2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
11 TcMethInfo, buildClass,
13 mkNewTyConRhs, mkDataTyConRhs
16 #include "HsVersions.h"
32 import Data.List ( partition )
38 ------------------------------------------------------
39 buildSynTyCon :: Name -> [TyVar]
41 -> Kind -- ^ Kind of the RHS
43 -> Maybe (TyCon, [Type]) -- ^ family instance if applicable
45 buildSynTyCon tc_name tvs rhs rhs_kind parent mb_family
46 | Just fam_inst_info <- mb_family
47 = ASSERT( isNoParent parent )
48 fixM $ \ tycon_rec -> do
49 { fam_parent <- mkFamInstParentInfo tc_name tvs fam_inst_info tycon_rec
50 ; return (mkSynTyCon tc_name kind tvs rhs fam_parent) }
53 = return (mkSynTyCon tc_name kind tvs rhs parent)
55 kind = mkArrowKinds (map tyVarKind tvs) rhs_kind
57 ------------------------------------------------------
58 buildAlgTyCon :: Name -> [TyVar]
59 -> ThetaType -- ^ Stupid theta
62 -> Bool -- ^ True <=> want generics functions
63 -> Bool -- ^ True <=> was declared in GADT syntax
65 -> Maybe (TyCon, [Type]) -- ^ family instance if applicable
68 buildAlgTyCon tc_name tvs stupid_theta rhs is_rec want_generics gadt_syn
70 | Just fam_inst_info <- mb_family
71 = -- We need to tie a knot as the coercion of a data instance depends
72 -- on the instance representation tycon and vice versa.
73 ASSERT( isNoParent parent )
74 fixM $ \ tycon_rec -> do
75 { fam_parent <- mkFamInstParentInfo tc_name tvs fam_inst_info tycon_rec
76 ; return (mkAlgTyCon tc_name kind tvs stupid_theta rhs
77 fam_parent is_rec want_generics gadt_syn) }
80 = return (mkAlgTyCon tc_name kind tvs stupid_theta rhs
81 parent is_rec want_generics gadt_syn)
83 kind = mkArrowKinds (map tyVarKind tvs) liftedTypeKind
85 -- | If a family tycon with instance types is given, the current tycon is an
86 -- instance of that family and we need to
88 -- (1) create a coercion that identifies the family instance type and the
89 -- representation type from Step (1); ie, it is of the form
90 -- `Co tvs :: F ts ~ R tvs', where `Co' is the name of the coercion,
91 -- `F' the family tycon and `R' the (derived) representation tycon,
93 -- (2) produce a `TyConParent' value containing the parent and coercion
96 mkFamInstParentInfo :: Name -> [TyVar]
99 -> TcRnIf m n TyConParent
100 mkFamInstParentInfo tc_name tvs (family, instTys) rep_tycon
101 = do { -- Create the coercion
102 ; co_tycon_name <- newImplicitBinder tc_name mkInstTyCoOcc
103 ; let co_tycon = mkFamInstCo co_tycon_name tvs
104 family instTys rep_tycon
105 ; return $ FamInstTyCon family instTys co_tycon }
107 ------------------------------------------------------
108 mkAbstractTyConRhs :: AlgTyConRhs
109 mkAbstractTyConRhs = AbstractTyCon
111 mkDataTyConRhs :: [DataCon] -> AlgTyConRhs
115 is_enum = not (null cons) && all is_enum_con cons
116 -- See Note [Enumeration types] in TyCon
120 | (_tvs, theta, arg_tys, _res) <- dataConSig con
121 = null theta && null arg_tys
124 mkNewTyConRhs :: Name -> TyCon -> DataCon -> TcRnIf m n AlgTyConRhs
125 -- ^ Monadic because it makes a Name for the coercion TyCon
126 -- We pass the Name of the parent TyCon, as well as the TyCon itself,
127 -- because the latter is part of a knot, whereas the former is not.
