2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[TcInstDecls]{Typechecking instance declarations}
7 #include "HsVersions.h"
18 import HsSyn ( InstDecl(..), FixityDecl, Sig(..),
19 SpecInstSig(..), HsBinds(..), Bind(..),
20 MonoBinds(..), GRHSsAndBinds, Match,
21 InPat(..), OutPat(..), HsExpr(..), HsLit(..),
22 Stmt, Qual, ArithSeqInfo, Fake,
23 PolyType(..), MonoType )
24 import RnHsSyn ( RenamedHsBinds(..), RenamedMonoBinds(..),
25 RenamedInstDecl(..), RenamedFixityDecl(..),
26 RenamedSig(..), RenamedSpecInstSig(..),
27 RnName(..){-incl instance Outputable-}
29 import TcHsSyn ( TcIdOcc(..), TcHsBinds(..),
30 TcMonoBinds(..), TcExpr(..), tcIdType,
32 mkHsDictLam, mkHsDictApp )
36 import GenSpecEtc ( checkSigTyVars )
37 import Inst ( Inst, InstOrigin(..), InstanceMapper(..),
38 newDicts, newMethod, LIE(..), emptyLIE, plusLIE )
39 import TcBinds ( tcPragmaSigs )
40 import TcDeriv ( tcDeriving )
41 import TcEnv ( tcLookupClass, tcTyVarScope, newLocalId )
42 import TcGRHSs ( tcGRHSsAndBinds )
43 import TcInstUtil ( InstInfo(..), mkInstanceRelatedIds, buildInstanceEnvs )
44 import TcKind ( TcKind, unifyKind )
45 import TcMatches ( tcMatchesFun )
46 import TcMonoType ( tcContext, tcMonoTypeKind )
47 import TcSimplify ( tcSimplifyAndCheck, tcSimplifyThetas )
48 import TcType ( TcType(..), TcTyVar(..),
49 tcInstSigTyVars, tcInstType, tcInstTheta
51 import Unify ( unifyTauTy )
54 import Bag ( emptyBag, unitBag, unionBags, unionManyBags,
55 concatBag, foldBag, bagToList )
56 import CmdLineOpts ( opt_GlasgowExts, opt_CompilingPrelude,
57 opt_OmitDefaultInstanceMethods,
58 opt_SpecialiseOverloaded )
59 import Class ( GenClass, GenClassOp,
60 isCcallishClass, classBigSig,
61 classOps, classOpLocalType,
64 import Id ( GenId, idType, isDefaultMethodId_maybe )
65 import ListSetOps ( minusList )
66 import Maybes ( maybeToBool, expectJust )
67 import Name ( getLocalName, origName, nameOf )
68 import PrelVals ( nO_EXPLICIT_METHOD_ERROR_ID )
69 import PrelMods ( pRELUDE )
70 import PprType ( GenType, GenTyVar, GenClass, GenClassOp, TyCon,
75 import RnUtils ( RnEnv(..) )
76 import TyCon ( isSynTyCon, derivedFor )
77 import Type ( GenType(..), ThetaType(..), mkTyVarTys,
78 splitSigmaTy, splitAppTy, isTyVarTy, matchTy, mkSigmaTy,
79 getTyCon_maybe, maybeBoxedPrimType
81 import TyVar ( GenTyVar, mkTyVarSet )
82 import TysWiredIn ( stringTy )
83 import Unique ( Unique )
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 tcInstDecls1 :: Bag RenamedInstDecl
162 -> [RenamedSpecInstSig]
163 -> Module -- module name for deriving
164 -> RnEnv -- for renaming derivings
165 -> [RenamedFixityDecl] -- fixities for deriving
166 -> TcM s (Bag InstInfo,
170 tcInstDecls1 inst_decls specinst_sigs mod_name rn_env fixities
171 = -- Do the ordinary instance declarations
172 mapBagNF_Tc (tcInstDecl1 mod_name) inst_decls
173 `thenNF_Tc` \ inst_info_bags ->
175 decl_inst_info = concatBag inst_info_bags
177 -- Handle "derived" instances; note that we only do derivings
178 -- for things in this module; we ignore deriving decls from
179 -- interfaces! We pass fixities, because they may be used
180 -- in deriving Read and Show.
