode *yaml.Node
@@ -21,14 +21,14 @@ func keysOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *Exp
 		} else if node.Kind == yaml.SequenceNode {
 			targetNode = getIndicies(node)
 		} else {
-			return nil, fmt.Errorf("Cannot get keys of %v, keys only works for maps and arrays", node.Tag)
+			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 results, nil
+	return context.ChildContext(results), nil
 }
 
 func getMapKeys(node *yaml.Node) *yaml.Node {

pkg/yqlib/operator_length.go

@@ -7,17 +7,21 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-func lengthOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*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)
 		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:
@@ -31,5 +35,5 @@ func lengthOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *E
 		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

@@ -9,77 +9,19 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-type crossFunctionCalculation func(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error)
-
-func doCrossFunc(d *dataTreeNavigator, contextList *list.List, expressionNode *ExpressionNode, calculation crossFunctionCalculation) (*list.List, error) {
-	var results = list.New()
-	lhs, err := d.GetMatchingNodes(contextList, expressionNode.Lhs)
-	if err != nil {
-		return nil, err
-	}
-	log.Debugf("crossFunction LHS len: %v", lhs.Len())
-
-	rhs, err := d.GetMatchingNodes(contextList, expressionNode.Rhs)
-
-	if err != nil {
-		return nil, err
-	}
-
-	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
-}
-
-func crossFunction(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode, calculation crossFunctionCalculation) (*list.List, error) {
-	var results = list.New()
-
-	var evaluateAllTogether = true
-	for matchEl := matchingNodes.Front(); matchEl != nil; matchEl = matchEl.Next() {
-		evaluateAllTogether = evaluateAllTogether && matchEl.Value.(*CandidateNode).EvaluateTogether
-		if !evaluateAllTogether {
-			break
-		}
-	}
-	if evaluateAllTogether {
-		return doCrossFunc(d, matchingNodes, expressionNode, calculation)
-	}
-
-	for matchEl := matchingNodes.Front(); matchEl != nil; matchEl = matchEl.Next() {
-		contextList := nodeToMap(matchEl.Value.(*CandidateNode))
-		innerResults, err := doCrossFunc(d, contextList, expressionNode, calculation)
-		if err != nil {
-			return nil, err
-		}
-		results.PushBackList(innerResults)
-	}
-
-	return results, nil
-}
-
 type multiplyPreferences struct {
-	AppendArrays  bool
+	AppendArrays    bool
-	TraversePrefs traversePreferences
+	DeepMergeArrays bool
+	TraversePrefs   traversePreferences
 }
 
-func multiplyOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func multiplyOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- MultiplyOperator")
-	return crossFunction(d, matchingNodes, expressionNode, multiply(expressionNode.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) {
+func multiply(preferences multiplyPreferences) func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
-	return func(d *dataTreeNavigator, 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)
@@ -89,18 +31,38 @@ func multiply(preferences multiplyPreferences) func(d *dataTreeNavigator, lhs *C
 			(lhs.Node.Kind == yaml.SequenceNode && rhs.Node.Kind == yaml.SequenceNode) {
 
 			var newBlank = lhs.CreateChild(nil, &yaml.Node{})
-			var newThing, err = mergeObjects(d, newBlank, lhs, multiplyPreferences{})
+			var newThing, err = mergeObjects(d, context, newBlank, lhs, multiplyPreferences{})
 			if err != nil {
 				return nil, err
 			}
-			return mergeObjects(d, newThing, rhs, preferences)
+			return mergeObjects(d, context, newThing, rhs, preferences)
 		} else if lhs.Node.Tag == "!!int" && rhs.Node.Tag == "!!int" {
 			return multiplyIntegers(lhs, rhs)
+		} else if (lhs.Node.Tag == "!!int" || lhs.Node.Tag == "!!float") && (rhs.Node.Tag == "!!int" || rhs.Node.Tag == "!!float") {
+			return multiplyFloats(lhs, rhs)
 		}
 		return nil, fmt.Errorf("Cannot multiply %v with %v", lhs.Node.Tag, rhs.Node.Tag)
 	}
 }
 
