2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[Inst]{The @Inst@ type: dictionaries or method instances}
8 LIE, emptyLIE, unitLIE, plusLIE, consLIE,
9 plusLIEs, mkLIE, isEmptyLIE, lieToList, listToLIE,
13 pprInst, pprInsts, pprInstsInFull, tidyInsts, tidyMoreInsts,
15 newDictsFromOld, newDicts, cloneDict,
16 newOverloadedLit, newIPDict,
17 newMethod, newMethodFromName, newMethodWithGivenTy,
18 tcInstClassOp, tcInstCall, tcInstDataCon, tcSyntaxName,
20 tyVarsOfInst, tyVarsOfInsts, tyVarsOfLIE,
21 ipNamesOfInst, ipNamesOfInsts, fdPredsOfInst, fdPredsOfInsts,
22 instLoc, getDictClassTys, dictPred,
24 lookupInst, LookupInstResult(..),
26 isDict, isClassDict, isMethod,
27 isLinearInst, linearInstType, isIPDict, isInheritableInst,
28 isTyVarDict, isStdClassTyVarDict, isMethodFor,
29 instBindingRequired, instCanBeGeneralised,
34 InstOrigin(..), InstLoc(..), pprInstLoc
37 #include "HsVersions.h"
39 import {-# SOURCE #-} TcExpr( tcExpr )
41 import HsSyn ( HsLit(..), HsOverLit(..), HsExpr(..) )
42 import TcHsSyn ( TcExpr, TcId, TcIdSet,
43 mkHsTyApp, mkHsDictApp, mkHsConApp, zonkId,
47 import TcEnv ( tcGetInstEnv, tcLookupId, tcLookupTyCon, checkWellStaged, topIdLvl )
48 import InstEnv ( InstLookupResult(..), lookupInstEnv )
49 import TcMType ( zonkTcType, zonkTcTypes, zonkTcPredType, zapToType,
50 zonkTcThetaType, tcInstTyVar, tcInstType, tcInstTyVars
52 import TcType ( Type, TcType, TcThetaType, TcTyVarSet,
53 SourceType(..), PredType, TyVarDetails(VanillaTv),
54 tcSplitForAllTys, tcSplitForAllTys, mkTyConApp,
55 tcSplitPhiTy, mkGenTyConApp,
56 isIntTy,isFloatTy, isIntegerTy, isDoubleTy,
57 tcIsTyVarTy, mkPredTy, mkTyVarTy, mkTyVarTys,
58 tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, tidyPred,
59 isClassPred, isTyVarClassPred, isLinearPred, predHasFDs,
60 getClassPredTys, getClassPredTys_maybe, mkPredName,
61 isInheritablePred, isIPPred,
62 tidyType, tidyTypes, tidyFreeTyVars, tcSplitSigmaTy
64 import CoreFVs ( idFreeTyVars )
65 import DataCon ( DataCon,dataConSig )
66 import Id ( Id, idName, idType, mkUserLocal, mkSysLocal, mkLocalId, setIdUnique )
67 import PrelInfo ( isStandardClass, isCcallishClass, isNoDictClass )
68 import Name ( Name, mkMethodOcc, getOccName )
69 import PprType ( pprPred, pprParendType )
70 import Subst ( substTy, substTyWith, substTheta, mkTyVarSubst )
71 import Literal ( inIntRange )
73 import VarEnv ( TidyEnv, emptyTidyEnv, lookupSubstEnv, SubstResult(..) )
74 import VarSet ( elemVarSet, emptyVarSet, unionVarSet )
75 import TysWiredIn ( floatDataCon, doubleDataCon )
76 import PrelNames( fromIntegerName, fromRationalName, rationalTyConName )
77 import BasicTypes( IPName(..), mapIPName, ipNameName )
78 import UniqSupply( uniqsFromSupply )
86 instName :: Inst -> Name
