Created
September 29, 2013 22:15
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import Prelude hiding (map) | |
-- Generalizar el mapeo (por ejemplo) consiste en definirlo | |
class Mappeable f where | |
map :: (a -> b) -> f a -> f b | |
-- Implementarlo para listas es directo | |
instance Mappeable [] where | |
map _ [] = [] | |
map f (x:xs) = f x:map f xs | |
-- Si creamos nuestro tipo, por ejemplo un árbol binario | |
data Tree a = Leaf a | Node (Tree a) (Tree a) deriving Show | |
-- sería | |
instance Mappeable Tree where | |
map f (Leaf x) = Leaf (f x) | |
map f (Node l r) = Node (map f l) (map f r) | |
-- Así, cualquier función puede generalizar el mapeo, | |
-- ¡sobre cualquier tipo MAPPEABLE!, por ejemplo | |
sumar2 :: (Num a, Mappeable f) => f a -> f a | |
sumar2 = map (2+) | |
-- Entonces podemos usar dicha función GENERICA sobre cualquier | |
-- tipo Mappeable | |
test1 = sumar2 [1..5] | |
test2 = sumar2 (Node (Node (Leaf 3) (Leaf 4)) (Node (Leaf 6) (Leaf 7))) | |
{- | |
*Main> test1 | |
[3,4,5,6,7] | |
*Main> test2 | |
Node (Node (Leaf 5) (Leaf 6)) (Node (Leaf 8) (Leaf 9)) | |
-} |
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