On Friday 06 May 2005 17:32, Mark Goldman wrote:
if I had a function f that took x y and z in that order, is there some way that I can supply y and z and get back a function that takes x? This question comes about after talking with a prof about currying and wether it buys you anything.
If you define rotl3 f x y z = f y z x -- rotate left first 3 arguments then, assuming f :: a -> b -> c -> d, rotl3 f :: b -> c -> a -> d and thus rotl3 f your_y your_z :: a -> d The already mentioned standard function 'flip' is equal to the left and right rotation for 2 arguments: flip = rotl2 = rotr2 = \f x y -> f y x You can imagine a family of 'rotl<n>' and 'rotr<n>' functions, indexed by the natural numbers. Unfortunately Haskell's type system(?) is not strong enough to declare the whole family at one stroke. Would it be useful to have the first 3 to 5 instances in the standard library, i.e. rotl3, rotr3, rotl4, rotr4, rotl5, rotr5? (You could also name them rotate_left3, ...) HTH Ben