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,
19 RenamedMonoBinds, 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,
35 simpleInstInfoTy, newDFunName, tcExtendTyVarEnv,
38 import InstEnv ( InstEnv, extendInstEnv )
39 import TcMonoType ( tcTyVars, tcHsSigType, kcHsSigType, checkSigTyVars )
40 import TcSimplify ( tcSimplifyCheck )
41 import HscTypes ( HomeSymbolTable, DFunId,
42 ModDetails(..), PackageInstEnv, PersistentRenamerState
45 import DataCon ( classDataCon )
46 import Class ( Class, DefMeth(..), classBigSig )
47 import Var ( idName, idType )
48 import VarSet ( emptyVarSet )
49 import Maybes ( maybeToBool )
50 import MkId ( mkDictFunId )
51 import FunDeps ( checkInstFDs )
52 import Generics ( validGenericInstanceType )
53 import Module ( Module, foldModuleEnv )
54 import Name ( getSrcLoc )
55 import NameSet ( emptyNameSet, nameSetToList )
56 import PrelInfo ( eRROR_ID )
57 import PprType ( pprClassPred, pprPred )
58 import TyCon ( TyCon, isSynTyCon )
59 import Type ( splitDFunTy, isTyVarTy,
60 splitTyConApp_maybe, splitDictTy,
62 tyVarsOfTypes, mkClassPred, mkTyVarTy,
65 import Subst ( mkTopTyVarSubst, substClasses )
66 import VarSet ( varSetElems )
67 import TysWiredIn ( genericTyCons, isFFIArgumentTy, isFFIImportResultTy )
68 import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
70 import SrcLoc ( SrcLoc )
71 import VarSet ( varSetElems )
72 import Unique ( Uniquable(..) )
73 import BasicTypes ( NewOrData(..), Fixity )
74 import ErrUtils ( dumpIfSet_dyn )
75 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
76 assocElts, extendAssoc_C,
77 equivClassesByUniq, minusList
79 import List ( partition )
83 Typechecking instance declarations is done in two passes. The first
84 pass, made by @tcInstDecls1@, collects information to be used in the
87 This pre-processed info includes the as-yet-unprocessed bindings
88 inside the instance declaration. These are type-checked in the second
89 pass, when the class-instance envs and GVE contain all the info from
90 all the instance and value decls. Indeed that's the reason we need
91 two passes over the instance decls.
94 Here is the overall algorithm.
95 Assume that we have an instance declaration
97 instance c => k (t tvs) where b
101 $LIE_c$ is the LIE for the context of class $c$
103 $betas_bar$ is the free variables in the class method type, excluding the
106 $LIE_cop$ is the LIE constraining a particular class method
108 $tau_cop$ is the tau type of a class method
110 $LIE_i$ is the LIE for the context of instance $i$
112 $X$ is the instance constructor tycon
114 $gammas_bar$ is the set of type variables of the instance
116 $LIE_iop$ is the LIE for a particular class method instance
118 $tau_iop$ is the tau type for this instance of a class method
120 $alpha$ is the class variable
122 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
124 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
127 ToDo: Update the list above with names actually in the code.
131 First, make the LIEs for the class and instance contexts, which means
132 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
133 and make LIElistI and LIEI.
