[Haskell-cafe] How to define instance for type synonym with parameter.

[Vasyl Pasternak]

>
> Aren't ErrorT and ReaderT instances of Applicative already? (At least in
> 'transformers' package?)
>
>

what difference between 'mtl' and 'transformers' packages ? 'mtl' goes
with Haskell Platform as standard package, so what is the benefit of
'transformers' library ?

Thanks,
Vasyl