Deal correctly with infix type constructors in GADT decls

[ghc-hetmet.git] / compiler / typecheck / TcHsType.lhs

diff --git a/compiler/typecheck/TcHsType.lhs b/compiler/typecheck/TcHsType.lhs
index 968ccfb..e4b1267 100644 (file)
--- a/compiler/typecheck/TcHsType.lhs
+++ b/compiler/typecheck/TcHsType.lhs
@@ -543,23 +543,26 @@ GADT constructor signatures
 
 \begin{code}
 tcLHsConResTy :: LHsType Name -> TcM (TyCon, [TcType])
-tcLHsConResTy ty@(L span _) 
-  = setSrcSpan span $ 
-    addErrCtxt (gadtResCtxt ty) $
-    tc_con_res ty []
-
-tc_con_res (L _ (HsAppTy fun res_ty)) res_tys
-  = do { res_ty' <- dsHsType res_ty
-       ; tc_con_res fun (res_ty' : res_tys) }
-
-tc_con_res ty@(L _ (HsTyVar name)) res_tys
-  = do { thing <- tcLookup name
-       ; case thing of
-           AGlobal (ATyCon tc) -> return (tc, res_tys)
-           other -> failWithTc (badGadtDecl ty)
-       }
-
-tc_con_res ty _ = failWithTc (badGadtDecl ty)
+tcLHsConResTy res_ty
+  = addErrCtxt (gadtResCtxt res_ty) $
+    case get_largs res_ty [] of
+          (HsTyVar tc_name, args) 
+             -> do { args' <- mapM dsHsType args
+                   ; thing <- tcLookup tc_name
+                   ; case thing of
+                       AGlobal (ATyCon tc) -> return (tc, args')
+                       other -> failWithTc (badGadtDecl res_ty) }
+          other -> failWithTc (badGadtDecl res_ty)
+  where
+       -- We can't call dsHsType on res_ty, and then do tcSplitTyConApp_maybe
+       -- because that causes a black hole, and for good reason.  Building
+       -- the type means expanding type synonyms, and we can't do that
+       -- inside the "knot".  So we have to work by steam.
+    get_largs (L _ ty) args = get_args ty args
+    get_args (HsAppTy fun arg)                   args = get_largs fun (arg:args)
+    get_args (HsParTy ty)                        args = get_largs ty  args
+    get_args (HsOpTy ty1 (L span tc) ty2) args = get_args (HsTyVar tc) (ty1:ty2:args)
+    get_args ty                          args = (ty, reverse args)
 
 gadtResCtxt ty
   = hang (ptext SLIT("In the result type of a data constructor:"))