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(..),
15 MonoBinds(..), HsExpr(..), HsLit(..), Sig(..),
16 andMonoBindList, collectMonoBinders, isClassDecl
18 import HsTypes ( HsType (..), HsTyVarBndr(..), toHsTyVar )
19 import HsPat ( InPat (..) )
20 import HsMatches ( Match (..) )
21 import RnHsSyn ( RenamedHsBinds, RenamedInstDecl, RenamedHsDecl,
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, splitSigmaTy, isTyVarTy,
60 splitTyConApp_maybe, splitDictTy_maybe,
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 RnHsSyn -- ( RenamedMonoBinds )
74 import VarSet ( varSetElems )
75 import UniqFM ( mapUFM )
76 import Unique ( Uniquable(..) )
77 import BasicTypes ( NewOrData(..) )
78 import ErrUtils ( dumpIfSet_dyn )
79 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
80 assocElts, extendAssoc_C,
81 equivClassesByUniq, minusList
83 import List ( intersect, (\\), partition )
87 Typechecking instance declarations is done in two passes. The first
88 pass, made by @tcInstDecls1@, collects information to be used in the
91 This pre-processed info includes the as-yet-unprocessed bindings
92 inside the instance declaration. These are type-checked in the second
93 pass, when the class-instance envs and GVE contain all the info from
94 all the instance and value decls. Indeed that's the reason we need
95 two passes over the instance decls.
98 Here is the overall algorithm.
99 Assume that we have an instance declaration
101 instance c => k (t tvs) where b
105 $LIE_c$ is the LIE for the context of class $c$
107 $betas_bar$ is the free variables in the class method type, excluding the
110 $LIE_cop$ is the LIE constraining a particular class method
112 $tau_cop$ is the tau type of a class method
114 $LIE_i$ is the LIE for the context of instance $i$
116 $X$ is the instance constructor tycon
118 $gammas_bar$ is the set of type variables of the instance
120 $LIE_iop$ is the LIE for a particular class method instance
122 $tau_iop$ is the tau type for this instance of a class method
124 $alpha$ is the class variable
126 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
128 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
131 ToDo: Update the list above with names actually in the code.
135 First, make the LIEs for the class and instance contexts, which means
136 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
137 and make LIElistI and LIEI.
139 Then process each method in turn.
141 order the instance methods according to the ordering of the class methods
143 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
145 Create final dictionary function from bindings generated already
147 df = lambda inst_tyvars
154 in <op1,op2,...,opn,sd1,...,sdm>
156 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
157 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
161 %************************************************************************
163 \subsection{Extracting instance decls}
165 %************************************************************************
167 Gather up the instance declarations from their various sources
170 tcInstDecls1 :: PersistentCompilerState
171 -> HomeSymbolTable -- Contains instances
172 -> TcEnv -- Contains IdInfo for dfun ids
173 -> (Name -> Maybe Fixity) -- for deriving Show and Read
174 -> Module -- Module for deriving
177 -> TcM (PersistentCompilerState, InstEnv, [InstInfo], RenamedHsBinds)
179 tcInstDecls1 pcs hst unf_env get_fixity mod local_tycons decls
181 inst_decls = [inst_decl | InstD inst_decl <- decls]
182 clas_decls = [clas_decl | TyClD clas_decl <- decls, isClassDecl clas_decl]
184 -- (1) Do the ordinary instance declarations
185 mapNF_Tc (tcInstDecl1 mod unf_env) inst_decls `thenNF_Tc` \ inst_infos ->
187 -- (2) Instances from generic class declarations
188 getGenericInstances mod clas_decls `thenTc` \ generic_inst_info ->
190 -- Next, construct the instance environment so far, consisting of
191 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
192 -- b) imported instance decls (not in the home package) inst_env1
193 -- c) other modules in this package (gotten from hst) inst_env2
194 -- d) local instance decls inst_env3
195 -- e) generic instances inst_env4
196 -- The result of (b) replaces the cached InstEnv in the PCS
198 (local_inst_info, imported_inst_info)
199 = partition isLocalInst (concat inst_infos)
201 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
203 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
205 addInstDFuns (pcs_insts pcs) imported_dfuns `thenNF_Tc` \ inst_env1 ->
206 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
207 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
208 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
210 -- (3) Compute instances from "deriving" clauses;
211 -- note that we only do derivings for things in this module;
212 -- we ignore deriving decls from interfaces!
