Haskell point-free compilation type

Question

So I'm really new to Haskell, but I was playing around with the point free notation and came across this issue. I'm in the console:

> let c = (.)negate > :t c > (a -> Integer) -> a -> Integer -> a

but negate takes a Number, so why is it being constrained to an Integer type?

bheklilr · Accepted Answer · 2015-09-25 18:14:13Z

7

This is another case of the extended defaulting rules in GHCi. Do :set -XNoMonomorphismRestriction or just do

> :set +m -- multiline input in GHCi > let c :: (Num a) => (b -> a) -> b -> a -> b | c = (.) negate | > :t c Num a => (b -> a) -> b -> a -> b

answered Sep 25, 2015 at 18:14

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2 Comments

Just a note, you don't need multi line input; you can write let x :: T; x = t.

@user2407038 You don't need it, and you can also use :{ and :}, but I prefer :set +m, it's more like how IPython does multi-line input.