X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FbasicTypes%2FDataCon.lhs;h=3de990512874051f580f4c7c54f216eefd284d91;hb=f06f40fb77bc67e87cbb5e7b8b3fca9a18c7a905;hp=af19a586139492f2f3dbbcabcdf61edc899723c1;hpb=19e64b50409a331ddf816cb4c7f33d646dabd43a;p=ghc-hetmet.git

diff --git a/compiler/basicTypes/DataCon.lhs b/compiler/basicTypes/DataCon.lhs
index af19a58..3de9905 100644
--- a/compiler/basicTypes/DataCon.lhs
+++ b/compiler/basicTypes/DataCon.lhs
@@ -38,11 +38,12 @@ import Type		( Type, ThetaType,
 import Coercion		( isEqPred, mkEqPred )
 import TyCon		( TyCon, FieldLabel, tyConDataCons, 
 			  isProductTyCon, isTupleTyCon, isUnboxedTupleTyCon,
-                          isNewTyCon, isRecursiveTyCon )
+                          isNewTyCon, isClosedNewTyCon, isRecursiveTyCon,
+                          tyConFamInst_maybe )
 import Class		( Class, classTyCon )
 import Name		( Name, NamedThing(..), nameUnique, mkSysTvName, mkSystemName )
-+ import Var		( TyVar, CoVar, Id, mkTyVar, tyVarKind, setVarUnique,
-+                           mkCoVar )
+import Var		( TyVar, CoVar, Id, mkTyVar, tyVarKind, setVarUnique,
+                          mkCoVar )
 import BasicTypes	( Arity, StrictnessMark(..) )
 import Outputable
 import Unique		( Unique, Uniquable(..) )
@@ -104,21 +105,55 @@ data constructor.  The type checker translates it into either the wrapper Id
 
 The data con has one or two Ids associated with it:
 
-  The "worker Id", is the actual data constructor.
-	Its type may be different to the Haskell source constructor
-	because:
-		- useless dict args are dropped
-		- strict args may be flattened
-	The worker is very like a primop, in that it has no binding.
+The "worker Id", is the actual data constructor.
+* Every data constructor (newtype or data type) has a worker
 
+* The worker is very like a primop, in that it has no binding.
 
+* For a *data* type, the worker *is* the data constructor;
+  it has no unfolding
 
-  The "wrapper Id", $WC, whose type is exactly what it looks like
-	in the source program. It is an ordinary function,
-	and it gets a top-level binding like any other function.
+* For a *newtype*, the worker has a compulsory unfolding which 
+  does a cast, e.g.
+	newtype T = MkT Int
+	The worker for MkT has unfolding
+		\(x:Int). x `cast` sym CoT
+  Here CoT is the type constructor, witnessing the FC axiom
+	axiom CoT : T = Int
 
-	The wrapper Id isn't generated for a data type if the worker
-	and wrapper are identical. 
+The "wrapper Id", $WC, goes as follows
+
+* Its type is exactly what it looks like in the source program. 
+
+* It is an ordinary function, and it gets a top-level binding 
+  like any other function.
+
+* The wrapper Id isn't generated for a data type if there is
+  nothing for the wrapper to do.  That is, if its defn would be
+	$wC = C
+
+Why might the wrapper have anything to do?  Two reasons:
+
+* Unboxing strict fields (with -funbox-strict-fields)
+	data T = MkT !(Int,Int)
+	$wMkT :: (Int,Int) -> T
+	$wMkT (x,y) = MkT x y
+  Notice that the worker has two fields where the wapper has 
+  just one.  That is, the worker has type
+		MkT :: Int -> Int -> T
+
+* Equality constraints for GADTs
+	data T a where { MkT :: a -> T [a] }
+
+  The worker gets a type with explicit equality
+  constraints, thus:
+	MkT :: forall a b. (a=[b]) => b -> T a
+
+  The wrapper has the programmer-specified type:
+	$wMkT :: a -> T [a]
+	$wMkT a x = MkT [a] a [a] x
+  The third argument is a coerion
+	[a] :: [a]:=:[a]
 
 
 
@@ -425,7 +460,8 @@ mkDataCon name declared_infix
 		  dcStupidTheta = stupid_theta, dcTheta = theta,
 		  dcOrigArgTys = orig_arg_tys, dcTyCon = tycon, 
 		  dcRepArgTys = rep_arg_tys,
-		  dcStrictMarks = arg_stricts, dcRepStrictness = rep_arg_stricts,
+		  dcStrictMarks = arg_stricts, 
+		  dcRepStrictness = rep_arg_stricts,
 		  dcFields = fields, dcTag = tag, dcRepType = ty,
 		  dcIds = ids }
 
@@ -572,6 +608,8 @@ dataConUserType :: DataCon -> Type
 --	T :: forall a. a -> T [a]
 -- rather than
 --	T :: forall b. forall a. (a=[b]) => a -> T b
+-- NB: If the constructor is part of a data instance, the result type
+-- mentions the family tycon, not the internal one.
 dataConUserType  (MkData { dcUnivTyVars = univ_tvs, 
 			   dcExTyVars = ex_tvs, dcEqSpec = eq_spec,
 			   dcTheta = theta, dcOrigArgTys = arg_tys,
@@ -579,7 +617,9 @@ dataConUserType  (MkData { dcUnivTyVars = univ_tvs,
   = mkForAllTys ((univ_tvs `minusList` map fst eq_spec) ++ ex_tvs) $
     mkFunTys (mkPredTys theta) $
     mkFunTys arg_tys $
-    mkTyConApp tycon (map (substTyVar subst) univ_tvs)
+    case tyConFamInst_maybe tycon of
+      Nothing             -> mkTyConApp tycon (map (substTyVar subst) univ_tvs)
+      Just (ftc, insttys) -> mkTyConApp ftc insttys	    -- data instance
   where
     subst = mkTopTvSubst eq_spec
 
@@ -688,9 +728,10 @@ splitProductType str ty
 deepSplitProductType_maybe ty
   = do { (res@(tycon, tycon_args, _, _)) <- splitProductType_maybe ty
        ; let {result 
-             | isNewTyCon tycon && not (isRecursiveTyCon tycon)
+             | isClosedNewTyCon tycon && not (isRecursiveTyCon tycon)
              = deepSplitProductType_maybe (newTyConInstRhs tycon tycon_args)
-             | isNewTyCon tycon = Nothing  -- cannot unbox through recursive newtypes
+             | isNewTyCon tycon = Nothing  -- cannot unbox through recursive
+					   -- newtypes nor through families
              | otherwise = Just res}
        ; result
        }