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,
19 tcSyntaxName, tcStdSyntaxName,
21 tyVarsOfInst, tyVarsOfInsts, tyVarsOfLIE,
22 ipNamesOfInst, ipNamesOfInsts, fdPredsOfInst, fdPredsOfInsts,
23 instLoc, getDictClassTys, dictPred,
25 lookupInst, LookupInstResult(..),
27 isDict, isClassDict, isMethod,
28 isLinearInst, linearInstType, isIPDict, isInheritableInst,
29 isTyVarDict, isStdClassTyVarDict, isMethodFor,
30 instBindingRequired, instCanBeGeneralised,
35 InstOrigin(..), InstLoc(..), pprInstLoc
38 #include "HsVersions.h"
40 import {-# SOURCE #-} TcExpr( tcCheckSigma )
42 import HsSyn ( HsLit(..), HsOverLit(..), HsExpr(..) )
43 import TcHsSyn ( TcExpr, TcId, TcIdSet,
44 mkHsTyApp, mkHsDictApp, mkHsConApp, zonkId,
48 import TcEnv ( tcGetInstEnv, tcLookupId, tcLookupTyCon, checkWellStaged, topIdLvl )
49 import InstEnv ( InstLookupResult(..), lookupInstEnv )
50 import TcMType ( zonkTcType, zonkTcTypes, zonkTcPredType,
51 zonkTcThetaType, tcInstTyVar, tcInstType, tcInstTyVars
53 import TcType ( Type, TcType, TcThetaType, TcTyVarSet,
54 SourceType(..), PredType, TyVarDetails(VanillaTv),
55 tcSplitForAllTys, tcSplitForAllTys, mkTyConApp,
56 tcSplitPhiTy, mkGenTyConApp,
57 isIntTy,isFloatTy, isIntegerTy, isDoubleTy,
58 tcIsTyVarTy, mkPredTy, mkTyVarTy, mkTyVarTys,
59 tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, tidyPred,
60 isClassPred, isTyVarClassPred, isLinearPred,
61 getClassPredTys, getClassPredTys_maybe, mkPredName,
62 isInheritablePred, isIPPred,
63 tidyType, tidyTypes, tidyFreeTyVars, tcSplitSigmaTy
65 import CoreFVs ( idFreeTyVars )
66 import DataCon ( DataCon,dataConSig )
67 import Id ( Id, idName, idType, mkUserLocal, mkSysLocal, mkLocalId, setIdUnique )
68 import PrelInfo ( isStandardClass, isCcallishClass, isNoDictClass )
69 import Name ( Name, mkMethodOcc, getOccName )
70 import PprType ( pprPred, pprParendType )
71 import Subst ( substTy, substTyWith, substTheta, mkTyVarSubst )
72 import Literal ( inIntRange )
74 import VarEnv ( TidyEnv, emptyTidyEnv, lookupSubstEnv, SubstResult(..) )
75 import VarSet ( elemVarSet, emptyVarSet, unionVarSet )
76 import TysWiredIn ( floatDataCon, doubleDataCon )
77 import PrelNames( fromIntegerName, fromRationalName, rationalTyConName )
78 import BasicTypes( IPName(..), mapIPName, ipNameName )
79 import UniqSupply( uniqsFromSupply )
87 instName :: Inst -> Name
88 instName inst = idName (instToId inst)
90 instToId :: Inst -> TcId
91 instToId (Dict id _ _) = id
92 instToId (Method id _ _ _ _ _) = id
93 instToId (LitInst id _ _ _) = id
95 instLoc (Dict _ _ loc) = loc
96 instLoc (Method _ _ _ _ _ loc) = loc
97 instLoc (LitInst _ _ _ loc) = loc
99 dictPred (Dict _ pred _ ) = pred
100 dictPred inst = pprPanic "dictPred" (ppr inst)
102 getDictClassTys (Dict _ pred _) = getClassPredTys pred
104 -- fdPredsOfInst is used to get predicates that contain functional
105 -- dependencies *or* might do so. The "might do" part is because
