2 % (c) The University of Glasgow 2006
3 % (c) The AQUA Project, Glasgow University, 1996-1998
6 TcTyClsDecls: Typecheck type and class declarations
10 tcTyAndClassDecls, tcFamInstDecl, mkAuxBinds
13 #include "HsVersions.h"
27 import TysWiredIn ( unitTy )
35 import MkId ( rEC_SEL_ERROR_ID )
51 import Unique ( mkBuiltinUnique )
56 import Control.Monad ( mplus )
60 %************************************************************************
62 \subsection{Type checking for type and class declarations}
64 %************************************************************************
68 Consider a mutually-recursive group, binding
69 a type constructor T and a class C.
71 Step 1: getInitialKind
72 Construct a KindEnv by binding T and C to a kind variable
75 In that environment, do a kind check
77 Step 3: Zonk the kinds
79 Step 4: buildTyConOrClass
80 Construct an environment binding T to a TyCon and C to a Class.
81 a) Their kinds comes from zonking the relevant kind variable
82 b) Their arity (for synonyms) comes direct from the decl
83 c) The funcional dependencies come from the decl
84 d) The rest comes a knot-tied binding of T and C, returned from Step 4
85 e) The variances of the tycons in the group is calculated from
89 In this environment, walk over the decls, constructing the TyCons and Classes.
90 This uses in a strict way items (a)-(c) above, which is why they must
91 be constructed in Step 4. Feed the results back to Step 4.
92 For this step, pass the is-recursive flag as the wimp-out flag
96 Step 6: Extend environment
97 We extend the type environment with bindings not only for the TyCons and Classes,
98 but also for their "implicit Ids" like data constructors and class selectors
100 Step 7: checkValidTyCl
101 For a recursive group only, check all the decls again, just
102 to check all the side conditions on validity. We could not
103 do this before because we were in a mutually recursive knot.
105 Identification of recursive TyCons
106 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
107 The knot-tying parameters: @rec_details_list@ is an alist mapping @Name@s to
110 Identifying a TyCon as recursive serves two purposes
112 1. Avoid infinite types. Non-recursive newtypes are treated as
113 "transparent", like type synonyms, after the type checker. If we did
114 this for all newtypes, we'd get infinite types. So we figure out for
115 each newtype whether it is "recursive", and add a coercion if so. In
116 effect, we are trying to "cut the loops" by identifying a loop-breaker.
118 2. Avoid infinite unboxing. This is nothing to do with newtypes.
122 Well, this function diverges, but we don't want the strictness analyser
123 to diverge. But the strictness analyser will diverge because it looks
124 deeper and deeper into the structure of T. (I believe there are
125 examples where the function does something sane, and the strictness
126 analyser still diverges, but I can't see one now.)
128 Now, concerning (1), the FC2 branch currently adds a coercion for ALL
129 newtypes. I did this as an experiment, to try to expose cases in which
130 the coercions got in the way of optimisations. If it turns out that we
131 can indeed always use a coercion, then we don't risk recursive types,
132 and don't need to figure out what the loop breakers are.
134 For newtype *families* though, we will always have a coercion, so they
135 are always loop breakers! So you can easily adjust the current
136 algorithm by simply treating all newtype families as loop breakers (and
137 indeed type families). I think.
140 tcTyAndClassDecls :: ModDetails -> [LTyClDecl Name]
141 -> TcM (TcGblEnv, -- Input env extended by types and classes
142 -- and their implicit Ids,DataCons
143 HsValBinds Name) -- Renamed bindings for record selectors
144 -- Fails if there are any errors
146 tcTyAndClassDecls boot_details allDecls
147 = checkNoErrs $ -- The code recovers internally, but if anything gave rise to
148 -- an error we'd better stop now, to avoid a cascade
149 do { -- Omit instances of type families; they are handled together
150 -- with the *heads* of class instances
151 ; let decls = filter (not . isFamInstDecl . unLoc) allDecls
153 -- First check for cyclic type synonysm or classes
154 -- See notes with checkCycleErrs
155 ; checkCycleErrs decls
157 ; traceTc (text "tcTyAndCl" <+> ppr mod)
158 ; (syn_tycons, alg_tyclss) <- fixM (\ ~(_rec_syn_tycons, rec_alg_tyclss) ->
159 do { let { -- Seperate ordinary synonyms from all other type and
160 -- class declarations and add all associated type
161 -- declarations from type classes. The latter is
162 -- required so that the temporary environment for the
163 -- knot includes all associated family declarations.
164 ; (syn_decls, alg_decls) = partition (isSynDecl . unLoc)
166 ; alg_at_decls = concatMap addATs alg_decls
168 -- Extend the global env with the knot-tied results
169 -- for data types and classes
171 -- We must populate the environment with the loop-tied
172 -- T's right away, because the kind checker may "fault
173 -- in" some type constructors that recursively
175 ; let gbl_things = mkGlobalThings alg_at_decls rec_alg_tyclss
176 ; tcExtendRecEnv gbl_things $ do
178 -- Kind-check the declarations
179 { (kc_syn_decls, kc_alg_decls) <- kcTyClDecls syn_decls alg_decls
181 ; let { -- Calculate rec-flag
182 ; calc_rec = calcRecFlags boot_details rec_alg_tyclss
183 ; tc_decl = addLocM (tcTyClDecl calc_rec) }
185 -- Type-check the type synonyms, and extend the envt
186 ; syn_tycons <- tcSynDecls kc_syn_decls
187 ; tcExtendGlobalEnv syn_tycons $ do
189 -- Type-check the data types and classes
190 { alg_tyclss <- mapM tc_decl kc_alg_decls
191 ; return (syn_tycons, concat alg_tyclss)
193 -- Finished with knot-tying now
194 -- Extend the environment with the finished things
195 ; tcExtendGlobalEnv (syn_tycons ++ alg_tyclss) $ do
197 -- Perform the validity check
198 { traceTc (text "ready for validity check")
199 ; mapM_ (addLocM checkValidTyCl) decls
200 ; traceTc (text "done")
202 -- Add the implicit things;
203 -- we want them in the environment because
204 -- they may be mentioned in interface files
205 -- NB: All associated types and their implicit things will be added a
206 -- second time here. This doesn't matter as the definitions are
208 ; let { implicit_things = concatMap implicitTyThings alg_tyclss
209 ; aux_binds = mkAuxBinds alg_tyclss }
210 ; traceTc ((text "Adding" <+> ppr alg_tyclss)
211 $$ (text "and" <+> ppr implicit_things))
212 ; env <- tcExtendGlobalEnv implicit_things getGblEnv
213 ; return (env, aux_binds) }
216 -- Pull associated types out of class declarations, to tie them into the
218 -- NB: We put them in the same place in the list as `tcTyClDecl' will
219 -- eventually put the matching `TyThing's. That's crucial; otherwise,
220 -- the two argument lists of `mkGlobalThings' don't match up.
