3 reportUnsolved, reportUnsolvedDeriv,
4 reportUnsolvedWantedEvVars, warnDefaulting,
5 unifyCtxt, typeExtraInfoMsg,
6 kindErrorTcS, misMatchErrorTcS, flattenForAllErrorTcS,
7 occursCheckErrorTcS, solverDepthErrorTcS
10 #include "HsVersions.h"
23 import HsExpr ( pprMatchContext )
29 import ListSetOps( equivClasses )
34 import StaticFlags( opt_PprStyle_Debug )
35 import Data.List( partition )
36 import Control.Monad( when, unless )
39 %************************************************************************
41 \section{Errors and contexts}
43 %************************************************************************
45 ToDo: for these error messages, should we note the location as coming
46 from the insts, or just whatever seems to be around in the monad just
50 reportUnsolved :: (CanonicalCts, Bag Implication) -> TcM ()
51 reportUnsolved (unsolved_flats, unsolved_implics)
55 = do { unsolved <- mapBagM zonkWanted unsolved
56 -- Zonk to un-flatten any flatten-skols
57 ; env0 <- tcInitTidyEnv
58 ; let tidy_env = tidyFreeTyVars env0 (tyVarsOfWanteds unsolved)
59 tidy_unsolved = tidyWanteds tidy_env unsolved
60 err_ctxt = CEC { cec_encl = []
62 , cec_tidy = tidy_env }
63 ; traceTc "reportUnsolved" (ppr unsolved)
64 ; reportTidyWanteds err_ctxt tidy_unsolved }
66 unsolved = mkWantedConstraints unsolved_flats unsolved_implics
69 reportUnsolvedWantedEvVars :: Bag WantedEvVar -> TcM ()
70 reportUnsolvedWantedEvVars wanteds
74 = do { wanteds <- mapBagM zonkWantedEvVar wanteds
75 ; env0 <- tcInitTidyEnv
76 ; let tidy_env = tidyFreeTyVars env0 (tyVarsOfWantedEvVars wanteds)
77 tidy_unsolved = tidyWantedEvVars tidy_env wanteds
78 err_ctxt = CEC { cec_encl = []
80 , cec_tidy = tidy_env }
81 ; groupErrs (reportFlat err_ctxt) (bagToList tidy_unsolved) }
83 reportUnsolvedDeriv :: [PredType] -> WantedLoc -> TcM ()
84 reportUnsolvedDeriv unsolved loc
89 do { unsolved <- zonkTcThetaType unsolved
90 ; env0 <- tcInitTidyEnv
91 ; let tidy_env = tidyFreeTyVars env0 (tyVarsOfTheta unsolved)
92 tidy_unsolved = map (tidyPred tidy_env) unsolved
93 err_ctxt = CEC { cec_encl = []
95 , cec_tidy = tidy_env }
96 ; reportFlat err_ctxt tidy_unsolved (ctLocOrigin loc) }
98 alt_fix = vcat [ptext (sLit "Alternatively, use a standalone 'deriving instance' declaration,"),
99 nest 2 $ ptext (sLit "so you can specify the instance context yourself")]
101 --------------------------------------------
102 -- Internal functions
103 --------------------------------------------
106 = CEC { cec_encl :: [Implication] -- Enclosing implications
108 , cec_tidy :: TidyEnv
109 , cec_extra :: SDoc -- Add this to each error message
112 reportTidyImplic :: ReportErrCtxt -> Implication -> TcM ()
113 reportTidyImplic ctxt implic
114 = reportTidyWanteds ctxt' (ic_wanted implic)
116 ctxt' = ctxt { cec_encl = implic : cec_encl ctxt }
118 reportTidyWanteds :: ReportErrCtxt -> WantedConstraints -> TcM ()
119 reportTidyWanteds ctxt unsolved
120 = do { let (flats, implics) = splitWanteds unsolved
121 (ambigs, non_ambigs) = partition is_ambiguous (bagToList flats)
122 (tv_eqs, others) = partition is_tv_eq non_ambigs
124 ; groupErrs (reportEqErrs ctxt) tv_eqs
125 ; when (null tv_eqs) $ groupErrs (reportFlat ctxt) others
126 ; when (null tv_eqs) $ mapBagM_ (reportTidyImplic ctxt) implics
128 -- Only report ambiguity if no other errors happened
129 -- See Note [Avoiding spurious errors]
130 ; when (isEmptyBag implics && null non_ambigs) $
131 reportAmbigErrs ctxt skols ambigs }
133 skols = foldr (unionVarSet . ic_skols) emptyVarSet (cec_encl ctxt)
135 -- Report equalities of form (a~ty) first. They are usually
136 -- skolem-equalities, and they cause confusing knock-on
137 -- effects in other errors; see test T4093b.
