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 import TcHsSyn ( TcIdOcc(..), TcHsBinds(..),
28 TcMonoBinds(..), TcExpr(..), tcIdType,
30 mkHsDictLam, mkHsDictApp )
34 import GenSpecEtc ( checkSigTyVars )
35 import Inst ( Inst, InstOrigin(..), InstanceMapper(..),
36 newDicts, newMethod, LIE(..), emptyLIE, plusLIE )
37 import TcBinds ( tcPragmaSigs )
38 import TcDeriv ( tcDeriving )
39 import TcEnv ( tcLookupClass, tcTyVarScope, newLocalId )
40 import TcGRHSs ( tcGRHSsAndBinds )
41 import TcInstUtil ( InstInfo(..), mkInstanceRelatedIds, buildInstanceEnvs )
42 import TcKind ( TcKind, unifyKind )
43 import TcMatches ( tcMatchesFun )
44 import TcMonoType ( tcContext, tcMonoTypeKind )
45 import TcSimplify ( tcSimplifyAndCheck, tcSimplifyThetas )
46 import TcType ( TcType(..), TcTyVar(..),
47 tcInstSigTyVars, tcInstType, tcInstTheta
49 import Unify ( unifyTauTy )
52 import Bag ( emptyBag, unitBag, unionBags, unionManyBags,
53 concatBag, foldBag, bagToList )
54 import CmdLineOpts ( opt_GlasgowExts, opt_CompilingPrelude,
55 opt_OmitDefaultInstanceMethods,
56 opt_SpecialiseOverloaded )
57 import Class ( GenClass, GenClassOp,
58 isCcallishClass, getClassBigSig,
59 getClassOps, getClassOpLocalType )
60 import CoreUtils ( escErrorMsg )
61 import Id ( GenId, idType, isDefaultMethodId_maybe )
62 import ListSetOps ( minusList )
63 import Maybes ( maybeToBool, expectJust )
64 import Name ( Name, getTagFromClassOpName )
66 import PrelInfo ( pAT_ERROR_ID )
67 import PprType ( GenType, GenTyVar, GenClass, GenClassOp, TyCon,
71 import RnUtils ( GlobalNameMappers(..), GlobalNameMapper(..) )
72 import TyCon ( derivedFor )
73 import Type ( GenType(..), ThetaType(..), mkTyVarTys,
74 splitSigmaTy, splitAppTy, isTyVarTy, matchTy, mkSigmaTy,
75 getTyCon_maybe, maybeBoxedPrimType )
76 import TyVar ( GenTyVar, mkTyVarSet )
77 import TysWiredIn ( stringTy )
78 import Unique ( Unique )
83 Typechecking instance declarations is done in two passes. The first
84 pass, made by @tcInstDecls1@, collects information to be used in the
87 This pre-processed info includes the as-yet-unprocessed bindings
88 inside the instance declaration. These are type-checked in the second
89 pass, when the class-instance envs and GVE contain all the info from
90 all the instance and value decls. Indeed that's the reason we need
91 two passes over the instance decls.
94 Here is the overall algorithm.
95 Assume that we have an instance declaration
97 instance c => k (t tvs) where b
101 $LIE_c$ is the LIE for the context of class $c$
103 $betas_bar$ is the free variables in the class method type, excluding the
106 $LIE_cop$ is the LIE constraining a particular class method
108 $tau_cop$ is the tau type of a class method
110 $LIE_i$ is the LIE for the context of instance $i$
112 $X$ is the instance constructor tycon
114 $gammas_bar$ is the set of type variables of the instance
116 $LIE_iop$ is the LIE for a particular class method instance
118 $tau_iop$ is the tau type for this instance of a class method
120 $alpha$ is the class variable
122 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
124 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
127 ToDo: Update the list above with names actually in the code.
131 First, make the LIEs for the class and instance contexts, which means
132 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
133 and make LIElistI and LIEI.
