2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcInstDecls]{Typechecking instance declarations}
7 module TcInstDcls ( tcInstDecls1, tcInstDecls2, tcAddDeclCtxt ) where
9 #include "HsVersions.h"
12 import CmdLineOpts ( DynFlag(..), dopt )
14 import HsSyn ( HsDecl(..), InstDecl(..), TyClDecl(..), InPat(..),
15 MonoBinds(..), HsExpr(..), HsLit(..), Sig(..), Match(..),
16 andMonoBindList, collectMonoBinders, isClassDecl
18 import HsTypes ( HsType (..), HsTyVarBndr(..), toHsTyVar )
19 import RnHsSyn ( RenamedHsBinds, RenamedInstDecl, RenamedHsDecl, RenamedMonoBinds,
20 RenamedTyClDecl, RenamedHsType,
21 extractHsTyVars, maybeGenericMatch
23 import TcHsSyn ( TcMonoBinds, mkHsConApp )
24 import TcBinds ( tcSpecSigs )
25 import TcClassDcl ( tcMethodBind, badMethodErr )
27 import Inst ( InstOrigin(..),
28 newDicts, newClassDicts,
29 LIE, emptyLIE, plusLIE, plusLIEs )
30 import TcDeriv ( tcDeriving )
31 import TcEnv ( TcEnv, tcExtendGlobalValEnv,
32 tcExtendTyVarEnvForMeths, TyThing (..),
33 tcAddImportedIdInfo, tcInstId, tcLookupClass,
34 newDFunName, tcExtendTyVarEnv
36 import InstEnv ( InstInfo(..), InstEnv, pprInstInfo, classDataCon,
37 simpleInstInfoTyCon, simpleInstInfoTy, isLocalInst,
39 import TcMonoType ( tcTyVars, tcHsSigType, tcHsType, kcHsSigType )
40 import TcSimplify ( tcSimplifyAndCheck )
41 import TcType ( zonkTcSigTyVars )
42 import HscTypes ( PersistentCompilerState(..), HomeSymbolTable, DFunId,
45 import Bag ( emptyBag, unitBag, unionBags, unionManyBags,
46 foldBag, Bag, listToBag
48 import Class ( Class, DefMeth(..), classBigSig )
49 import Var ( idName, idType )
50 import Maybes ( maybeToBool, expectJust )
51 import MkId ( mkDictFunId )
52 import Generics ( validGenericInstanceType )
53 import Module ( Module, foldModuleEnv )
54 import Name ( isLocallyDefined )
55 import NameSet ( emptyNameSet, nameSetToList )
56 import PrelInfo ( eRROR_ID )
57 import PprType ( pprConstraint, pprPred )
58 import TyCon ( TyCon, isSynTyCon, tyConDerivings )
59 import Type ( mkTyVarTys, splitDFunTy, isTyVarTy,
60 splitTyConApp_maybe, splitDictTy,
61 splitAlgTyConApp_maybe, classesToPreds, classesOfPreds,
62 unUsgTy, tyVarsOfTypes, mkClassPred, mkTyVarTy,
65 import Subst ( mkTopTyVarSubst, substClasses, substTheta )
66 import VarSet ( mkVarSet, varSetElems )
67 import TysWiredIn ( genericTyCons, isFFIArgumentTy, isFFIResultTy )
68 import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
69 import Name ( Name, NameEnv, extendNameEnv_C, emptyNameEnv,
70 plusNameEnv_C, nameEnvElts )
71 import FiniteMap ( mapFM )
72 import SrcLoc ( SrcLoc )
73 import VarSet ( varSetElems )
74 import UniqFM ( mapUFM )
75 import Unique ( Uniquable(..) )
76 import BasicTypes ( NewOrData(..), Fixity )
77 import ErrUtils ( dumpIfSet_dyn )
78 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
79 assocElts, extendAssoc_C,
80 equivClassesByUniq, minusList
82 import List ( intersect, (\\), partition )
86 Typechecking instance declarations is done in two passes. The first
87 pass, made by @tcInstDecls1@, collects information to be used in the
90 This pre-processed info includes the as-yet-unprocessed bindings
91 inside the instance declaration. These are type-checked in the second
92 pass, when the class-instance envs and GVE contain all the info from
93 all the instance and value decls. Indeed that's the reason we need
94 two passes over the instance decls.