181 tcDeriving mod_name rn_env decl_inst_info fixities
182 `thenTc` \ (deriv_inst_info, deriv_binds, ddump_deriv) ->
185 inst_info = deriv_inst_info `unionBags` decl_inst_info
188 -- Handle specialise instance pragmas
189 tcSpecInstSigs inst_info specinst_sigs
190 `thenTc` \ spec_inst_info ->
193 spec_inst_info = emptyBag -- For now
195 full_inst_info = inst_info `unionBags` spec_inst_info
197 returnTc (full_inst_info, deriv_binds, ddump_deriv)
200 tcInstDecl1 :: FAST_STRING -> RenamedInstDecl -> NF_TcM s (Bag InstInfo)
204 poly_ty@(HsForAllTy tyvar_names context inst_ty)
206 from_here inst_mod uprags pragmas src_loc)
207 = -- Prime error recovery, set source location
208 recoverNF_Tc (returnNF_Tc emptyBag) $
209 tcAddSrcLoc src_loc $
212 tcLookupClass class_name `thenNF_Tc` \ (clas_kind, clas) ->
217 -- Typecheck the context and instance type
218 tcTyVarScope (map de_rn tyvar_names) (\ tyvars ->
219 tcContext context `thenTc` \ theta ->
220 tcMonoTypeKind inst_ty `thenTc` \ (tau_kind, tau) ->
221 unifyKind clas_kind tau_kind `thenTc_`
222 returnTc (tyvars, theta, tau)
223 ) `thenTc` \ (inst_tyvars, inst_theta, inst_tau) ->
225 -- Check for respectable instance type
226 scrutiniseInstanceType from_here clas inst_tau
227 `thenTc` \ (inst_tycon,arg_tys) ->
229 -- Deal with the case where we are deriving
230 -- and importing the same instance
231 if (not from_here && (clas `derivedFor` inst_tycon)
232 && all isTyVarTy arg_tys)
234 if not opt_CompilingPrelude && maybeToBool inst_mod &&
235 mod_name == expectJust "inst_mod" inst_mod
237 -- Imported instance came from this module;
238 -- discard and derive fresh instance
241 -- Imported instance declared in another module;
242 -- report duplicate instance error
243 failTc (derivingWhenInstanceImportedErr inst_mod clas inst_tycon)
246 -- Make the dfun id and constant-method ids
247 mkInstanceRelatedIds from_here inst_mod pragmas
248 clas inst_tyvars inst_tau inst_theta uprags
249 `thenTc` \ (dfun_id, dfun_theta, const_meth_ids) ->
251 returnTc (unitBag (InstInfo clas inst_tyvars inst_tau inst_theta
252 dfun_theta dfun_id const_meth_ids
253 binds from_here inst_mod src_loc uprags))
257 %************************************************************************
259 \subsection{Type-checking instance declarations, pass 2}
261 %************************************************************************
264 tcInstDecls2 :: Bag InstInfo
265 -> NF_TcM s (LIE s, TcHsBinds s)
267 tcInstDecls2 inst_decls
268 = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyBinds)) inst_decls
270 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
271 tc2 `thenNF_Tc` \ (lie2, binds2) ->
272 returnNF_Tc (lie1 `plusLIE` lie2,
273 binds1 `ThenBinds` binds2)
277 ======= New documentation starts here (Sept 92) ==============
279 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
280 the dictionary function for this instance declaration. For example
282 instance Foo a => Foo [a] where
286 might generate something like
288 dfun.Foo.List dFoo_a = let op1 x = ...
294 HOWEVER, if the instance decl has no context, then it returns a
295 bigger @HsBinds@ with declarations for each method. For example
297 instance Foo [a] where
303 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
304 const.Foo.op1.List a x = ...
305 const.Foo.op2.List a y = ...
307 This group may be mutually recursive, because (for example) there may
308 be no method supplied for op2 in which case we'll get
310 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
312 that is, the default method applied to the dictionary at this type.
314 What we actually produce in either case is:
316 AbsBinds [a] [dfun_theta_dicts]
317 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
318 { d = (sd1,sd2, ..., op1, op2, ...)
323 The "maybe" says that we only ask AbsBinds to make global constant methods
324 if the dfun_theta is empty.
