Very naive REPL

repl/command.go

@@ -0,0 +1,42 @@
+package repl
+
+import (
+	"fmt"
+	"os"
+)
+
+var (
+	helpCmd = Command{
+		Name:  ".help",
+		Usage: " type `.help` for help",
+		Action: func(r *REPL, args []string) error {
+			for _, cmd := range r.Commands {
+				fmt.Printf("%-20s\t%s\n", cmd.Name, cmd.Usage)
+			}
+
+			return nil
+		},
+	}
+	clearCmd = Command{
+		Name:  ".clear",
+		Usage: " type `.clear` to clear the screen",
+		Action: func(r *REPL, args []string) error {
+			_, _ = os.Stdout.Write([]byte("\033[2J\033[H"))
+			return nil
+		},
+	}
+	exitCmd = Command{
+		Name:  ".exit",
+		Usage: " type `.exit` to exit this REPL",
+		Action: func(r *REPL, args []string) error {
+			os.Exit(0)
+			return nil
+		},
+	}
+)
+
+type Command struct {
+	Name   string
+	Usage  string
+	Action func(r *REPL, args []string) error
+}

repl/input.go

@@ -0,0 +1,9 @@
+package repl
+
+import (
+	"strings"
+)
+
+func parseInput(args string) []string {
+	return strings.Split(args, " ")
+}

repl/repl.go

@@ -0,0 +1,54 @@
+// Package repl Basic UI for the user
+package repl
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+var DefaultCfg = REPLCfg{
+	PS1: "\r> ",
+}
+
+type REPLCfg struct {
+	PS1 string
+}
+
+type REPL struct {
+	Cfg      REPLCfg
+	Commands map[string]Command
+}
+
+func NewREPL(cfg REPLCfg) *REPL {
+	return &REPL{
+		Cfg: cfg,
+		Commands: map[string]Command{
+			helpCmd.Name:  helpCmd,
+			clearCmd.Name: clearCmd,
+			exitCmd.Name:  exitCmd,
+		},
+	}
+}
+
+func (r *REPL) printPrompt() {
+	_, _ = os.Stdout.Write([]byte(r.Cfg.PS1))
+}
+
+func (r *REPL) Start() {
+	reader := bufio.NewScanner(os.Stdin)
+	r.printPrompt()
+	for reader.Scan() {
+		input := reader.Text()
+		args := parseInput(input)
+
+		command, exists := r.Commands[args[0]]
+		if exists {
+			_ = command.Action(r, args[1:])
+		} else {
+			fmt.Printf("No such command `%s`\n", args[0])
+		}
+
+		r.printPrompt()
+	}
+}