X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FbasicTypes%2FDataCon.lhs;h=7ecf666014e52d0cf8e7b847fef46aef47fcf5c3;hp=851bf661da52d639a68ea60a66e7ed5d89aedf6b;hb=98c68a1c5b63aadf9c7917274519d95bbe9394d4;hpb=5862b2c52a1d678ef54ddbbdbcec93999bc247cc

diff --git a/compiler/basicTypes/DataCon.lhs b/compiler/basicTypes/DataCon.lhs
index 851bf66..7ecf666 100644
--- a/compiler/basicTypes/DataCon.lhs
+++ b/compiler/basicTypes/DataCon.lhs
@@ -87,15 +87,20 @@ differently, as follows.
 
 Note [Data Constructor Naming]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Each data constructor C has two, and possibly three, Names associated with it:
+Each data constructor C has two, and possibly up to four, Names associated with it:
 
-			     OccName	Name space	Used for
+			     OccName	Name space	Name of
   ---------------------------------------------------------------------------
-  * The "source data con" 	C	DataName	The DataCon itself
-  * The "real data con"		C	VarName		Its worker Id
-  * The "wrapper data con"	$WC	VarName		Wrapper Id (optional)
-
-Each of these three has a distinct Unique.  The "source data con" name
+  * The "data con itself" 	C	DataName	DataCon
+  * The "worker data con"	C	VarName		Id (the worker)
+  * The "wrapper data con"	$WC	VarName		Id (the wrapper)
+  * The "newtype coercion"      :CoT    TcClsName	TyCon
+ 
+EVERY data constructor (incl for newtypes) has the former two (the
+data con itself, and its worker.  But only some data constructors have a
+wrapper (see Note [The need for a wrapper]).
+
+Each of these three has a distinct Unique.  The "data con itself" name
 appears in the output of the renamer, and names the Haskell-source
 data constructor.  The type checker translates it into either the wrapper Id
 (if it exists) or worker Id (otherwise).
@@ -129,6 +134,8 @@ The "wrapper Id", $WC, goes as follows
   nothing for the wrapper to do.  That is, if its defn would be
 	$wC = C
 
+Note [The need for a wrapper]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Why might the wrapper have anything to do?  Two reasons:
 
 * Unboxing strict fields (with -funbox-strict-fields)
@@ -152,6 +159,8 @@ Why might the wrapper have anything to do?  Two reasons:
   The third argument is a coerion
 	[a] :: [a]:=:[a]
 
+INVARIANT: the dictionary constructor for a class
+	   never has a wrapper.
 
 
 A note about the stupid context
@@ -329,19 +338,21 @@ data DataCon
 	dcRepTyCon  :: TyCon,		-- Result tycon, T
 
 	dcRepType   :: Type,	-- Type of the constructor
-				-- 	forall a x y. (a:=:(x,y), Ord x) => x -> y -> MkT a
+				-- 	forall a x y. (a:=:(x,y), x~y, Ord x) =>
+                                --        x -> y -> T a
 				-- (this is *not* of the constructor wrapper Id:
 				--  see Note [Data con representation] below)
 	-- Notice that the existential type parameters come *second*.  
 	-- Reason: in a case expression we may find:
-	--	case (e :: T t) of { MkT b (d:Ord b) (x:t) (xs:[b]) -> ... }
+	--	case (e :: T t) of
+        --        MkT x y co1 co2 (d:Ord x) (v:r) (w:F s) -> ...
 	-- It's convenient to apply the rep-type of MkT to 't', to get
-	--	forall b. Ord b => ...
+	--	forall x y. (t:=:(x,y), x~y, Ord x) => x -> y -> T t
 	-- and use that to check the pattern.  Mind you, this is really only
-	-- use in CoreLint.
+	-- used in CoreLint.
 
 
-	-- Finally, the curried worker function that corresponds to the constructor
+	-- The curried worker function that corresponds to the constructor:
 	-- It doesn't have an unfolding; the code generator saturates these Ids
 	-- and allocates a real constructor when it finds one.
 	--
@@ -367,7 +378,7 @@ data DataConIds
 	-- The 'Nothing' case of DCIds is important
 	-- Not only is this efficient,
 	-- but it also ensures that the wrapper is replaced
-	-- by the worker (becuase it *is* the worker)
+	-- by the worker (because it *is* the worker)
 	-- even when there are no args. E.g. in
 	-- 		f (:) x
 	-- the (:) *is* the worker.