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 { -- The TyCon might be over-saturated, but that's ok for tcLookupFamInst
73 ; maybeFamInst <- tcLookupFamInst tycon tys
74 ; case maybeFamInst of
75 Nothing -> return Nothing
76 Just (rep_tc, rep_tys) -> return $ Just (mkTyConApp rep_tc rep_tys,
77 mkTyConApp coe_tc rep_tys)
79 coe_tc = expectJust "TcTyFuns.tcUnfoldSynFamInst"
80 (tyConFamilyCoercion_maybe rep_tc)
82 tcUnfoldSynFamInst _other = return Nothing
85 Normalise 'Type's and 'PredType's by unfolding type family applications where
86 possible (ie, we treat family instances as a TRS). Also zonk meta variables.
88 tcNormaliseFamInst ty = (co, ty')
92 -- |Normalise the given type as far as possible with toplevel equalities.
93 -- This results in a coercion witnessing the type equality, in addition to the
96 tcNormaliseFamInst :: TcType -> TcM (CoercionI, TcType)
97 tcNormaliseFamInst = tcGenericNormaliseFamInst tcUnfoldSynFamInst
100 Generic normalisation of 'Type's and 'PredType's; ie, walk the type term and
101 apply the normalisation function gives as the first argument to every TyConApp
102 and every TyVarTy subterm.
104 tcGenericNormaliseFamInst fun ty = (co, ty')
107 This function is (by way of using smart constructors) careful to ensure that
108 the returned coercion is exactly IdCo (and not some semantically equivalent,
109 but syntactically different coercion) whenever (ty' `tcEqType` ty). This
110 makes it easy for the caller to determine whether the type changed. BUT
111 even if we return IdCo, ty' may be *syntactically* different from ty due to
112 unfolded closed type synonyms (by way of tcCoreView). In the interest of
113 good error messages, callers should discard ty' in favour of ty in this case.
116 tcGenericNormaliseFamInst :: (TcType -> TcM (Maybe (TcType, Coercion)))
117 -- what to do with type functions and tyvars
118 -> TcType -- old type
119 -> TcM (CoercionI, TcType) -- (coercion, new type)
120 tcGenericNormaliseFamInst fun ty
121 | Just ty' <- tcView ty = tcGenericNormaliseFamInst fun ty'
122 tcGenericNormaliseFamInst fun (TyConApp tyCon tys)
123 = do { (cois, ntys) <- mapAndUnzipM (tcGenericNormaliseFamInst fun) tys
124 ; let tycon_coi = mkTyConAppCoI tyCon ntys cois
125 ; maybe_ty_co <- fun (mkTyConApp tyCon ntys) -- use normalised args!
126 ; case maybe_ty_co of
127 -- a matching family instance exists
129 do { let first_coi = mkTransCoI tycon_coi (ACo co)
130 ; (rest_coi, nty) <- tcGenericNormaliseFamInst fun ty'
131 ; let fix_coi = mkTransCoI first_coi rest_coi
132 ; return (fix_coi, nty)
134 -- no matching family instance exists
135 -- we do not do anything
136 Nothing -> return (tycon_coi, mkTyConApp tyCon ntys)
138 tcGenericNormaliseFamInst fun (AppTy ty1 ty2)
139 = do { (coi1,nty1) <- tcGenericNormaliseFamInst fun ty1
140 ; (coi2,nty2) <- tcGenericNormaliseFamInst fun ty2
141 ; return (mkAppTyCoI nty1 coi1 nty2 coi2, mkAppTy nty1 nty2)
143 tcGenericNormaliseFamInst fun (FunTy ty1 ty2)
144 = do { (coi1,nty1) <- tcGenericNormaliseFamInst fun ty1
145 ; (coi2,nty2) <- tcGenericNormaliseFamInst fun ty2
146 ; return (mkFunTyCoI nty1 coi1 nty2 coi2, mkFunTy nty1 nty2)
148 tcGenericNormaliseFamInst fun (ForAllTy tyvar ty1)
149 = do { (coi,nty1) <- tcGenericNormaliseFamInst fun ty1
150 ; return (mkForAllTyCoI tyvar coi, mkForAllTy tyvar nty1)
152 tcGenericNormaliseFamInst fun ty@(TyVarTy tv)
154 = do { traceTc (text "tcGenericNormaliseFamInst" <+> ppr ty)
155 ; res <- lookupTcTyVar tv
158 do { maybe_ty' <- fun ty
160 Nothing -> return (IdCo, ty)
162 do { (coi2, ty'') <- tcGenericNormaliseFamInst fun ty'
163 ; return (ACo co1 `mkTransCoI` coi2, ty'')
166 IndirectTv ty' -> tcGenericNormaliseFamInst fun ty'
170 tcGenericNormaliseFamInst fun (PredTy predty)
171 = do { (coi, pred') <- tcGenericNormaliseFamInstPred fun predty
172 ; return (coi, PredTy pred') }
174 ---------------------------------
175 tcGenericNormaliseFamInstPred :: (TcType -> TcM (Maybe (TcType,Coercion)))
177 -> TcM (CoercionI, TcPredType)
179 tcGenericNormaliseFamInstPred fun (ClassP cls tys)
180 = do { (cois, tys')<- mapAndUnzipM (tcGenericNormaliseFamInst fun) tys
181 ; return (mkClassPPredCoI cls tys' cois, ClassP cls tys')
183 tcGenericNormaliseFamInstPred fun (IParam ipn ty)
184 = do { (coi, ty') <- tcGenericNormaliseFamInst fun ty
185 ; return $ (mkIParamPredCoI ipn coi, IParam ipn ty')
187 tcGenericNormaliseFamInstPred fun (EqPred ty1 ty2)
188 = do { (coi1, ty1') <- tcGenericNormaliseFamInst fun ty1
189 ; (coi2, ty2') <- tcGenericNormaliseFamInst fun ty2
190 ; return (mkEqPredCoI ty1' coi1 ty2' coi2, EqPred ty1' ty2') }
194 %************************************************************************
196 Normalisation of instances wrt to equalities
198 %************************************************************************
201 tcReduceEqs :: [Inst] -- locals
203 -> TcM ([Inst], -- normalised locals (w/o equalities)
204 [Inst], -- normalised wanteds (including equalities)
205 TcDictBinds, -- bindings for all simplified dictionaries
206 Bool) -- whether any flexibles where instantiated
207 tcReduceEqs locals wanteds
208 = do { let (local_eqs , local_dicts) = partition isEqInst locals
209 (wanteds_eqs, wanteds_dicts) = partition isEqInst wanteds
210 ; eqCfg1 <- normaliseEqs (local_eqs ++ wanteds_eqs)
211 ; eqCfg2 <- normaliseDicts False local_dicts
212 ; eqCfg3 <- normaliseDicts True wanteds_dicts
213 ; eqCfg <- propagateEqs (eqCfg1 `unionEqConfig` eqCfg2
214 `unionEqConfig` eqCfg3)
215 ; finaliseEqsAndDicts eqCfg
220 %************************************************************************
222 Equality Configurations
224 %************************************************************************
226 We maintain normalised equalities together with the skolems introduced as
227 intermediates during flattening of equalities as well as
230 -- |Configuration of normalised equalities used during solving.
