2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[TcInstDecls]{Typechecking instance declarations}
12 #include "HsVersions.h"
14 import HsSyn ( HsDecl(..), InstDecl(..),
15 HsBinds(..), MonoBinds(..), GRHSsAndBinds(..), GRHS(..),
16 HsExpr(..), InPat(..), HsLit(..), Sig(..),
18 collectMonoBinders, andMonoBinds
20 import HsBinds ( sigsForMe )
21 import RnHsSyn ( RenamedHsBinds, RenamedMonoBinds,
22 RenamedInstDecl, RenamedHsExpr,
23 RenamedSig, RenamedHsDecl
25 import TcHsSyn ( TcMonoBinds, TcIdOcc(..), TcIdBndr,
26 maybeBoxedPrimType, tcIdType
29 import TcBinds ( tcPragmaSigs )
30 import TcClassDcl ( tcMethodBind, badMethodErr )
32 import RnMonad ( RnNameSupply )
33 import Inst ( Inst, InstOrigin(..),
34 newDicts, LIE, emptyLIE, plusLIE, plusLIEs )
35 import TcDeriv ( tcDeriving )
36 import TcEnv ( GlobalValueEnv, tcExtendGlobalValEnv, tcAddImportedIdInfo )
37 import TcInstUtil ( InstInfo(..), mkInstanceRelatedIds, classDataCon )
38 import TcKind ( TcKind, unifyKind )
39 import TcMonoType ( tcHsType )
40 import TcSimplify ( tcSimplifyAndCheck )
41 import TcType ( TcType, TcTyVar, TcTyVarSet,
42 zonkSigTyVar, tcInstSigTyVars, tcInstType, tcInstTheta
45 import Bag ( emptyBag, unitBag, unionBags, unionManyBags,
46 foldBag, bagToList, Bag
48 import CmdLineOpts ( opt_GlasgowExts )
49 import Class ( classBigSig, Class )
50 import Id ( isNullaryDataCon, dataConArgTys, replaceIdInfo, idName, Id )
51 import Maybes ( maybeToBool, seqMaybe, catMaybes )
52 import Name ( nameOccName, mkLocalName,
53 isLocallyDefined, Module,
56 import PrelVals ( eRROR_ID )
57 import PprType ( pprParendType, pprConstraint )
58 import SrcLoc ( SrcLoc, noSrcLoc )
59 import TyCon ( isSynTyCon, isDataTyCon, tyConDerivings )
60 import Type ( Type, ThetaType, isUnpointedType,
61 splitSigmaTy, isTyVarTy, mkSigmaTy,
62 splitTyConApp_maybe, splitDictTy_maybe,
63 splitAlgTyConApp_maybe, splitRhoTy,
66 import TyVar ( zipTyVarEnv, mkTyVarSet, tyVarSetToList, TyVar )
67 import TysPrim ( byteArrayPrimTyCon, mutableByteArrayPrimTyCon )
68 import TysWiredIn ( stringTy )
69 import Unique ( Unique, cCallableClassKey, cReturnableClassKey, Uniquable(..) )
73 Typechecking instance declarations is done in two passes. The first
74 pass, made by @tcInstDecls1@, collects information to be used in the
77 This pre-processed info includes the as-yet-unprocessed bindings
78 inside the instance declaration. These are type-checked in the second
79 pass, when the class-instance envs and GVE contain all the info from
80 all the instance and value decls. Indeed that's the reason we need
81 two passes over the instance decls.
84 Here is the overall algorithm.
85 Assume that we have an instance declaration
87 instance c => k (t tvs) where b
91 $LIE_c$ is the LIE for the context of class $c$
93 $betas_bar$ is the free variables in the class method type, excluding the
96 $LIE_cop$ is the LIE constraining a particular class method
98 $tau_cop$ is the tau type of a class method
100 $LIE_i$ is the LIE for the context of instance $i$
102 $X$ is the instance constructor tycon
104 $gammas_bar$ is the set of type variables of the instance
106 $LIE_iop$ is the LIE for a particular class method instance
108 $tau_iop$ is the tau type for this instance of a class method
110 $alpha$ is the class variable
112 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
114 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
117 ToDo: Update the list above with names actually in the code.
121 First, make the LIEs for the class and instance contexts, which means
122 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
123 and make LIElistI and LIEI.