+func multiplyFloats(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 = "!!float"
+
+	lhsNum, err := strconv.ParseFloat(lhs.Node.Value, 64)
+	if err != nil {
+		return nil, err
+	}
+	rhsNum, err := strconv.ParseFloat(rhs.Node.Value, 64)
+	if err != nil {
+		return nil, err
+	}
+	target.Node.Value = fmt.Sprintf("%v", lhsNum*rhsNum)
+	return target, nil
+}
+
 func multiplyIntegers(lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
 	target := lhs.CreateChild(nil, &yaml.Node{})
 	target.Node.Kind = yaml.ScalarNode
@@ -119,14 +81,14 @@ func multiplyIntegers(lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, e
 	return target, nil
 }
 
-func mergeObjects(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode, preferences multiplyPreferences) (*CandidateNode, error) {
+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{DontFollowAlias: true}}
+		TraversePreferences: traversePreferences{DontFollowAlias: true, IncludeMapKeys: true}}
-	err := recursiveDecent(d, results, nodeToMap(rhs), prefs)
+	err := recursiveDecent(d, results, context.SingleChildContext(rhs), prefs)
 	if err != nil {
 		return nil, err
 	}
@@ -137,7 +99,12 @@ 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), preferences)
+		candidate := el.Value.(*CandidateNode)
+		if candidate.Node.Tag == "!!merge" {
+			continue
+		}
+
+		err := applyAssignment(d, context, pathIndexToStartFrom, lhs, candidate, preferences)
 		if err != nil {
 			return nil, err
 		}
@@ -145,24 +112,25 @@ func mergeObjects(d *dataTreeNavigator, lhs *CandidateNode, rhs *CandidateNode,
 	return lhs, nil
 }
 
-func applyAssignment(d *dataTreeNavigator, pathIndexToStartFrom int, lhs *CandidateNode, rhs *CandidateNode, preferences multiplyPreferences) error {
+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", NodeToString(lhs), NodeToString(rhs))
+	log.Debugf("merge - applyAssignment lhs %v, rhs: %v", lhs.GetKey(), rhs.GetKey())
 
 	lhsPath := rhs.Path[pathIndexToStartFrom:]
 
 	assignmentOp := &Operation{OperationType: assignAttributesOpType}
-	if rhs.Node.Kind == yaml.ScalarNode || rhs.Node.Kind == yaml.AliasNode {
+	if shouldAppendArrays && rhs.Node.Kind == yaml.SequenceNode {
+		assignmentOp.OperationType = addAssignOpType
+	} else if !preferences.DeepMergeArrays && rhs.Node.Kind == yaml.SequenceNode ||
+		(rhs.Node.Kind == yaml.ScalarNode || rhs.Node.Kind == yaml.AliasNode) {
 		assignmentOp.OperationType = assignOpType
 		assignmentOp.UpdateAssign = false
-	} else if shouldAppendArrays && rhs.Node.Kind == yaml.SequenceNode {
-		assignmentOp.OperationType = addAssignOpType
 	}
 	rhsOp := &Operation{OperationType: valueOpType, CandidateNode: rhs}
 
-	assignmentOpNode := &ExpressionNode{Operation: assignmentOp, Lhs: createTraversalTree(lhsPath, preferences.TraversePrefs), Rhs: &ExpressionNode{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

