different flavours of Monad Transformer Library (fwd)

[Wolfgang Jeltsch]

Am Mittwoch, 7. Januar 2009 21:28 schrieb Antoine Latter:
> On Wed, Jan 7, 2009 at 11:23 AM, Mauro J. Jaskelioff <mjj at cs.nott.ac.uk> 
wrote:
> > Hi, sorry for the late reply,
> >
> > I also like Ross' idea of monads being synonyms for transformers at Id.
> > It removes lots of repeated code.
>
> There's a cost to that technique.
>
> Parsec3 introduced parsec as a monad transformer, and the parsec base
> monad is implemented as the transformer wrapped around the identity
> monad.
>
> There's a significant speed regression to doing so - I have a branch
> of Parsec3 which re-introduces a proper base monad and shares (some)
> code via typeclasses.  This puts us back at Parsec2 numbers.
>
> I don't have any hard data on hand at the moment, it's been a while.
>
> -Antoine

Isn’t it possible to make GHC more clever to remove this speed penalty?

Best wishes,
Wolfgang