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 = mkFamInstCoercion 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 = -- We define datatypes with no constructors to not be
116 -- enumerations; this fixes trac #2578, Otherwise we
117 -- end up generating an empty table for
118 -- <mod>_<type>_closure_tbl
119 -- which is used by tagToEnum# to map Int# to constructors
120 -- in an enumeration. The empty table apparently upset
123 all isNullarySrcDataCon cons
126 mkNewTyConRhs :: Name -> TyCon -> DataCon -> TcRnIf m n AlgTyConRhs
127 -- ^ Monadic because it makes a Name for the coercion TyCon
128 -- We pass the Name of the parent TyCon, as well as the TyCon itself,
129 -- because the latter is part of a knot, whereas the former is not.
130 mkNewTyConRhs tycon_name tycon con
131 = do { co_tycon_name <- newImplicitBinder tycon_name mkNewTyCoOcc
132 ; let co_tycon = mkNewTypeCoercion co_tycon_name tycon etad_tvs etad_rhs
133 cocon_maybe | all_coercions || isRecursiveTyCon tycon
137 ; traceIf (text "mkNewTyConRhs" <+> ppr cocon_maybe)
138 ; return (NewTyCon { data_con = con,
140 nt_etad_rhs = (etad_tvs, etad_rhs),
141 nt_co = cocon_maybe } ) }
142 -- Coreview looks through newtypes with a Nothing
143 -- for nt_co, or uses explicit coercions otherwise
145 -- If all_coercions is True then we use coercions for all newtypes
146 -- otherwise we use coercions for recursive newtypes and look through
147 -- non-recursive newtypes
149 tvs = tyConTyVars tycon
150 inst_con_ty = applyTys (dataConUserType con) (mkTyVarTys tvs)
151 rhs_ty = ASSERT( isFunTy inst_con_ty ) funArgTy inst_con_ty
152 -- Instantiate the data con with the
153 -- type variables from the tycon
154 -- NB: a newtype DataCon has a type that must look like
155 -- forall tvs. <arg-ty> -> T tvs
156 -- Note that we *can't* use dataConInstOrigArgTys here because
157 -- the newtype arising from class Foo a => Bar a where {}
158 -- has a single argument (Foo a) that is a *type class*, so
159 -- dataConInstOrigArgTys returns [].
161 etad_tvs :: [TyVar] -- Matched lazily, so that mkNewTypeCoercion can
162 etad_rhs :: Type -- return a TyCon without pulling on rhs_ty
163 -- See Note [Tricky iface loop] in LoadIface
164 (etad_tvs, etad_rhs) = eta_reduce (reverse tvs) rhs_ty
166 eta_reduce :: [TyVar] -- Reversed
168 -> ([TyVar], Type) -- Eta-reduced version (tyvars in normal order)
169 eta_reduce (a:as) ty | Just (fun, arg) <- splitAppTy_maybe ty,
170 Just tv <- getTyVar_maybe arg,
172 not (a `elemVarSet` tyVarsOfType fun)
174 eta_reduce tvs ty = (reverse tvs, ty)
177 ------------------------------------------------------
178 buildDataCon :: Name -> Bool
180 -> [Name] -- Field labels
181 -> [TyVar] -> [TyVar] -- Univ and ext
182 -> [(TyVar,Type)] -- Equality spec
183 -> ThetaType -- Does not include the "stupid theta"
184 -- or the GADT equalities
185 -> [Type] -> Type -- Argument and result types
186 -> TyCon -- Rep tycon
187 -> TcRnIf m n DataCon
188 -- A wrapper for DataCon.mkDataCon that
189 -- a) makes the worker Id
190 -- b) makes the wrapper Id if necessary, including
191 -- allocating its unique (hence monadic)
192 buildDataCon src_name declared_infix arg_stricts field_lbls
193 univ_tvs ex_tvs eq_spec ctxt arg_tys res_ty rep_tycon
194 = do { wrap_name <- newImplicitBinder src_name mkDataConWrapperOcc
195 ; work_name <- newImplicitBinder src_name mkDataConWorkerOcc
196 -- This last one takes the name of the data constructor in the source
197 -- code, which (for Haskell source anyway) will be in the DataName name
198 -- space, and puts it into the VarName name space
201 stupid_ctxt = mkDataConStupidTheta rep_tycon arg_tys univ_tvs
202 data_con = mkDataCon src_name declared_infix
203 arg_stricts field_lbls
204 univ_tvs ex_tvs eq_spec ctxt
205 arg_tys res_ty rep_tycon
207 dc_ids = mkDataConIds wrap_name work_name data_con
212 -- The stupid context for a data constructor should be limited to
213 -- the type variables mentioned in the arg_tys
214 -- ToDo: Or functionally dependent on?
215 -- This whole stupid theta thing is, well, stupid.