135 Then process each method in turn.
137 order the instance methods according to the ordering of the class methods
139 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
141 Create final dictionary function from bindings generated already
143 df = lambda inst_tyvars
150 in <op1,op2,...,opn,sd1,...,sdm>
152 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
153 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
157 tcInstDecls1 :: Bag RenamedInstDecl
158 -> [RenamedSpecInstSig]
159 -> FAST_STRING -- module name for deriving
160 -> GlobalNameMappers -- renamer fns for deriving
161 -> [RenamedFixityDecl] -- fixities for deriving
162 -> TcM s (Bag InstInfo,
166 tcInstDecls1 inst_decls specinst_sigs mod_name renamer_name_funs fixities
167 = -- Do the ordinary instance declarations
168 mapBagNF_Tc (tcInstDecl1 mod_name) inst_decls
169 `thenNF_Tc` \ inst_info_bags ->
171 decl_inst_info = concatBag inst_info_bags
173 -- Handle "derived" instances; note that we only do derivings
174 -- for things in this module; we ignore deriving decls from
175 -- interfaces! We pass fixities, because they may be used
176 -- in deriving Read and Show.
177 tcDeriving mod_name renamer_name_funs decl_inst_info fixities
178 `thenTc` \ (deriv_inst_info, deriv_binds, ddump_deriv) ->
181 inst_info = deriv_inst_info `unionBags` decl_inst_info
184 -- Handle specialise instance pragmas
185 tcSpecInstSigs inst_info specinst_sigs
186 `thenTc` \ spec_inst_info ->
189 spec_inst_info = emptyBag -- For now
191 full_inst_info = inst_info `unionBags` spec_inst_info
193 returnTc (full_inst_info, deriv_binds, ddump_deriv)
196 tcInstDecl1 :: FAST_STRING -> RenamedInstDecl -> NF_TcM s (Bag InstInfo)
200 poly_ty@(HsForAllTy tyvar_names context inst_ty)
202 from_here inst_mod uprags pragmas src_loc)
203 = -- Prime error recovery, set source location
204 recoverNF_Tc (returnNF_Tc emptyBag) $
205 tcAddSrcLoc src_loc $
208 tcLookupClass class_name `thenNF_Tc` \ (clas_kind, clas) ->
210 -- Typecheck the context and instance type
211 tcTyVarScope tyvar_names (\ tyvars ->
212 tcContext context `thenTc` \ theta ->
213 tcMonoTypeKind inst_ty `thenTc` \ (tau_kind, tau) ->
214 unifyKind clas_kind tau_kind `thenTc_`
215 returnTc (tyvars, theta, tau)
216 ) `thenTc` \ (inst_tyvars, inst_theta, inst_tau) ->
218 -- Check for respectable instance type
219 scrutiniseInstanceType from_here clas inst_tau
220 `thenTc` \ (inst_tycon,arg_tys) ->
222 -- Deal with the case where we are deriving
223 -- and importing the same instance
224 if (not from_here && (clas `derivedFor` inst_tycon)
225 && all isTyVarTy arg_tys)
227 if mod_name == inst_mod then
228 -- Imported instance came from this module;
229 -- discard and derive fresh instance
232 -- Imported instance declared in another module;
233 -- report duplicate instance error
234 failTc (derivingWhenInstanceImportedErr inst_mod clas inst_tycon)
237 -- Make the dfun id and constant-method ids
238 mkInstanceRelatedIds from_here inst_mod pragmas
239 clas inst_tyvars inst_tau inst_theta uprags
240 `thenTc` \ (dfun_id, dfun_theta, const_meth_ids) ->
242 returnTc (unitBag (InstInfo clas inst_tyvars inst_tau inst_theta
243 dfun_theta dfun_id const_meth_ids
244 binds from_here inst_mod src_loc uprags))
248 %************************************************************************
250 \subsection{Type-checking instance declarations, pass 2}
252 %************************************************************************
255 tcInstDecls2 :: Bag InstInfo
256 -> NF_TcM s (LIE s, TcHsBinds s)
258 tcInstDecls2 inst_decls
259 = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyBinds)) inst_decls
261 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
262 tc2 `thenNF_Tc` \ (lie2, binds2) ->
263 returnNF_Tc (lie1 `plusLIE` lie2,
264 binds1 `ThenBinds` binds2)
268 ======= New documentation starts here (Sept 92) ==============
270 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
271 the dictionary function for this instance declaration. For example
273 instance Foo a => Foo [a] where
277 might generate something like
279 dfun.Foo.List dFoo_a = let op1 x = ...
285 HOWEVER, if the instance decl has no context, then it returns a
286 bigger @HsBinds@ with declarations for each method. For example
288 instance Foo [a] where
294 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
295 const.Foo.op1.List a x = ...
