-- 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/
m...@glyphic.com
-}
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