add english version

en/code/src/apps/ch.2.3/panic_and_recover/main.go

@@ -0,0 +1,31 @@
+// Example code for Chapter 2.3 from "Build Web Application with Golang"
+// Purpose: Showing how to use `panic()` and `recover()`
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+var user = os.Getenv("USER")
+
+func check_user() {
+	if user == "" {
+		panic("no value for $USER")
+	}
+	fmt.Println("Environment Variable `USER` =", user)
+}
+func throwsPanic(f func()) (b bool) {
+	defer func() {
+		if x := recover(); x != nil {
+			fmt.Println("Panic message =", x);
+			b = true
+		}
+	}()
+	f() // if f causes panic, it will recover
+	return
+}
+func main(){
+	didPanic := throwsPanic(check_user)
+	fmt.Println("didPanic =", didPanic)
+}