[antlr-interest] NoViableAlException

[Fabian Haupt]

My first attempt was to use regexps in perl,
but the error messages don't have enough structure, (and I was too lazy 
to write all those regexps..)

Since I've had a very good experience with antlr some years ago, I 
thought I'll use that, then I'll get the ast for free ;)

I have refactored my grammar and am currently in the process of 
eliminating prefixes in the tokens. (by hand .. is there a tool for that??)

Never heard of jflex, sound interesting, though *read* ;)

Thanks
Fabian

On 11/13/2010 03:55 PM, Joachim Schrod wrote:
> Jim Idle wrote:
>
>> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
>> bounces at antlr.org] On Behalf Of Joachim Schrod
>>>
>>> Fabian Haupt wrote:
>>>>
>>>> I'm getting a NoViableAltException: line 1:55 no viable alternative
>>> at
>>>> input '.[CheckIntegrity'
>>>>
>>>> with the input of
>>>> 'The lower level block specifies a right link block of 0.
>>>> [CheckIntegrity+343^%SYS.DATABASE:%SYS]'
>>>> starting with the 'test' rule.
>>>>
>>>>
>>>> this is the grammar:
>>>> ----------------------------
>>>> grammar integrit;
>>>>
>>>> options {
>>>>     language= Java;
>>>> }
>>>>
>>>>
>>>> test:'The lower level block specifies a right link block of '+INT+'.'
>>>> WS debugnote NEWLINE;
>>>>
>>>> firstNodePtrWrong: INT+'. We were expecting it to point to ';
>>>>
>>>>
>>>> debugnote:'['+ID+'+'+INT+'^%SYS.DATABASE:%SYS'+']';
>>>>
>>>> ID  :   ('a'..'z'|'A'..'Z')+ ;
>>>> INT :   '0'..'9'+ ;
>>>> NEWLINE:('\r'? '\n');
>>>> WS  :   (' '|'\t')+ {skip();} ;
>>>
>>> Without running it --
>>> You demand a WS in the test rule that will never appear there as you
>>> skip that token. Don't you mean NEWLINE there?
>>
>> This is correct, you are asking for WS that will be skipped, but also, hard
>> coding the specific message is so long will get you in to trouble I think.
>> You are probably better off with awk for something like this I think.
>
> If Fabian's error messages are basically just regexps, probably.
> But if the information structure is context free, ANTLR is a very
> good bet.
>
> I'm currently using ANTLR to extract data from invoice texts in PDF
> files and to assure that I detect all information and that the
> expected invoice structure is complete and hasn't changed. This is
> very hard to do with regexps, but has the same base problem as
> Fabian: Lots of long constant text strings that serve basically as
> keywords and mark `places' in that PDF document. ANTLR is a great
> tool to accomplish structure checking, with it's parser generation
> facilities. If the lexical input is highly unstructured, it's a bit
> of a pain in the back, but can be handled. (I ran into similar
> lexer problem as Fabian. Eventually, I resolved them by using
> jflex. ;-))
>
> Cheers,
> 	Joachim
>