221 addATs decl@(L _ (ClassDecl {tcdATs = ats})) = decl : ats
224 mkGlobalThings :: [LTyClDecl Name] -- The decls
225 -> [TyThing] -- Knot-tied, in 1-1 correspondence with the decls
227 -- Driven by the Decls, and treating the TyThings lazily
228 -- make a TypeEnv for the new things
229 mkGlobalThings decls things
230 = map mk_thing (decls `zipLazy` things)
232 mk_thing (L _ (ClassDecl {tcdLName = L _ name}), ~(AClass cl))
234 mk_thing (L _ decl, ~(ATyCon tc))
235 = (tcdName decl, ATyCon tc)
239 %************************************************************************
241 Type checking family instances
243 %************************************************************************
245 Family instances are somewhat of a hybrid. They are processed together with
246 class instance heads, but can contain data constructors and hence they share a
247 lot of kinding and type checking code with ordinary algebraic data types (and
251 tcFamInstDecl :: LTyClDecl Name -> TcM TyThing
252 tcFamInstDecl (L loc decl)
253 = -- Prime error recovery, set source location
256 do { -- type families require -XTypeFamilies and can't be in an
258 ; type_families <- doptM Opt_TypeFamilies
259 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
260 ; checkTc type_families $ badFamInstDecl (tcdLName decl)
261 ; checkTc (not is_boot) $ badBootFamInstDeclErr
263 -- Perform kind and type checking
264 ; tc <- tcFamInstDecl1 decl
265 ; checkValidTyCon tc -- Remember to check validity;
266 -- no recursion to worry about here
267 ; return (ATyCon tc) }
269 tcFamInstDecl1 :: TyClDecl Name -> TcM TyCon
272 tcFamInstDecl1 (decl@TySynonym {tcdLName = L loc tc_name})
273 = kcIdxTyPats decl $ \k_tvs k_typats resKind family ->
274 do { -- check that the family declaration is for a synonym
275 unless (isSynTyCon family) $
276 addErr (wrongKindOfFamily family)
278 ; -- (1) kind check the right-hand side of the type equation
279 ; k_rhs <- kcCheckHsType (tcdSynRhs decl) resKind
281 -- we need the exact same number of type parameters as the family
283 ; let famArity = tyConArity family
284 ; checkTc (length k_typats == famArity) $
285 wrongNumberOfParmsErr famArity
287 -- (2) type check type equation
288 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
289 ; t_typats <- mapM tcHsKindedType k_typats
290 ; t_rhs <- tcHsKindedType k_rhs
292 -- (3) check the well-formedness of the instance
293 ; checkValidTypeInst t_typats t_rhs
295 -- (4) construct representation tycon
296 ; rep_tc_name <- newFamInstTyConName tc_name loc
297 ; buildSynTyCon rep_tc_name t_tvs (SynonymTyCon t_rhs)
298 (typeKind t_rhs) (Just (family, t_typats))
301 -- "newtype instance" and "data instance"
302 tcFamInstDecl1 (decl@TyData {tcdND = new_or_data, tcdLName = L loc tc_name,
304 = kcIdxTyPats decl $ \k_tvs k_typats resKind fam_tycon ->
305 do { -- check that the family declaration is for the right kind
306 unless (isAlgTyCon fam_tycon) $
307 addErr (wrongKindOfFamily fam_tycon)
309 ; -- (1) kind check the data declaration as usual
310 ; k_decl <- kcDataDecl decl k_tvs
311 ; let k_ctxt = tcdCtxt k_decl
312 k_cons = tcdCons k_decl
314 -- result kind must be '*' (otherwise, we have too few patterns)
315 ; checkTc (isLiftedTypeKind resKind) $ tooFewParmsErr (tyConArity fam_tycon)
317 -- (2) type check indexed data type declaration
318 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
319 ; unbox_strict <- doptM Opt_UnboxStrictFields
321 -- kind check the type indexes and the context
322 ; t_typats <- mapM tcHsKindedType k_typats
323 ; stupid_theta <- tcHsKindedContext k_ctxt
326 -- (a) left-hand side contains no type family applications
327 -- (vanilla synonyms are fine, though, and we checked for
329 ; mapM_ checkTyFamFreeness t_typats
331 -- (b) a newtype has exactly one constructor
332 ; checkTc (new_or_data == DataType || isSingleton k_cons) $
333 newtypeConError tc_name (length k_cons)
335 -- (4) construct representation tycon
336 ; rep_tc_name <- newFamInstTyConName tc_name loc
337 ; let ex_ok = True -- Existentials ok for type families!
338 ; fixM (\ rep_tycon -> do
339 { let orig_res_ty = mkTyConApp fam_tycon t_typats
340 ; data_cons <- tcConDecls unbox_strict ex_ok rep_tycon
341 (t_tvs, orig_res_ty) k_cons
344 DataType -> return (mkDataTyConRhs data_cons)
345 NewType -> ASSERT( not (null data_cons) )
346 mkNewTyConRhs rep_tc_name rep_tycon (head data_cons)
347 ; buildAlgTyCon rep_tc_name t_tvs stupid_theta tc_rhs Recursive
348 False h98_syntax (Just (fam_tycon, t_typats))
349 -- We always assume that indexed types are recursive. Why?
350 -- (1) Due to their open nature, we can never be sure that a
351 -- further instance might not introduce a new recursive
352 -- dependency. (2) They are always valid loop breakers as
353 -- they involve a coercion.
357 h98_syntax = case cons of -- All constructors have same shape
358 L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False
361 tcFamInstDecl1 d = pprPanic "tcFamInstDecl1" (ppr d)
363 -- Kind checking of indexed types
366 -- Kind check type patterns and kind annotate the embedded type variables.
368 -- * Here we check that a type instance matches its kind signature, but we do
369 -- not check whether there is a pattern for each type index; the latter
370 -- check is only required for type synonym instances.
372 kcIdxTyPats :: TyClDecl Name
373 -> ([LHsTyVarBndr Name] -> [LHsType Name] -> Kind -> TyCon -> TcM a)
374 -- ^^kinded tvs ^^kinded ty pats ^^res kind
376 kcIdxTyPats decl thing_inside
377 = kcHsTyVars (tcdTyVars decl) $ \tvs ->
378 do { fam_tycon <- tcLookupLocatedTyCon (tcdLName decl)
379 ; let { (kinds, resKind) = splitKindFunTys (tyConKind fam_tycon)
380 ; hs_typats = fromJust $ tcdTyPats decl }
382 -- we may not have more parameters than the kind indicates
383 ; checkTc (length kinds >= length hs_typats) $
384 tooManyParmsErr (tcdLName decl)
386 -- type functions can have a higher-kinded result
387 ; let resultKind = mkArrowKinds (drop (length hs_typats) kinds) resKind
388 ; typats <- zipWithM kcCheckHsType hs_typats kinds
389 ; thing_inside tvs typats resultKind fam_tycon
395 %************************************************************************
399 %************************************************************************
401 We need to kind check all types in the mutually recursive group
402 before we know the kind of the type variables. For example:
405 op :: D b => a -> b -> b
408 bop :: (Monad c) => ...
410 Here, the kind of the locally-polymorphic type variable "b"
411 depends on *all the uses of class D*. For example, the use of
412 Monad c in bop's type signature means that D must have kind Type->Type.
414 However type synonyms work differently. They can have kinds which don't
415 just involve (->) and *:
416 type R = Int# -- Kind #
417 type S a = Array# a -- Kind * -> #
418 type T a b = (# a,b #) -- Kind * -> * -> (# a,b #)
419 So we must infer their kinds from their right-hand sides *first* and then
420 use them, whereas for the mutually recursive data types D we bring into
421 scope kind bindings D -> k, where k is a kind variable, and do inference.
425 This treatment of type synonyms only applies to Haskell 98-style synonyms.
426 General type functions can be recursive, and hence, appear in `alg_decls'.
428 The kind of a type family is solely determinded by its kind signature;
429 hence, only kind signatures participate in the construction of the initial
430 kind environment (as constructed by `getInitialKind'). In fact, we ignore
431 instances of families altogether in the following. However, we need to
432 include the kinds of associated families into the construction of the
433 initial kind environment. (This is handled by `allDecls').
