Cleanup (re type function parsing)

Mon Jul 31 17:20:56 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Cleanup (re type function parsing)

3 files changed, 47 insertions, 19 deletions

diff --git a/compiler/hsSyn/HsDecls.lhs b/compiler/hsSyn/HsDecls.lhs
index f2bf9d3904..059fe4d341 100644
--- a/compiler/hsSyn/HsDecls.lhs
+++ b/compiler/hsSyn/HsDecls.lhs
@@ -329,6 +329,24 @@ Interface file code:
 -- for a module.  That's why (despite the misnomer) IfaceSig and ForeignType
 -- are both in TyClDecl
 
+-- Representation of type functions and associated data types & synonyms
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- 'TyData' and 'TySynonym' have a field 'tcdPats::Maybe [LHsType name]', with
+-- the following meaning:
+--
+--   * If it is 'Nothing', we have a *vanilla* data type declaration or type
+--     synonym declaration and 'tcdVars' contains the type parameters of the
+--     type constructor.
+--
+--   * If it is 'Just pats', we have the definition of an associated data type
+--     or a type function equations (toplevel or nested in an instance
+--     declarations).  Then, 'pats' are type patterns for the type-indexes of
+--     the type constructor and 'tcdVars' are the variables in those
+--     patterns.  Hence, the arity of the type constructor is 'length tcdPats'
+--     and *not* 'length tcdVars'.
+--
+-- In both cases, 'tcdVars' collects all variables we need to quantify over.
+
 type LTyClDecl name = Located (TyClDecl name)
 
 data TyClDecl name
@@ -368,6 +386,8 @@ data TyClDecl name
   | TySynonym {	tcdLName  :: Located name,	        -- type constructor
 		tcdTyVars :: [LHsTyVarBndr name],	-- type variables
 		tcdTyPats :: Maybe [LHsType name],	-- Type patterns
+							-- 'Nothing' => vanilla
+							--   type synonym
 		tcdSynRhs :: LHsType name	        -- synonym expansion
     }
 
@@ -378,7 +398,8 @@ data TyClDecl name
 		tcdSigs    :: [LSig name],		-- Methods' signatures
 		tcdMeths   :: LHsBinds name,		-- Default methods
 		tcdATs	   :: [LTyClDecl name]		-- Associated types; ie
-							--   only 'TyData'
+							--   only 'TyData',
+							--   'TyFunction',
 							--   and 'TySynonym'
     }
 
@@ -653,7 +674,8 @@ data InstDecl name
 				-- figures out the quantified type variables for us.
 		(LHsBinds name)
 		[LSig name]	-- User-supplied pragmatic info
-		[LTyClDecl name]-- Associated types
+		[LTyClDecl name]-- Associated types (ie, 'TyData' and
+				-- 'TySynonym' only)
 
 instance (OutputableBndr name) => Outputable (InstDecl name) where
 
diff --git a/compiler/parser/Parser.y.pp b/compiler/parser/Parser.y.pp
index 7b9786fa03..158043bcb8 100644
--- a/compiler/parser/Parser.y.pp
+++ b/compiler/parser/Parser.y.pp
@@ -467,7 +467,7 @@ cl_decl :: { LTyClDecl RdrName }
 	: 'class' tycl_hdr fds where
 		{% do { let { (binds, sigs, ats)           = 
 			        cvBindsAndSigs (unLoc $4)
-		            ; (ctxt, tc, tvs, Just tparms) = unLoc $2}
+		            ; (ctxt, tc, tvs, tparms) = unLoc $2}
                       ; checkTyVars tparms False  -- only type vars allowed
 		      ; return $ L (comb4 $1 $2 $3 $4) 
 				   (mkClassDecl (ctxt, tc, tvs) 
@@ -505,19 +505,25 @@ ty_decl :: { LTyClDecl RdrName }
 
         -- data type or newtype declaration
 	| data_or_newtype tycl_hdr constrs deriving
-		{ L (comb4 $1 $2 $3 $4)	-- We need the location on tycl_hdr 
-					-- in case constrs and deriving are
-					-- both empty
-		    (mkTyData (unLoc $1) (unLoc $2) Nothing 
-		       (reverse (unLoc $3)) (unLoc $4)) }
+		{% do { let {(ctxt, tc, tvs, tparms) = unLoc $2}
+                      ; tpats <- checkTyVars tparms True -- can have type pats
+		      ; return $
+			  L (comb4 $1 $2 $3 $4)
+			           -- We need the location on tycl_hdr in case 
+				   -- constrs and deriving are both empty
+			    (mkTyData (unLoc $1) (ctxt, tc, tvs, tpats) 
+			     Nothing (reverse (unLoc $3)) (unLoc $4)) } }
 
