[project @ 2004-04-02 12:38:33 by simonpj]

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

diff --git a/ghc/compiler/typecheck/TcType.lhs b/ghc/compiler/typecheck/TcType.lhs
index 753ad4f..0e430f4 100644 (file)
--- a/ghc/compiler/typecheck/TcType.lhs
+++ b/ghc/compiler/typecheck/TcType.lhs
@@ -22,7 +22,7 @@ module TcType (
 
   --------------------------------
   -- TyVarDetails
-  TyVarDetails(..), isUserTyVar, isSkolemTyVar, 
+  TyVarDetails(..), isUserTyVar, isSkolemTyVar, isExistentialTyVar,
   tyVarBindingInfo,
 
   --------------------------------
@@ -248,6 +248,14 @@ data TyVarDetails
    | PatSigTv  -- Scoped type variable, introduced by a pattern
                -- type signature       \ x::a -> e
 
+   | ExistTv   -- An existential type variable bound by a pattern for
+               -- a data constructor with an existential type. E.g.
+               --      data T = forall a. Eq a => MkT a
+               --      f (MkT x) = ...
+               -- The pattern MkT x will allocate an existential type
+               -- variable for 'a'.  We distinguish these from all others
+               -- on one place, namely InstEnv.lookupInstEnv.
+
    | VanillaTv -- Everything else
 
 isUserTyVar :: TcTyVar -> Bool -- Avoid unifying these if possible
@@ -257,10 +265,16 @@ isUserTyVar tv = case tcTyVarDetails tv of
 
 isSkolemTyVar :: TcTyVar -> Bool
 isSkolemTyVar tv = case tcTyVarDetails tv of
-                     SigTv  -> True
-                     ClsTv  -> True
-                     InstTv -> True
-                     oteher -> False
+                     SigTv   -> True
+                     ClsTv   -> True
+                     InstTv  -> True
+                     ExistTv -> True
+                     other   -> False
+
+isExistentialTyVar :: TcTyVar -> Bool
+isExistentialTyVar tv = case tcTyVarDetails tv of
+                             ExistTv -> True
+                             other   -> False
 
 tyVarBindingInfo :: TcTyVar -> SDoc    -- Used in checkSigTyVars
 tyVarBindingInfo tv
@@ -271,6 +285,7 @@ tyVarBindingInfo tv
     details ClsTv     = ptext SLIT("class declaration")
     details InstTv    = ptext SLIT("instance declaration")
     details PatSigTv  = ptext SLIT("pattern type signature")
+    details ExistTv   = ptext SLIT("existential constructor")
     details VanillaTv = ptext SLIT("//vanilla//")      -- Ditto
 \end{code}
 
@@ -866,7 +881,9 @@ toDNType ty
 checkRepTyCon :: (TyCon -> Bool) -> Type -> Bool
        -- Look through newtypes
        -- Non-recursive ones are transparent to splitTyConApp,
-       -- but recursive ones aren't
+       -- but recursive ones aren't.  Manuel had:
+       --      newtype T = MkT (Ptr T)
+       -- and wanted it to work...
 checkRepTyCon check_tc ty 
   | Just (tc,_) <- splitTyConApp_maybe (repType ty) = check_tc tc
   | otherwise                                      = False
@@ -1121,7 +1138,7 @@ match (TyVarTy v) ty tmpls k senv
   | v `elemVarSet` tmpls
   =     -- v is a template variable
     case lookupSubstEnv senv v of
-       Nothing | typeKind ty == tyVarKind v    
+       Nothing | typeKind ty `isSubKind` tyVarKind v   
                        -- We do a kind check, just as in the uVarX above
                        -- The kind check is needed to avoid bogus matches
                        -- of (a b) with (c d), where the kinds don't match
@@ -1156,12 +1173,14 @@ match (PredTy (ClassP c1 tys1)) (PredTy (ClassP c2 tys2)) tmpls k senv
 match (FunTy arg1 res1) (FunTy arg2 res2) tmpls k senv
   = match arg1 arg2 tmpls (match res1 res2 tmpls k) senv
 
+       -- If the template is an application, try to make the 
+       -- thing we are matching look like an application
 match (AppTy fun1 arg1) ty2 tmpls k senv 
   = case tcSplitAppTy_maybe ty2 of
        Just (fun2,arg2) -> match fun1 fun2 tmpls (match arg1 arg2 tmpls k) senv
        Nothing          -> Nothing     -- Fail
 
--- Newtypes are opaque; predicate types should not happen
+       -- Newtypes are opaque; predicate types should not happen
 match (NewTcApp tc1 tys1) (NewTcApp tc2 tys2) tmpls k senv
   | tc1 == tc2 = match_list_exactly tys1 tys2 tmpls k senv
 match (TyConApp tc1 tys1) (TyConApp tc2 tys2) tmpls k senv