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(..), HsType(..),
15 MonoBinds(..), HsExpr(..), HsLit(..), Sig(..),
16 andMonoBindList, collectMonoBinders, isClassDecl
18 import RnHsSyn ( RenamedHsBinds, RenamedInstDecl, RenamedHsDecl, RenamedMonoBinds,
19 RenamedTyClDecl, RenamedHsType,
20 extractHsTyVars, maybeGenericMatch
22 import TcHsSyn ( TcMonoBinds, mkHsConApp )
23 import TcBinds ( tcSpecSigs )
24 import TcClassDcl ( tcMethodBind, badMethodErr )
26 import TcType ( tcInstType )
27 import Inst ( InstOrigin(..),
28 newDicts, newClassDicts, instToId,
29 LIE, mkLIE, emptyLIE, plusLIE, plusLIEs )
30 import TcDeriv ( tcDeriving )
31 import TcEnv ( TcEnv, tcExtendGlobalValEnv,
32 tcExtendTyVarEnvForMeths,
33 tcAddImportedIdInfo, tcLookupClass,
34 InstInfo(..), pprInstInfo, simpleInstInfoTyCon, simpleInstInfoTy,
35 newDFunName, tcExtendTyVarEnv
37 import InstEnv ( InstEnv, extendInstEnv )
38 import TcMonoType ( tcTyVars, tcHsSigType, kcHsSigType, checkSigTyVars )
39 import TcSimplify ( tcSimplifyCheck )
40 import HscTypes ( HomeSymbolTable, DFunId,
41 ModDetails(..), PackageInstEnv, PersistentRenamerState
44 import DataCon ( classDataCon )
45 import Class ( Class, DefMeth(..), classBigSig )
46 import Var ( idName, idType )
47 import VarSet ( emptyVarSet )
48 import Maybes ( maybeToBool )
49 import MkId ( mkDictFunId )
50 import FunDeps ( checkInstFDs )
51 import Generics ( validGenericInstanceType )
52 import Module ( Module, foldModuleEnv )
53 import Name ( getSrcLoc )
54 import NameSet ( emptyNameSet, nameSetToList )
55 import PrelInfo ( eRROR_ID )
56 import PprType ( pprClassPred, pprPred )
57 import TyCon ( TyCon, isSynTyCon )
58 import Type ( splitDFunTy, isTyVarTy,
59 splitTyConApp_maybe, splitDictTy,
61 tyVarsOfTypes, mkClassPred, mkTyVarTy,
64 import Subst ( mkTopTyVarSubst, substClasses )
65 import VarSet ( varSetElems )
66 import TysWiredIn ( genericTyCons, isFFIArgumentTy, isFFIImportResultTy )
67 import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
69 import SrcLoc ( SrcLoc )
70 import VarSet ( varSetElems )
71 import Unique ( Uniquable(..) )
72 import BasicTypes ( NewOrData(..), Fixity )
73 import ErrUtils ( dumpIfSet_dyn )
74 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
75 assocElts, extendAssoc_C,
76 equivClassesByUniq, minusList
78 import List ( partition )
82 Typechecking instance declarations is done in two passes. The first
83 pass, made by @tcInstDecls1@, collects information to be used in the
86 This pre-processed info includes the as-yet-unprocessed bindings
87 inside the instance declaration. These are type-checked in the second
88 pass, when the class-instance envs and GVE contain all the info from
89 all the instance and value decls. Indeed that's the reason we need
90 two passes over the instance decls.
93 Here is the overall algorithm.
94 Assume that we have an instance declaration
96 instance c => k (t tvs) where b
100 $LIE_c$ is the LIE for the context of class $c$
102 $betas_bar$ is the free variables in the class method type, excluding the
105 $LIE_cop$ is the LIE constraining a particular class method
107 $tau_cop$ is the tau type of a class method
109 $LIE_i$ is the LIE for the context of instance $i$
111 $X$ is the instance constructor tycon
113 $gammas_bar$ is the set of type variables of the instance
115 $LIE_iop$ is the LIE for a particular class method instance
117 $tau_iop$ is the tau type for this instance of a class method
119 $alpha$ is the class variable
121 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
123 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
126 ToDo: Update the list above with names actually in the code.
130 First, make the LIEs for the class and instance contexts, which means
131 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
132 and make LIElistI and LIEI.
