Currently, yes; I was experimenting with type families.  But it's pretty simple to get it to compile on 6.6.1:

- remove the {-# LANGUAGE #-} pragma and replace with {-# OPTIONS_GHC -fglasgow-exts -fallow-undecidable-instances #-}

 

- change the class declaration for MonadPrompter from

> class Monad m => MonadPrompter m where
>    type PromptType m :: * -> *
>    prompt :: PromptType m a -> m a
 

to

 

> class Monad m => MonadPrompter p m | m -> p where

>    prompt :: p a -> m a

 

- change all the instance declarations from something like this:

 

> instance MonadPrompter (XXX) where

>    type PromptType (XXX) = YYY

>    prompt = ...

 

to something like this:

 

> instance MonadPrompter YYY (XXX) where

>    prompt = ...

 

& you're done.

 

  -- ryan