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WillNess/foldl foldr and back.hs

Last active August 29, 2015 14:06
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foldl foldr and back.hs
Prelude> foldr (\x k-> k . (:) x) id [1..4] []
[4,3,2,1]
Prelude> foldl (\k x-> k . (:) x) id [1..4] []
[1,2,3,4]
Prelude>
Prelude> foldr (\x r-> (:) x r) [] [1..4]
[1,2,3,4]
Prelude> foldl (\r x-> (:) x r) [] [1..4]
[4,3,2,1]
Prelude>
foldr f z xs == foldl (\k x-> k . f x) id xs z
foldl f z xs == foldr (\x k-> k . flip f x) id xs z
foldr f z xs == foldl (\k x r-> k (f x r)) id xs z
foldl f z xs == foldr (\x k r-> k (f r x)) id xs z
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