Re: binary operators on integers - Mailing list pgsql-patches

Marko Kreen <marko@l-t.ee> writes:
> I can still reproduce it:
> marko=# SELECT 5 & ~6;
> ERROR:  Unable to identify a right operator '&' for type 'int4'
>         You may need to add parentheses or an explicit cast

Correct, we did not rejigger the operator precedence.

I played around with this a little bit, and find that the attached patch
makes the above case work as desired --- essentially, it changes things
so that
    a_expr Op Op a_expr
will be parsed as
    a_expr Op (Op a_expr)
not
    (a_expr Op) Op a_expr
which is what you get now because Op is marked left-associative.

Now, this is a situation where we can't fix one case without breaking
another, namely the case where you really DID want the first Op to be
parsed as a postfix operator.  Thus the problem moves over to here:

regression=# select 4! ~ 10;
ERROR:  Unable to identify an operator '!' for types 'int4' and 'int4'
        You will have to retype this query using an explicit cast
regression=# select (4!) ~ 10;
 ?column?
----------
 f
(1 row)

whereas this worked without parens in 7.0.

Given the infrequency of use of postfix operators compared to prefix,
I am inclined to think that we should change the grammar to make the
latter easier to use at the expense of the former.  On the other hand,
it seems there's a pretty large risk of backwards-incompatibility here.
Comments?

BTW, the regress tests do not break, so they contain no examples where
it makes a difference.

            regards, tom lane


*** src/backend/parser/gram.y.orig    Sat Jan 20 12:37:52 2001
--- src/backend/parser/gram.y    Sat Jan 20 13:03:17 2001
***************
*** 383,388 ****
--- 383,389 ----
  %nonassoc    OVERLAPS
  %nonassoc    BETWEEN
  %nonassoc    IN
+ %left        POSTFIXOP        /* dummy for postfix Op rules */
  %left        Op                /* multi-character ops and user-defined operators */
  %nonassoc    NOTNULL
  %nonassoc    ISNULL
***************
*** 4312,4320 ****
                  {    $$ = makeA_Expr(OP, "+", NULL, $2); }
          | '-' a_expr                    %prec UMINUS
                  {    $$ = doNegate($2); }
!         | '%' a_expr
                  {    $$ = makeA_Expr(OP, "%", NULL, $2); }
!         | '^' a_expr
                  {    $$ = makeA_Expr(OP, "^", NULL, $2); }
          | a_expr '%'
                  {    $$ = makeA_Expr(OP, "%", $1, NULL); }
--- 4313,4321 ----
                  {    $$ = makeA_Expr(OP, "+", NULL, $2); }
          | '-' a_expr                    %prec UMINUS
                  {    $$ = doNegate($2); }
!         | '%' a_expr                    %prec UMINUS
                  {    $$ = makeA_Expr(OP, "%", NULL, $2); }
!         | '^' a_expr                    %prec UMINUS
                  {    $$ = makeA_Expr(OP, "^", NULL, $2); }
          | a_expr '%'
                  {    $$ = makeA_Expr(OP, "%", $1, NULL); }
***************
*** 4353,4361 ****

          | a_expr Op a_expr
                  {    $$ = makeA_Expr(OP, $2, $1, $3); }
!         | Op a_expr
                  {    $$ = makeA_Expr(OP, $1, NULL, $2); }
!         | a_expr Op
                  {    $$ = makeA_Expr(OP, $2, $1, NULL); }

          | a_expr AND a_expr
--- 4354,4362 ----

          | a_expr Op a_expr
                  {    $$ = makeA_Expr(OP, $2, $1, $3); }
!         | Op a_expr                    %prec UMINUS
                  {    $$ = makeA_Expr(OP, $1, NULL, $2); }
!         | a_expr Op                    %prec POSTFIXOP
                  {    $$ = makeA_Expr(OP, $2, $1, NULL); }

          | a_expr AND a_expr
***************
*** 4560,4568 ****
                  {    $$ = makeA_Expr(OP, "+", NULL, $2); }
          | '-' b_expr                    %prec UMINUS
                  {    $$ = doNegate($2); }
!         | '%' b_expr
                  {    $$ = makeA_Expr(OP, "%", NULL, $2); }
!         | '^' b_expr
                  {    $$ = makeA_Expr(OP, "^", NULL, $2); }
          | b_expr '%'
                  {    $$ = makeA_Expr(OP, "%", $1, NULL); }
--- 4561,4569 ----
                  {    $$ = makeA_Expr(OP, "+", NULL, $2); }
          | '-' b_expr                    %prec UMINUS
                  {    $$ = doNegate($2); }
!         | '%' b_expr                    %prec UMINUS
                  {    $$ = makeA_Expr(OP, "%", NULL, $2); }
!         | '^' b_expr                    %prec UMINUS
                  {    $$ = makeA_Expr(OP, "^", NULL, $2); }
          | b_expr '%'
                  {    $$ = makeA_Expr(OP, "%", $1, NULL); }
***************
*** 4589,4597 ****

          | b_expr Op b_expr
                  {    $$ = makeA_Expr(OP, $2, $1, $3); }
!         | Op b_expr
                  {    $$ = makeA_Expr(OP, $1, NULL, $2); }
!         | b_expr Op
                  {    $$ = makeA_Expr(OP, $2, $1, NULL); }
          ;

--- 4590,4598 ----

          | b_expr Op b_expr
                  {    $$ = makeA_Expr(OP, $2, $1, $3); }
!         | Op b_expr                    %prec UMINUS
                  {    $$ = makeA_Expr(OP, $1, NULL, $2); }
!         | b_expr Op                    %prec POSTFIXOP
                  {    $$ = makeA_Expr(OP, $2, $1, NULL); }
          ;