I've run into a small problem whilst doing some manual type checking, to see if I could match the results given by hugs
prelude> :t foldr filter foldr filter :: [a] -> [a -> Bool] -> [a] -- This was fine and was the same as my answer, so I tested it with prelude> foldr filter [1,2,3,4] [even,odd] -- and the answer was indeed an empty list
-- However I got stuck when attempting to derive the result of map (foldr filter) -- Hugs says that: prelude> :t map (foldr filter) map (foldr filter) :: [[a]] -> [[a -> Bool] -> [a]]
Two main questions:
1/ How does hugs derive this answer?
2/ What input can I give so that it yields a correct result? I've tried giving it a list of lists but it fails...
Any pointers would be greatly appreciated! Many Thanks, Lee
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