Re: [Haskell-cafe] Re: Memoizing partially evaluated computations.

On Wed, Mar 18, 2009 at 6:21 AM, Chung-chieh Shan wrote:

Sebastiaan Visser wrote in article < D86A7D11-F95F-4A27-A13C-2D78AFDA2E02@cs.uu.nl> in gmane.comp.lang.haskell.cafe:

...

Suppose I have a list of IO computations that depends on a few very time consuming pure operations. The pure operations are not dependent on the real world:

...

computation :: [IO Int] computation = [ smallIOfunc timeConsumingPureOperation0 , smallIOfunc timeConsumingPureOperation1 , smallIOfunc timeConsumingPureOperation2 , smallIOfunc timeConsumingPureOperation3 ] where smallIOfunc a = print a >> return a

I take it that, because you "do not really have the control to change things `deep' inside the code", it is not an option to redefine

computation = [ smallIOfunc x0 , smallIOfunc x1 , smallIOfunc x2 , smallIOfunc x3 ] where smallIOfunc a = print a >> return a x0 = timeConsumingPureOperation0 x1 = timeConsumingPureOperation1 x2 = timeConsumingPureOperation2 x3 = timeConsumingPureOperation3

Um, just to clarify, this code is exactly equivalent to the original, including sharing behavior. The only time a let (or where) clause changes sharing is if the variable is used more than once in the body. Luke