213 -- This stuff computes a context for the derived instance decl, so it
214 -- needs to know about all the instances possible; hecne inst_env4
215 tcDeriving (pcs_PRS pcs) mod inst_env4 get_fixity local_tycons
216 `thenTc` \ (deriv_inst_info, deriv_binds) ->
217 addInstInfos inst_env4 deriv_inst_info
218 `thenNF_Tc` \ final_inst_env ->
220 returnTc (pcs { pcs_insts = inst_env1 },
222 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
225 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
226 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
228 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
229 addInstDFuns dfuns infos
230 = getDOptsTc `thenTc` \ dflags ->
231 extendInstEnv dflags dfuns infos `bind` \ (inst_env', errs) ->
232 addErrsTc errs `thenNF_Tc_`
240 tcInstDecl1 :: Module -> TcEnv -> RenamedInstDecl -> NF_TcM [InstInfo]
241 -- Deal with a single instance declaration
242 tcInstDecl1 mod unf_env (InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
243 = -- Prime error recovery, set source location
244 recoverNF_Tc (returnNF_Tc []) $
245 tcAddSrcLoc src_loc $
247 -- Type-check all the stuff before the "where"
248 tcHsSigType poly_ty `thenTc` \ poly_ty' ->
250 (tyvars, theta, dict_ty) = splitSigmaTy poly_ty'
251 (clas, inst_tys) = case splitDictTy_maybe dict_ty of
253 Nothing -> pprPanic "tcInstDecl1" (ppr poly_ty)
256 (case maybe_dfun_name of
257 Nothing -> -- A source-file instance declaration
259 -- Check for respectable instance type, and context
260 -- but only do this for non-imported instance decls.
261 -- Imported ones should have been checked already, and may indeed
262 -- contain something illegal in normal Haskell, notably
263 -- instance CCallable [Char]
264 scrutiniseInstanceHead clas inst_tys `thenNF_Tc_`
265 mapNF_Tc scrutiniseInstanceConstraint theta `thenNF_Tc_`
267 -- Make the dfun id and return it
268 newDFunName mod clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
269 returnNF_Tc (True, mkDictFunId dfun_name clas tyvars inst_tys theta)
271 Just dfun_name -> -- An interface-file instance declaration
273 returnNF_Tc (False, mkDictFunId dfun_name clas tyvars inst_tys theta)
274 ) `thenNF_Tc` \ (is_local, dfun_id) ->
276 returnTc [InstInfo { iLocal = is_local,
277 iClass = clas, iTyVars = tyvars, iTys = inst_tys,
278 iTheta = theta, iDFunId = dfun_id,
279 iBinds = binds, iLoc = src_loc, iPrags = uprags }]
283 %************************************************************************
285 \subsection{Extracting generic instance declaration from class declarations}
287 %************************************************************************
289 @getGenericInstances@ extracts the generic instance declarations from a class
290 declaration. For exmaple
295 op{ x+y } (Inl v) = ...
296 op{ x+y } (Inr v) = ...
297 op{ x*y } (v :*: w) = ...
300 gives rise to the instance declarations
302 instance C (x+y) where
306 instance C (x*y) where
314 getGenericInstances :: Module -> [RenamedTyClDecl] -> TcM [InstInfo]
315 getGenericInstances mod class_decls
316 = mapTc (get_generics mod) class_decls `thenTc` \ gen_inst_infos ->
318 gen_inst_info = concat gen_inst_infos
320 getDOptsTc `thenTc` \ dflags ->
321 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
322 (vcat (map pprInstInfo gen_inst_info)))
324 returnTc gen_inst_info
326 get_generics mod decl@(ClassDecl context class_name tyvar_names
327 fundeps class_sigs def_methods pragmas
330 = returnTc [] -- The comon case:
331 -- no generic default methods, or
332 -- its an imported class decl (=> has no methods at all)
334 | otherwise -- A local class decl with generic default methods
335 = recoverNF_Tc (returnNF_Tc []) $
337 tcLookupClass class_name `thenTc` \ clas ->
339 -- Make an InstInfo out of each group
340 mapTc (mkGenericInstance mod clas loc) groups `thenTc` \ inst_infos ->
342 -- Check that there is only one InstInfo for each type constructor
343 -- The main way this can fail is if you write
344 -- f {| a+b |} ... = ...
345 -- f {| x+y |} ... = ...
346 -- Then at this point we'll have an InstInfo for each
348 bad_groups = [group | group <- equivClassesByUniq get_uniq inst_infos,
350 get_uniq inst = getUnique (simpleInstInfoTyCon inst)
352 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
354 -- Check that there is an InstInfo for each generic type constructor
356 missing = genericTyCons `minusList` map simpleInstInfoTyCon inst_infos
358 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
363 -- Group the declarations by type pattern
364 groups :: [(RenamedHsType, RenamedMonoBinds)]
365 groups = assocElts (getGenericBinds def_methods)
368 ---------------------------------
369 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
370 -- Takes a group of method bindings, finds the generic ones, and returns
371 -- them in finite map indexed by the type parameter in the definition.