327 For an instance declaration, say,
329 instance (C1 a, C2 b) => C (T a b) where
332 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
333 function whose type is
335 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
337 Notice that we pass it the superclass dictionaries at the instance type; this
338 is the ``Mark Jones optimisation''. The stuff before the "=>" here
339 is the @dfun_theta@ below.
341 First comes the easy case of a non-local instance decl.
344 tcInstDecl2 :: InstInfo
345 -> NF_TcM s (LIE s, TcHsBinds s)
347 tcInstDecl2 (InstInfo _ _ _ _ _ _ _ _ False{-import-} _ _ _)
348 = returnNF_Tc (emptyLIE, EmptyBinds)
350 tcInstDecl2 (InstInfo clas inst_tyvars inst_ty
351 inst_decl_theta dfun_theta
352 dfun_id const_meth_ids monobinds
353 True{-here-} inst_mod locn uprags)
354 = -- Prime error recovery
355 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyBinds)) $
358 -- Get the class signature
359 tcInstSigTyVars inst_tyvars `thenNF_Tc` \ (inst_tyvars', _, tenv) ->
362 super_classes, sc_sel_ids,
363 class_ops, op_sel_ids, defm_ids) = classBigSig clas
365 tcInstType tenv inst_ty `thenNF_Tc` \ inst_ty' ->
366 tcInstTheta tenv dfun_theta `thenNF_Tc` \ dfun_theta' ->
367 tcInstTheta tenv inst_decl_theta `thenNF_Tc` \ inst_decl_theta' ->
369 sc_theta' = super_classes `zip` (repeat inst_ty')
370 origin = InstanceDeclOrigin
371 mk_method sel_id = newMethodId sel_id inst_ty' origin locn
373 -- Create dictionary Ids from the specified instance contexts.
374 newDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
375 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
376 newDicts origin inst_decl_theta' `thenNF_Tc` \ (inst_decl_dicts, _) ->
377 newDicts origin [(clas,inst_ty')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
379 -- Create method variables
380 mapAndUnzipNF_Tc mk_method op_sel_ids `thenNF_Tc` \ (meth_insts_s, meth_ids) ->
382 -- Collect available Insts
384 avail_insts -- These insts are in scope; quite a few, eh?
385 = unionManyBags (this_dict : dfun_arg_dicts : meth_insts_s)
388 = if opt_OmitDefaultInstanceMethods then
389 makeInstanceDeclNoDefaultExpr origin meth_ids defm_ids inst_ty' clas inst_mod
391 makeInstanceDeclDefaultMethodExpr origin meth_ids defm_ids inst_ty' this_dict_id
393 processInstBinds clas mk_method_expr inst_tyvars' avail_insts meth_ids monobinds
394 `thenTc` \ (insts_needed, method_mbinds) ->
396 -- Create the dict and method binds
398 = VarMonoBind this_dict_id (Dictionary sc_dict_ids meth_ids)
400 dict_and_method_binds
401 = dict_bind `AndMonoBinds` method_mbinds
403 inst_tyvars_set' = mkTyVarSet inst_tyvars'
405 -- Check the overloading constraints of the methods and superclasses
406 tcAddErrCtxt (bindSigCtxt meth_ids) (
408 inst_tyvars_set' -- Local tyvars
410 (sc_dicts `unionBags` insts_needed) -- Need to get defns for all these
411 ) `thenTc` \ (const_lie, super_binds) ->
413 -- Check that we *could* construct the superclass dictionaries,
414 -- even though we are *actually* going to pass the superclass dicts in;
415 -- the check ensures that the caller will never have a problem building
417 tcAddErrCtxt superClassSigCtxt (
419 inst_tyvars_set' -- Local tyvars
420 inst_decl_dicts -- The instance dictionaries available
421 sc_dicts -- The superclass dicationaries reqd
423 -- Ignore the result; we're only doing
424 -- this to make sure it can be done.
426 -- Now process any SPECIALIZE pragmas for the methods
428 spec_sigs = [ s | s@(SpecSig _ _ _ _) <- uprags ]
430 tcPragmaSigs spec_sigs `thenTc` \ (_, spec_binds, spec_lie) ->
432 -- Complete the binding group, adding any spec_binds
437 ((this_dict_id, RealId dfun_id)
438 : (meth_ids `zip` (map RealId const_meth_ids)))
439 -- const_meth_ids will often be empty
441 (RecBind dict_and_method_binds)
447 returnTc (const_lie `plusLIE` spec_lie, inst_binds)
450 @mkMethodId@ manufactures an id for a local method.
