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 -> Module -- Module for deriving
176 -> TcM (PersistentCompilerState, InstEnv, [InstInfo], RenamedHsBinds)
178 tcInstDecls1 pcs hst unf_env 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 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, dict_ty) = splitSigmaTy poly_ty'
250 (clas, inst_tys) = case splitDictTy_maybe dict_ty of
252 Nothing -> pprPanic "tcInstDecl1" (ppr poly_ty)
255 (case maybe_dfun_name of
256 Nothing -> -- A source-file instance declaration
258 -- Check for respectable instance type, and context
259 -- but only do this for non-imported instance decls.
260 -- Imported ones should have been checked already, and may indeed
261 -- contain something illegal in normal Haskell, notably
262 -- instance CCallable [Char]
263 scrutiniseInstanceHead clas inst_tys `thenNF_Tc_`
264 mapNF_Tc scrutiniseInstanceConstraint theta `thenNF_Tc_`
266 -- Make the dfun id and return it
267 newDFunName mod clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
268 returnNF_Tc (True, mkDictFunId dfun_name clas tyvars inst_tys theta)
270 Just dfun_name -> -- An interface-file instance declaration
272 returnNF_Tc (False, mkDictFunId dfun_name clas tyvars inst_tys theta)
273 ) `thenNF_Tc` \ (is_local, dfun_id) ->
275 returnTc [InstInfo { iLocal = is_local,
276 iClass = clas, iTyVars = tyvars, iTys = inst_tys,
277 iTheta = theta, iDFunId = dfun_id,
278 iBinds = binds, iLoc = src_loc, iPrags = uprags }]
282 %************************************************************************
284 \subsection{Extracting generic instance declaration from class declarations}
286 %************************************************************************
288 @getGenericInstances@ extracts the generic instance declarations from a class
289 declaration. For exmaple
294 op{ x+y } (Inl v) = ...
295 op{ x+y } (Inr v) = ...
296 op{ x*y } (v :*: w) = ...
299 gives rise to the instance declarations
301 instance C (x+y) where
305 instance C (x*y) where
313 getGenericInstances :: Module -> [RenamedTyClDecl] -> TcM [InstInfo]
314 getGenericInstances mod class_decls
315 = mapTc (get_generics mod) class_decls `thenTc` \ gen_inst_infos ->
317 gen_inst_info = concat gen_inst_infos
319 getDOptsTc `thenTc` \ dflags ->
320 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
321 (vcat (map pprInstInfo gen_inst_info)))
323 returnTc gen_inst_info
325 get_generics mod decl@(ClassDecl context class_name tyvar_names
326 fundeps class_sigs def_methods pragmas
329 = returnTc [] -- The comon case:
330 -- no generic default methods, or
331 -- its an imported class decl (=> has no methods at all)
333 | otherwise -- A local class decl with generic default methods
334 = recoverNF_Tc (returnNF_Tc []) $
336 tcLookupClass class_name `thenTc` \ clas ->
338 -- Make an InstInfo out of each group
339 mapTc (mkGenericInstance mod clas loc) groups `thenTc` \ inst_infos ->
341 -- Check that there is only one InstInfo for each type constructor
342 -- The main way this can fail is if you write
343 -- f {| a+b |} ... = ...
344 -- f {| x+y |} ... = ...
345 -- Then at this point we'll have an InstInfo for each
347 bad_groups = [group | group <- equivClassesByUniq get_uniq inst_infos,
349 get_uniq inst = getUnique (simpleInstInfoTyCon inst)
351 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
353 -- Check that there is an InstInfo for each generic type constructor
355 missing = genericTyCons `minusList` map simpleInstInfoTyCon inst_infos
357 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
362 -- Group the declarations by type pattern
363 groups :: [(RenamedHsType, RenamedMonoBinds)]
364 groups = assocElts (getGenericBinds def_methods)
367 ---------------------------------
368 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
369 -- Takes a group of method bindings, finds the generic ones, and returns
370 -- them in finite map indexed by the type parameter in the definition.
