Re: [Haskell-beginners] weird constraint

Remember that a -> b -> a is equivalent to a -> (b -> a) So: (forall a. Num a => a -> a) . (a -> (b -> a)) Becomes: (Num (b -> a). (b -> a) -> (b -> a)) . (a -> (b -> a)) Then: Num (b -> a). a -> (b -> a) Finally: Num (b -> a). a -> b -> a On 16/01/2019 15:52, Dimitri DeFigueiredo wrote:

Could someone help me make sense of this Num constraint given by GHCi? I was expecting to get:

inc . const :: Num a => a -> b -> a

rather than:

inc . const :: Num (b -> a) => a -> b -> a

Here's the transcript:

GHCi, version 8.6.3: http://www.haskell.org/ghc/  :? for help Prelude> inc x = x + 1 Prelude> :t inc inc :: Num a => a -> a Prelude> :t const const :: a -> b -> a Prelude> :t inc . const inc . const :: Num (b -> a) => a -> b -> a Prelude>

Thanks,

Dimitri