Make FamInst warning-free

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

diff --git a/compiler/typecheck/FamInst.lhs b/compiler/typecheck/FamInst.lhs
index f85f6b9..8e8df88 100644 (file)
--- a/compiler/typecheck/FamInst.lhs
+++ b/compiler/typecheck/FamInst.lhs
@@ -5,8 +5,6 @@ module FamInst (
         checkFamInstConsistency, tcExtendLocalFamInstEnv
     ) where
 
-#include "HsVersions.h"
-
 import HscTypes
 import FamInstEnv
 import TcMType
@@ -18,8 +16,9 @@ import Name
 import Module
 import SrcLoc
 import Outputable
-import UniqFM
+import LazyUniqFM
 import FiniteMap
+import FastString
 
 import Maybe
 import Monad
@@ -174,31 +173,41 @@ checkForConflicts inst_envs famInst
                         Nothing        -> panic "FamInst.checkForConflicts"
                         Just (tc, tys) -> tc `mkTyConApp` tys
              }
-       ; (tvs', _, tau') <- tcInstSkolType FamInstSkol ty
+       ; (_, _, tau') <- tcInstSkolType FamInstSkol ty
 
        ; let (fam, tys') = tcSplitTyConApp tau'
 
        ; let { matches   = lookupFamInstEnvUnify inst_envs fam tys'
             ; conflicts = [ conflictingFamInst
-                          | match@(conflictingFamInst, _) <- matches
-                          , conflicting fam tys' tycon match 
+                          | match@((conflictingFamInst, _), _) <- matches
+                          , conflicting tycon match 
                           ]
             }
        ; unless (null conflicts) $
           conflictInstErr famInst (head conflicts)
        }
   where
-    -- In the case of data/newtype instances, any overlap is a conflict (as
-    -- these instances imply injective type mappings).
-    conflicting _   _    tycon _                 | isAlgTyCon tycon = True
-    conflicting fam tys' tycon (subst, cFamInst) | otherwise     =
-      panic "FamInst.checkForConflicts: overlap check for indexed synonyms is still missing"
-
+      -- * 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
   = addFamInstLoc famInst $
-    addErr (hang (ptext SLIT("Conflicting family instance declarations:"))
+    addErr (hang (ptext (sLit "Conflicting family instance declarations:"))
               2 (pprFamInsts [famInst, conflictingFamInst]))
 
+addFamInstLoc :: FamInst -> TcRn a -> TcRn a
 addFamInstLoc famInst thing_inside
   = setSrcSpan (mkSrcSpan loc loc) thing_inside
   where