X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FFamInst.lhs;h=67c526d657bf1567c291709eff28000d67041e06;hb=a769050d7c133dac1fbe9c50c2e212243bdbf980;hp=eed79ca2c7c121a31f9f18528bcc24d1292e02f3;hpb=edaf4b7be527a8c029f4f3855b57d538d764b500;p=ghc-hetmet.git

diff --git a/compiler/typecheck/FamInst.lhs b/compiler/typecheck/FamInst.lhs
index eed79ca..67c526d 100644
--- a/compiler/typecheck/FamInst.lhs
+++ b/compiler/typecheck/FamInst.lhs
@@ -1,13 +1,6 @@
 The @FamInst@ type: family instance heads
 
 \begin{code}
-{-# OPTIONS -w #-}
--- The above warning supression flag is a temporary kludge.
--- While working on this module you are encouraged to remove it and fix
--- any warnings in the module. See
---     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
--- for details
-
 module FamInst ( 
         checkFamInstConsistency, tcExtendLocalFamInstEnv
     ) where
@@ -43,6 +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
@@ -180,7 +183,7 @@ 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'
 
@@ -194,9 +197,9 @@ checkForConflicts inst_envs famInst
 	   conflictInstErr famInst (head conflicts)
        }
   where
-      -- * In the case of data family instances, any overlap is fundamentally a 
+      -- - 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 
+      -- - 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.
@@ -208,11 +211,13 @@ checkForConflicts inst_envs famInst
         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:"))
 	       2 (pprFamInsts [famInst, conflictingFamInst]))
 
+addFamInstLoc :: FamInst -> TcRn a -> TcRn a
 addFamInstLoc famInst thing_inside
   = setSrcSpan (mkSrcSpan loc loc) thing_inside
   where