87 instName inst = idName (instToId inst)
89 instToId :: Inst -> TcId
90 instToId (Dict id _ _) = id
91 instToId (Method id _ _ _ _ _) = id
92 instToId (LitInst id _ _ _) = id
94 instLoc (Dict _ _ loc) = loc
95 instLoc (Method _ _ _ _ _ loc) = loc
96 instLoc (LitInst _ _ _ loc) = loc
98 dictPred (Dict _ pred _ ) = pred
99 dictPred inst = pprPanic "dictPred" (ppr inst)
101 getDictClassTys (Dict _ pred _) = getClassPredTys pred
103 -- fdPredsOfInst is used to get predicates that contain functional
104 -- dependencies; i.e. should participate in improvement
105 fdPredsOfInst (Dict _ pred _) | predHasFDs pred = [pred]
107 fdPredsOfInst (Method _ _ _ theta _ _) = filter predHasFDs theta
108 fdPredsOfInst other = []
110 fdPredsOfInsts :: [Inst] -> [PredType]
111 fdPredsOfInsts insts = concatMap fdPredsOfInst insts
113 isInheritableInst (Dict _ pred _) = isInheritablePred pred
114 isInheritableInst (Method _ _ _ theta _ _) = all isInheritablePred theta
115 isInheritableInst other = True
118 ipNamesOfInsts :: [Inst] -> [Name]
119 ipNamesOfInst :: Inst -> [Name]
120 -- Get the implicit parameters mentioned by these Insts
121 -- NB: ?x and %x get different Names
122 ipNamesOfInsts insts = [n | inst <- insts, n <- ipNamesOfInst inst]
124 ipNamesOfInst (Dict _ (IParam n _) _) = [ipNameName n]
125 ipNamesOfInst (Method _ _ _ theta _ _) = [ipNameName n | IParam n _ <- theta]
126 ipNamesOfInst other = []
128 tyVarsOfInst :: Inst -> TcTyVarSet
129 tyVarsOfInst (LitInst _ _ ty _) = tyVarsOfType ty
130 tyVarsOfInst (Dict _ pred _) = tyVarsOfPred pred
131 tyVarsOfInst (Method _ id tys _ _ _) = tyVarsOfTypes tys `unionVarSet` idFreeTyVars id
132 -- The id might have free type variables; in the case of
133 -- locally-overloaded class methods, for example
136 tyVarsOfInsts insts = foldr (unionVarSet . tyVarsOfInst) emptyVarSet insts
137 tyVarsOfLIE lie = tyVarsOfInsts (lieToList lie)
143 isDict :: Inst -> Bool
144 isDict (Dict _ _ _) = True
147 isClassDict :: Inst -> Bool
148 isClassDict (Dict _ pred _) = isClassPred pred
149 isClassDict other = False
151 isTyVarDict :: Inst -> Bool
152 isTyVarDict (Dict _ pred _) = isTyVarClassPred pred
153 isTyVarDict other = False
155 isIPDict :: Inst -> Bool
156 isIPDict (Dict _ pred _) = isIPPred pred
157 isIPDict other = False
159 isMethod :: Inst -> Bool
160 isMethod (Method _ _ _ _ _ _) = True
161 isMethod other = False
163 isMethodFor :: TcIdSet -> Inst -> Bool
164 isMethodFor ids (Method uniq id tys _ _ loc) = id `elemVarSet` ids
165 isMethodFor ids inst = False
167 isLinearInst :: Inst -> Bool
168 isLinearInst (Dict _ pred _) = isLinearPred pred
169 isLinearInst other = False
170 -- We never build Method Insts that have
171 -- linear implicit paramters in them.