97 Here is the overall algorithm.
98 Assume that we have an instance declaration
100 instance c => k (t tvs) where b
104 $LIE_c$ is the LIE for the context of class $c$
106 $betas_bar$ is the free variables in the class method type, excluding the
109 $LIE_cop$ is the LIE constraining a particular class method
111 $tau_cop$ is the tau type of a class method
113 $LIE_i$ is the LIE for the context of instance $i$
115 $X$ is the instance constructor tycon
117 $gammas_bar$ is the set of type variables of the instance
119 $LIE_iop$ is the LIE for a particular class method instance
121 $tau_iop$ is the tau type for this instance of a class method
123 $alpha$ is the class variable
125 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
127 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
130 ToDo: Update the list above with names actually in the code.
134 First, make the LIEs for the class and instance contexts, which means
135 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
136 and make LIElistI and LIEI.
138 Then process each method in turn.
140 order the instance methods according to the ordering of the class methods
142 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
144 Create final dictionary function from bindings generated already
146 df = lambda inst_tyvars
153 in <op1,op2,...,opn,sd1,...,sdm>
155 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
156 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
160 %************************************************************************
162 \subsection{Extracting instance decls}
164 %************************************************************************
166 Gather up the instance declarations from their various sources
169 tcInstDecls1 :: PersistentCompilerState
170 -> HomeSymbolTable -- Contains instances
171 -> TcEnv -- Contains IdInfo for dfun ids
172 -> (Name -> Maybe Fixity) -- for deriving Show and Read
173 -> Module -- Module for deriving
176 -> TcM (PersistentCompilerState, InstEnv, [InstInfo], RenamedHsBinds)
178 tcInstDecls1 pcs hst unf_env get_fixity mod local_tycons decls
180 inst_decls = [inst_decl | InstD inst_decl <- decls]
181 clas_decls = [clas_decl | TyClD clas_decl <- decls, isClassDecl clas_decl]
183 -- (1) Do the ordinary instance declarations
184 mapNF_Tc (tcInstDecl1 mod unf_env) inst_decls `thenNF_Tc` \ inst_infos ->
186 -- (2) Instances from generic class declarations
187 getGenericInstances mod clas_decls `thenTc` \ generic_inst_info ->
189 -- Next, construct the instance environment so far, consisting of
190 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
191 -- b) imported instance decls (not in the home package) inst_env1
192 -- c) other modules in this package (gotten from hst) inst_env2
193 -- d) local instance decls inst_env3
194 -- e) generic instances inst_env4
195 -- The result of (b) replaces the cached InstEnv in the PCS
197 (local_inst_info, imported_inst_info)
198 = partition isLocalInst (concat inst_infos)
200 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
202 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
204 addInstDFuns (pcs_insts pcs) imported_dfuns `thenNF_Tc` \ inst_env1 ->
205 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
206 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
207 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
209 -- (3) Compute instances from "deriving" clauses;
210 -- note that we only do derivings for things in this module;
211 -- we ignore deriving decls from interfaces!
212 -- This stuff computes a context for the derived instance decl, so it
213 -- needs to know about all the instances possible; hecne inst_env4
214 tcDeriving (pcs_PRS pcs) mod inst_env4 get_fixity local_tycons
215 `thenTc` \ (deriv_inst_info, deriv_binds) ->
216 addInstInfos inst_env4 deriv_inst_info
217 `thenNF_Tc` \ final_inst_env ->
219 returnTc (pcs { pcs_insts = inst_env1 },
221 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
224 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
225 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
227 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
228 addInstDFuns dfuns infos
229 = getDOptsTc `thenTc` \ dflags ->
230 extendInstEnv dflags dfuns infos `bind` \ (inst_env', errs) ->
231 addErrsTc errs `thenNF_Tc_`
239 tcInstDecl1 :: Module -> TcEnv -> RenamedInstDecl -> NF_TcM [InstInfo]
240 -- Deal with a single instance declaration
241 tcInstDecl1 mod unf_env (InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
242 = -- Prime error recovery, set source location
243 recoverNF_Tc (returnNF_Tc []) $
244 tcAddSrcLoc src_loc $
246 -- Type-check all the stuff before the "where"
247 tcHsSigType poly_ty `thenTc` \ poly_ty' ->
249 (tyvars, theta, clas, inst_tys) = splitDFunTy poly_ty'
252 (case maybe_dfun_name of
253 Nothing -> -- A source-file instance declaration
255 -- Check for respectable instance type, and context
256 -- but only do this for non-imported instance decls.