232 data EqConfig = EqConfig { eqs :: [RewriteInst] -- all equalities
233 , locals :: [Inst] -- given dicts
234 , wanteds :: [Inst] -- wanted dicts
235 , binds :: TcDictBinds -- bindings
236 , skolems :: TyVarSet -- flattening skolems
239 addSkolems :: EqConfig -> TyVarSet -> EqConfig
240 addSkolems eqCfg newSkolems
241 = eqCfg {skolems = skolems eqCfg `unionVarSet` newSkolems}
243 addEq :: EqConfig -> RewriteInst -> EqConfig
244 addEq eqCfg eq = eqCfg {eqs = eq : eqs eqCfg}
246 unionEqConfig :: EqConfig -> EqConfig -> EqConfig
247 unionEqConfig eqc1 eqc2 = EqConfig
248 { eqs = eqs eqc1 ++ eqs eqc2
249 , locals = locals eqc1 ++ locals eqc2
250 , wanteds = wanteds eqc1 ++ wanteds eqc2
251 , binds = binds eqc1 `unionBags` binds eqc2
252 , skolems = skolems eqc1 `unionVarSet` skolems eqc2
255 emptyEqConfig :: EqConfig
256 emptyEqConfig = EqConfig
261 , skolems = emptyVarSet
264 instance Outputable EqConfig where
265 ppr (EqConfig {eqs = eqs, locals = locals, wanteds = wanteds, binds = binds})
266 = vcat [ppr eqs, ppr locals, ppr wanteds, ppr binds]
269 The set of operations on an equality configuration. We obtain the initialise
270 configuration by normalisation ('normaliseEqs'), solve the equalities by
271 propagation ('propagateEqs'), and eventually finalise the configuration when
272 no further propoagation is possible.
275 -- |Turn a set of equalities into an equality configuration for solving.
277 -- Precondition: The Insts are zonked.
279 normaliseEqs :: [Inst] -> TcM EqConfig
281 = do { ASSERTM2( allM wantedEqInstIsUnsolved eqs, ppr eqs )
282 ; traceTc $ ptext (sLit "Entering normaliseEqs")
284 ; (eqss, skolemss) <- mapAndUnzipM normEqInst eqs
285 ; return $ emptyEqConfig { eqs = concat eqss
286 , skolems = unionVarSets skolemss
290 -- |Flatten the type arguments of all dictionaries, returning the result as a
291 -- equality configuration. The dictionaries go into the 'wanted' component if
292 -- the second argument is 'True'.
294 -- Precondition: The Insts are zonked.
296 normaliseDicts :: Bool -> [Inst] -> TcM EqConfig
297 normaliseDicts isWanted insts
298 = do { traceTc $ hang (ptext (sLit "Entering normaliseDicts") <+>
299 ptext (if isWanted then sLit "[Wanted] for"
300 else sLit "[Local] for"))
302 ; (insts', eqss, bindss, skolemss) <- mapAndUnzip4M (normDict isWanted)
305 ; traceTc $ hang (ptext (sLit "normaliseDicts returns"))
306 4 (ppr insts' $$ ppr eqss)
307 ; return $ emptyEqConfig { eqs = concat eqss
308 , locals = if isWanted then [] else insts'
309 , wanteds = if isWanted then insts' else []
310 , binds = unionManyBags bindss
311 , skolems = unionVarSets skolemss
315 -- |Solves the equalities as far as possible by applying propagation rules.
317 propagateEqs :: EqConfig -> TcM EqConfig
318 propagateEqs eqCfg@(EqConfig {eqs = todoEqs})
319 = do { traceTc $ hang (ptext (sLit "Entering propagateEqs:"))
322 ; propagate todoEqs (eqCfg {eqs = []})
325 -- |Finalise a set of equalities and associated dictionaries after
326 -- propagation. The returned Boolean value is `True' iff any flexible
327 -- variables, except those introduced by flattening (i.e., those in the
328 -- `skolems' component of the argument) where instantiated. The first returned
329 -- set of instances are the locals (without equalities) and the second set are
330 -- all residual wanteds, including equalities.
332 finaliseEqsAndDicts :: EqConfig
333 -> TcM ([Inst], [Inst], TcDictBinds, Bool)
334 finaliseEqsAndDicts (EqConfig { eqs = eqs
340 = do { traceTc $ ptext (sLit "finaliseEqsAndDicts")
341 ; (eqs', subst_binds, locals', wanteds') <- substitute eqs locals wanteds
342 ; (eqs'', improved) <- instantiateAndExtract eqs' (null locals) skolems
343 ; let final_binds = subst_binds `unionBags` binds
345 -- Assert that all cotvs of wanted equalities are still unfilled, and
346 -- zonk all final insts, to make any improvement visible
347 ; ASSERTM2( allM wantedEqInstIsUnsolved eqs'', ppr eqs'' )
348 ; zonked_locals <- zonkInsts locals'
349 ; zonked_wanteds <- zonkInsts (eqs'' ++ wanteds')
350 ; return (zonked_locals, zonked_wanteds, final_binds, improved)
355 %************************************************************************
357 Normalisation of equalities
359 %************************************************************************
361 A normal equality is a properly oriented equality with associated coercion
362 that contains at most one family equality (in its left-hand side) is oriented
363 such that it may be used as a reqrite rule. It has one of the following two
366 (1) co :: F t1..tn ~ t (family equalities)
367 (2) co :: x ~ t (variable equalities)
369 Variable equalities fall again in two classes:
371 (2a) co :: x ~ t, where t is *not* a variable, or
372 (2b) co :: x ~ y, where x > y.
