Comments only

[ghc-hetmet.git] / compiler / types / Unify.lhs

diff --git a/compiler/types/Unify.lhs b/compiler/types/Unify.lhs
index c1ef798..7195e5b 100644 (file)
--- a/compiler/types/Unify.lhs
+++ b/compiler/types/Unify.lhs
@@ -206,7 +206,7 @@ match_kind :: MatchEnv -> TvSubstEnv -> TyVar -> Type -> Maybe TvSubstEnv
 -- Match the kind of the template tyvar with the kind of Type
 -- Note [Matching kinds]
 match_kind menv subst tv ty
-  | isCoVar tv = do { let (ty1,ty2) = splitCoercionKind (tyVarKind tv)
+  | isCoVar tv = do { let (ty1,ty2) = coVarKind tv
                          (ty3,ty4) = coercionKind ty
                    ; subst1 <- match menv subst ty1 ty3
                    ; match menv subst1 ty2 ty4 }
@@ -384,7 +384,7 @@ dataConCannotMatch tys con
 data Refinement = Reft InScopeSet InternalReft 
 
 type InternalReft = TyVarEnv (Coercion, Type)
--- INVARIANT:   a->(co,ty)   then   co :: (a:=:ty)
+-- INVARIANT:   a->(co,ty)   then   co :: (a~ty)
 -- Not necessarily idemopotent
 
 instance Outputable Refinement where
@@ -401,7 +401,7 @@ isEmptyRefinement (Reft _ env) = isEmptyVarEnv env
 refineType :: Refinement -> Type -> Maybe (Coercion, Type)
 -- Apply the refinement to the type.
 -- If (refineType r ty) = (co, ty')
--- Then co :: ty:=:ty'
+-- Then co :: ty~ty'
 -- Nothing => the refinement does nothing to this type
 refineType (Reft in_scope env) ty
   | not (isEmptyVarEnv env),           -- Common case
@@ -427,7 +427,7 @@ refinePred (Reft in_scope env) pred
 refineResType :: Refinement -> Type -> Maybe (Coercion, Type)
 -- Like refineType, but returns the 'sym' coercion
 -- If (refineResType r ty) = (co, ty')
--- Then co :: ty':=:ty
+-- Then co :: ty'~ty
 refineResType reft ty
   = case refineType reft ty of
       Just (co, ty1) -> Just (mkSymCoercion co, ty1)
@@ -617,8 +617,8 @@ uVar :: TvSubstEnv  -- An existing substitution to extend
      -> UM TvSubstEnv
 
 -- PRE-CONDITION: in the call (uVar swap r tv1 ty), we know that
---     if swap=False   (tv1:=:ty)
---     if swap=True    (ty:=:tv1)
+--     if swap=False   (tv1~ty)
+--     if swap=True    (ty~tv1)
 
 uVar subst tv1 ty
  = -- Check to see whether tv1 is refined by the substitution
@@ -640,7 +640,7 @@ uUnrefined subst tv1 ty2 ty2'
   = uUnrefined subst tv1 ty2 ty2''     -- Unwrap synonyms
                -- This is essential, in case we have
                --      type Foo a = a
-               -- and then unify a :=: Foo a
+               -- and then unify a ~ Foo a
 
 uUnrefined subst tv1 ty2 (TyVarTy tv2)
   | tv1 == tv2         -- Same type variable
@@ -656,15 +656,6 @@ uUnrefined subst tv1 ty2 (TyVarTy tv2)
        ; b2 <- tvBindFlag tv2
        ; case (b1,b2) of
            (BindMe, _)          -> bind tv1 ty2
-
-           (AvoidMe, BindMe)    -> bind tv2 ty1
-           (AvoidMe, _)         -> bind tv1 ty2
-
-           (WildCard, WildCard) -> return subst
-           (WildCard, Skolem)   -> return subst
-           (WildCard, _)        -> bind tv2 ty1
-
-           (Skolem, WildCard)   -> return subst
            (Skolem, Skolem)     -> failWith (misMatch ty1 ty2)
            (Skolem, _)          -> bind tv2 ty1
        }
@@ -704,29 +695,33 @@ bindTv :: TvSubstEnv -> TyVar -> Type -> UM TvSubstEnv
 bindTv subst tv ty     -- ty is not a type variable
   = do  { b <- tvBindFlag tv
        ; case b of
-           Skolem   -> failWith (misMatch (TyVarTy tv) ty)
-           WildCard -> return subst
-           _other   -> return $ extendVarEnv subst tv ty
+           Skolem -> failWith (misMatch (TyVarTy tv) ty)
+           BindMe -> return $ extendVarEnv subst tv ty
        }
 \end{code}
 
 %************************************************************************
 %*                                                                     *
-               Unification monad
+               Binding decisions
 %*                                                                     *
 %************************************************************************
 
 \begin{code}
 data BindFlag 
   = BindMe     -- A regular type variable
-  | AvoidMe    -- Like BindMe but, given the choice, avoid binding it
 
   | Skolem     -- This type variable is a skolem constant
                -- Don't bind it; it only matches itself
+\end{code}
+
 
-  | WildCard   -- This type variable matches anything,
-               -- and does not affect the substitution
+%************************************************************************
+%*                                                                     *
+               Unification monad
+%*                                                                     *
+%************************************************************************
 
+\begin{code}
 newtype UM a = UM { unUM :: (TyVar -> BindFlag)
                         -> MaybeErr Message a }