172 -- Hence no need to look for Methods
175 linearInstType :: Inst -> TcType -- %x::t --> t
176 linearInstType (Dict _ (IParam _ ty) _) = ty
179 isStdClassTyVarDict (Dict _ pred _) = case getClassPredTys_maybe pred of
180 Just (clas, [ty]) -> isStandardClass clas && tcIsTyVarTy ty
184 Two predicates which deal with the case where class constraints don't
185 necessarily result in bindings. The first tells whether an @Inst@
186 must be witnessed by an actual binding; the second tells whether an
187 @Inst@ can be generalised over.
190 instBindingRequired :: Inst -> Bool
191 instBindingRequired (Dict _ (ClassP clas _) _) = not (isNoDictClass clas)
192 instBindingRequired other = True
194 instCanBeGeneralised :: Inst -> Bool
195 instCanBeGeneralised (Dict _ (ClassP clas _) _) = not (isCcallishClass clas)
196 instCanBeGeneralised other = True
200 %************************************************************************
202 \subsection{Building dictionaries}
204 %************************************************************************
207 newDicts :: InstOrigin
211 = getInstLoc orig `thenM` \ loc ->
212 newDictsAtLoc loc theta
214 cloneDict :: Inst -> TcM Inst
215 cloneDict (Dict id ty loc) = newUnique `thenM` \ uniq ->
216 returnM (Dict (setIdUnique id uniq) ty loc)
218 newDictsFromOld :: Inst -> TcThetaType -> TcM [Inst]
219 newDictsFromOld (Dict _ _ loc) theta = newDictsAtLoc loc theta
221 -- Local function, similar to newDicts,
222 -- but with slightly different interface
223 newDictsAtLoc :: InstLoc
226 newDictsAtLoc inst_loc theta
227 = newUniqueSupply `thenM` \ us ->
228 returnM (zipWith mk_dict (uniqsFromSupply us) theta)
230 mk_dict uniq pred = Dict (mkLocalId (mkPredName uniq loc pred) (mkPredTy pred))
232 loc = instLocSrcLoc inst_loc
234 -- For vanilla implicit parameters, there is only one in scope
235 -- at any time, so we used to use the name of the implicit parameter itself
236 -- But with splittable implicit parameters there may be many in
237 -- scope, so we make up a new name.
238 newIPDict :: InstOrigin -> IPName Name -> Type
239 -> TcM (IPName Id, Inst)
240 newIPDict orig ip_name ty
241 = getInstLoc orig `thenM` \ inst_loc@(InstLoc _ loc _) ->
242 newUnique `thenM` \ uniq ->
244 pred = IParam ip_name ty
245 id = mkLocalId (mkPredName uniq loc pred) (mkPredTy pred)
247 returnM (mapIPName (\n -> id) ip_name, Dict id pred inst_loc)
252 %************************************************************************
254 \subsection{Building methods (calls of overloaded functions)}
256 %************************************************************************
260 tcInstCall :: InstOrigin -> TcType -> TcM (ExprCoFn, TcType)
261 tcInstCall orig fun_ty -- fun_ty is usually a sigma-type
262 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
263 newDicts orig theta `thenM` \ dicts ->
264 extendLIEs dicts `thenM_`
266 inst_fn e = mkHsDictApp (mkHsTyApp e (mkTyVarTys tyvars)) (map instToId dicts)
268 returnM (mkCoercion inst_fn, tau)
270 tcInstDataCon :: InstOrigin -> DataCon
271 -> TcM ([TcType], -- Types to instantiate at
272 [Inst], -- Existential dictionaries to apply to
273 [TcType], -- Argument types of constructor
274 TcType, -- Result type
275 [TyVar]) -- Existential tyvars
276 tcInstDataCon orig data_con
278 (tvs, stupid_theta, ex_tvs, ex_theta, arg_tys, tycon) = dataConSig data_con
279 -- We generate constraints for the stupid theta even when
280 -- pattern matching (as the Report requires)
282 tcInstTyVars VanillaTv (tvs ++ ex_tvs) `thenM` \ (all_tvs', ty_args', tenv) ->
284 stupid_theta' = substTheta tenv stupid_theta
285 ex_theta' = substTheta tenv ex_theta
286 arg_tys' = map (substTy tenv) arg_tys
288 n_normal_tvs = length tvs
289 ex_tvs' = drop n_normal_tvs all_tvs'
290 result_ty = mkTyConApp tycon (take n_normal_tvs ty_args')
292 newDicts orig stupid_theta' `thenM` \ stupid_dicts ->
293 newDicts orig ex_theta' `thenM` \ ex_dicts ->
295 -- Note that we return the stupid theta *only* in the LIE;
296 -- we don't otherwise use it at all
297 extendLIEs stupid_dicts `thenM_`
299 returnM (ty_args', ex_dicts, arg_tys', result_ty, ex_tvs')
301 newMethodFromName :: InstOrigin -> TcType -> Name -> TcM TcId
302 newMethodFromName origin ty name
303 = tcLookupId name `thenM` \ id ->
304 -- Use tcLookupId not tcLookupGlobalId; the method is almost
305 -- always a class op, but with -fno-implicit-prelude GHC is
306 -- meant to find whatever thing is in scope, and that may
307 -- be an ordinary function.
