Re: parser dilemma - Mailing list pgsql-hackers

Andrew Dunstan írta:
> Zoltan Boszormenyi wrote:
>> Martijn van Oosterhout írta:
>>> On Thu, Apr 19, 2007 at 11:19:40AM +0200, Zoltan Boszormenyi wrote:
>>>  
>>>>> The problem comes from cases like
>>>>>
>>>>>     colname coltype DEFAULT 5! GENERATED ...
>>>>>
>>>>> Since b_expr allows postfix operators, it takes one more token of
>>>>> lookahead than we have to tell if the default expression is "5!"
>>>>> or "5!GENERATED ...".
>>>>>       
>>>
>>> ISTM that as long as:
>>>
>>>  colname coltype DEFAULT (5!) GENERATED ...
>>>
>>> works I don't see why it would be a problem to require the parentheses
>>> in this case. Postfis operators are not going to be that common here I
>>> think.
>>>
>>> Have a nice day,
>>>   
>>
>> You mean like this one?
>> ------------------------------------------------------------------------
>> *** gram.y.old  2007-04-20 09:23:16.000000000 +0200
>> --- gram.y      2007-04-20 09:25:34.000000000 +0200
>> ***************
>> *** 7550,7557 ****
>>                                { $$ = (Node *) makeA_Expr(AEXPR_OP, 
>> $2, $1, $3, @2); }
>>                        | qual_Op 
>> b_expr                                        %prec Op
>>                                { $$ = (Node *) makeA_Expr(AEXPR_OP, 
>> $1, NULL, $2, @1); }
>> !                       | b_expr 
>> qual_Op                                        %prec POSTFIXOP
>> !                               { $$ = (Node *) makeA_Expr(AEXPR_OP, 
>> $2, $1, NULL, @2); }
>>                        | b_expr IS DISTINCT FROM 
>> b_expr                %prec IS
>>                                {
>>                                        $$ = (Node *) 
>> makeSimpleA_Expr(AEXPR_DISTINCT, "=", $1, $5, @2);
>> --- 7550,7557 ----
>>                                { $$ = (Node *) makeA_Expr(AEXPR_OP, 
>> $2, $1, $3, @2); }
>>                        | qual_Op 
>> b_expr                                        %prec Op
>>                                { $$ = (Node *) makeA_Expr(AEXPR_OP, 
>> $1, NULL, $2, @1); }
>> !                       | '(' b_expr qual_Op    
>> ')'                             %prec POSTFIXOP
>> !                               { $$ = (Node *) makeA_Expr(AEXPR_OP, 
>> $3, $2, NULL, @3); }
>>                        | b_expr IS DISTINCT FROM 
>> b_expr                %prec IS
>>                                {
>>                                        $$ = (Node *) 
>> makeSimpleA_Expr(AEXPR_DISTINCT, "=", $1, $5, @2);
>> ------------------------------------------------------------------------
>>
>> This change alone brings 13 reduce/reduce conflicts.
>>
>>
>
> No - that's not what you do. All you need to do is remove those 2 
> lines from the b_expr rules. The postfix rule will still be in a_expr 
> and the parenthesized bit is taken care of in the ( a_expr ) rule for 
> c_expr.
>
> cheers
>
> andrew

I just sent a new patch that marks GENERATED as %right,
which also solved the problem.

Best regards,
Zoltán

-- 
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Zoltán Böszörményi
Cybertec Geschwinde & Schönig GmbH
http://www.postgresql.at/