373 getGenericBinds EmptyMonoBinds = emptyAssoc
374 getGenericBinds (AndMonoBinds m1 m2)
375 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
377 getGenericBinds (FunMonoBind id infixop matches loc)
378 = mapAssoc wrap (foldr add emptyAssoc matches)
380 add match env = case maybeGenericMatch match of
382 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
384 wrap ms = FunMonoBind id infixop ms loc
386 ---------------------------------
387 mkGenericInstance :: Module -> Class -> SrcLoc
388 -> (RenamedHsType, RenamedMonoBinds)
391 mkGenericInstance mod clas loc (hs_ty, binds)
392 -- Make a generic instance declaration
393 -- For example: instance (C a, C b) => C (a+b) where { binds }
395 = -- Extract the universally quantified type variables
396 tcTyVars (nameSetToList (extractHsTyVars hs_ty))
397 (kcHsSigType hs_ty) `thenTc` \ tyvars ->
398 tcExtendTyVarEnv tyvars $
400 -- Type-check the instance type, and check its form
401 tcHsSigType hs_ty `thenTc` \ inst_ty ->
402 checkTc (validGenericInstanceType inst_ty)
403 (badGenericInstanceType binds) `thenTc_`
405 -- Make the dictionary function.
406 newDFunName mod clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
408 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
410 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
413 returnTc (InstInfo { iLocal = True,
414 iClass = clas, iTyVars = tyvars, iTys = inst_tys,
415 iTheta = inst_theta, iDFunId = dfun_id, iBinds = binds,
416 iLoc = loc, iPrags = [] })
420 %************************************************************************
422 \subsection{Type-checking instance declarations, pass 2}
424 %************************************************************************
427 tcInstDecls2 :: [InstInfo]
428 -> NF_TcM (LIE, TcMonoBinds)
430 tcInstDecls2 inst_decls
431 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
432 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
433 (map tcInstDecl2 inst_decls)
435 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
436 tc2 `thenNF_Tc` \ (lie2, binds2) ->
437 returnNF_Tc (lie1 `plusLIE` lie2,
438 binds1 `AndMonoBinds` binds2)
441 ======= New documentation starts here (Sept 92) ==============
443 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
444 the dictionary function for this instance declaration. For example
446 instance Foo a => Foo [a] where
450 might generate something like
452 dfun.Foo.List dFoo_a = let op1 x = ...
458 HOWEVER, if the instance decl has no context, then it returns a
459 bigger @HsBinds@ with declarations for each method. For example
461 instance Foo [a] where
467 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
468 const.Foo.op1.List a x = ...
469 const.Foo.op2.List a y = ...
471 This group may be mutually recursive, because (for example) there may
472 be no method supplied for op2 in which case we'll get
474 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
476 that is, the default method applied to the dictionary at this type.
478 What we actually produce in either case is:
480 AbsBinds [a] [dfun_theta_dicts]
481 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
482 { d = (sd1,sd2, ..., op1, op2, ...)
487 The "maybe" says that we only ask AbsBinds to make global constant methods
488 if the dfun_theta is empty.
491 For an instance declaration, say,
493 instance (C1 a, C2 b) => C (T a b) where
496 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
497 function whose type is
499 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
501 Notice that we pass it the superclass dictionaries at the instance type; this
502 is the ``Mark Jones optimisation''. The stuff before the "=>" here
503 is the @dfun_theta@ below.
505 First comes the easy case of a non-local instance decl.
508 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
510 tcInstDecl2 (InstInfo { iClass = clas, iTyVars = inst_tyvars, iTys = inst_tys,
511 iTheta = inst_decl_theta, iDFunId = dfun_id,
512 iBinds = monobinds, iLoc = locn, iPrags = uprags })
513 | not (isLocallyDefined dfun_id)
514 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
517 = -- Prime error recovery
518 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
521 -- Instantiate the instance decl with tc-style type variables
522 tcInstId dfun_id `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
524 (clas, inst_tys') = expectJust "tcInstDecl2" (splitDictTy_maybe dict_ty')
525 origin = InstanceDeclOrigin
527 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
529 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
530 sel_names = [idName sel_id | (sel_id, _) <- op_items]
532 -- Instantiate the theta found in the original instance decl
533 inst_decl_theta' = substTheta (mkTopTyVarSubst inst_tyvars (mkTyVarTys inst_tyvars'))
536 -- Instantiate the super-class context with inst_tys
537 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
539 -- Find any definitions in monobinds that aren't from the class
540 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
542 -- Check that all the method bindings come from this class
543 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
545 -- Create dictionary Ids from the specified instance contexts.