372 getGenericBinds EmptyMonoBinds = emptyAssoc
373 getGenericBinds (AndMonoBinds m1 m2)
374 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
376 getGenericBinds (FunMonoBind id infixop matches loc)
377 = mapAssoc wrap (foldr add emptyAssoc matches)
379 add match env = case maybeGenericMatch match of
381 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
383 wrap ms = FunMonoBind id infixop ms loc
385 ---------------------------------
386 mkGenericInstance :: Module -> Class -> SrcLoc
387 -> (RenamedHsType, RenamedMonoBinds)
390 mkGenericInstance mod 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 mod 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 { iLocal = True,
413 iClass = clas, iTyVars = tyvars, iTys = inst_tys,
414 iTheta = inst_theta, iDFunId = dfun_id, iBinds = binds,
415 iLoc = loc, iPrags = [] })
419 %************************************************************************
421 \subsection{Type-checking instance declarations, pass 2}
423 %************************************************************************
426 tcInstDecls2 :: [InstInfo]
427 -> NF_TcM (LIE, TcMonoBinds)
429 tcInstDecls2 inst_decls
430 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
431 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
432 (map tcInstDecl2 inst_decls)
434 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
435 tc2 `thenNF_Tc` \ (lie2, binds2) ->
436 returnNF_Tc (lie1 `plusLIE` lie2,
437 binds1 `AndMonoBinds` binds2)
440 ======= New documentation starts here (Sept 92) ==============
442 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
443 the dictionary function for this instance declaration. For example
445 instance Foo a => Foo [a] where
449 might generate something like
451 dfun.Foo.List dFoo_a = let op1 x = ...
457 HOWEVER, if the instance decl has no context, then it returns a
458 bigger @HsBinds@ with declarations for each method. For example
460 instance Foo [a] where
466 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
467 const.Foo.op1.List a x = ...
468 const.Foo.op2.List a y = ...
470 This group may be mutually recursive, because (for example) there may
471 be no method supplied for op2 in which case we'll get
473 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
475 that is, the default method applied to the dictionary at this type.
477 What we actually produce in either case is:
479 AbsBinds [a] [dfun_theta_dicts]
480 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
481 { d = (sd1,sd2, ..., op1, op2, ...)
486 The "maybe" says that we only ask AbsBinds to make global constant methods
487 if the dfun_theta is empty.
490 For an instance declaration, say,
492 instance (C1 a, C2 b) => C (T a b) where
495 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
496 function whose type is
498 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
500 Notice that we pass it the superclass dictionaries at the instance type; this
501 is the ``Mark Jones optimisation''. The stuff before the "=>" here
502 is the @dfun_theta@ below.
504 First comes the easy case of a non-local instance decl.
507 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
509 tcInstDecl2 (InstInfo { iClass = clas, iTyVars = inst_tyvars, iTys = inst_tys,
510 iTheta = inst_decl_theta, iDFunId = dfun_id,
511 iBinds = monobinds, iLoc = locn, iPrags = uprags })
512 | not (isLocallyDefined dfun_id)
513 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
516 = -- Prime error recovery
517 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
520 -- Instantiate the instance decl with tc-style type variables
521 tcInstId dfun_id `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
523 (clas, inst_tys') = expectJust "tcInstDecl2" (splitDictTy_maybe dict_ty')
524 origin = InstanceDeclOrigin
526 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
528 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
529 sel_names = [idName sel_id | (sel_id, _) <- op_items]
531 -- Instantiate the theta found in the original instance decl
532 inst_decl_theta' = substTheta (mkTopTyVarSubst inst_tyvars (mkTyVarTys inst_tyvars'))
535 -- Instantiate the super-class context with inst_tys
536 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
538 -- Find any definitions in monobinds that aren't from the class
539 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
541 -- Check that all the method bindings come from this class
542 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
544 -- Create dictionary Ids from the specified instance contexts.