296 const.Foo.op2.List a y = ...
298 This group may be mutually recursive, because (for example) there may
299 be no method supplied for op2 in which case we'll get
301 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
303 that is, the default method applied to the dictionary at this type.
305 What we actually produce in either case is:
307 AbsBinds [a] [dfun_theta_dicts]
308 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
309 { d = (sd1,sd2, ..., op1, op2, ...)
314 The "maybe" says that we only ask AbsBinds to make global constant methods
315 if the dfun_theta is empty.
318 For an instance declaration, say,
320 instance (C1 a, C2 b) => C (T a b) where
323 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
324 function whose type is
326 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
328 Notice that we pass it the superclass dictionaries at the instance type; this
329 is the ``Mark Jones optimisation''. The stuff before the "=>" here
330 is the @dfun_theta@ below.
332 First comes the easy case of a non-local instance decl.
335 tcInstDecl2 :: InstInfo
336 -> NF_TcM s (LIE s, TcHsBinds s)
338 tcInstDecl2 (InstInfo _ _ _ _ _ _ _ _ False{-import-} _ _ _)
339 = returnNF_Tc (emptyLIE, EmptyBinds)
341 tcInstDecl2 (InstInfo clas inst_tyvars inst_ty
342 inst_decl_theta dfun_theta
343 dfun_id const_meth_ids monobinds
344 True{-here-} inst_mod locn uprags)
345 = -- Prime error recovery
346 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyBinds)) $
349 -- Get the class signature
350 tcInstSigTyVars inst_tyvars `thenNF_Tc` \ (inst_tyvars', _, tenv) ->
353 super_classes, sc_sel_ids,
354 class_ops, op_sel_ids, defm_ids) = getClassBigSig clas
356 tcInstType tenv inst_ty `thenNF_Tc` \ inst_ty' ->
357 tcInstTheta tenv dfun_theta `thenNF_Tc` \ dfun_theta' ->
358 tcInstTheta tenv inst_decl_theta `thenNF_Tc` \ inst_decl_theta' ->
360 sc_theta' = super_classes `zip` (repeat inst_ty')
361 origin = InstanceDeclOrigin
362 mk_method sel_id = newMethodId sel_id inst_ty' origin locn
364 -- Create dictionary Ids from the specified instance contexts.
365 newDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
366 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
367 newDicts origin inst_decl_theta' `thenNF_Tc` \ (inst_decl_dicts, _) ->
368 newDicts origin [(clas,inst_ty')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
370 -- Create method variables
371 mapAndUnzipNF_Tc mk_method op_sel_ids `thenNF_Tc` \ (meth_insts_s, meth_ids) ->
373 -- Collect available Insts
375 avail_insts -- These insts are in scope; quite a few, eh?
376 = unionManyBags (this_dict : dfun_arg_dicts : meth_insts_s)
379 = if opt_OmitDefaultInstanceMethods then
380 makeInstanceDeclNoDefaultExpr origin meth_ids defm_ids inst_ty' clas inst_mod
382 makeInstanceDeclDefaultMethodExpr origin meth_ids defm_ids inst_ty' this_dict_id
384 processInstBinds mk_method_expr inst_tyvars' avail_insts meth_ids monobinds
385 `thenTc` \ (insts_needed, method_mbinds) ->
387 -- Create the dict and method binds
389 = VarMonoBind this_dict_id (Dictionary sc_dict_ids meth_ids)
391 dict_and_method_binds
392 = dict_bind `AndMonoBinds` method_mbinds
394 inst_tyvars_set' = mkTyVarSet inst_tyvars'
396 -- Check the overloading constraints of the methods and superclasses
397 tcAddErrCtxt (bindSigCtxt meth_ids) (
399 inst_tyvars_set' -- Local tyvars
401 (sc_dicts `unionBags` insts_needed) -- Need to get defns for all these
402 ) `thenTc` \ (const_lie, super_binds) ->
404 -- Check that we *could* construct the superclass dictionaries,
405 -- even though we are *actually* going to pass the superclass dicts in;
406 -- the check ensures that the caller will never have a problem building
408 tcAddErrCtxt superClassSigCtxt (
410 inst_tyvars_set' -- Local tyvars
411 inst_decl_dicts -- The instance dictionaries available
412 sc_dicts -- The superclass dicationaries reqd
414 -- Ignore the result; we're only doing
415 -- this to make sure it can be done.
