Update README.md

Author: antonmedv

README.md

@@ -98,6 +98,44 @@ func main() {
 }
 ```
 
+[Play Online](https://play.golang.org/p/4S4brsIvU4i)
+
+```go
+package main
+
+import (
+	"fmt"
+	"github.com/antonmedv/expr"
+)
+
+type Tweet struct {
+	Len int
+}
+
+type Env struct {
+	Tweets []Tweet
+}
+
+func main() {
+	code := `all(Tweets, {.Len <= 240})`
+
+	program, err := expr.Compile(code, expr.Env(Env{}))
+	if err != nil {
+		panic(err)
+	}
+
+	env := Env{
+		Tweets: []Tweet{{42}, {98}, {69}},
+	}
+	output, err := expr.Run(program, env)
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Println(output)
+}
+```
+
 ## Contributing
 
 **Expr** consist of a few packages for parsing source code to AST, type checking AST, compiling to bytecode and VM for running bytecode program.