[antlr-interest] Why is ANTLR getting lost?

[Jon Schewe]

shmuel siegel wrote:
> Jon Schewe wrote:
>> I've figured out that ANTLR is dying in the DFA when it's trying to
>> determine which branch of the constraintDecl rule to follow. 
>> Attached is the grammar, suggestions on how to resolve this are very
>> welcome.
>>
>> Test case is here:
>>  /**
>>   * @throws RecognitionException
>>   */
>>  @Test
>>  public void testConstraintDecl0() throws RecognitionException {
>>    final String data = "constraint3: 5.0 <= 6 + 6 * a[1 + 3] * c - 1
>> <= 10.0;";
>>
>>    final GHOCESLexer lexer = new GHOCESLexer(new
>> ANTLRStringStream(data));
>>    final CommonTokenStream tokens = new CommonTokenStream(lexer);
>>    final GHOCESParser parser = new GHOCESParser(tokens);
>>    final GHOCESParser.constraintDecl_return r = parser.constraintDecl();
>>    Assert.assertNotNull(r);
>>  }
>>
> I can't tell you why but I can tell you that the dfa predictor is
> failing on
>        (addExpr[true] EQ) => addExpr[true] EQ addExpr[false]
>      | (number LE addExpr[true] LE) => lb=number LE addExpr[false] LE
> ub=number
>      | (addExpr[true] LE) => ae+=addExpr[true] LE ae+=addExpr[false]
>
> Note that the second alternative satisfies the conditions of the
> condition of the third alternative. If you eliminate the third
> alternative, the rule works. The rule also works if you change the
> third alternative to be different then the second, say by adding LE
> before addExpr. I suspect that something is wrong with the dfa predictor.
>
I need both alternatives to do the tree rewrite correctly.  I removed
the extra sytantatic predicate on the third alternative, but that didn't
help. 

-- 
Jon Schewe | http://mtu.net/~jpschewe
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