[antlr-interest] about parse key words

[David-Sarah Hopwood]

Renee Luo wrote:
> Hi there,
> 
> I have a problem with parse key words.  Like in PL/SQL "EXIT"  is key word.
> But some variable names also include this key word.

This is quite a common requirement. The approach I use is to declare a
keyword rule that has all keyword tokens as alternatives, and then make
the identifier rule explicitly allow either a keyword or a
non-keyword-identifier:

  DECLARE : 'DECLARE' ;
  BEGIN   : 'BEGIN' ;
  ...
  keyword : DECLARE | BEGIN | ... ;

  NonKeywordIdentifier : IdentifierStart IdentifierContinue* ;

  identifier : NonKeywordIdentifier | keyword ;

Note that this may result in grammar ambiguities unless the language has
been very carefully designed to avoid them. Some of these ambiguities might
have to be resolved using predicates.

-- 
David-Sarah Hopwood  ⚥  http://davidsarah.livejournal.com

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