haskell - Are there any use cases for this function : foo :: (b -> c) -> (a -> b) -> (a -> c) -


for function :

foo :: (b -> c) -> (a -> b) -> (a -> c)

taken http://www.seas.upenn.edu/~cis194/spring13/lectures/04-higher-order.html

is function no practical use ? (b -> c) cannot constructed unless type c input parameter within function ?

and same (a -> b) -> (a -> c) : b & c not input parameters these functions.

are there use cases function ?

if question using function composition in practice, here small example. let's assume want write function sum of squares of elements of list of numbers. how that? well, write like: squaresum xs = sum (map (^2)) xs. can use function composition instead: squaresum = sum . map (^2)(i use . function composition here instead of foo, doesn't matter). example shows function obtained using function composition(it practical @ least in sense compiles , works correctly). benefits of function composition become more obvious when need compose multiple functions(possibly partially applied).


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