From e141f7da4832580aed8c238197e06f6d00737615 Mon Sep 17 00:00:00 2001
From: Marc Vertes <mvertes@free.fr>
Date: Fri, 8 Sep 2023 11:42:44 +0200
Subject: cli: use flags in command line

Also isolate repl in a separate function.
Introduce `run` function for executing programs, letting room for
other verbs to be done later: test, debug, ...
Use file path as argument. Standard input redirect is no more mandatory.
---
 main.go | 109 +++++++++++++++++++++++++++++++++++++++++++---------------------
 1 file changed, 73 insertions(+), 36 deletions(-)

diff --git a/main.go b/main.go
index 037614c..4ae57da 100644
--- a/main.go
+++ b/main.go
@@ -3,6 +3,7 @@ package main
 import (
 	"bufio"
 	"errors"
+	"flag"
 	"fmt"
 	"io"
 	"log"
@@ -20,42 +21,7 @@ type Interpreter interface {
 
 func main() {
 	log.SetFlags(log.Lshortfile)
-	var interp Interpreter = vm0.New(golang.GoParser)
-	if len(os.Args) > 1 && os.Args[1] == "1" {
-		interp = codegen.NewInterpreter(golang.GoParser)
-		interp.(*codegen.Interpreter).AddSym(fmt.Println, "println")
-	}
-	in := os.Stdin
-
-	if isatty(in) {
-		// Provide an interactive line oriented Read Eval Print Loop (REPL).
-		liner := bufio.NewScanner(in)
-		text, prompt := "", "> "
-		fmt.Print(prompt)
-		for liner.Scan() {
-			text += liner.Text()
-			res, err := interp.Eval(text + "\n")
-			if err == nil {
-				if res != nil {
-					fmt.Println(": ", res)
-				}
-				text, prompt = "", "> "
-			} else if errors.Is(err, scanner.ErrBlock) {
-				prompt = ">> "
-			} else {
-				fmt.Println("Error:", err)
-				text, prompt = "", "> "
-			}
-			fmt.Print(prompt)
-		}
-		return
-	}
-
-	buf, err := io.ReadAll(in)
-	if err != nil {
-		log.Fatal(err)
-	}
-	if _, err := interp.Eval(string(buf)); err != nil {
+	if err := run(os.Args[1:]); err != nil {
 		log.Fatal(err)
 	}
 }
@@ -69,3 +35,74 @@ func isatty(in io.Reader) bool {
 	stat, err := s.Stat()
 	return err == nil && stat.Mode()&os.ModeCharDevice != 0
 }
+
+// repl executes an interactive line oriented Read Eval Print Loop (REPL).
+func repl(interp Interpreter, in io.Reader) (err error) {
+	liner := bufio.NewScanner(in)
+	text, prompt := "", "> "
+	fmt.Print(prompt)
+	for liner.Scan() {
+		text += liner.Text()
+		res, err := interp.Eval(text + "\n")
+		if err == nil {
+			if res != nil {
+				fmt.Println(": ", res)
+			}
+			text, prompt = "", "> "
+		} else if errors.Is(err, scanner.ErrBlock) {
+			prompt = ">> "
+		} else {
+			fmt.Println("Error:", err)
+			text, prompt = "", "> "
+		}
+		fmt.Print(prompt)
+	}
+	return
+}
+
+func run(arg []string) (err error) {
+	var i int
+
+	rflag := flag.NewFlagSet("run", flag.ContinueOnError)
+	rflag.IntVar(&i, "i", 1, "set interpreter version for execution, possible values: 0, 1")
+	rflag.Usage = func() {
+		fmt.Println("Usage: parscan run [options] [path] [args]")
+		fmt.Println("Options:")
+		rflag.PrintDefaults()
+	}
+	if err = rflag.Parse(arg); err != nil {
+		return err
+	}
+	args := rflag.Args()
+
+	var interp Interpreter
+	switch i {
+	case 0:
+		interp = vm0.New(golang.GoParser)
+	case 1:
+		interp = codegen.NewInterpreter(golang.GoParser)
+		interp.(*codegen.Interpreter).AddSym(fmt.Println, "println")
+	default:
+		return fmt.Errorf("invalid interpreter version: %v", i)
+	}
+
+	log.Println("args:", args)
+	in := os.Stdin
+	if len(args) > 0 {
+		if in, err = os.Open(arg[0]); err != nil {
+			return err
+		}
+		defer in.Close()
+	}
+
+	if isatty(in) {
+		return repl(interp, in)
+	}
+
+	buf, err := io.ReadAll(in)
+	if err != nil {
+		return err
+	}
+	_, err = interp.Eval(string(buf))
+	return err
+}
-- 
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