[Haskell-cafe] type-level programming support library

John Van Enk vanenkj at gmail.com
Mon Mar 30 14:54:44 EDT 2009

I suppose having a good description of what I'd like to do might help: I'd
like to be able to make an N-Tuple an instance of a type class.

class Foo a where

instance Foo (,) where

instance Foo (,,) where
The different kindedness of (,) and (,,) prevent this from working.


On Mon, Mar 30, 2009 at 2:00 PM, Martijn van Steenbergen <
martijn at van.steenbergen.nl> wrote:

> John Van Enk wrote:
>>  > Haskell not having 'polymorphic kinds'.
>>  Is there a good description of why Haskell doesn't have polymorphic
>> kinds?
> IANA expert but polymorphic kinds belong to a set of reasonably new
> influences (e.g. from dependently typed programming languages and generic
> programming) and they haven't been 1) polished enough to be a widely
> accepted standard or 2) simply haven't been implemented yet (low priority,
> etc).
> Besides that, I sometimes see polymorphic kinds in GHC error messages, so I
> suspect that at least parts of GHC already support them.
> Martijn.

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