1 Normalisation of type terms relative to type instances as well as
2 normalisation and entailment checking of equality constraints.
6 -- type normalisation wrt to toplevel equalities only
9 -- instance normalisation wrt to equalities
13 misMatchMsg, failWithMisMatch,
18 #include "HsVersions.h"
30 import TypeRep ( Type(..) )
39 import SrcLoc ( Located(..) )
49 %************************************************************************
51 Normalisation of types wrt toplevel equality schemata
53 %************************************************************************
55 Unfold a single synonym family instance and yield the witnessing coercion.
56 Return 'Nothing' if the given type is either not synonym family instance
57 or is a synonym family instance that has no matching instance declaration.
58 (Applies only if the type family application is outermost.)
60 For example, if we have
62 :Co:R42T a :: T [a] ~ :R42T a
64 then 'T [Int]' unfolds to (:R42T Int, :Co:R42T Int).
67 tcUnfoldSynFamInst :: Type -> TcM (Maybe (Type, Coercion))
68 tcUnfoldSynFamInst (TyConApp tycon tys)
69 | not (isOpenSynTyCon tycon) -- unfold *only* _synonym_ family instances
72 = do { -- we only use the indexing arguments for matching,
73 -- not the additional ones
74 ; maybeFamInst <- tcLookupFamInst tycon idxTys
75 ; case maybeFamInst of
76 Nothing -> return Nothing
77 Just (rep_tc, rep_tys) -> return $ Just (mkTyConApp rep_tc tys',
78 mkTyConApp coe_tc tys')
80 tys' = rep_tys ++ restTys
81 coe_tc = expectJust "TcTyFuns.tcUnfoldSynFamInst"
82 (tyConFamilyCoercion_maybe rep_tc)
86 (idxTys, restTys) = splitAt n tys
87 tcUnfoldSynFamInst _other = return Nothing
90 Normalise 'Type's and 'PredType's by unfolding type family applications where
91 possible (ie, we treat family instances as a TRS). Also zonk meta variables.
93 tcNormaliseFamInst ty = (co, ty')
97 -- |Normalise the given type as far as possible with toplevel equalities.
98 -- This results in a coercion witnessing the type equality, in addition to the
101 tcNormaliseFamInst :: TcType -> TcM (CoercionI, TcType)
102 tcNormaliseFamInst = tcGenericNormaliseFamInst tcUnfoldSynFamInst
105 Generic normalisation of 'Type's and 'PredType's; ie, walk the type term and
106 apply the normalisation function gives as the first argument to every TyConApp
107 and every TyVarTy subterm.
109 tcGenericNormaliseFamInst fun ty = (co, ty')
112 This function is (by way of using smart constructors) careful to ensure that
113 the returned coercion is exactly IdCo (and not some semantically equivalent,
114 but syntactically different coercion) whenever (ty' `tcEqType` ty). This
115 makes it easy for the caller to determine whether the type changed. BUT
116 even if we return IdCo, ty' may be *syntactically* different from ty due to
117 unfolded closed type synonyms (by way of tcCoreView). In the interest of
118 good error messages, callers should discard ty' in favour of ty in this case.
121 tcGenericNormaliseFamInst :: (TcType -> TcM (Maybe (TcType, Coercion)))
122 -- what to do with type functions and tyvars
123 -> TcType -- old type
124 -> TcM (CoercionI, TcType) -- (coercion, new type)
125 tcGenericNormaliseFamInst fun ty
126 | Just ty' <- tcView ty = tcGenericNormaliseFamInst fun ty'
127 tcGenericNormaliseFamInst fun (TyConApp tyCon tys)
128 = do { (cois, ntys) <- mapAndUnzipM (tcGenericNormaliseFamInst fun) tys
129 ; let tycon_coi = mkTyConAppCoI tyCon ntys cois
130 ; maybe_ty_co <- fun (mkTyConApp tyCon ntys) -- use normalised args!
131 ; case maybe_ty_co of
132 -- a matching family instance exists
134 do { let first_coi = mkTransCoI tycon_coi (ACo co)
135 ; (rest_coi, nty) <- tcGenericNormaliseFamInst fun ty'
136 ; let fix_coi = mkTransCoI first_coi rest_coi
137 ; return (fix_coi, nty)
139 -- no matching family instance exists
140 -- we do not do anything
141 Nothing -> return (tycon_coi, mkTyConApp tyCon ntys)
143 tcGenericNormaliseFamInst fun (AppTy ty1 ty2)
144 = do { (coi1,nty1) <- tcGenericNormaliseFamInst fun ty1
145 ; (coi2,nty2) <- tcGenericNormaliseFamInst fun ty2
146 ; return (mkAppTyCoI nty1 coi1 nty2 coi2, mkAppTy nty1 nty2)
148 tcGenericNormaliseFamInst fun (FunTy ty1 ty2)
149 = do { (coi1,nty1) <- tcGenericNormaliseFamInst fun ty1
150 ; (coi2,nty2) <- tcGenericNormaliseFamInst fun ty2
151 ; return (mkFunTyCoI nty1 coi1 nty2 coi2, mkFunTy nty1 nty2)
153 tcGenericNormaliseFamInst fun (ForAllTy tyvar ty1)
154 = do { (coi,nty1) <- tcGenericNormaliseFamInst fun ty1
155 ; return (mkForAllTyCoI tyvar coi, mkForAllTy tyvar nty1)
157 tcGenericNormaliseFamInst fun ty@(TyVarTy tv)
159 = do { traceTc (text "tcGenericNormaliseFamInst" <+> ppr ty)
160 ; res <- lookupTcTyVar tv
163 do { maybe_ty' <- fun ty
165 Nothing -> return (IdCo, ty)
167 do { (coi2, ty'') <- tcGenericNormaliseFamInst fun ty'
168 ; return (ACo co1 `mkTransCoI` coi2, ty'')
171 IndirectTv ty' -> tcGenericNormaliseFamInst fun ty'
175 tcGenericNormaliseFamInst fun (PredTy predty)
176 = do { (coi, pred') <- tcGenericNormaliseFamInstPred fun predty
177 ; return (coi, PredTy pred') }
179 ---------------------------------
180 tcGenericNormaliseFamInstPred :: (TcType -> TcM (Maybe (TcType,Coercion)))
182 -> TcM (CoercionI, TcPredType)
184 tcGenericNormaliseFamInstPred fun (ClassP cls tys)
185 = do { (cois, tys')<- mapAndUnzipM (tcGenericNormaliseFamInst fun) tys
186 ; return (mkClassPPredCoI cls tys' cois, ClassP cls tys')
188 tcGenericNormaliseFamInstPred fun (IParam ipn ty)
189 = do { (coi, ty') <- tcGenericNormaliseFamInst fun ty
190 ; return $ (mkIParamPredCoI ipn coi, IParam ipn ty')
192 tcGenericNormaliseFamInstPred fun (EqPred ty1 ty2)
193 = do { (coi1, ty1') <- tcGenericNormaliseFamInst fun ty1
194 ; (coi2, ty2') <- tcGenericNormaliseFamInst fun ty2
195 ; return (mkEqPredCoI ty1' coi1 ty2' coi2, EqPred ty1' ty2') }
199 %************************************************************************
201 Normalisation of instances wrt to equalities
203 %************************************************************************
206 tcReduceEqs :: [Inst] -- locals
208 -> TcM ([Inst], -- normalised locals (w/o equalities)
209 [Inst], -- normalised wanteds (including equalities)
210 TcDictBinds, -- bindings for all simplified dictionaries
211 Bool) -- whether any flexibles where instantiated
212 tcReduceEqs locals wanteds
213 = do { let (local_eqs , local_dicts) = partition isEqInst locals
214 (wanteds_eqs, wanteds_dicts) = partition isEqInst wanteds
215 ; eqCfg1 <- normaliseEqs (local_eqs ++ wanteds_eqs)
216 ; eqCfg2 <- normaliseDicts False local_dicts
217 ; eqCfg3 <- normaliseDicts True wanteds_dicts
218 ; eqCfg <- propagateEqs (eqCfg1 `unionEqConfig` eqCfg2
219 `unionEqConfig` eqCfg3)
220 ; finaliseEqsAndDicts eqCfg
225 %************************************************************************
227 Equality Configurations
229 %************************************************************************
231 We maintain normalised equalities together with the skolems introduced as
232 intermediates during flattening of equalities as well as
234 !!!TODO: We probably now can do without the skolem set. It's not used during
235 finalisation in the current code.
