Update README.md

Author: antonmedv

README.md

@@ -65,53 +65,36 @@ Also, I have an embeddable code editor written in JavaScript which allows editin
 
 ## Examples
 
-[demo.go](./docs/examples/demo.go)
+[Play Online](https://play.golang.org/p/z7T8ytJ1T1d)
 
 ```go
 package main
 
 import (
 	"fmt"
-	"time"
-
 	"github.com/antonmedv/expr"
 )
 
-var expressions = []string{
-	"foo > 0",
-	"bar.Value in ['a', 'b', 'c']",
-	"name matches '^hello.+$'",
-	"now().Sub(startedAt).String()",
-	"all(tweets, {len(.Message) <= 280}) ? '👍' : '👎'",
-}
+func main() {
+	env := map[string]interface{}{
+		"greet":   "Hello, %v!",
+		"names":   []string{"world", "you"},
+		"sprintf": fmt.Sprintf,
+	}
 
-var environment = map[string]interface{}{
-	"foo":       1,
-	"bar":       struct{ Value string }{"c"},
-	"name":      "hello world",
-	"startedAt": time.Now(),
-	"now":       func() time.Time { return time.Now() },
-	"tweets":    []tweet{{"first tweet"}},
-}
+	code := `sprintf(greet, names[0])`
 
-type tweet struct {
-	Message string
-}
+	program, err := expr.Compile(code, expr.Env(env))
+	if err != nil {
+		panic(err)
+	}
 
-func main() {
-	for _, input := range expressions {
-		program, err := expr.Compile(input, expr.Env(environment))
-		if err != nil {
-			panic(err)
-		}
-
-		output, err := expr.Run(program, environment)
-		if err != nil {
-			panic(err)
-		}
-
-		fmt.Println(output)
+	output, err := expr.Run(program, env)
+	if err != nil {
+		panic(err)
 	}
+
+	fmt.Println(output)
 }
 ```