308 getInstLoc origin `thenM` \ loc ->
309 tcInstClassOp loc id [ty] `thenM` \ inst ->
310 extendLIE inst `thenM_`
311 returnM (instToId inst)
313 newMethodWithGivenTy orig id tys theta tau
314 = getInstLoc orig `thenM` \ loc ->
315 newMethod loc id tys theta tau `thenM` \ inst ->
316 extendLIE inst `thenM_`
317 returnM (instToId inst)
319 --------------------------------------------
320 -- tcInstClassOp, and newMethod do *not* drop the
321 -- Inst into the LIE; they just returns the Inst
322 -- This is important because they are used by TcSimplify
325 tcInstClassOp :: InstLoc -> Id -> [TcType] -> TcM Inst
326 tcInstClassOp inst_loc sel_id tys
328 (tyvars,rho) = tcSplitForAllTys (idType sel_id)
329 rho_ty = ASSERT( length tyvars == length tys )
330 substTyWith tyvars tys rho
331 (preds,tau) = tcSplitPhiTy rho_ty
333 newMethod inst_loc sel_id tys preds tau
335 ---------------------------
336 newMethod inst_loc id tys theta tau
337 = newUnique `thenM` \ new_uniq ->
339 meth_id = mkUserLocal (mkMethodOcc (getOccName id)) new_uniq tau loc
340 inst = Method meth_id id tys theta tau inst_loc
341 loc = instLocSrcLoc inst_loc
346 In newOverloadedLit we convert directly to an Int or Integer if we
347 know that's what we want. This may save some time, by not
348 temporarily generating overloaded literals, but it won't catch all
349 cases (the rest are caught in lookupInst).