128 mkNewTyConRhs tycon_name tycon con
129 = do { co_tycon_name <- newImplicitBinder tycon_name mkNewTyCoOcc
130 ; let co_tycon = mkNewTypeCo co_tycon_name tycon etad_tvs etad_rhs
131 ; traceIf (text "mkNewTyConRhs" <+> ppr co_tycon)
132 ; return (NewTyCon { data_con = con,
134 nt_etad_rhs = (etad_tvs, etad_rhs),
135 nt_co = co_tycon } ) }
136 -- Coreview looks through newtypes with a Nothing
137 -- for nt_co, or uses explicit coercions otherwise
139 tvs = tyConTyVars tycon
140 inst_con_ty = applyTys (dataConUserType con) (mkTyVarTys tvs)
141 rhs_ty = ASSERT( isFunTy inst_con_ty ) funArgTy inst_con_ty
142 -- Instantiate the data con with the
143 -- type variables from the tycon
144 -- NB: a newtype DataCon has a type that must look like
145 -- forall tvs. <arg-ty> -> T tvs
146 -- Note that we *can't* use dataConInstOrigArgTys here because
147 -- the newtype arising from class Foo a => Bar a where {}
148 -- has a single argument (Foo a) that is a *type class*, so
149 -- dataConInstOrigArgTys returns [].
151 etad_tvs :: [TyVar] -- Matched lazily, so that mkNewTypeCo can
152 etad_rhs :: Type -- return a TyCon without pulling on rhs_ty
153 -- See Note [Tricky iface loop] in LoadIface
154 (etad_tvs, etad_rhs) = eta_reduce (reverse tvs) rhs_ty
156 eta_reduce :: [TyVar] -- Reversed
158 -> ([TyVar], Type) -- Eta-reduced version (tyvars in normal order)
159 eta_reduce (a:as) ty | Just (fun, arg) <- splitAppTy_maybe ty,
160 Just tv <- getTyVar_maybe arg,
162 not (a `elemVarSet` tyVarsOfType fun)
164 eta_reduce tvs ty = (reverse tvs, ty)
167 ------------------------------------------------------
168 buildDataCon :: Name -> Bool
170 -> [Name] -- Field labels
171 -> [TyVar] -> [TyVar] -- Univ and ext
172 -> [(TyVar,Type)] -- Equality spec
173 -> ThetaType -- Does not include the "stupid theta"
174 -- or the GADT equalities
175 -> [Type] -> Type -- Argument and result types
176 -> TyCon -- Rep tycon
177 -> TcRnIf m n DataCon
178 -- A wrapper for DataCon.mkDataCon that
179 -- a) makes the worker Id
180 -- b) makes the wrapper Id if necessary, including
181 -- allocating its unique (hence monadic)
182 buildDataCon src_name declared_infix arg_stricts field_lbls
183 univ_tvs ex_tvs eq_spec ctxt arg_tys res_ty rep_tycon
184 = do { wrap_name <- newImplicitBinder src_name mkDataConWrapperOcc
185 ; work_name <- newImplicitBinder src_name mkDataConWorkerOcc
186 -- This last one takes the name of the data constructor in the source
187 -- code, which (for Haskell source anyway) will be in the DataName name
188 -- space, and puts it into the VarName name space
191 stupid_ctxt = mkDataConStupidTheta rep_tycon arg_tys univ_tvs
192 data_con = mkDataCon src_name declared_infix
193 arg_stricts field_lbls
194 univ_tvs ex_tvs eq_spec ctxt
195 arg_tys res_ty rep_tycon
197 dc_ids = mkDataConIds wrap_name work_name data_con
202 -- The stupid context for a data constructor should be limited to
203 -- the type variables mentioned in the arg_tys
204 -- ToDo: Or functionally dependent on?
205 -- This whole stupid theta thing is, well, stupid.