374 The types t, t1, ..., tn may not contain any occurrences of synonym
375 families. Moreover, in Forms (2) & (3), the left-hand side may not occur in
376 the right-hand side, and the relation x > y is an arbitrary, but total order
381 = RewriteVar -- Form (2) above
382 { rwi_var :: TyVar -- may be rigid or flexible
383 , rwi_right :: TcType -- contains no synonym family applications
384 , rwi_co :: EqInstCo -- the wanted or given coercion
386 , rwi_name :: Name -- no semantic significance (cf. TcRnTypes.EqInst)
387 , rwi_swapped :: Bool -- swapped orientation of original EqInst
389 | RewriteFam -- Forms (1) above
390 { rwi_fam :: TyCon -- synonym family tycon
391 , rwi_args :: [Type] -- contain no synonym family applications
392 , rwi_right :: TcType -- contains no synonym family applications
393 , rwi_co :: EqInstCo -- the wanted or given coercion
395 , rwi_name :: Name -- no semantic significance (cf. TcRnTypes.EqInst)
396 , rwi_swapped :: Bool -- swapped orientation of original EqInst
399 isWantedRewriteInst :: RewriteInst -> Bool
400 isWantedRewriteInst = isWantedCo . rwi_co
402 rewriteInstToInst :: RewriteInst -> TcM Inst
403 rewriteInstToInst eq@(RewriteVar {rwi_var = tv})
404 = deriveEqInst eq (mkTyVarTy tv) (rwi_right eq) (rwi_co eq)
405 rewriteInstToInst eq@(RewriteFam {rwi_fam = fam, rwi_args = args})
406 = deriveEqInst eq (mkTyConApp fam args) (rwi_right eq) (rwi_co eq)
408 -- Derive an EqInst based from a RewriteInst, possibly swapping the types
411 deriveEqInst :: RewriteInst -> TcType -> TcType -> EqInstCo -> TcM Inst
412 deriveEqInst rewrite ty1 ty2 co
413 = do { co_adjusted <- if not swapped then return co
414 else mkSymEqInstCo co (ty2, ty1)
418 , tci_co = co_adjusted
419 , tci_loc = rwi_loc rewrite
420 , tci_name = rwi_name rewrite
424 swapped = rwi_swapped rewrite
425 (left, right) = if not swapped then (ty1, ty2) else (ty2, ty1)
427 instance Outputable RewriteInst where
428 ppr (RewriteFam {rwi_fam = fam, rwi_args = args, rwi_right = rhs, rwi_co =co})
429 = hsep [ pprEqInstCo co <+> text "::"
430 , ppr (mkTyConApp fam args)
434 ppr (RewriteVar {rwi_var = tv, rwi_right = rhs, rwi_co =co})
435 = hsep [ pprEqInstCo co <+> text "::"
441 pprEqInstCo :: EqInstCo -> SDoc
442 pprEqInstCo (Left cotv) = ptext (sLit "Wanted") <+> ppr cotv
443 pprEqInstCo (Right co) = ptext (sLit "Local") <+> ppr co
446 The following functions turn an arbitrary equality into a set of normal
447 equalities. This implements the WFlat and LFlat rules of the paper in one
448 sweep. However, we use flexible variables for both locals and wanteds, and
449 avoid to carry around the unflattening substitution \Sigma (for locals) by
450 already updating the skolems for locals with the family application that they
451 represent - i.e., they will turn into that family application on the next
452 zonking (which only happens after finalisation).
454 In a corresponding manner, normDict normalises class dictionaries by
455 extracting any synonym family applications and generation appropriate normal
458 Whenever we encounter a loopy equality (of the form a ~ T .. (F ...a...) ...),
459 we drop that equality and raise an error if it is a wanted or a warning if it
463 normEqInst :: Inst -> TcM ([RewriteInst], TyVarSet)
464 -- Normalise one equality.
466 = ASSERT( isEqInst inst )
467 do { traceTc $ ptext (sLit "normEqInst of ") <+>
468 pprEqInstCo co <+> text "::" <+>
469 ppr ty1 <+> text "~" <+> ppr ty2
470 ; res <- go ty1 ty2 co
471 ; traceTc $ ptext (sLit "normEqInst returns") <+> ppr res
475 (ty1, ty2) = eqInstTys inst
476 co = eqInstCoercion inst
478 -- look through synonyms
479 go ty1 ty2 co | Just ty1' <- tcView ty1 = go ty1' ty2 co
480 go ty1 ty2 co | Just ty2' <- tcView ty2 = go ty1 ty2' co
482 -- left-to-right rule with type family head
483 go ty1@(TyConApp con args) ty2 co
484 | isOpenSynTyConApp ty1 -- only if not oversaturated
485 = mkRewriteFam False con args ty2 co
487 -- right-to-left rule with type family head
488 go ty1 ty2@(TyConApp con args) co
489 | isOpenSynTyConApp ty2 -- only if not oversaturated
490 = do { co' <- mkSymEqInstCo co (ty2, ty1)
491 ; mkRewriteFam True con args ty1 co'
494 -- no outermost family
496 = do { (ty1', co1, ty1_eqs, ty1_skolems) <- flattenType inst ty1
497 ; (ty2', co2, ty2_eqs, ty2_skolems) <- flattenType inst ty2
498 ; let ty12_eqs = ty1_eqs ++ ty2_eqs
499 sym_co2 = mkSymCoercion co2
501 ; (co', ty12_eqs') <- adjustCoercions co co1 sym_co2 eqTys ty12_eqs
502 ; eqs <- checkOrientation ty1' ty2' co' inst
503 ; if isLoopyEquality eqs ty12_eqs'
504 then do { if isWantedCo (tci_co inst)
506 addErrCtxt (ptext (sLit "Rejecting loopy equality")) $
509 warnDroppingLoopyEquality ty1 ty2
510 ; return ([], emptyVarSet) -- drop the equality
513 return (eqs ++ ty12_eqs',
514 ty1_skolems `unionVarSet` ty2_skolems)
517 mkRewriteFam swapped con args ty2 co
518 = do { (args', cargs, args_eqss, args_skolemss)
519 <- mapAndUnzip4M (flattenType inst) args
520 ; (ty2', co2, ty2_eqs, ty2_skolems) <- flattenType inst ty2
521 ; let co1 = mkTyConApp con cargs
522 sym_co2 = mkSymCoercion co2
523 all_eqs = concat args_eqss ++ ty2_eqs
524 eqTys = (mkTyConApp con args', ty2')
525 ; (co', all_eqs') <- adjustCoercions co co1 sym_co2 eqTys all_eqs
526 ; let thisRewriteFam = RewriteFam
531 , rwi_loc = tci_loc inst
532 , rwi_name = tci_name inst
533 , rwi_swapped = swapped
535 ; return $ (thisRewriteFam : all_eqs',
536 unionVarSets (ty2_skolems:args_skolemss))
539 -- If the original equality has the form a ~ T .. (F ...a...) ..., we will
540 -- have a variable equality with 'a' on the lhs as the first equality.
541 -- Then, check whether 'a' occurs in the lhs of any family equality
542 -- generated by flattening.
543 isLoopyEquality (RewriteVar {rwi_var = tv}:_) eqs
544 = any inRewriteFam eqs
546 inRewriteFam (RewriteFam {rwi_args = args})
547 = tv `elemVarSet` tyVarsOfTypes args
548 inRewriteFam _ = False
549 isLoopyEquality _ _ = False
551 normDict :: Bool -> Inst -> TcM (Inst, [RewriteInst], TcDictBinds, TyVarSet)
552 -- Normalise one dictionary or IP constraint.
553 normDict isWanted inst@(Dict {tci_pred = ClassP clas args})
554 = do { (args', cargs, args_eqss, args_skolemss)
555 <- mapAndUnzip4M (flattenType inst) args
556 ; let rewriteCo = PredTy $ ClassP clas cargs
557 eqs = concat args_eqss
558 pred' = ClassP clas args'
560 then -- don't generate a binding if there is nothing to flatten
561 return (inst, [], emptyBag, emptyVarSet)
563 ; (inst', bind) <- mkDictBind inst isWanted rewriteCo pred'
564 ; eqs' <- if isWanted then return eqs else mapM wantedToLocal eqs
565 ; return (inst', eqs', bind, unionVarSets args_skolemss)
567 normDict _isWanted inst
568 = return (inst, [], emptyBag, emptyVarSet)
569 -- !!!TODO: Still need to normalise IP constraints.
