-- Here's a expansion of the ideas presented for tracking the argument used -- to create a partially applied function: -- -- Based on simple pairs -- add :: Int -> Int -> Int add x y = x + y addr :: Int -> (Int, Int -> Int) addr a = (a, add a) -- a list of partially applied functions adds = [addr 3, addr 5, addr 7, addr 3, addr 5, addr 8] -- an example usage of the list k = map (\ f -> (snd f) 10 ) adds -- filtering add3s = filter (\ f -> fst f == 3) adds addEvens = filter (\f -> even $ fst f) adds --addEvens = [add 8] k3 = map (\ f -> (snd f) 10) add3s keven = map (\ f -> (snd f) 10) addEvens -- -- Generalized: -- data TaggedPartial a b c = TAG a (b -> c) tag :: (a -> b -> c) -> a -> TaggedPartial a b c tag f a = TAG a (f a) -- "create a tagged partially applied function tap :: TaggedPartial a b c -> b -> c tap (TAG _ f) b = f b -- "tagged partial function apply" ttest :: TaggedPartial a b c -> (a -> Bool) -> Bool ttest (TAG a _) f = f a -- "tagged tag test" tadds = [tag add 3, tag add 5, tag add 7, tag add 3, tag add 5, tag add 8] tk = map (\ f -> tap f 10) tadds tadd3s = filter (\ f -> ttest f (==3)) tadds taddEvens = filter (\ f -> ttest f even) tadds tk3 = map (\ f -> tap f 10) tadd3s tkeven = map (\ f -> tap f 10) taddEvens -- -- The examples of map and filter usage, show that the arguments to -- tap and ttest are awkwardly flipped. Hence: -- pat :: b -> TaggedPartial a b c -> c pat = flip tap testt :: (a -> Bool) -> TaggedPartial a b c -> Bool testt = flip ttest tk' = map (pat 10) tadds tadd3s' = filter (testt (==3)) tadds taddEvens' = filter (testt even) tadds tk3' = map (pat 10) tadd3s' tkeven' = map (pat 10) taddEvens' {- Mark Lentczner http://www.ozonehouse.com/mark/ mark@glyphic.com -}