238 -- |Configuration of normalised equalities used during solving.
240 data EqConfig = EqConfig { eqs :: [RewriteInst] -- all equalities
241 , locals :: [Inst] -- given dicts
242 , wanteds :: [Inst] -- wanted dicts
243 , binds :: TcDictBinds -- bindings
244 , skolems :: TyVarSet -- flattening skolems
247 addSkolems :: EqConfig -> TyVarSet -> EqConfig
248 addSkolems eqCfg newSkolems
249 = eqCfg {skolems = skolems eqCfg `unionVarSet` newSkolems}
251 addEq :: EqConfig -> RewriteInst -> EqConfig
252 addEq eqCfg eq = eqCfg {eqs = eq : eqs eqCfg}
254 unionEqConfig :: EqConfig -> EqConfig -> EqConfig
255 unionEqConfig eqc1 eqc2 = EqConfig
256 { eqs = eqs eqc1 ++ eqs eqc2
257 , locals = locals eqc1 ++ locals eqc2
258 , wanteds = wanteds eqc1 ++ wanteds eqc2
259 , binds = binds eqc1 `unionBags` binds eqc2
260 , skolems = skolems eqc1 `unionVarSet` skolems eqc2
263 emptyEqConfig :: EqConfig
264 emptyEqConfig = EqConfig
269 , skolems = emptyVarSet
272 instance Outputable EqConfig where
273 ppr (EqConfig {eqs = eqs, locals = locals, wanteds = wanteds, binds = binds})
274 = vcat [ppr eqs, ppr locals, ppr wanteds, ppr binds]
277 The set of operations on an equality configuration. We obtain the initialise
278 configuration by normalisation ('normaliseEqs'), solve the equalities by
279 propagation ('propagateEqs'), and eventually finalise the configuration when
280 no further propoagation is possible.
283 -- |Turn a set of equalities into an equality configuration for solving.
285 -- Precondition: The Insts are zonked.
287 normaliseEqs :: [Inst] -> TcM EqConfig
289 = do { ASSERTM2( allM isValidWantedEqInst eqs, ppr eqs )
290 ; traceTc $ ptext (sLit "Entering normaliseEqs")
292 ; (eqss, skolemss) <- mapAndUnzipM normEqInst eqs
293 ; return $ emptyEqConfig { eqs = concat eqss
294 , skolems = unionVarSets skolemss
298 -- |Flatten the type arguments of all dictionaries, returning the result as a
299 -- equality configuration. The dictionaries go into the 'wanted' component if
300 -- the second argument is 'True'.
302 -- Precondition: The Insts are zonked.
304 normaliseDicts :: Bool -> [Inst] -> TcM EqConfig
305 normaliseDicts isWanted insts
306 = do { traceTc $ ptext (sLit "Entering normaliseDicts") <+>
307 ptext (if isWanted then sLit "[Wanted]" else sLit "[Local]")
308 ; (insts', eqss, bindss, skolemss) <- mapAndUnzip4M (normDict isWanted)
310 ; return $ emptyEqConfig { eqs = concat eqss
311 , locals = if isWanted then [] else insts'
312 , wanteds = if isWanted then insts' else []
313 , binds = unionManyBags bindss
314 , skolems = unionVarSets skolemss
318 -- |Solves the equalities as far as possible by applying propagation rules.
320 propagateEqs :: EqConfig -> TcM EqConfig
321 propagateEqs eqCfg@(EqConfig {eqs = todoEqs})
322 = do { traceTc $ hang (ptext (sLit "Entering propagateEqs:"))
325 ; propagate todoEqs (eqCfg {eqs = []})
328 -- |Finalise a set of equalities and associated dictionaries after
329 -- propagation. The returned Boolean value is `True' iff any flexible
330 -- variables, except those introduced by flattening (i.e., those in the
331 -- `skolems' component of the argument) where instantiated. The first returned
332 -- set of instances are the locals (without equalities) and the second set are
333 -- all residual wanteds, including equalities.
335 finaliseEqsAndDicts :: EqConfig
336 -> TcM ([Inst], [Inst], TcDictBinds, Bool)
337 finaliseEqsAndDicts (EqConfig { eqs = eqs
343 = do { traceTc $ ptext (sLit "finaliseEqsAndDicts")
344 ; (eqs', subst_binds, locals', wanteds') <- substitute eqs locals wanteds
345 ; (eqs'', improved) <- instantiateAndExtract eqs' (null locals) skolems
346 ; let final_binds = subst_binds `unionBags` binds
348 -- Assert that all cotvs of wanted equalities are still unfilled, and
349 -- zonk all final insts, to make any improvement visible
350 ; ASSERTM2( allM isValidWantedEqInst eqs'', ppr eqs'' )
351 ; zonked_locals <- zonkInsts locals'
352 ; zonked_wanteds <- zonkInsts (eqs'' ++ wanteds')
353 ; return (zonked_locals, zonked_wanteds, final_binds, improved)
358 %************************************************************************
360 Normalisation of equalities
362 %************************************************************************
364 A normal equality is a properly oriented equality with associated coercion
365 that contains at most one family equality (in its left-hand side) is oriented
366 such that it may be used as a reqrite rule. It has one of the following two
369 (1) co :: F t1..tn ~ t (family equalities)
370 (2) co :: x ~ t (variable equalities)
372 Variable equalities fall again in two classes:
374 (2a) co :: x ~ t, where t is *not* a variable, or
375 (2b) co :: x ~ y, where x > y.