451 It's rather turgid stuff, because there are two cases:
453 (a) For methods with no local polymorphism, we can make an Inst of the
454 class-op selector function and a corresp InstId;
455 which is good because then other methods which call
456 this one will do so directly.
458 (b) For methods with local polymorphism, we can't do this. For example,
461 op :: (Num b) => a -> b -> a
463 Here the type of the class-op-selector is
465 forall a b. (Foo a, Num b) => a -> b -> a
467 The locally defined method at (say) type Float will have type
469 forall b. (Num b) => Float -> b -> Float
471 and the one is not an instance of the other.
473 So for these we just make a local (non-Inst) id with a suitable type.
478 newMethodId sel_id inst_ty origin loc
479 = let (sel_tyvars,sel_theta,sel_tau) = splitSigmaTy (idType sel_id)
480 (_:meth_theta) = sel_theta -- The local theta is all except the
481 -- first element of the context
484 -- Ah! a selector for a class op with no local polymorphism
485 -- Build an Inst for this
486 [clas_tyvar] -> newMethod origin (RealId sel_id) [inst_ty]
488 -- Ho! a selector for a class op with local polymorphism.
489 -- Just make a suitably typed local id for this
490 (clas_tyvar:local_tyvars) ->
491 tcInstType [(clas_tyvar,inst_ty)]
492 (mkSigmaTy local_tyvars meth_theta sel_tau)
493 `thenNF_Tc` \ method_ty ->
494 newLocalId (getLocalName sel_id) method_ty `thenNF_Tc` \ meth_id ->
495 returnNF_Tc (emptyLIE, meth_id)
498 The next function makes a default method which calls the global default method, at
499 the appropriate instance type.
501 See the notes under default decls in TcClassDcl.lhs.
504 makeInstanceDeclDefaultMethodExpr
511 -> NF_TcM s (TcExpr s)
513 makeInstanceDeclDefaultMethodExpr origin meth_ids defm_ids inst_ty this_dict tag
514 = newDicts origin op_theta `thenNF_Tc` \ (op_lie,op_dicts) ->
516 -- def_op_id = /\ op_tyvars -> \ op_dicts ->
517 -- defm_id inst_ty op_tyvars this_dict op_dicts
519 mkHsTyLam op_tyvars (
520 mkHsDictLam op_dicts (
521 mkHsDictApp (mkHsTyApp (HsVar (RealId defm_id))
522 (inst_ty : mkTyVarTys op_tyvars))
523 (this_dict : op_dicts)
527 meth_id = meth_ids !! idx
528 defm_id = defm_ids !! idx
529 (op_tyvars, op_theta, op_tau) = splitSigmaTy (tcIdType meth_id)
531 makeInstanceDeclNoDefaultExpr
539 -> NF_TcM s (TcExpr s)
541 makeInstanceDeclNoDefaultExpr origin meth_ids defm_ids inst_ty clas inst_mod tag
542 = newDicts origin op_theta `thenNF_Tc` \ (op_lie, op_dicts) ->
544 -- Produce a warning if the default instance method
545 -- has been omitted when one exists in the class
546 warnTc (not err_defm_ok)
547 (omitDefaultMethodWarn clas_op clas_name inst_ty)
549 returnNF_Tc (mkHsTyLam op_tyvars (
550 mkHsDictLam op_dicts (
551 HsApp (mkHsTyApp (HsVar (RealId nO_EXPLICIT_METHOD_ERROR_ID)) [op_tau])
552 (HsLitOut (HsString (_PK_ error_msg)) stringTy))))
555 meth_id = meth_ids !! idx
556 clas_op = (classOps clas) !! idx
557 defm_id = defm_ids !! idx
558 (op_tyvars,op_theta,op_tau) = splitSigmaTy (tcIdType meth_id)
560 Just (_, _, err_defm_ok) = isDefaultMethodId_maybe defm_id
562 mod_str = case inst_mod of { Nothing -> pRELUDE; Just m -> m }
564 error_msg = _UNPK_ mod_str ++ "." ++ _UNPK_ clas_name ++ "."