417 -- Now process any SPECIALIZE pragmas for the methods
419 spec_sigs = [ s | s@(SpecSig _ _ _ _) <- uprags ]
421 tcPragmaSigs spec_sigs `thenTc` \ (_, spec_binds, spec_lie) ->
423 -- Complete the binding group, adding any spec_binds
428 ((this_dict_id, RealId dfun_id)
429 : (meth_ids `zip` (map RealId const_meth_ids)))
430 -- const_meth_ids will often be empty
432 (RecBind dict_and_method_binds)
438 returnTc (const_lie `plusLIE` spec_lie, inst_binds)
441 @mkMethodId@ manufactures an id for a local method.
442 It's rather turgid stuff, because there are two cases:
444 (a) For methods with no local polymorphism, we can make an Inst of the
445 class-op selector function and a corresp InstId;
446 which is good because then other methods which call
447 this one will do so directly.
449 (b) For methods with local polymorphism, we can't do this. For example,
452 op :: (Num b) => a -> b -> a
454 Here the type of the class-op-selector is
456 forall a b. (Foo a, Num b) => a -> b -> a
458 The locally defined method at (say) type Float will have type
460 forall b. (Num b) => Float -> b -> Float
462 and the one is not an instance of the other.
464 So for these we just make a local (non-Inst) id with a suitable type.
469 newMethodId sel_id inst_ty origin loc
470 = let (sel_tyvars,sel_theta,sel_tau) = splitSigmaTy (idType sel_id)
471 (_:meth_theta) = sel_theta -- The local theta is all except the
472 -- first element of the context
475 -- Ah! a selector for a class op with no local polymorphism
476 -- Build an Inst for this
477 [clas_tyvar] -> newMethod origin (RealId sel_id) [inst_ty]
479 -- Ho! a selector for a class op with local polymorphism.
480 -- Just make a suitably typed local id for this
481 (clas_tyvar:local_tyvars) ->
482 tcInstType [(clas_tyvar,inst_ty)]
483 (mkSigmaTy local_tyvars meth_theta sel_tau)
484 `thenNF_Tc` \ method_ty ->
485 newLocalId (getOccurrenceName sel_id) method_ty `thenNF_Tc` \ meth_id ->
486 returnNF_Tc (emptyLIE, meth_id)
489 The next function makes a default method which calls the global default method, at
490 the appropriate instance type.
492 See the notes under default decls in TcClassDcl.lhs.
495 makeInstanceDeclDefaultMethodExpr
502 -> NF_TcM s (TcExpr s)
504 makeInstanceDeclDefaultMethodExpr origin meth_ids defm_ids inst_ty this_dict tag
505 = newDicts origin op_theta `thenNF_Tc` \ (op_lie,op_dicts) ->
507 -- def_op_id = /\ op_tyvars -> \ op_dicts ->
508 -- defm_id inst_ty op_tyvars this_dict op_dicts
510 mkHsTyLam op_tyvars (
511 mkHsDictLam op_dicts (
512 mkHsDictApp (mkHsTyApp (HsVar (RealId defm_id))
513 (inst_ty : mkTyVarTys op_tyvars))
514 (this_dict : op_dicts)
518 meth_id = meth_ids !! idx
519 defm_id = defm_ids !! idx
520 (op_tyvars, op_theta, op_tau) = splitSigmaTy (tcIdType meth_id)
522 makeInstanceDeclNoDefaultExpr
530 -> NF_TcM s (TcExpr s)
532 makeInstanceDeclNoDefaultExpr origin meth_ids defm_ids inst_ty clas inst_mod tag
533 = newDicts origin op_theta `thenNF_Tc` \ (op_lie, op_dicts) ->
535 -- Produce a warning if the default instance method
536 -- has been omitted when one exists in the class
537 warnTc (not err_defm_ok)
538 (omitDefaultMethodWarn clas_op clas_name inst_ty)
540 returnNF_Tc (mkHsTyLam op_tyvars (
541 mkHsDictLam op_dicts (
542 HsApp (mkHsTyApp (HsVar (RealId pAT_ERROR_ID)) [op_tau])
543 (HsLitOut (HsString (_PK_ error_msg)) stringTy))))
546 meth_id = meth_ids !! idx
547 clas_op = (getClassOps clas) !! idx
548 defm_id = defm_ids !! idx
549 (op_tyvars,op_theta,op_tau) = splitSigmaTy (tcIdType meth_id)
551 Just (_, _, err_defm_ok) = isDefaultMethodId_maybe defm_id
553 error_msg = "%E" -- => No explicit method for \"
554 ++ escErrorMsg error_str
556 error_str = _UNPK_ inst_mod ++ "." ++ _UNPK_ clas_name ++ "."
