Haskell Platform call for consensus: add transformers and revise the mtl package to depend on it

Ross Paterson ross at soi.city.ac.uk
Thu Nov 4 08:11:18 EDT 2010

On Wed, Nov 03, 2010 at 12:44:33PM -0400, Brent Yorgey wrote:
> As an experience report, I just ported the diagrams
> package to mtl-2.  As a matter of fact it did require some changes,
> because one place in the code explicitly used the Cont constructor
> which had to be changed to ContT (and some Identity wrapping and
> unwrapping added).  But it wasn't a big deal and it works fine now.

The transformers package has (in Control.Monad.Trans.Cont) a function

   cont :: ((a -> r) -> r) -> Cont r a

to serve as a plugin replacement for the Cont constructor (and similarly
for the other base monads that are now type synonyms).

One could argue that these should be re-exported by mtl-2, but I was
aiming for maximum compatibility.

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