565 ++ (ppShow 80 (ppr PprForUser inst_ty)) ++ "."
566 ++ (ppShow 80 (ppr PprForUser clas_op)) ++ "\""
568 clas_name = nameOf (origName clas)
572 %************************************************************************
574 \subsection{Processing each method}
576 %************************************************************************
578 @processInstBinds@ returns a @MonoBinds@ which binds
579 all the method ids (which are passed in). It is used
580 - both for instance decls,
581 - and to compile the default-method declarations in a class decl.
583 Any method ids which don't have a binding have a suitable default
584 binding created for them. The actual right-hand side used is
585 created using a function which is passed in, because the right thing to
586 do differs between instance and class decls.
591 -> (Int -> NF_TcM s (TcExpr s)) -- Function to make default method
592 -> [TcTyVar s] -- Tyvars for this instance decl
593 -> LIE s -- available Insts
594 -> [TcIdOcc s] -- Local method ids in tag order
595 -- (instance tyvars are free in their types)
597 -> TcM s (LIE s, -- These are required
600 processInstBinds clas mk_default_method_rhs inst_tyvars avail_insts method_ids monobinds
602 -- Process the explicitly-given method bindings
603 processInstBinds1 clas inst_tyvars avail_insts method_ids monobinds
604 `thenTc` \ (tags, insts_needed_in_methods, method_binds) ->
606 -- Find the methods not handled, and make default method bindings for them.
608 unmentioned_tags = [1.. length method_ids] `minusList` tags
610 mapNF_Tc mk_default_method unmentioned_tags
611 `thenNF_Tc` \ default_bind_list ->
613 returnTc (insts_needed_in_methods,
614 foldr AndMonoBinds method_binds default_bind_list)
616 -- From a tag construct us the passed-in function to construct
617 -- the binding for the default method
618 mk_default_method tag = mk_default_method_rhs tag `thenNF_Tc` \ rhs ->
619 returnNF_Tc (VarMonoBind (method_ids !! (tag-1)) rhs)
625 -> [TcTyVar s] -- Tyvars for this instance decl
626 -> LIE s -- available Insts
627 -> [TcIdOcc s] -- Local method ids in tag order (instance tyvars are free),
629 -> TcM s ([Int], -- Class-op tags accounted for
630 LIE s, -- These are required
633 processInstBinds1 clas inst_tyvars avail_insts method_ids EmptyMonoBinds
634 = returnTc ([], emptyLIE, EmptyMonoBinds)
636 processInstBinds1 clas inst_tyvars avail_insts method_ids (AndMonoBinds mb1 mb2)
637 = processInstBinds1 clas inst_tyvars avail_insts method_ids mb1
638 `thenTc` \ (op_tags1,dicts1,method_binds1) ->
639 processInstBinds1 clas inst_tyvars avail_insts method_ids mb2
640 `thenTc` \ (op_tags2,dicts2,method_binds2) ->
641 returnTc (op_tags1 ++ op_tags2,
642 dicts1 `unionBags` dicts2,
643 AndMonoBinds method_binds1 method_binds2)
647 processInstBinds1 clas inst_tyvars avail_insts method_ids mbind
649 -- Find what class op is being defined here. The complication is
650 -- that we could have a PatMonoBind or a FunMonoBind. If the
651 -- former, it should only bind a single variable, or else we're in
652 -- trouble (I'm not sure what the static semantics of methods
653 -- defined in a pattern binding with multiple patterns is!)
654 -- Renamer has reduced us to these two cases.
656 (op,locn) = case mbind of
657 FunMonoBind op _ _ locn -> (op, locn)
658 PatMonoBind (VarPatIn op) _ locn -> (op, locn)
660 occ = getLocalName op
661 origin = InstanceDeclOrigin
665 -- Make a method id for the method
667 tag = classOpTagByString clas occ
668 method_id = method_ids !! (tag-1)
670 method_ty = tcIdType method_id
671 (method_tyvars, method_theta, method_tau) = splitSigmaTy method_ty
673 newDicts origin method_theta `thenNF_Tc` \ (method_dicts,method_dict_ids) ->
675 case (method_tyvars, method_dict_ids) of
677 ([],[]) -> -- The simple case; no local polymorphism or overloading in the method
679 -- Type check the method itself
680 tcMethodBind method_id method_tau mbind `thenTc` \ (mbind', lieIop) ->
681 returnTc ([tag], lieIop, mbind')
683 other -> -- It's a locally-polymorphic and/or overloaded method; UGH!