557 ++ (ppShow 80 (ppr PprForUser inst_ty)) ++ "."
558 ++ (ppShow 80 (ppr PprForUser clas_op)) ++ "\""
560 (_, clas_name) = getOrigName clas
564 %************************************************************************
566 \subsection{Processing each method}
568 %************************************************************************
570 @processInstBinds@ returns a @MonoBinds@ which binds
571 all the method ids (which are passed in). It is used
572 - both for instance decls,
573 - and to compile the default-method declarations in a class decl.
575 Any method ids which don't have a binding have a suitable default
576 binding created for them. The actual right-hand side used is
577 created using a function which is passed in, because the right thing to
578 do differs between instance and class decls.
582 :: (Int -> NF_TcM s (TcExpr s)) -- Function to make default method
583 -> [TcTyVar s] -- Tyvars for this instance decl
584 -> LIE s -- available Insts
585 -> [TcIdOcc s] -- Local method ids in tag order
586 -- (instance tyvars are free in their types)
588 -> TcM s (LIE s, -- These are required
591 processInstBinds mk_default_method_rhs inst_tyvars avail_insts method_ids monobinds
593 -- Process the explicitly-given method bindings
594 processInstBinds1 inst_tyvars avail_insts method_ids monobinds
595 `thenTc` \ (tags, insts_needed_in_methods, method_binds) ->
597 -- Find the methods not handled, and make default method bindings for them.
599 unmentioned_tags = [1.. length method_ids] `minusList` tags
601 mapNF_Tc mk_default_method unmentioned_tags
602 `thenNF_Tc` \ default_bind_list ->
604 returnTc (insts_needed_in_methods,
605 foldr AndMonoBinds method_binds default_bind_list)
607 -- From a tag construct us the passed-in function to construct
608 -- the binding for the default method
609 mk_default_method tag = mk_default_method_rhs tag `thenNF_Tc` \ rhs ->
610 returnNF_Tc (VarMonoBind (method_ids !! (tag-1)) rhs)
615 :: [TcTyVar s] -- Tyvars for this instance decl
616 -> LIE s -- available Insts
617 -> [TcIdOcc s] -- Local method ids in tag order (instance tyvars are free),
619 -> TcM s ([Int], -- Class-op tags accounted for
620 LIE s, -- These are required
623 processInstBinds1 inst_tyvars avail_insts method_ids EmptyMonoBinds
624 = returnTc ([], emptyLIE, EmptyMonoBinds)
626 processInstBinds1 inst_tyvars avail_insts method_ids (AndMonoBinds mb1 mb2)
627 = processInstBinds1 inst_tyvars avail_insts method_ids mb1
628 `thenTc` \ (op_tags1,dicts1,method_binds1) ->
629 processInstBinds1 inst_tyvars avail_insts method_ids mb2
630 `thenTc` \ (op_tags2,dicts2,method_binds2) ->
631 returnTc (op_tags1 ++ op_tags2,
632 dicts1 `unionBags` dicts2,
633 AndMonoBinds method_binds1 method_binds2)
637 processInstBinds1 inst_tyvars avail_insts method_ids mbind
639 -- Find what class op is being defined here. The complication is
640 -- that we could have a PatMonoBind or a FunMonoBind. If the
641 -- former, it should only bind a single variable, or else we're in
642 -- trouble (I'm not sure what the static semantics of methods
643 -- defined in a pattern binding with multiple patterns is!)
644 -- Renamer has reduced us to these two cases.
