Re: very specific question on Ada syntax

[Robert Dewar <robert_dewar@my-deja.com>]

In article <9573th$isv$1@nnrp1.deja.com>,
  Ted Dennison <dennison@telepath.com> wrote:
> To the best of my knowledge, flex has no "last token"
> function in its API. It can do *character* context, but not
> token context. Thus to properly handle this situation with
> lex, you'd have to hack it in manually with inserted C code
> (most likely by passing info back from the parser).

That's not the way I would do it at all. I would do it the
same way that the GNAT lexer does things, which is to keep
a global variable which remembers the previous token. That's
useful for posting error messages anyway.

There is absolutely NO problem in coding this in lex, remember
that in lex, the whole idea is that each recognized token
causes the execution of "inserted C code", this C code is
not a hack, it is the essence of how flex works. I definitely
would NOT do it by passing information back from the parser.

See scans.ads and the entry to scn.adb in the GNAT sources
for details on how this is done in GNAT. The issue of whether
the lexer is written by hand or generated by flex is quite
irrelevant in considering how to handle this situation.


>
> I just checked the Ada95 lex spec available from the AdaIC
site
> (http://www.adaic.org/standards/95lrm_rat/lexer9x.l
> ). It indeed contains no context information in the token
definitions,
> and thus should have the same problem. The relevent entries
are:
> -------------------------------------------
> "'"                     return(TIC);
> "'"."'"                 return(char_lit);
> -------------------------------------------
>
> --
> T.E.D.
>
> http://www.telepath.com/~dennison/Ted/TED.html
>
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