106 -- a constraint (C a b) might have a superclass with FDs
107 -- Leaving these in is really important for the call to fdPredsOfInsts
108 -- in TcSimplify.inferLoop, because the result is fed to 'grow',
109 -- which is supposed to be conservative
110 fdPredsOfInst (Dict _ pred _) = [pred]
111 fdPredsOfInst (Method _ _ _ theta _ _) = theta
112 fdPredsOfInst other = [] -- LitInsts etc
114 fdPredsOfInsts :: [Inst] -> [PredType]
115 fdPredsOfInsts insts = concatMap fdPredsOfInst insts
117 isInheritableInst (Dict _ pred _) = isInheritablePred pred
118 isInheritableInst (Method _ _ _ theta _ _) = all isInheritablePred theta
119 isInheritableInst other = True
122 ipNamesOfInsts :: [Inst] -> [Name]
123 ipNamesOfInst :: Inst -> [Name]
124 -- Get the implicit parameters mentioned by these Insts
125 -- NB: ?x and %x get different Names
126 ipNamesOfInsts insts = [n | inst <- insts, n <- ipNamesOfInst inst]
128 ipNamesOfInst (Dict _ (IParam n _) _) = [ipNameName n]
129 ipNamesOfInst (Method _ _ _ theta _ _) = [ipNameName n | IParam n _ <- theta]
130 ipNamesOfInst other = []
132 tyVarsOfInst :: Inst -> TcTyVarSet
133 tyVarsOfInst (LitInst _ _ ty _) = tyVarsOfType ty
134 tyVarsOfInst (Dict _ pred _) = tyVarsOfPred pred
135 tyVarsOfInst (Method _ id tys _ _ _) = tyVarsOfTypes tys `unionVarSet` idFreeTyVars id
136 -- The id might have free type variables; in the case of
137 -- locally-overloaded class methods, for example
140 tyVarsOfInsts insts = foldr (unionVarSet . tyVarsOfInst) emptyVarSet insts
141 tyVarsOfLIE lie = tyVarsOfInsts (lieToList lie)
147 isDict :: Inst -> Bool
148 isDict (Dict _ _ _) = True
151 isClassDict :: Inst -> Bool
152 isClassDict (Dict _ pred _) = isClassPred pred
153 isClassDict other = False
155 isTyVarDict :: Inst -> Bool
156 isTyVarDict (Dict _ pred _) = isTyVarClassPred pred
157 isTyVarDict other = False
159 isIPDict :: Inst -> Bool
160 isIPDict (Dict _ pred _) = isIPPred pred
161 isIPDict other = False
163 isMethod :: Inst -> Bool
164 isMethod (Method _ _ _ _ _ _) = True
165 isMethod other = False
167 isMethodFor :: TcIdSet -> Inst -> Bool
168 isMethodFor ids (Method uniq id tys _ _ loc) = id `elemVarSet` ids
169 isMethodFor ids inst = False
171 isLinearInst :: Inst -> Bool
172 isLinearInst (Dict _ pred _) = isLinearPred pred
173 isLinearInst other = False
174 -- We never build Method Insts that have
175 -- linear implicit paramters in them.
176 -- Hence no need to look for Methods
179 linearInstType :: Inst -> TcType -- %x::t --> t
180 linearInstType (Dict _ (IParam _ ty) _) = ty
183 isStdClassTyVarDict (Dict _ pred _) = case getClassPredTys_maybe pred of
184 Just (clas, [ty]) -> isStandardClass clas && tcIsTyVarTy ty
188 Two predicates which deal with the case where class constraints don't
189 necessarily result in bindings. The first tells whether an @Inst@
190 must be witnessed by an actual binding; the second tells whether an
191 @Inst@ can be generalised over.
