On Tue, Jun 23, 2009 at 6:05 PM, Eric Dedieu <[email protected]> wrote:
> So > > 1) How can I use transformers instead of the mtl? This is in no > tutorial, and searchinf for "mtl" on the haskell wiki yields no > result at all. > cabal install transformers (you need cabal-install to do this... consult #haskell if confused) perhaps: > ghc-pkg hide mtl (I think mtl and transformers fight over the Control.Monad module) Then import Control.Monad.Trans.State instead of Control.Monad.State. All else should be well, if I am not forgetting something. > > 2) What should be the Haskell98-compatible type signature for my play2 > function, instead of (MonadState [a] m, Eq a) => > a -> m Bool ? That depends on the monad library. In transformers it would be: (Monad m, Eq a) => a -> StateT [a] m Bool State s is just a type synonym for StateT s Identity, so this works for State as well. Luke
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