571 checkOrientation :: Type -> Type -> EqInstCo -> Inst -> TcM [RewriteInst]
572 -- Performs the occurs check, decomposition, and proper orientation
573 -- (returns a singleton, or an empty list in case of a trivial equality)
574 -- NB: We cannot assume that the two types already have outermost type
575 -- synonyms expanded due to the recursion in the case of type applications.
576 checkOrientation ty1 ty2 co inst
579 -- look through synonyms
580 go ty1 ty2 | Just ty1' <- tcView ty1 = go ty1' ty2
581 go ty1 ty2 | Just ty2' <- tcView ty2 = go ty1 ty2'
583 -- identical types => trivial
586 = do { mkIdEqInstCo co ty1
590 -- two tvs, left greater => unchanged
591 go ty1@(TyVarTy tv1) ty2@(TyVarTy tv2)
593 = mkRewriteVar False tv1 ty2 co
595 -- two tvs, right greater => swap
597 = do { co' <- mkSymEqInstCo co (ty2, ty1)
598 ; mkRewriteVar True tv2 ty1 co'
601 -- only lhs is a tv => unchanged
602 go ty1@(TyVarTy tv1) ty2
603 | ty1 `tcPartOfType` ty2 -- occurs check!
604 = occurCheckErr ty1 ty2
606 = mkRewriteVar False tv1 ty2 co
608 -- only rhs is a tv => swap
609 go ty1 ty2@(TyVarTy tv2)
610 | ty2 `tcPartOfType` ty1 -- occurs check!
611 = occurCheckErr ty2 ty1
613 = do { co' <- mkSymEqInstCo co (ty2, ty1)
614 ; mkRewriteVar True tv2 ty1 co'
617 -- type applications => decompose
619 | Just (ty1_l, ty1_r) <- repSplitAppTy_maybe ty1 -- won't split fam apps
620 , Just (ty2_l, ty2_r) <- repSplitAppTy_maybe ty2
621 = do { (co_l, co_r) <- mkAppEqInstCo co (ty1_l, ty2_l) (ty1_r, ty2_r)
622 ; eqs_l <- checkOrientation ty1_l ty2_l co_l inst
623 ; eqs_r <- checkOrientation ty1_r ty2_r co_r inst
624 ; return $ eqs_l ++ eqs_r
626 -- !!!TODO: would be more efficient to handle the FunApp and the data
627 -- constructor application explicitly.
629 -- inconsistency => type error
631 = ASSERT( (not . isForAllTy $ ty1) && (not . isForAllTy $ ty2) )
634 mkRewriteVar swapped tv ty co = return [RewriteVar
638 , rwi_loc = tci_loc inst
639 , rwi_name = tci_name inst
640 , rwi_swapped = swapped
643 flattenType :: Inst -- context to get location & name
644 -> Type -- the type to flatten
645 -> TcM (Type, -- the flattened type
646 Coercion, -- coercion witness of flattening wanteds
647 [RewriteInst], -- extra equalities
648 TyVarSet) -- new intermediate skolems
649 -- Removes all family synonyms from a type by moving them into extra equalities
653 -- look through synonyms
654 go ty | Just ty' <- tcView ty
655 = do { (ty_flat, co, eqs, skolems) <- go ty'
657 then -- unchanged, keep the old type with folded synonyms
658 return (ty, ty, [], emptyVarSet)
660 return (ty_flat, co, eqs, skolems)
663 -- type variable => nothing to do
665 = return (ty, ty, [] , emptyVarSet)
667 -- type family application & family arity matches number of args
668 -- => flatten to "gamma :: F t1'..tn' ~ alpha" (alpha & gamma fresh)
669 go ty@(TyConApp con args)
670 | isOpenSynTyConApp ty -- only if not oversaturated
671 = do { (args', cargs, args_eqss, args_skolemss) <- mapAndUnzip4M go args
672 ; alpha <- newFlexiTyVar (typeKind ty)
673 ; let alphaTy = mkTyVarTy alpha
674 ; cotv <- newMetaCoVar (mkTyConApp con args') alphaTy
675 ; let thisRewriteFam = RewriteFam
678 , rwi_right = alphaTy
679 , rwi_co = mkWantedCo cotv
680 , rwi_loc = tci_loc inst
681 , rwi_name = tci_name inst
685 mkTyConApp con cargs `mkTransCoercion` mkTyVarTy cotv,
686 thisRewriteFam : concat args_eqss,
687 unionVarSets args_skolemss `extendVarSet` alpha)
688 } -- adding new unflatten var inst
690 -- data constructor application => flatten subtypes
691 -- NB: Special cased for efficiency - could be handled as type application
692 go ty@(TyConApp con args)
693 | not (isOpenSynTyCon con) -- don't match oversaturated family apps
694 = do { (args', cargs, args_eqss, args_skolemss) <- mapAndUnzip4M go args
696 then -- unchanged, keep the old type with folded synonyms
697 return (ty, ty, [], emptyVarSet)
699 return (mkTyConApp con args',
700 mkTyConApp con cargs,
702 unionVarSets args_skolemss)
705 -- function type => flatten subtypes
706 -- NB: Special cased for efficiency - could be handled as type application
707 go ty@(FunTy ty_l ty_r)
708 = do { (ty_l', co_l, eqs_l, skolems_l) <- go ty_l
709 ; (ty_r', co_r, eqs_r, skolems_r) <- go ty_r
710 ; if null eqs_l && null eqs_r
711 then -- unchanged, keep the old type with folded synonyms
712 return (ty, ty, [], emptyVarSet)
714 return (mkFunTy ty_l' ty_r',
717 skolems_l `unionVarSet` skolems_r)
720 -- type application => flatten subtypes
722 | Just (ty_l, ty_r) <- repSplitAppTy_maybe ty
723 -- need to use the smart split as ty may be an
724 -- oversaturated family application
725 = do { (ty_l', co_l, eqs_l, skolems_l) <- go ty_l
726 ; (ty_r', co_r, eqs_r, skolems_r) <- go ty_r
727 ; if null eqs_l && null eqs_r
728 then -- unchanged, keep the old type with folded synonyms
729 return (ty, ty, [], emptyVarSet)
731 return (mkAppTy ty_l' ty_r',
734 skolems_l `unionVarSet` skolems_r)
737 -- forall type => panic if the body contains a type family
738 -- !!!TODO: As long as the family does not contain a quantified variable
739 -- we might pull it out, but what if it does contain a quantified
741 go ty@(ForAllTy _ body)
742 | null (tyFamInsts body)
743 = return (ty, ty, [] , emptyVarSet)
745 = panic "TcTyFuns.flattenType: synonym family in a rank-n type"
747 -- we should never see a predicate type
749 = panic "TcTyFuns.flattenType: unexpected PredType"
751 go _ = panic "TcTyFuns: suppress bogus warning"
753 adjustCoercions :: EqInstCo -- coercion of original equality
754 -> Coercion -- coercion witnessing the left rewrite
755 -> Coercion -- coercion witnessing the right rewrite
756 -> (Type, Type) -- types of flattened equality
757 -> [RewriteInst] -- equalities from flattening
758 -> TcM (EqInstCo, -- coercion for flattened equality
759 [RewriteInst]) -- final equalities from flattening
760 -- Depending on whether we flattened a local or wanted equality, that equality's
761 -- coercion and that of the new equalities produced during flattening are
763 adjustCoercions (Left cotv) co1 co2 (ty_l, ty_r) all_eqs
764 -- wanted => generate a fresh coercion variable for the flattened equality
765 = do { cotv' <- newMetaCoVar ty_l ty_r
766 ; writeMetaTyVar cotv $
767 (co1 `mkTransCoercion` TyVarTy cotv' `mkTransCoercion` co2)
768 ; return (Left cotv', all_eqs)
771 adjustCoercions co@(Right _) _co1 _co2 _eqTys all_eqs
772 -- local => turn all new equalities into locals and update (but not zonk)
774 = do { all_eqs' <- mapM wantedToLocal all_eqs
775 ; return (co, all_eqs')
778 mkDictBind :: Inst -- original instance
779 -> Bool -- is this a wanted contraint?