436 kcTyClDecls :: [LTyClDecl Name] -> [Located (TyClDecl Name)]
437 -> TcM ([LTyClDecl Name], [Located (TyClDecl Name)])
438 kcTyClDecls syn_decls alg_decls
439 = do { -- First extend the kind env with each data type, class, and
440 -- indexed type, mapping them to a type variable
441 let initialKindDecls = concat [allDecls decl | L _ decl <- alg_decls]
442 ; alg_kinds <- mapM getInitialKind initialKindDecls
443 ; tcExtendKindEnv alg_kinds $ do
445 -- Now kind-check the type synonyms, in dependency order
446 -- We do these differently to data type and classes,
447 -- because a type synonym can be an unboxed type
449 -- and a kind variable can't unify with UnboxedTypeKind
450 -- So we infer their kinds in dependency order
451 { (kc_syn_decls, syn_kinds) <- kcSynDecls (calcSynCycles syn_decls)
452 ; tcExtendKindEnv syn_kinds $ do
454 -- Now kind-check the data type, class, and kind signatures,
455 -- returning kind-annotated decls; we don't kind-check
456 -- instances of indexed types yet, but leave this to
458 { kc_alg_decls <- mapM (wrapLocM kcTyClDecl)
459 (filter (not . isFamInstDecl . unLoc) alg_decls)
461 ; return (kc_syn_decls, kc_alg_decls) }}}
463 -- get all declarations relevant for determining the initial kind
465 allDecls (decl@ClassDecl {tcdATs = ats}) = decl : [ at
468 allDecls decl | isFamInstDecl decl = []
471 ------------------------------------------------------------------------
472 getInitialKind :: TyClDecl Name -> TcM (Name, TcKind)
473 -- Only for data type, class, and indexed type declarations
474 -- Get as much info as possible from the data, class, or indexed type decl,
475 -- so as to maximise usefulness of error messages
477 = do { arg_kinds <- mapM (mk_arg_kind . unLoc) (tyClDeclTyVars decl)
478 ; res_kind <- mk_res_kind decl
479 ; return (tcdName decl, mkArrowKinds arg_kinds res_kind) }
481 mk_arg_kind (UserTyVar _) = newKindVar
482 mk_arg_kind (KindedTyVar _ kind) = return kind
484 mk_res_kind (TyFamily { tcdKind = Just kind }) = return kind
485 mk_res_kind (TyData { tcdKindSig = Just kind }) = return kind
486 -- On GADT-style declarations we allow a kind signature
487 -- data T :: *->* where { ... }
488 mk_res_kind _ = return liftedTypeKind
492 kcSynDecls :: [SCC (LTyClDecl Name)]
493 -> TcM ([LTyClDecl Name], -- Kind-annotated decls
494 [(Name,TcKind)]) -- Kind bindings
497 kcSynDecls (group : groups)
498 = do { (decl, nk) <- kcSynDecl group
499 ; (decls, nks) <- tcExtendKindEnv [nk] (kcSynDecls groups)
500 ; return (decl:decls, nk:nks) }
503 kcSynDecl :: SCC (LTyClDecl Name)
504 -> TcM (LTyClDecl Name, -- Kind-annotated decls
505 (Name,TcKind)) -- Kind bindings
506 kcSynDecl (AcyclicSCC (L loc decl))
507 = tcAddDeclCtxt decl $
508 kcHsTyVars (tcdTyVars decl) (\ k_tvs ->
509 do { traceTc (text "kcd1" <+> ppr (unLoc (tcdLName decl)) <+> brackets (ppr (tcdTyVars decl))
510 <+> brackets (ppr k_tvs))
511 ; (k_rhs, rhs_kind) <- kcHsType (tcdSynRhs decl)
512 ; traceTc (text "kcd2" <+> ppr (unLoc (tcdLName decl)))
513 ; let tc_kind = foldr (mkArrowKind . kindedTyVarKind) rhs_kind k_tvs
514 ; return (L loc (decl { tcdTyVars = k_tvs, tcdSynRhs = k_rhs }),
515 (unLoc (tcdLName decl), tc_kind)) })
517 kcSynDecl (CyclicSCC decls)
518 = do { recSynErr decls; failM } -- Fail here to avoid error cascade
519 -- of out-of-scope tycons
521 kindedTyVarKind :: LHsTyVarBndr Name -> Kind
522 kindedTyVarKind (L _ (KindedTyVar _ k)) = k
523 kindedTyVarKind x = pprPanic "kindedTyVarKind" (ppr x)
525 ------------------------------------------------------------------------
526 kcTyClDecl :: TyClDecl Name -> TcM (TyClDecl Name)
527 -- Not used for type synonyms (see kcSynDecl)
529 kcTyClDecl decl@(TyData {})
530 = ASSERT( not . isFamInstDecl $ decl ) -- must not be a family instance
531 kcTyClDeclBody decl $
534 kcTyClDecl decl@(TyFamily {})
535 = kcFamilyDecl [] decl -- the empty list signals a toplevel decl
537 kcTyClDecl decl@(ClassDecl {tcdCtxt = ctxt, tcdSigs = sigs, tcdATs = ats})
538 = kcTyClDeclBody decl $ \ tvs' ->
539 do { ctxt' <- kcHsContext ctxt
540 ; ats' <- mapM (wrapLocM (kcFamilyDecl tvs')) ats
541 ; sigs' <- mapM (wrapLocM kc_sig) sigs
542 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdSigs = sigs',
545 kc_sig (TypeSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
546 ; return (TypeSig nm op_ty') }
547 kc_sig other_sig = return other_sig
549 kcTyClDecl decl@(ForeignType {})
552 kcTyClDecl (TySynonym {}) = panic "kcTyClDecl TySynonym"
554 kcTyClDeclBody :: TyClDecl Name
555 -> ([LHsTyVarBndr Name] -> TcM a)
557 -- getInitialKind has made a suitably-shaped kind for the type or class
558 -- Unpack it, and attribute those kinds to the type variables
559 -- Extend the env with bindings for the tyvars, taken from
560 -- the kind of the tycon/class. Give it to the thing inside, and
561 -- check the result kind matches
562 kcTyClDeclBody decl thing_inside
563 = tcAddDeclCtxt decl $
564 do { tc_ty_thing <- tcLookupLocated (tcdLName decl)
565 ; let tc_kind = case tc_ty_thing of
567 _ -> pprPanic "kcTyClDeclBody" (ppr tc_ty_thing)
568 (kinds, _) = splitKindFunTys tc_kind
569 hs_tvs = tcdTyVars decl
570 kinded_tvs = ASSERT( length kinds >= length hs_tvs )
571 [ L loc (KindedTyVar (hsTyVarName tv) k)
572 | (L loc tv, k) <- zip hs_tvs kinds]
573 ; tcExtendKindEnvTvs kinded_tvs (thing_inside kinded_tvs) }
575 -- Kind check a data declaration, assuming that we already extended the
576 -- kind environment with the type variables of the left-hand side (these
577 -- kinded type variables are also passed as the second parameter).
579 kcDataDecl :: TyClDecl Name -> [LHsTyVarBndr Name] -> TcM (TyClDecl Name)
580 kcDataDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
582 = do { ctxt' <- kcHsContext ctxt
583 ; cons' <- mapM (wrapLocM kc_con_decl) cons
584 ; return (decl {tcdTyVars = tvs, tcdCtxt = ctxt', tcdCons = cons'}) }
586 -- doc comments are typechecked to Nothing here
587 kc_con_decl (ConDecl name expl ex_tvs ex_ctxt details res _) = do
588 kcHsTyVars ex_tvs $ \ex_tvs' -> do
589 ex_ctxt' <- kcHsContext ex_ctxt
590 details' <- kc_con_details details
592 ResTyH98 -> return ResTyH98
593 ResTyGADT ty -> do { ty' <- kcHsSigType ty; return (ResTyGADT ty') }
594 return (ConDecl name expl ex_tvs' ex_ctxt' details' res' Nothing)
596 kc_con_details (PrefixCon btys)
597 = do { btys' <- mapM kc_larg_ty btys
598 ; return (PrefixCon btys') }
599 kc_con_details (InfixCon bty1 bty2)
600 = do { bty1' <- kc_larg_ty bty1
601 ; bty2' <- kc_larg_ty bty2
602 ; return (InfixCon bty1' bty2') }
603 kc_con_details (RecCon fields)
604 = do { fields' <- mapM kc_field fields
605 ; return (RecCon fields') }
607 kc_field (ConDeclField fld bty d) = do { bty' <- kc_larg_ty bty
608 ; return (ConDeclField fld bty' d) }
610 kc_larg_ty bty = case new_or_data of
611 DataType -> kcHsSigType bty
612 NewType -> kcHsLiftedSigType bty
613 -- Can't allow an unlifted type for newtypes, because we're effectively
614 -- going to remove the constructor while coercing it to a lifted type.