546 newClassDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
547 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
548 newDicts origin inst_decl_theta' `thenNF_Tc` \ (inst_decl_dicts, _) ->
549 newClassDicts origin [(clas,inst_tys')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
551 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
552 tcExtendGlobalValEnv dm_ids (
553 -- Default-method Ids may be mentioned in synthesised RHSs
555 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
557 monobinds uprags True)
559 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_lies_w_ids) ->
561 -- Deal with SPECIALISE instance pragmas by making them
562 -- look like SPECIALISE pragmas for the dfun
564 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
566 tcExtendGlobalValEnv [dfun_id] (
567 tcSpecSigs dfun_prags
568 ) `thenTc` \ (prag_binds, prag_lie) ->
570 -- Check the overloading constraints of the methods and superclasses
572 -- tcMethodBind has checked that the class_tyvars havn't
573 -- been unified with each other or another type, but we must
574 -- still zonk them before passing them to tcSimplifyAndCheck
575 zonkTcSigTyVars inst_tyvars' `thenNF_Tc` \ zonked_inst_tyvars ->
577 inst_tyvars_set = mkVarSet zonked_inst_tyvars
579 (meth_lies, meth_ids) = unzip meth_lies_w_ids
581 -- These insts are in scope; quite a few, eh?
582 avail_insts = this_dict `plusLIE`
583 dfun_arg_dicts `plusLIE`
585 unionManyBags meth_lies
587 methods_lie = plusLIEs insts_needed_s
590 -- Ditto method bindings
591 tcAddErrCtxt methodCtxt (
593 (ptext SLIT("instance declaration context"))
594 inst_tyvars_set -- Local tyvars
597 ) `thenTc` \ (const_lie1, lie_binds1) ->
599 -- Check that we *could* construct the superclass dictionaries,
600 -- even though we are *actually* going to pass the superclass dicts in;
601 -- the check ensures that the caller will never have
602 --a problem building them.
603 tcAddErrCtxt superClassCtxt (
605 (ptext SLIT("instance declaration context"))
606 inst_tyvars_set -- Local tyvars
607 inst_decl_dicts -- The instance dictionaries available
608 sc_dicts -- The superclass dicationaries reqd
610 -- Ignore the result; we're only doing
611 -- this to make sure it can be done.
613 -- Now do the simplification again, this time to get the
614 -- bindings; this time we use an enhanced "avails"
615 -- Ignore errors because they come from the *previous* tcSimplify
618 (ptext SLIT("instance declaration context"))
620 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
621 -- get bound by just selecting from this_dict!!
623 ) `thenTc` \ (const_lie2, lie_binds2) ->
626 -- Create the result bindings
628 dict_constr = classDataCon clas
629 scs_and_meths = sc_dict_ids ++ meth_ids
633 = -- Blatant special case for CCallable, CReturnable
634 -- If the dictionary is empty then we should never
635 -- select anything from it, so we make its RHS just
636 -- emit an error message. This in turn means that we don't
637 -- mention the constructor, which doesn't exist for CCallable, CReturnable
638 -- Hardly beautiful, but only three extra lines.
639 HsApp (TyApp (HsVar eRROR_ID) [(unUsgTy . idType) this_dict_id])
640 (HsLit (HsString msg))
642 | otherwise -- The common case
643 = mkHsConApp dict_constr inst_tys' (map HsVar (sc_dict_ids ++ meth_ids))
644 -- We don't produce a binding for the dict_constr; instead we
645 -- rely on the simplifier to unfold this saturated application
646 -- We do this rather than generate an HsCon directly, because
647 -- it means that the special cases (e.g. dictionary with only one
648 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
649 -- than needing to be repeated here.
652 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
654 dict_bind = VarMonoBind this_dict_id dict_rhs
655 method_binds = andMonoBindList method_binds_s
661 [(inst_tyvars', dfun_id, this_dict_id)]
662 emptyNameSet -- No inlines (yet)
663 (lie_binds1 `AndMonoBinds`
664 lie_binds2 `AndMonoBinds`
665 method_binds `AndMonoBinds`
668 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
669 main_bind `AndMonoBinds` prag_binds)
673 %************************************************************************
675 \subsection{Checking for a decent instance type}
677 %************************************************************************
679 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
680 it must normally look like: @instance Foo (Tycon a b c ...) ...@
682 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
683 flag is on, or (2)~the instance is imported (they must have been
684 compiled elsewhere). In these cases, we let them go through anyway.