377 The types t, t1, ..., tn may not contain any occurrences of synonym
378 families. Moreover, in Forms (2) & (3), the left-hand side may not occur in
379 the right-hand side, and the relation x > y is an arbitrary, but total order
382 !!!TODO: We may need to keep track of swapping for error messages (and to
383 re-orient on finilisation).
387 = RewriteVar -- Form (2) above
388 { rwi_var :: TyVar -- may be rigid or flexible
389 , rwi_right :: TcType -- contains no synonym family applications
390 , rwi_co :: EqInstCo -- the wanted or given coercion
392 , rwi_name :: Name -- no semantic significance (cf. TcRnTypes.EqInst)
393 , rwi_swapped :: Bool -- swapped orientation of original EqInst
395 | RewriteFam -- Forms (1) above
396 { rwi_fam :: TyCon -- synonym family tycon
397 , rwi_args :: [Type] -- contain no synonym family applications
398 , rwi_right :: TcType -- contains no synonym family applications
399 , rwi_co :: EqInstCo -- the wanted or given coercion
401 , rwi_name :: Name -- no semantic significance (cf. TcRnTypes.EqInst)
402 , rwi_swapped :: Bool -- swapped orientation of original EqInst
405 isWantedRewriteInst :: RewriteInst -> Bool
406 isWantedRewriteInst = isWantedCo . rwi_co
408 rewriteInstToInst :: RewriteInst -> TcM Inst
409 rewriteInstToInst eq@(RewriteVar {rwi_var = tv})
410 = deriveEqInst eq (mkTyVarTy tv) (rwi_right eq) (rwi_co eq)
411 rewriteInstToInst eq@(RewriteFam {rwi_fam = fam, rwi_args = args})
412 = deriveEqInst eq (mkTyConApp fam args) (rwi_right eq) (rwi_co eq)
414 -- Derive an EqInst based from a RewriteInst, possibly swapping the types
417 deriveEqInst :: RewriteInst -> TcType -> TcType -> EqInstCo -> TcM Inst
418 deriveEqInst rewrite ty1 ty2 co
419 = do { co_adjusted <- if not swapped then return co
420 else mkSymEqInstCo co (ty2, ty1)
424 , tci_co = co_adjusted
425 , tci_loc = rwi_loc rewrite
426 , tci_name = rwi_name rewrite
430 swapped = rwi_swapped rewrite
431 (left, right) = if not swapped then (ty1, ty2) else (ty2, ty1)
433 instance Outputable RewriteInst where
434 ppr (RewriteFam {rwi_fam = fam, rwi_args = args, rwi_right = rhs, rwi_co =co})
435 = hsep [ pprEqInstCo co <+> text "::"
436 , ppr (mkTyConApp fam args)
440 ppr (RewriteVar {rwi_var = tv, rwi_right = rhs, rwi_co =co})
441 = hsep [ pprEqInstCo co <+> text "::"
447 pprEqInstCo :: EqInstCo -> SDoc
448 pprEqInstCo (Left cotv) = ptext (sLit "Wanted") <+> ppr cotv
449 pprEqInstCo (Right co) = ptext (sLit "Local") <+> ppr co
452 The following functions turn an arbitrary equality into a set of normal
453 equalities. This implements the WFlat and LFlat rules of the paper in one
454 sweep. However, we use flexible variables for both locals and wanteds, and
455 avoid to carry around the unflattening substitution \Sigma (for locals) by
456 already updating the skolems for locals with the family application that they
457 represent - i.e., they will turn into that family application on the next
458 zonking (which only happens after finalisation).
460 In a corresponding manner, normDict normalises class dictionaries by
461 extracting any synonym family applications and generation appropriate normal
464 Whenever we encounter a loopy equality (of the form a ~ T .. (F ...a...) ...),
465 we drop that equality and raise an error if it is a wanted or a warning if it
469 normEqInst :: Inst -> TcM ([RewriteInst], TyVarSet)
470 -- Normalise one equality.
472 = ASSERT( isEqInst inst )
473 go ty1 ty2 (eqInstCoercion inst)
475 (ty1, ty2) = eqInstTys inst
477 -- look through synonyms
478 go ty1 ty2 co | Just ty1' <- tcView ty1 = go ty1' ty2 co
479 go ty1 ty2 co | Just ty2' <- tcView ty2 = go ty1 ty2' co
481 -- left-to-right rule with type family head
482 go (TyConApp con args) ty2 co
484 = mkRewriteFam False con args ty2 co
486 -- right-to-left rule with type family head
487 go ty1 ty2@(TyConApp con args) co
489 = do { co' <- mkSymEqInstCo co (ty2, ty1)
490 ; mkRewriteFam True con args ty1 co'
493 -- no outermost family
495 = do { (ty1', co1, ty1_eqs, ty1_skolems) <- flattenType inst ty1
496 ; (ty2', co2, ty2_eqs, ty2_skolems) <- flattenType inst ty2
497 ; let ty12_eqs = ty1_eqs ++ ty2_eqs
498 sym_co2 = mkSymCoercion co2
500 ; (co', ty12_eqs') <- adjustCoercions co co1 sym_co2 eqTys ty12_eqs
501 ; eqs <- checkOrientation ty1' ty2' co' inst
502 ; if isLoopyEquality eqs ty12_eqs'
503 then do { if isWantedCo (tci_co inst)
505 addErrCtxt (ptext (sLit "Rejecting loopy equality")) $
508 warnDroppingLoopyEquality ty1 ty2
509 ; return ([], emptyVarSet) -- drop the equality
512 return (eqs ++ ty12_eqs',
513 ty1_skolems `unionVarSet` ty2_skolems)
516 mkRewriteFam swapped con args ty2 co
517 = do { (args', cargs, args_eqss, args_skolemss)
518 <- mapAndUnzip4M (flattenType inst) args
519 ; (ty2', co2, ty2_eqs, ty2_skolems) <- flattenType inst ty2
520 ; let co1 = mkTyConApp con cargs
521 sym_co2 = mkSymCoercion co2
522 all_eqs = concat args_eqss ++ ty2_eqs
523 eqTys = (mkTyConApp con args', ty2')
524 ; (co', all_eqs') <- adjustCoercions co co1 sym_co2 eqTys all_eqs
525 ; let thisRewriteFam = RewriteFam
530 , rwi_loc = tci_loc inst
531 , rwi_name = tci_name inst
532 , rwi_swapped = swapped
534 ; return $ (thisRewriteFam : all_eqs',
535 unionVarSets (ty2_skolems:args_skolemss))
538 -- If the original equality has the form a ~ T .. (F ...a...) ..., we will
539 -- have a variable equality with 'a' on the lhs as the first equality.
