[Haskell-cafe] Type inference for lambda function

[Viktor Dukhovni]

On Thu, Oct 21, 2021 at 08:40:45PM +0200, Matthias Güdemann wrote:

> This is what I get using ghci
> 
> λ> :t (\a b -> a + b)
> (\a b -> a + b) :: Num a => a -> a -> a
>
> but when loading a .hs file with just this function (without signature)
> 
> add = \a b -> a + b
> 
> I get
> 
> λ> :t add
> add :: Integer -> Integer -> Integer

Compare:

    $ ghci -XNoMonomorphismRestriction
    λ> x = \a b -> a + b
    λ> :t x
    x :: Num a => a -> a -> a

with

    $ ghci -XMonomorphismRestriction
    λ> x = \a b -> a + b
    λ> :t x
    x :: Integer -> Integer -> Integer

-- 
    Viktor.