646 (op,locn) = case mbind of
647 FunMonoBind op _ locn -> (op, locn)
648 PatMonoBind (VarPatIn op) _ locn -> (op, locn)
650 occ = getOccurrenceName op
651 origin = InstanceDeclOrigin
655 -- Make a method id for the method
656 let tag = getTagFromClassOpName op
657 method_id = method_ids !! (tag-1)
659 TcId method_bndr = method_id
660 method_ty = idType method_bndr
661 (method_tyvars, method_theta, method_tau) = splitSigmaTy method_ty
663 newDicts origin method_theta `thenNF_Tc` \ (method_dicts,method_dict_ids) ->
665 case (method_tyvars, method_dict_ids) of
667 ([],[]) -> -- The simple case; no local polymorphism or overloading in the method
669 -- Type check the method itself
670 tcMethodBind method_id method_tau mbind `thenTc` \ (mbind', lieIop) ->
671 returnTc ([tag], lieIop, mbind')
673 other -> -- It's a locally-polymorphic and/or overloaded method; UGH!
675 -- Make a new id for (a) the local, non-overloaded method
676 -- and (b) the locally-overloaded method
677 -- The latter is needed just so we can return an AbsBinds wrapped
678 -- up inside a MonoBinds.
680 newLocalId occ method_tau `thenNF_Tc` \ local_id ->
681 newLocalId occ method_ty `thenNF_Tc` \ copy_id ->
683 inst_method_tyvars = inst_tyvars ++ method_tyvars
685 -- Typecheck the method
686 tcMethodBind local_id method_tau mbind `thenTc` \ (mbind', lieIop) ->
688 -- Check the overloading part of the signature.
689 -- Simplify everything fully, even though some
690 -- constraints could "really" be left to the next
691 -- level out. The case which forces this is
693 -- class Foo a where { op :: Bar a => a -> a }
695 -- Here we must simplify constraints on "a" to catch all
696 -- the Bar-ish things.
697 tcAddErrCtxt (methodSigCtxt op method_ty) (
699 (mkTyVarSet inst_method_tyvars)
700 (method_dicts `plusLIE` avail_insts)
702 ) `thenTc` \ (f_dicts, dict_binds) ->
706 VarMonoBind method_id
711 [(local_id, copy_id)]
718 tcMethodBind :: TcIdOcc s -> TcType s -> RenamedMonoBinds
719 -> TcM s (TcMonoBinds s, LIE s)
721 tcMethodBind meth_id meth_ty (FunMonoBind name matches locn)
722 = tcMatchesFun name meth_ty matches `thenTc` \ (rhs', lie) ->
723 returnTc (FunMonoBind meth_id rhs' locn, lie)
725 tcMethodBind meth_id meth_ty pbind@(PatMonoBind pat grhss_and_binds locn)
726 -- pat is sure to be a (VarPatIn op)
727 = tcAddErrCtxt (patMonoBindsCtxt pbind) $
728 tcGRHSsAndBinds grhss_and_binds `thenTc` \ (grhss_and_binds', lie, rhs_ty) ->
729 unifyTauTy meth_ty rhs_ty `thenTc_`
730 returnTc (PatMonoBind (VarPat meth_id) grhss_and_binds' locn, lie)
734 %************************************************************************
736 \subsection{Type-checking specialise instance pragmas}
738 %************************************************************************
742 tcSpecInstSigs :: E -> CE -> TCE
743 -> Bag InstInfo -- inst decls seen (declared and derived)
744 -> [RenamedSpecInstSig] -- specialise instance upragmas
745 -> TcM (Bag InstInfo) -- new, overlapped, inst decls
747 tcSpecInstSigs e ce tce inst_infos []
750 tcSpecInstSigs e ce tce inst_infos sigs
751 = buildInstanceEnvs inst_infos `thenTc` \ inst_mapper ->
752 tc_inst_spec_sigs inst_mapper sigs `thenNF_Tc` \ spec_inst_infos ->
753 returnTc spec_inst_infos
755 tc_inst_spec_sigs inst_mapper []
756 = returnNF_Tc emptyBag
757 tc_inst_spec_sigs inst_mapper (sig:sigs)
758 = tcSpecInstSig e ce tce inst_infos inst_mapper sig `thenNF_Tc` \ info_sig ->
759 tc_inst_spec_sigs inst_mapper sigs `thenNF_Tc` \ info_sigs ->
760 returnNF_Tc (info_sig `unionBags` info_sigs)
762 tcSpecInstSig :: E -> CE -> TCE
765 -> RenamedSpecInstSig
766 -> NF_TcM (Bag InstInfo)
768 tcSpecInstSig e ce tce inst_infos inst_mapper (SpecInstSig class_name ty src_loc)
