mtl, transformers, and monads-fd are in an unhappy place

Henning Thielemann schlepptop at
Sun Sep 12 08:39:32 EDT 2010

Bryan O'Sullivan schrieb:
> Hi, gents -
> I've lately been writing some application code that, by virtue of the
> libraries it uses, depends on both mtl and monads-fd. Alas, this means
> that I have two incompatible versions of some of the most widely used
> monad transformers in scope, and I have to carefully import the right
> version of Control.Monad.Trans:
> {-# LANGUAGE PackageImports #-}
> import qualified "mtl" Control.Monad.Trans as M
> import qualified "monads-fd" Control.Monad.Trans as F

In transformers-0.2 the module Control.Monad.Trans was split into
Control.Monad.Trans.Class and Control.Monad.IO.Class. Thus if the
transformers-dependent packages switch to transformers-0.2 you do not
need PackageImports.

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