Factor REPL into CLI part and agnostic part and add tests

This is to facilitate reuse of the REPL.  It also makes testing possible.

Author: ncw

main.go

@@ -12,7 +12,8 @@ import (
 	"runtime/pprof"
 
 	_ "github.com/go-python/gpython/builtin"
-	"github.com/go-python/gpython/repl"
+	"github.com/go-python/gpython/repl/cli"
+
 	//_ "github.com/go-python/gpython/importlib"
 	"io/ioutil"
 	"log"
@@ -62,7 +63,7 @@ func main() {
 	args := flag.Args()
 	py.MustGetModule("sys").Globals["argv"] = pysys.MakeArgv(args)
 	if len(args) == 0 {
-		repl.Run()
+		cli.RunREPL()
 		return
 	}
 	prog := args[0]

repl/cli/cli.go

@@ -0,0 +1,149 @@
+// Copyright 2018 The go-python Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Read Eval Print Loop for CLI
+package cli
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"os/user"
+	"path/filepath"
+
+	"github.com/go-python/gpython/py"
+	"github.com/go-python/gpython/repl"
+	"github.com/peterh/liner"
+)
+
+const HistoryFileName = ".gpyhistory"
+
+// homeDirectory finds the home directory or returns ""
+func homeDirectory() string {
+	usr, err := user.Current()
+	if err == nil {
+		return usr.HomeDir
+	}
+	// Fall back to reading $HOME - work around user.Current() not
+	// working for cross compiled binaries on OSX.
+	// https://github.com/golang/go/issues/6376
+	return os.Getenv("HOME")
+}
+
+// Holds state for readline services
+type readline struct {
+	*liner.State
+	repl        *repl.REPL
+	historyFile string
+	module      *py.Module
+	prompt      string
+}
+
+// newReadline creates a new instance of readline
+func newReadline(repl *repl.REPL) *readline {
+	rl := &readline{
+		State: liner.NewLiner(),
+		repl:  repl,
+	}
+	home := homeDirectory()
+	if home != "" {
+		rl.historyFile = filepath.Join(home, HistoryFileName)
+	}
+	rl.SetTabCompletionStyle(liner.TabPrints)
+	rl.SetWordCompleter(rl.Completer)
+	return rl
+}
+
+// readHistory reads the history into the term
+func (rl *readline) ReadHistory() error {
+	f, err := os.Open(rl.historyFile)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	_, err = rl.State.ReadHistory(f)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// writeHistory writes the history from the term
+func (rl *readline) WriteHistory() error {
+	f, err := os.OpenFile(rl.historyFile, os.O_RDWR|os.O_APPEND|os.O_CREATE, 0666)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	_, err = rl.State.WriteHistory(f)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// Close the readline and write history
+func (rl *readline) Close() error {
+	err := rl.State.Close()
+	if err != nil {
+		return err
+	}
+	if rl.historyFile != "" {
+		err := rl.WriteHistory()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// Completer takes the currently edited line with the cursor
+// position and returns the completion candidates for the partial word
+// to be completed. If the line is "Hello, wo!!!" and the cursor is
+// before the first '!', ("Hello, wo!!!", 9) is passed to the
+// completer which may returns ("Hello, ", {"world", "Word"}, "!!!")
+// to have "Hello, world!!!".
+func (rl *readline) Completer(line string, pos int) (head string, completions []string, tail string) {
+	return rl.repl.Completer(line, pos)
+}
+
+// SetPrompt sets the current terminal prompt
+func (rl *readline) SetPrompt(prompt string) {
+	rl.prompt = prompt
+}
+
+// Print prints the output
+func (rl *readline) Print(out string) {
+	_, _ = os.Stdout.WriteString(out + "\n")
+}
+
+// RunREPL starts the REPL loop
+func RunREPL() {
+	repl := repl.New()
+	rl := newReadline(repl)
+	repl.SetUI(rl)
+	defer rl.Close()
+	err := rl.ReadHistory()
+	if err != nil {
+		fmt.Printf("Failed to open history: %v\n", err)
+	}
+
+	fmt.Printf("Gpython 3.4.0\n")
+
+	for {
+		line, err := rl.Prompt(rl.prompt)
+		if err != nil {
+			if err == io.EOF {
+				fmt.Printf("\n")
+				break
+			}
+			fmt.Printf("Problem reading line: %v\n", err)
+			continue
+		}
+		if line != "" {
+			rl.AppendHistory(line)
+		}
+		rl.repl.Run(line)
+	}
+}