[Haskell-cafe] Memoization-question

[Donnie Jones]

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 at 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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