On 2015-12-20 08:01 PM, Noon Silk wrote:
{-# LANGUAGE NoMonomorphismRestriction #-}
data Status = Foo | Bar
data Rec m a = Rec { get :: m a , status :: Status }
defRec :: (Monad m) => Rec m a defRec = undefined
myRec :: (Monad m) => Rec m a myRec = Rec x y where Rec x y = defRec
Why this is an ambiguous-type error is a really long story. But a factor is analogous to "show . read". Another factor is that since you turn off the monomorphism restriction, there is a type generalization step, and the generalizing of y's type is separate from the generalization of x's type. I have found this solution, it works by connecting types to suppress the generalize step: {-# LANGUAGE NoMonomorphismRestriction, ScopedTypeVariables #-} ... myRec :: forall m a. (Monad m) => Rec m a myRec = Rec x y where Rec x y = defRec :: Rec m a