Hello!

   I ran the query
update producers SET cor_id = producer_id % 9 + 1;

   and found that result is eqiuvalent to
update producers SET cor_id = producer_id % 9;

   I added parens:
update producers SET cor_id = (producer_id % 9) + 1;

   and got what I needed.

   Is it a bug, a feature, or I just misinterpreted the syntax?

Oleg.
---- 
    Oleg Broytmann     http://members.xoom.com/phd2/     phd2@earthling.net
           Programmers don't die, they just GOSUB without RETURN.


Wed, 17 Mar 1999 11:49:55 +0300 (MSK)
Oleg Broytmann <phd@sun.med.ru>
Modulo syntax
> Hello!
> 
>    I ran the query
> update producers SET cor_id = producer_id % 9 + 1;
> 
>    and found that result is eqiuvalent to
> update producers SET cor_id = producer_id % 9;
> 
>    I added parens:
> update producers SET cor_id = (producer_id % 9) + 1;
> 
>    and got what I needed.

Looks like a bug.  We have associativity for +, -, * and /, but not %.
>From gram.y:

	%left       '+' '-'
	%left       '*' '/'

I will add '%' to that.

-- 
  Bruce Momjian                        |  http://www.op.net/~candle
  maillist@candle.pha.pa.us            |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

Wed, 17 Mar 1999 11:21:41 -0500 (EST)
Bruce Momjian <maillist@candle.pha.pa.us>
Re: [HACKERS] Modulo syntax
Fixed now.

> Hello!
> 
>    I ran the query
> update producers SET cor_id = producer_id % 9 + 1;
> 
>    and found that result is eqiuvalent to
> update producers SET cor_id = producer_id % 9;
> 
>    I added parens:
> update producers SET cor_id = (producer_id % 9) + 1;
> 
>    and got what I needed.
> 
>    Is it a bug, a feature, or I just misinterpreted the syntax?
> 
> Oleg.
> ---- 
>     Oleg Broytmann     http://members.xoom.com/phd2/     phd2@earthling.net
>            Programmers don't die, they just GOSUB without RETURN.
> 
> 
> 


-- 
  Bruce Momjian                        |  http://www.op.net/~candle
  maillist@candle.pha.pa.us            |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

Wed, 17 Mar 1999 17:01:56 -0500 (EST)
Bruce Momjian <maillist@candle.pha.pa.us>
Re: [HACKERS] Modulo syntax
> >    I ran the query
> > update producers SET cor_id = producer_id % 9 + 1;
> >    and found that result is eqiuvalent to
> > update producers SET cor_id = producer_id % 9;
> >    I added parens:
> > update producers SET cor_id = (producer_id % 9) + 1;
> >    and got what I needed.
> Looks like a bug.  We have associativity for +, -, * and /, but not %.
> From gram.y:
>         %left       '+' '-'
>         %left       '*' '/'
> I will add '%' to that.

This will not fix the associativity problem, unless you *also* go
through and add the explicit syntax *throughout* gram.y, as is
currently done for '+', '-', etc.

I'm pretty sure that we don't want to do this, since there are way too
many other operators which would need the same treatment.

The correct solution will be to identify the operator as a particular
class in scan.l, include that class in the associativity declarations,
and then handle that class in the body of gram.y. Sort of like we do
for generic operators already, but with some discrimination between
them. To be done right, we should look up the precedence in a db
table, to allow new operators to participate in the scheme. In any
case, gram.y will become more complex...

Unless we are going to solve this, I would suggest backing out the
change in gram.y.

                        - Tom

Fri, 26 Mar 1999 15:57:06 +0000
Thomas Lockhart <lockhart@alumni.caltech.edu>
Re: [HACKERS] Modulo syntax
> > >    I ran the query
> > > update producers SET cor_id = producer_id % 9 + 1;
> > >    and found that result is eqiuvalent to
> > > update producers SET cor_id = producer_id % 9;
> > >    I added parens:
> > > update producers SET cor_id = (producer_id % 9) + 1;
> > >    and got what I needed.
> > Looks like a bug.  We have associativity for +, -, * and /, but not %.
> > From gram.y:
> >         %left       '+' '-'
> >         %left       '*' '/'
> > I will add '%' to that.
> 
> This will not fix the associativity problem, unless you *also* go
> through and add the explicit syntax *throughout* gram.y, as is
> currently done for '+', '-', etc.
> 
> I'm pretty sure that we don't want to do this, since there are way too
> many other operators which would need the same treatment.

I did this for %.  I felt it was common enough and similar to / that
people should expect it to have / associativity.  I did not play with
any other operators.

> 
> The correct solution will be to identify the operator as a particular
> class in scan.l, include that class in the associativity declarations,
> and then handle that class in the body of gram.y. Sort of like we do
> for generic operators already, but with some discrimination between
> them. To be done right, we should look up the precedence in a db
> table, to allow new operators to participate in the scheme. In any
> case, gram.y will become more complex...

Yikes.  Don't think we want to go there.
> 
> Unless we are going to solve this, I would suggest backing out the
> change in gram.y.

I would like to keep % as a special case like /.

-- 
  Bruce Momjian                        |  http://www.op.net/~candle
  maillist@candle.pha.pa.us            |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

Fri, 26 Mar 1999 11:47:06 -0500 (EST)
Bruce Momjian <maillist@candle.pha.pa.us>
Re: [HACKERS] Modulo syntax