125 Then process each method in turn.
127 order the instance methods according to the ordering of the class methods
129 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
131 Create final dictionary function from bindings generated already
133 df = lambda inst_tyvars
140 in <op1,op2,...,opn,sd1,...,sdm>
142 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
143 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
147 tcInstDecls1 :: GlobalValueEnv -- Contains IdInfo for dfun ids
149 -> Module -- module name for deriving
150 -> RnNameSupply -- for renaming derivings
151 -> TcM s (Bag InstInfo,
155 tcInstDecls1 unf_env decls mod_name rn_name_supply
156 = -- Do the ordinary instance declarations
157 mapNF_Tc (tcInstDecl1 unf_env mod_name)
158 [inst_decl | InstD inst_decl <- decls] `thenNF_Tc` \ inst_info_bags ->
160 decl_inst_info = unionManyBags inst_info_bags
162 -- Handle "derived" instances; note that we only do derivings
163 -- for things in this module; we ignore deriving decls from
165 tcDeriving mod_name rn_name_supply decl_inst_info
166 `thenTc` \ (deriv_inst_info, deriv_binds, ddump_deriv) ->
169 full_inst_info = deriv_inst_info `unionBags` decl_inst_info
171 returnTc (full_inst_info, deriv_binds, ddump_deriv)
174 tcInstDecl1 :: GlobalValueEnv -> Module -> RenamedInstDecl -> NF_TcM s (Bag InstInfo)
176 tcInstDecl1 unf_env mod_name (InstDecl poly_ty binds uprags (Just dfun_name) src_loc)
177 = -- Prime error recovery, set source location
178 recoverNF_Tc (returnNF_Tc emptyBag) $
179 tcAddSrcLoc src_loc $
181 -- Type-check all the stuff before the "where"
182 tcHsType poly_ty `thenTc` \ poly_ty' ->
184 (tyvars, theta, dict_ty) = splitSigmaTy poly_ty'
185 (clas, inst_tys) = case splitDictTy_maybe dict_ty of
186 Nothing -> pprPanic "tcInstDecl1" (ppr poly_ty)
190 -- Check for respectable instance type
191 scrutiniseInstanceType clas inst_tys `thenTc_`
193 -- Make the dfun id and constant-method ids
195 (dfun_id, dfun_theta) = mkInstanceRelatedIds dfun_name
196 clas tyvars inst_tys theta
197 -- Add info from interface file
198 final_dfun_id = tcAddImportedIdInfo unf_env dfun_id
200 returnTc (unitBag (InstInfo clas tyvars inst_tys theta
201 dfun_theta final_dfun_id
202 binds src_loc uprags))
206 %************************************************************************
208 \subsection{Type-checking instance declarations, pass 2}
210 %************************************************************************
213 tcInstDecls2 :: Bag InstInfo
214 -> NF_TcM s (LIE s, TcMonoBinds s)
216 tcInstDecls2 inst_decls
217 = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
219 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
220 tc2 `thenNF_Tc` \ (lie2, binds2) ->
221 returnNF_Tc (lie1 `plusLIE` lie2,
222 binds1 `AndMonoBinds` binds2)
226 ======= New documentation starts here (Sept 92) ==============
228 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
229 the dictionary function for this instance declaration. For example
231 instance Foo a => Foo [a] where
235 might generate something like
237 dfun.Foo.List dFoo_a = let op1 x = ...
243 HOWEVER, if the instance decl has no context, then it returns a
244 bigger @HsBinds@ with declarations for each method. For example
246 instance Foo [a] where
252 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
253 const.Foo.op1.List a x = ...
254 const.Foo.op2.List a y = ...
256 This group may be mutually recursive, because (for example) there may
257 be no method supplied for op2 in which case we'll get
259 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
261 that is, the default method applied to the dictionary at this type.
