Robustify lookupFamInstEnv, plus some refactoring

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

diff --git a/compiler/typecheck/FamInst.lhs b/compiler/typecheck/FamInst.lhs
index 5f4b2a3..5a3a664 100644 (file)
--- a/compiler/typecheck/FamInst.lhs
+++ b/compiler/typecheck/FamInst.lhs
@@ -11,7 +11,6 @@ import TcMType
 import TcType
 import TcRnMonad
 import TyCon
-import Type
 import Name
 import Module
 import SrcLoc
@@ -178,38 +177,13 @@ checkForConflicts inst_envs famInst
                -- (since we do unification).  
                -- We use tcInstSkolType because we don't want to allocate
                -- fresh *meta* type variables.  
-       ; let { tycon = famInstTyCon famInst
-            ; ty    = case tyConFamInst_maybe tycon of
-                        Nothing        -> panic "FamInst.checkForConflicts"
-                        Just (tc, tys) -> tc `mkTyConApp` tys
-             }
-       ; (_, _, tau') <- tcInstSkolType FamInstSkol ty
-
-       ; let (fam, tys') = tcSplitTyConApp tau'
-
-       ; let { matches   = lookupFamInstEnvUnify inst_envs fam tys'
-            ; conflicts = [ conflictingFamInst
-                          | match@((conflictingFamInst, _), _) <- matches
-                          , conflicting tycon match 
-                          ]
-            }
+
+       ; skol_tvs <- tcInstSkolTyVars FamInstSkol (tyConTyVars (famInstTyCon famInst))
+       ; let conflicts = lookupFamInstEnvConflicts inst_envs famInst skol_tvs
        ; unless (null conflicts) $
-          conflictInstErr famInst (head conflicts)
+          conflictInstErr famInst (fst (head conflicts))
        }
   where
-      -- - In the case of data family instances, any overlap is fundamentally a
-      --   conflict (as these instances imply injective type mappings).
-      -- - In the case of type family instances, overlap is admitted as long as
-      --   the right-hand sides of the overlapping rules coincide under the
-      --   overlap substitution.  We require that they are syntactically equal;
-      --   anything else would be difficult to test for at this stage.
-    conflicting tycon1 ((famInst2, _), subst) 
-      | isAlgTyCon tycon1 = True
-      | otherwise         = not (rhs1 `tcEqType` rhs2)
-      where
-        tycon2 = famInstTyCon famInst2
-        rhs1   = substTy subst $ synTyConType tycon1
-        rhs2   = substTy subst $ synTyConType tycon2
 
 conflictInstErr :: FamInst -> FamInst -> TcRn ()
 conflictInstErr famInst conflictingFamInst