615 -- And newtypes can't be bang'd
616 kcDataDecl d _ = pprPanic "kcDataDecl" (ppr d)
618 -- Kind check a family declaration or type family default declaration.
620 kcFamilyDecl :: [LHsTyVarBndr Name] -- tyvars of enclosing class decl if any
621 -> TyClDecl Name -> TcM (TyClDecl Name)
622 kcFamilyDecl classTvs decl@(TyFamily {tcdKind = kind})
623 = kcTyClDeclBody decl $ \tvs' ->
624 do { mapM_ unifyClassParmKinds tvs'
625 ; return (decl {tcdTyVars = tvs',
626 tcdKind = kind `mplus` Just liftedTypeKind})
627 -- default result kind is '*'
630 unifyClassParmKinds (L _ (KindedTyVar n k))
631 | Just classParmKind <- lookup n classTyKinds = unifyKind k classParmKind
632 | otherwise = return ()
633 unifyClassParmKinds x = pprPanic "kcFamilyDecl/unifyClassParmKinds" (ppr x)
634 classTyKinds = [(n, k) | L _ (KindedTyVar n k) <- classTvs]
635 kcFamilyDecl _ (TySynonym {}) -- type family defaults
636 = panic "TcTyClsDecls.kcFamilyDecl: not implemented yet"
637 kcFamilyDecl _ d = pprPanic "kcFamilyDecl" (ppr d)
641 %************************************************************************
643 \subsection{Type checking}
645 %************************************************************************
648 tcSynDecls :: [LTyClDecl Name] -> TcM [TyThing]
649 tcSynDecls [] = return []
650 tcSynDecls (decl : decls)
651 = do { syn_tc <- addLocM tcSynDecl decl
652 ; syn_tcs <- tcExtendGlobalEnv [syn_tc] (tcSynDecls decls)
653 ; return (syn_tc : syn_tcs) }
656 tcSynDecl :: TyClDecl Name -> TcM TyThing
658 (TySynonym {tcdLName = L _ tc_name, tcdTyVars = tvs, tcdSynRhs = rhs_ty})
659 = tcTyVarBndrs tvs $ \ tvs' -> do
660 { traceTc (text "tcd1" <+> ppr tc_name)
661 ; rhs_ty' <- tcHsKindedType rhs_ty
662 ; tycon <- buildSynTyCon tc_name tvs' (SynonymTyCon rhs_ty')
663 (typeKind rhs_ty') Nothing
664 ; return (ATyCon tycon)
666 tcSynDecl d = pprPanic "tcSynDecl" (ppr d)
669 tcTyClDecl :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
671 tcTyClDecl calc_isrec decl
672 = tcAddDeclCtxt decl (tcTyClDecl1 calc_isrec decl)
674 -- "type family" declarations
675 tcTyClDecl1 :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
676 tcTyClDecl1 _calc_isrec
677 (TyFamily {tcdFlavour = TypeFamily,
678 tcdLName = L _ tc_name, tcdTyVars = tvs,
679 tcdKind = Just kind}) -- NB: kind at latest added during kind checking
680 = tcTyVarBndrs tvs $ \ tvs' -> do
681 { traceTc (text "type family: " <+> ppr tc_name)
683 -- Check that we don't use families without -XTypeFamilies
684 ; idx_tys <- doptM Opt_TypeFamilies
685 ; checkTc idx_tys $ badFamInstDecl tc_name
687 -- Check for no type indices
688 ; checkTc (not (null tvs)) (noIndexTypes tc_name)
690 ; tycon <- buildSynTyCon tc_name tvs' (OpenSynTyCon kind Nothing) kind Nothing
691 ; return [ATyCon tycon]
694 -- "data family" declaration
695 tcTyClDecl1 _calc_isrec
696 (TyFamily {tcdFlavour = DataFamily,
697 tcdLName = L _ tc_name, tcdTyVars = tvs, tcdKind = mb_kind})
698 = tcTyVarBndrs tvs $ \ tvs' -> do
699 { traceTc (text "data family: " <+> ppr tc_name)
700 ; extra_tvs <- tcDataKindSig mb_kind
701 ; let final_tvs = tvs' ++ extra_tvs -- we may not need these
704 -- Check that we don't use families without -XTypeFamilies
705 ; idx_tys <- doptM Opt_TypeFamilies
706 ; checkTc idx_tys $ badFamInstDecl tc_name
708 -- Check for no type indices
709 ; checkTc (not (null tvs)) (noIndexTypes tc_name)
711 ; tycon <- buildAlgTyCon tc_name final_tvs []
712 mkOpenDataTyConRhs Recursive False True Nothing
713 ; return [ATyCon tycon]
716 -- "newtype" and "data"
717 -- NB: not used for newtype/data instances (whether associated or not)
718 tcTyClDecl1 calc_isrec
719 (TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdTyVars = tvs,
720 tcdLName = L _ tc_name, tcdKindSig = mb_ksig, tcdCons = cons})
721 = tcTyVarBndrs tvs $ \ tvs' -> do
722 { extra_tvs <- tcDataKindSig mb_ksig
723 ; let final_tvs = tvs' ++ extra_tvs
724 ; stupid_theta <- tcHsKindedContext ctxt
725 ; want_generic <- doptM Opt_Generics
726 ; unbox_strict <- doptM Opt_UnboxStrictFields
727 ; empty_data_decls <- doptM Opt_EmptyDataDecls
728 ; kind_signatures <- doptM Opt_KindSignatures
729 ; existential_ok <- doptM Opt_ExistentialQuantification
730 ; gadt_ok <- doptM Opt_GADTs
731 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
732 ; let ex_ok = existential_ok || gadt_ok -- Data cons can have existential context
734 -- Check that we don't use GADT syntax in H98 world
735 ; checkTc (gadt_ok || h98_syntax) (badGadtDecl tc_name)
737 -- Check that we don't use kind signatures without Glasgow extensions
738 ; checkTc (kind_signatures || isNothing mb_ksig) (badSigTyDecl tc_name)
740 -- Check that the stupid theta is empty for a GADT-style declaration
741 ; checkTc (null stupid_theta || h98_syntax) (badStupidTheta tc_name)
743 -- Check that a newtype has exactly one constructor
744 -- Do this before checking for empty data decls, so that
745 -- we don't suggest -XEmptyDataDecls for newtypes
746 ; checkTc (new_or_data == DataType || isSingleton cons)
747 (newtypeConError tc_name (length cons))
749 -- Check that there's at least one condecl,
750 -- or else we're reading an hs-boot file, or -XEmptyDataDecls
751 ; checkTc (not (null cons) || empty_data_decls || is_boot)
752 (emptyConDeclsErr tc_name)
754 ; tycon <- fixM (\ tycon -> do
755 { let res_ty = mkTyConApp tycon (mkTyVarTys final_tvs)
756 ; data_cons <- tcConDecls unbox_strict ex_ok
757 tycon (final_tvs, res_ty) cons
759 if null cons && is_boot -- In a hs-boot file, empty cons means
760 then return AbstractTyCon -- "don't know"; hence Abstract
761 else case new_or_data of
762 DataType -> return (mkDataTyConRhs data_cons)
763 NewType -> ASSERT( not (null data_cons) )
764 mkNewTyConRhs tc_name tycon (head data_cons)
765 ; buildAlgTyCon tc_name final_tvs stupid_theta tc_rhs is_rec
766 (want_generic && canDoGenerics data_cons) h98_syntax Nothing
768 ; return [ATyCon tycon]
771 is_rec = calc_isrec tc_name
772 h98_syntax = case cons of -- All constructors have same shape
773 L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False
776 tcTyClDecl1 calc_isrec
777 (ClassDecl {tcdLName = L _ class_name, tcdTyVars = tvs,
778 tcdCtxt = ctxt, tcdMeths = meths,
779 tcdFDs = fundeps, tcdSigs = sigs, tcdATs = ats} )
780 = tcTyVarBndrs tvs $ \ tvs' -> do
781 { ctxt' <- tcHsKindedContext ctxt
782 ; fds' <- mapM (addLocM tc_fundep) fundeps
783 ; atss <- mapM (addLocM (tcTyClDecl1 (const Recursive))) ats
784 -- NB: 'ats' only contains "type family" and "data family"
785 -- declarations as well as type family defaults
786 ; let ats' = map (setAssocFamilyPermutation tvs') (concat atss)
787 ; sig_stuff <- tcClassSigs class_name sigs meths
788 ; clas <- fixM (\ clas ->
789 let -- This little knot is just so we can get
790 -- hold of the name of the class TyCon, which we
791 -- need to look up its recursiveness
792 tycon_name = tyConName (classTyCon clas)
793 tc_isrec = calc_isrec tycon_name
795 buildClass False {- Must include unfoldings for selectors -}
796 class_name tvs' ctxt' fds' ats'
798 ; return (AClass clas : ats')
799 -- NB: Order is important due to the call to `mkGlobalThings' when
800 -- tying the the type and class declaration type checking knot.