780 -> Coercion -- coercion witnessing the rewrite
781 -> PredType -- coerced predicate
782 -> TcM (Inst, -- new inst
783 TcDictBinds) -- binding for coerced dictionary
784 mkDictBind dict isWanted rewriteCo pred
785 = do { dict' <- newDictBndr loc pred
786 -- relate the old inst to the new one
787 -- target_dict = source_dict `cast` st_co
788 ; let (target_dict, source_dict, st_co)
789 | isWanted = (dict, dict', mkSymCoercion rewriteCo)
790 | otherwise = (dict', dict, rewriteCo)
792 -- co :: dict ~ dict'
793 -- hence, if isWanted
794 -- dict = dict' `cast` sym co
796 -- dict' = dict `cast` co
797 expr = HsVar $ instToId source_dict
798 cast_expr = HsWrap (WpCast st_co) expr
799 rhs = L (instLocSpan loc) cast_expr
800 binds = instToDictBind target_dict rhs
801 ; return (dict', binds)
806 -- gamma ::^l Fam args ~ alpha
807 -- => gamma ::^w Fam args ~ alpha, with alpha := Fam args & gamma := Fam args
808 -- (the update of alpha will not be apparent during propagation, as we
809 -- never follow the indirections of meta variables; it will be revealed
810 -- when the equality is zonked)
812 -- NB: It's crucial to update *both* alpha and gamma, as gamma may already
813 -- have escaped into some other coercions during normalisation.
815 wantedToLocal :: RewriteInst -> TcM RewriteInst
816 wantedToLocal eq@(RewriteFam {rwi_fam = fam,
818 rwi_right = TyVarTy alpha,
819 rwi_co = Left gamma})
820 = do { writeMetaTyVar alpha (mkTyConApp fam args)
821 ; writeMetaTyVar gamma (mkTyConApp fam args)
822 ; return $ eq {rwi_co = mkGivenCo $ mkTyVarTy gamma}
824 wantedToLocal _ = panic "TcTyFuns.wantedToLocal"
828 %************************************************************************
830 Propagation of equalities
832 %************************************************************************
834 Apply the propagation rules exhaustively.
837 propagate :: [RewriteInst] -> EqConfig -> TcM EqConfig
838 propagate [] eqCfg = return eqCfg
839 propagate (eq:eqs) eqCfg
840 = do { optEqs <- applyTop eq
843 -- Top applied to 'eq' => retry with new equalities
844 Just (eqs2, skolems2)
845 -> propagate (eqs2 ++ eqs) (eqCfg `addSkolems` skolems2)
847 -- Top doesn't apply => try subst rules with all other
848 -- equalities, after that 'eq' can go into the residual list
850 -> do { (eqs', eqCfg') <- applySubstRules eq eqs eqCfg
851 ; propagate eqs' (eqCfg' `addEq` eq)
855 applySubstRules :: RewriteInst -- currently considered eq
856 -> [RewriteInst] -- todo eqs list
857 -> EqConfig -- residual
858 -> TcM ([RewriteInst], EqConfig) -- new todo & residual
859 applySubstRules eq todoEqs (eqConfig@EqConfig {eqs = resEqs})
860 = do { (newEqs_t, unchangedEqs_t, skolems_t) <- mapSubstRules eq todoEqs
861 ; (newEqs_r, unchangedEqs_r, skolems_r) <- mapSubstRules eq resEqs
862 ; return (newEqs_t ++ newEqs_r ++ unchangedEqs_t,
863 eqConfig {eqs = unchangedEqs_r}
864 `addSkolems` (skolems_t `unionVarSet` skolems_r))
867 mapSubstRules :: RewriteInst -- try substituting this equality
868 -> [RewriteInst] -- into these equalities
869 -> TcM ([RewriteInst], [RewriteInst], TyVarSet)
871 = do { (newEqss, unchangedEqss, skolemss) <- mapAndUnzip3M (substRules eq) eqs
872 ; return (concat newEqss, concat unchangedEqss, unionVarSets skolemss)
876 = do {traceTc $ hang (ptext (sLit "Trying subst rules with"))
877 4 (ppr eq1 $$ ppr eq2)
879 -- try the SubstFam rule
880 ; optEqs <- applySubstFam eq1 eq2
882 Just (eqs, skolems) -> return (eqs, [], skolems)
884 { -- try the SubstVarVar rule
885 optEqs <- applySubstVarVar eq1 eq2
887 Just (eqs, skolems) -> return (eqs, [], skolems)
889 { -- try the SubstVarFam rule
890 optEqs <- applySubstVarFam eq1 eq2
892 Just eq -> return ([eq], [], emptyVarSet)
893 Nothing -> return ([], [eq2], emptyVarSet)
894 -- if no rule matches, we return the equlity we tried to
895 -- substitute into unchanged
899 Attempt to apply the Top rule. The rule is
903 co' :: [s1/x1, .., sm/xm]s ~ t with co = g s1..sm |> co'
905 where g :: forall x1..xm. F u1..um ~ s and [s1/x1, .., sm/xm]u1 == t1.
907 Returns Nothing if the rule could not be applied. Otherwise, the resulting
908 equality is normalised and a list of the normal equalities is returned.
911 applyTop :: RewriteInst -> TcM (Maybe ([RewriteInst], TyVarSet))
913 applyTop eq@(RewriteFam {rwi_fam = fam, rwi_args = args})
914 = do { optTyCo <- tcUnfoldSynFamInst (TyConApp fam args)
916 Nothing -> return Nothing
917 Just (lhs, rewrite_co)
918 -> do { co' <- mkRightTransEqInstCo co rewrite_co (lhs, rhs)
919 ; eq' <- deriveEqInst eq lhs rhs co'
920 ; liftM Just $ normEqInst eq'
927 applyTop _ = return Nothing
930 Attempt to apply the SubstFam rule. The rule is
932 co1 :: F t1..tn ~ t & co2 :: F t1..tn ~ s
934 co1 :: F t1..tn ~ t & co2' :: t ~ s with co2 = co1 |> co2'
936 where co1 may be a wanted only if co2 is a wanted, too.