540 -- Then, check whether 'a' occurs in the lhs of any family equality
541 -- generated by flattening.
542 isLoopyEquality (RewriteVar {rwi_var = tv}:_) eqs
543 = any inRewriteFam eqs
545 inRewriteFam (RewriteFam {rwi_args = args})
546 = tv `elemVarSet` tyVarsOfTypes args
547 inRewriteFam _ = False
548 isLoopyEquality _ _ = False
550 normDict :: Bool -> Inst -> TcM (Inst, [RewriteInst], TcDictBinds, TyVarSet)
551 -- Normalise one dictionary or IP constraint.
552 normDict isWanted inst@(Dict {tci_pred = ClassP clas args})
553 = do { (args', cargs, args_eqss, args_skolemss)
554 <- mapAndUnzip4M (flattenType inst) args
555 ; let rewriteCo = PredTy $ ClassP clas cargs
556 eqs = concat args_eqss
557 pred' = ClassP clas args'
559 then -- don't generate a binding if there is nothing to flatten
560 return (inst, [], emptyBag, emptyVarSet)
562 ; (inst', bind) <- mkDictBind inst isWanted rewriteCo pred'
563 ; eqs' <- if isWanted then return eqs else mapM wantedToLocal eqs
564 ; return (inst', eqs', bind, unionVarSets args_skolemss)
566 normDict _isWanted inst
567 = return (inst, [], emptyBag, emptyVarSet)
568 -- !!!TODO: Still need to normalise IP constraints.
570 checkOrientation :: Type -> Type -> EqInstCo -> Inst -> TcM [RewriteInst]
571 -- Performs the occurs check, decomposition, and proper orientation
572 -- (returns a singleton, or an empty list in case of a trivial equality)
573 -- NB: We cannot assume that the two types already have outermost type
574 -- synonyms expanded due to the recursion in the case of type applications.
575 checkOrientation ty1 ty2 co inst
576 = do { traceTc $ ptext (sLit "checkOrientation of ") <+>
577 pprEqInstCo co <+> text "::" <+>
578 ppr ty1 <+> text "~" <+> ppr ty2
580 ; traceTc $ ptext (sLit "checkOrientation returns") <+> ppr eqs
584 -- look through synonyms
585 go ty1 ty2 | Just ty1' <- tcView ty1 = go ty1' ty2
586 go ty1 ty2 | Just ty2' <- tcView ty2 = go ty1 ty2'
588 -- identical types => trivial
591 = do { mkIdEqInstCo co ty1
595 -- two tvs, left greater => unchanged
596 go ty1@(TyVarTy tv1) ty2@(TyVarTy tv2)
598 = mkRewriteVar False tv1 ty2 co
600 -- two tvs, right greater => swap
602 = do { co' <- mkSymEqInstCo co (ty2, ty1)
603 ; mkRewriteVar True tv2 ty1 co'
606 -- only lhs is a tv => unchanged
607 go ty1@(TyVarTy tv1) ty2
608 | ty1 `tcPartOfType` ty2 -- occurs check!
609 = occurCheckErr ty1 ty2
611 = mkRewriteVar False tv1 ty2 co
613 -- only rhs is a tv => swap
614 go ty1 ty2@(TyVarTy tv2)
615 | ty2 `tcPartOfType` ty1 -- occurs check!
616 = occurCheckErr ty2 ty1
618 = do { co' <- mkSymEqInstCo co (ty2, ty1)
619 ; mkRewriteVar True tv2 ty1 co'
622 -- type applications => decompose
624 | Just (ty1_l, ty1_r) <- repSplitAppTy_maybe ty1 -- won't split fam apps
625 , Just (ty2_l, ty2_r) <- repSplitAppTy_maybe ty2
626 = do { (co_l, co_r) <- mkAppEqInstCo co (ty1_l, ty2_l) (ty1_r, ty2_r)
627 ; eqs_l <- checkOrientation ty1_l ty2_l co_l inst
628 ; eqs_r <- checkOrientation ty1_r ty2_r co_r inst
629 ; return $ eqs_l ++ eqs_r
631 -- !!!TODO: would be more efficient to handle the FunApp and the data
632 -- constructor application explicitly.
634 -- inconsistency => type error
636 = ASSERT( (not . isForAllTy $ ty1) && (not . isForAllTy $ ty2) )
639 mkRewriteVar swapped tv ty co = return [RewriteVar
643 , rwi_loc = tci_loc inst
644 , rwi_name = tci_name inst
645 , rwi_swapped = swapped
648 flattenType :: Inst -- context to get location & name
649 -> Type -- the type to flatten
650 -> TcM (Type, -- the flattened type
651 Coercion, -- coercion witness of flattening wanteds
652 [RewriteInst], -- extra equalities
653 TyVarSet) -- new intermediate skolems
654 -- Removes all family synonyms from a type by moving them into extra equalities
658 -- look through synonyms
659 go ty | Just ty' <- tcView ty
660 = do { (ty_flat, co, eqs, skolems) <- go ty'
662 then -- unchanged, keep the old type with folded synonyms
663 return (ty, ty, [], emptyVarSet)
665 return (ty_flat, co, eqs, skolems)
668 -- type variable => nothing to do
670 = return (ty, ty, [] , emptyVarSet)
672 -- type family application
673 -- => flatten to "gamma :: F t1'..tn' ~ alpha" (alpha & gamma fresh)
674 go ty@(TyConApp con args)
676 = do { (args', cargs, args_eqss, args_skolemss) <- mapAndUnzip4M go args
677 ; alpha <- newFlexiTyVar (typeKind ty)
678 ; let alphaTy = mkTyVarTy alpha
679 ; cotv <- newMetaCoVar (mkTyConApp con args') alphaTy
680 ; let thisRewriteFam = RewriteFam
683 , rwi_right = alphaTy
684 , rwi_co = mkWantedCo cotv
685 , rwi_loc = tci_loc inst
686 , rwi_name = tci_name inst
690 mkTyConApp con cargs `mkTransCoercion` mkTyVarTy cotv,
691 thisRewriteFam : concat args_eqss,
692 unionVarSets args_skolemss `extendVarSet` alpha)
693 } -- adding new unflatten var inst
695 -- data constructor application => flatten subtypes
696 -- NB: Special cased for efficiency - could be handled as type application
697 go ty@(TyConApp con args)
698 = do { (args', cargs, args_eqss, args_skolemss) <- mapAndUnzip4M go args
700 then -- unchanged, keep the old type with folded synonyms
701 return (ty, ty, [], emptyVarSet)
703 return (mkTyConApp con args',
704 mkTyConApp con cargs,
706 unionVarSets args_skolemss)
709 -- function type => flatten subtypes
710 -- NB: Special cased for efficiency - could be handled as type application
711 go ty@(FunTy ty_l ty_r)
712 = do { (ty_l', co_l, eqs_l, skolems_l) <- go ty_l
713 ; (ty_r', co_r, eqs_r, skolems_r) <- go ty_r
714 ; if null eqs_l && null eqs_r
715 then -- unchanged, keep the old type with folded synonyms
716 return (ty, ty, [], emptyVarSet)
718 return (mkFunTy ty_l' ty_r',
721 skolems_l `unionVarSet` skolems_r)
724 -- type application => flatten subtypes