803 tc_fundep (tvs1, tvs2) = do { tvs1' <- mapM tcLookupTyVar tvs1 ;
804 ; tvs2' <- mapM tcLookupTyVar tvs2 ;
805 ; return (tvs1', tvs2') }
808 (ForeignType {tcdLName = L _ tc_name, tcdExtName = tc_ext_name})
809 = return [ATyCon (mkForeignTyCon tc_name tc_ext_name liftedTypeKind 0)]
811 tcTyClDecl1 _ d = pprPanic "tcTyClDecl1" (ppr d)
813 -----------------------------------
814 tcConDecls :: Bool -> Bool -> TyCon -> ([TyVar], Type)
815 -> [LConDecl Name] -> TcM [DataCon]
816 tcConDecls unbox ex_ok rep_tycon res_tmpl cons
817 = mapM (addLocM (tcConDecl unbox ex_ok rep_tycon res_tmpl)) cons
819 tcConDecl :: Bool -- True <=> -funbox-strict_fields
820 -> Bool -- True <=> -XExistentialQuantificaton or -XGADTs
821 -> TyCon -- Representation tycon
822 -> ([TyVar], Type) -- Return type template (with its template tyvars)
826 tcConDecl unbox_strict existential_ok rep_tycon res_tmpl -- Data types
827 (ConDecl name _ tvs ctxt details res_ty _)
828 = addErrCtxt (dataConCtxt name) $
829 tcTyVarBndrs tvs $ \ tvs' -> do
830 { ctxt' <- tcHsKindedContext ctxt
831 ; checkTc (existential_ok || (null tvs && null (unLoc ctxt)))
832 (badExistential name)
833 ; (univ_tvs, ex_tvs, eq_preds, res_ty') <- tcResultType res_tmpl tvs' res_ty
835 tc_datacon is_infix field_lbls btys
836 = do { (arg_tys, stricts) <- mapAndUnzipM (tcConArg unbox_strict) btys
837 ; buildDataCon (unLoc name) is_infix
839 univ_tvs ex_tvs eq_preds ctxt' arg_tys
841 -- NB: we put data_tc, the type constructor gotten from the
842 -- constructor type signature into the data constructor;
843 -- that way checkValidDataCon can complain if it's wrong.
846 PrefixCon btys -> tc_datacon False [] btys
847 InfixCon bty1 bty2 -> tc_datacon True [] [bty1,bty2]
848 RecCon fields -> tc_datacon False field_names btys
850 field_names = map (unLoc . cd_fld_name) fields
851 btys = map cd_fld_type fields
855 -- data instance T (b,c) where
856 -- TI :: forall e. e -> T (e,e)
858 -- The representation tycon looks like this:
859 -- data :R7T b c where
860 -- TI :: forall b1 c1. (b1 ~ c1) => b1 -> :R7T b1 c1
861 -- In this case orig_res_ty = T (e,e)
863 tcResultType :: ([TyVar], Type) -- Template for result type; e.g.
864 -- data instance T [a] b c = ...
865 -- gives template ([a,b,c], T [a] b c)
866 -> [TyVar] -- where MkT :: forall x y z. ...
868 -> TcM ([TyVar], -- Universal
869 [TyVar], -- Existential (distinct OccNames from univs)
870 [(TyVar,Type)], -- Equality predicates
871 Type) -- Typechecked return type
872 -- We don't check that the TyCon given in the ResTy is
873 -- the same as the parent tycon, becuase we are in the middle
874 -- of a recursive knot; so it's postponed until checkValidDataCon
876 tcResultType (tmpl_tvs, res_ty) dc_tvs ResTyH98
877 = return (tmpl_tvs, dc_tvs, [], res_ty)
878 -- In H98 syntax the dc_tvs are the existential ones
879 -- data T a b c = forall d e. MkT ...
880 -- The {a,b,c} are tc_tvs, and {d,e} are dc_tvs
882 tcResultType (tmpl_tvs, res_tmpl) dc_tvs (ResTyGADT res_ty)
883 -- E.g. data T [a] b c where
884 -- MkT :: forall x y z. T [(x,y)] z z
886 -- Univ tyvars Eq-spec
890 -- Existentials are the leftover type vars: [x,y]
891 -- So we return ([a,b,z], [x,y], [a~(x,y),b~z], T [(x,y)] z z)
892 = do { res_ty' <- tcHsKindedType res_ty
893 ; let Just subst = tcMatchTy (mkVarSet tmpl_tvs) res_tmpl res_ty'
895 -- /Lazily/ figure out the univ_tvs etc
896 -- Each univ_tv is either a dc_tv or a tmpl_tv
897 (univ_tvs, eq_spec) = foldr choose ([], []) tidy_tmpl_tvs
898 choose tmpl (univs, eqs)
899 | Just ty <- lookupTyVar subst tmpl
900 = case tcGetTyVar_maybe ty of
901 Just tv | not (tv `elem` univs)
903 _other -> (tmpl:univs, (tmpl,ty):eqs)
904 | otherwise = pprPanic "tcResultType" (ppr res_ty)
905 ex_tvs = dc_tvs `minusList` univ_tvs
907 ; return (univ_tvs, ex_tvs, eq_spec, res_ty') }
909 -- NB: tmpl_tvs and dc_tvs are distinct, but
910 -- we want them to be *visibly* distinct, both for
911 -- interface files and general confusion. So rename
912 -- the tc_tvs, since they are not used yet (no
913 -- consequential renaming needed)
914 (_, tidy_tmpl_tvs) = mapAccumL tidy_one init_occ_env tmpl_tvs
915 init_occ_env = initTidyOccEnv (map getOccName dc_tvs)
916 tidy_one env tv = (env', setTyVarName tv (tidyNameOcc name occ'))
919 (env', occ') = tidyOccName env (getOccName name)
922 tcConArg :: Bool -- True <=> -funbox-strict_fields
924 -> TcM (TcType, StrictnessMark)
925 tcConArg unbox_strict bty
926 = do { arg_ty <- tcHsBangType bty
927 ; let bang = getBangStrictness bty
928 ; return (arg_ty, chooseBoxingStrategy unbox_strict arg_ty bang) }
930 -- We attempt to unbox/unpack a strict field when either:
931 -- (i) The field is marked '!!', or
932 -- (ii) The field is marked '!', and the -funbox-strict-fields flag is on.
