[Haskell-cafe] using type variables in type declarations inside function

[Li-yao Xia]

Hi Dennis,

Use ScopedTypeVariables.

{-# LANGUAGE ScopedTypeVariables #-}

myFunc :: forall a b c. a -> b -> c  -- explicit binders
...
     helper :: a -> [b]

On 04/12/2018 03:47 PM, Dennis Raddle wrote:
> Let's say I've written a function on three types.
> 
> myFunc :: a -> b -> c
> myFunc x y z = ...
>    where
>      helper :: a -> [b]
>      helper xx = ...
> 
> 
> Notice that I'm attempting to declare 'helper' using my type variables. 
> I've noticed that this results in an error.
> 
> Is this actually possible, and how?
> 
> D
> 
> 
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