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
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D-98693 Ilmenau
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