Hello Mattias, I think you will find this thread from the haskell-cafe mailing list quite helpful. Re: [Haskell-cafe] Memoization http://www.mail-archive.com/haskell-cafe@haskell.org/msg09924.html Also, the Haskell wiki contains comments about techniques for memoization along with references at the bottom. Haskell wiki Memoization: http://www.haskell.org/haskellwiki/Memoization Hope that helps. __ Donnie Jones On Thu, Dec 11, 2008 at 10:18 AM, Mattias Bengtsson < moonlite@dtek.chalmers.se> wrote:
The program below computes (f 27) almost instantly but if i replace the definition of (f n) below with (f n = f (n - 1) * f (n -1)) then it takes around 12s to terminate. I realize this is because the original version caches results and only has to calculate, for example, (f 25) once instead of (i guess) four times. There is probably a good reason why this isn't caught by the compiler. But I'm interested in why. Anyone care to explain?
main = print (f 27)
f 0 = 1 f n = let f' = f (n-1) in f' * f'
(compiled with ghc --make -O2)
Mattias
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