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From: Jacques Le Normand <rathereasy@gmail.com>
To: caml-list@inria.fr
Content-Type: text/plain; charset=ISO-8859-1
Subject: [Caml-list] lexer errors

How can I get some decent lexer error reporting?

Here's my program:


{
  open Lexing
}

rule lex = parse
  | "foo" {()}
  | "\n" {lex lexbuf}

{
  let main () =
    let lexbuf = from_channel stdin in
      try
	let rec loop () =
	  let x = lex lexbuf in
	    loop x
	in
	  loop ()
      with
	| _ ->
	    let x = lexbuf.Lexing.lex_curr_p in
	      Printf.printf
		"line %d, character %d\n"
		x.pos_lnum (x.pos_cnum - x.pos_bol)

  let _ = main ()
}

running:

	ocamlc -I ~/ocaml/ ~/ocaml/test_lexer2.ml -o ~/ocaml/test.o
	echo foo > ~/temp.txt
	echo bar >> ~/temp.txt
	~/ocaml/test.o < ~/temp.txt

outputs the incorrect line:

       line 1, character 4

(Should be line 2, character 1)