X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FFamInst.lhs;h=67c526d657bf1567c291709eff28000d67041e06;hb=9bcd95bad83ee937c178970e8b729732e680fe1e;hp=fd98fe919a9ab64da5b930e1c73ba2cc1ce6dee5;hpb=0eef3f31e57ab863792f68937889ef25e6257f08;p=ghc-hetmet.git

diff --git a/compiler/typecheck/FamInst.lhs b/compiler/typecheck/FamInst.lhs
index fd98fe9..67c526d 100644
--- 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
@@ -37,6 +36,16 @@ check whether the instances in the two modules are consistent, *unless* we can
 be certain that the instances of the two modules have already been checked for
 consistency during the compilation of modules that we import.
 
+Why do we need to check?  Consider 
+   module X1 where	  	  module X2 where
+    data T1			    data T2
+    type instance F T1 b = Int	    type instance F a T2 = Char
+    f1 :: F T1 a -> Int		    f2 :: Char -> F a T2
+    f1 x = x			    f2 x = x
+
+Now if we import both X1 and X2 we could make (f2 . f1) :: Int -> Char.
+Notice that neither instance is an orphan.
+
 How do we know which pairs of modules have already been checked?  Any pair of
 modules where both modules occur in the `HscTypes.dep_finsts' set (of the
 `HscTypes.Dependencies') of one of our directly imported modules must have
@@ -174,31 +183,41 @@ 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