135 Then process each method in turn.
137 order the instance methods according to the ordering of the class methods
139 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
141 Create final dictionary function from bindings generated already
143 df = lambda inst_tyvars
150 in <op1,op2,...,opn,sd1,...,sdm>
152 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
153 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
157 %************************************************************************
159 \subsection{Extracting instance decls}
161 %************************************************************************
163 Gather up the instance declarations from their various sources
166 tcInstDecls1 :: PackageInstEnv
167 -> PersistentRenamerState
168 -> HomeSymbolTable -- Contains instances
169 -> TcEnv -- Contains IdInfo for dfun ids
170 -> (Name -> Maybe Fixity) -- for deriving Show and Read
171 -> Module -- Module for deriving
173 -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
175 tcInstDecls1 inst_env0 prs hst unf_env get_fixity this_mod decls
177 inst_decls = [inst_decl | InstD inst_decl <- decls]
178 tycl_decls = [decl | TyClD decl <- decls]
179 clas_decls = filter isClassDecl tycl_decls
181 -- (1) Do the ordinary instance declarations
182 mapNF_Tc tcInstDecl1 inst_decls `thenNF_Tc` \ inst_infos ->
184 -- (2) Instances from generic class declarations
185 getGenericInstances clas_decls `thenTc` \ generic_inst_info ->
187 -- Next, construct the instance environment so far, consisting of
188 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
189 -- b) imported instance decls (not in the home package) inst_env1
190 -- c) other modules in this package (gotten from hst) inst_env2
191 -- d) local instance decls inst_env3
192 -- e) generic instances inst_env4
193 -- The result of (b) replaces the cached InstEnv in the PCS
195 (local_inst_info, imported_inst_info)
196 = partition (isLocalThing this_mod . iDFunId) (concat inst_infos)
198 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
200 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
202 addInstDFuns inst_env0 imported_dfuns `thenNF_Tc` \ inst_env1 ->
203 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
204 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
205 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
207 -- (3) Compute instances from "deriving" clauses;
208 -- note that we only do derivings for things in this module;
209 -- we ignore deriving decls from interfaces!
210 -- This stuff computes a context for the derived instance decl, so it
211 -- needs to know about all the instances possible; hecne inst_env4
212 tcDeriving prs this_mod inst_env4 get_fixity tycl_decls
213 `thenTc` \ (deriv_inst_info, deriv_binds) ->
214 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
218 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
221 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
222 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
224 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
225 addInstDFuns dfuns infos
226 = getDOptsTc `thenTc` \ dflags ->
228 (inst_env', errs) = extendInstEnv dflags dfuns infos
230 addErrsTc errs `thenNF_Tc_`
235 tcInstDecl1 :: RenamedInstDecl -> NF_TcM [InstInfo]
236 -- Deal with a single instance declaration
237 tcInstDecl1 decl@(InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
238 = -- Prime error recovery, set source location
239 recoverNF_Tc (returnNF_Tc []) $
240 tcAddSrcLoc src_loc $
242 -- Type-check all the stuff before the "where"
243 tcAddErrCtxt (instDeclCtxt poly_ty) (
245 ) `thenTc` \ poly_ty' ->
247 (tyvars, theta, clas, inst_tys) = splitDFunTy poly_ty'
250 (case maybe_dfun_name of
251 Nothing -> -- A source-file instance declaration
253 -- Check for respectable instance type, and context
254 -- but only do this for non-imported instance decls.
255 -- Imported ones should have been checked already, and may indeed
256 -- contain something illegal in normal Haskell, notably
257 -- instance CCallable [Char]
258 getDOptsTc `thenTc` \ dflags ->
259 checkInstValidity dflags theta clas inst_tys `thenTc_`
261 -- Make the dfun id and return it
262 newDFunName clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
263 returnNF_Tc (True, dfun_name)
265 Just dfun_name -> -- An interface-file instance declaration
267 returnNF_Tc (False, dfun_name)
268 ) `thenNF_Tc` \ (is_local, dfun_name) ->
271 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
273 returnTc [InstInfo { iDFunId = dfun_id,
274 iBinds = binds, iPrags = uprags }]
278 %************************************************************************
280 \subsection{Extracting generic instance declaration from class declarations}
282 %************************************************************************
284 @getGenericInstances@ extracts the generic instance declarations from a class
285 declaration. For exmaple
290 op{ x+y } (Inl v) = ...
291 op{ x+y } (Inr v) = ...
292 op{ x*y } (v :*: w) = ...
295 gives rise to the instance declarations
297 instance C (x+y) where
301 instance C (x*y) where
309 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
310 getGenericInstances class_decls
311 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
313 gen_inst_info = concat gen_inst_infos
315 getDOptsTc `thenTc` \ dflags ->
316 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
317 (vcat (map pprInstInfo gen_inst_info)))
319 returnTc gen_inst_info
321 get_generics decl@(ClassDecl {tcdMeths = Nothing})
322 = returnTc [] -- Imported class decls
324 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
326 = returnTc [] -- The comon case: no generic default methods
328 | otherwise -- A local class decl with generic default methods
329 = recoverNF_Tc (returnNF_Tc []) $
331 tcLookupClass class_name `thenTc` \ clas ->
333 -- Make an InstInfo out of each group
334 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
336 -- Check that there is only one InstInfo for each type constructor
337 -- The main way this can fail is if you write
338 -- f {| a+b |} ... = ...
