Super-monster patch implementing the new typechecker -- at last

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

diff --git a/compiler/typecheck/FamInst.lhs b/compiler/typecheck/FamInst.lhs
index 89dffbf..e2da795 100644 (file)
--- a/compiler/typecheck/FamInst.lhs
+++ b/compiler/typecheck/FamInst.lhs
@@ -2,7 +2,7 @@ The @FamInst@ type: family instance heads
 
 \begin{code}
 module FamInst ( 
-        checkFamInstConsistency, tcExtendLocalFamInstEnv
+        checkFamInstConsistency, tcExtendLocalFamInstEnv, tcGetFamInstEnvs
     ) where
 
 import HscTypes
@@ -11,17 +11,16 @@ import TcMType
 import TcType
 import TcRnMonad
 import TyCon
-import Type
 import Name
 import Module
 import SrcLoc
 import Outputable
-import LazyUniqFM
+import UniqFM
 import FiniteMap
 import FastString
 
-import Maybe
-import Monad
+import Maybes
+import Control.Monad
 \end{code}
 
 
@@ -36,6 +35,16 @@ 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
@@ -107,8 +116,8 @@ checkFamInstConsistency famInstMods directlyImpMods
     -- already loaded in the EPS or they are in the HPT.
     --
     check modInstsEnv (ModulePair m1 m2)
-      = let { instEnv1 = fromJust . lookupModuleEnv modInstsEnv $ m1
-           ; instEnv2 = fromJust . lookupModuleEnv modInstsEnv $ m2
+      = let { instEnv1 = (expectJust "checkFamInstConsistency") . lookupModuleEnv modInstsEnv $ m1
+           ; instEnv2 = (expectJust "checkFamInstConsistency") . lookupModuleEnv modInstsEnv $ m2
            ; insts1   = famInstEnvElts instEnv1
            }
         in
@@ -168,38 +177,14 @@ 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
@@ -212,4 +197,17 @@ addFamInstLoc famInst thing_inside
   = setSrcSpan (mkSrcSpan loc loc) thing_inside
   where
     loc = getSrcLoc famInst
+\end{code} 
+
+\begin{code} 
+
+tcGetFamInstEnvs :: TcM (FamInstEnv, FamInstEnv)
+-- Gets both the external-package inst-env
+-- and the home-pkg inst env (includes module being compiled)
+tcGetFamInstEnvs 
+  = do { eps <- getEps; env <- getGblEnv
+       ; return (eps_fam_inst_env eps, tcg_fam_inst_env env) 
+       }
+
+
 \end{code}