206 mkDataConStupidTheta :: TyCon -> [Type] -> [TyVar] -> [PredType]
207 mkDataConStupidTheta tycon arg_tys univ_tvs
208 | null stupid_theta = [] -- The common case
209 | otherwise = filter in_arg_tys stupid_theta
211 tc_subst = zipTopTvSubst (tyConTyVars tycon) (mkTyVarTys univ_tvs)
212 stupid_theta = substTheta tc_subst (tyConStupidTheta tycon)
213 -- Start by instantiating the master copy of the
214 -- stupid theta, taken from the TyCon
216 arg_tyvars = tyVarsOfTypes arg_tys
217 in_arg_tys pred = not $ isEmptyVarSet $
218 tyVarsOfPred pred `intersectVarSet` arg_tyvars
222 ------------------------------------------------------
224 type TcMethInfo = (Name, DefMethSpec, Type) -- A temporary intermediate, to communicate
225 -- between tcClassSigs and buildClass
227 buildClass :: Bool -- True <=> do not include unfoldings
229 -- Used when importing a class without -O
230 -> Name -> [TyVar] -> ThetaType
231 -> [FunDep TyVar] -- Functional dependencies
232 -> [TyThing] -- Associated types
233 -> [TcMethInfo] -- Method info
234 -> RecFlag -- Info for type constructor
237 buildClass no_unf class_name tvs sc_theta fds ats sig_stuff tc_isrec
238 = do { traceIf (text "buildClass")
239 ; tycon_name <- newImplicitBinder class_name mkClassTyConOcc
240 ; datacon_name <- newImplicitBinder class_name mkClassDataConOcc
241 -- The class name is the 'parent' for this datacon, not its tycon,
242 -- because one should import the class to get the binding for
245 ; fixM (\ rec_clas -> do { -- Only name generation inside loop
247 ; op_items <- mapM (mk_op_item rec_clas) sig_stuff
248 -- Build the selector id and default method id
250 ; let (eq_theta, dict_theta) = partition isEqPred sc_theta
252 -- We only make selectors for the *value* superclasses,
253 -- not equality predicates
254 ; sc_sel_names <- mapM (newImplicitBinder class_name . mkSuperDictSelOcc)
255 [1..length dict_theta]
256 ; let sc_sel_ids = [ mkDictSelId no_unf sc_name rec_clas
257 | sc_name <- sc_sel_names]
258 -- We number off the Dict superclass selectors, 1, 2, 3 etc so that we
259 -- can construct names for the selectors. Thus
260 -- class (C a, C b) => D a b where ...
261 -- gives superclass selectors
263 -- (We used to call them D_C, but now we can have two different
264 -- superclasses both called C!)
266 ; let use_newtype = null eq_theta && (length dict_theta + length sig_stuff == 1)
267 -- Use a newtype if the data constructor has
268 -- (a) exactly one value field
269 -- (b) no existential or equality-predicate fields
270 -- i.e. exactly one operation or superclass taken together
271 -- See note [Class newtypes and equality predicates]
273 -- We play a bit fast and loose by treating the dictionary
274 -- superclasses as ordinary arguments. That means that in
277 -- we don't get a newtype with no arguments!
278 args = sc_sel_names ++ op_names
279 op_tys = [ty | (_,_,ty) <- sig_stuff]
280 op_names = [op | (op,_,_) <- sig_stuff]
281 arg_tys = map mkPredTy dict_theta ++ op_tys
282 rec_tycon = classTyCon rec_clas
284 ; dict_con <- buildDataCon datacon_name
285 False -- Not declared infix
286 (map (const HsNoBang) args)
288 tvs [{- no existentials -}]
289 [{- No GADT equalities -}]
292 (mkTyConApp rec_tycon (mkTyVarTys tvs))
295 ; rhs <- if use_newtype
296 then mkNewTyConRhs tycon_name rec_tycon dict_con
297 else return (mkDataTyConRhs [dict_con])
299 ; let { clas_kind = mkArrowKinds (map tyVarKind tvs) liftedTypeKind
301 ; tycon = mkClassTyCon tycon_name clas_kind tvs
302 rhs rec_clas tc_isrec
303 -- A class can be recursive, and in the case of newtypes
304 -- this matters. For example
305 -- class C a where { op :: C b => a -> b -> Int }
306 -- Because C has only one operation, it is represented by
307 -- a newtype, and it should be a *recursive* newtype.
308 -- [If we don't make it a recursive newtype, we'll expand the
309 -- newtype like a synonym, but that will lead to an infinite
311 ; atTyCons = [tycon | ATyCon tycon <- ats]
313 ; result = mkClass class_name tvs fds
314 (eq_theta ++ dict_theta) -- Equalities first
315 (length eq_theta) -- Number of equalities
319 ; traceIf (text "buildClass" <+> ppr tycon)
323 mk_op_item :: Class -> TcMethInfo -> TcRnIf n m ClassOpItem
324 mk_op_item rec_clas (op_name, dm_spec, _)
325 = do { dm_info <- case dm_spec of
326 NoDM -> return NoDefMeth
327 GenericDM -> return GenDefMeth
328 VanillaDM -> do { dm_name <- newImplicitBinder op_name mkDefaultMethodOcc
329 ; return (DefMeth dm_name) }
330 ; return (mkDictSelId no_unf op_name rec_clas, dm_info) }
333 Note [Class newtypes and equality predicates]
334 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
336 class (a ~ F b) => C a b where
339 We cannot represent this by a newtype, even though it's not
340 existential, and there's only one value field, because we do
341 capture an equality predicate:
344 MkC :: forall a b. (a ~ F b) => (a->b) -> C a b
346 We need to access this equality predicate when we get passes a C
347 dictionary. See Trac #2238