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

On 23 Jun 2012, at 21:27, Anton Kholomiov wrote:

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.

transformers-0.2.2.0 transformers-0.3.0.0

So when I'm doing

import Control.Monad.Trans (0.2.2.0)

Ehm... seems like you're importing mtl instead of transformers. AFAIK there is no "Control.Monad.Trans" module in transformers.

I get the error

And when I'm doing

import Control.Monad.Trans.Class (0.2.2.0)

It compiles.

Anton

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