[antlr-interest] MySQL's YACC grammar to ANTLR: could not even do k=1 for decision

[David Maier]

Hi,


I am currently migrating the MySQL grammar from YACC to ANTLR. I am now hitting the problem to get a lot of error messages like:

" internal error: org.antlr.tool.Grammar.createLookaheadDFA(Grammar.java:1279): could not even do k=1 for decision <n>"

So I tried the following workarounds:

* Increased the timeout during the generation of the Parser's Java code: This did not solve the problem and ended up in out of memory errors
* Did set k=1, which helps to avoid the error message but introduces limitations regarding the look ahead and so causes new problems

So I think the right solution will be to remove ambiguous rules. I already began to remove 'Epsilon' rules and I can imagine that there are other ambiguous rules in the grammar as well. The problem I have is to find them easily. So the error message above contains the decision number <n>. Is it easily possible to find the rule in my grammar's source code which is related to this decision number <n>? How to do that.

Another idea would be to implement an algorithm which starts at a single token definition and creates a tree by substituting the rules back. The idea is that a rule is ambiguous if it is part of 2 different paths in this tree. So for instance:

rule1: rule2 | rule3;
rule2: TOKEN1;
rule3: rule4 | rule5;  
rule4: TOKEN1;
rule5: TOKEN2;

would result in the following tree for TOKEN1:

TOKEN1 -> rule2 -> rule1;
       -> rul4 -> rule3 -> rule1;

I am wondering if there is already such a tool available to find ambiguous rules, is there?

BTW: Future information can be found here: http://community.ingres.com/wiki/Ingres_Migration_Tool_Set_Idiom_MySQL

Advise would be highly appreciated! Thanks in advance for your help!


Regards, David


--
David Maier
Senior Software Engineer

Ingres Germany GmbH
Weimarer Straße 1a
D-98693 Ilmenau

PHONE:  +49.3677.6785-59
FAX:    +49.3677.6785-23
MAIL:   david.maier at ingres.com

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