257 -- Imported ones should have been checked already, and may indeed
258 -- contain something illegal in normal Haskell, notably
259 -- instance CCallable [Char]
260 scrutiniseInstanceHead clas inst_tys `thenNF_Tc_`
261 mapNF_Tc scrutiniseInstanceConstraint theta `thenNF_Tc_`
263 -- Make the dfun id and return it
264 newDFunName mod clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
265 returnNF_Tc (True, mkDictFunId dfun_name clas tyvars inst_tys theta)
267 Just dfun_name -> -- An interface-file instance declaration
269 returnNF_Tc (False, mkDictFunId dfun_name clas tyvars inst_tys theta)
270 ) `thenNF_Tc` \ (is_local, dfun_id) ->
272 returnTc [InstInfo { iLocal = is_local,
273 iClass = clas, iTyVars = tyvars, iTys = inst_tys,
274 iTheta = theta, iDFunId = dfun_id,
275 iBinds = binds, iLoc = src_loc, iPrags = uprags }]
279 %************************************************************************
281 \subsection{Extracting generic instance declaration from class declarations}
283 %************************************************************************
285 @getGenericInstances@ extracts the generic instance declarations from a class
286 declaration. For exmaple
291 op{ x+y } (Inl v) = ...
292 op{ x+y } (Inr v) = ...
293 op{ x*y } (v :*: w) = ...
296 gives rise to the instance declarations
298 instance C (x+y) where
302 instance C (x*y) where
310 getGenericInstances :: Module -> [RenamedTyClDecl] -> TcM [InstInfo]
311 getGenericInstances mod class_decls
312 = mapTc (get_generics mod) class_decls `thenTc` \ gen_inst_infos ->
314 gen_inst_info = concat gen_inst_infos
316 getDOptsTc `thenTc` \ dflags ->
317 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
318 (vcat (map pprInstInfo gen_inst_info)))
320 returnTc gen_inst_info
322 get_generics mod decl@(ClassDecl context class_name tyvar_names
323 fundeps class_sigs def_methods
326 = returnTc [] -- The comon case:
327 -- no generic default methods, or
328 -- its an imported class decl (=> has no methods at all)
330 | otherwise -- A local class decl with generic default methods
331 = recoverNF_Tc (returnNF_Tc []) $
333 tcLookupClass class_name `thenTc` \ clas ->
335 -- Make an InstInfo out of each group
336 mapTc (mkGenericInstance mod clas loc) groups `thenTc` \ inst_infos ->
338 -- Check that there is only one InstInfo for each type constructor
339 -- The main way this can fail is if you write
340 -- f {| a+b |} ... = ...
341 -- f {| x+y |} ... = ...
342 -- Then at this point we'll have an InstInfo for each
344 bad_groups = [group | group <- equivClassesByUniq get_uniq inst_infos,
346 get_uniq inst = getUnique (simpleInstInfoTyCon inst)
348 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
350 -- Check that there is an InstInfo for each generic type constructor
352 missing = genericTyCons `minusList` map simpleInstInfoTyCon inst_infos
354 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
359 -- Group the declarations by type pattern
360 groups :: [(RenamedHsType, RenamedMonoBinds)]
361 groups = assocElts (getGenericBinds def_methods)
364 ---------------------------------
365 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
366 -- Takes a group of method bindings, finds the generic ones, and returns
367 -- them in finite map indexed by the type parameter in the definition.