263 What we actually produce in either case is:
265 AbsBinds [a] [dfun_theta_dicts]
266 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
267 { d = (sd1,sd2, ..., op1, op2, ...)
272 The "maybe" says that we only ask AbsBinds to make global constant methods
273 if the dfun_theta is empty.
276 For an instance declaration, say,
278 instance (C1 a, C2 b) => C (T a b) where
281 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
282 function whose type is
284 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
286 Notice that we pass it the superclass dictionaries at the instance type; this
287 is the ``Mark Jones optimisation''. The stuff before the "=>" here
288 is the @dfun_theta@ below.
290 First comes the easy case of a non-local instance decl.
293 tcInstDecl2 :: InstInfo -> NF_TcM s (LIE s, TcMonoBinds s)
295 tcInstDecl2 (InstInfo clas inst_tyvars inst_tys
296 inst_decl_theta dfun_theta
299 | not (isLocallyDefined dfun_id)
300 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
303 -- I deleted this "optimisation" because when importing these
304 -- instance decls the renamer would look for the dfun bindings and they weren't there.
305 -- This would be fixable, but it seems simpler just to produce a tiny void binding instead,
306 -- even though it's never used.
308 -- This case deals with CCallable etc, which don't need any bindings
310 = returnNF_Tc (emptyLIE, EmptyBinds)
314 = -- Prime error recovery
315 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
318 -- Get the class signature
320 origin = InstanceDeclOrigin
322 sc_theta, sc_sel_ids,
323 op_sel_ids, defm_ids) = classBigSig clas
326 -- Instantiate the instance decl with tc-style type variables
327 tcInstSigTyVars inst_tyvars `thenNF_Tc` \ (inst_tyvars', _, tenv) ->
328 mapNF_Tc (tcInstType tenv) inst_tys `thenNF_Tc` \ inst_tys' ->
329 tcInstTheta tenv dfun_theta `thenNF_Tc` \ dfun_theta' ->
330 tcInstTheta tenv inst_decl_theta `thenNF_Tc` \ inst_decl_theta' ->
332 -- Instantiate the super-class context with inst_tys
333 tcInstTheta (zipTyVarEnv class_tyvars inst_tys') sc_theta `thenNF_Tc` \ sc_theta' ->
335 -- Create dictionary Ids from the specified instance contexts.
336 newDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
337 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
338 newDicts origin inst_decl_theta' `thenNF_Tc` \ (inst_decl_dicts, _) ->
339 newDicts origin [(clas,inst_tys')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
341 -- Check that all the method bindings come from this class
343 check_from_this_class (bndr, loc)
344 | nameOccName bndr `elem` sel_names = returnNF_Tc ()
345 | otherwise = tcAddSrcLoc loc $
346 addErrTc (badMethodErr bndr clas)
347 sel_names = map getOccName op_sel_ids
348 bndrs = bagToList (collectMonoBinders monobinds)
350 mapNF_Tc check_from_this_class bndrs `thenNF_Tc_`
352 tcExtendGlobalValEnv (catMaybes defm_ids) (
354 -- Default-method Ids may be mentioned in synthesised RHSs
355 mapAndUnzip3Tc (tcMethodBind clas origin inst_tys' inst_tyvars' monobinds uprags True)
356 (op_sel_ids `zip` defm_ids)
357 ) `thenTc` \ (method_binds_s, insts_needed_s, meth_lies_w_ids) ->
359 -- Deal with SPECIALISE instance pragmas
361 dfun_prags = [Sig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
363 tcExtendGlobalValEnv [dfun_id] (
364 tcPragmaSigs dfun_prags
365 ) `thenTc` \ (prag_info_fn, prag_binds, prag_lie) ->
367 -- Check the overloading constraints of the methods and superclasses
368 mapNF_Tc zonkSigTyVar inst_tyvars' `thenNF_Tc` \ zonked_inst_tyvars ->
371 inst_tyvars_set = mkTyVarSet zonked_inst_tyvars
373 (meth_lies, meth_ids) = unzip meth_lies_w_ids
375 -- These insts are in scope; quite a few, eh?
