scExpr env e@(Var v) = returnUs (varUsage env v UnkOcc, e)
scExpr env (Note n e) = scExpr env e `thenUs` \ (usg,e') ->
returnUs (usg, Note n e')
+scExpr env (Cast e co)= scExpr env e `thenUs` \ (usg,e') ->
+ returnUs (usg, Cast e' co)
scExpr env (Lam b e) = scExpr (extendBndr env b) e `thenUs` \ (usg,e') ->
returnUs (usg, Lam b e')