Re: different flavours of Monad Transformer Library (fwd)

Am Mittwoch, 7. Januar 2009 21:28 schrieb Antoine Latter:

On Wed, Jan 7, 2009 at 11:23 AM, Mauro J. Jaskelioff 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