-pprConDecl (ConDecl con expl tvs cxt details (ResTyGADT res_ty))
- = sep [pprHsForAll expl tvs cxt, ppr con <+> ppr_details details]
+pprConDecl (ConDecl con expl tvs cxt (PrefixCon arg_tys) (ResTyGADT res_ty))
+ = ppr con <+> dcolon <+>
+ sep [pprHsForAll expl tvs cxt, ppr (foldr mk_fun_ty res_ty arg_tys)]