diff --git a/doc/progs/json3.go b/doc/progs/json3.go
new file mode 100644
index 0000000..a04fdfa
--- /dev/null
+++ b/doc/progs/json3.go
@@ -0,0 +1,73 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"reflect"
+)
+
+func Decode() {
+	b := []byte(`{"Name":"Wednesday","Age":6,"Parents":["Gomez","Morticia"]}`)
+
+	var f interface{}
+	err := json.Unmarshal(b, &f)
+
+	// STOP OMIT
+
+	if err != nil {
+		panic(err)
+	}
+
+	expected := map[string]interface{}{
+		"Name": "Wednesday",
+		"Age":  float64(6),
+		"Parents": []interface{}{
+			"Gomez",
+			"Morticia",
+		},
+	}
+
+	if !reflect.DeepEqual(f, expected) {
+		log.Panicf("Error unmarshalling %q, expected %q, got %q", b, expected, f)
+	}
+
+	f = map[string]interface{}{
+		"Name": "Wednesday",
+		"Age":  6,
+		"Parents": []interface{}{
+			"Gomez",
+			"Morticia",
+		},
+	}
+
+	// STOP OMIT
+
+	m := f.(map[string]interface{})
+
+	for k, v := range m {
+		switch vv := v.(type) {
+		case string:
+			fmt.Println(k, "is string", vv)
+		case int:
+			fmt.Println(k, "is int", vv)
+		case []interface{}:
+			fmt.Println(k, "is an array:")
+			for i, u := range vv {
+				fmt.Println(i, u)
+			}
+		default:
+			fmt.Println(k, "is of a type I don't know how to handle")
+		}
+	}
+
+	// STOP OMIT
+}
+
+func main() {
+	Decode()
+}