Implement #PN5

app/main.go

@@ -20,26 +20,76 @@ const (
 	GetCommandResultError
 )
 
-func getCommand(ctx *Context) (string, error) {
+type Command struct {
+	command_type CommandType
+	tokens       []string
+}
+
+func makeCommandNone() Command {
+	return Command{
+		command_type: CommandTypeNone,
+		tokens:       nil,
+	}
+}
+
+func makeCommand(command_type CommandType, tokens []string) Command {
+	if command_type == CommandTypeNone {
+		return Command{
+			command_type: command_type,
+			tokens:       nil,
+		}
+	} else {
+		return Command{
+			command_type: command_type,
+			tokens:       tokens,
+		}
+	}
+}
+
+type CommandType int
+
+const (
+	CommandTypeNone CommandType = iota
+	CommandTypeExternal
+	CommandTypeBuiltinExit
+)
+
+func getCommand(ctx *Context) (Command, error) {
 	fmt.Print("$ ")
 	command_line, err := bufio.NewReader(ctx.stdin).ReadString('\n')
 	if err != nil {
-		return "", err
+		return makeCommandNone(), err
 	}
-	command, err := parseCommand(ctx, command_line)
+	command, err := parseCommand(command_line)
 	if err != nil {
-		return "", err
+		fmt.Fprintln(ctx.stderr, err)
+		return makeCommandNone(), nil
 	}
 	return command, nil
 }
 
-func parseCommand(ctx *Context, command_line string) (string, error) {
-	_ = ctx
-	return command_line[:len(command_line)-1], nil
+func parseTokens(str string) []string {
+	tokens := make([]string, 2)
+	tokens[0] = str[:len(str)-1]
+	return tokens
 }
 
-func handleCommand(ctx Context, command string) {
-	fmt.Fprintln(ctx.stderr, command+": command not found")
+func parseCommand(command_line string) (Command, error) {
+	tokens := parseTokens(command_line)
+	if tokens[0] == "exit" {
+		return makeCommand(CommandTypeBuiltinExit, tokens), nil
+	}
+	return makeCommandNone(), fmt.Errorf("%s: command not found", tokens[0])
+}
+
+func handleCommand(ctx Context, command Command) {
+	_ = ctx
+	switch command.command_type {
+	case CommandTypeNone:
+		return
+	case CommandTypeBuiltinExit:
+		os.Exit(0)
+	}
 }
 
 func main() {