352 newOverloadedLit :: InstOrigin
356 newOverloadedLit orig lit expected_ty
357 = zapToType expected_ty `thenM_`
358 -- The expected type might be a 'hole' type variable,
359 -- in which case we must zap it to an ordinary type variable
360 new_over_lit orig lit expected_ty
362 new_over_lit orig lit@(HsIntegral i fi) expected_ty
363 | fi /= fromIntegerName -- Do not generate a LitInst for rebindable
364 -- syntax. Reason: tcSyntaxName does unification
365 -- which is very inconvenient in tcSimplify
366 = tcSyntaxName orig expected_ty fromIntegerName fi `thenM` \ (expr, _) ->
367 returnM (HsApp expr (HsLit (HsInteger i)))
369 | Just expr <- shortCutIntLit i expected_ty
373 = newLitInst orig lit expected_ty
375 new_over_lit orig lit@(HsFractional r fr) expected_ty
376 | fr /= fromRationalName -- c.f. HsIntegral case
377 = tcSyntaxName orig expected_ty fromRationalName fr `thenM` \ (expr, _) ->
378 mkRatLit r `thenM` \ rat_lit ->
379 returnM (HsApp expr rat_lit)
381 | Just expr <- shortCutFracLit r expected_ty
385 = newLitInst orig lit expected_ty
387 newLitInst orig lit expected_ty
388 = getInstLoc orig `thenM` \ loc ->
389 newUnique `thenM` \ new_uniq ->
391 lit_inst = LitInst lit_id lit expected_ty loc
392 lit_id = mkSysLocal FSLIT("lit") new_uniq expected_ty
394 extendLIE lit_inst `thenM_`
395 returnM (HsVar (instToId lit_inst))
397 shortCutIntLit :: Integer -> TcType -> Maybe TcExpr
399 | isIntTy ty && inIntRange i -- Short cut for Int
400 = Just (HsLit (HsInt i))
401 | isIntegerTy ty -- Short cut for Integer
402 = Just (HsLit (HsInteger i))
403 | otherwise = Nothing
405 shortCutFracLit :: Rational -> TcType -> Maybe TcExpr
408 = Just (mkHsConApp floatDataCon [] [HsLit (HsFloatPrim f)])
410 = Just (mkHsConApp doubleDataCon [] [HsLit (HsDoublePrim f)])
411 | otherwise = Nothing
413 mkRatLit :: Rational -> TcM TcExpr
415 = tcLookupTyCon rationalTyConName `thenM` \ rat_tc ->
417 rational_ty = mkGenTyConApp rat_tc []
419 returnM (HsLit (HsRat r rational_ty))
423 %************************************************************************
427 %************************************************************************
429 Zonking makes sure that the instance types are fully zonked,
430 but doesn't do the same for any of the Ids in an Inst. There's no
431 need, and it's a lot of extra work.
434 zonkInst :: Inst -> TcM Inst
435 zonkInst (Dict id pred loc)
436 = zonkTcPredType pred `thenM` \ new_pred ->
437 returnM (Dict id new_pred loc)
439 zonkInst (Method m id tys theta tau loc)
440 = zonkId id `thenM` \ new_id ->
441 -- Essential to zonk the id in case it's a local variable
442 -- Can't use zonkIdOcc because the id might itself be
443 -- an InstId, in which case it won't be in scope
445 zonkTcTypes tys `thenM` \ new_tys ->
446 zonkTcThetaType theta `thenM` \ new_theta ->
447 zonkTcType tau `thenM` \ new_tau ->
448 returnM (Method m new_id new_tys new_theta new_tau loc)
450 zonkInst (LitInst id lit ty loc)
451 = zonkTcType ty `thenM` \ new_ty ->
452 returnM (LitInst id lit new_ty loc)
454 zonkInsts insts = mappM zonkInst insts
458 %************************************************************************
460 \subsection{Printing}
462 %************************************************************************
464 ToDo: improve these pretty-printing things. The ``origin'' is really only
465 relevant in error messages.