686 We can also have instances for functions: @instance Foo (a -> b) ...@.
689 scrutiniseInstanceConstraint pred
690 = getDOptsTc `thenTc` \ dflags -> case () of
692 | dopt Opt_AllowUndecidableInstances dflags
695 | Just (clas,tys) <- getClassTys_maybe pred,
700 -> addErrTc (instConstraintErr pred)
702 scrutiniseInstanceHead clas inst_taus
703 = getDOptsTc `thenTc` \ dflags -> case () of
706 -- A user declaration of a CCallable/CReturnable instance
707 -- must be for a "boxed primitive" type.
708 (clas `hasKey` cCallableClassKey
709 && not (ccallable_type dflags first_inst_tau))
711 (clas `hasKey` cReturnableClassKey
712 && not (creturnable_type first_inst_tau))
713 -> addErrTc (nonBoxedPrimCCallErr clas first_inst_tau)
716 -- It is obviously illegal to have an explicit instance
717 -- for something that we are also planning to `derive'
718 | maybeToBool alg_tycon_app_maybe && clas `elem` (tyConDerivings alg_tycon)
719 -> addErrTc (derivingWhenInstanceExistsErr clas first_inst_tau)
720 -- Kind check will have ensured inst_taus is of length 1
722 -- Allow anything for AllowUndecidableInstances
723 | dopt Opt_AllowUndecidableInstances dflags
726 -- If GlasgowExts then check at least one isn't a type variable
727 | dopt Opt_GlasgowExts dflags
728 -> if all isTyVarTy inst_taus
729 then addErrTc (instTypeErr clas inst_taus
730 (text "There must be at least one non-type-variable in the instance head"))
733 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
734 | not (length inst_taus == 1 &&
735 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
736 not (isSynTyCon tycon) && -- ...but not a synonym
737 all isTyVarTy arg_tys && -- Applied to type variables
738 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
739 -- This last condition checks that all the type variables are distinct
741 -> addErrTc (instTypeErr clas inst_taus
742 (text "the instance type must be of form (T a b c)" $$
743 text "where T is not a synonym, and a,b,c are distinct type variables")
750 (first_inst_tau : _) = inst_taus
752 -- Stuff for algebraic or -> type
753 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
754 Just (tycon, arg_tys) = maybe_tycon_app
756 -- Stuff for an *algebraic* data type
757 alg_tycon_app_maybe = splitAlgTyConApp_maybe first_inst_tau
758 -- The "Alg" part looks through synonyms
759 Just (alg_tycon, _, _) = alg_tycon_app_maybe
761 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
762 creturnable_type ty = isFFIResultTy ty
766 %************************************************************************
768 \subsection{Error messages}
770 %************************************************************************
773 tcAddDeclCtxt decl thing_inside
780 (ClassDecl _ name _ _ _ _ _ _ loc) -> (name, loc, "class")
781 (TySynonym name _ _ loc) -> (name, loc, "type synonym")
782 (TyData NewType _ name _ _ _ _ _ loc _ _) -> (name, loc, "newtype")
783 (TyData DataType _ name _ _ _ _ _ loc _ _) -> (name, loc, "data type")
785 ctxt = hsep [ptext SLIT("In the"), text thing,
786 ptext SLIT("declaration for"), quotes (ppr name)]
790 instConstraintErr pred
791 = hang (ptext SLIT("Illegal constraint") <+>
792 quotes (pprPred pred) <+>
793 ptext SLIT("in instance context"))
794 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
796 badGenericInstanceType binds
797 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
800 missingGenericInstances missing
801 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
805 dupGenericInsts inst_infos
806 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
807 nest 4 (vcat (map (ppr . simpleInstInfoTy) inst_infos)),
808 ptext SLIT("All the type patterns for a generic type constructor must be identical")
811 instTypeErr clas tys msg
812 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes (pprConstraint clas tys),
816 derivingWhenInstanceExistsErr clas tycon
817 = hang (hsep [ptext SLIT("Deriving class"),
819 ptext SLIT("type"), quotes (ppr tycon)])
820 4 (ptext SLIT("when an explicit instance exists"))
822 nonBoxedPrimCCallErr clas inst_ty
823 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
824 4 (hsep [ ptext SLIT("class"), ppr clas, ptext SLIT("type"),
827 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
828 superClassCtxt = ptext SLIT("When checking the superclasses of an instance declaration")