On Wed, Oct 17, 2012 at 06:17:28PM +0300, Roman Cheplyaka wrote: > * Serge D. Mechveliani <mech...@botik.ru> [2012-10-17 19:02:37+0400] > > People, > > consider the following contrived program for division with remainder: > > > > ---------------------------------------------------------------- > > qRem :: Int -> Int -> (Int, Int) > > qRem m n = if m < 0 || n <= 0 then error "\nwrong arguments in qRem.\n" > > else qRem' 0 m > > where > > qRem' q r = if r < n then (q, r) else qRem' (succ q) (r - n) > > You need to force evaluation of 'q' here, otherwise it becomes a growing > chain of 'succ' applications. > > E.g. > > qRem' q r = if r < n then (q, r) else (qRem' $! succ q) (r - n)
This looks as a natural explanation. 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. And now it occurs that setting $! in some places may make many parts of it somewhat 100 times less expensive -- ? Somehow difficult to admit. Regards, Sergei _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
