divRem by `-' performance

[Roman Cheplyaka]

* Serge D. Mechveliani <mechvel at botik.ru> [2012-10-17 19:37:38+0400]
> But it is generally difficult for me to admit that sometimes it is 
> desirable to use strinctess annotation.
> I programmed DoCon for 6 years, and it does not have any bit of 
> strictness annotation, and I always had an impression that it is all
> right with performance.

Yeah, I was also surprised that this is news to you :)

> And now it occurs that setting  $!  in some places may make many parts
> of it somewhat 100 times less expensive 
> -- ?
> Somehow difficult to admit.

Laziness is subtle. Sometimes you make an innocent change to a program,
but it changes the time when things are evaluated, and that affects
memory/performance significantly.

In general, you'd rather understand evaluation order in your program if
you want decent performance.

Roman