138 is_tv_eq c | EqPred ty1 ty2 <- wantedEvVarPred c
139 = tcIsTyVarTy ty1 || tcIsTyVarTy ty2
142 -- Treat it as "ambiguous" if
143 -- (a) it is a class constraint
144 -- (b) it constrains only type variables
145 -- (else we'd prefer to report it as "no instance for...")
146 -- (c) it mentions type variables that are not skolems
147 is_ambiguous d = isTyVarClassPred pred
148 && not (tyVarsOfPred pred `subVarSet` skols)
150 pred = wantedEvVarPred d
152 reportFlat :: ReportErrCtxt -> [PredType] -> CtOrigin -> TcM ()
153 reportFlat ctxt flats origin
154 = do { unless (null dicts) $ reportDictErrs ctxt dicts origin
155 ; unless (null eqs) $ reportEqErrs ctxt eqs origin
156 ; unless (null ips) $ reportIPErrs ctxt ips origin
157 ; ASSERT( null others ) return () }
159 (dicts, non_dicts) = partition isClassPred flats
160 (eqs, non_eqs) = partition isEqPred non_dicts
161 (ips, others) = partition isIPPred non_eqs
163 --------------------------------------------
165 --------------------------------------------
167 groupErrs :: ([PredType] -> CtOrigin -> TcM ()) -- Deal with one group
168 -> [WantedEvVar] -- Unsolved wanteds
170 -- Group together insts with the same origin
171 -- We want to report them together in error messages
175 groupErrs report_err (wanted : wanteds)
176 = do { setCtLoc the_loc $
177 report_err the_vars (ctLocOrigin the_loc)
178 ; groupErrs report_err others }
180 the_loc = wantedEvVarLoc wanted
181 the_key = mk_key the_loc
182 the_vars = map wantedEvVarPred (wanted:friends)
183 (friends, others) = partition is_friend wanteds
184 is_friend friend = mk_key (wantedEvVarLoc friend) == the_key
186 mk_key :: WantedLoc -> (SrcSpan, String)
187 mk_key loc = (ctLocSpan loc, showSDoc (ppr (ctLocOrigin loc)))
188 -- It may seem crude to compare the error messages,
189 -- but it makes sure that we combine just what the user sees,
190 -- and it avoids need equality on InstLocs.