@@ -5,6 +5,27 @@ import (
 )
 
 var multiplyOperatorScenarios = []expressionScenario{
+	{
+		description: "Multiply integers",
+		expression:  `3 * 4`,
+		expected: []string{
+			"D0, P[], (!!int)::12\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		expression: `3 * 4.5`,
+		expected: []string{
+			"D0, P[], (!!float)::13.5\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		expression: `4.5 * 3`,
+		expected: []string{
+			"D0, P[], (!!float)::13.5\n",
+		},
+	},
 	{
 		skipDoc:    true,
 		document:   `{a: {also: [1]}, b: {also: me}}`,
@@ -13,6 +34,30 @@ 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}`,
@@ -92,7 +137,7 @@ 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",
 		},
@@ -100,16 +145,10 @@ var multiplyOperatorScenarios = []expressionScenario{
 	{
 		description:           "Merge keeps style of LHS",
 		dontFormatInputForDoc: true,
-		document: `a: {things: great}
+		document:              "a: {things: great}\nb:\n  also: \"me\"",
-b:
+		expression:            `. * {"a":.b}`,
-  also: "me"
-`,
-		expression: `. * {"a":.b}`,
 		expected: []string{
-			`D0, P[], (!!map)::a: {things: great, also: "me"}
+			"D0, P[], (!!map)::a: {things: great, also: \"me\"}\nb:\n    also: \"me\"\n",
-b:
-    also: "me"
-`,
 		},
 	},
 	{
@@ -139,11 +178,19 @@ b:
 	{
 		skipDoc:    true,
 		document:   `{a: [{thing: one}], b: [{missing: two, thing: two}]}`,
-		expression: `.a *? .b`,
+		expression: `.a *?d .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}}`,
@@ -160,6 +207,15 @@ b:
 			"D0, P[a], (!!map)::{thing: [1, 2, 3, 4]}\n",
 		},
 	},
+	{
+		description:    "Merge, deeply merging arrays",
+		subdescription: "Merging arrays deeply means arrays are merge like objects, with indexes as their key. In this case, we merge the first item in the array, and do nothing with the second.",
+		document:       `{a: [{name: fred, age: 12}, {name: bob, age: 32}], b: [{name: fred, age: 34}]}`,
+		expression:     `.a *d .b`,
+		expected: []string{
+			"D0, P[a], (!!seq)::[{name: fred, age: 34}, {name: bob, age: 32}]\n",
+		},
+	},
 	{
 		description: "Merge to prefix an element",
 		document:    `{a: cat, b: dog}`,

pkg/yqlib/operator_path.go

@@ -16,12 +16,12 @@ func createPathNodeFor(pathElement interface{}) *yaml.Node {
 	}
 }
 
-func getPathOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*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"}
 
@@ -35,5 +35,5 @@ func getPathOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionN
 		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, expressionNode *ExpressionNode) (*list.List, error) {
+	//lhs may update the variable context, we should pass that into the RHS
-	lhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.Lhs)
+	// 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, expressionNode.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

@@ -11,20 +11,20 @@ type recursiveDescentPreferences struct {
 	RecurseArray        bool
 }
 
-func recursiveDescentOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func recursiveDescentOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	var results = list.New()
 
 	preferences := expressionNode.Operation.Preferences.(recursiveDescentPreferences)
-	err := recursiveDecent(d, results, matchMap, preferences)
+	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 {
+func recursiveDecent(d *dataTreeNavigator, results *list.List, context Context, preferences recursiveDescentPreferences) error {
-	for el := matchMap.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 
 		candidate.Node = unwrapDoc(candidate.Node)
@@ -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_reduce.go