134 Then process each method in turn.
136 order the instance methods according to the ordering of the class methods
138 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
140 Create final dictionary function from bindings generated already
142 df = lambda inst_tyvars
149 in <op1,op2,...,opn,sd1,...,sdm>
151 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
152 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
156 %************************************************************************
158 \subsection{Extracting instance decls}
160 %************************************************************************
162 Gather up the instance declarations from their various sources
165 tcInstDecls1 :: PackageInstEnv
166 -> PersistentRenamerState
167 -> HomeSymbolTable -- Contains instances
168 -> TcEnv -- Contains IdInfo for dfun ids
169 -> (Name -> Maybe Fixity) -- for deriving Show and Read
170 -> Module -- Module for deriving
172 -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
174 tcInstDecls1 inst_env0 prs hst unf_env get_fixity mod decls
176 inst_decls = [inst_decl | InstD inst_decl <- decls]
177 tycl_decls = [decl | TyClD decl <- decls]
178 clas_decls = filter isClassDecl tycl_decls
180 -- (1) Do the ordinary instance declarations
181 mapNF_Tc (tcInstDecl1 unf_env) inst_decls `thenNF_Tc` \ inst_infos ->
183 -- (2) Instances from generic class declarations
184 getGenericInstances clas_decls `thenTc` \ generic_inst_info ->
186 -- Next, construct the instance environment so far, consisting of
187 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
188 -- b) imported instance decls (not in the home package) inst_env1
189 -- c) other modules in this package (gotten from hst) inst_env2
190 -- d) local instance decls inst_env3
191 -- e) generic instances inst_env4
192 -- The result of (b) replaces the cached InstEnv in the PCS
194 (local_inst_info, imported_inst_info) = partition iLocal (concat inst_infos)
196 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
198 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
200 addInstDFuns inst_env0 imported_dfuns `thenNF_Tc` \ inst_env1 ->
201 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
202 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
203 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
205 -- (3) Compute instances from "deriving" clauses;
206 -- note that we only do derivings for things in this module;
207 -- we ignore deriving decls from interfaces!
208 -- This stuff computes a context for the derived instance decl, so it
209 -- needs to know about all the instances possible; hecne inst_env4
210 tcDeriving prs mod inst_env4 get_fixity tycl_decls `thenTc` \ (deriv_inst_info, deriv_binds) ->
211 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
215 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
218 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
219 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
221 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
222 addInstDFuns dfuns infos
223 = getDOptsTc `thenTc` \ dflags ->
225 (inst_env', errs) = extendInstEnv dflags dfuns infos
227 addErrsTc errs `thenNF_Tc_`
232 tcInstDecl1 :: TcEnv -> RenamedInstDecl -> NF_TcM [InstInfo]
233 -- Deal with a single instance declaration
234 tcInstDecl1 unf_env decl@(InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
235 = -- Prime error recovery, set source location
236 recoverNF_Tc (returnNF_Tc []) $
237 tcAddSrcLoc src_loc $
239 -- Type-check all the stuff before the "where"
240 tcAddErrCtxt (instDeclCtxt poly_ty) (
242 ) `thenTc` \ poly_ty' ->
244 (tyvars, theta, clas, inst_tys) = splitDFunTy poly_ty'
247 (case maybe_dfun_name of
248 Nothing -> -- A source-file instance declaration
250 -- Check for respectable instance type, and context
251 -- but only do this for non-imported instance decls.
252 -- Imported ones should have been checked already, and may indeed
253 -- contain something illegal in normal Haskell, notably
254 -- instance CCallable [Char]
255 getDOptsTc `thenTc` \ dflags ->
256 checkInstValidity dflags theta clas inst_tys `thenTc_`
258 -- Make the dfun id and return it
259 newDFunName clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
260 returnNF_Tc (True, dfun_name)
262 Just dfun_name -> -- An interface-file instance declaration
264 returnNF_Tc (False, dfun_name)
265 ) `thenNF_Tc` \ (is_local, dfun_name) ->
268 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
270 returnTc [InstInfo { iLocal = is_local, iDFunId = dfun_id,
271 iBinds = binds, iPrags = uprags }]
275 %************************************************************************
277 \subsection{Extracting generic instance declaration from class declarations}
279 %************************************************************************
281 @getGenericInstances@ extracts the generic instance declarations from a class
282 declaration. For exmaple
287 op{ x+y } (Inl v) = ...