725 go ty@(AppTy ty_l ty_r)
726 = do { (ty_l', co_l, eqs_l, skolems_l) <- go ty_l
727 ; (ty_r', co_r, eqs_r, skolems_r) <- go ty_r
728 ; if null eqs_l && null eqs_r
729 then -- unchanged, keep the old type with folded synonyms
730 return (ty, ty, [], emptyVarSet)
732 return (mkAppTy ty_l' ty_r',
735 skolems_l `unionVarSet` skolems_r)
738 -- forall type => panic if the body contains a type family
739 -- !!!TODO: As long as the family does not contain a quantified variable
740 -- we might pull it out, but what if it does contain a quantified
742 go ty@(ForAllTy _ body)
743 | null (tyFamInsts body)
744 = return (ty, ty, [] , emptyVarSet)
746 = panic "TcTyFuns.flattenType: synonym family in a rank-n type"
748 -- we should never see a predicate type
750 = panic "TcTyFuns.flattenType: unexpected PredType"
752 adjustCoercions :: EqInstCo -- coercion of original equality
753 -> Coercion -- coercion witnessing the left rewrite
754 -> Coercion -- coercion witnessing the right rewrite
755 -> (Type, Type) -- types of flattened equality
756 -> [RewriteInst] -- equalities from flattening
757 -> TcM (EqInstCo, -- coercion for flattened equality
758 [RewriteInst]) -- final equalities from flattening
759 -- Depending on whether we flattened a local or wanted equality, that equality's
760 -- coercion and that of the new equalities produced during flattening are
762 adjustCoercions (Left cotv) co1 co2 (ty_l, ty_r) all_eqs
763 -- wanted => generate a fresh coercion variable for the flattened equality
764 = do { cotv' <- newMetaCoVar ty_l ty_r
765 ; writeMetaTyVar cotv $
766 (co1 `mkTransCoercion` TyVarTy cotv' `mkTransCoercion` co2)
767 ; return (Left cotv', all_eqs)
770 adjustCoercions co@(Right _) _co1 _co2 _eqTys all_eqs
771 -- local => turn all new equalities into locals and update (but not zonk)
773 = do { all_eqs' <- mapM wantedToLocal all_eqs
774 ; return (co, all_eqs')
777 mkDictBind :: Inst -- original instance
778 -> Bool -- is this a wanted contraint?
779 -> Coercion -- coercion witnessing the rewrite
780 -> PredType -- coerced predicate
781 -> TcM (Inst, -- new inst
782 TcDictBinds) -- binding for coerced dictionary
783 mkDictBind dict isWanted rewriteCo pred
784 = do { dict' <- newDictBndr loc pred
785 -- relate the old inst to the new one
786 -- target_dict = source_dict `cast` st_co
787 ; let (target_dict, source_dict, st_co)
788 | isWanted = (dict, dict', mkSymCoercion rewriteCo)
789 | otherwise = (dict', dict, rewriteCo)
791 -- co :: dict ~ dict'
792 -- hence, if isWanted
793 -- dict = dict' `cast` sym co
795 -- dict' = dict `cast` co
796 expr = HsVar $ instToId source_dict
797 cast_expr = HsWrap (WpCast st_co) expr
798 rhs = L (instLocSpan loc) cast_expr
799 binds = instToDictBind target_dict rhs
800 ; return (dict', binds)
805 -- gamma :: Fam args ~ alpha
806 -- => alpha :: Fam args ~ alpha, with alpha := Fam args
807 -- (the update of alpha will not be apparent during propagation, as we
808 -- never follow the indirections of meta variables; it will be revealed
809 -- when the equality is zonked)
810 wantedToLocal :: RewriteInst -> TcM RewriteInst
811 wantedToLocal eq@(RewriteFam {rwi_fam = fam,
813 rwi_right = alphaTy@(TyVarTy alpha)})
814 = do { writeMetaTyVar alpha (mkTyConApp fam args)
815 ; return $ eq {rwi_co = mkGivenCo alphaTy}
817 wantedToLocal _ = panic "TcTyFuns.wantedToLocal"
821 %************************************************************************
823 Propagation of equalities
825 %************************************************************************
827 Apply the propagation rules exhaustively.
830 propagate :: [RewriteInst] -> EqConfig -> TcM EqConfig
831 propagate [] eqCfg = return eqCfg
832 propagate (eq:eqs) eqCfg
833 = do { optEqs <- applyTop eq
836 -- Top applied to 'eq' => retry with new equalities
837 Just (eqs2, skolems2)
838 -> propagate (eqs2 ++ eqs) (eqCfg `addSkolems` skolems2)
840 -- Top doesn't apply => try subst rules with all other
841 -- equalities, after that 'eq' can go into the residual list
843 -> do { (eqs', eqCfg') <- applySubstRules eq eqs eqCfg
844 ; propagate eqs' (eqCfg' `addEq` eq)
848 applySubstRules :: RewriteInst -- currently considered eq
849 -> [RewriteInst] -- todo eqs list
850 -> EqConfig -- residual
851 -> TcM ([RewriteInst], EqConfig) -- new todo & residual
852 applySubstRules eq todoEqs (eqConfig@EqConfig {eqs = resEqs})
853 = do { (newEqs_t, unchangedEqs_t, skolems_t) <- mapSubstRules eq todoEqs
854 ; (newEqs_r, unchangedEqs_r, skolems_r) <- mapSubstRules eq resEqs
855 ; return (newEqs_t ++ newEqs_r ++ unchangedEqs_t,
856 eqConfig {eqs = unchangedEqs_r}
857 `addSkolems` (skolems_t `unionVarSet` skolems_r))
860 mapSubstRules :: RewriteInst -- try substituting this equality
861 -> [RewriteInst] -- into these equalities
862 -> TcM ([RewriteInst], [RewriteInst], TyVarSet)
864 = do { (newEqss, unchangedEqss, skolemss) <- mapAndUnzip3M (substRules eq) eqs
865 ; return (concat newEqss, concat unchangedEqss, unionVarSets skolemss)
869 = do { -- try the SubstFam rule
870 optEqs <- applySubstFam eq1 eq2
872 Just (eqs, skolems) -> return (eqs, [], skolems)
874 { -- try the SubstVarVar rule
875 optEqs <- applySubstVarVar eq1 eq2
877 Just (eqs, skolems) -> return (eqs, [], skolems)
879 { -- try the SubstVarFam rule
880 optEqs <- applySubstVarFam eq1 eq2
882 Just eq -> return ([eq], [], emptyVarSet)
883 Nothing -> return ([], [eq2], emptyVarSet)
884 -- if no rule matches, we return the equlity we tried to
885 -- substitute into unchanged
889 Attempt to apply the Top rule. The rule is
893 co' :: [s1/x1, .., sm/xm]s ~ t with co = g s1..sm |> co'
895 where g :: forall x1..xm. F u1..um ~ s and [s1/x1, .., sm/xm]u1 == t1.
