[Haskell-cafe] Monadic tunnelling: the art of threading one monad through another

[Henning Thielemann]

On Thu, 12 Jul 2007, Jules Bean wrote:

> I think the best you can do is:
>
> MonadIO io => (String -> io()) -> io ()
>
> 'MonadIO' lets you lift one way but not the other. Correct me if I'm wrong.
>
> As for that: yes, that would be great. It would be great if more
> libraries made their callbacks had signatures like that.

Then these libraries would depend on MTL and thus on functional
dependencies. It would be great if one could split MTL into a Haskell 98
part and a non-98 part.