194 instBindingRequired :: Inst -> Bool
195 instBindingRequired (Dict _ (ClassP clas _) _) = not (isNoDictClass clas)
196 instBindingRequired other = True
198 instCanBeGeneralised :: Inst -> Bool
199 instCanBeGeneralised (Dict _ (ClassP clas _) _) = not (isCcallishClass clas)
200 instCanBeGeneralised other = True
204 %************************************************************************
206 \subsection{Building dictionaries}
208 %************************************************************************
211 newDicts :: InstOrigin
215 = getInstLoc orig `thenM` \ loc ->
216 newDictsAtLoc loc theta
218 cloneDict :: Inst -> TcM Inst
219 cloneDict (Dict id ty loc) = newUnique `thenM` \ uniq ->
220 returnM (Dict (setIdUnique id uniq) ty loc)
222 newDictsFromOld :: Inst -> TcThetaType -> TcM [Inst]
223 newDictsFromOld (Dict _ _ loc) theta = newDictsAtLoc loc theta
225 -- Local function, similar to newDicts,
226 -- but with slightly different interface
227 newDictsAtLoc :: InstLoc
230 newDictsAtLoc inst_loc theta
231 = newUniqueSupply `thenM` \ us ->
232 returnM (zipWith mk_dict (uniqsFromSupply us) theta)
234 mk_dict uniq pred = Dict (mkLocalId (mkPredName uniq loc pred) (mkPredTy pred))
236 loc = instLocSrcLoc inst_loc
238 -- For vanilla implicit parameters, there is only one in scope
239 -- at any time, so we used to use the name of the implicit parameter itself
240 -- But with splittable implicit parameters there may be many in
241 -- scope, so we make up a new name.
242 newIPDict :: InstOrigin -> IPName Name -> Type
243 -> TcM (IPName Id, Inst)
244 newIPDict orig ip_name ty
245 = getInstLoc orig `thenM` \ inst_loc@(InstLoc _ loc _) ->
246 newUnique `thenM` \ uniq ->
248 pred = IParam ip_name ty
249 id = mkLocalId (mkPredName uniq loc pred) (mkPredTy pred)
251 returnM (mapIPName (\n -> id) ip_name, Dict id pred inst_loc)
256 %************************************************************************
258 \subsection{Building methods (calls of overloaded functions)}
260 %************************************************************************
264 tcInstCall :: InstOrigin -> TcType -> TcM (ExprCoFn, TcType)
265 tcInstCall orig fun_ty -- fun_ty is usually a sigma-type
266 = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) ->
267 newDicts orig theta `thenM` \ dicts ->
268 extendLIEs dicts `thenM_`
270 inst_fn e = mkHsDictApp (mkHsTyApp e (mkTyVarTys tyvars)) (map instToId dicts)
272 returnM (mkCoercion inst_fn, tau)
274 tcInstDataCon :: InstOrigin -> DataCon
275 -> TcM ([TcType], -- Types to instantiate at
276 [Inst], -- Existential dictionaries to apply to
277 [TcType], -- Argument types of constructor
278 TcType, -- Result type
279 [TyVar]) -- Existential tyvars
280 tcInstDataCon orig data_con
282 (tvs, stupid_theta, ex_tvs, ex_theta, arg_tys, tycon) = dataConSig data_con
283 -- We generate constraints for the stupid theta even when
284 -- pattern matching (as the Report requires)
286 tcInstTyVars VanillaTv (tvs ++ ex_tvs) `thenM` \ (all_tvs', ty_args', tenv) ->
288 stupid_theta' = substTheta tenv stupid_theta
289 ex_theta' = substTheta tenv ex_theta
290 arg_tys' = map (substTy tenv) arg_tys
292 n_normal_tvs = length tvs
293 ex_tvs' = drop n_normal_tvs all_tvs'
294 result_ty = mkTyConApp tycon (take n_normal_tvs ty_args')
296 newDicts orig stupid_theta' `thenM` \ stupid_dicts ->
297 newDicts orig ex_theta' `thenM` \ ex_dicts ->
299 -- Note that we return the stupid theta *only* in the LIE;
300 -- we don't otherwise use it at all
301 extendLIEs stupid_dicts `thenM_`
303 returnM (ty_args', ex_dicts, arg_tys', result_ty, ex_tvs')
305 newMethodFromName :: InstOrigin -> TcType -> Name -> TcM TcId
306 newMethodFromName origin ty name
307 = tcLookupId name `thenM` \ id ->
308 -- Use tcLookupId not tcLookupGlobalId; the method is almost
309 -- always a class op, but with -fno-implicit-prelude GHC is
310 -- meant to find whatever thing is in scope, and that may
311 -- be an ordinary function.