685 -- Make a new id for (a) the local, non-overloaded method
686 -- and (b) the locally-overloaded method
687 -- The latter is needed just so we can return an AbsBinds wrapped
688 -- up inside a MonoBinds.
690 newLocalId occ method_tau `thenNF_Tc` \ local_id ->
691 newLocalId occ method_ty `thenNF_Tc` \ copy_id ->
693 inst_method_tyvars = inst_tyvars ++ method_tyvars
695 -- Typecheck the method
696 tcMethodBind local_id method_tau mbind `thenTc` \ (mbind', lieIop) ->
698 -- Check the overloading part of the signature.
699 -- Simplify everything fully, even though some
700 -- constraints could "really" be left to the next
701 -- level out. The case which forces this is
703 -- class Foo a where { op :: Bar a => a -> a }
705 -- Here we must simplify constraints on "a" to catch all
706 -- the Bar-ish things.
707 tcAddErrCtxt (methodSigCtxt op method_ty) (
709 (mkTyVarSet inst_method_tyvars)
710 (method_dicts `plusLIE` avail_insts)
712 ) `thenTc` \ (f_dicts, dict_binds) ->
716 VarMonoBind method_id
721 [(local_id, copy_id)]
728 tcMethodBind :: TcIdOcc s -> TcType s -> RenamedMonoBinds
729 -> TcM s (TcMonoBinds s, LIE s)
731 tcMethodBind meth_id meth_ty (FunMonoBind name inf matches locn)
732 = tcMatchesFun name meth_ty matches `thenTc` \ (rhs', lie) ->
733 returnTc (FunMonoBind meth_id inf rhs' locn, lie)
735 tcMethodBind meth_id meth_ty pbind@(PatMonoBind pat grhss_and_binds locn)
736 -- pat is sure to be a (VarPatIn op)
737 = tcAddErrCtxt (patMonoBindsCtxt pbind) $
738 tcGRHSsAndBinds grhss_and_binds `thenTc` \ (grhss_and_binds', lie, rhs_ty) ->
739 unifyTauTy meth_ty rhs_ty `thenTc_`
740 returnTc (PatMonoBind (VarPat meth_id) grhss_and_binds' locn, lie)
744 %************************************************************************
746 \subsection{Type-checking specialise instance pragmas}
748 %************************************************************************
752 tcSpecInstSigs :: E -> CE -> TCE
753 -> Bag InstInfo -- inst decls seen (declared and derived)
754 -> [RenamedSpecInstSig] -- specialise instance upragmas
755 -> TcM (Bag InstInfo) -- new, overlapped, inst decls
757 tcSpecInstSigs e ce tce inst_infos []
760 tcSpecInstSigs e ce tce inst_infos sigs
761 = buildInstanceEnvs inst_infos `thenTc` \ inst_mapper ->
762 tc_inst_spec_sigs inst_mapper sigs `thenNF_Tc` \ spec_inst_infos ->
763 returnTc spec_inst_infos
765 tc_inst_spec_sigs inst_mapper []
766 = returnNF_Tc emptyBag
767 tc_inst_spec_sigs inst_mapper (sig:sigs)
768 = tcSpecInstSig e ce tce inst_infos inst_mapper sig `thenNF_Tc` \ info_sig ->
769 tc_inst_spec_sigs inst_mapper sigs `thenNF_Tc` \ info_sigs ->
770 returnNF_Tc (info_sig `unionBags` info_sigs)
772 tcSpecInstSig :: E -> CE -> TCE
775 -> RenamedSpecInstSig
776 -> NF_TcM (Bag InstInfo)
778 tcSpecInstSig e ce tce inst_infos inst_mapper (SpecInstSig class_name ty src_loc)
779 = recoverTc emptyBag (
780 tcAddSrcLoc src_loc (
782 clas = lookupCE ce class_name -- Renamer ensures this can't fail
784 -- Make some new type variables, named as in the specialised instance type
785 ty_names = extractMonoTyNames ???is_tyvarish_name??? ty
786 (tmpl_e,inst_tmpls,inst_tmpl_tys) = mkTVE ty_names
788 babyTcMtoTcM (tcInstanceType ce tce tmpl_e True src_loc ty)
789 `thenTc` \ inst_ty ->
