global and local variables with scope

also reworked arg parsing, now has --debug flag

bin/main.ml

@@ -1,19 +1,27 @@
-let printUsage () =
-  print_endline "Usage: jlox [script]";
-  exit 64
+type args = { debug : bool; file_name : string option }
+
+let parse_args () : args =
+  let usage_msg = "mlox [--debug] [<file>]" in
+  let debug = ref false in
+  let anon = ref [] in
+  let anon_fun s = anon := s :: !anon in
+  let spec = [ ("--debug", Arg.Set debug, "Debug mode") ] in
+  let () = Arg.parse spec anon_fun usage_msg in
+  let debug = !debug in
+  let file_and_args = List.rev !anon in
+  let file_name = List.nth_opt file_and_args 0 in
+  { debug; file_name }
 
 let () =
-  let argc = Array.length Sys.argv in
-  match argc - 1 with
-  | 0 -> Lox.runRepl ()
-  | 1 -> (
-      let path = Sys.argv.(1) in
+  let { debug; file_name } = parse_args () in
+  match file_name with
+  | None -> Lox.runRepl ~debug ()
+  | Some file_name -> (
       (* Printf.printf "Running script %s\n" path; *)
-      let ic = open_in path in
+      let ic = open_in file_name in
       let source = In_channel.input_all ic in
-      match Lox.run source with
+      match Lox.run ~debug source with
       | Error e ->
           Lox.Error.print_error e;
           exit 1
       | Ok () -> exit 0)
-  | _ -> printUsage ()