[Haskell-cafe] transformers problem: Could not deduce MonadTrans (StateT s) ??

Anton Kholomiov anton.kholomiov at gmail.com
Sat Jun 23 19:27:42 CEST 2012

At last..

No, it wants me to define an instance for
(StateT s) which is supposed to be defined
be the authors of the library.

Actually I discovered that I have two libraries
called transformers.


So when I'm doing

import Control.Monad.Trans (

I get the error

And when I'm doing

import Control.Monad.Trans.Class (

It compiles.

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