769 = recoverTc emptyBag (
770 tcAddSrcLoc src_loc (
772 clas = lookupCE ce class_name -- Renamer ensures this can't fail
774 -- Make some new type variables, named as in the specialised instance type
775 ty_names = extractMonoTyNames (==) ty
776 (tmpl_e,inst_tmpls,inst_tmpl_tys) = mkTVE ty_names
778 babyTcMtoTcM (tcInstanceType ce tce tmpl_e True src_loc ty)
779 `thenTc` \ inst_ty ->
781 maybe_tycon = case maybeAppDataTyCon inst_ty of
782 Just (tc,_,_) -> Just tc
785 maybe_unspec_inst = lookup_unspec_inst clas maybe_tycon inst_infos
787 -- Check that we have a local instance declaration to specialise
788 checkMaybeTc maybe_unspec_inst
789 (specInstUnspecInstNotFoundErr clas inst_ty src_loc) `thenTc_`
791 -- Create tvs to substitute for tmpls while simplifying the context
792 copyTyVars inst_tmpls `thenNF_Tc` \ (tv_e, inst_tvs, inst_tv_tys) ->
794 Just (InstInfo _ unspec_tyvars unspec_inst_ty unspec_theta
795 _ _ _ binds True{-from here-} mod _ uprag) = maybe_unspec_inst
797 subst = case matchTy unspec_inst_ty inst_ty of
799 Nothing -> panic "tcSpecInstSig:matchTy"
801 subst_theta = instantiateThetaTy subst unspec_theta
802 subst_tv_theta = instantiateThetaTy tv_e subst_theta
804 mk_spec_origin clas ty
805 = InstanceSpecOrigin inst_mapper clas ty src_loc
807 tcSimplifyThetas mk_spec_origin subst_tv_theta
808 `thenTc` \ simpl_tv_theta ->
810 simpl_theta = [ (clas, tv_to_tmpl tv) | (clas, tv) <- simpl_tv_theta ]
812 tv_tmpl_map = inst_tv_tys `zipEqual` inst_tmpl_tys
813 tv_to_tmpl tv = assoc "tcSpecInstSig" tv_tmpl_map tv
815 mkInstanceRelatedIds e True{-from here-} mod NoInstancePragmas src_loc
816 clas inst_tmpls inst_ty simpl_theta uprag
817 `thenTc` \ (dfun_id, dfun_theta, const_meth_ids) ->
819 getSwitchCheckerTc `thenNF_Tc` \ sw_chkr ->
820 (if sw_chkr SpecialiseTrace then
821 pprTrace "Specialised Instance: "
822 (ppAboves [ppCat [if null simpl_theta then ppNil else ppr PprDebug simpl_theta,
823 if null simpl_theta then ppNil else ppStr "=>",
825 pprParendGenType PprDebug inst_ty],
826 ppCat [ppStr " derived from:",
827 if null unspec_theta then ppNil else ppr PprDebug unspec_theta,
828 if null unspec_theta then ppNil else ppStr "=>",
830 pprParendGenType PprDebug unspec_inst_ty]])
833 returnTc (unitBag (InstInfo clas inst_tmpls inst_ty simpl_theta
834 dfun_theta dfun_id const_meth_ids
835 binds True{-from here-} mod src_loc uprag))
839 lookup_unspec_inst clas maybe_tycon inst_infos
840 = case filter (match_info match_inst_ty) (bagToList inst_infos) of
842 (info:_) -> Just info
844 match_info match_ty (InstInfo inst_clas _ inst_ty _ _ _ _ _ from_here _ _ _)
845 = from_here && clas == inst_clas &&
846 match_ty inst_ty && is_plain_instance inst_ty
848 match_inst_ty = case maybe_tycon of
849 Just tycon -> match_tycon tycon
852 match_tycon tycon inst_ty = case (maybeAppDataTyCon inst_ty) of
853 Just (inst_tc,_,_) -> tycon == inst_tc
856 match_fun inst_ty = isFunType inst_ty
859 is_plain_instance inst_ty
860 = case (maybeAppDataTyCon inst_ty) of
861 Just (_,tys,_) -> all isTyVarTemplateTy tys
862 Nothing -> case maybeUnpackFunTy inst_ty of
863 Just (arg, res) -> isTyVarTemplateTy arg && isTyVarTemplateTy res
864 Nothing -> error "TcInstDecls:is_plain_instance"
869 Checking for a decent instance type
870 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
871 @scrutiniseInstanceType@ checks the type {\em and} its syntactic constraints:
872 it must normally look like: @instance Foo (Tycon a b c ...) ...@
874 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
875 flag is on, or (2)~the instance is imported (they must have been
876 compiled elsewhere). In these cases, we let them go through anyway.