@@ -0,0 +1,59 @@
+package yqlib
+
+import (
+	"container/list"
+	"fmt"
+)
+
+func reduceOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("-- reduceOp")
+	//.a as $var reduce (0; . + $var)
+	//lhs is the assignment operator
+	//rhs is the reduce block
+	// '.' refers to the current accumulator, initialised to 0
+	// $var references a single element from the .a
+
+	//ensure lhs is actually an assignment
+	//and rhs is a block (empty)
+	if expressionNode.Lhs.Operation.OperationType != assignVariableOpType {
+		return Context{}, fmt.Errorf("reduce must be given a variables assignment, got %v instead", expressionNode.Lhs.Operation.OperationType.Type)
+	} else if expressionNode.Rhs.Operation.OperationType != blockOpType {
+		return Context{}, fmt.Errorf("reduce must be given a block, got %v instead", expressionNode.Rhs.Operation.OperationType.Type)
+	}
+
+	arrayExpNode := expressionNode.Lhs.Lhs
+	array, err := d.GetMatchingNodes(context, arrayExpNode)
+
+	log.Debugf("array of %v things", array.MatchingNodes.Len())
+
+	if err != nil {
+		return Context{}, err
+	}
+
+	variableName := expressionNode.Lhs.Rhs.Operation.StringValue
+
+	initExp := expressionNode.Rhs.Lhs
+
+	accum, err := d.GetMatchingNodes(context, initExp)
+	if err != nil {
+		return Context{}, err
+	}
+
+	log.Debugf("with variable %v", variableName)
+
+	blockExp := expressionNode.Rhs.Rhs
+	for el := array.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		log.Debugf("REDUCING WITH %v", NodeToString(candidate))
+		l := list.New()
+		l.PushBack(candidate)
+		accum.SetVariable(variableName, l)
+
+		accum, err = d.GetMatchingNodes(accum, blockExp)
+		if err != nil {
+			return Context{}, err
+		}
+	}
+
+	return accum, nil
+}

pkg/yqlib/operator_reduce_test.go

@@ -0,0 +1,40 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var reduceOperatorScenarios = []expressionScenario{
+	{
+		description: "Sum numbers",
+		document:    `[10,2, 5, 3]`,
+		expression:  `.[] as $item ireduce (0; . + $item)`,
+		expected: []string{
+			"D0, P[], (!!int)::20\n",
+		},
+	},
+	{
+		description: "Merge all yaml files together",
+		document:    `a: cat`,
+		document2:   `b: dog`,
+		expression:  `. as $item ireduce ({}; . * $item )`,
+		expected: []string{
+			"D0, P[], (!!map)::a: cat\nb: dog\n",
+		},
+	},
+	{
+		description: "Convert an array to an object",
+		document:    `[{name: Cathy, has: apples},{name: Bob, has: bananas}]`,
+		expression:  `.[] as $item ireduce ({}; .[$item | .name] = ($item | .has) )`,
+		expected: []string{
+			"D0, P[], (!!map)::Cathy: apples\nBob: bananas\n",
+		},
+	},
+}
+
+func TestReduceOperatorScenarios(t *testing.T) {
+	for _, tt := range reduceOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentScenarios(t, "Reduce", reduceOperatorScenarios)
+}

pkg/yqlib/operator_select.go

@@ -4,28 +4,29 @@ import (
 	"container/list"
 )
 
-func selectOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*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)
-
+		childContext := context.SingleChildContext(candidate)
-		rhs, err := d.GetMatchingNodes(nodeToMap(candidate), expressionNode.Rhs)
+		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, expressionNo
 			}
 		}
 	}
-	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, context Context, expressionNode *ExpressionNode) (Context, error) {
-
+	return context, nil
-func selfOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*list.List, error) {
-	return matchMap, 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, expressionNode *ExpressionNode) (*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), expressionNode.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() {
+		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

@@ -1,18 +1,14 @@
 package yqlib
 
-import (
+func splitDocumentOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
-	"container/list"
-)
-
-func splitDocumentOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*list.List, error) {
 	log.Debugf("-- splitDocumentOperator")
 
 	var index uint = 0
-	for el := matchMap.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		candidate.Document = index
 		index = index + 1
 	}
 
-	return matchMap, nil
+	return context, nil
 }

pkg/yqlib/operator_strings.go

@@ -8,32 +8,32 @@ import (
 	"gopkg.in/yaml.v3"
 )
 
-func joinStringOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func joinStringOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- joinStringOperator")
 	joinStr := ""
 
