[Haskell-cafe] explicit big lambdas

[Nicolas Frisby]

Alternatively:

let f :: <some type involving a>
    f = ...

    f' :: a -> <some type involving a>
    f' _ = f
in f' (undefined :: Int) <normal f arguments>

On Thu, Mar 18, 2010 at 12:10 PM, Max Bolingbroke
<batterseapower at hotmail.com> wrote:
> Hi Paul,
>
> You should be able to introduce \Lambda at the source level by writing
> a type signature with an explicit "forall". Similarly you can then
> instantiate these \Lambdas by using a type signature which is an
> instance of the foralled type at the use site:
>
> ~~~
> -- id will get a \Lambda in Core
> id :: forall a. a -> a
> id x = x
>
> -- this use of id will have Int applied as the first type argument in Core
> main = print $ (id :: Int -> Int) 10
> ~~~
>
> This *should* extend smoothly to RankNTypes and other situations where
> GHC can't do good type inference.
>
> The typechecker doesn't know about big lambdas (they are added to Core
> by the desugarer from the output of the typechecker) so there is no
> better way to do this AFAIK.
>
> Cheers,
> Max
>
>
> On 18 March 2010 15:07, Paul Brauner <paul.brauner at loria.fr> wrote:
>> Hi again,
>>
>> is there a way in some haskell extension to explicit (system F's) big
>> lambdas and (term Type) applications in order to help type inference?
>>
>> If not: is there a way to provide ghc directly with core code before
>> the type checking phase?
>>
>> Paul
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>>
>>
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