Eric Allen Wohlstadter writes:
I would like to be able to make a list that contains functions which take arguments of a certain type 'a'. However I don't know how many 'a' arguments there are. For example I'd like to be able to make a list of f,g, and h.
f::a->b g::a->a->b h::a->a->a->b [f,g,h]
Now I could make a function l that takes a list of 'a'. l::[a]->b However, I want to be able to curry the a's one at a time.
My solution so far is declare a type Element like this: data Element a b c d = One a | Two b | Three c | Four d and then I can make my list like this, [One f,Two g,Three h]
This gets very ugly. Do you guys have any ideas?
Eric Wohlstadter UCDavis Software Engineering
Hi. It looks a lot like a folding task. It would be nice if you could formulate it the l::[a]->b way, and feed in the arguments in a lazy list. Failing that, how about a product of lists, instead of a list of sums? data Bunch a b = Bunch {nones :: [b], ones :: [a->b], twos :: [a->a->b], threes :: [a->a->a->b], fours :: [a->a->a->a->b]} emptyBunch = Bunch [] [] [] [] [] applyBunch b arg = Bunch (map ($arg) (ones b)) (map ($arg) (twos b)) (map ($arg) (threes b)) (map ($arg) (fours b)) [] f x1 = () g x1 x2 = () h x1 x2 x3 = () fgh = emptyBunch {ones=[f], twos=[g], threes=[h]} test = take 5 (map nones (iterate (\b -> applyBunch b "foo") fgh)) Regards, Tom