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Date: Thu, 5 Apr 2007 17:37:47 +0300
From: "Janne Hellsten" <jjhellst@gmail.com>
To: caml-list@inria.fr
Subject: Matching start of input in lexer created with ocamllex
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Hi,

I'd like to match the beginning of input (or beginning of line) in my
lexer.  Is there an easy way to do that?

I have a lexer that looks something like this (simplified):

rule initial = parse
  | '!' [' ' '\t']* "for" { FOR (current_loc ()) }
  | ident as id { IDENT (id, current_loc ()) }
  | '!' { BANG (current_loc ()) }

The !for token should only be matched at the beginning of a
line/input.  However, in the above lexer, there's nothing that
prevents !for from being matched in the middle of an input string.
This causes a problem: An input string containing !forbidXyz will be
lexed FOR, IDENT "bidXyz".  I'd like to lex it as BANG, IDENT
"forbidXyz".

Thank you for your help!

Janne