Re: [Haskell-cafe] Haskell and "memoization"

Am Mittwoch 16 Dezember 2009 05:08:39 schrieb Gregory Crosswhite:

Haskell does not maintain a cache mapping function calls to their values, so if you have some function f and call it with, say, the argument 7 in two different places in your code, then it will re-evaluate the function at each point. The only time it will not do this is when it can see explicitly that the value will be shared, i.e. situations like "g (f 7) (f 7)" should only result in one evaluation of f 7 in simple cases, presuming the compiler is sufficiently smart.

Not even then, necessarily. And it's not always a good idea. f k = [1 .. 20^k] g xs ys = genericLength (ys ++ xs) Finding out when to share is really hard.

Cheers, Greg