339 -- f {| x+y |} ... = ...
340 -- Then at this point we'll have an InstInfo for each
342 tc_inst_infos :: [(TyCon, InstInfo)]
343 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
345 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
347 get_uniq (tc,_) = getUnique tc
349 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
351 -- Check that there is an InstInfo for each generic type constructor
353 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
355 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
360 -- Group the declarations by type pattern
361 groups :: [(RenamedHsType, RenamedMonoBinds)]
362 groups = assocElts (getGenericBinds def_methods)
365 ---------------------------------
366 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
367 -- Takes a group of method bindings, finds the generic ones, and returns
368 -- them in finite map indexed by the type parameter in the definition.
370 getGenericBinds EmptyMonoBinds = emptyAssoc
371 getGenericBinds (AndMonoBinds m1 m2)
372 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
374 getGenericBinds (FunMonoBind id infixop matches loc)
375 = mapAssoc wrap (foldl add emptyAssoc matches)
376 -- Using foldl not foldr is vital, else
377 -- we reverse the order of the bindings!
379 add env match = case maybeGenericMatch match of
381 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
383 wrap ms = FunMonoBind id infixop ms loc
385 ---------------------------------
386 mkGenericInstance :: Class -> SrcLoc
387 -> (RenamedHsType, RenamedMonoBinds)
390 mkGenericInstance clas loc (hs_ty, binds)
391 -- Make a generic instance declaration
392 -- For example: instance (C a, C b) => C (a+b) where { binds }
394 = -- Extract the universally quantified type variables
395 tcTyVars (nameSetToList (extractHsTyVars hs_ty))
396 (kcHsSigType hs_ty) `thenTc` \ tyvars ->
397 tcExtendTyVarEnv tyvars $
399 -- Type-check the instance type, and check its form
400 tcHsSigType hs_ty `thenTc` \ inst_ty ->
401 checkTc (validGenericInstanceType inst_ty)
402 (badGenericInstanceType binds) `thenTc_`
404 -- Make the dictionary function.
405 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
407 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
409 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
412 returnTc (InstInfo { iDFunId = dfun_id,
413 iBinds = binds, iPrags = [] })
417 %************************************************************************
419 \subsection{Type-checking instance declarations, pass 2}
421 %************************************************************************
424 tcInstDecls2 :: [InstInfo]
425 -> NF_TcM (LIE, TcMonoBinds)
427 tcInstDecls2 inst_decls
428 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
429 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
430 (map tcInstDecl2 inst_decls)
432 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
433 tc2 `thenNF_Tc` \ (lie2, binds2) ->
434 returnNF_Tc (lie1 `plusLIE` lie2,
435 binds1 `AndMonoBinds` binds2)
438 ======= New documentation starts here (Sept 92) ==============
440 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
441 the dictionary function for this instance declaration. For example
443 instance Foo a => Foo [a] where
447 might generate something like
449 dfun.Foo.List dFoo_a = let op1 x = ...
455 HOWEVER, if the instance decl has no context, then it returns a
456 bigger @HsBinds@ with declarations for each method. For example
458 instance Foo [a] where
464 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
465 const.Foo.op1.List a x = ...
466 const.Foo.op2.List a y = ...
468 This group may be mutually recursive, because (for example) there may
469 be no method supplied for op2 in which case we'll get
471 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
473 that is, the default method applied to the dictionary at this type.
475 What we actually produce in either case is:
477 AbsBinds [a] [dfun_theta_dicts]
478 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
479 { d = (sd1,sd2, ..., op1, op2, ...)
484 The "maybe" says that we only ask AbsBinds to make global constant methods
485 if the dfun_theta is empty.
488 For an instance declaration, say,
490 instance (C1 a, C2 b) => C (T a b) where
493 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
494 function whose type is
496 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
498 Notice that we pass it the superclass dictionaries at the instance type; this
499 is the ``Mark Jones optimisation''. The stuff before the "=>" here
500 is the @dfun_theta@ below.