878 We can also have instances for functions: @instance Foo (a -> b) ...@.
881 scrutiniseInstanceType from_here clas inst_tau
883 | not (maybeToBool inst_tycon_maybe)
884 = failTc (instTypeErr inst_tau)
886 -- IMPORTED INSTANCES ARE OK (but see tcInstDecl1)
888 = returnTc (inst_tycon,arg_tys)
891 | not (all isTyVarTy arg_tys ||
894 = failTc (instTypeErr inst_tau)
897 -- It is obviously illegal to have an explicit instance
898 -- for something that we are also planning to `derive'
899 -- Though we can have an explicit instance which is more
900 -- specific than the derived instance
901 | clas `derivedFor` inst_tycon
902 && all isTyVarTy arg_tys
903 = failTc (derivingWhenInstanceExistsErr clas inst_tycon)
906 -- A user declaration of a _CCallable/_CReturnable instance
907 -- must be for a "boxed primitive" type.
909 && not opt_CompilingPrelude -- which allows anything
910 && maybeToBool (maybeBoxedPrimType inst_tau)
911 = failTc (nonBoxedPrimCCallErr clas inst_tau)
914 = returnTc (inst_tycon,arg_tys)
917 (possible_tycon, arg_tys) = splitAppTy inst_tau
918 inst_tycon_maybe = getTyCon_maybe possible_tycon
919 inst_tycon = expectJust "tcInstDecls1:inst_tycon" inst_tycon_maybe
926 SynTy tc _ _ -> ppBesides [ppStr "The type synonym `", ppr sty tc, rest_of_msg]
927 TyVarTy tv -> ppBesides [ppStr "The type variable `", ppr sty tv, rest_of_msg]
928 other -> ppBesides [ppStr "The type `", ppr sty ty, rest_of_msg]
930 rest_of_msg = ppStr "' cannot be used as an instance type."
932 derivingWhenInstanceExistsErr clas tycon sty
933 = ppHang (ppBesides [ppStr "Deriving class `", ppr sty clas, ppStr "' type `", ppr sty tycon, ppStr "'"])
934 4 (ppStr "when an explicit instance exists")
936 derivingWhenInstanceImportedErr inst_mod clas tycon sty
937 = ppHang (ppBesides [ppStr "Deriving class `", ppr sty clas, ppStr "' type `", ppr sty tycon, ppStr "'"])
938 4 (ppBesides [ppStr "when an instance declared in module `", ppPStr inst_mod, ppStr "' has been imported"])
940 nonBoxedPrimCCallErr clas inst_ty sty
941 = ppHang (ppStr "Instance isn't for a `boxed-primitive' type")
942 4 (ppBesides [ ppStr "class `", ppr sty clas, ppStr "' type `",
943 ppr sty inst_ty, ppStr "'"])
945 omitDefaultMethodWarn clas_op clas_name inst_ty sty
946 = ppCat [ppStr "Warning: Omitted default method for",
947 ppr sty clas_op, ppStr "in instance",
948 ppPStr clas_name, pprParendGenType sty inst_ty]
951 patMonoBindsCtxt pbind sty
952 = ppHang (ppStr "In a pattern binding:")
955 methodSigCtxt name ty sty
956 = ppHang (ppBesides [ppStr "When matching the definition of class method `",
957 ppr sty name, ppStr "' to its signature :" ])
960 bindSigCtxt method_ids sty
961 = ppHang (ppStr "When checking type signatures for: ")
962 4 (ppInterleave (ppStr ", ") (map (ppr sty) method_ids))
964 superClassSigCtxt sty
965 = ppStr "When checking superclass constraints on instance declaration"