545 newClassDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
546 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
547 newDicts origin inst_decl_theta' `thenNF_Tc` \ (inst_decl_dicts, _) ->
548 newClassDicts origin [(clas,inst_tys')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
550 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
551 tcExtendGlobalValEnv dm_ids (
552 -- Default-method Ids may be mentioned in synthesised RHSs
554 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
556 monobinds uprags True)
558 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_lies_w_ids) ->
560 -- Deal with SPECIALISE instance pragmas by making them
561 -- look like SPECIALISE pragmas for the dfun
563 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
565 tcExtendGlobalValEnv [dfun_id] (
566 tcSpecSigs dfun_prags
567 ) `thenTc` \ (prag_binds, prag_lie) ->
569 -- Check the overloading constraints of the methods and superclasses
571 -- tcMethodBind has checked that the class_tyvars havn't
572 -- been unified with each other or another type, but we must
573 -- still zonk them before passing them to tcSimplifyAndCheck
574 zonkTcSigTyVars inst_tyvars' `thenNF_Tc` \ zonked_inst_tyvars ->
576 inst_tyvars_set = mkVarSet zonked_inst_tyvars
578 (meth_lies, meth_ids) = unzip meth_lies_w_ids
580 -- These insts are in scope; quite a few, eh?
581 avail_insts = this_dict `plusLIE`
582 dfun_arg_dicts `plusLIE`
584 unionManyBags meth_lies
586 methods_lie = plusLIEs insts_needed_s
589 -- Ditto method bindings
590 tcAddErrCtxt methodCtxt (
592 (ptext SLIT("instance declaration context"))
593 inst_tyvars_set -- Local tyvars
596 ) `thenTc` \ (const_lie1, lie_binds1) ->
598 -- Check that we *could* construct the superclass dictionaries,
599 -- even though we are *actually* going to pass the superclass dicts in;
600 -- the check ensures that the caller will never have
601 --a problem building them.
602 tcAddErrCtxt superClassCtxt (
604 (ptext SLIT("instance declaration context"))
605 inst_tyvars_set -- Local tyvars
606 inst_decl_dicts -- The instance dictionaries available
607 sc_dicts -- The superclass dicationaries reqd
609 -- Ignore the result; we're only doing
610 -- this to make sure it can be done.
612 -- Now do the simplification again, this time to get the
613 -- bindings; this time we use an enhanced "avails"
614 -- Ignore errors because they come from the *previous* tcSimplify
617 (ptext SLIT("instance declaration context"))
619 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
620 -- get bound by just selecting from this_dict!!
622 ) `thenTc` \ (const_lie2, lie_binds2) ->
625 -- Create the result bindings
627 dict_constr = classDataCon clas
628 scs_and_meths = sc_dict_ids ++ meth_ids
632 = -- Blatant special case for CCallable, CReturnable
633 -- If the dictionary is empty then we should never
634 -- select anything from it, so we make its RHS just
635 -- emit an error message. This in turn means that we don't
636 -- mention the constructor, which doesn't exist for CCallable, CReturnable
637 -- Hardly beautiful, but only three extra lines.
638 HsApp (TyApp (HsVar eRROR_ID) [(unUsgTy . idType) this_dict_id])
639 (HsLit (HsString msg))
641 | otherwise -- The common case
642 = mkHsConApp dict_constr inst_tys' (map HsVar (sc_dict_ids ++ meth_ids))
643 -- We don't produce a binding for the dict_constr; instead we
644 -- rely on the simplifier to unfold this saturated application
645 -- We do this rather than generate an HsCon directly, because
646 -- it means that the special cases (e.g. dictionary with only one
647 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
648 -- than needing to be repeated here.
651 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
653 dict_bind = VarMonoBind this_dict_id dict_rhs
654 method_binds = andMonoBindList method_binds_s
660 [(inst_tyvars', dfun_id, this_dict_id)]
661 emptyNameSet -- No inlines (yet)
662 (lie_binds1 `AndMonoBinds`
663 lie_binds2 `AndMonoBinds`
664 method_binds `AndMonoBinds`
667 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
668 main_bind `AndMonoBinds` prag_binds)
672 %************************************************************************
674 \subsection{Checking for a decent instance type}
676 %************************************************************************
678 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
679 it must normally look like: @instance Foo (Tycon a b c ...) ...@
681 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
682 flag is on, or (2)~the instance is imported (they must have been
683 compiled elsewhere). In these cases, we let them go through anyway.
