different flavours of Monad Template Library

Ross Paterson ross at soi.city.ac.uk
Mon Jan 5 07:24:36 EST 2009

On Mon, Jan 05, 2009 at 12:54:20PM +0100, Henning Thielemann wrote:
> You mean that Control.Monad.Trans.Identity is not a good name, because  
> Identity is not a transformer?

Yes, and that Control.Monad.Identity is the right name (and that the
transformers package is supposed to be usable in its own right).

> Since mtl-split is not a drop-in replacement for mtl, we cannot expect a  
> quick change from mtl to mtl-split in all the packages that currently  
> import mtl. Thus we have to think about a route of transition and a  
> package which can be installed in parallel to mtl is a first step, I  
> think.

My understanding is that GHC will allow both to be installed, and allow
packages that use transformers and those that use mtl to be used together
in the same program.  What you can't do is use both transformers and
mtl directly in the same package, but that's no big loss.

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