502 First comes the easy case of a non-local instance decl.
506 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
507 -- tcInstDecl2 is called *only* on InstInfos
509 tcInstDecl2 (InstInfo { iDFunId = dfun_id,
510 iBinds = monobinds, iPrags = uprags })
511 = -- Prime error recovery
512 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
513 tcAddSrcLoc (getSrcLoc dfun_id) $
515 -- Instantiate the instance decl with tc-style type variables
516 tcInstType (idType dfun_id) `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
518 (clas, inst_tys') = splitDictTy dict_ty'
519 origin = InstanceDeclOrigin
521 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
523 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
524 sel_names = [idName sel_id | (sel_id, _) <- op_items]
526 -- Instantiate the super-class context with inst_tys
527 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
529 -- Find any definitions in monobinds that aren't from the class
530 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
532 -- The type variable from the dict fun actually scope
533 -- over the bindings. They were gotten from
534 -- the original instance declaration
535 (inst_tyvars, _) = splitForAllTys (idType dfun_id)
537 -- Check that all the method bindings come from this class
538 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
540 -- Create dictionary Ids from the specified instance contexts.
541 newClassDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
542 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
543 newClassDicts origin [(clas,inst_tys')] `thenNF_Tc` \ [this_dict] ->
545 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
546 tcExtendGlobalValEnv dm_ids (
547 -- Default-method Ids may be mentioned in synthesised RHSs
549 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
551 monobinds uprags True)
553 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
555 -- Deal with SPECIALISE instance pragmas by making them
556 -- look like SPECIALISE pragmas for the dfun
558 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
560 tcExtendGlobalValEnv [dfun_id] (
561 tcSpecSigs dfun_prags
562 ) `thenTc` \ (prag_binds, prag_lie) ->
564 -- Check the overloading constraints of the methods and superclasses
566 -- These insts are in scope; quite a few, eh?
567 avail_insts = [this_dict] ++
572 methods_lie = plusLIEs insts_needed_s
575 -- Simplify the constraints from methods
576 tcAddErrCtxt methodCtxt (
578 (ptext SLIT("instance declaration context"))
582 ) `thenTc` \ (const_lie1, lie_binds1) ->
584 -- Figure out bindings for the superclass context
585 tcAddErrCtxt superClassCtxt (
587 (ptext SLIT("instance declaration context"))
589 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
590 -- get bound by just selecting from this_dict!!
592 ) `thenTc` \ (const_lie2, lie_binds2) ->
594 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
596 -- Create the result bindings
598 dict_constr = classDataCon clas
599 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
600 this_dict_id = instToId this_dict
604 = -- Blatant special case for CCallable, CReturnable
605 -- If the dictionary is empty then we should never
606 -- select anything from it, so we make its RHS just
607 -- emit an error message. This in turn means that we don't
608 -- mention the constructor, which doesn't exist for CCallable, CReturnable
609 -- Hardly beautiful, but only three extra lines.
610 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
611 (HsLit (HsString msg))
613 | otherwise -- The common case
614 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
615 -- We don't produce a binding for the dict_constr; instead we
616 -- rely on the simplifier to unfold this saturated application
617 -- We do this rather than generate an HsCon directly, because
618 -- it means that the special cases (e.g. dictionary with only one
619 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
620 -- than needing to be repeated here.
623 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
625 dict_bind = VarMonoBind this_dict_id dict_rhs
626 method_binds = andMonoBindList method_binds_s
631 (map instToId dfun_arg_dicts)
632 [(inst_tyvars', dfun_id, this_dict_id)]
633 emptyNameSet -- No inlines (yet)
634 (lie_binds1 `AndMonoBinds`
635 lie_binds2 `AndMonoBinds`
636 method_binds `AndMonoBinds`
639 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
640 main_bind `AndMonoBinds` prag_binds)
644 %************************************************************************
646 \subsection{Checking for a decent instance type}
648 %************************************************************************
650 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
651 it must normally look like: @instance Foo (Tycon a b c ...) ...@
653 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
654 flag is on, or (2)~the instance is imported (they must have been
655 compiled elsewhere). In these cases, we let them go through anyway.