369 getGenericBinds EmptyMonoBinds = emptyAssoc
370 getGenericBinds (AndMonoBinds m1 m2)
371 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
373 getGenericBinds (FunMonoBind id infixop matches loc)
374 = mapAssoc wrap (foldr add emptyAssoc matches)
376 add match env = case maybeGenericMatch match of
378 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
380 wrap ms = FunMonoBind id infixop ms loc
382 ---------------------------------
383 mkGenericInstance :: Module -> Class -> SrcLoc
384 -> (RenamedHsType, RenamedMonoBinds)
387 mkGenericInstance mod clas loc (hs_ty, binds)
388 -- Make a generic instance declaration
389 -- For example: instance (C a, C b) => C (a+b) where { binds }
391 = -- Extract the universally quantified type variables
392 tcTyVars (nameSetToList (extractHsTyVars hs_ty))
393 (kcHsSigType hs_ty) `thenTc` \ tyvars ->
394 tcExtendTyVarEnv tyvars $
396 -- Type-check the instance type, and check its form
397 tcHsSigType hs_ty `thenTc` \ inst_ty ->
398 checkTc (validGenericInstanceType inst_ty)
399 (badGenericInstanceType binds) `thenTc_`
401 -- Make the dictionary function.
402 newDFunName mod clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
404 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
406 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
409 returnTc (InstInfo { iLocal = True,
410 iClass = clas, iTyVars = tyvars, iTys = inst_tys,
411 iTheta = inst_theta, iDFunId = dfun_id, iBinds = binds,
412 iLoc = loc, iPrags = [] })
416 %************************************************************************
418 \subsection{Type-checking instance declarations, pass 2}
420 %************************************************************************
423 tcInstDecls2 :: [InstInfo]
424 -> NF_TcM (LIE, TcMonoBinds)
426 tcInstDecls2 inst_decls
427 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
428 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
429 (map tcInstDecl2 inst_decls)
431 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
432 tc2 `thenNF_Tc` \ (lie2, binds2) ->
433 returnNF_Tc (lie1 `plusLIE` lie2,
434 binds1 `AndMonoBinds` binds2)
437 ======= New documentation starts here (Sept 92) ==============
439 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
440 the dictionary function for this instance declaration. For example
442 instance Foo a => Foo [a] where
446 might generate something like
448 dfun.Foo.List dFoo_a = let op1 x = ...
454 HOWEVER, if the instance decl has no context, then it returns a
455 bigger @HsBinds@ with declarations for each method. For example
457 instance Foo [a] where
463 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
464 const.Foo.op1.List a x = ...
465 const.Foo.op2.List a y = ...
467 This group may be mutually recursive, because (for example) there may
468 be no method supplied for op2 in which case we'll get
470 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
472 that is, the default method applied to the dictionary at this type.
474 What we actually produce in either case is:
476 AbsBinds [a] [dfun_theta_dicts]
477 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
478 { d = (sd1,sd2, ..., op1, op2, ...)
483 The "maybe" says that we only ask AbsBinds to make global constant methods
484 if the dfun_theta is empty.
487 For an instance declaration, say,
489 instance (C1 a, C2 b) => C (T a b) where
492 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
493 function whose type is
495 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
497 Notice that we pass it the superclass dictionaries at the instance type; this
498 is the ``Mark Jones optimisation''. The stuff before the "=>" here
499 is the @dfun_theta@ below.
501 First comes the easy case of a non-local instance decl.
504 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
506 tcInstDecl2 (InstInfo { iClass = clas, iTyVars = inst_tyvars, iTys = inst_tys,
507 iTheta = inst_decl_theta, iDFunId = dfun_id,
508 iBinds = monobinds, iLoc = locn, iPrags = uprags })
509 | not (isLocallyDefined dfun_id)
510 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
513 = -- Prime error recovery
514 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
517 -- Instantiate the instance decl with tc-style type variables
518 tcInstId dfun_id `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
520 (clas, inst_tys') = splitDictTy dict_ty'
521 origin = InstanceDeclOrigin
523 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
525 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
526 sel_names = [idName sel_id | (sel_id, _) <- op_items]
528 -- Instantiate the theta found in the original instance decl
529 inst_decl_theta' = substTheta (mkTopTyVarSubst inst_tyvars (mkTyVarTys inst_tyvars'))
532 -- Instantiate the super-class context with inst_tys
533 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
535 -- Find any definitions in monobinds that aren't from the class
536 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
538 -- Check that all the method bindings come from this class
539 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
541 -- Create dictionary Ids from the specified instance contexts.
