higher-order functions (sliding window)

higher-order.hs

windowMap :: ( a -> a -> b) -> [a] -> [b]
windowMap func list =
    let zipped = zip list (tail list)
    in map (uncurry func) zipped

windowScan :: (b -> a -> a -> b) -> b -> [a] -> [b]
windowScan func accumulator list =
    let zipped = zip list (tail list)
        func' = \ acc -> uncurry (func acc)
    in scanl func' accumulator zipped

windowFold :: (b -> a -> a -> b) -> b -> [a] -> b
windowFold func accumulator list =
    let zipped = zip list (tail list)
        func' = \ acc -> uncurry (func acc)
    in foldl func' accumulator zipped

list = [1..8]

testWindowMap :: [Integer] -> [Integer]
testWindowMap aList = 
    windowMap (+) aList

testWindowScan :: [Integer] -> [Integer]
testWindowScan aList = 
    windowScan scanFunc 1000 aList

scanFunc :: Integer -> Integer -> Integer -> Integer
scanFunc accumulator a b = accumulator - (a * b)

-- attempt to generalize the windowing behavior over multiple higher-order functions

window :: (((a, a) -> b) -> [(a, a)] -> r) -> (a -> a -> b) -> [a] -> r
window higherOrderFunc mergeApplicator list =
    let zipped = zip list (tail list)
    in higherOrderFunc (uncurry mergeApplicator) zipped

-- it works for map
windowMap' = window map
-- it doesn't work for scan, different function signature
-- windowScan' = window scanl

testWindowMap' :: [Integer] -> [Integer]
testWindowMap' aList = 
    windowMap' (+) aList