897 Returns Nothing if the rule could not be applied. Otherwise, the resulting
898 equality is normalised and a list of the normal equalities is returned.
901 applyTop :: RewriteInst -> TcM (Maybe ([RewriteInst], TyVarSet))
903 applyTop eq@(RewriteFam {rwi_fam = fam, rwi_args = args})
904 = do { optTyCo <- tcUnfoldSynFamInst (TyConApp fam args)
906 Nothing -> return Nothing
907 Just (lhs, rewrite_co)
908 -> do { co' <- mkRightTransEqInstCo co rewrite_co (lhs, rhs)
909 ; eq' <- deriveEqInst eq lhs rhs co'
910 ; liftM Just $ normEqInst eq'
917 applyTop _ = return Nothing
920 Attempt to apply the SubstFam rule. The rule is
922 co1 :: F t1..tn ~ t & co2 :: F t1..tn ~ s
924 co1 :: F t1..tn ~ t & co2' :: t ~ s with co2 = co1 |> co2'
926 where co1 may be a wanted only if co2 is a wanted, too.
928 Returns Nothing if the rule could not be applied. Otherwise, the equality
929 co2' is normalised and a list of the normal equalities is returned. (The
930 equality co1 is not returned as it remain unaltered.)
933 applySubstFam :: RewriteInst
935 -> TcM (Maybe ([RewriteInst], TyVarSet))
936 applySubstFam eq1@(RewriteFam {rwi_fam = fam1, rwi_args = args1})
937 eq2@(RewriteFam {rwi_fam = fam2, rwi_args = args2})
938 | fam1 == fam2 && tcEqTypes args1 args2 &&
939 (isWantedRewriteInst eq2 || not (isWantedRewriteInst eq1))
940 -- !!!TODO: tcEqTypes is insufficient as it does not look through type synonyms
941 -- !!!Check whether anything breaks by making tcEqTypes look through synonyms.
942 -- !!!Should be ok and we don't want three type equalities.
943 = do { co2' <- mkRightTransEqInstCo co2 co1 (lhs, rhs)
944 ; eq2' <- deriveEqInst eq2 lhs rhs co2'
945 ; liftM Just $ normEqInst eq2'
950 co1 = eqInstCoType (rwi_co eq1)
952 applySubstFam _ _ = return Nothing
955 Attempt to apply the SubstVarVar rule. The rule is
957 co1 :: x ~ t & co2 :: x ~ s
959 co1 :: x ~ t & co2' :: t ~ s with co2 = co1 |> co2'
961 where co1 may be a wanted only if co2 is a wanted, too.
963 Returns Nothing if the rule could not be applied. Otherwise, the equality
964 co2' is normalised and a list of the normal equalities is returned. (The
965 equality co1 is not returned as it remain unaltered.)
968 applySubstVarVar :: RewriteInst
970 -> TcM (Maybe ([RewriteInst], TyVarSet))
971 applySubstVarVar eq1@(RewriteVar {rwi_var = tv1})
972 eq2@(RewriteVar {rwi_var = tv2})
974 (isWantedRewriteInst eq2 || not (isWantedRewriteInst eq1))
975 = do { co2' <- mkRightTransEqInstCo co2 co1 (lhs, rhs)
976 ; eq2' <- deriveEqInst eq2 lhs rhs co2'
977 ; liftM Just $ normEqInst eq2'
982 co1 = eqInstCoType (rwi_co eq1)
984 applySubstVarVar _ _ = return Nothing
987 Attempt to apply the SubstVarFam rule. The rule is
989 co1 :: x ~ t & co2 :: F s1..sn ~ s
991 co1 :: x ~ t & co2' :: [t/x](F s1..sn) ~ s
992 with co2 = [co1/x](F s1..sn) |> co2'
994 where x occurs in F s1..sn. (co1 may be local or wanted.)
996 Returns Nothing if the rule could not be applied. Otherwise, the equality
997 co2' is returned. (The equality co1 is not returned as it remain unaltered.)
1000 applySubstVarFam :: RewriteInst -> RewriteInst -> TcM (Maybe RewriteInst)
1001 applySubstVarFam eq1@(RewriteVar {rwi_var = tv1})
1002 eq2@(RewriteFam {rwi_fam = fam2, rwi_args = args2})
1003 | tv1 `elemVarSet` tyVarsOfTypes args2
1004 = do { let co1Subst = substTyWith [tv1] [co1] (mkTyConApp fam2 args2)
1005 args2' = substTysWith [tv1] [rhs1] args2
1006 lhs2 = mkTyConApp fam2 args2'
1007 ; co2' <- mkRightTransEqInstCo co2 co1Subst (lhs2, rhs2)
1008 ; return $ Just (eq2 {rwi_args = args2', rwi_co = co2'})
1011 rhs1 = rwi_right eq1
1012 rhs2 = rwi_right eq2
1013 co1 = eqInstCoType (rwi_co eq1)
1015 applySubstVarFam _ _ = return Nothing
1019 %************************************************************************
1021 Finalisation of equalities
1023 %************************************************************************
1025 Exhaustive substitution of all variable equalities of the form co :: x ~ t
1026 (both local and wanted) into the left-hand sides of all other equalities. This
1027 may lead to recursive equalities; i.e., (1) we need to apply the substitution
1028 implied by one variable equality exhaustively before turning to the next and
1029 (2) we need an occurs check.
1031 We also apply the same substitutions to the local and wanted class and IP
1034 The treatment of flexibles in wanteds is quite subtle. We absolutely want to
1035 substitute them into right-hand sides of equalities, to avoid getting two
1036 competing instantiations for a type variables; e.g., consider
1038 F s ~ alpha, alpha ~ t
1040 If we don't substitute `alpha ~ t', we may instantiate t with `F s' instead.
1041 This would be bad as `F s' is less useful, eg, as an argument to a class
1044 However, there is no reason why we would want to *substitute* `alpha ~ t' into a
1045 class constraint. We rather wait until `alpha' is instantiated to `t` and
1046 save the extra dictionary binding that substitution would introduce.
