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, splitDFunTy, isTyVarTy,
60 splitTyConApp_maybe, splitDictTy,
61 splitAlgTyConApp_maybe, classesToPreds, classesOfPreds,
62 unUsgTy, tyVarsOfTypes, mkClassPred, mkTyVarTy,
65 import Subst ( mkTopTyVarSubst, substClasses, substTheta )
66 import VarSet ( mkVarSet, varSetElems )
67 import TysWiredIn ( genericTyCons, isFFIArgumentTy, isFFIResultTy )
68 import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
69 import Name ( Name, NameEnv, extendNameEnv_C, emptyNameEnv,
70 plusNameEnv_C, nameEnvElts )
71 import FiniteMap ( mapFM )
72 import SrcLoc ( SrcLoc )
73 import 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, clas, inst_tys) = splitDFunTy poly_ty'
253 (case maybe_dfun_name of
254 Nothing -> -- A source-file instance declaration
256 -- Check for respectable instance type, and context
257 -- but only do this for non-imported instance decls.
258 -- Imported ones should have been checked already, and may indeed
259 -- contain something illegal in normal Haskell, notably
260 -- instance CCallable [Char]
261 scrutiniseInstanceHead clas inst_tys `thenNF_Tc_`
262 mapNF_Tc scrutiniseInstanceConstraint theta `thenNF_Tc_`
264 -- Make the dfun id and return it
265 newDFunName mod clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
266 returnNF_Tc (True, mkDictFunId dfun_name clas tyvars inst_tys theta)
268 Just dfun_name -> -- An interface-file instance declaration
270 returnNF_Tc (False, mkDictFunId dfun_name clas tyvars inst_tys theta)
271 ) `thenNF_Tc` \ (is_local, dfun_id) ->
273 returnTc [InstInfo { iLocal = is_local,
274 iClass = clas, iTyVars = tyvars, iTys = inst_tys,
275 iTheta = theta, iDFunId = dfun_id,
276 iBinds = binds, iLoc = src_loc, iPrags = uprags }]
280 %************************************************************************
282 \subsection{Extracting generic instance declaration from class declarations}
284 %************************************************************************
286 @getGenericInstances@ extracts the generic instance declarations from a class
287 declaration. For exmaple
292 op{ x+y } (Inl v) = ...
293 op{ x+y } (Inr v) = ...
294 op{ x*y } (v :*: w) = ...
297 gives rise to the instance declarations
299 instance C (x+y) where
303 instance C (x*y) where
311 getGenericInstances :: Module -> [RenamedTyClDecl] -> TcM [InstInfo]
312 getGenericInstances mod class_decls
313 = mapTc (get_generics mod) class_decls `thenTc` \ gen_inst_infos ->
315 gen_inst_info = concat gen_inst_infos
317 getDOptsTc `thenTc` \ dflags ->
318 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
319 (vcat (map pprInstInfo gen_inst_info)))
321 returnTc gen_inst_info
323 get_generics mod decl@(ClassDecl context class_name tyvar_names
324 fundeps class_sigs def_methods
327 = returnTc [] -- The comon case:
328 -- no generic default methods, or
329 -- its an imported class decl (=> has no methods at all)
331 | otherwise -- A local class decl with generic default methods
332 = recoverNF_Tc (returnNF_Tc []) $
334 tcLookupClass class_name `thenTc` \ clas ->
336 -- Make an InstInfo out of each group
337 mapTc (mkGenericInstance mod clas loc) groups `thenTc` \ inst_infos ->
339 -- Check that there is only one InstInfo for each type constructor
340 -- The main way this can fail is if you write
341 -- f {| a+b |} ... = ...
342 -- f {| x+y |} ... = ...
343 -- Then at this point we'll have an InstInfo for each
345 bad_groups = [group | group <- equivClassesByUniq get_uniq inst_infos,
347 get_uniq inst = getUnique (simpleInstInfoTyCon inst)
349 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
351 -- Check that there is an InstInfo for each generic type constructor
353 missing = genericTyCons `minusList` map simpleInstInfoTyCon 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 (foldr add emptyAssoc matches)
377 add match env = case maybeGenericMatch match of
379 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
381 wrap ms = FunMonoBind id infixop ms loc
383 ---------------------------------
384 mkGenericInstance :: Module -> Class -> SrcLoc
385 -> (RenamedHsType, RenamedMonoBinds)
388 mkGenericInstance mod clas loc (hs_ty, binds)
389 -- Make a generic instance declaration
390 -- For example: instance (C a, C b) => C (a+b) where { binds }
392 = -- Extract the universally quantified type variables
393 tcTyVars (nameSetToList (extractHsTyVars hs_ty))
394 (kcHsSigType hs_ty) `thenTc` \ tyvars ->
395 tcExtendTyVarEnv tyvars $
397 -- Type-check the instance type, and check its form
398 tcHsSigType hs_ty `thenTc` \ inst_ty ->
399 checkTc (validGenericInstanceType inst_ty)
400 (badGenericInstanceType binds) `thenTc_`
402 -- Make the dictionary function.
