Big tidy-up of deriving code

[ghc-hetmet.git] / compiler / basicTypes / DataCon.lhs

diff --git a/compiler/basicTypes/DataCon.lhs b/compiler/basicTypes/DataCon.lhs
index 0b0dead..0fb7fae 100644 (file)
--- a/compiler/basicTypes/DataCon.lhs
+++ b/compiler/basicTypes/DataCon.lhs
@@ -1,4 +1,5 @@
 %
+% (c) The University of Glasgow 2006
 % (c) The GRASP/AQUA Project, Glasgow University, 1998
 %
 \section[DataCon]{@DataCon@: Data Constructors}
@@ -29,27 +30,18 @@ module DataCon (
 
 #include "HsVersions.h"
 
-import Type            ( Type, ThetaType, 
-                         substTyWith, substTyVar, mkTopTvSubst, 
-                         mkForAllTys, mkFunTys, mkTyConApp, mkTyVarTy, mkTyVarTys, 
-                         splitTyConApp_maybe, newTyConInstRhs, 
-                         mkPredTys, isStrictPred, pprType, mkPredTy
-                       )
-import Coercion                ( isEqPred, mkEqPred )
-import TyCon           ( TyCon, FieldLabel, tyConDataCons, 
-                         isProductTyCon, isTupleTyCon, isUnboxedTupleTyCon,
-                          isNewTyCon, isRecursiveTyCon )
-import Class           ( Class, classTyCon )
-import Name            ( Name, NamedThing(..), nameUnique, mkSysTvName, mkSystemName )
-+ import Var           ( TyVar, CoVar, Id, mkTyVar, tyVarKind, setVarUnique,
-+                           mkCoVar )
-import BasicTypes      ( Arity, StrictnessMark(..) )
+import Type
+import Coercion
+import TyCon
+import Class
+import Name
+import Var
+import BasicTypes
 import Outputable
-import Unique          ( Unique, Uniquable(..) )
-import ListSetOps      ( assoc, minusList )
-import Util            ( zipEqual, zipWithEqual )
-import List            ( partition )
-import Maybes           ( expectJust )
+import Unique
+import ListSetOps
+import Util
+import Maybes
 import FastString
 \end{code}
 
@@ -261,6 +253,9 @@ data DataCon
                -- [This is a change (Oct05): previously, vanilla datacons guaranteed to
                --  have the same type variables as their parent TyCon, but that seems ugly.]
 
+       -- INVARIANT: the UnivTyVars and ExTyVars all have distinct OccNames
+       -- Reason: less confusing, and easier to generate IfaceSyn
+
        dcEqSpec :: [(TyVar,Type)],     -- Equalities derived from the result type, 
                                        -- *as written by the programmer*
                -- This field allows us to move conveniently between the two ways
@@ -314,6 +309,7 @@ data DataCon
                                        -- and *including* existential dictionaries
 
        dcRepStrictness :: [StrictnessMark],    -- One for each *representation* argument       
+               -- See also Note [Data-con worker strictness] in MkId.lhs
 
        dcRepType   :: Type,    -- Type of the constructor
                                --      forall a x y. (a:=:(x,y), Ord x) => x -> y -> MkT a
@@ -444,22 +440,29 @@ mkDataCon name declared_infix
          eq_spec theta
          orig_arg_tys tycon
          stupid_theta ids
+-- Warning: mkDataCon is not a good place to check invariants. 
+-- If the programmer writes the wrong result type in the decl, thus:
+--     data T a where { MkT :: S }
+-- then it's possible that the univ_tvs may hit an assertion failure
+-- if you pull on univ_tvs.  This case is checked by checkValidDataCon,
+-- so the error is detected properly... it's just that asaertions here
+-- are a little dodgy.
+
   = ASSERT( not (any isEqPred theta) )
        -- We don't currently allow any equality predicates on
        -- a data constructor (apart from the GADT ones in eq_spec)
     con
   where
     is_vanilla = null ex_tvs && null eq_spec && null theta
-    con = ASSERT( is_vanilla || not (isNewTyCon tycon) )
-               -- Invariant: newtypes have a vanilla data-con
-         MkData {dcName = name, dcUnique = nameUnique name, 
+    con = MkData {dcName = name, dcUnique = nameUnique name, 
                  dcVanilla = is_vanilla, dcInfix = declared_infix,
                  dcUnivTyVars = univ_tvs, dcExTyVars = ex_tvs, 
                  dcEqSpec = eq_spec, 
                  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 }
 
@@ -606,6 +609,8 @@ 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,
@@ -613,7 +618,9 @@ 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 (substTyVars subst univ_tvs)
+      Just (ftc, insttys) -> mkTyConApp ftc insttys        -- data instance
   where
     subst = mkTopTvSubst eq_spec
 
@@ -722,9 +729,10 @@ 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
        }
@@ -746,6 +754,6 @@ computeRep stricts tys
     unbox MarkedStrict    ty = [(MarkedStrict,    ty)]
     unbox MarkedUnboxed   ty = zipEqual "computeRep" (dataConRepStrictness arg_dc) arg_tys
                                where
-                                 (tycon, tycon_args, arg_dc, arg_tys) 
+                                 (_tycon, _tycon_args, arg_dc, arg_tys) 
                                      = deepSplitProductType "unbox_strict_arg_ty" ty
 \end{code}