newtypes, and predicates are meaningful.
* look through usage types
-The "tc" prefix is for "typechechecker", because the type checker
+The "tc" prefix is for "TypeChecker", because the type checker
is the principal client.
\begin{code}
tcSplitTyConApp_maybe (TyConApp tc tys) = Just (tc, tys)
tcSplitTyConApp_maybe (FunTy arg res) = Just (funTyCon, [arg,res])
tcSplitTyConApp_maybe (AppTy arg res) = Just (funTyCon, [arg,res])
-tcSplitTyConApp_maybe (PredTy (ClassP _ [ty'])) = tcSplitTyConApp_maybe ty'
-- Newtypes are opaque, so they may be split
-- However, predicates are not treated
-- as tycon applications by the type checker
+
+-- XXX - 2006-09-24: This case is hard-coded in (rendering predicates opaque as well)
+-- to make the newly reworked newtype-deriving work on the trivial case:
+-- newtype T = T () deriving (Eq, Ord)
+-- Please remove this if the newtype-deriving scheme no longer produces a PredTy.
+tcSplitTyConApp_maybe (PredTy (ClassP _ [ty'])) = tcSplitTyConApp_maybe ty'
+
tcSplitTyConApp_maybe other = Nothing
-----------------------