If you want to defer the choice of 's' you've to make it appear in the type
signature of test1, so you've to introduce an artificial parameter even if
we're interested only in its type. e.g.:
data Proxy (s :: * - * - *) -- useful because we can't have an argument
of type 's' directly, since it's
I was trying to create a typeclass for an abstract Stack class, and ran
into some problems. The following 'works' fine:
{-# OPTIONS_GHC -XEmptyDataDecls -XFlexibleContexts
-fno-monomorphism-restriction #-}
module Stack where
data Void
class Stack s where
push_ :: s a r - b - s b (s a r)