288 op{ x+y } (Inr v) = ...
289 op{ x*y } (v :*: w) = ...
292 gives rise to the instance declarations
294 instance C (x+y) where
298 instance C (x*y) where
306 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
307 getGenericInstances class_decls
308 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
310 gen_inst_info = concat gen_inst_infos
312 getDOptsTc `thenTc` \ dflags ->
313 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
314 (vcat (map pprInstInfo gen_inst_info)))
316 returnTc gen_inst_info
318 get_generics decl@(ClassDecl {tcdMeths = Nothing})
319 = returnTc [] -- Imported class decls
321 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
323 = returnTc [] -- The comon case: no generic default methods
325 | otherwise -- A local class decl with generic default methods
326 = recoverNF_Tc (returnNF_Tc []) $
328 tcLookupClass class_name `thenTc` \ clas ->
330 -- Make an InstInfo out of each group
331 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
333 -- Check that there is only one InstInfo for each type constructor
334 -- The main way this can fail is if you write
335 -- f {| a+b |} ... = ...
336 -- f {| x+y |} ... = ...
337 -- Then at this point we'll have an InstInfo for each
339 tc_inst_infos :: [(TyCon, InstInfo)]
340 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
342 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
344 get_uniq (tc,_) = getUnique tc
346 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
348 -- Check that there is an InstInfo for each generic type constructor
350 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
352 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
357 -- Group the declarations by type pattern
358 groups :: [(RenamedHsType, RenamedMonoBinds)]
359 groups = assocElts (getGenericBinds def_methods)
362 ---------------------------------
363 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
364 -- Takes a group of method bindings, finds the generic ones, and returns
365 -- them in finite map indexed by the type parameter in the definition.
367 getGenericBinds EmptyMonoBinds = emptyAssoc
368 getGenericBinds (AndMonoBinds m1 m2)
369 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
371 getGenericBinds (FunMonoBind id infixop matches loc)
372 = mapAssoc wrap (foldl add emptyAssoc matches)
373 -- Using foldl not foldr is vital, else
374 -- we reverse the order of the bindings!
376 add env match = case maybeGenericMatch match of
378 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
380 wrap ms = FunMonoBind id infixop ms loc
382 ---------------------------------
383 mkGenericInstance :: Class -> SrcLoc
384 -> (RenamedHsType, RenamedMonoBinds)
387 mkGenericInstance 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 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, iDFunId = dfun_id,
410 iBinds = binds, iPrags = [] })
414 %************************************************************************
416 \subsection{Type-checking instance declarations, pass 2}
418 %************************************************************************
421 tcInstDecls2 :: [InstInfo]
422 -> NF_TcM (LIE, TcMonoBinds)
424 tcInstDecls2 inst_decls
425 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
426 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
427 (map tcInstDecl2 inst_decls)
429 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
430 tc2 `thenNF_Tc` \ (lie2, binds2) ->
431 returnNF_Tc (lie1 `plusLIE` lie2,
432 binds1 `AndMonoBinds` binds2)
435 ======= New documentation starts here (Sept 92) ==============
437 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
438 the dictionary function for this instance declaration. For example
440 instance Foo a => Foo [a] where
444 might generate something like
446 dfun.Foo.List dFoo_a = let op1 x = ...
452 HOWEVER, if the instance decl has no context, then it returns a
453 bigger @HsBinds@ with declarations for each method. For example
455 instance Foo [a] where
461 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
462 const.Foo.op1.List a x = ...
463 const.Foo.op2.List a y = ...
465 This group may be mutually recursive, because (for example) there may
466 be no method supplied for op2 in which case we'll get
468 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
470 that is, the default method applied to the dictionary at this type.
472 What we actually produce in either case is:
474 AbsBinds [a] [dfun_theta_dicts]
475 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
476 { d = (sd1,sd2, ..., op1, op2, ...)
481 The "maybe" says that we only ask AbsBinds to make global constant methods
482 if the dfun_theta is empty.