312 getInstLoc origin `thenM` \ loc ->
313 tcInstClassOp loc id [ty] `thenM` \ inst ->
314 extendLIE inst `thenM_`
315 returnM (instToId inst)
317 newMethodWithGivenTy orig id tys theta tau
318 = getInstLoc orig `thenM` \ loc ->
319 newMethod loc id tys theta tau `thenM` \ inst ->
320 extendLIE inst `thenM_`
321 returnM (instToId inst)
323 --------------------------------------------
324 -- tcInstClassOp, and newMethod do *not* drop the
325 -- Inst into the LIE; they just returns the Inst
326 -- This is important because they are used by TcSimplify
329 tcInstClassOp :: InstLoc -> Id -> [TcType] -> TcM Inst
330 tcInstClassOp inst_loc sel_id tys
332 (tyvars,rho) = tcSplitForAllTys (idType sel_id)
333 rho_ty = ASSERT( length tyvars == length tys )
334 substTyWith tyvars tys rho
335 (preds,tau) = tcSplitPhiTy rho_ty
337 newMethod inst_loc sel_id tys preds tau
339 ---------------------------
340 newMethod inst_loc id tys theta tau
341 = newUnique `thenM` \ new_uniq ->
343 meth_id = mkUserLocal (mkMethodOcc (getOccName id)) new_uniq tau loc
344 inst = Method meth_id id tys theta tau inst_loc
345 loc = instLocSrcLoc inst_loc
350 In newOverloadedLit we convert directly to an Int or Integer if we
351 know that's what we want. This may save some time, by not
352 temporarily generating overloaded literals, but it won't catch all
353 cases (the rest are caught in lookupInst).
356 newOverloadedLit :: InstOrigin
360 newOverloadedLit orig lit@(HsIntegral i fi) expected_ty
361 | fi /= fromIntegerName -- Do not generate a LitInst for rebindable
362 -- syntax. Reason: tcSyntaxName does unification
363 -- which is very inconvenient in tcSimplify
364 = tcSyntaxName orig expected_ty (fromIntegerName, HsVar fi) `thenM` \ (_,expr) ->
365 returnM (HsApp expr (HsLit (HsInteger i)))
367 | Just expr <- shortCutIntLit i expected_ty
371 = newLitInst orig lit expected_ty
373 newOverloadedLit orig lit@(HsFractional r fr) expected_ty
374 | fr /= fromRationalName -- c.f. HsIntegral case
375 = tcSyntaxName orig expected_ty (fromRationalName, HsVar fr) `thenM` \ (_,expr) ->
376 mkRatLit r `thenM` \ rat_lit ->
377 returnM (HsApp expr rat_lit)
379 | Just expr <- shortCutFracLit r expected_ty
383 = newLitInst orig lit expected_ty
385 newLitInst orig lit expected_ty
386 = getInstLoc orig `thenM` \ loc ->
387 newUnique `thenM` \ new_uniq ->
389 lit_inst = LitInst lit_id lit expected_ty loc
390 lit_id = mkSysLocal FSLIT("lit") new_uniq expected_ty
392 extendLIE lit_inst `thenM_`
393 returnM (HsVar (instToId lit_inst))
395 shortCutIntLit :: Integer -> TcType -> Maybe TcExpr
397 | isIntTy ty && inIntRange i -- Short cut for Int
398 = Just (HsLit (HsInt i))
399 | isIntegerTy ty -- Short cut for Integer
400 = Just (HsLit (HsInteger i))
401 | otherwise = Nothing
403 shortCutFracLit :: Rational -> TcType -> Maybe TcExpr