1047 Moreover, we may substitute wanted equalities only into wanted dictionaries.
1050 * Given that we apply the substitution corresponding to a single equality
1051 exhaustively, before turning to the next, and because we eliminate recursive
1052 equalities, all opportunities for subtitution will have been exhausted after
1053 we have considered each equality once.
1056 substitute :: [RewriteInst] -- equalities
1057 -> [Inst] -- local class dictionaries
1058 -> [Inst] -- wanted class dictionaries
1059 -> TcM ([RewriteInst], -- equalities after substitution
1060 TcDictBinds, -- all newly generated dictionary bindings
1061 [Inst], -- local dictionaries after substitution
1062 [Inst]) -- wanted dictionaries after substitution
1063 substitute eqs locals wanteds = subst eqs [] emptyBag locals wanteds
1065 subst [] res binds locals wanteds
1066 = return (res, binds, locals, wanteds)
1068 subst (eq@(RewriteVar {rwi_var = tv, rwi_right = ty, rwi_co = co}):eqs)
1069 res binds locals wanteds
1070 = do { traceTc $ ptext (sLit "TcTyFuns.substitute:") <+> ppr eq
1072 ; let coSubst = zipOpenTvSubst [tv] [eqInstCoType co]
1073 tySubst = zipOpenTvSubst [tv] [ty]
1074 ; eqs' <- mapM (substEq eq coSubst tySubst) eqs
1075 ; res' <- mapM (substEq eq coSubst tySubst) res
1077 -- only susbtitute local equalities into local dictionaries
1078 ; (lbinds, locals') <- if not (isWantedCo co)
1081 (substDict eq coSubst tySubst False)
1086 -- flexible tvs in wanteds will be instantiated anyway, there is
1087 -- no need to substitute them into dictionaries
1088 ; (wbinds, wanteds') <- if not (isMetaTyVar tv && isWantedCo co)
1091 (substDict eq coSubst tySubst True)
1094 return ([], wanteds)
1096 ; let binds' = unionManyBags $ binds : lbinds ++ wbinds
1097 ; subst eqs' (eq:res') binds' locals' wanteds'
1099 subst (eq:eqs) res binds locals wanteds
1100 = subst eqs (eq:res) binds locals wanteds
1102 -- We have, co :: tv ~ ty
1103 -- => apply [ty/tv] to right-hand side of eq2
1104 -- (but only if tv actually occurs in the right-hand side of eq2)
1105 substEq (RewriteVar {rwi_var = tv, rwi_right = ty})
1107 | tv `elemVarSet` tyVarsOfType (rwi_right eq2)
1108 = do { let co1Subst = mkSymCoercion $ substTy coSubst (rwi_right eq2)
1109 right2' = substTy tySubst (rwi_right eq2)
1111 RewriteVar {rwi_var = tv2} -> mkTyVarTy tv2
1112 RewriteFam {rwi_fam = fam,
1113 rwi_args = args} ->mkTyConApp fam args
1114 ; co2' <- mkLeftTransEqInstCo (rwi_co eq2) co1Subst (left2, right2')
1116 RewriteVar {rwi_var = tv2} | tv2 `elemVarSet` tyVarsOfType ty
1117 -> occurCheckErr left2 right2'
1118 _ -> return $ eq2 {rwi_right = right2', rwi_co = co2'}
1125 -- We have, co :: tv ~ ty
1126 -- => apply [ty/tv] to dictionary predicate
1127 -- (but only if tv actually occurs in the predicate)
1128 substDict (RewriteVar {rwi_var = tv}) coSubst tySubst isWanted dict
1130 , tv `elemVarSet` tyVarsOfPred (tci_pred dict)
1131 = do { let co1Subst = PredTy (substPred coSubst (tci_pred dict))
1132 pred' = substPred tySubst (tci_pred dict)
1133 ; (dict', binds) <- mkDictBind dict isWanted co1Subst pred'
1134 ; return (binds, dict')
1138 substDict _ _ _ _ dict
1139 = return (emptyBag, dict)
1140 -- !!!TODO: Still need to substitute into IP constraints.
1143 For any *wanted* variable equality of the form co :: alpha ~ t or co :: a ~
1144 alpha, we instantiate alpha with t or a, respectively, and set co := id.
1145 Return all remaining wanted equalities. The Boolean result component is True
1146 if at least one instantiation of a flexible that is *not* a skolem from
1147 flattening was performed.
1150 instantiateAndExtract :: [RewriteInst] -> Bool -> TyVarSet -> TcM ([Inst], Bool)
1151 instantiateAndExtract eqs localsEmpty skolems
1152 = do { results <- mapM inst wanteds
1153 ; let residuals = [eq | Left eq <- results]
1154 only_skolems = and [tv `elemVarSet` skolems | Right tv <- results]
1155 ; residuals' <- mapM rewriteInstToInst residuals
1156 ; return (residuals', not only_skolems)
1159 wanteds = filter (isWantedCo . rwi_co) eqs
1160 checkingMode = length eqs > length wanteds || not localsEmpty
1161 -- no local equalities or dicts => checking mode
1163 inst eq@(RewriteVar {rwi_var = tv1, rwi_right = ty2, rwi_co = co})
1167 = doInst (rwi_swapped eq) tv1 ty2 co eq
1170 | Just tv2 <- tcGetTyVar_maybe ty2
1172 = doInst (not $ rwi_swapped eq) tv2 (mkTyVarTy tv1) co eq
1174 -- co :: F args ~ alpha, and we are in checking mode (ie, no locals)
1175 inst eq@(RewriteFam {rwi_fam = fam, rwi_args = args, rwi_right = ty2,
1177 | Just tv2 <- tcGetTyVar_maybe ty2
1179 , checkingMode || tv2 `elemVarSet` skolems
1180 -- !!!TODO: this is too liberal, even if tv2 is in
1181 -- skolems we shouldn't instantiate if tvs occurs
1182 -- in other equalities that may propagate it into the
1184 = doInst (not $ rwi_swapped eq) tv2 (mkTyConApp fam args) co eq
1186 inst eq = return $ Left eq
1188 doInst _swapped _tv _ty (Right ty) _eq
1189 = pprPanic "TcTyFuns.doInst: local eq: " (ppr ty)
1190 doInst swapped tv ty (Left cotv) eq
1191 = do { lookupTV <- lookupTcTyVar tv
1192 ; uMeta swapped tv lookupTV ty cotv
1195 -- meta variable has been filled already
1196 -- => keep the equality
1197 uMeta _swapped tv (IndirectTv fill_ty) ty _cotv
1199 ptext (sLit "flexible") <+> ppr tv <+>
1200 ptext (sLit "already filled with") <+> ppr fill_ty <+>
1201 ptext (sLit "meant to fill with") <+> ppr ty
1205 -- type variable meets type variable
1206 -- => check that tv2 hasn't been updated yet and choose which to update
1207 uMeta swapped tv1 (DoneTv details1) (TyVarTy tv2) cotv
1209 = panic "TcTyFuns.uMeta: normalisation shouldn't allow x ~ x"
1212 = do { lookupTV2 <- lookupTcTyVar tv2
1215 uMeta swapped tv1 (DoneTv details1) ty cotv
1217 uMetaVar swapped tv1 details1 tv2 details2 cotv
1220 ------ Beyond this point we know that ty2 is not a type variable
1222 -- signature skolem meets non-variable type
1223 -- => cannot update (retain the equality)!