-	rhs, err := d.GetMatchingNodes(matchMap, expressionNode.Rhs)
+	rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-	if rhs.Front() != nil {
+	if rhs.MatchingNodes.Front() != nil {
-		joinStr = rhs.Front().Value.(*CandidateNode).Node.Value
+		joinStr = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 	}
 
 	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)
 		node := unwrapDoc(candidate.Node)
 		if node.Kind != yaml.SequenceNode {
-			return nil, fmt.Errorf("Cannot join with %v, can only join arrays of scalars", node.Tag)
+			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 results, nil
+	return context.ChildContext(results), nil
 }
 
 func join(content []*yaml.Node, joinStr string) *yaml.Node {
@@ -49,35 +49,35 @@ func join(content []*yaml.Node, joinStr string) *yaml.Node {
 	return &yaml.Node{Kind: yaml.ScalarNode, Value: strings.Join(stringsToJoin, joinStr), Tag: "!!str"}
 }
 
-func splitStringOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func splitStringOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- splitStringOperator")
 	splitStr := ""
 
-	rhs, err := d.GetMatchingNodes(matchMap, expressionNode.Rhs)
+	rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-	if rhs.Front() != nil {
+	if rhs.MatchingNodes.Front() != nil {
-		splitStr = rhs.Front().Value.(*CandidateNode).Node.Value
+		splitStr = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 	}
 
 	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)
 		node := unwrapDoc(candidate.Node)
 		if node.Tag == "!!null" {
 			continue
 		}
 		if node.Tag != "!!str" {
-			return nil, fmt.Errorf("Cannot split %v, can only split strings", node.Tag)
+			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 results, nil
+	return context.ChildContext(results), nil
 }
 
 func split(value string, spltStr string) *yaml.Node {

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, expressionNode *ExpressionNode) (*list.List, error) {
+func assignStyleOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
 	log.Debugf("AssignStyleOperator: %v")
 	var style yaml.Style
 	if !expressionNode.Operation.UpdateAssign {
-		rhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.Rhs)
+		rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
-		if rhs.Front() != nil {
+		if rhs.MatchingNodes.Front() != nil {
-			style, err = parseStyle(rhs.Front().Value.(*CandidateNode).Node.Value)
+			style, err = parseStyle(rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 		}
 	}
 
-	lhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.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 expressionNode.Operation.UpdateAssign {
-			rhs, err := d.GetMatchingNodes(nodeToMap(candidate), expressionNode.Rhs)
+			rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 
-			if rhs.Front() != nil {
+			if rhs.MatchingNodes.Front() != nil {
-				style, err = parseStyle(rhs.Front().Value.(*CandidateNode).Node.Value)
+				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, express
 		candidate.Node.Style = style
 	}
 
-	return matchingNodes, nil
+	return context, nil
 }
 
-func getStyleOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*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 {
@@ -104,5 +104,5 @@ func getStyleOperator(d *dataTreeNavigator, matchingNodes *list.List, expression
 		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, expressionNode *ExpressionNode) (*list.List, error) {
+func assignTagOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 
 	log.Debugf("AssignTagOperator: %v")
 	tag := ""
 
 	if !expressionNode.Operation.UpdateAssign {
-		rhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.Rhs)
+		rhs, err := d.GetMatchingNodes(context, expressionNode.Rhs)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
-		if rhs.Front() != nil {
+		if rhs.MatchingNodes.Front() != nil {
-			tag = rhs.Front().Value.(*CandidateNode).Node.Value
+			tag = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 		}
 	}
 
-	lhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.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 expressionNode.Operation.UpdateAssign {
-			rhs, err := d.GetMatchingNodes(nodeToMap(candidate), expressionNode.Rhs)
+			rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 			if err != nil {
-				return nil, err
+				return Context{}, err
 			}
 
-			if rhs.Front() != nil {
+			if rhs.MatchingNodes.Front() != nil {
-				tag = rhs.Front().Value.(*CandidateNode).Node.Value
+				tag = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
 			}
 		}
 		unwrapDoc(candidate.Node).Tag = tag
 	}
 