791 maybe_tycon = case maybeAppDataTyCon inst_ty of
792 Just (tc,_,_) -> Just tc
795 maybe_unspec_inst = lookup_unspec_inst clas maybe_tycon inst_infos
797 -- Check that we have a local instance declaration to specialise
798 checkMaybeTc maybe_unspec_inst
799 (specInstUnspecInstNotFoundErr clas inst_ty src_loc) `thenTc_`
801 -- Create tvs to substitute for tmpls while simplifying the context
802 copyTyVars inst_tmpls `thenNF_Tc` \ (tv_e, inst_tvs, inst_tv_tys) ->
804 Just (InstInfo _ unspec_tyvars unspec_inst_ty unspec_theta
805 _ _ _ binds True{-from here-} mod _ uprag) = maybe_unspec_inst
807 subst = case matchTy unspec_inst_ty inst_ty of
809 Nothing -> panic "tcSpecInstSig:matchTy"
811 subst_theta = instantiateThetaTy subst unspec_theta
812 subst_tv_theta = instantiateThetaTy tv_e subst_theta
814 mk_spec_origin clas ty
815 = InstanceSpecOrigin inst_mapper clas ty src_loc
817 tcSimplifyThetas mk_spec_origin subst_tv_theta
818 `thenTc` \ simpl_tv_theta ->
820 simpl_theta = [ (clas, tv_to_tmpl tv) | (clas, tv) <- simpl_tv_theta ]
822 tv_tmpl_map = inst_tv_tys `zipEqual` inst_tmpl_tys
823 tv_to_tmpl tv = assoc "tcSpecInstSig" tv_tmpl_map tv
825 mkInstanceRelatedIds e True{-from here-} mod NoInstancePragmas src_loc
826 clas inst_tmpls inst_ty simpl_theta uprag
827 `thenTc` \ (dfun_id, dfun_theta, const_meth_ids) ->
829 getSwitchCheckerTc `thenNF_Tc` \ sw_chkr ->
830 (if sw_chkr SpecialiseTrace then
831 pprTrace "Specialised Instance: "
832 (ppAboves [ppCat [if null simpl_theta then ppNil else ppr PprDebug simpl_theta,
833 if null simpl_theta then ppNil else ppStr "=>",
835 pprParendGenType PprDebug inst_ty],
836 ppCat [ppStr " derived from:",
837 if null unspec_theta then ppNil else ppr PprDebug unspec_theta,
838 if null unspec_theta then ppNil else ppStr "=>",
840 pprParendGenType PprDebug unspec_inst_ty]])
843 returnTc (unitBag (InstInfo clas inst_tmpls inst_ty simpl_theta
844 dfun_theta dfun_id const_meth_ids
845 binds True{-from here-} mod src_loc uprag))
849 lookup_unspec_inst clas maybe_tycon inst_infos
850 = case filter (match_info match_inst_ty) (bagToList inst_infos) of
852 (info:_) -> Just info
854 match_info match_ty (InstInfo inst_clas _ inst_ty _ _ _ _ _ from_here _ _ _)
855 = from_here && clas == inst_clas &&
856 match_ty inst_ty && is_plain_instance inst_ty
858 match_inst_ty = case maybe_tycon of
859 Just tycon -> match_tycon tycon
862 match_tycon tycon inst_ty = case (maybeAppDataTyCon inst_ty) of
863 Just (inst_tc,_,_) -> tycon == inst_tc
866 match_fun inst_ty = isFunType inst_ty
869 is_plain_instance inst_ty
870 = case (maybeAppDataTyCon inst_ty) of
871 Just (_,tys,_) -> all isTyVarTemplateTy tys
872 Nothing -> case maybeUnpackFunTy inst_ty of
873 Just (arg, res) -> isTyVarTemplateTy arg && isTyVarTemplateTy res
874 Nothing -> error "TcInstDecls:is_plain_instance"
879 Checking for a decent instance type
880 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
881 @scrutiniseInstanceType@ checks the type {\em and} its syntactic constraints:
882 it must normally look like: @instance Foo (Tycon a b c ...) ...@
884 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
885 flag is on, or (2)~the instance is imported (they must have been
886 compiled elsewhere). In these cases, we let them go through anyway.