934 -- We have turned off unboxing of newtypes because coercions make unboxing
935 -- and reboxing more complicated
936 chooseBoxingStrategy :: Bool -> TcType -> HsBang -> StrictnessMark
937 chooseBoxingStrategy unbox_strict_fields arg_ty bang
939 HsNoBang -> NotMarkedStrict
940 HsStrict | unbox_strict_fields
941 && can_unbox arg_ty -> MarkedUnboxed
942 HsUnbox | can_unbox arg_ty -> MarkedUnboxed
945 -- we can unbox if the type is a chain of newtypes with a product tycon
947 can_unbox arg_ty = case splitTyConApp_maybe arg_ty of
949 Just (arg_tycon, tycon_args) ->
950 not (isRecursiveTyCon arg_tycon) && -- Note [Recusive unboxing]
951 isProductTyCon arg_tycon &&
952 (if isNewTyCon arg_tycon then
953 can_unbox (newTyConInstRhs arg_tycon tycon_args)
957 Note [Recursive unboxing]
958 ~~~~~~~~~~~~~~~~~~~~~~~~~
959 Be careful not to try to unbox this!
961 But it's the *argument* type that matters. This is fine:
963 because Int is non-recursive.
966 %************************************************************************
970 %************************************************************************
972 Validity checking is done once the mutually-recursive knot has been
973 tied, so we can look at things freely.
976 checkCycleErrs :: [LTyClDecl Name] -> TcM ()
977 checkCycleErrs tyclss
981 = do { mapM_ recClsErr cls_cycles
982 ; failM } -- Give up now, because later checkValidTyCl
983 -- will loop if the synonym is recursive
985 cls_cycles = calcClassCycles tyclss
987 checkValidTyCl :: TyClDecl Name -> TcM ()
988 -- We do the validity check over declarations, rather than TyThings
989 -- only so that we can add a nice context with tcAddDeclCtxt
991 = tcAddDeclCtxt decl $
992 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
993 ; traceTc (text "Validity of" <+> ppr thing)
995 ATyCon tc -> checkValidTyCon tc
996 AClass cl -> checkValidClass cl
997 _ -> panic "checkValidTyCl"
998 ; traceTc (text "Done validity of" <+> ppr thing)
1001 -------------------------
1002 -- For data types declared with record syntax, we require
1003 -- that each constructor that has a field 'f'
1004 -- (a) has the same result type
1005 -- (b) has the same type for 'f'
1006 -- module alpha conversion of the quantified type variables
1007 -- of the constructor.
1009 -- Note that we allow existentials to match becuase the
1010 -- fields can never meet. E.g
1012 -- T1 { f1 :: b, f2 :: a, f3 ::Int } :: T
1013 -- T2 { f1 :: c, f2 :: c, f3 ::Int } :: T
1014 -- Here we do not complain about f1,f2 because they are existential
1016 checkValidTyCon :: TyCon -> TcM ()
1019 = case synTyConRhs tc of
1020 OpenSynTyCon _ _ -> return ()
1021 SynonymTyCon ty -> checkValidType syn_ctxt ty
1023 = do -- Check the context on the data decl
1024 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc)
1026 -- Check arg types of data constructors
1027 mapM_ (checkValidDataCon tc) data_cons
1029 -- Check that fields with the same name share a type
1030 mapM_ check_fields groups
1033 syn_ctxt = TySynCtxt name
1035 data_cons = tyConDataCons tc
1037 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
1038 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
1039 get_fields con = dataConFieldLabels con `zip` repeat con
1040 -- dataConFieldLabels may return the empty list, which is fine
1042 -- See Note [GADT record selectors] in MkId.lhs
1043 -- We must check (a) that the named field has the same
1044 -- type in each constructor
1045 -- (b) that those constructors have the same result type
1047 -- However, the constructors may have differently named type variable
1048 -- and (worse) we don't know how the correspond to each other. E.g.
1049 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
1050 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
1052 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
1053 -- result type against other candidates' types BOTH WAYS ROUND.
1054 -- If they magically agrees, take the substitution and
1055 -- apply them to the latter ones, and see if they match perfectly.
1056 check_fields ((label, con1) : other_fields)
1057 -- These fields all have the same name, but are from
1058 -- different constructors in the data type
1059 = recoverM (return ()) $ mapM_ checkOne other_fields
1060 -- Check that all the fields in the group have the same type
1061 -- NB: this check assumes that all the constructors of a given
1062 -- data type use the same type variables
1064 (tvs1, _, _, res1) = dataConSig con1
1066 fty1 = dataConFieldType con1 label
1068 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
1069 = do { checkFieldCompat label con1 con2 ts1 res1 res2 fty1 fty2
1070 ; checkFieldCompat label con2 con1 ts2 res2 res1 fty2 fty1 }
1072 (tvs2, _, _, res2) = dataConSig con2
1074 fty2 = dataConFieldType con2 label
1075 check_fields [] = panic "checkValidTyCon/check_fields []"
1077 checkFieldCompat :: Name -> DataCon -> DataCon -> TyVarSet
1078 -> Type -> Type -> Type -> Type -> TcM ()
1079 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
1080 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
1081 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
1083 mb_subst1 = tcMatchTy tvs1 res1 res2
1084 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
1086 -------------------------------
1087 checkValidDataCon :: TyCon -> DataCon -> TcM ()
1088 checkValidDataCon tc con
1089 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
1090 addErrCtxt (dataConCtxt con) $
1091 do { let tc_tvs = tyConTyVars tc
1092 res_ty_tmpl = mkFamilyTyConApp tc (mkTyVarTys tc_tvs)
1093 actual_res_ty = dataConOrigResTy con
1094 ; checkTc (isJust (tcMatchTy (mkVarSet tc_tvs)
1097 (badDataConTyCon con res_ty_tmpl actual_res_ty)
1098 ; checkValidMonoType (dataConOrigResTy con)
1099 -- Disallow MkT :: T (forall a. a->a)
1100 -- Reason: it's really the argument of an equality constraint
1101 ; checkValidType ctxt (dataConUserType con)
1102 ; when (isNewTyCon tc) (checkNewDataCon con)
1105 ctxt = ConArgCtxt (dataConName con)
1107 -------------------------------
1108 checkNewDataCon :: DataCon -> TcM ()
1109 -- Checks for the data constructor of a newtype
1111 = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
1113 ; checkTc (null eq_spec) (newtypePredError con)
1114 -- Return type is (T a b c)
1115 ; checkTc (null ex_tvs && null eq_theta && null dict_theta) (newtypeExError con)
1117 ; checkTc (not (any isMarkedStrict (dataConStrictMarks con)))
1118 (newtypeStrictError con)
1122 (_univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, _res_ty) = dataConFullSig con
1124 -------------------------------
1125 checkValidClass :: Class -> TcM ()
1127 = do { constrained_class_methods <- doptM Opt_ConstrainedClassMethods
1128 ; multi_param_type_classes <- doptM Opt_MultiParamTypeClasses
1129 ; fundep_classes <- doptM Opt_FunctionalDependencies
1131 -- Check that the class is unary, unless GlaExs
1132 ; checkTc (notNull tyvars) (nullaryClassErr cls)
1133 ; checkTc (multi_param_type_classes || unary) (classArityErr cls)
1134 ; checkTc (fundep_classes || null fundeps) (classFunDepsErr cls)
1136 -- Check the super-classes
1137 ; checkValidTheta (ClassSCCtxt (className cls)) theta
1139 -- Check the class operations
1140 ; mapM_ (check_op constrained_class_methods) op_stuff
1142 -- Check that if the class has generic methods, then the
1143 -- class has only one parameter. We can't do generic
1144 -- multi-parameter type classes!
