mkDataCon,
dataConRepType, dataConSig, dataConName, dataConTag, dataConTyCon,
dataConArgTys, dataConOrigArgTys, dataConInstOrigArgTys,
- dataConRepArgTys, dataConTheta,
+ dataConRepArgTys, dataConTheta,
dataConFieldLabels, dataConStrictMarks,
dataConSourceArity, dataConRepArity,
- dataConNumInstArgs, dataConId, dataConWrapId, dataConRepStrictness,
+ dataConNumInstArgs, dataConWorkId, dataConWrapId, dataConRepStrictness,
isNullaryDataCon, isTupleCon, isUnboxedTupleCon,
- isExistentialDataCon, classDataCon,
+ isExistentialDataCon, classDataCon, dataConExistentialTyVars,
splitProductType_maybe, splitProductType,
) where
import {-# SOURCE #-} Subst( substTyWith )
import {-# SOURCE #-} PprType( pprType )
-import Type ( Type, TauType, ThetaType,
+import Type ( Type, ThetaType,
mkForAllTys, mkFunTys, mkTyConApp,
mkTyVarTys, splitTyConApp_maybe, repType,
mkPredTys, isStrictType
)
-import TyCon ( TyCon, tyConDataCons, tyConDataConsIfAvailable, isProductTyCon,
+import TyCon ( TyCon, tyConDataCons, tyConDataCons, isProductTyCon,
isTupleTyCon, isUnboxedTupleTyCon, isRecursiveTyCon )
import Class ( Class, classTyCon )
import Name ( Name, NamedThing(..), nameUnique )
import CmdLineOpts ( opt_UnboxStrictFields )
import Maybe
import ListSetOps ( assoc )
-import Util ( zipEqual, zipWithEqual, equalLength )
+import Util ( zipEqual, zipWithEqual, equalLength, notNull )
\end{code}
The worker is very like a primop, in that it has no binding,
+A note about the stupid context
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Data types can have a context:
+
+ data (Eq a, Ord b) => T a b = T1 a b | T2 a
+
+and that makes the constructors have a context too
+(notice that T2's context is "thinned"):
+
+ T1 :: (Eq a, Ord b) => a -> b -> T a b
+ T2 :: (Eq a) => a -> T a b
+
+Furthermore, this context pops up when pattern matching
+(though GHC hasn't implemented this, but it is in H98, and
+I've fixed GHC so that it now does):
+
+ f (T2 x) = x
+gets inferred type
+ f :: Eq a => T a b -> a
+
+I say the context is "stupid" because the dictionaries passed
+are immediately discarded -- they do nothing and have no benefit.
+It's a flaw in the language.
+
+Up to now [March 2002] I have put this stupid context into the type of
+the "wrapper" constructors functions, T1 and T2, but that turned out
+to be jolly inconvenient for generics, and record update, and other
+functions that build values of type T (because they don't have
+suitable dictionaries available).
+
+So now I've taken the stupid context out. I simply deal with it
+separately in the type checker on occurrences of a constructor, either
+in an expression or in a pattern.
+
+
%************************************************************************
%* *
-- data Eq a => T a = forall b. Ord b => MkT a [b]
dcRepType :: Type, -- Type of the constructor
- -- forall ab . Ord b => a -> [b] -> MkT a
- -- (this is *not* of the constructor Id:
+ -- forall a b . Ord b => a -> [b] -> MkT a
+ -- (this is *not* of the constructor wrapper Id:
-- see notes after this data type declaration)
+ --
+ -- 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]) -> ... }
+ -- It's convenient to apply the rep-type of MkT to 't', to get
+ -- forall b. Ord b => ...
+ -- and use that to check the pattern. Mind you, this is really only
+ -- use in CoreLint.
+
-- The next six fields express the type of the constructor, in pieces
-- e.g.
-- dcOrigArgTys = [a,List b]
-- dcTyCon = T
- dcTyVars :: [TyVar], -- Type vars and context for the data type decl
+ dcTyVars :: [TyVar], -- Type vars for the data type decl
-- These are ALWAYS THE SAME AS THE TYVARS
-- FOR THE PARENT TyCon. We occasionally rely on
-- this just to avoid redundant instantiation
- dcTheta :: ThetaType,
+
+ dcStupidTheta :: ThetaType, -- This is a "thinned" version of the context of
+ -- the data decl.