888 We can also have instances for functions: @instance Foo (a -> b) ...@.
891 scrutiniseInstanceType from_here clas inst_tau
893 | not (maybeToBool inst_tycon_maybe) || isSynTyCon inst_tycon
894 = failTc (instTypeErr inst_tau)
896 -- IMPORTED INSTANCES ARE OK (but see tcInstDecl1)
898 = returnTc (inst_tycon,arg_tys)
901 | not (all isTyVarTy arg_tys ||
904 = failTc (instTypeErr inst_tau)
907 -- It is obviously illegal to have an explicit instance
908 -- for something that we are also planning to `derive'
909 -- Though we can have an explicit instance which is more
910 -- specific than the derived instance
911 | clas `derivedFor` inst_tycon
912 && all isTyVarTy arg_tys
913 = failTc (derivingWhenInstanceExistsErr clas inst_tycon)
916 -- A user declaration of a CCallable/CReturnable instance
917 -- must be for a "boxed primitive" type.
919 && not opt_CompilingPrelude -- which allows anything
920 && maybeToBool (maybeBoxedPrimType inst_tau)
921 = failTc (nonBoxedPrimCCallErr clas inst_tau)
924 = returnTc (inst_tycon,arg_tys)
927 (possible_tycon, arg_tys) = splitAppTy inst_tau
928 inst_tycon_maybe = getTyCon_maybe possible_tycon
929 inst_tycon = expectJust "tcInstDecls1:inst_tycon" inst_tycon_maybe
936 SynTy tc _ _ -> ppBesides [ppStr "The type synonym `", ppr sty tc, rest_of_msg]
937 TyVarTy tv -> ppBesides [ppStr "The type variable `", ppr sty tv, rest_of_msg]
938 other -> ppBesides [ppStr "The type `", ppr sty ty, rest_of_msg]
940 rest_of_msg = ppStr "' cannot be used as an instance type."
942 derivingWhenInstanceExistsErr clas tycon sty
943 = ppHang (ppBesides [ppStr "Deriving class `", ppr sty clas, ppStr "' type `", ppr sty tycon, ppStr "'"])
944 4 (ppStr "when an explicit instance exists")
946 derivingWhenInstanceImportedErr inst_mod clas tycon sty
947 = ppHang (ppBesides [ppStr "Deriving class `", ppr sty clas, ppStr "' type `", ppr sty tycon, ppStr "'"])
948 4 (ppBesides [ppStr "when an instance declared in module `", pp_mod, ppStr "' has been imported"])
950 pp_mod = case inst_mod of
951 Nothing -> ppPStr SLIT("the standard Prelude")
952 Just m -> ppBesides [ppStr "module `", ppPStr m, ppStr "'"]
954 nonBoxedPrimCCallErr clas inst_ty sty
955 = ppHang (ppStr "Instance isn't for a `boxed-primitive' type")
956 4 (ppBesides [ ppStr "class `", ppr sty clas, ppStr "' type `",
957 ppr sty inst_ty, ppStr "'"])
959 omitDefaultMethodWarn clas_op clas_name inst_ty sty
960 = ppCat [ppStr "Warning: Omitted default method for",
961 ppr sty clas_op, ppStr "in instance",
962 ppPStr clas_name, pprParendGenType sty inst_ty]
965 patMonoBindsCtxt pbind sty
966 = ppHang (ppStr "In a pattern binding:")
969 methodSigCtxt name ty sty
970 = ppHang (ppBesides [ppStr "When matching the definition of class method `",
971 ppr sty name, ppStr "' to its signature :" ])
974 bindSigCtxt method_ids sty
975 = ppHang (ppStr "When checking type signatures for: ")
976 4 (ppInterleave (ppStr ", ") (map (ppr sty) method_ids))
978 superClassSigCtxt sty
979 = ppStr "When checking superclass constraints on instance declaration"