-	return matchingNodes, nil
+	return context, nil
 }
 
-func getTagOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*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"}
 		result := candidate.CreateChild(nil, node)
 		results.PushBack(result)
 	}
 
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_traverse_path.go

@@ -10,31 +10,32 @@ import (
 )
 
 type traversePreferences struct {
-	DontFollowAlias bool
+	DontFollowAlias      bool
-	IncludeMapKeys  bool
+	IncludeMapKeys       bool
-	DontAutoCreate  bool // by default, we automatically create entries on the fly.
+	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) {
+func splat(d *dataTreeNavigator, context Context, prefs traversePreferences) (Context, error) {
-	return traverseNodesWithArrayIndices(matches, make([]*yaml.Node, 0), prefs)
+	return traverseNodesWithArrayIndices(context, make([]*yaml.Node, 0), prefs)
 }
 
-func traversePathOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func traversePathOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
-	log.Debugf("-- Traversing")
+	log.Debugf("-- traversePathOperator")
-	var matchingNodeMap = list.New()
+	var matches = list.New()
 
-	for el := matchMap.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
-		newNodes, err := traverse(d, el.Value.(*CandidateNode), expressionNode.Operation)
+		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
 
@@ -55,7 +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)
-		return traverseMap(matchingNode, operation.StringValue, operation.Preferences.(traversePreferences), 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))
@@ -64,43 +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, matchingNode.CreateChild(nil, matchingNode.Node.Content[0]), 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, expressionNode *ExpressionNode) (*list.List, error) {
+func traverseArrayOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
-	// rhs is a collect expression that will yield indexes to retreive of the arrays
 
-	rhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.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
+	// rhs is a collect expression that will yield indexes to retreive of the arrays
-	return traverseNodesWithArrayIndices(matchingNodes, indicesToTraverse, traversePreferences{})
+
+	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")
@@ -111,28 +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(matchingNode.CreateChild(nil, matchingNode.Node.Content[0]), 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
 		}
@@ -187,7 +204,7 @@ func keyMatches(key *yaml.Node, wantedKey string) bool {
 	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)
 
@@ -195,13 +212,24 @@ func traverseMap(matchingNode *CandidateNode, key string, prefs traversePreferen
 		return nil, err
 	}
 
-	if !prefs.DontAutoCreate && 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)
+		node.Content = append(node.Content, keyNode, valueNode)
-		candidateNode := matchingNode.CreateChild(key, valueNode)
+
-		newMatches.Set(candidateNode.GetKey(), candidateNode)
+		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()
@@ -237,11 +265,16 @@ func doTraverseMap(newMatches *orderedmap.OrderedMap, candidate *CandidateNode,
 		} else if splat || keyMatches(key, wantedKey) {
 			log.Debug("MATCHED")
 			if prefs.IncludeMapKeys {
+				log.Debug("including key")
 				candidateNode := candidate.CreateChild(key.Value, key)
+				candidateNode.IsMapKey = true
 				newMatches.Set(fmt.Sprintf("keyOf-%v", candidateNode.GetKey()), candidateNode)
 			}
-			candidateNode := candidate.CreateChild(key.Value, value)
+			if !prefs.DontIncludeMapValues {
-			newMatches.Set(candidateNode.GetKey(), candidateNode)
+				log.Debug("including value")
+				candidateNode := candidate.CreateChild(key.Value, value)
+				newMatches.Set(candidateNode.GetKey(), candidateNode)
+			}
 		}
 	}
 

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, context Context, expressionNode *ExpressionNode) (Context, error) {
-
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
-func unionOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
-	lhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.Lhs)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-	rhs, err := d.GetMatchingNodes(matchingNodes, expressionNode.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, context Context, expressionNode *ExpressionNode) (Context, error) {
-
-func valueOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*list.List, error) {
 	log.Debug("value = %v", expressionNode.Operation.CandidateNode.Node.Value)
-	return nodeToMap(expressionNode.Operation.CandidateNode), nil
+	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