403 newDFunName mod clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
405 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
407 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
410 returnTc (InstInfo { iLocal = True,
411 iClass = clas, iTyVars = tyvars, iTys = inst_tys,
412 iTheta = inst_theta, iDFunId = dfun_id, iBinds = binds,
413 iLoc = loc, 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.
505 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
507 tcInstDecl2 (InstInfo { iClass = clas, iTyVars = inst_tyvars, iTys = inst_tys,
508 iTheta = inst_decl_theta, iDFunId = dfun_id,
509 iBinds = monobinds, iLoc = locn, iPrags = uprags })
510 | not (isLocallyDefined dfun_id)
511 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
514 = -- Prime error recovery
515 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
518 -- Instantiate the instance decl with tc-style type variables
519 tcInstId dfun_id `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
521 (clas, inst_tys') = splitDictTy dict_ty'
522 origin = InstanceDeclOrigin
524 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
526 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
527 sel_names = [idName sel_id | (sel_id, _) <- op_items]
529 -- Instantiate the theta found in the original instance decl
530 inst_decl_theta' = substTheta (mkTopTyVarSubst inst_tyvars (mkTyVarTys inst_tyvars'))
533 -- Instantiate the super-class context with inst_tys
534 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
536 -- Find any definitions in monobinds that aren't from the class
537 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
539 -- Check that all the method bindings come from this class
540 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
542 -- Create dictionary Ids from the specified instance contexts.
543 newClassDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
544 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
545 newDicts origin inst_decl_theta' `thenNF_Tc` \ (inst_decl_dicts, _) ->
546 newClassDicts origin [(clas,inst_tys')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
548 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
549 tcExtendGlobalValEnv dm_ids (
550 -- Default-method Ids may be mentioned in synthesised RHSs
552 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
554 monobinds uprags True)
556 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_lies_w_ids) ->
558 -- Deal with SPECIALISE instance pragmas by making them
559 -- look like SPECIALISE pragmas for the dfun
561 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
563 tcExtendGlobalValEnv [dfun_id] (
564 tcSpecSigs dfun_prags
565 ) `thenTc` \ (prag_binds, prag_lie) ->
567 -- Check the overloading constraints of the methods and superclasses
569 -- tcMethodBind has checked that the class_tyvars havn't
570 -- been unified with each other or another type, but we must
571 -- still zonk them before passing them to tcSimplifyAndCheck
572 zonkTcSigTyVars inst_tyvars' `thenNF_Tc` \ zonked_inst_tyvars ->
574 inst_tyvars_set = mkVarSet zonked_inst_tyvars
576 (meth_lies, meth_ids) = unzip meth_lies_w_ids
578 -- These insts are in scope; quite a few, eh?
579 avail_insts = this_dict `plusLIE`
580 dfun_arg_dicts `plusLIE`
582 unionManyBags meth_lies
584 methods_lie = plusLIEs insts_needed_s
587 -- Ditto method bindings
588 tcAddErrCtxt methodCtxt (
590 (ptext SLIT("instance declaration context"))
591 inst_tyvars_set -- Local tyvars
594 ) `thenTc` \ (const_lie1, lie_binds1) ->
596 -- Check that we *could* construct the superclass dictionaries,
597 -- even though we are *actually* going to pass the superclass dicts in;
598 -- the check ensures that the caller will never have
599 --a problem building them.
600 tcAddErrCtxt superClassCtxt (
602 (ptext SLIT("instance declaration context"))
603 inst_tyvars_set -- Local tyvars
604 inst_decl_dicts -- The instance dictionaries available
605 sc_dicts -- The superclass dicationaries reqd
607 -- Ignore the result; we're only doing
608 -- this to make sure it can be done.
610 -- Now do the simplification again, this time to get the
611 -- bindings; this time we use an enhanced "avails"
612 -- Ignore errors because they come from the *previous* tcSimplify
615 (ptext SLIT("instance declaration context"))
617 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
618 -- get bound by just selecting from this_dict!!
620 ) `thenTc` \ (const_lie2, lie_binds2) ->
623 -- Create the result bindings
625 dict_constr = classDataCon clas
626 scs_and_meths = sc_dict_ids ++ meth_ids
630 = -- Blatant special case for CCallable, CReturnable
631 -- If the dictionary is empty then we should never
632 -- select anything from it, so we make its RHS just
633 -- emit an error message. This in turn means that we don't
634 -- mention the constructor, which doesn't exist for CCallable, CReturnable
635 -- Hardly beautiful, but only three extra lines.
636 HsApp (TyApp (HsVar eRROR_ID) [(unUsgTy . idType) this_dict_id])
637 (HsLit (HsString msg))
639 | otherwise -- The common case
640 = mkHsConApp dict_constr inst_tys' (map HsVar (sc_dict_ids ++ meth_ids))
641 -- We don't produce a binding for the dict_constr; instead we
642 -- rely on the simplifier to unfold this saturated application
643 -- We do this rather than generate an HsCon directly, because
644 -- it means that the special cases (e.g. dictionary with only one
645 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
646 -- than needing to be repeated here.
