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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: lexical ambiguity
Newsgroups: comp.lang.ada
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Date: Wed, 7 Jun 2006 11:02:51 +0200
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Date: 2006-06-07T11:02:41+02:00
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On 06 Jun 2006 13:38:06 +0200, M E Leypold wrote:

> Georg Bauhaus <bauhaus@futureapps.de> writes:
> 
>> On Mon, 2006-06-05 at 22:11 +0000, Jeffrey R. Carter wrote:
>>> Keith Thompson wrote:
>>> > 
>>> > If I recall correctly, it's sufficient to remember what the previous
>>> > token was.  A character literal cannot follow an identifier.
>>> 
>>> Right, so it must be either an attribute, a qualified expression, or an 
>>> error. 
>> 
>> Though the previous token shouldn't be a reserved word, as in
>> 
>>  if'('="-"("="('='=',',','=','))
> 
> Or 
> 
>    return'a'; 
> 
> So now (question to all): Is the following rule enough?
> 
>    - "'" is the beginning of a character literal if the token before
>      "'" has not been an identifier (reserved words not counted as
>      identifier in this case).

It does not differ from the case of +/-. In the infix context, i.e. after
an operand (whatever it might be), ' is an infix operation as well as +/-.
In the prefix context, where an operand is expected ' introduces a
character literal (=operand), +/- do an unary prefix operation.

Your rule is wrong: 'A' and 'B'. "and" is a reserved word. Then of course
"..." comments should be parsed before. Which gives you a nice vicious
circle around ' " ' and " ' ". (:-))

The bottom line: parsing has state.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de