1145 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
1148 (tyvars, fundeps, theta, _, _, op_stuff) = classExtraBigSig cls
1149 unary = isSingleton tyvars
1150 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
1152 check_op constrained_class_methods (sel_id, dm)
1153 = addErrCtxt (classOpCtxt sel_id tau) $ do
1154 { checkValidTheta SigmaCtxt (tail theta)
1155 -- The 'tail' removes the initial (C a) from the
1156 -- class itself, leaving just the method type
1158 ; traceTc (text "class op type" <+> ppr op_ty <+> ppr tau)
1159 ; checkValidType (FunSigCtxt op_name) tau
1161 -- Check that the type mentions at least one of
1162 -- the class type variables...or at least one reachable
1163 -- from one of the class variables. Example: tc223
1164 -- class Error e => Game b mv e | b -> mv e where
1165 -- newBoard :: MonadState b m => m ()
1166 -- Here, MonadState has a fundep m->b, so newBoard is fine
1167 ; let grown_tyvars = grow theta (mkVarSet tyvars)
1168 ; checkTc (tyVarsOfType tau `intersectsVarSet` grown_tyvars)
1169 (noClassTyVarErr cls sel_id)
1171 -- Check that for a generic method, the type of
1172 -- the method is sufficiently simple
1173 ; checkTc (dm /= GenDefMeth || validGenericMethodType tau)
1174 (badGenericMethodType op_name op_ty)
1177 op_name = idName sel_id
1178 op_ty = idType sel_id
1179 (_,theta1,tau1) = tcSplitSigmaTy op_ty
1180 (_,theta2,tau2) = tcSplitSigmaTy tau1
1181 (theta,tau) | constrained_class_methods = (theta1 ++ theta2, tau2)
1182 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
1183 -- Ugh! The function might have a type like
1184 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
1185 -- With -XConstrainedClassMethods, we want to allow this, even though the inner
1186 -- forall has an (Eq a) constraint. Whereas in general, each constraint
1187 -- in the context of a for-all must mention at least one quantified
1188 -- type variable. What a mess!
1192 %************************************************************************
1194 Building record selectors
1196 %************************************************************************
1199 mkAuxBinds :: [TyThing] -> HsValBinds Name
1200 mkAuxBinds ty_things
1201 = ValBindsOut [(NonRecursive, b) | b <- binds] sigs
1203 (sigs, binds) = unzip rec_sels
1204 rec_sels = map mkRecSelBind [ (tc,fld)
1205 | ATyCon tc <- ty_things
1206 , fld <- tyConFields tc ]
1209 mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name)
1210 mkRecSelBind (tycon, sel_name)
1211 = (L loc (IdSig sel_id), unitBag (L loc sel_bind))
1213 loc = getSrcSpan tycon
1214 sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo
1215 rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty }
1217 -- Find a representative constructor, con1
1218 all_cons = tyConDataCons tycon
1219 cons_w_field = [ con | con <- all_cons
1220 , sel_name `elem` dataConFieldLabels con ]
1221 con1 = ASSERT( not (null cons_w_field) ) head cons_w_field
1223 -- Selector type; Note [Polymorphic selectors]
1224 field_ty = dataConFieldType con1 sel_name
1225 (field_tvs, field_theta, field_tau)
1226 | is_naughty = ([], [], unitTy)
1227 | otherwise = tcSplitSigmaTy field_ty
1228 data_ty = dataConOrigResTy con1
1229 data_tvs = tyVarsOfType data_ty
1230 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)
1231 sel_ty = mkForAllTys (varSetElems data_tvs ++ field_tvs) $
1232 mkPhiTy (dataConStupidTheta con1) $ -- Urgh!
1233 mkPhiTy field_theta $ -- Urgh!
1234 mkFunTy data_ty field_tau
1236 -- Make the binding: sel (C2 { fld = x }) = x
1237 -- sel (C7 { fld = x }) = x
1238 -- where cons_w_field = [C2,C7]
1239 sel_bind = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt)
1240 mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)]
1242 mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields)
1243 rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing }
1244 rec_field = HsRecField { hsRecFieldId = sel_lname
1245 , hsRecFieldArg = nlVarPat field_var
1246 , hsRecPun = False }
1247 match_body | is_naughty = ExplicitTuple [] Boxed
1248 | otherwise = HsVar field_var
1249 sel_lname = L loc sel_name
1250 field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc
1252 -- Add catch-all default case unless the case is exhaustive
1253 -- We do this explicitly so that we get a nice error message that
1254 -- mentions this particular record selector
1255 deflt | length cons_w_field == length all_cons = []
1256 | otherwise = [mkSimpleMatch [nlWildPat]
1257 (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
1259 msg_lit = HsStringPrim $ mkFastString $
1260 occNameString (getOccName sel_name)
1263 tyConFields :: TyCon -> [FieldLabel]
1265 | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc))
1269 Note [Polymorphic selectors]
1270 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1271 When a record has a polymorphic field, we pull the foralls out to the front.
1272 data T = MkT { f :: forall a. [a] -> a }
1273 Then f :: forall a. T -> [a] -> a
1274 NOT f :: T -> forall a. [a] -> a
1276 This is horrid. It's only needed in deeply obscure cases, which I hate.
1277 The only case I know is test tc163, which is worth looking at. It's far
1278 from clear that this test should succeed at all!
1280 Note [Naughty record selectors]
1281 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1282 A "naughty" field is one for which we can't define a record
1283 selector, because an existential type variable would escape. For example:
1284 data T = forall a. MkT { x,y::a }
1285 We obviously can't define
1287 Nevertheless we *do* put a RecSelId into the type environment
1288 so that if the user tries to use 'x' as a selector we can bleat
1289 helpfully, rather than saying unhelpfully that 'x' is not in scope.
1290 Hence the sel_naughty flag, to identify record selectors that don't really exist.
1292 In general, a field is naughty if its type mentions a type variable that
1293 isn't in the result type of the constructor.
1295 We make a dummy binding for naughty selectors, so that they can be treated
1296 uniformly, apart from their sel_naughty field. The function is never called.
1298 Note [GADT record selectors]
1299 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1300 For GADTs, we require that all constructors with a common field 'f' have the same
1301 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
1304 T1 { f :: Maybe a } :: T [a]
1305 T2 { f :: Maybe a, y :: b } :: T [a]
1307 and now the selector takes that result type as its argument:
1308 f :: forall a. T [a] -> Maybe a
1310 Details: the "real" types of T1,T2 are:
1311 T1 :: forall r a. (r~[a]) => a -> T r
1312 T2 :: forall r a b. (r~[a]) => a -> b -> T r
1314 So the selector loooks like this:
1315 f :: forall a. T [a] -> Maybe a
1318 T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g))
1319 T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g))
1321 Note the forall'd tyvars of the selector are just the free tyvars
1322 of the result type; there may be other tyvars in the constructor's
1323 type (e.g. 'b' in T2).
1325 Note the need for casts in the result!
1327 Note [Selector running example]
1328 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1329 It's OK to combine GADTs and type families. Here's a running example:
1331 data instance T [a] where
1332 T1 { fld :: b } :: T [Maybe b]
1334 The representation type looks like this
1336 T1 { fld :: b } :: :R7T (Maybe b)
1338 and there's coercion from the family type to the representation type
1339 :CoR7T a :: T [a] ~ :R7T a
1341 The selector we want for fld looks like this:
1343 fld :: forall b. T [Maybe b] -> b
1344 fld = /\b. \(d::T [Maybe b]).