406 = Just (mkHsConApp floatDataCon [] [HsLit (HsFloatPrim f)])
408 = Just (mkHsConApp doubleDataCon [] [HsLit (HsDoublePrim f)])
409 | otherwise = Nothing
411 mkRatLit :: Rational -> TcM TcExpr
413 = tcLookupTyCon rationalTyConName `thenM` \ rat_tc ->
415 rational_ty = mkGenTyConApp rat_tc []
417 returnM (HsLit (HsRat r rational_ty))
421 %************************************************************************
425 %************************************************************************
427 Zonking makes sure that the instance types are fully zonked,
428 but doesn't do the same for any of the Ids in an Inst. There's no
429 need, and it's a lot of extra work.
432 zonkInst :: Inst -> TcM Inst
433 zonkInst (Dict id pred loc)
434 = zonkTcPredType pred `thenM` \ new_pred ->
435 returnM (Dict id new_pred loc)
437 zonkInst (Method m id tys theta tau loc)
438 = zonkId id `thenM` \ new_id ->
439 -- Essential to zonk the id in case it's a local variable
440 -- Can't use zonkIdOcc because the id might itself be
441 -- an InstId, in which case it won't be in scope
443 zonkTcTypes tys `thenM` \ new_tys ->
444 zonkTcThetaType theta `thenM` \ new_theta ->
445 zonkTcType tau `thenM` \ new_tau ->
446 returnM (Method m new_id new_tys new_theta new_tau loc)
448 zonkInst (LitInst id lit ty loc)
449 = zonkTcType ty `thenM` \ new_ty ->
450 returnM (LitInst id lit new_ty loc)
452 zonkInsts insts = mappM zonkInst insts
456 %************************************************************************
458 \subsection{Printing}
460 %************************************************************************
462 ToDo: improve these pretty-printing things. The ``origin'' is really only
463 relevant in error messages.
466 instance Outputable Inst where
467 ppr inst = pprInst inst
469 pprInsts :: [Inst] -> SDoc
470 pprInsts insts = parens (sep (punctuate comma (map pprInst insts)))
473 = vcat (map go insts)
475 go inst = sep [quotes (ppr inst), nest 2 (pprInstLoc (instLoc inst))]
477 pprInst (LitInst u lit ty loc)
478 = hsep [ppr lit, ptext SLIT("at"), ppr ty, show_uniq u]
480 pprInst (Dict u pred loc) = pprPred pred <+> show_uniq u
482 pprInst m@(Method u id tys theta tau loc)
483 = hsep [ppr id, ptext SLIT("at"),
484 brackets (sep (map pprParendType tys)) {- ,
485 ptext SLIT("theta"), ppr theta,
486 ptext SLIT("tau"), ppr tau
490 show_uniq u = ifPprDebug (text "{-" <> ppr u <> text "-}")
492 tidyInst :: TidyEnv -> Inst -> Inst
493 tidyInst env (LitInst u lit ty loc) = LitInst u lit (tidyType env ty) loc
494 tidyInst env (Dict u pred loc) = Dict u (tidyPred env pred) loc
495 tidyInst env (Method u id tys theta tau loc) = Method u id (tidyTypes env tys) theta tau loc
497 tidyMoreInsts :: TidyEnv -> [Inst] -> (TidyEnv, [Inst])
498 -- This function doesn't assume that the tyvars are in scope
