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sdiehl/list_combinator.hs

Created April 8, 2016 13:42
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list_combinator.hs
list :: [b] -> (a -> b) -> [a] -> [b]
list def f xs = case xs of
[] -> def
_ -> fmap f xs
example :: [String]
example = list ["a"] show [1,2,3]
@ezrosent
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ezrosent commented Apr 8, 2016

Not sure if this is simpler, but it avoids the pattern-match so it could be easier to generalize

import Data.Maybe (listToMaybe)

list :: [b] -> (a -> b) -> [a] -> [b]
list def f xs = maybe def (const (fmap f xs)) (listToMaybe xs)

@dmjio
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dmjio commented Apr 8, 2016

2 cents

list :: [b] -> (a -> b) -> [a] -> [b]
list def f xs = bool (f <$> xs) def (null xs)

@jstimpfle
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Are functions like null instead of pattern match always so bad?

list def f xs = if null xs then def else fmap f xs

Feels more straightforward at least.

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