In message <[EMAIL PROTECTED]>, Ben Rudiak-Gould writes: > >> instance DeepSeq (IO a) where deepSeq = seq > >This is an interesting instance (which is not to say I think it's >wrong). It means the original poster's code won't work.
There is a bit similar issue with the instance for (a -> b). You might suppose that deepSeq of a function would turn the function to a representation that had the property that no function application would cause any complex computation, instead every function application would just look up from a precomputed (by deepSeq) table of values mapping each element of the domain to the codomain of the function. So I'm thinking the instance should be as follows: >instance (Enum a, Bounded a, DeepSeq b) => DeepSeq (a -> b) where > deepSeq f y = foldr deepSeq y [f i | i <- [minBound .. maxBound]] Though I'm not sure this will work, it might also require that 'f' is memoized to work correctly, such that recomputation of the thunks will not occur if 'y' uses 'f'. The theory behind this is the observation that functions can be thought of as a collection of thunks of the codomain type indexed by the values of the domain. For a practical application that would require this kind of approach, see http://haskell.org/hawiki/ControlOperation, in there, the use of unsafePerformIO is premised on the assumption that everything has been evaluated. So this would require the above kind of instances for deepSeq to allow use of functions in conjunction with the control operation. There are obviously some performance issues with this approach. -- Esa Pulkkinen _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