499 -- so it works like tidyOpenType, returning a TidyEnv
500 tidyMoreInsts env insts
501 = (env', map (tidyInst env') insts)
503 env' = tidyFreeTyVars env (tyVarsOfInsts insts)
505 tidyInsts :: [Inst] -> (TidyEnv, [Inst])
506 tidyInsts insts = tidyMoreInsts emptyTidyEnv insts
508 showLIE :: SDoc -> TcM () -- Debugging
510 = do { lie_var <- getLIEVar ;
511 lie <- readMutVar lie_var ;
512 traceTc (str <+> pprInstsInFull (lieToList lie)) }
516 %************************************************************************
518 \subsection{Looking up Insts}
520 %************************************************************************
523 data LookupInstResult s
525 | SimpleInst TcExpr -- Just a variable, type application, or literal
526 | GenInst [Inst] TcExpr -- The expression and its needed insts
528 lookupInst :: Inst -> TcM (LookupInstResult s)
529 -- It's important that lookupInst does not put any new stuff into
530 -- the LIE. Instead, any Insts needed by the lookup are returned in
531 -- the LookupInstResult, where they can be further processed by tcSimplify
535 lookupInst dict@(Dict _ pred@(ClassP clas tys) loc)
536 = getDOpts `thenM` \ dflags ->
537 tcGetInstEnv `thenM` \ inst_env ->
538 case lookupInstEnv dflags inst_env clas tys of
540 FoundInst tenv dfun_id
541 -> -- It's possible that not all the tyvars are in
542 -- the substitution, tenv. For example:
543 -- instance C X a => D X where ...
544 -- (presumably there's a functional dependency in class C)
545 -- Hence the mk_ty_arg to instantiate any un-substituted tyvars.
546 getStage `thenM` \ use_stage ->
547 checkWellStaged (ptext SLIT("instance for") <+> quotes (ppr pred))
548 (topIdLvl dfun_id) use_stage `thenM_`
549 traceTc (text "lookupInst" <+> ppr dfun_id <+> ppr (topIdLvl dfun_id) <+> ppr use_stage) `thenM_`
551 (tyvars, rho) = tcSplitForAllTys (idType dfun_id)
552 mk_ty_arg tv = case lookupSubstEnv tenv tv of
553 Just (DoneTy ty) -> returnM ty
554 Nothing -> tcInstTyVar VanillaTv tv `thenM` \ tc_tv ->
555 returnM (mkTyVarTy tc_tv)
557 mappM mk_ty_arg tyvars `thenM` \ ty_args ->
559 dfun_rho = substTy (mkTyVarSubst tyvars ty_args) rho
560 (theta, _) = tcSplitPhiTy dfun_rho
561 ty_app = mkHsTyApp (HsVar dfun_id) ty_args
564 returnM (SimpleInst ty_app)
566 newDictsAtLoc loc theta `thenM` \ dicts ->
568 rhs = mkHsDictApp ty_app (map instToId dicts)
570 returnM (GenInst dicts rhs)
572 other -> returnM NoInstance
574 lookupInst (Dict _ _ _) = returnM NoInstance
578 lookupInst inst@(Method _ id tys theta _ loc)
579 = newDictsAtLoc loc theta `thenM` \ dicts ->
580 returnM (GenInst dicts (mkHsDictApp (mkHsTyApp (HsVar id) tys) (map instToId dicts)))
584 -- Look for short cuts first: if the literal is *definitely* a
585 -- int, integer, float or a double, generate the real thing here.
586 -- This is essential (see nofib/spectral/nucleic).