376 avail_insts = this_dict `plusLIE`
377 dfun_arg_dicts `plusLIE`
379 unionManyBags meth_lies
381 methods_lie = plusLIEs insts_needed_s
384 -- Ditto method bindings
385 tcAddErrCtxt methodCtxt (
387 (ptext SLIT("instance declaration context"))
388 inst_tyvars_set -- Local tyvars
391 ) `thenTc` \ (const_lie1, lie_binds1) ->
393 -- Check that we *could* construct the superclass dictionaries,
394 -- even though we are *actually* going to pass the superclass dicts in;
395 -- the check ensures that the caller will never have
396 --a problem building them.
397 tcAddErrCtxt superClassCtxt (
399 (ptext SLIT("instance declaration context"))
400 inst_tyvars_set -- Local tyvars
401 inst_decl_dicts -- The instance dictionaries available
402 sc_dicts -- The superclass dicationaries reqd
404 -- Ignore the result; we're only doing
405 -- this to make sure it can be done.
407 -- Now do the simplification again, this time to get the
408 -- bindings; this time we use an enhanced "avails"
409 -- Ignore errors because they come from the *previous* tcSimplify
412 (ptext SLIT("instance declaration context"))
414 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
415 -- get bound by just selecting from this_dict!!
417 ) `thenTc` \ (const_lie2, lie_binds2) ->
420 -- Create the result bindings
422 dict_constr = classDataCon clas
423 scs_and_meths = sc_dict_ids ++ meth_ids
427 = -- Blatant special case for CCallable, CReturnable
428 -- If the dictionary is empty then we should never
429 -- select anything from it, so we make its RHS just
430 -- emit an error message. This in turn means that we don't
431 -- mention the constructor, which doesn't exist for CCallable, CReturnable
432 -- Hardly beautiful, but only three extra lines.
433 HsApp (TyApp (HsVar (RealId eRROR_ID)) [tcIdType this_dict_id])
434 (HsLitOut (HsString msg) stringTy)
436 | otherwise -- The common case
437 = HsCon dict_constr inst_tys' (map HsVar (sc_dict_ids ++ meth_ids))
438 -- We don't produce a binding for the dict_constr; instead we
439 -- just generate the saturated constructor directly
441 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
443 dict_bind = VarMonoBind this_dict_id dict_rhs
444 method_binds = andMonoBinds method_binds_s
446 final_dfun_id = replaceIdInfo dfun_id (prag_info_fn (idName dfun_id))
452 [(inst_tyvars', RealId final_dfun_id, this_dict_id)]
453 (lie_binds1 `AndMonoBinds`
454 lie_binds2 `AndMonoBinds`
455 method_binds `AndMonoBinds`
458 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
459 main_bind `AndMonoBinds` prag_binds)
463 %************************************************************************
465 \subsection{Checking for a decent instance type}
467 %************************************************************************
469 @scrutiniseInstanceType@ checks the type {\em and} its syntactic constraints:
470 it must normally look like: @instance Foo (Tycon a b c ...) ...@
472 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
473 flag is on, or (2)~the instance is imported (they must have been
474 compiled elsewhere). In these cases, we let them go through anyway.
476 We can also have instances for functions: @instance Foo (a -> b) ...@.
479 scrutiniseInstanceType clas inst_taus
480 | -- CCALL CHECK (a).... urgh!
481 -- To verify that a user declaration of a CCallable/CReturnable
482 -- instance is OK, we must be able to see the constructor(s)
483 -- of the instance type (see next guard.)
485 -- We flag this separately to give a more precise error msg.
487 (uniqueOf clas == cCallableClassKey || uniqueOf clas == cReturnableClassKey)
488 && is_alg_tycon_app && not constructors_visible
489 = failWithTc (invisibleDataConPrimCCallErr clas first_inst_tau)
492 -- A user declaration of a CCallable/CReturnable instance
493 -- must be for a "boxed primitive" type.