485 For an instance declaration, say,
487 instance (C1 a, C2 b) => C (T a b) where
490 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
491 function whose type is
493 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
495 Notice that we pass it the superclass dictionaries at the instance type; this
496 is the ``Mark Jones optimisation''. The stuff before the "=>" here
497 is the @dfun_theta@ below.
499 First comes the easy case of a non-local instance decl.
502 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
504 tcInstDecl2 (InstInfo { iLocal = is_local, iDFunId = dfun_id,
505 iBinds = monobinds, iPrags = uprags })
507 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
510 = -- Prime error recovery
511 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
512 tcAddSrcLoc (getSrcLoc dfun_id) $
514 -- Instantiate the instance decl with tc-style type variables
515 tcInstType (idType dfun_id) `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
517 (clas, inst_tys') = splitDictTy dict_ty'
518 origin = InstanceDeclOrigin
520 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
522 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
523 sel_names = [idName sel_id | (sel_id, _) <- op_items]
525 -- Instantiate the super-class context with inst_tys
526 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
528 -- Find any definitions in monobinds that aren't from the class
529 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
531 -- The type variable from the dict fun actually scope
532 -- over the bindings. They were gotten from
533 -- the original instance declaration
534 (inst_tyvars, _) = splitForAllTys (idType dfun_id)
536 -- Check that all the method bindings come from this class
537 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
539 -- Create dictionary Ids from the specified instance contexts.
540 newClassDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
541 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
542 newClassDicts origin [(clas,inst_tys')] `thenNF_Tc` \ [this_dict] ->
544 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
545 tcExtendGlobalValEnv dm_ids (
546 -- Default-method Ids may be mentioned in synthesised RHSs
548 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
550 monobinds uprags True)
552 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
554 -- Deal with SPECIALISE instance pragmas by making them
555 -- look like SPECIALISE pragmas for the dfun
557 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
559 tcExtendGlobalValEnv [dfun_id] (
560 tcSpecSigs dfun_prags
561 ) `thenTc` \ (prag_binds, prag_lie) ->
563 -- Check the overloading constraints of the methods and superclasses
565 -- These insts are in scope; quite a few, eh?
566 avail_insts = [this_dict] ++
571 methods_lie = plusLIEs insts_needed_s
574 -- Simplify the constraints from methods
575 tcAddErrCtxt methodCtxt (
577 (ptext SLIT("instance declaration context"))
581 ) `thenTc` \ (const_lie1, lie_binds1) ->
583 -- Figure out bindings for the superclass context
584 tcAddErrCtxt superClassCtxt (
586 (ptext SLIT("instance declaration context"))
588 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
589 -- get bound by just selecting from this_dict!!
591 ) `thenTc` \ (const_lie2, lie_binds2) ->
593 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
595 -- Create the result bindings
597 dict_constr = classDataCon clas
598 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
599 this_dict_id = instToId this_dict
603 = -- Blatant special case for CCallable, CReturnable
604 -- If the dictionary is empty then we should never
605 -- select anything from it, so we make its RHS just
606 -- emit an error message. This in turn means that we don't
607 -- mention the constructor, which doesn't exist for CCallable, CReturnable
608 -- Hardly beautiful, but only three extra lines.
609 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
610 (HsLit (HsString msg))
612 | otherwise -- The common case
613 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
614 -- We don't produce a binding for the dict_constr; instead we
615 -- rely on the simplifier to unfold this saturated application
616 -- We do this rather than generate an HsCon directly, because
617 -- it means that the special cases (e.g. dictionary with only one
618 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
619 -- than needing to be repeated here.
622 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
624 dict_bind = VarMonoBind this_dict_id dict_rhs
625 method_binds = andMonoBindList method_binds_s
630 (map instToId dfun_arg_dicts)
631 [(inst_tyvars', dfun_id, this_dict_id)]
632 emptyNameSet -- No inlines (yet)
633 (lie_binds1 `AndMonoBinds`
634 lie_binds2 `AndMonoBinds`
635 method_binds `AndMonoBinds`
638 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
639 main_bind `AndMonoBinds` prag_binds)
643 %************************************************************************
645 \subsection{Checking for a decent instance type}
647 %************************************************************************
649 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
650 it must normally look like: @instance Foo (Tycon a b c ...) ...@
652 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
653 flag is on, or (2)~the instance is imported (they must have been
654 compiled elsewhere). In these cases, we let them go through anyway.