@@ -4,10 +4,11 @@ import (
 	"container/list"
 	"fmt"
 
+	"github.com/jinzhu/copier"
 	"gopkg.in/yaml.v3"
 )
 
-type operatorHandler func(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error)
+type operatorHandler func(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error)
 
 func unwrapDoc(node *yaml.Node) *yaml.Node {
 	if node.Kind == yaml.DocumentNode {
@@ -16,8 +17,67 @@ func unwrapDoc(node *yaml.Node) *yaml.Node {
 	return node
 }
 
-func emptyOperator(d *dataTreeNavigator, matchingNodes *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+func emptyOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
-	return list.New(), nil
+	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 {
@@ -29,22 +89,25 @@ func createBooleanCandidate(owner *CandidateNode, value bool) *CandidateNode {
 	return owner.CreateChild(nil, node)
 }
 
-func nodeToMap(candidate *CandidateNode) *list.List {
+func createTraversalTree(path []interface{}, traversePrefs traversePreferences, targetKey bool) *ExpressionNode {
-	elMap := list.New()
-	elMap.PushBack(candidate)
-	return elMap
-}
-
-func createTraversalTree(path []interface{}, traversePrefs traversePreferences) *ExpressionNode {
 	if len(path) == 0 {
 		return &ExpressionNode{Operation: &Operation{OperationType: selfReferenceOpType}}
 	} else if len(path) == 1 {
-		return &ExpressionNode{Operation: &Operation{OperationType: traversePathOpType, Preferences: traversePrefs, 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),
+		Lhs:       createTraversalTree(path[0:1], traversePrefs, false),
-		Rhs:       createTraversalTree(path[1:], traversePrefs),
+		Rhs:       createTraversalTree(path[1:], traversePrefs, targetKey),
 	}
 }

pkg/yqlib/operators_test.go

@@ -27,7 +27,6 @@ type expressionScenario struct {
 }
 
 func testScenario(t *testing.T, s *expressionScenario) {
-	var results *list.List
 	var err error
 
 	node, err := NewExpressionParser().ParseExpression(s.expression)
@@ -66,13 +65,13 @@ func testScenario(t *testing.T, s *expressionScenario) {
 		os.Setenv("myenv", s.environmentVariable)
 	}
 
-	results, err = NewDataTreeNavigator().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 {
@@ -252,12 +251,12 @@ func documentOutput(t *testing.T, w *bufio.Writer, s expressionScenario, formatt
 
 	}
 
-	results, err := NewDataTreeNavigator().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/printer.go

@@ -74,14 +74,14 @@ func (p *resultsPrinter) safelyFlush(writer *bufio.Writer) {
 
 func (p *resultsPrinter) PrintResults(matchingNodes *list.List) error {
 	log.Debug("PrintResults for %v matches", matchingNodes.Len())
-	var err error
 	if p.outputToJSON {
 		explodeOp := Operation{OperationType: explodeOpType}
 		explodeNode := ExpressionNode{Operation: &explodeOp}
-		matchingNodes, err = p.treeNavigator.GetMatchingNodes(matchingNodes, &explodeNode)
+		context, err := p.treeNavigator.GetMatchingNodes(Context{MatchingNodes: matchingNodes}, &explodeNode)
 		if err != nil {
 			return err
 		}
+		matchingNodes = context.MatchingNodes
 	}
 
 	bufferedWriter := bufio.NewWriter(p.writer)

pkg/yqlib/printer_test.go

@@ -3,6 +3,7 @@ package yqlib
 import (
 	"bufio"
 	"bytes"
+	"container/list"
 	"strings"
 	"testing"
 