468 instance Outputable Inst where
469 ppr inst = pprInst inst
471 pprInsts :: [Inst] -> SDoc
472 pprInsts insts = parens (sep (punctuate comma (map pprInst insts)))
475 = vcat (map go insts)
477 go inst = sep [quotes (ppr inst), nest 2 (pprInstLoc (instLoc inst))]
479 pprInst (LitInst u lit ty loc)
480 = hsep [ppr lit, ptext SLIT("at"), ppr ty, show_uniq u]
482 pprInst (Dict u pred loc) = pprPred pred <+> show_uniq u
484 pprInst m@(Method u id tys theta tau loc)
485 = hsep [ppr id, ptext SLIT("at"),
486 brackets (sep (map pprParendType tys)) {- ,
487 ptext SLIT("theta"), ppr theta,
488 ptext SLIT("tau"), ppr tau
492 show_uniq u = ifPprDebug (text "{-" <> ppr u <> text "-}")
494 tidyInst :: TidyEnv -> Inst -> Inst
495 tidyInst env (LitInst u lit ty loc) = LitInst u lit (tidyType env ty) loc
496 tidyInst env (Dict u pred loc) = Dict u (tidyPred env pred) loc
497 tidyInst env (Method u id tys theta tau loc) = Method u id (tidyTypes env tys) theta tau loc
499 tidyMoreInsts :: TidyEnv -> [Inst] -> (TidyEnv, [Inst])
500 -- This function doesn't assume that the tyvars are in scope
501 -- so it works like tidyOpenType, returning a TidyEnv
502 tidyMoreInsts env insts
503 = (env', map (tidyInst env') insts)
505 env' = tidyFreeTyVars env (tyVarsOfInsts insts)
507 tidyInsts :: [Inst] -> (TidyEnv, [Inst])
508 tidyInsts insts = tidyMoreInsts emptyTidyEnv insts
510 showLIE :: SDoc -> TcM () -- Debugging
512 = do { lie_var <- getLIEVar ;
513 lie <- readMutVar lie_var ;
514 traceTc (str <+> pprInstsInFull (lieToList lie)) }
518 %************************************************************************
520 \subsection{Looking up Insts}
522 %************************************************************************
525 data LookupInstResult s
527 | SimpleInst TcExpr -- Just a variable, type application, or literal
528 | GenInst [Inst] TcExpr -- The expression and its needed insts
530 lookupInst :: Inst -> TcM (LookupInstResult s)
531 -- It's important that lookupInst does not put any new stuff into
532 -- the LIE. Instead, any Insts needed by the lookup are returned in
533 -- the LookupInstResult, where they can be further processed by tcSimplify
537 lookupInst dict@(Dict _ pred@(ClassP clas tys) loc)
538 = getDOpts `thenM` \ dflags ->
539 tcGetInstEnv `thenM` \ inst_env ->
540 case lookupInstEnv dflags inst_env clas tys of
542 FoundInst tenv dfun_id
543 -> -- It's possible that not all the tyvars are in
544 -- the substitution, tenv. For example:
545 -- instance C X a => D X where ...
546 -- (presumably there's a functional dependency in class C)
547 -- Hence the mk_ty_arg to instantiate any un-substituted tyvars.
548 getStage `thenM` \ use_stage ->
549 checkWellStaged (ptext SLIT("instance for") <+> quotes (ppr pred))
550 (topIdLvl dfun_id) use_stage `thenM_`
551 traceTc (text "lookupInst" <+> ppr dfun_id <+> ppr (topIdLvl dfun_id) <+> ppr use_stage) `thenM_`
553 (tyvars, rho) = tcSplitForAllTys (idType dfun_id)
554 mk_ty_arg tv = case lookupSubstEnv tenv tv of
555 Just (DoneTy ty) -> returnM ty
556 Nothing -> tcInstTyVar VanillaTv tv `thenM` \ tc_tv ->
557 returnM (mkTyVarTy tc_tv)
559 mappM mk_ty_arg tyvars `thenM` \ ty_args ->
561 dfun_rho = substTy (mkTyVarSubst tyvars ty_args) rho
562 (theta, _) = tcSplitPhiTy dfun_rho
563 ty_app = mkHsTyApp (HsVar dfun_id) ty_args
566 returnM (SimpleInst ty_app)
568 newDictsAtLoc loc theta `thenM` \ dicts ->
570 rhs = mkHsDictApp ty_app (map instToId dicts)
572 returnM (GenInst dicts rhs)
574 other -> returnM NoInstance
576 lookupInst (Dict _ _ _) = returnM NoInstance
580 lookupInst inst@(Method _ id tys theta _ loc)
581 = newDictsAtLoc loc theta `thenM` \ dicts ->
582 returnM (GenInst dicts (mkHsDictApp (mkHsTyApp (HsVar id) tys) (map instToId dicts)))
586 -- Look for short cuts first: if the literal is *definitely* a
587 -- int, integer, float or a double, generate the real thing here.