685 We can also have instances for functions: @instance Foo (a -> b) ...@.
688 scrutiniseInstanceConstraint pred
689 = getDOptsTc `thenTc` \ dflags -> case () of
691 | dopt Opt_AllowUndecidableInstances dflags
694 | Just (clas,tys) <- getClassTys_maybe pred,
699 -> addErrTc (instConstraintErr pred)
701 scrutiniseInstanceHead clas inst_taus
702 = getDOptsTc `thenTc` \ dflags -> case () of
705 -- A user declaration of a CCallable/CReturnable instance
706 -- must be for a "boxed primitive" type.
707 (clas `hasKey` cCallableClassKey
708 && not (ccallable_type dflags first_inst_tau))
710 (clas `hasKey` cReturnableClassKey
711 && not (creturnable_type first_inst_tau))
712 -> addErrTc (nonBoxedPrimCCallErr clas first_inst_tau)
715 -- It is obviously illegal to have an explicit instance
716 -- for something that we are also planning to `derive'
717 | maybeToBool alg_tycon_app_maybe && clas `elem` (tyConDerivings alg_tycon)
718 -> addErrTc (derivingWhenInstanceExistsErr clas first_inst_tau)
719 -- Kind check will have ensured inst_taus is of length 1
721 -- Allow anything for AllowUndecidableInstances
722 | dopt Opt_AllowUndecidableInstances dflags
725 -- If GlasgowExts then check at least one isn't a type variable
726 | dopt Opt_GlasgowExts dflags
727 -> if all isTyVarTy inst_taus
728 then addErrTc (instTypeErr clas inst_taus
729 (text "There must be at least one non-type-variable in the instance head"))
732 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
733 | not (length inst_taus == 1 &&
734 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
735 not (isSynTyCon tycon) && -- ...but not a synonym
736 all isTyVarTy arg_tys && -- Applied to type variables
737 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
738 -- This last condition checks that all the type variables are distinct
740 -> addErrTc (instTypeErr clas inst_taus
741 (text "the instance type must be of form (T a b c)" $$
742 text "where T is not a synonym, and a,b,c are distinct type variables")
749 (first_inst_tau : _) = inst_taus
751 -- Stuff for algebraic or -> type
752 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
753 Just (tycon, arg_tys) = maybe_tycon_app
755 -- Stuff for an *algebraic* data type
756 alg_tycon_app_maybe = splitAlgTyConApp_maybe first_inst_tau
757 -- The "Alg" part looks through synonyms
758 Just (alg_tycon, _, _) = alg_tycon_app_maybe
760 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
761 creturnable_type ty = isFFIResultTy ty
765 %************************************************************************
767 \subsection{Error messages}
769 %************************************************************************
772 tcAddDeclCtxt decl thing_inside
779 (ClassDecl _ name _ _ _ _ _ _ loc) -> (name, loc, "class")
780 (TySynonym name _ _ loc) -> (name, loc, "type synonym")
781 (TyData NewType _ name _ _ _ _ _ loc _ _) -> (name, loc, "newtype")
782 (TyData DataType _ name _ _ _ _ _ loc _ _) -> (name, loc, "data type")
784 ctxt = hsep [ptext SLIT("In the"), text thing,
785 ptext SLIT("declaration for"), quotes (ppr name)]
789 instConstraintErr pred
790 = hang (ptext SLIT("Illegal constraint") <+>
791 quotes (pprPred pred) <+>
792 ptext SLIT("in instance context"))
793 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
795 badGenericInstanceType binds
796 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
799 missingGenericInstances missing
800 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
804 dupGenericInsts inst_infos
805 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
806 nest 4 (vcat (map (ppr . simpleInstInfoTy) inst_infos)),
807 ptext SLIT("All the type patterns for a generic type constructor must be identical")
810 instTypeErr clas tys msg
811 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes (pprConstraint clas tys),
815 derivingWhenInstanceExistsErr clas tycon
816 = hang (hsep [ptext SLIT("Deriving class"),
818 ptext SLIT("type"), quotes (ppr tycon)])
819 4 (ptext SLIT("when an explicit instance exists"))
821 nonBoxedPrimCCallErr clas inst_ty
822 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
823 4 (hsep [ ptext SLIT("class"), ppr clas, ptext SLIT("type"),
826 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
827 superClassCtxt = ptext SLIT("When checking the superclasses of an instance declaration")