938 Returns Nothing if the rule could not be applied. Otherwise, the equality
939 co2' is normalised and a list of the normal equalities is returned. (The
940 equality co1 is not returned as it remain unaltered.)
943 applySubstFam :: RewriteInst
945 -> TcM (Maybe ([RewriteInst], TyVarSet))
946 applySubstFam eq1@(RewriteFam {rwi_fam = fam1, rwi_args = args1})
947 eq2@(RewriteFam {rwi_fam = fam2, rwi_args = args2})
949 -- rule matches => rewrite
950 | fam1 == fam2 && tcEqTypes args1 args2 &&
951 (isWantedRewriteInst eq2 || not (isWantedRewriteInst eq1))
952 = do { co2' <- mkRightTransEqInstCo co2 co1 (lhs, rhs)
953 ; eq2' <- deriveEqInst eq2 lhs rhs co2'
954 ; liftM Just $ normEqInst eq2'
957 -- rule would match with eq1 and eq2 swapped => put eq2 into todo list
958 | fam1 == fam2 && tcEqTypes args1 args2 &&
959 (isWantedRewriteInst eq1 || not (isWantedRewriteInst eq2))
960 = return $ Just ([eq2], emptyVarSet)
965 co1 = eqInstCoType (rwi_co eq1)
968 applySubstFam _ _ = return Nothing
971 Attempt to apply the SubstVarVar rule. The rule is
973 co1 :: x ~ t & co2 :: x ~ s
975 co1 :: x ~ t & co2' :: t ~ s with co2 = co1 |> co2'
977 where co1 may be a wanted only if co2 is a wanted, too.
979 Returns Nothing if the rule could not be applied. Otherwise, the equality
980 co2' is normalised and a list of the normal equalities is returned. (The
981 equality co1 is not returned as it remain unaltered.)
984 applySubstVarVar :: RewriteInst
986 -> TcM (Maybe ([RewriteInst], TyVarSet))
987 applySubstVarVar eq1@(RewriteVar {rwi_var = tv1})
988 eq2@(RewriteVar {rwi_var = tv2})
990 -- rule matches => rewrite
992 (isWantedRewriteInst eq2 || not (isWantedRewriteInst eq1))
993 = do { co2' <- mkRightTransEqInstCo co2 co1 (lhs, rhs)
994 ; eq2' <- deriveEqInst eq2 lhs rhs co2'
995 ; liftM Just $ normEqInst eq2'
998 -- rule would match with eq1 and eq2 swapped => put eq2 into todo list
1000 (isWantedRewriteInst eq1 || not (isWantedRewriteInst eq2))
1001 = return $ Just ([eq2], emptyVarSet)
1006 co1 = eqInstCoType (rwi_co eq1)
1009 applySubstVarVar _ _ = return Nothing
1012 Attempt to apply the SubstVarFam rule. The rule is
1014 co1 :: x ~ t & co2 :: F s1..sn ~ s
1016 co1 :: x ~ t & co2' :: [t/x](F s1..sn) ~ s
1017 with co2 = [co1/x](F s1..sn) |> co2'
1019 where x occurs in F s1..sn. (co1 may be local or wanted.)
1021 Returns Nothing if the rule could not be applied. Otherwise, the equality
1022 co2' is returned. (The equality co1 is not returned as it remain unaltered.)
1025 applySubstVarFam :: RewriteInst -> RewriteInst -> TcM (Maybe RewriteInst)
1027 -- rule matches => rewrite
1028 applySubstVarFam eq1@(RewriteVar {rwi_var = tv1})
1029 eq2@(RewriteFam {rwi_fam = fam2, rwi_args = args2})
1030 | tv1 `elemVarSet` tyVarsOfTypes args2
1031 = do { let co1Subst = substTyWith [tv1] [co1] (mkTyConApp fam2 args2)
1032 args2' = substTysWith [tv1] [rhs1] args2
1033 lhs2 = mkTyConApp fam2 args2'
1034 ; co2' <- mkRightTransEqInstCo co2 co1Subst (lhs2, rhs2)
1035 ; return $ Just (eq2 {rwi_args = args2', rwi_co = co2'})
1038 rhs1 = rwi_right eq1
1039 rhs2 = rwi_right eq2
1040 co1 = eqInstCoType (rwi_co eq1)
1043 -- rule would match with eq1 and eq2 swapped => put eq2 into todo list
1044 applySubstVarFam (RewriteFam {rwi_args = args1})
1045 eq2@(RewriteVar {rwi_var = tv2})
1046 | tv2 `elemVarSet` tyVarsOfTypes args1
1049 applySubstVarFam _ _ = return Nothing
1053 %************************************************************************
1055 Finalisation of equalities
1057 %************************************************************************
1059 Exhaustive substitution of all variable equalities of the form co :: x ~ t
1060 (both local and wanted) into the left-hand sides of all other equalities. This
1061 may lead to recursive equalities; i.e., (1) we need to apply the substitution
1062 implied by one variable equality exhaustively before turning to the next and
1063 (2) we need an occurs check.
1065 We also apply the same substitutions to the local and wanted class and IP
1068 The treatment of flexibles in wanteds is quite subtle. We absolutely want to
1069 substitute them into right-hand sides of equalities, to avoid getting two
1070 competing instantiations for a type variables; e.g., consider
1072 F s ~ alpha, alpha ~ t
1074 If we don't substitute `alpha ~ t', we may instantiate t with `F s' instead.
1075 This would be bad as `F s' is less useful, eg, as an argument to a class
1078 However, there is no reason why we would want to *substitute* `alpha ~ t' into a
1079 class constraint. We rather wait until `alpha' is instantiated to `t` and
1080 save the extra dictionary binding that substitution would introduce.
1081 Moreover, we may substitute wanted equalities only into wanted dictionaries.
1084 * Given that we apply the substitution corresponding to a single equality
1085 exhaustively, before turning to the next, and because we eliminate recursive
1086 equalities, all opportunities for subtitution will have been exhausted after
1087 we have considered each equality once.
