[antlr-interest] Re: SQL grammar, help on ambig warns

[lgcraymer]

Ruslan--

One likely scenario is that somewhere in your grammar you have a rule 
which follows character_string_type with "LPAREN" and ANTLR can't tell 
whether to assign an LPAREN to that or to "character_string_type" in 
the optional subrule.  You may need a syntactic predicate to 
disambiguate ...

--Loring

--- In antlr-interest at y..., Ruslan Zasukhin <sunshine at p...> wrote:
> Hi Guys,
> 
> At last of end we have found time to work on our own SQL 92 grammar.
> We can compile grammar without errors.
> Problem only with some ambig warns.
> 
> For example, I get warn
> 
> > E:\antlr272a2\OBL\OBL_SQLGrammar.g:342:23: warning: nondeterminism 
upon
> > E:\antlr272a2\OBL\OBL_SQLGrammar.g:342:23:     k==1:LPAREN
> > E:\antlr272a2\OBL\OBL_SQLGrammar.g:342:23:     between alts 1 and 
2 of block
> 
> on this rule:  (By the way, k = 1 for parser, for k = 2 the same 
problem)
> 
> --------------------------------------------------------------
> character_string_type
>     :    ( "character" | "char" )
>             (    "varying" LPAREN! unsigned_integer RPAREN!
>             |     ( LPAREN! unsigned_integer RPAREN! )?     <<<<<< 
here
>             )
>     |    ("varchar" | "string")
>             (     LPAREN! unsigned_integer
>                      (COMMA! character_string_literal)? RPAREN! )
>     ;    
> --------------------------------------------------------------
> 
> Is this rule incorrect ???
> 
> If remove ?  Then it compiles fine.
> 
> Also when I look into generated C++ Parser, for code of problematic 
line
> I see that ANTLR test on tokens from MANY MANY other rules (that 
probably
> call this one). 
> 
> I can understand why this is needed, just was surprised.
> I did think that each rule is self-contained, but it seems generated 
code
> depend on where and how a rule is called also.
> 
> 
> -- 
> Best regards,
> Ruslan Zasukhin      [ I feel the need...the need for speed ]
> -------------------------------------------------------------
> e-mail: ruslan at p...
> web: http://www.paradigmasoft.com
> 
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> -------------------------------------------------------------


 

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