216 mkDataConStupidTheta :: TyCon -> [Type] -> [TyVar] -> [PredType]
217 mkDataConStupidTheta tycon arg_tys univ_tvs
218 | null stupid_theta = [] -- The common case
219 | otherwise = filter in_arg_tys stupid_theta
221 tc_subst = zipTopTvSubst (tyConTyVars tycon) (mkTyVarTys univ_tvs)
222 stupid_theta = substTheta tc_subst (tyConStupidTheta tycon)
223 -- Start by instantiating the master copy of the
224 -- stupid theta, taken from the TyCon
226 arg_tyvars = tyVarsOfTypes arg_tys
227 in_arg_tys pred = not $ isEmptyVarSet $
228 tyVarsOfPred pred `intersectVarSet` arg_tyvars
232 ------------------------------------------------------
234 type TcMethInfo = (Name, DefMethSpec, Type) -- A temporary intermediate, to communicate
235 -- between tcClassSigs and buildClass
237 buildClass :: Bool -- True <=> do not include unfoldings
239 -- Used when importing a class without -O
240 -> Name -> [TyVar] -> ThetaType
241 -> [FunDep TyVar] -- Functional dependencies
242 -> [TyThing] -- Associated types
243 -> [TcMethInfo] -- Method info
244 -> RecFlag -- Info for type constructor
247 buildClass no_unf class_name tvs sc_theta fds ats sig_stuff tc_isrec
248 = do { traceIf (text "buildClass")
249 ; tycon_name <- newImplicitBinder class_name mkClassTyConOcc
250 ; datacon_name <- newImplicitBinder class_name mkClassDataConOcc
251 -- The class name is the 'parent' for this datacon, not its tycon,
252 -- because one should import the class to get the binding for
255 ; fixM (\ rec_clas -> do { -- Only name generation inside loop
257 ; op_items <- mapM (mk_op_item rec_clas) sig_stuff
258 -- Build the selector id and default method id
260 ; let (eq_theta, dict_theta) = partition isEqPred sc_theta
262 -- We only make selectors for the *value* superclasses,
263 -- not equality predicates
264 ; sc_sel_names <- mapM (newImplicitBinder class_name . mkSuperDictSelOcc)
265 [1..length dict_theta]
266 ; let sc_sel_ids = [ mkDictSelId no_unf sc_name rec_clas
267 | sc_name <- sc_sel_names]
268 -- We number off the Dict superclass selectors, 1, 2, 3 etc so that we
269 -- can construct names for the selectors. Thus
270 -- class (C a, C b) => D a b where ...
271 -- gives superclass selectors
273 -- (We used to call them D_C, but now we can have two different
274 -- superclasses both called C!)
276 ; let use_newtype = null eq_theta && (length dict_theta + length sig_stuff == 1)
277 -- Use a newtype if the data constructor has
278 -- (a) exactly one value field
279 -- (b) no existential or equality-predicate fields
280 -- i.e. exactly one operation or superclass taken together
281 -- See note [Class newtypes and equality predicates]
283 -- We play a bit fast and loose by treating the dictionary
284 -- superclasses as ordinary arguments. That means that in
287 -- we don't get a newtype with no arguments!
288 args = sc_sel_names ++ op_names
289 op_tys = [ty | (_,_,ty) <- sig_stuff]
290 op_names = [op | (op,_,_) <- sig_stuff]
291 arg_tys = map mkPredTy dict_theta ++ op_tys
292 rec_tycon = classTyCon rec_clas
294 ; dict_con <- buildDataCon datacon_name
295 False -- Not declared infix
296 (map (const HsNoBang) args)
298 tvs [{- no existentials -}]
299 [{- No GADT equalities -}]
302 (mkTyConApp rec_tycon (mkTyVarTys tvs))
305 ; rhs <- if use_newtype
306 then mkNewTyConRhs tycon_name rec_tycon dict_con
307 else return (mkDataTyConRhs [dict_con])
309 ; let { clas_kind = mkArrowKinds (map tyVarKind tvs) liftedTypeKind
311 ; tycon = mkClassTyCon tycon_name clas_kind tvs
312 rhs rec_clas tc_isrec
313 -- A class can be recursive, and in the case of newtypes
314 -- this matters. For example
315 -- class C a where { op :: C b => a -> b -> Int }
316 -- Because C has only one operation, it is represented by
317 -- a newtype, and it should be a *recursive* newtype.
318 -- [If we don't make it a recursive newtype, we'll expand the
319 -- newtype like a synonym, but that will lead to an infinite
321 ; atTyCons = [tycon | ATyCon tycon <- ats]
323 ; result = mkClass class_name tvs fds
324 (eq_theta ++ dict_theta) -- Equalities first
325 (length eq_theta) -- Number of equalities
329 ; traceIf (text "buildClass" <+> ppr tycon)
333 mk_op_item :: Class -> TcMethInfo -> TcRnIf n m ClassOpItem
334 mk_op_item rec_clas (op_name, dm_spec, _)
335 = do { dm_info <- case dm_spec of
336 NoDM -> return NoDefMeth
337 GenericDM -> return GenDefMeth
338 VanillaDM -> do { dm_name <- newImplicitBinder op_name mkDefaultMethodOcc
339 ; return (DefMeth dm_name) }
340 ; return (mkDictSelId no_unf op_name rec_clas, dm_info) }
343 Note [Class newtypes and equality predicates]
344 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
346 class (a ~ F b) => C a b where
349 We cannot represent this by a newtype, even though it's not
350 existential, and there's only one value field, because we do
351 capture an equality predicate:
354 MkC :: forall a b. (a ~ F b) => (a->b) -> C a b
356 We need to access this equality predicate when we get passes a C
357 dictionary. See Trac #2238