add a nice readline experience (with history!)

go.mod

@@ -1,3 +1,5 @@
 module git.yetaga.in/alazyreader/prosper
 
 go 1.15
+
+require github.com/peterh/liner v1.2.1

go.sum

@@ -0,0 +1,4 @@
+github.com/mattn/go-runewidth v0.0.3 h1:a+kO+98RDGEfo6asOGMmpodZq4FNtnGP54yps8BzLR4=
+github.com/mattn/go-runewidth v0.0.3/go.mod h1:LwmH8dsx7+W8Uxz3IHJYH5QSwggIsqBzpuz5H//U1FU=
+github.com/peterh/liner v1.2.1 h1:O4BlKaq/LWu6VRWmol4ByWfzx6MfXc5Op5HETyIy5yg=
+github.com/peterh/liner v1.2.1/go.mod h1:CRroGNssyjTd/qIG2FyxByd2S8JEAZXBl4qUrZf8GS0=

main.go

@@ -1,12 +1,14 @@
 package main
 
 import (
-	"bufio"
 	"errors"
 	"flag"
 	"fmt"
 	"os"
+	"path/filepath"
 	"strings"
+
+	"github.com/peterh/liner"
 )
 
 type libraryFiles []string
@@ -20,10 +22,41 @@ func (l *libraryFiles) Set(value string) error {
 	return nil
 }
 
+func historyFn() string {
+	dataHome := os.Getenv("XDG_DATA_HOME")
+	home := os.Getenv("HOME")
+	if dataHome == "" {
+		dataHome = filepath.Join(home, ".local/share/")
+	}
+	prosperDir := filepath.Join(dataHome, "prosper")
+	os.MkdirAll(prosperDir, 0755)
+	return filepath.Join(prosperDir, ".history")
+}
+
+func completer(d Dictionary) liner.Completer {
+	return func(line string) []string {
+		candidates := []string{}
+		words := strings.Split(line, " ")
+		for w := range d {
+			if strings.HasPrefix(w, words[len(words)-1]) {
+				// must reconstruct the _full_ line to return for the completer
+				pref := strings.Join(words[:len(words)-1], " ")
+				if len(pref) != 0 {
+					candidates = append(candidates, pref+" "+w)
+				} else {
+					candidates = append(candidates, w)
+				}
+			}
+		}
+		return candidates
+	}
+}
+
 func main() {
 	// flag setup
 	var libs libraryFiles
 	flag.Var(&libs, "l", "propser library file (may be repeated)")
+	debug := flag.Bool("debug", false, "output debugging information")
 	flag.Parse()
 
 	// create main context
@@ -64,27 +97,60 @@ func main() {
 		}
 	}
 
-	reader := bufio.NewReader(os.Stdin)
+	// set up liner
+	line := liner.NewLiner()
+	line.SetCtrlCAborts(true)
+	line.SetCompleter(completer(dict))
+
+	historyFile := historyFn()
+
+	if f, err := os.Open(historyFile); err == nil {
+		_, err := line.ReadHistory(f)
+		if err != nil && *debug {
+			fmt.Printf("error reading line history: %v", err)
+		}
+		f.Close()
+	}
+
+	defer func() {
+		if f, err := os.Create(historyFile); err != nil {
+			if *debug {
+				fmt.Printf("Error writing history file: %v", err)
+			}
+		} else {
+			line.WriteHistory(f)
+			f.Close()
+		}
+		line.Close()
+	}()
+
+	// Welcome banner
 	fmt.Print("prosper\n")
 
 	// read loop
 	for {
-		if c.Flags["Immediate"] {
+		p := "> "
-			fmt.Print("> ")
+		if !c.Flags["Immediate"] {
-		} else {
+			p = "    "
-			fmt.Print("    ")
 		}
 
-		line, err := reader.ReadString('\n')
+		// read line
-		if err != nil {
+		l, err := line.Prompt(p)
+		if err == liner.ErrPromptAborted {
+			fmt.Println("ctrl-C caught (try BYE)")
+			continue
+		} else if err != nil {
 			fmt.Println(err.Error())
 			os.Exit(1)
 		}
-		line = strings.TrimSpace(line)
+
-		err = c.Eval(line + " ") // append a space to make sure we always close out our parse loop
+		// parse line
+		l = strings.TrimSpace(l)
+		line.AppendHistory(l)
+		err = c.Eval(l + " ") // append a space to make sure we always close out our parse loop
 		if errors.Is(err, ErrExit) {
 			fmt.Printf("bye\n")
-			os.Exit(0)
+			break
 		} else if err != nil {
 			fmt.Printf("error in evaluation: %v\n", err)
 		} else if c.Flags["Immediate"] {