Edit: it is running, testFunc :: (forall a m. (Conf a, MonadIO m) => m a) -> TestType is the solution ;) ---------- Thanks, i tried it with your code changes but then i ll only get a type mismatch Test.hs:12:11: Couldn't match expected type `forall a. (Conf a, MonadIO m) => m a' against inferred type `forall a (m1 :: * -> *). (Conf a, MonadIO m1) => m1 a' In the expression: TestType In the definition of `testFunc': testFunc = TestType Miguel Mitrofanov schrieb:
/ Error message suggests that you've used "Conf" improperly. />/ />/ testFunc :: (forall a. Conf a, MonadIO m => m a) -> TestType />/ />/ is illegal, as I recall, you should use another pair of brackets: />/ />/ testFunc :: (forall a. (Conf a, MonadIO m) => m a) -> TestType />/ />/ Alexander Treptow wrote: />>/ Hi, />>/ i got a little problem and don't know how to solve that. Hope you can />>/ help me. />>/ />>/ code: />>/ ---------- />>/ module Test where />>/ {-# LANGUAGE Rank2Types, RankNTypes #-} />>/ import Control.Monad.Trans />>/ />>/ data TestType = TestType />>/ {tst :: (Conf a, MonadIO m) => m a} />>/ />>/ class Conf a where />>/ get :: MonadIO m => m a />>/ />>/ testFunc :: (forall a. Conf a, MonadIO m => m a) -> TestType />>/ testFunc = TestType />>/ -------------- />>/ error: />>/ -------------- />>/ Test.hs:11:23 />>/ Class `Conf' used as a type />>/ In the type signature for `testFunc': />>/ testFunc :: (forall a. Conf a, (MonadIO m) => m a) -> TestType />>/ -------------- />>/ />>/ explanation: />>/ I need a data type that creates a record with a member that has no fixed />>/ type, because its not known at compile-time. The Rank2Types language />>/ extension fits that need, but i figured out that i ll need to make that />>/ time monadic to avoid the use of unsafePerformIO in the program that />>/ uses this lib. />>/ />>/ Thanks and greetings, />>/ Alex />>/ />>/ _______________________________________________ />>/ Haskell-Cafe mailing list />>/ Haskell-Cafe at haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe />>/ http://www.haskell.org/mailman/listinfo/haskell-cafe />>/ />/ /