1345 case d `cast` :CoR7T (Maybe b) of
1348 The scrutinee of the case has type :R7T (Maybe b), which can be
1349 gotten by appying the eq_spec to the univ_tvs of the data con.
1351 %************************************************************************
1355 %************************************************************************
1358 resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1359 resultTypeMisMatch field_name con1 con2
1360 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1361 ptext (sLit "have a common field") <+> quotes (ppr field_name) <> comma],
1362 nest 2 $ ptext (sLit "but have different result types")]
1364 fieldTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1365 fieldTypeMisMatch field_name con1 con2
1366 = sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1367 ptext (sLit "give different types for field"), quotes (ppr field_name)]
1369 dataConCtxt :: Outputable a => a -> SDoc
1370 dataConCtxt con = ptext (sLit "In the definition of data constructor") <+> quotes (ppr con)
1372 classOpCtxt :: Var -> Type -> SDoc
1373 classOpCtxt sel_id tau = sep [ptext (sLit "When checking the class method:"),
1374 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
1376 nullaryClassErr :: Class -> SDoc
1378 = ptext (sLit "No parameters for class") <+> quotes (ppr cls)
1380 classArityErr :: Class -> SDoc
1382 = vcat [ptext (sLit "Too many parameters for class") <+> quotes (ppr cls),
1383 parens (ptext (sLit "Use -XMultiParamTypeClasses to allow multi-parameter classes"))]
1385 classFunDepsErr :: Class -> SDoc
1387 = vcat [ptext (sLit "Fundeps in class") <+> quotes (ppr cls),
1388 parens (ptext (sLit "Use -XFunctionalDependencies to allow fundeps"))]
1390 noClassTyVarErr :: Class -> Var -> SDoc
1391 noClassTyVarErr clas op
1392 = sep [ptext (sLit "The class method") <+> quotes (ppr op),
1393 ptext (sLit "mentions none of the type variables of the class") <+>
1394 ppr clas <+> hsep (map ppr (classTyVars clas))]
1396 genericMultiParamErr :: Class -> SDoc
1397 genericMultiParamErr clas
1398 = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
1399 ptext (sLit "cannot have generic methods")
1401 badGenericMethodType :: Name -> Kind -> SDoc
1402 badGenericMethodType op op_ty
1403 = hang (ptext (sLit "Generic method type is too complex"))
1404 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
1405 ptext (sLit "You can only use type variables, arrows, lists, and tuples")])
1407 recSynErr :: [LTyClDecl Name] -> TcRn ()
1409 = setSrcSpan (getLoc (head sorted_decls)) $
1410 addErr (sep [ptext (sLit "Cycle in type synonym declarations:"),
1411 nest 2 (vcat (map ppr_decl sorted_decls))])
1413 sorted_decls = sortLocated syn_decls
1414 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
1416 recClsErr :: [Located (TyClDecl Name)] -> TcRn ()
1418 = setSrcSpan (getLoc (head sorted_decls)) $
1419 addErr (sep [ptext (sLit "Cycle in class declarations (via superclasses):"),
1420 nest 2 (vcat (map ppr_decl sorted_decls))])
1422 sorted_decls = sortLocated cls_decls
1423 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
1425 sortLocated :: [Located a] -> [Located a]
1426 sortLocated things = sortLe le things
1428 le (L l1 _) (L l2 _) = l1 <= l2
1430 badDataConTyCon :: DataCon -> Type -> Type -> SDoc
1431 badDataConTyCon data_con res_ty_tmpl actual_res_ty
1432 = hang (ptext (sLit "Data constructor") <+> quotes (ppr data_con) <+>
1433 ptext (sLit "returns type") <+> quotes (ppr actual_res_ty))
1434 2 (ptext (sLit "instead of an instance of its parent type") <+> quotes (ppr res_ty_tmpl))
1436 badGadtDecl :: Name -> SDoc
1438 = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
1439 , nest 2 (parens $ ptext (sLit "Use -XGADTs to allow GADTs")) ]
1441 badExistential :: Located Name -> SDoc
1442 badExistential con_name
1443 = hang (ptext (sLit "Data constructor") <+> quotes (ppr con_name) <+>
1444 ptext (sLit "has existential type variables, or a context"))
1445 2 (parens $ ptext (sLit "Use -XExistentialQuantification or -XGADTs to allow this"))
1447 badStupidTheta :: Name -> SDoc
1448 badStupidTheta tc_name
1449 = ptext (sLit "A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
1451 newtypeConError :: Name -> Int -> SDoc
1452 newtypeConError tycon n
1453 = sep [ptext (sLit "A newtype must have exactly one constructor,"),
1454 nest 2 $ ptext (sLit "but") <+> quotes (ppr tycon) <+> ptext (sLit "has") <+> speakN n ]
1456 newtypeExError :: DataCon -> SDoc
1458 = sep [ptext (sLit "A newtype constructor cannot have an existential context,"),
1459 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1461 newtypeStrictError :: DataCon -> SDoc
1462 newtypeStrictError con
1463 = sep [ptext (sLit "A newtype constructor cannot have a strictness annotation,"),
1464 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1466 newtypePredError :: DataCon -> SDoc
1467 newtypePredError con
1468 = sep [ptext (sLit "A newtype constructor must have a return type of form T a1 ... an"),
1469 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does not")]
1471 newtypeFieldErr :: DataCon -> Int -> SDoc
1472 newtypeFieldErr con_name n_flds
1473 = sep [ptext (sLit "The constructor of a newtype must have exactly one field"),
1474 nest 2 $ ptext (sLit "but") <+> quotes (ppr con_name) <+> ptext (sLit "has") <+> speakN n_flds]
1476 badSigTyDecl :: Name -> SDoc
1477 badSigTyDecl tc_name
1478 = vcat [ ptext (sLit "Illegal kind signature") <+>
1479 quotes (ppr tc_name)
1480 , nest 2 (parens $ ptext (sLit "Use -XKindSignatures to allow kind signatures")) ]
1482 noIndexTypes :: Name -> SDoc
1483 noIndexTypes tc_name
1484 = ptext (sLit "Type family constructor") <+> quotes (ppr tc_name)
1485 <+> ptext (sLit "must have at least one type index parameter")
1487 badFamInstDecl :: Outputable a => a -> SDoc
1488 badFamInstDecl tc_name
1489 = vcat [ ptext (sLit "Illegal family instance for") <+>
1490 quotes (ppr tc_name)
1491 , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ]
1493 tooManyParmsErr :: Located Name -> SDoc
1494 tooManyParmsErr tc_name
1495 = ptext (sLit "Family instance has too many parameters:") <+>
1496 quotes (ppr tc_name)
1498 tooFewParmsErr :: Arity -> SDoc
1499 tooFewParmsErr arity
1500 = ptext (sLit "Family instance has too few parameters; expected") <+>
1503 wrongNumberOfParmsErr :: Arity -> SDoc
1504 wrongNumberOfParmsErr exp_arity
1505 = ptext (sLit "Number of parameters must match family declaration; expected")
1508 badBootFamInstDeclErr :: SDoc
1509 badBootFamInstDeclErr =
1510 ptext (sLit "Illegal family instance in hs-boot file")
1512 wrongKindOfFamily :: TyCon -> SDoc
1513 wrongKindOfFamily family =
1514 ptext (sLit "Wrong category of family instance; declaration was for a") <+>
1517 kindOfFamily | isSynTyCon family = ptext (sLit "type synonym")
1518 | isAlgTyCon family = ptext (sLit "data type")
1519 | otherwise = pprPanic "wrongKindOfFamily" (ppr family)
1521 emptyConDeclsErr :: Name -> SDoc
1522 emptyConDeclsErr tycon
1523 = sep [quotes (ppr tycon) <+> ptext (sLit "has no constructors"),
1524 nest 2 $ ptext (sLit "(-XEmptyDataDecls permits this)")]