[antlr-interest] Token Mismatch

[Brisard, Fred D]

Thanks Matt,

 

I better go reread that section.  

 

Fred Brisard 



________________________________

From: Matt Palmer [mailto:mattpalms at gmail.com] 
Sent: Thursday, July 24, 2008 4:02 PM
To: Brisard, Fred D
Cc: antlr-interest at antlr.org
Subject: Re: [antlr-interest] Token Mismatch

 

Hi Fred,

I am also a novice, but I have a copy of the antlr reference to hand,
and this situation is mentioned.  The suggestion is to use semantic
predicates to resolve whether the rule is an ID or a keyword.

e.g.

r : keyCALL ID ';' {System.out.println("invoke "+$ID.text);} ;

keyCALL : {input.LT(1).getText().equals("call")}? ID ;

ID: 'a'..'z'+ ;

WS: (' '|'\n'|'\r')+ {$channel=HIDDEN;} ;


The idea is that the keyCALL rule is also just an ID token (so both
match as IDs), but with a semantic predicate that only matches if the
text is explicitly "call".  Note: I haven't tested this grammar - I just
modified the example in the book to match your example.

Regards,

Matt Palmer.

On Thu, Jul 24, 2008 at 6:33 PM, Brisard, Fred D <Fred.Brisard at ca.com>
wrote:

I'm sure this is a novice question but I can't seem to find an answer
that I feel comfortable with.

It seems like any literal specified in the parser rules becomes an
implied token.

Using the basic example T.g -

grammar T;

/** Match things like "call foo;" */

r : 'call' ID ';' {System.out.println("invoke "+$ID.text);} ;

ID: 'a'..'z'+ ;

WS: (' '|'\n'|'\r')+ {$channel=HIDDEN;} ;

I get a MismatchedTokenException I run this in the ANTLRWorks debugger
for the input

call call;

I would like the second call to be identified as a token of type ID.

Any help is appreciated

 

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