Re: is lex useful? (Tyson Richard DOWD)
5 Jul 1996 11:48:25 -0400

          From comp.compilers

Related articles
[22 earlier articles]
Re: is lex useful? (1996-06-30)
Re: is lex useful? (1996-06-30)
Re: is lex useful? (1996-07-01)
Re: is lex useful? (1996-07-02)
Re: is lex useful? (1996-07-02)
Re: is lex useful? (1996-07-04)
Re: is lex useful? (1996-07-05)
| List of all articles for this month |

From: (Tyson Richard DOWD)
Newsgroups: comp.compilers
Date: 5 Jul 1996 11:48:25 -0400
Organization: Comp Sci, University of Melbourne
References: 96-06-101 96-06-118 96-06-123 96-06-141
Keywords: lex

>[For the double underscore thing, whether in C or lex, I'd recognize
>identifiers as a string of letters, digits, and underscores, then look for
>a double underscore and if I found one, produce a helpful "this language
>doesn't permit double underscores in your identifiers" message rather than
>a generic and mysterious "syntax error". -John]

This is a good idea, although I think in this case it is not likely to
be a syntax error, but have a different meaning altogether such as a
scope qualifier or something (its pretty arbitrary to say 'oh, we just don't
support __ because the people writing the parser wanted a challenge').

So there would be another pattern that matches on identifiers with __
and uses that for something else (or just an identifier + __ + identifer
in the parser, not the lexer). If you were doing it in C, you'd see the
second _, and know that you had seen the end of one token and the __ token
follows (so do a ungetc or something -- depends how you've buffered input).

That's just a guess anyway, what was the reason why '__' wasn't allowed in
identifiers anyway?

              Tyson Dowd

Post a followup to this message

Return to the comp.compilers page.
Search the comp.compilers archives again.