588 -- This is essential (see nofib/spectral/nucleic).
589 -- [Same shortcut as in newOverloadedLit, but we
590 -- may have done some unification by now]
593 lookupInst inst@(LitInst u (HsIntegral i from_integer_name) ty loc)
594 | Just expr <- shortCutIntLit i ty
595 = returnM (GenInst [] expr) -- GenInst, not SimpleInst, because
596 -- expr may be a constructor application
598 = ASSERT( from_integer_name == fromIntegerName ) -- A LitInst invariant
599 tcLookupId fromIntegerName `thenM` \ from_integer ->
600 tcInstClassOp loc from_integer [ty] `thenM` \ method_inst ->
601 returnM (GenInst [method_inst]
602 (HsApp (HsVar (instToId method_inst)) (HsLit (HsInteger i))))
605 lookupInst inst@(LitInst u (HsFractional f from_rat_name) ty loc)
606 | Just expr <- shortCutFracLit f ty
607 = returnM (GenInst [] expr)
610 = ASSERT( from_rat_name == fromRationalName ) -- A LitInst invariant
611 tcLookupId fromRationalName `thenM` \ from_rational ->
612 tcInstClassOp loc from_rational [ty] `thenM` \ method_inst ->
613 mkRatLit f `thenM` \ rat_lit ->
614 returnM (GenInst [method_inst] (HsApp (HsVar (instToId method_inst)) rat_lit))
619 %************************************************************************
623 %************************************************************************
626 Suppose we are doing the -fno-implicit-prelude thing, and we encounter
627 a do-expression. We have to find (>>) in the current environment, which is
628 done by the rename. Then we have to check that it has the same type as
629 Control.Monad.(>>). Or, more precisely, a compatible type. One 'customer' had
632 (>>) :: HB m n mn => m a -> n b -> mn b
634 So the idea is to generate a local binding for (>>), thus:
636 let then72 :: forall a b. m a -> m b -> m b
637 then72 = ...something involving the user's (>>)...
639 ...the do-expression...
641 Now the do-expression can proceed using then72, which has exactly
644 In fact tcSyntaxName just generates the RHS for then72, because we only
645 want an actual binding in the do-expression case. For literals, we can
646 just use the expression inline.
649 tcSyntaxName :: InstOrigin
650 -> TcType -- Type to instantiate it at
651 -> Name -> Name -- (Standard name, user name)
652 -> TcM (TcExpr, TcType) -- Suitable expression with its type
654 -- NB: tcSyntaxName calls tcExpr, and hence can do unification.
655 -- So we do not call it from lookupInst, which is called from tcSimplify
657 tcSyntaxName orig ty std_nm user_nm
659 = newMethodFromName orig ty std_nm `thenM` \ id ->
660 returnM (HsVar id, idType id)
663 = tcLookupId std_nm `thenM` \ std_id ->
665 -- C.f. newMethodAtLoc
666 ([tv], _, tau) = tcSplitSigmaTy (idType std_id)
667 tau1 = substTyWith [tv] [ty] tau
669 addErrCtxtM (syntaxNameCtxt user_nm orig tau1) $
670 tcExpr (HsVar user_nm) tau1 `thenM` \ user_fn ->
671 returnM (user_fn, tau1)
673 syntaxNameCtxt name orig ty tidy_env
674 = getInstLoc orig `thenM` \ inst_loc ->
676 msg = vcat [ptext SLIT("When checking that") <+> quotes (ppr name) <+>
677 ptext SLIT("(needed by a syntactic construct)"),
678 nest 2 (ptext SLIT("has the required type:") <+> ppr (tidyType tidy_env ty)),
679 nest 2 (pprInstLoc inst_loc)]
681 returnM (tidy_env, msg)