542 newClassDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
543 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
544 newDicts origin inst_decl_theta' `thenNF_Tc` \ (inst_decl_dicts, _) ->
545 newClassDicts origin [(clas,inst_tys')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
547 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
548 tcExtendGlobalValEnv dm_ids (
549 -- Default-method Ids may be mentioned in synthesised RHSs
551 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
553 monobinds uprags True)
555 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_lies_w_ids) ->
557 -- Deal with SPECIALISE instance pragmas by making them
558 -- look like SPECIALISE pragmas for the dfun
560 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
562 tcExtendGlobalValEnv [dfun_id] (
563 tcSpecSigs dfun_prags
564 ) `thenTc` \ (prag_binds, prag_lie) ->
566 -- Check the overloading constraints of the methods and superclasses
568 -- tcMethodBind has checked that the class_tyvars havn't
569 -- been unified with each other or another type, but we must
570 -- still zonk them before passing them to tcSimplifyAndCheck
571 zonkTcSigTyVars inst_tyvars' `thenNF_Tc` \ zonked_inst_tyvars ->
573 inst_tyvars_set = mkVarSet zonked_inst_tyvars
575 (meth_lies, meth_ids) = unzip meth_lies_w_ids
577 -- These insts are in scope; quite a few, eh?
578 avail_insts = this_dict `plusLIE`
579 dfun_arg_dicts `plusLIE`
581 unionManyBags meth_lies
583 methods_lie = plusLIEs insts_needed_s
586 -- Ditto method bindings
587 tcAddErrCtxt methodCtxt (
589 (ptext SLIT("instance declaration context"))
590 inst_tyvars_set -- Local tyvars
593 ) `thenTc` \ (const_lie1, lie_binds1) ->
595 -- Check that we *could* construct the superclass dictionaries,
596 -- even though we are *actually* going to pass the superclass dicts in;
597 -- the check ensures that the caller will never have
598 --a problem building them.
599 tcAddErrCtxt superClassCtxt (
601 (ptext SLIT("instance declaration context"))
602 inst_tyvars_set -- Local tyvars
603 inst_decl_dicts -- The instance dictionaries available
604 sc_dicts -- The superclass dicationaries reqd
606 -- Ignore the result; we're only doing
607 -- this to make sure it can be done.
609 -- Now do the simplification again, this time to get the
610 -- bindings; this time we use an enhanced "avails"
611 -- Ignore errors because they come from the *previous* tcSimplify
614 (ptext SLIT("instance declaration context"))
616 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
617 -- get bound by just selecting from this_dict!!
619 ) `thenTc` \ (const_lie2, lie_binds2) ->
622 -- Create the result bindings
624 dict_constr = classDataCon clas
625 scs_and_meths = sc_dict_ids ++ meth_ids
629 = -- Blatant special case for CCallable, CReturnable
630 -- If the dictionary is empty then we should never
631 -- select anything from it, so we make its RHS just
632 -- emit an error message. This in turn means that we don't
633 -- mention the constructor, which doesn't exist for CCallable, CReturnable
634 -- Hardly beautiful, but only three extra lines.
635 HsApp (TyApp (HsVar eRROR_ID) [(unUsgTy . idType) this_dict_id])
636 (HsLit (HsString msg))
638 | otherwise -- The common case
639 = mkHsConApp dict_constr inst_tys' (map HsVar (sc_dict_ids ++ meth_ids))
640 -- We don't produce a binding for the dict_constr; instead we
641 -- rely on the simplifier to unfold this saturated application
642 -- We do this rather than generate an HsCon directly, because
643 -- it means that the special cases (e.g. dictionary with only one
644 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
645 -- than needing to be repeated here.
648 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
650 dict_bind = VarMonoBind this_dict_id dict_rhs
651 method_binds = andMonoBindList method_binds_s
657 [(inst_tyvars', dfun_id, this_dict_id)]
658 emptyNameSet -- No inlines (yet)
659 (lie_binds1 `AndMonoBinds`
660 lie_binds2 `AndMonoBinds`
661 method_binds `AndMonoBinds`
664 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
665 main_bind `AndMonoBinds` prag_binds)
669 %************************************************************************
671 \subsection{Checking for a decent instance type}
673 %************************************************************************
675 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
676 it must normally look like: @instance Foo (Tycon a b c ...) ...@
678 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
679 flag is on, or (2)~the instance is imported (they must have been
680 compiled elsewhere). In these cases, we let them go through anyway.
