MTL vs Transformers. Any status update?

Ross Paterson ross at
Mon Nov 30 06:59:57 EST 2009

On Sun, Nov 29, 2009 at 11:37:45AM -0800, Alexander Dunlap wrote:
> What is the plan for letting the two co-exist? Is everyone going to
> have to write instances that work with both monads-{tf,fd} and then
> export duplicate functions that have monad classes in their
> signatures?

Most clients just use the transformers to make composite monads, and
the classes to get the operations.  They can just pick one or the
other for their private use.

People defining and exporting their own monads will probably want to
make them instances of both versions of the classes.

If a package's interface uses the transformers (or the Haskell 98 classes
MonadTrans and MonadIO), it will work with both monads packages.

That leaves the packages that have FD or TF classes in their interfaces.

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