657 We can also have instances for functions: @instance Foo (a -> b) ...@.
660 checkInstValidity dflags theta clas inst_tys
661 | null errs = returnTc ()
662 | otherwise = addErrsTc errs `thenNF_Tc_` failTc
664 errs = checkInstHead dflags theta clas inst_tys ++
665 [err | pred <- theta, err <- checkInstConstraint dflags pred]
667 checkInstConstraint dflags pred
668 | dopt Opt_AllowUndecidableInstances dflags
671 | Just (clas,tys) <- getClassTys_maybe pred,
676 = [instConstraintErr pred]
678 checkInstHead dflags theta clas inst_taus
680 -- A user declaration of a CCallable/CReturnable instance
681 -- must be for a "boxed primitive" type.
682 (clas `hasKey` cCallableClassKey
683 && not (ccallable_type dflags first_inst_tau))
685 (clas `hasKey` cReturnableClassKey
686 && not (creturnable_type first_inst_tau))
687 = [nonBoxedPrimCCallErr clas first_inst_tau]
689 -- If GlasgowExts then check at least one isn't a type variable
690 | dopt Opt_GlasgowExts dflags
691 = -- GlasgowExts case
692 check_tyvars dflags clas inst_taus ++ check_fundeps dflags theta clas inst_taus
694 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
695 | not (length inst_taus == 1 &&
696 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
697 not (isSynTyCon tycon) && -- ...but not a synonym
698 all isTyVarTy arg_tys && -- Applied to type variables
699 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
700 -- This last condition checks that all the type variables are distinct
702 = [instTypeErr clas inst_taus
703 (text "the instance type must be of form (T a b c)" $$
704 text "where T is not a synonym, and a,b,c are distinct type variables")]
710 (first_inst_tau : _) = inst_taus
712 -- Stuff for algebraic or -> type
713 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
714 Just (tycon, arg_tys) = maybe_tycon_app
716 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
717 creturnable_type ty = isFFIImportResultTy dflags ty
719 check_tyvars dflags clas inst_taus
720 -- Check that at least one isn't a type variable
721 -- unless -fallow-undecideable-instances
722 | dopt Opt_AllowUndecidableInstances dflags = []
723 | not (all isTyVarTy inst_taus) = []
724 | otherwise = [the_err]
726 the_err = instTypeErr clas inst_taus msg
727 msg = ptext SLIT("There must be at least one non-type-variable in the instance head")
729 check_fundeps dflags theta clas inst_taus
730 | checkInstFDs theta clas inst_taus = []
731 | otherwise = [the_err]
733 the_err = instTypeErr clas inst_taus msg
734 msg = ptext SLIT("the instance types do not agree with the functional dependencies of the class")
738 %************************************************************************
740 \subsection{Error messages}
742 %************************************************************************
745 tcAddDeclCtxt decl thing_inside
746 = tcAddSrcLoc (tcdLoc decl) $
751 ClassDecl {} -> "class"
752 TySynonym {} -> "type synonym"
753 TyData {tcdND = NewType} -> "newtype"
754 TyData {tcdND = DataType} -> "data type"
756 ctxt = hsep [ptext SLIT("In the"), text thing,
757 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
759 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
761 doc = case inst_ty of
762 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
763 HsPredTy pred -> ppr pred
764 other -> ppr inst_ty -- Don't expect this
768 instConstraintErr pred
769 = hang (ptext SLIT("Illegal constraint") <+>
770 quotes (pprPred pred) <+>
771 ptext SLIT("in instance context"))
772 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
774 badGenericInstanceType binds
775 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
778 missingGenericInstances missing
779 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
783 dupGenericInsts tc_inst_infos
784 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
785 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
786 ptext SLIT("All the type patterns for a generic type constructor must be identical")
789 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
791 instTypeErr clas tys msg
792 = sep [ptext SLIT("Illegal instance declaration for") <+>
793 quotes (pprClassPred clas tys),
797 nonBoxedPrimCCallErr clas inst_ty
798 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
799 4 (pprClassPred clas [inst_ty])
801 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
802 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")