1090 substitute :: [RewriteInst] -- equalities
1091 -> [Inst] -- local class dictionaries
1092 -> [Inst] -- wanted class dictionaries
1093 -> TcM ([RewriteInst], -- equalities after substitution
1094 TcDictBinds, -- all newly generated dictionary bindings
1095 [Inst], -- local dictionaries after substitution
1096 [Inst]) -- wanted dictionaries after substitution
1097 substitute eqs locals wanteds = subst eqs [] emptyBag locals wanteds
1099 subst [] res binds locals wanteds
1100 = return (res, binds, locals, wanteds)
1102 subst (eq@(RewriteVar {rwi_var = tv, rwi_right = ty, rwi_co = co}):eqs)
1103 res binds locals wanteds
1104 = do { traceTc $ ptext (sLit "TcTyFuns.substitute:") <+> ppr eq
1106 ; let coSubst = zipOpenTvSubst [tv] [eqInstCoType co]
1107 tySubst = zipOpenTvSubst [tv] [ty]
1108 ; eqs' <- mapM (substEq eq coSubst tySubst) eqs
1109 ; res' <- mapM (substEq eq coSubst tySubst) res
1111 -- only susbtitute local equalities into local dictionaries
1112 ; (lbinds, locals') <- if not (isWantedCo co)
1115 (substDict eq coSubst tySubst False)
1120 -- flexible tvs in wanteds will be instantiated anyway, there is
1121 -- no need to substitute them into dictionaries
1122 ; (wbinds, wanteds') <- if not (isMetaTyVar tv && isWantedCo co)
1125 (substDict eq coSubst tySubst True)
1128 return ([], wanteds)
1130 ; let binds' = unionManyBags $ binds : lbinds ++ wbinds
1131 ; subst eqs' (eq:res') binds' locals' wanteds'
1133 subst (eq:eqs) res binds locals wanteds
1134 = subst eqs (eq:res) binds locals wanteds
1136 -- We have, co :: tv ~ ty
1137 -- => apply [ty/tv] to right-hand side of eq2
1138 -- (but only if tv actually occurs in the right-hand side of eq2)
1139 substEq (RewriteVar {rwi_var = tv, rwi_right = ty})
1141 | tv `elemVarSet` tyVarsOfType (rwi_right eq2)
1142 = do { let co1Subst = mkSymCoercion $ substTy coSubst (rwi_right eq2)
1143 right2' = substTy tySubst (rwi_right eq2)
1145 RewriteVar {rwi_var = tv2} -> mkTyVarTy tv2
1146 RewriteFam {rwi_fam = fam,
1147 rwi_args = args} ->mkTyConApp fam args
1148 ; co2' <- mkLeftTransEqInstCo (rwi_co eq2) co1Subst (left2, right2')
1150 RewriteVar {rwi_var = tv2} | tv2 `elemVarSet` tyVarsOfType ty
1151 -> occurCheckErr left2 right2'
1152 _ -> return $ eq2 {rwi_right = right2', rwi_co = co2'}
1159 -- We have, co :: tv ~ ty
1160 -- => apply [ty/tv] to dictionary predicate
1161 -- (but only if tv actually occurs in the predicate)
1162 substDict (RewriteVar {rwi_var = tv}) coSubst tySubst isWanted dict
1164 , tv `elemVarSet` tyVarsOfPred (tci_pred dict)
1165 = do { let co1Subst = PredTy (substPred coSubst (tci_pred dict))
1166 pred' = substPred tySubst (tci_pred dict)
1167 ; (dict', binds) <- mkDictBind dict isWanted co1Subst pred'
1168 ; return (binds, dict')
1172 substDict _ _ _ _ dict
1173 = return (emptyBag, dict)
1174 -- !!!TODO: Still need to substitute into IP constraints.
1177 For any *wanted* variable equality of the form co :: alpha ~ t or co :: a ~
1178 alpha, we instantiate alpha with t or a, respectively, and set co := id.
1179 Return all remaining wanted equalities. The Boolean result component is True
1180 if at least one instantiation of a flexible that is *not* a skolem from
1181 flattening was performed.
1183 We need to instantiate all flexibles that arose as skolems during flattening
1184 of wanteds before we instantiate any other flexibles. Consider F delta ~
1185 alpha, F alpha ~ delta, where alpha is a skolem and delta a free flexible. We
1186 need to produce F (F delta) ~ delta (and not F (F alpha) ~ alpha). Otherwise,
1187 we may wrongly claim to having performed an improvement, which can lead to
1188 non-termination of the combined class-family solver.
1191 instantiateAndExtract :: [RewriteInst] -> Bool -> TyVarSet -> TcM ([Inst], Bool)
1192 instantiateAndExtract eqs localsEmpty skolems
1193 = do { traceTc $ hang (ptext (sLit "instantiateAndExtract:"))
1194 4 (ppr eqs $$ ppr skolems)
1195 -- start by *only* instantiating skolem flexibles from flattening
1196 ; unflat_wanteds <- liftM catMaybes $
1197 mapM (inst (`elemVarSet` skolems)) wanteds
1198 -- only afterwards instantiate free flexibles
1199 ; residuals <- liftM catMaybes $ mapM (inst (const True)) unflat_wanteds
1200 ; let improvement = length residuals < length unflat_wanteds
1201 ; residuals' <- mapM rewriteInstToInst residuals
1202 ; return (residuals', improvement)
1205 wanteds = filter (isWantedCo . rwi_co) eqs
1206 checkingMode = length eqs > length wanteds || not localsEmpty
1207 -- no local equalities or dicts => checking mode
1209 -- co :: alpha ~ t or co :: a ~ alpha
1210 inst mayInst eq@(RewriteVar {rwi_var = tv1, rwi_right = ty2, rwi_co = co})
1211 = do { flexi_tv1 <- isFlexible mayInst tv1
1212 ; maybe_flexi_tv2 <- isFlexibleTy mayInst ty2
1213 ; case (flexi_tv1, maybe_flexi_tv2) of
1215 -> -- co :: alpha ~ t
1216 doInst (rwi_swapped eq) tv1 ty2 co eq
1218 -> -- co :: a ~ alpha
1219 doInst (not $ rwi_swapped eq) tv2 (mkTyVarTy tv1) co eq
1220 _ -> return $ Just eq
1223 -- co :: F args ~ alpha, and we are in checking mode (ie, no locals)
1224 inst mayInst eq@(RewriteFam {rwi_fam = fam, rwi_args = args,
1225 rwi_right = ty2, rwi_co = co})
1226 | Just tv2 <- tcGetTyVar_maybe ty2
1228 , mayInst tv2 && (checkingMode || tv2 `elemVarSet` skolems)
1229 -- !!!FIXME: this is too liberal, even if tv2 is in
1230 -- skolems we shouldn't instantiate if tvs occurs
1231 -- in other equalities that may propagate it into the
1233 = doInst (not $ rwi_swapped eq) tv2 (mkTyConApp fam args) co eq
1235 inst _mayInst eq = return $ Just eq
1237 -- tv is a meta var and not filled
1238 isFlexible mayInst tv
1239 | isMetaTyVar tv && mayInst tv = liftM isFlexi $ readMetaTyVar tv
1240 | otherwise = return False
1242 -- type is a tv that is a meta var and not filled
1243 isFlexibleTy mayInst ty
1244 | Just tv <- tcGetTyVar_maybe ty = do {flexi <- isFlexible mayInst tv
1245 ; if flexi then return $ Just tv
1248 | otherwise = return Nothing
1250 doInst _swapped _tv _ty (Right ty) _eq
1251 = pprPanic "TcTyFuns.doInst: local eq: " (ppr ty)
1252 doInst swapped tv ty (Left cotv) eq
1253 = do { lookupTV <- lookupTcTyVar tv
1254 ; uMeta swapped tv lookupTV ty cotv
1257 -- meta variable has been filled already
1258 -- => keep the equality
1259 uMeta _swapped tv (IndirectTv fill_ty) ty _cotv
1261 ptext (sLit "flexible") <+> ppr tv <+>
1262 ptext (sLit "already filled with") <+> ppr fill_ty <+>
1263 ptext (sLit "meant to fill with") <+> ppr ty
1267 -- type variable meets type variable
1268 -- => check that tv2 hasn't been updated yet and choose which to update
1269 uMeta swapped tv1 (DoneTv details1) (TyVarTy tv2) cotv
1271 = panic "TcTyFuns.uMeta: normalisation shouldn't allow x ~ x"
1274 = do { lookupTV2 <- lookupTcTyVar tv2
1277 uMeta swapped tv1 (DoneTv details1) ty cotv
1279 uMetaVar swapped tv1 details1 tv2 details2 cotv
1282 ------ Beyond this point we know that ty2 is not a type variable
1284 -- signature skolem meets non-variable type
1285 -- => cannot update (retain the equality)!
