[antlr-interest] Re: Parser and infinite recursion... ?

[lgcraymer]

They aren't functionally equivalent; the derivation series

logic_1 -> logic_3 -> logic_4 -> logic_1

is possible in your example 2.

--Loring

--- In antlr-interest at yahoogroups.com, "jbfraleigh" <jbfraleigh at h...>
wrote:
> Hello -- 
> 
>    I was wondering if someone might be able to explain to me why code 
> example 1 works (doesn't produce any error/warning messages) while 
> code example 2 does not work (and hopefully how to fix it).  The 
> output from code example 2 follows the code.  Note that the only 
> difference occurs in "logic_1" where I've changed the definition 
> from: "logic_2" to "logic_2 | logic_3."
> 
> --- Code Example 1:
> 
> logic_1	: logic_2 ;
> logic_2	: (LPAREN logic_3 RPAREN) ;
> logic_3	: logic_4 ((AND|OR) logic_4)* ;
> logic_4	: logic_1 | if_br ;
> 
> ========================
> 
> --- Code Example 2:
> 
> logic_1	: logic_2 | logic 3;
> logic_2	: (LPAREN logic_3 RPAREN) ;
> logic_3	: logic_4 ((AND|OR) logic_4)* ;
> logic_4	: logic_1 | if_br ;
> 
> ========================
> 
> --- Output from Example 2:
> 
> ANTLR Parser Generator   Version 2.7.2   1989-2003 jGuru.com
> xx.g:14:21: infinite recursion to rule logic_3 from rule logic_1
> xx.g:17:11: infinite recursion to rule logic_3 from rule logic_4
> xx.g:16:11: infinite recursion to rule logic_3 from rule logic_3
> xx.g:14:21: infinite recursion to rule logic_3 from rule logic_1
> xx.g:14: warning:nondeterminism between alts 1 and 2 of block upon
> xx.g:14:     k==1:LPAREN
> Exiting due to errors.
> 
> ========================
> 
> This should be functionally equivalent to the following code, which 
> does work:
> 
> Code Example 3:
> 
> logic_1	: logic_2 ;
> logic_2	: logic_3 ((AND|OR) logic_3)* ;
> logic_3	: (LPAREN logic_1 RPAREN) | if_br ;
> 
> ========================
> 
> Thanks in advance for any help.



 
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