649 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
651 dict_bind = VarMonoBind this_dict_id dict_rhs
652 method_binds = andMonoBindList method_binds_s
658 [(inst_tyvars', dfun_id, this_dict_id)]
659 emptyNameSet -- No inlines (yet)
660 (lie_binds1 `AndMonoBinds`
661 lie_binds2 `AndMonoBinds`
662 method_binds `AndMonoBinds`
665 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
666 main_bind `AndMonoBinds` prag_binds)
670 %************************************************************************
672 \subsection{Checking for a decent instance type}
674 %************************************************************************
676 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
677 it must normally look like: @instance Foo (Tycon a b c ...) ...@
679 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
680 flag is on, or (2)~the instance is imported (they must have been
681 compiled elsewhere). In these cases, we let them go through anyway.
683 We can also have instances for functions: @instance Foo (a -> b) ...@.
686 scrutiniseInstanceConstraint pred
687 = getDOptsTc `thenTc` \ dflags -> case () of
689 | dopt Opt_AllowUndecidableInstances dflags
692 | Just (clas,tys) <- getClassTys_maybe pred,
697 -> addErrTc (instConstraintErr pred)
699 scrutiniseInstanceHead clas inst_taus
700 = getDOptsTc `thenTc` \ dflags -> case () of
703 -- A user declaration of a CCallable/CReturnable instance
704 -- must be for a "boxed primitive" type.
705 (clas `hasKey` cCallableClassKey
706 && not (ccallable_type dflags first_inst_tau))
708 (clas `hasKey` cReturnableClassKey
709 && not (creturnable_type first_inst_tau))
710 -> addErrTc (nonBoxedPrimCCallErr clas first_inst_tau)
713 -- It is obviously illegal to have an explicit instance
714 -- for something that we are also planning to `derive'
715 | maybeToBool alg_tycon_app_maybe && clas `elem` (tyConDerivings alg_tycon)
716 -> addErrTc (derivingWhenInstanceExistsErr clas first_inst_tau)
717 -- Kind check will have ensured inst_taus is of length 1
719 -- Allow anything for AllowUndecidableInstances
720 | dopt Opt_AllowUndecidableInstances dflags
723 -- If GlasgowExts then check at least one isn't a type variable
724 | dopt Opt_GlasgowExts dflags
725 -> if all isTyVarTy inst_taus
726 then addErrTc (instTypeErr clas inst_taus
727 (text "There must be at least one non-type-variable in the instance head"))
730 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
731 | not (length inst_taus == 1 &&
732 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
733 not (isSynTyCon tycon) && -- ...but not a synonym
734 all isTyVarTy arg_tys && -- Applied to type variables
735 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
736 -- This last condition checks that all the type variables are distinct
738 -> addErrTc (instTypeErr clas inst_taus
739 (text "the instance type must be of form (T a b c)" $$
740 text "where T is not a synonym, and a,b,c are distinct type variables")
747 (first_inst_tau : _) = inst_taus
749 -- Stuff for algebraic or -> type
750 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
751 Just (tycon, arg_tys) = maybe_tycon_app
753 -- Stuff for an *algebraic* data type
754 alg_tycon_app_maybe = splitAlgTyConApp_maybe first_inst_tau
755 -- The "Alg" part looks through synonyms
756 Just (alg_tycon, _, _) = alg_tycon_app_maybe
758 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
759 creturnable_type ty = isFFIResultTy ty
763 %************************************************************************
765 \subsection{Error messages}
767 %************************************************************************
770 tcAddDeclCtxt decl thing_inside
777 (ClassDecl _ name _ _ _ _ _ loc) -> (name, loc, "class")
778 (TySynonym name _ _ loc) -> (name, loc, "type synonym")
779 (TyData NewType _ name _ _ _ _ loc _ _) -> (name, loc, "newtype")
780 (TyData DataType _ name _ _ _ _ loc _ _) -> (name, loc, "data type")
782 ctxt = hsep [ptext SLIT("In the"), text thing,
783 ptext SLIT("declaration for"), quotes (ppr name)]
787 instConstraintErr pred
788 = hang (ptext SLIT("Illegal constraint") <+>
789 quotes (pprPred pred) <+>
790 ptext SLIT("in instance context"))
791 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
793 badGenericInstanceType binds
794 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
797 missingGenericInstances missing
798 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
802 dupGenericInsts inst_infos
803 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
804 nest 4 (vcat (map (ppr . simpleInstInfoTy) inst_infos)),
805 ptext SLIT("All the type patterns for a generic type constructor must be identical")
808 instTypeErr clas tys msg
809 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes (pprConstraint clas tys),
813 derivingWhenInstanceExistsErr clas tycon
814 = hang (hsep [ptext SLIT("Deriving class"),
816 ptext SLIT("type"), quotes (ppr tycon)])
817 4 (ptext SLIT("when an explicit instance exists"))
819 nonBoxedPrimCCallErr clas inst_ty
820 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
821 4 (hsep [ ptext SLIT("class"), ppr clas, ptext SLIT("type"),
824 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
825 superClassCtxt = ptext SLIT("When checking the superclasses of an instance declaration")