682 We can also have instances for functions: @instance Foo (a -> b) ...@.
685 scrutiniseInstanceConstraint pred
686 = getDOptsTc `thenTc` \ dflags -> case () of
688 | dopt Opt_AllowUndecidableInstances dflags
691 | Just (clas,tys) <- getClassTys_maybe pred,
696 -> addErrTc (instConstraintErr pred)
698 scrutiniseInstanceHead clas inst_taus
699 = getDOptsTc `thenTc` \ dflags -> case () of
702 -- A user declaration of a CCallable/CReturnable instance
703 -- must be for a "boxed primitive" type.
704 (clas `hasKey` cCallableClassKey
705 && not (ccallable_type dflags first_inst_tau))
707 (clas `hasKey` cReturnableClassKey
708 && not (creturnable_type first_inst_tau))
709 -> addErrTc (nonBoxedPrimCCallErr clas first_inst_tau)
712 -- It is obviously illegal to have an explicit instance
713 -- for something that we are also planning to `derive'
714 | maybeToBool alg_tycon_app_maybe && clas `elem` (tyConDerivings alg_tycon)
715 -> addErrTc (derivingWhenInstanceExistsErr clas first_inst_tau)
716 -- Kind check will have ensured inst_taus is of length 1
718 -- Allow anything for AllowUndecidableInstances
719 | dopt Opt_AllowUndecidableInstances dflags
722 -- If GlasgowExts then check at least one isn't a type variable
723 | dopt Opt_GlasgowExts dflags
724 -> if all isTyVarTy inst_taus
725 then addErrTc (instTypeErr clas inst_taus
726 (text "There must be at least one non-type-variable in the instance head"))
729 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
730 | not (length inst_taus == 1 &&
731 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
732 not (isSynTyCon tycon) && -- ...but not a synonym
733 all isTyVarTy arg_tys && -- Applied to type variables
734 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
735 -- This last condition checks that all the type variables are distinct
737 -> addErrTc (instTypeErr clas inst_taus
738 (text "the instance type must be of form (T a b c)" $$
739 text "where T is not a synonym, and a,b,c are distinct type variables")
746 (first_inst_tau : _) = inst_taus
748 -- Stuff for algebraic or -> type
749 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
750 Just (tycon, arg_tys) = maybe_tycon_app
752 -- Stuff for an *algebraic* data type
753 alg_tycon_app_maybe = splitAlgTyConApp_maybe first_inst_tau
754 -- The "Alg" part looks through synonyms
755 Just (alg_tycon, _, _) = alg_tycon_app_maybe
757 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
758 creturnable_type ty = isFFIResultTy ty
762 %************************************************************************
764 \subsection{Error messages}
766 %************************************************************************
769 tcAddDeclCtxt decl thing_inside
776 (ClassDecl _ name _ _ _ _ _ loc) -> (name, loc, "class")
777 (TySynonym name _ _ loc) -> (name, loc, "type synonym")
778 (TyData NewType _ name _ _ _ _ loc _ _) -> (name, loc, "newtype")
779 (TyData DataType _ name _ _ _ _ loc _ _) -> (name, loc, "data type")
781 ctxt = hsep [ptext SLIT("In the"), text thing,
782 ptext SLIT("declaration for"), quotes (ppr name)]
786 instConstraintErr pred
787 = hang (ptext SLIT("Illegal constraint") <+>
788 quotes (pprPred pred) <+>
789 ptext SLIT("in instance context"))
790 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
792 badGenericInstanceType binds
793 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
796 missingGenericInstances missing
797 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
801 dupGenericInsts inst_infos
802 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
803 nest 4 (vcat (map (ppr . simpleInstInfoTy) inst_infos)),
804 ptext SLIT("All the type patterns for a generic type constructor must be identical")
807 instTypeErr clas tys msg
808 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes (pprConstraint clas tys),
812 derivingWhenInstanceExistsErr clas tycon
813 = hang (hsep [ptext SLIT("Deriving class"),
815 ptext SLIT("type"), quotes (ppr tycon)])
816 4 (ptext SLIT("when an explicit instance exists"))
818 nonBoxedPrimCCallErr clas inst_ty
819 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
820 4 (hsep [ ptext SLIT("class"), ppr clas, ptext SLIT("type"),
823 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
824 superClassCtxt = ptext SLIT("When checking the superclasses of an instance declaration")