From 21565ef2e0d3ed912fa2cea556b1ebbfe9202262 Mon Sep 17 00:00:00 2001
From: deoxxa <deoxxa@fknsrs.biz>
Date: Sat, 5 Dec 2015 22:45:57 +1100
Subject: [PATCH] add simple REPL

---
 repl/repl.go | 115 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)
 create mode 100644 repl/repl.go

diff --git a/repl/repl.go b/repl/repl.go
new file mode 100644
index 00000000..0d70cc05
--- /dev/null
+++ b/repl/repl.go
@@ -0,0 +1,115 @@
+// Package repl implements a REPL (read-eval-print loop) for otto.
+package repl
+
+import (
+	"fmt"
+	"io"
+	"strings"
+	"sync/atomic"
+
+	"github.com/robertkrimen/otto"
+	"gopkg.in/readline.v1"
+)
+
+var counter uint32
+
+// DebuggerHandler implements otto's debugger handler signature, providing a
+// simple drop-in debugger implementation.
+func DebuggerHandler(vm *otto.Otto) {
+	i := atomic.AddUint32(&counter, 1)
+
+	// purposefully ignoring the error here - we can't do anything useful with
+	// it except panicking, and that'd be pretty rude. it'd be easy enough for a
+	// consumer to define an equivalent function that _does_ panic if desired.
+	_ = RunWithPrompt(vm, fmt.Sprintf("DEBUGGER[%d]>", i))
+}
+
+// Run creates a REPL with the default prompt and no prelude.
+func Run(vm *otto.Otto) error {
+	return RunWithPromptAndPrelude(vm, "", "")
+}
+
+// RunWithPrompt runs a REPL with the given prompt and no prelude.
+func RunWithPrompt(vm *otto.Otto, prompt string) error {
+	return RunWithPromptAndPrelude(vm, prompt, "")
+}
+
+// RunWithPrelude runs a REPL with the default prompt and the given prelude.
+func RunWithPrelude(vm *otto.Otto, prelude string) error {
+	return RunWithPromptAndPrelude(vm, "", prelude)
+}
+
+// RunWithPromptAndPrelude runs a REPL with the given prompt and prelude.
+func RunWithPromptAndPrelude(vm *otto.Otto, prompt, prelude string) error {
+	if prompt == "" {
+		prompt = ">"
+	}
+
+	prompt = strings.Trim(prompt, " ")
+	prompt += " "
+
+	rl, err := readline.New(prompt)
+	if err != nil {
+		return err
+	}
+
+	if prelude != "" {
+		if _, err := io.Copy(rl.Stderr(), strings.NewReader(prelude+"\n")); err != nil {
+			return err
+		}
+
+		rl.Refresh()
+	}
+
+	var d []string
+
+	for {
+		l, err := rl.Readline()
+		if err != nil {
+			if err == readline.ErrInterrupt {
+				if d != nil {
+					d = nil
+
+					rl.SetPrompt(prompt)
+					rl.Refresh()
+
+					continue
+				}
+
+				break
+			}
+
+			return err
+		}
+
+		if l == "" {
+			continue
+		}
+
+		d = append(d, l)
+
+		s, err := vm.Compile("repl", strings.Join(d, "\n"))
+		if err != nil {
+			rl.SetPrompt(strings.Repeat(" ", len(prompt)))
+		} else {
+			rl.SetPrompt(prompt)
+
+			d = nil
+
+			v, err := vm.Eval(s)
+			if err != nil {
+				if oerr, ok := err.(*otto.Error); ok {
+					io.Copy(rl.Stdout(), strings.NewReader(oerr.String()))
+				} else {
+					io.Copy(rl.Stdout(), strings.NewReader(err.Error()))
+				}
+			} else {
+				rl.Stdout().Write([]byte(v.String() + "\n"))
+			}
+		}
+
+		rl.Refresh()
+	}
+
+	return rl.Close()
+}