[antlr-interest] Expression parser expecting token at EOF

Micheal J open.zone at virgin.net
Tue Mar 21 10:26:30 PST 2006

Hi Aaron,

> I apologize if this is the wrong forum for this message, but 
> I'm still new here (so punt me the right direction if need 
> be).  I've written a parser for what I think is a relatively 
> simple grammar for expressions.  I'm using antlr 2.7.5 with 
> C# as the language.

ANTLR 2.7.6 has been out for a while now.

> I noticed that when I provided the input "test" to the 
> expression element that it would fail when attempting to do a 
> lookahead(1).  So I narrowed the problem down to the variant 
> element that is listed in the grammer and reduced the variant 
> element to only allow one expression for ease of reading.
> I wrote a small C# wrapper around this that calls variant() 
> on the parser.
> The sample works for the inputs "test(20)" and "test[20]", 
> but fails for "test". The problem appears to be in the output 
> code to "variantAtoms" which performs a switch(LA(1)) and 
> then requires a token to be present or it throws 
> NoViableAltException and my execution is done.
> Ironically, if I enter "test)" it works.  variantAtom has a 
> case statement for RPAREN and for the life of me I can't 
> understand where in the tree it would expect to see RPAREN as 
> the next token.
> Thanks in advance...

I tried your grammar with ANTLR 2.7.6 (language=C#) and it works as

"test" => fails because variant is defined as "IDENT variantAtoms"
"test)" => fails for same reason since ")" is not matched as a

"test(20)", "test[20" => recognized.



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