[antlr-interest] Continue parsing after an error

[Gordon Tyler]

The grammar you have defined says, roughly:

Parse any number of '[' or ']' until you reach EOF.

It does not describe what to do if something other than '[' or ']' are found before EOF is found.

You have defined a token, OTHER, to match the other stuff, but your parse rules do not reference OTHER. Perhaps something like this would work:

root : (expressions | OTHER)* EOF -> ^(ROOT_TOKEN expressions) ;



-----Original Message-----
From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-bounces at antlr.org] On Behalf Of Luchesar Cekov
Sent: June 30, 2010 10:10 AM
To: antlr-interest at antlr.org
Cc: Valerio Malenchino
Subject: [antlr-interest] Continue parsing after an error

Dear ANTLR enthusiasts,

I am struggling with a problem. The parser jumps to the end of file from 
the middle of the document.

The setup is as follow:
    * I have two alternatives flowed by EOF
    * during parse time in the middle of the document next token can not 
match either alternatives start

This leads to parsing termination because the parser jumps to the EndOfFile.

A simple grammar the illustrates the problem is

===============
tokens {ROOT_TOKEN;}
root
    : expressions EOF -> ^(ROOT_TOKEN expressions) ;
expressions : ('[' | ']')* ;
OTHER   : . ;
===============

If then I try parsing "[[][]]sdsdf[]][]][" the parsing will stop and the 
first "s" and will try to recover as if the EOF was the next token.
When looking at the generated Parser it looks like if there is no viable 
alternative in the top rule in this case "root" the parser will behave 
as if it reached the EOF and will skip the rest of the tokens.

The result AST will contain only children up until the first illegal 
token "s".

I cannot see where my mistake is. It looks like the parser should not do 
that. Can you suggest a workaround for the problem?

Thanks in advance,
Luchesar
-- 

Luchesar Cekov
Software Engineer
+44 (0) 207 239 4949
*Ontology Systems*
www.ontology.com <http://www.ontology.com/>

	

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