1224 uMeta _swapped _tv (DoneTv (MetaTv (SigTv _) _)) _non_tv_ty _cotv
1227 -- updatable meta variable meets non-variable type
1228 -- => occurs check, monotype check, and kinds match check, then update
1229 uMeta swapped tv (DoneTv (MetaTv _ ref)) non_tv_ty cotv
1230 = do { -- occurs + monotype check
1231 ; mb_ty' <- checkTauTvUpdate tv non_tv_ty
1235 -- normalisation shouldn't leave families in non_tv_ty
1236 panic "TcTyFuns.uMeta: unexpected synonym family"
1238 do { checkUpdateMeta swapped tv ref ty' -- update meta var
1239 ; writeMetaTyVar cotv ty' -- update co var
1244 uMeta _ _ _ _ _ = panic "TcTyFuns.uMeta"
1246 -- uMetaVar: unify two type variables
1247 -- meta variable meets skolem
1249 uMetaVar swapped tv1 (MetaTv _ ref) tv2 (SkolemTv _) cotv
1250 = do { checkUpdateMeta swapped tv1 ref (mkTyVarTy tv2)
1251 ; writeMetaTyVar cotv (mkTyVarTy tv2)
1252 ; return $ Right tv1
1255 -- meta variable meets meta variable
1256 -- => be clever about which of the two to update
1257 -- (from TcUnify.uUnfilledVars minus boxy stuff)
1258 uMetaVar swapped tv1 (MetaTv info1 ref1) tv2 (MetaTv info2 ref2) cotv
1259 = do { tv <- case (info1, info2) of
1260 -- Avoid SigTvs if poss
1261 (SigTv _, _ ) | k1_sub_k2 -> update_tv2
1262 (_, SigTv _) | k2_sub_k1 -> update_tv1
1264 (_, _) | k1_sub_k2 -> if k2_sub_k1 &&
1266 then update_tv1 -- Same kinds
1268 | k2_sub_k1 -> update_tv1
1269 | otherwise -> kind_err >> return tv1
1270 -- Update the variable with least kind info
1271 -- See notes on type inference in Kind.lhs
1272 -- The "nicer to" part only applies if the two kinds are the same,
1273 -- so we can choose which to do.
1275 ; writeMetaTyVar cotv (mkTyVarTy tv2)
1279 -- Kinds should be guaranteed ok at this point
1280 update_tv1 = updateMeta tv1 ref1 (mkTyVarTy tv2)
1282 update_tv2 = updateMeta tv2 ref2 (mkTyVarTy tv1)
1285 kind_err = addErrCtxtM (unifyKindCtxt swapped tv1 (mkTyVarTy tv2)) $
1286 unifyKindMisMatch k1 k2
1290 k1_sub_k2 = k1 `isSubKind` k2
1291 k2_sub_k1 = k2 `isSubKind` k1
1293 nicer_to_update_tv1 = isSystemName (Var.varName tv1)
1294 -- Try to update sys-y type variables in preference to ones
1295 -- gotten (say) by instantiating a polymorphic function with
1296 -- a user-written type sig
1298 uMetaVar _ _ _ _ _ _ = panic "uMetaVar"
1302 %************************************************************************
1306 %************************************************************************
1308 The infamous couldn't match expected type soandso against inferred type
1309 somethingdifferent message.
1312 eqInstMisMatch :: Inst -> TcM a
1314 = ASSERT( isEqInst inst )
1315 setErrCtxt ctxt $ failWithMisMatch ty_act ty_exp
1317 (ty_act, ty_exp) = eqInstTys inst
1318 InstLoc _ _ ctxt = instLoc inst
1320 -----------------------
1321 failWithMisMatch :: TcType -> TcType -> TcM a
1322 -- Generate the message when two types fail to match,
1323 -- going to some trouble to make it helpful.
1324 -- The argument order is: actual type, expected type
1325 failWithMisMatch ty_act ty_exp
1326 = do { env0 <- tcInitTidyEnv
1327 ; ty_exp <- zonkTcType ty_exp
1328 ; ty_act <- zonkTcType ty_act
1329 ; failWithTcM (misMatchMsg env0 (ty_act, ty_exp))
1332 misMatchMsg :: TidyEnv -> (TcType, TcType) -> (TidyEnv, SDoc)
1333 misMatchMsg env0 (ty_act, ty_exp)
1334 = let (env1, pp_exp, extra_exp) = ppr_ty env0 ty_exp
1335 (env2, pp_act, extra_act) = ppr_ty env1 ty_act
1336 msg = sep [sep [ptext (sLit "Couldn't match expected type") <+> pp_exp,
1338 ptext (sLit "against inferred type") <+> pp_act],
1339 nest 2 (extra_exp $$ extra_act)]
1344 ppr_ty :: TidyEnv -> TcType -> (TidyEnv, SDoc, SDoc)
1346 = let (env1, tidy_ty) = tidyOpenType env ty
1347 (env2, extra) = ppr_extra env1 tidy_ty
1349 (env2, quotes (ppr tidy_ty), extra)
1351 -- (ppr_extra env ty) shows extra info about 'ty'
1352 ppr_extra :: TidyEnv -> Type -> (TidyEnv, SDoc)
1353 ppr_extra env (TyVarTy tv)
1354 | isTcTyVar tv && (isSkolemTyVar tv || isSigTyVar tv) && not (isUnk tv)
1355 = (env1, pprSkolTvBinding tv1)
1357 (env1, tv1) = tidySkolemTyVar env tv
1359 ppr_extra env _ty = (env, empty) -- Normal case
1362 Warn of loopy local equalities that were dropped.
1365 warnDroppingLoopyEquality :: TcType -> TcType -> TcM ()
1366 warnDroppingLoopyEquality ty1 ty2
1367 = do { env0 <- tcInitTidyEnv
1368 ; ty1 <- zonkTcType ty1
1369 ; ty2 <- zonkTcType ty2
1370 ; let (env1 , tidy_ty1) = tidyOpenType env0 ty1
1371 (_env2, tidy_ty2) = tidyOpenType env1 ty2
1372 ; addWarnTc $ hang (ptext (sLit "Dropping loopy given equality"))
1373 2 (quotes (ppr tidy_ty1 <+> text "~" <+> ppr tidy_ty2))