dvde:
Dear Haskellers,
I just want to share an observation. I had to convert a Double to a Float value in an inner loop of an application, and I used somethin like this:
xf = (fromRational $ toRational xd) :: Float
The program works on windows but it did not on OSX - it was too slow. Now, after big headaches and much frustration, I replaced the code above with this line (why didn't I come up with this earlier?):
xf = double2Float xd
and now everything works just fine.
I am not really surprised by the speed-up (and no-one should be), but I am still surprised how often such kinds of unobvious problems occur while programming in Haskell. So I write this email just to remind me and you to look out for such pitfalls.
There's no rewrite rule for this optimization. There's a ticket though with some of the solutions. -- Don