2009/3/18 Sebastiaan Visser
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
In my main function I would like to repeatedly print the values
main = forever $ sequence_ (map (>>=print) computation)
When I do this, all the time consuming operations will be reevaluated every run of the main loop. Is there a any (simple or smart) way to prevent the garbage collector from cleaning up the fully evaluated thunks inside my computation? As if it were something like this:
computation :: [IO Int] computation = [smallIOfunc 42, smallIOfunc 34385, smallIOfunc 3, smallIOfunc 55]
Of course I could plugin some kind of Int memoizer inside my computation, but I do not really have the control to change things `deep' inside the code. I want to have some form of snapshot of a list of partially evaluated IO computations...
Any suggestions?
Hi, If timeConsumingPureOperation is pure, the problem is thus not related to IO, and your question remains the same : how to memoize timeConsumingPureOperation for some arguments. Since you want to repeatidly call main, it seems a good idea to wrap your pure operation in a memoizing CAF (and give the wrapped version to smalIOFuncf). You can here : http://www.haskell.org/haskellwiki/Memoization HTH, Thu