[antlr-interest] unrelated rule causing warnings

[Sean Bridges]

'a' may match two rules, but given a start rule, isn't there always
only one way to parse 'a'?

The grammar also compiles without warning if I remove the from_clause
rule, which confuses me since from_clause does not refer to
column_reference.

Thanks,

Sean

On Wed, Jul 23, 2008 at 2:51 AM, Ian Moor <iwm at doc.ic.ac.uk> wrote:
>>Hello,
>>
>>This is a simplified version of the grammar I am working on.
>>
>>grammar Test;
>>
>>//comment out from_clause
>>//and warning in qualified_name
>>//goes away
>>from_clause
>>       :       'FROM' qualified_name ;
>>
>>column_reference
>>       :       (qualified_name PERIOD)? 'a';
>>
>>qualified_name
>>       :       ('a' PERIOD)? 'a';
>>
>>PERIOD  :       '.';
>>
>>WS
>>   : (' '|'\t'|'\n'|'\r')+ {channel=HIDDEN;};
>>
>>
>>
>>When I compile this with antlr 3 (or 3.1 beta) I get a warning for the
>>qualified_name rule,
>>
>> warning(202): Test.g:13:4: the decision cannot distinguish between
>>alternative(s) 1,2 for at least one input sequence
>>
>>If I comment out the from_clause rule, the grammar compiles without warning.
>>
>>Is my grammar ambiguous?  How does adding/removing the from_clause
>>rule change the ambiguity of the qualified_name rule?
>>
>>Thanks,
>>
>>Sean
>>
> The problem is that 'a'  is either  a column_reference or a qualified_name
>   Ian Moor
>
>