Haskell: How to compose `not` with a function of arbitrary arity?
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by Hynek -Pichi- Vychodil
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Published on 2009-01-05T17:54:03Z
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2010/03/15
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When I have some function of type like
f :: (Ord a) => a -> a -> Bool
f a b = a > b
I should like make function which wrap this function with not.
e.g. make function like this
g :: (Ord a) => a -> a -> Bool
g a b = not $ f a b
I can make combinator like
n f = (\a -> \b -> not $ f a b)
But I don't know how.
*Main> let n f = (\a -> \b -> not $ f a b)
n :: (t -> t1 -> Bool) -> t -> t1 -> Bool
Main> :t n f
n f :: (Ord t) => t -> t -> Bool
*Main> let g = n f
g :: () -> () -> Bool
What am I doing wrong?
And bonus question how I can do this for function with more and lest parameters e.g.
t -> Bool
t -> t1 -> Bool
t -> t1 -> t2 -> Bool
t -> t1 -> t2 -> t3 -> Bool
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