X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypes%2FTyCon.lhs;h=87ae25d1ca8eeabcf4c29c429cfd4a0b75187165;hb=37df27c6f21452c60c45b5cf6defc9003a41da15;hp=3a8209987aad9aafeece9264e0889e3d45c15a05;hpb=5822cb8d13aa3c05d2b46b4510c13d94b902eb21;p=ghc-hetmet.git

diff --git a/compiler/types/TyCon.lhs b/compiler/types/TyCon.lhs
index 3a82099..87ae25d 100644
--- a/compiler/types/TyCon.lhs
+++ b/compiler/types/TyCon.lhs
@@ -6,6 +6,13 @@
 The @TyCon@ datatype
 
 \begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
 module TyCon(
 	TyCon, FieldLabel,
 
@@ -26,7 +33,7 @@ module TyCon(
 	isEnumerationTyCon, isGadtSyntaxTyCon, isOpenTyCon,
 	assocTyConArgPoss_maybe, isTyConAssoc, setTyConArgPoss,
 	isTupleTyCon, isUnboxedTupleTyCon, isBoxedTupleTyCon, tupleTyConBoxity,
-	isRecursiveTyCon, newTyConRep, newTyConRhs, newTyConCo_maybe,
+	isRecursiveTyCon, newTyConRep, newTyConRhs, newTyConEtadRhs, newTyConCo_maybe,
 	isHiBootTyCon, isSuperKindTyCon,
         isCoercionTyCon_maybe, isCoercionTyCon,
         isImplicitTyCon,
@@ -243,10 +250,12 @@ data AlgTyConRhs
 				--  = the representation type of the tycon
 				-- The free tyvars of this type are the tyConTyVars
       
-        nt_co :: Maybe TyCon,   -- The coercion used to create the newtype
+        nt_co :: Maybe TyCon,   -- A CoercionTyCon used to create the newtype
                                 -- from the representation
-                                -- optional for non-recursive newtypes
+                                -- Optional for non-recursive newtypes
 				-- See Note [Newtype coercions]
+				-- Invariant: arity = #tvs in nt_etad_rhs;
+				--	See Note [Newtype eta]
 
 	nt_etad_rhs :: ([TyVar], Type) ,
 			-- The same again, but this time eta-reduced
@@ -326,7 +335,6 @@ data SynTyConRhs
 
 Note [Newtype coercions]
 ~~~~~~~~~~~~~~~~~~~~~~~~
-
 The NewTyCon field nt_co is a a TyCon (a coercion constructor in fact)
 which is used for coercing from the representation type of the
 newtype, to the newtype itself. For example,
@@ -390,6 +398,14 @@ we get:
 	w2 = w1
 And now Lint complains unless Foo T == Foo [], and that requires T==[]
 
+This point carries over to the newtype coercion, because we need to
+say 
+	w2 = w1 `cast` Foo CoT
+
+so the coercion tycon CoT must have 
+	kind:    T ~ []
+ and	arity:   0
+
 
 Note [Indexed data types] (aka data type families)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -871,6 +887,10 @@ newTyConRhs :: TyCon -> ([TyVar], Type)
 newTyConRhs (AlgTyCon {tyConTyVars = tvs, algTcRhs = NewTyCon { nt_rhs = rhs }}) = (tvs, rhs)
 newTyConRhs tycon = pprPanic "newTyConRhs" (ppr tycon)
 
+newTyConEtadRhs :: TyCon -> ([TyVar], Type)
+newTyConEtadRhs (AlgTyCon {algTcRhs = NewTyCon { nt_etad_rhs = tvs_rhs }}) = tvs_rhs
+newTyConEtadRhs tycon = pprPanic "newTyConEtadRhs" (ppr tycon)
+
 newTyConRep :: TyCon -> ([TyVar], Type)
 newTyConRep (AlgTyCon {tyConTyVars = tvs, algTcRhs = NewTyCon { nt_rep = rep }}) = (tvs, rep)
 newTyConRep tycon = pprPanic "newTyConRep" (ppr tycon)