[Haskell-cafe] Re: tail recursion ?
jon.fairbairn at cl.cam.ac.uk
Mon Jun 11 15:27:10 EDT 2007
H. <h._h._h._ at hotmail.com> writes:
> Jon Fairbairn <jon.fairbairn <at> cl.cam.ac.uk> writes:
> > The idea in Haskell is not to think of stepping through the
> > array. Look at accumArray and ixmap.
> Thanks for your answer.
> But I can't really see how the calc-function can be written more efficiently
> with accumArray or ixmap, perhaps you can write it as an example?
Well, for your example, neither is needed since you could
write something like:
upb = 10000
listArray (1,upb) (repeat False)
//map (\n->(2^n,True)) [1..floor (logBase 2 $ fromIntegral upb)]
a = listArray (1,upb) (repeat False)
b = a//map (\n->(2^n,not (a!(2^n)))) [1..floor (logBase 2 $ fromIntegral upb)]
but the first one is obviously better,
so it depends on what you really want to do.
Jón Fairbairn Jon.Fairbairn at cl.cam.ac.uk
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2007-05-07)
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