494 (uniqueOf clas == cCallableClassKey && not (ccallable_type first_inst_tau)) ||
495 (uniqueOf clas == cReturnableClassKey && not (creturnable_type first_inst_tau))
496 = failWithTc (nonBoxedPrimCCallErr clas first_inst_tau)
499 -- It is obviously illegal to have an explicit instance
500 -- for something that we are also planning to `derive'
501 | maybeToBool alg_tycon_app_maybe && clas `elem` (tyConDerivings alg_tycon)
502 = failWithTc (derivingWhenInstanceExistsErr clas first_inst_tau)
503 -- Kind check will have ensured inst_taus is of length 1
505 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
506 | not opt_GlasgowExts
507 && not (length inst_taus == 1 &&
508 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
509 not (isSynTyCon tycon) && -- ...but not a synonym
510 all isTyVarTy arg_tys && -- Applied to type variables
511 length (tyVarSetToList (tyVarsOfTypes arg_tys)) == length arg_tys
512 -- This last condition checks that all the type variables are distinct
514 = failWithTc (instTypeErr clas inst_taus
515 (text "the instance type must be of form (T a b c)" $$
516 text "where T is not a synonym, and a,b,c are distinct type variables")
523 (first_inst_tau : _) = inst_taus
525 -- Stuff for algebraic or -> type
526 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
527 Just (tycon, arg_tys) = maybe_tycon_app
529 -- Stuff for an *algebraic* data type
530 alg_tycon_app_maybe = splitAlgTyConApp_maybe first_inst_tau
531 -- The "Alg" part looks through synonyms
532 is_alg_tycon_app = maybeToBool alg_tycon_app_maybe
533 Just (alg_tycon, _, data_cons) = alg_tycon_app_maybe
535 constructors_visible = not (null data_cons)
538 -- These conditions come directly from what the DsCCall is capable of.
539 -- Totally grotesque. Green card should solve this.
541 ccallable_type ty = isUnpointedType ty || -- Allow CCallable Int# etc
542 maybeToBool (maybeBoxedPrimType ty) || -- Ditto Int etc
546 byte_arr_thing = case splitAlgTyConApp_maybe ty of
547 Just (tycon, ty_args, [data_con]) | isDataTyCon tycon ->
548 length data_con_arg_tys == 2 &&
549 maybeToBool maybe_arg2_tycon &&
550 (arg2_tycon == byteArrayPrimTyCon ||
551 arg2_tycon == mutableByteArrayPrimTyCon)
553 data_con_arg_tys = dataConArgTys data_con ty_args
554 (data_con_arg_ty1 : data_con_arg_ty2 : _) = data_con_arg_tys
555 maybe_arg2_tycon = splitTyConApp_maybe data_con_arg_ty2
556 Just (arg2_tycon,_) = maybe_arg2_tycon
560 creturnable_type ty = maybeToBool (maybeBoxedPrimType ty) ||
561 -- Or, a data type with a single nullary constructor
562 case (splitAlgTyConApp_maybe ty) of
563 Just (tycon, tys_applied, [data_con])
564 -> isNullaryDataCon data_con
570 instTypeErr clas tys msg
571 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes (pprConstraint clas tys),
575 derivingWhenInstanceExistsErr clas tycon
576 = hang (hsep [ptext SLIT("Deriving class"),
578 ptext SLIT("type"), quotes (ppr tycon)])
579 4 (ptext SLIT("when an explicit instance exists"))
581 nonBoxedPrimCCallErr clas inst_ty
582 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
583 4 (hsep [ ptext SLIT("class"), ppr clas, ptext SLIT("type"),
587 Declaring CCallable & CReturnable instances in a module different
588 from where the type was defined. Caused by importing data type
589 abstractly (either programmatically or by the renamer being over-eager
592 invisibleDataConPrimCCallErr clas inst_ty
593 = hang (hsep [ptext SLIT("Constructors for"), quotes (ppr inst_ty),
594 ptext SLIT("not visible when checking"),
595 quotes (ppr clas), ptext SLIT("instance")])
596 4 (hsep [text "(Try either importing", ppr inst_ty,
597 text "non-abstractly or compile using -fno-prune-tydecls ..)"])
599 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
600 superClassCtxt = ptext SLIT("When checking the superclasses of an instance declaration")