587 -- [Same shortcut as in newOverloadedLit, but we
588 -- may have done some unification by now]
591 lookupInst inst@(LitInst u (HsIntegral i from_integer_name) ty loc)
592 | Just expr <- shortCutIntLit i ty
593 = returnM (GenInst [] expr) -- GenInst, not SimpleInst, because
594 -- expr may be a constructor application
596 = ASSERT( from_integer_name == fromIntegerName ) -- A LitInst invariant
597 tcLookupId fromIntegerName `thenM` \ from_integer ->
598 tcInstClassOp loc from_integer [ty] `thenM` \ method_inst ->
599 returnM (GenInst [method_inst]
600 (HsApp (HsVar (instToId method_inst)) (HsLit (HsInteger i))))
603 lookupInst inst@(LitInst u (HsFractional f from_rat_name) ty loc)
604 | Just expr <- shortCutFracLit f ty
605 = returnM (GenInst [] expr)
608 = ASSERT( from_rat_name == fromRationalName ) -- A LitInst invariant
609 tcLookupId fromRationalName `thenM` \ from_rational ->
610 tcInstClassOp loc from_rational [ty] `thenM` \ method_inst ->
611 mkRatLit f `thenM` \ rat_lit ->
612 returnM (GenInst [method_inst] (HsApp (HsVar (instToId method_inst)) rat_lit))
617 %************************************************************************
621 %************************************************************************
624 Suppose we are doing the -fno-implicit-prelude thing, and we encounter
625 a do-expression. We have to find (>>) in the current environment, which is
626 done by the rename. Then we have to check that it has the same type as
627 Control.Monad.(>>). Or, more precisely, a compatible type. One 'customer' had
630 (>>) :: HB m n mn => m a -> n b -> mn b
632 So the idea is to generate a local binding for (>>), thus:
634 let then72 :: forall a b. m a -> m b -> m b
635 then72 = ...something involving the user's (>>)...
637 ...the do-expression...
639 Now the do-expression can proceed using then72, which has exactly
642 In fact tcSyntaxName just generates the RHS for then72, because we only
643 want an actual binding in the do-expression case. For literals, we can
644 just use the expression inline.
647 tcSyntaxName :: InstOrigin
648 -> TcType -- Type to instantiate it at
649 -> (Name, HsExpr Name) -- (Standard name, user name)
650 -> TcM (Name, TcExpr) -- (Standard name, suitable expression)
652 -- NB: tcSyntaxName calls tcExpr, and hence can do unification.
653 -- So we do not call it from lookupInst, which is called from tcSimplify
655 tcSyntaxName orig ty (std_nm, HsVar user_nm)
657 = tcStdSyntaxName orig ty std_nm
659 tcSyntaxName orig ty (std_nm, user_nm_expr)
660 = tcLookupId std_nm `thenM` \ std_id ->
662 -- C.f. newMethodAtLoc
663 ([tv], _, tau) = tcSplitSigmaTy (idType std_id)
664 tau1 = substTyWith [tv] [ty] tau
665 -- Actually, the "tau-type" might be a sigma-type in the
666 -- case of locally-polymorphic methods.
668 addErrCtxtM (syntaxNameCtxt user_nm_expr orig tau1) $
669 tcCheckSigma user_nm_expr tau1 `thenM` \ expr ->
670 returnM (std_nm, expr)
672 tcStdSyntaxName :: InstOrigin
673 -> TcType -- Type to instantiate it at
674 -> Name -- Standard name
675 -> TcM (Name, TcExpr) -- (Standard name, suitable expression)
677 tcStdSyntaxName orig ty std_nm
678 = newMethodFromName orig ty std_nm `thenM` \ id ->
679 returnM (std_nm, HsVar id)
681 syntaxNameCtxt name orig ty tidy_env
682 = getInstLoc orig `thenM` \ inst_loc ->
684 msg = vcat [ptext SLIT("When checking that") <+> quotes (ppr name) <+>
685 ptext SLIT("(needed by a syntactic construct)"),
686 nest 2 (ptext SLIT("has the required type:") <+> ppr (tidyType tidy_env ty)),
687 nest 2 (pprInstLoc inst_loc)]
689 returnM (tidy_env, msg)