1286 uMeta _swapped _tv (DoneTv (MetaTv (SigTv _) _)) _non_tv_ty _cotv
1289 -- updatable meta variable meets non-variable type
1290 -- => occurs check, monotype check, and kinds match check, then update
1291 uMeta swapped tv (DoneTv (MetaTv _ ref)) non_tv_ty cotv
1292 = do { -- occurs + monotype check
1293 ; mb_ty' <- checkTauTvUpdate tv non_tv_ty
1297 -- there may be a family in non_tv_ty due to an unzonked,
1298 -- but updated skolem for a local equality
1301 do { checkUpdateMeta swapped tv ref ty' -- update meta var
1302 ; writeMetaTyVar cotv ty' -- update co var
1307 uMeta _ _ _ _ _ = panic "TcTyFuns.uMeta"
1309 -- uMetaVar: unify two type variables
1310 -- meta variable meets skolem
1312 uMetaVar swapped tv1 (MetaTv _ ref) tv2 (SkolemTv _) cotv
1313 = do { checkUpdateMeta swapped tv1 ref (mkTyVarTy tv2)
1314 ; writeMetaTyVar cotv (mkTyVarTy tv2)
1318 -- meta variable meets meta variable
1319 -- => be clever about which of the two to update
1320 -- (from TcUnify.uUnfilledVars minus boxy stuff)
1321 uMetaVar swapped tv1 (MetaTv info1 ref1) tv2 (MetaTv info2 ref2) cotv
1322 = do { case (info1, info2) of
1323 -- Avoid SigTvs if poss
1324 (SigTv _, _ ) | k1_sub_k2 -> update_tv2
1325 (_, SigTv _) | k2_sub_k1 -> update_tv1
1327 (_, _) | k1_sub_k2 -> if k2_sub_k1 &&
1329 then update_tv1 -- Same kinds
1331 | k2_sub_k1 -> update_tv1
1332 | otherwise -> kind_err
1333 -- Update the variable with least kind info
1334 -- See notes on type inference in Kind.lhs
1335 -- The "nicer to" part only applies if the two kinds are the same,
1336 -- so we can choose which to do.
1338 ; writeMetaTyVar cotv (mkTyVarTy tv2)
1342 -- Kinds should be guaranteed ok at this point
1343 update_tv1 = updateMeta tv1 ref1 (mkTyVarTy tv2)
1344 update_tv2 = updateMeta tv2 ref2 (mkTyVarTy tv1)
1346 kind_err = addErrCtxtM (unifyKindCtxt swapped tv1 (mkTyVarTy tv2)) $
1347 unifyKindMisMatch k1 k2
1351 k1_sub_k2 = k1 `isSubKind` k2
1352 k2_sub_k1 = k2 `isSubKind` k1
1354 nicer_to_update_tv1 = isSystemName (Var.varName tv1)
1355 -- Try to update sys-y type variables in preference to ones
1356 -- gotten (say) by instantiating a polymorphic function with
1357 -- a user-written type sig
1359 uMetaVar _ _ _ _ _ _ = panic "uMetaVar"
1363 %************************************************************************
1367 %************************************************************************
1369 The infamous couldn't match expected type soandso against inferred type
1370 somethingdifferent message.
1373 eqInstMisMatch :: Inst -> TcM a
1375 = ASSERT( isEqInst inst )
1376 setErrCtxt ctxt $ failWithMisMatch ty_act ty_exp
1378 (ty_act, ty_exp) = eqInstTys inst
1379 InstLoc _ _ ctxt = instLoc inst
1381 -----------------------
1382 failWithMisMatch :: TcType -> TcType -> TcM a
1383 -- Generate the message when two types fail to match,
1384 -- going to some trouble to make it helpful.
1385 -- The argument order is: actual type, expected type
1386 failWithMisMatch ty_act ty_exp
1387 = do { env0 <- tcInitTidyEnv
1388 ; ty_exp <- zonkTcType ty_exp
1389 ; ty_act <- zonkTcType ty_act
1390 ; failWithTcM (misMatchMsg env0 (ty_act, ty_exp))
1393 misMatchMsg :: TidyEnv -> (TcType, TcType) -> (TidyEnv, SDoc)
1394 misMatchMsg env0 (ty_act, ty_exp)
1395 = let (env1, pp_exp, extra_exp) = ppr_ty env0 ty_exp
1396 (env2, pp_act, extra_act) = ppr_ty env1 ty_act
1397 msg = sep [sep [ptext (sLit "Couldn't match expected type") <+> pp_exp,
1399 ptext (sLit "against inferred type") <+> pp_act],
1400 nest 2 (extra_exp $$ extra_act)]
1405 ppr_ty :: TidyEnv -> TcType -> (TidyEnv, SDoc, SDoc)
1407 = let (env1, tidy_ty) = tidyOpenType env ty
1408 (env2, extra) = ppr_extra env1 tidy_ty
1410 (env2, quotes (ppr tidy_ty), extra)
1412 -- (ppr_extra env ty) shows extra info about 'ty'
1413 ppr_extra :: TidyEnv -> Type -> (TidyEnv, SDoc)
1414 ppr_extra env (TyVarTy tv)
1415 | isTcTyVar tv && (isSkolemTyVar tv || isSigTyVar tv) && not (isUnk tv)
1416 = (env1, pprSkolTvBinding tv1)
1418 (env1, tv1) = tidySkolemTyVar env tv
1420 ppr_extra env _ty = (env, empty) -- Normal case
1423 Warn of loopy local equalities that were dropped.
1426 warnDroppingLoopyEquality :: TcType -> TcType -> TcM ()
1427 warnDroppingLoopyEquality ty1 ty2
1428 = do { env0 <- tcInitTidyEnv
1429 ; ty1 <- zonkTcType ty1
1430 ; ty2 <- zonkTcType ty2
1431 ; let (env1 , tidy_ty1) = tidyOpenType env0 ty1
1432 (_env2, tidy_ty2) = tidyOpenType env1 ty2
1433 ; addWarnTc $ hang (ptext (sLit "Dropping loopy given equality"))
1434 2 (quotes (ppr tidy_ty1 <+> text "~" <+> ppr tidy_ty2))