@@ -16,6 +17,12 @@ a: apple
 a: coconut
 `
 
+func nodeToList(candidate *CandidateNode) *list.List {
+	elMap := list.New()
+	elMap.PushBack(candidate)
+	return elMap
+}
+
 func TestPrinterMultipleDocsInSequence(t *testing.T) {
 	var output bytes.Buffer
 	var writer = bufio.NewWriter(&output)
@@ -27,13 +34,13 @@ func TestPrinterMultipleDocsInSequence(t *testing.T) {
 	}
 
 	el := inputs.Front()
-	sample1 := nodeToMap(el.Value.(*CandidateNode))
+	sample1 := nodeToList(el.Value.(*CandidateNode))
 
 	el = el.Next()
-	sample2 := nodeToMap(el.Value.(*CandidateNode))
+	sample2 := nodeToList(el.Value.(*CandidateNode))
 
 	el = el.Next()
-	sample3 := nodeToMap(el.Value.(*CandidateNode))
+	sample3 := nodeToList(el.Value.(*CandidateNode))
 
 	err = printer.PrintResults(sample1)
 	if err != nil {
@@ -68,19 +75,19 @@ func TestPrinterMultipleFilesInSequence(t *testing.T) {
 	elNode := el.Value.(*CandidateNode)
 	elNode.Document = 0
 	elNode.FileIndex = 0
-	sample1 := nodeToMap(elNode)
+	sample1 := nodeToList(elNode)
 
 	el = el.Next()
 	elNode = el.Value.(*CandidateNode)
 	elNode.Document = 0
 	elNode.FileIndex = 1
-	sample2 := nodeToMap(elNode)
+	sample2 := nodeToList(elNode)
 
 	el = el.Next()
 	elNode = el.Value.(*CandidateNode)
 	elNode.Document = 0
 	elNode.FileIndex = 2
-	sample3 := nodeToMap(elNode)
+	sample3 := nodeToList(elNode)
 
 	err = printer.PrintResults(sample1)
 	if err != nil {

pkg/yqlib/stream_evaluator.go

@@ -41,11 +41,11 @@ func (s *streamEvaluator) EvaluateNew(expression string, printer Printer) error
 	inputList := list.New()
 	inputList.PushBack(candidateNode)
 
-	matches, errorParsing := s.treeNavigator.GetMatchingNodes(inputList, node)
+	result, errorParsing := s.treeNavigator.GetMatchingNodes(Context{MatchingNodes: inputList}, node)
 	if errorParsing != nil {
 		return errorParsing
 	}
-	return printer.PrintResults(matches)
+	return printer.PrintResults(result.MatchingNodes)
 }
 
 func (s *streamEvaluator) EvaluateFiles(expression string, filenames []string, printer Printer) error {
@@ -97,11 +97,11 @@ func (s *streamEvaluator) Evaluate(filename string, reader io.Reader, node *Expr
 		inputList := list.New()
 		inputList.PushBack(candidateNode)
 
-		matches, errorParsing := s.treeNavigator.GetMatchingNodes(inputList, node)
+		result, errorParsing := s.treeNavigator.GetMatchingNodes(Context{MatchingNodes: inputList}, node)
 		if errorParsing != nil {
 			return errorParsing
 		}
-		err := printer.PrintResults(matches)
+		err := printer.PrintResults(result.MatchingNodes)
 		if err != nil {
 			return err
 		}

release_instructions.txt

@@ -2,11 +2,13 @@
 - increment version in snapcraft.yaml
 - increment version in github-action/Dockerfile
 - make sure local build passes
+- commit version update changes
 - tag git with same version number
 - commit vX tag - this will trigger github actions
 - use github actions to publish docker and make github release
 - check github updated yq action in marketplace
 
+
 - snapcraft
   - will auto create a candidate, test it works then promote
   

snap/snapcraft.yaml

@@ -1,5 +1,5 @@
 name: yq
-version: '4.4.0'
+version: '4.6.1'
 summary: A lightweight and portable command-line YAML processor
 description: |
   The aim of the project is to be the jq or sed of yaml files.