656 We can also have instances for functions: @instance Foo (a -> b) ...@.
659 checkInstValidity dflags theta clas inst_tys
660 | null errs = returnTc ()
661 | otherwise = addErrsTc errs `thenNF_Tc_` failTc
663 errs = checkInstHead dflags theta clas inst_tys ++
664 [err | pred <- theta, err <- checkInstConstraint dflags pred]
666 checkInstConstraint dflags pred
667 | dopt Opt_AllowUndecidableInstances dflags
670 | Just (clas,tys) <- getClassTys_maybe pred,
675 = [instConstraintErr pred]
677 checkInstHead dflags theta clas inst_taus
679 -- A user declaration of a CCallable/CReturnable instance
680 -- must be for a "boxed primitive" type.
681 (clas `hasKey` cCallableClassKey
682 && not (ccallable_type dflags first_inst_tau))
684 (clas `hasKey` cReturnableClassKey
685 && not (creturnable_type first_inst_tau))
686 = [nonBoxedPrimCCallErr clas first_inst_tau]
688 -- If GlasgowExts then check at least one isn't a type variable
689 | dopt Opt_GlasgowExts dflags
690 = -- GlasgowExts case
691 check_tyvars dflags clas inst_taus ++ check_fundeps dflags theta clas inst_taus
693 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
694 | not (length inst_taus == 1 &&
695 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
696 not (isSynTyCon tycon) && -- ...but not a synonym
697 all isTyVarTy arg_tys && -- Applied to type variables
698 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
699 -- This last condition checks that all the type variables are distinct
701 = [instTypeErr clas inst_taus
702 (text "the instance type must be of form (T a b c)" $$
703 text "where T is not a synonym, and a,b,c are distinct type variables")]
709 (first_inst_tau : _) = inst_taus
711 -- Stuff for algebraic or -> type
712 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
713 Just (tycon, arg_tys) = maybe_tycon_app
715 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
716 creturnable_type ty = isFFIImportResultTy dflags ty
718 check_tyvars dflags clas inst_taus
719 -- Check that at least one isn't a type variable
720 -- unless -fallow-undecideable-instances
721 | dopt Opt_AllowUndecidableInstances dflags = []
722 | not (all isTyVarTy inst_taus) = []
723 | otherwise = [the_err]
725 the_err = instTypeErr clas inst_taus msg
726 msg = ptext SLIT("There must be at least one non-type-variable in the instance head")
728 check_fundeps dflags theta clas inst_taus
729 | checkInstFDs theta clas inst_taus = []
730 | otherwise = [the_err]
732 the_err = instTypeErr clas inst_taus msg
733 msg = ptext SLIT("the instance types do not agree with the functional dependencies of the class")
737 %************************************************************************
739 \subsection{Error messages}
741 %************************************************************************
744 tcAddDeclCtxt decl thing_inside
745 = tcAddSrcLoc (tcdLoc decl) $
750 ClassDecl {} -> "class"
751 TySynonym {} -> "type synonym"
752 TyData {tcdND = NewType} -> "newtype"
753 TyData {tcdND = DataType} -> "data type"
755 ctxt = hsep [ptext SLIT("In the"), text thing,
756 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
758 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
760 doc = case inst_ty of
761 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
762 HsPredTy pred -> ppr pred
763 other -> ppr inst_ty -- Don't expect this
767 instConstraintErr pred
768 = hang (ptext SLIT("Illegal constraint") <+>
769 quotes (pprPred pred) <+>
770 ptext SLIT("in instance context"))
771 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
773 badGenericInstanceType binds
774 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
777 missingGenericInstances missing
778 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
782 dupGenericInsts tc_inst_infos
783 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
784 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
785 ptext SLIT("All the type patterns for a generic type constructor must be identical")
788 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
790 instTypeErr clas tys msg
791 = sep [ptext SLIT("Illegal instance declaration for") <+>
792 quotes (pprClassPred clas tys),
796 nonBoxedPrimCCallErr clas inst_ty
797 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
798 4 (pprClassPred clas [inst_ty])
800 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
801 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")