Curry: An Integrated Functional Logic Language

A.2 Higher-Order Functions
Here are some “traditional” higher-order functions to show that the familiar functional programming
techniques can be applied in Curry. Note that the functions map, foldr, and filter are
predefined in Curry (see Appendix B).
-- Map a function on a list (predefined):
map :: (t1->t2) -> [t1] -> [t2]
map f [] = []
map f (x:xs) = f x:map f xs
-- Fold a list (predefined):
foldr :: (t1->t2->t2) -> t2 -> [t1] -> t2
foldr f a [] = a
foldr f a (x:xs) = f x (foldr f a xs)
-- Filter elements in a list (predefined):
filter :: (t -> Bool) -> [t] -> [t]
filter p [] = []
filter p (x:xs) = if p x then x:filter p xs
else filter p xs
-- Quicksort function:
quicksort :: [Int] -> [Int]
quicksort [] = []
quicksort (x:xs) = quicksort (filter ( x) xs)
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