+ -- "Thinned", because the Report says
+ -- to eliminate any constraints that don't mention
+ -- tyvars free in the arg types for this constructor
+ --
+ -- "Stupid", because the dictionaries aren't used for anything.
+ --
+ -- Indeed, [as of March 02] they are no
+ -- longer in the type of the dataConWrapId, because
+ -- that makes it harder to use the wrap-id to rebuild
+ -- values after record selection or in generics.
dcExTyVars :: [TyVar], -- Ditto for the context of the constructor,
dcExTheta :: ThetaType, -- the existentially quantified stuff
--
-- An entirely separate wrapper function is built in TcTyDecls
- dcId :: Id, -- The corresponding worker Id
+ dcWorkId :: Id, -- The corresponding worker Id
-- Takes dcRepArgTys as its arguments
dcWrapId :: Id -- The wrapper Id
%************************************************************************
%* *
-\subsection{Consruction}
+\subsection{Construction}
%* *
%************************************************************************
-> [StrictnessMark] -> [FieldLabel]
-> [TyVar] -> ThetaType
-> [TyVar] -> ThetaType
- -> [TauType] -> TyCon
+ -> [Type] -> TyCon
-> Id -> Id
-> DataCon
-- Can get the tag from the TyCon
con
where
con = MkData {dcName = name, dcUnique = nameUnique name,
- dcTyVars = tyvars, dcTheta = theta,
+ dcTyVars = tyvars, dcStupidTheta = theta,
dcOrigArgTys = orig_arg_tys,
dcRepArgTys = rep_arg_tys,
dcExTyVars = ex_tyvars, dcExTheta = ex_theta,
dcStrictMarks = real_stricts, dcRepStrictness = rep_arg_stricts,
dcFields = fields, dcTag = tag, dcTyCon = tycon, dcRepType = ty,
- dcId = work_id, dcWrapId = wrap_id}
+ dcWorkId = work_id, dcWrapId = wrap_id}
-- Strictness marks for source-args
-- *after unboxing choices*,
dataConRepType :: DataCon -> Type
dataConRepType = dcRepType
-dataConId :: DataCon -> Id
-dataConId = dcId
+dataConWorkId :: DataCon -> Id
+dataConWorkId = dcWorkId
dataConWrapId :: DataCon -> Id
dataConWrapId = dcWrapId
dataConSig :: DataCon -> ([TyVar], ThetaType,
[TyVar], ThetaType,
- [TauType], TyCon)
+ [Type], TyCon)
-dataConSig (MkData {dcTyVars = tyvars, dcTheta = theta,
+dataConSig (MkData {dcTyVars = tyvars, dcStupidTheta = theta,
dcExTyVars = ex_tyvars, dcExTheta = ex_theta,
dcOrigArgTys = arg_tys, dcTyCon = tycon})
= (tyvars, theta, ex_tyvars, ex_theta, arg_tys, tycon)
= map (substTyWith (tyvars ++ ex_tyvars) inst_tys) arg_tys
dataConTheta :: DataCon -> ThetaType
-dataConTheta dc = dcTheta dc
+dataConTheta dc = dcStupidTheta dc
+
+dataConExistentialTyVars :: DataCon -> [TyVar]
+dataConExistentialTyVars dc = dcExTyVars dc
-- And the same deal for the original arg tys:
dataConOrigArgTys :: DataCon -> [Type]
dataConOrigArgTys dc = dcOrigArgTys dc
-dataConRepArgTys :: DataCon -> [TauType]
+dataConRepArgTys :: DataCon -> [Type]
dataConRepArgTys dc = dcRepArgTys dc
\end{code}
isUnboxedTupleCon (MkData {dcTyCon = tc}) = isUnboxedTupleTyCon tc
isExistentialDataCon :: DataCon -> Bool
-isExistentialDataCon (MkData {dcExTyVars = tvs}) = not (null tvs)
+isExistentialDataCon (MkData {dcExTyVars = tvs}) = notNull tvs
\end{code}
-- and for constructors visible
-> Just (tycon, ty_args, data_con, dataConArgTys data_con ty_args)
where
- data_con = head (tyConDataConsIfAvailable tycon)
+ data_con = head (tyConDataCons tycon)
other -> Nothing
splitProductType str ty
projects / ghc-hetmet.git / blobdiff