[antlr-interest] Tokens as keywords

[Jim Idle]

Whether you need the predicate depends on the presence of optional identifiers that can be keywords. You need the predicate to avoid a warning saying that the upcoming keyword is ambiguous and assuming that the language expects it to be resolved this way. Consider something like:

xxxx id? ONLY?

id
 : Identifier
 | ONLY  -> Identifier[ONLY]
 ;

The original example just shows the mechanism and we cannot say where the predicates might be needed without the whole grammar.

Jim

> -----Original Message-----
> From: Johannes Luber [mailto:jaluber at gmx.de]
> Sent: Sunday, May 04, 2008 7:35 AM
> To: Jim Idle
> Cc: antlr-interest at antlr.org
> Subject: Re: [antlr-interest] Tokens as keywords
> 
> Jim Idle schrieb:
> > statement :  FIND tableName whereClause? orderByClause?;
> >
> > tableName
> >    : Identifier
> >    | (keywords)=>keywords
> >    ;
> 
> Just one additional comment: Order alternatives in such way that the
> last alternative is the one without a syntactic predicate. Thinking
> about it further, as one would order the lexer rules in such way that
> the keywords are recognized as such, no Identifier will match a keyword
> anyway. So you can remove that predicate anyway.
> 
> Johannes