         -- GADT declaration
         | data_or_newtype tycl_hdr opt_kind_sig 
 		 'where' gadt_constrlist
 		 deriving
-		{ L (comb4 $1 $2 $4 $5)
-		    (mkTyData (unLoc $1) (unLoc $2) $3
-		       (reverse (unLoc $5)) (unLoc $6)) }
+		{% do { let {(ctxt, tc, tvs, tparms) = unLoc $2}
+                      ; tpats <- checkTyVars tparms True -- can have type pats
+		      ; return $
+			  L (comb4 $1 $2 $4 $5)
+			    (mkTyData (unLoc $1) (ctxt, tc, tvs, tpats) $3
+			     (reverse (unLoc $5)) (unLoc $6)) } }
 
 opt_iso :: { Bool }
 	:       { False }
@@ -540,7 +546,7 @@ opt_kind_sig :: { Maybe Kind }
 	: 				{ Nothing }
 	| '::' kind			{ Just (unLoc $2) }
 
--- tycl_hdr parses the header of a type decl,
+-- tycl_hdr parses the header of a class or data type decl,
 -- which takes the form
 --	T a b
 -- 	Eq a => T a
@@ -550,7 +556,7 @@ opt_kind_sig :: { Maybe Kind }
 tycl_hdr :: { Located (LHsContext RdrName, 
 		       Located RdrName, 
 		       [LHsTyVarBndr RdrName],
-		       Maybe [LHsType RdrName]) }
+		       [LHsType RdrName]) }
 	: context '=>' type		{% checkTyClHdr $1         $3 >>= return.LL }
 	| type				{% checkTyClHdr (noLoc []) $1 >>= return.L1 }
 
diff --git a/compiler/parser/RdrHsSyn.lhs b/compiler/parser/RdrHsSyn.lhs
index b0cf2cf8cc..1867ce6755 100644
--- a/compiler/parser/RdrHsSyn.lhs
+++ b/compiler/parser/RdrHsSyn.lhs
@@ -35,7 +35,7 @@ module RdrHsSyn (
 	checkPrecP, 	      -- Int -> P Int
 	checkContext,	      -- HsType -> P HsContext
 	checkPred,	      -- HsType -> P HsPred
-	checkTyClHdr,         -- LHsContext RdrName -> LHsType RdrName -> P (LHsContext RdrName, Located RdrName, [LHsTyVarBndr RdrName])
+	checkTyClHdr,         -- LHsContext RdrName -> LHsType RdrName -> P (LHsContext RdrName, Located RdrName, [LHsTyVarBndr RdrName], [LHsType RdrName])
 	checkTyVars,          -- [LHsType RdrName] -> Bool -> P ()
 	checkSynHdr,	      -- LHsType RdrName -> P (Located RdrName, [LHsTyVarBndr RdrName], Maybe [LHsType RdrName])
 	checkTopTyClD,	      -- LTyClDecl RdrName -> P (HsDecl RdrName)
@@ -401,7 +401,8 @@ checkTyVars tparms nonVarsOk =
 
 -- Check whether the type arguments in a type synonym head are simply
 -- variables.  If not, we have a type equation of a type function and return
--- all patterns.
+-- all patterns.  If yes, we return 'Nothing' as the third component to
+-- indicate a vanilla type synonym.
 --
 checkSynHdr :: LHsType RdrName 
 	    -> Bool                             -- non-variables admitted?
@@ -409,7 +410,7 @@ checkSynHdr :: LHsType RdrName
 	          [LHsTyVarBndr RdrName],	-- parameters
 		  Maybe [LHsType RdrName])	-- type patterns
 checkSynHdr ty nonVarsOk = 
-  do { (_, tc, tvs, Just tparms) <- checkTyClHdr (noLoc []) ty
+  do { (_, tc, tvs, tparms) <- checkTyClHdr (noLoc []) ty
      ; typats <- checkTyVars tparms nonVarsOk
      ; return (tc, tvs, typats) }
 
@@ -420,8 +421,7 @@ checkTyClHdr :: LHsContext RdrName -> LHsType RdrName
   -> P (LHsContext RdrName,	     -- the type context
         Located RdrName,	     -- the head symbol (type or class name)
 	[LHsTyVarBndr RdrName],	     -- free variables of the non-context part
-	Maybe [LHsType RdrName])     -- parameters of head symbol; wrapped into
-				     -- 'Maybe' for 'mkTyData'
+	[LHsType RdrName])           -- parameters of head symbol
 -- The header of a type or class decl should look like
 --	(C a, D b) => T a b
 -- or	T a b
@@ -437,7 +437,7 @@ checkTyClHdr :: LHsContext RdrName -> LHsType RdrName
 checkTyClHdr (L l cxt) ty
   = do (tc, tvs, parms) <- gol ty []
        mapM_ chk_pred cxt
-       return (L l cxt, tc, tvs, Just parms)
+       return (L l cxt, tc, tvs, parms)
   where
     gol (L l ty) acc = go l ty acc