Implement subscriptions, and update example accordingly

example/main.go

@@ -3,12 +3,26 @@ package main
 import (
 	"fmt"
 	"tea"
+	"time"
 )
 
-type Model int
+type Model struct {
+	Choice int
+	Ticks  int
+}
+
+type TickMsg struct{}
+
+const tpl = `What to do today?
+
+%s
+
+Elapsed: %d seconds.
+
+(press j/k or up/down to select, q or esc to quit)`
 
 func main() {
-	p := tea.NewProgram(0, update, view)
+	p := tea.NewProgram(Model{0, 0}, update, view, []tea.Sub{tick})
 	if err := p.Start(); err != nil {
 		fmt.Println("could not start program:", err)
 	}
@@ -18,53 +32,57 @@ func update(msg tea.Msg, model tea.Model) (tea.Model, tea.Cmd) {
 	m, _ := model.(Model)
 
 	switch msg := msg.(type) {
+
 	case tea.KeyPressMsg:
 		switch msg {
-
 		case "j":
 			fallthrough
 		case "down":
-			m += 1
-			if m > 3 {
-				m = 3
+			m.Choice += 1
+			if m.Choice > 3 {
+				m.Choice = 3
 			}
-
 		case "k":
 			fallthrough
 		case "up":
-			m -= 1
-			if m < 0 {
-				m = 0
+			m.Choice -= 1
+			if m.Choice < 0 {
+				m.Choice = 0
 			}
-
 		case "q":
 			fallthrough
 		case "esc":
 			fallthrough
 		case "ctrl+c":
 			return m, tea.Quit
-
 		}
+
+	case TickMsg:
+		m.Ticks += 1
 	}
 
 	return m, nil
 }
 
+// Subscription
+func tick(_ tea.Model) tea.Msg {
+	time.Sleep(time.Second * 1)
+	return TickMsg{}
+}
+
 func view(model tea.Model) string {
 	m, _ := model.(Model)
+	c := m.Choice
 
 	choices := fmt.Sprintf(
 		"%s\n%s\n%s\n%s",
-		checkbox("Plant carrots", m == 0),
-		checkbox("Go to the market", m == 1),
-		checkbox("Read something", m == 2),
-		checkbox("See friends", m == 3),
+		checkbox("Plant carrots", c == 0),
+		checkbox("Go to the market", c == 1),
+		checkbox("Read something", c == 2),
+		checkbox("See friends", c == 3),
 	)
 
-	return fmt.Sprintf(
-		"What to do today?\n\n%s\n\n(press j/k or up/down to select, q or esc to quit)",
-		choices,
-	)
+	return fmt.Sprintf(tpl, choices, m.Ticks)
 }
 
 func checkbox(label string, checked bool) string {