Re: parser dilemma

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.

Best regards

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