192 -- Add the "arising from..." part to a message about bunch of dicts
193 addArising :: CtOrigin -> SDoc -> SDoc
194 addArising orig msg = msg $$ nest 2 (pprArising orig)
196 pprWithArising :: [WantedEvVar] -> (WantedLoc, SDoc)
197 -- Print something like
198 -- (Eq a) arising from a use of x at y
199 -- (Show a) arising froma use of p at q
200 -- Also return a location for the erroe message
202 = panic "pprWithArising"
203 pprWithArising [WantedEvVar ev loc]
204 = (loc, pprEvVarTheta [ev] <+> pprArising (ctLocOrigin loc))
205 pprWithArising ev_vars
206 = (first_loc, vcat (map ppr_one ev_vars))
208 first_loc = wantedEvVarLoc (head ev_vars)
209 ppr_one (WantedEvVar v loc)
210 = parens (pprPred (evVarPred v)) <+> pprArisingAt loc
212 addErrorReport :: ReportErrCtxt -> SDoc -> TcM ()
213 addErrorReport ctxt msg = addErrTcM (cec_tidy ctxt, msg $$ cec_extra ctxt)
215 pprErrCtxtLoc :: ReportErrCtxt -> SDoc
217 = case map (ctLocOrigin . ic_loc) (cec_encl ctxt) of
218 [] -> ptext (sLit "the top level") -- Should not happen
219 (orig:origs) -> ppr_skol orig $$
220 vcat [ ptext (sLit "or") <+> ppr_skol orig | orig <- origs ]
222 ppr_skol (PatSkol dc _) = ptext (sLit "the data constructor") <+> quotes (ppr dc)
223 ppr_skol skol_info = pprSkolInfo skol_info
225 couldNotDeduce :: [EvVar] -> [PredType] -> SDoc
226 couldNotDeduce givens wanteds
227 = sep [ ptext (sLit "Could not deduce") <+> pprTheta wanteds
228 , nest 2 $ ptext (sLit "from the context")
229 <+> pprEvVarTheta givens]
231 getUserGivens :: ReportErrCtxt -> Maybe [EvVar]
232 -- Just gs => Say "could not deduce ... from gs"
233 -- Nothing => No interesting givens, say something else
234 getUserGivens (CEC {cec_encl = ctxt})
235 | null user_givens = Nothing
236 | otherwise = Just user_givens
238 givens = foldl (\gs ic -> ic_given ic ++ gs) [] ctxt
239 user_givens | opt_PprStyle_Debug = givens
240 | otherwise = filterOut isSelfDict givens
241 -- In user mode, don't show the "self-dict" given
242 -- which is only added to do co-inductive solving
243 -- Rather an awkward hack, but there we are
244 -- This is the only use of isSelfDict, so it's not in an inner loop
248 %************************************************************************
250 Implicit parameter errors
252 %************************************************************************
255 reportIPErrs :: ReportErrCtxt -> [PredType] -> CtOrigin -> TcM ()
256 reportIPErrs ctxt ips orig
257 = addErrorReport ctxt $ addArising orig msg
259 msg | Just givens <- getUserGivens ctxt
260 = couldNotDeduce givens ips
262 = sep [ ptext (sLit "Unbound implicit parameter") <> plural ips
263 , nest 2 (pprTheta ips) ]
267 %************************************************************************
271 %************************************************************************
274 reportEqErrs :: ReportErrCtxt -> [PredType] -> CtOrigin -> TcM ()
275 reportEqErrs ctxt eqs orig
276 = mapM_ report_one eqs
279 report_one (EqPred ty1 ty2)
280 = do { (env1, extra) <- getWantedEqExtra emptyTvSubst env0 orig ty1 ty2
281 ; let ctxt' = ctxt { cec_tidy = env1
282 , cec_extra = cec_extra ctxt $$ extra }
283 ; reportEqErr ctxt' ty1 ty2 }
285 = pprPanic "reportEqErrs" (ppr pred)
287 reportEqErr :: ReportErrCtxt -> TcType -> TcType -> TcM ()
288 reportEqErr ctxt ty1 ty2
289 | Just tv1 <- tcGetTyVar_maybe ty1 = reportTyVarEqErr ctxt tv1 ty2
290 | Just tv2 <- tcGetTyVar_maybe ty2 = reportTyVarEqErr ctxt tv2 ty1
291 | otherwise -- Neither side is a type variable
292 -- Since the unsolved constraint is canonical,
293 -- it must therefore be of form (F tys ~ ty)
294 = addErrorReport ctxt (msg $$ mkTyFunInfoMsg ty1 ty2)
296 msg = case getUserGivens ctxt of
297 Just givens -> couldNotDeduce givens [EqPred ty1 ty2]
298 Nothing -> misMatchMsg ty1 ty2
300 reportTyVarEqErr :: ReportErrCtxt -> TcTyVar -> TcType -> TcM ()
301 reportTyVarEqErr ctxt tv1 ty2
303 , Just tv2 <- tcGetTyVar_maybe ty2
305 = -- sk ~ alpha: swap
306 reportTyVarEqErr ctxt tv2 ty1
309 = -- sk ~ ty, where ty isn't a meta-tyvar: mis-match
310 addErrTcM (misMatchMsgWithExtras (cec_tidy ctxt) ty1 ty2)
312 -- So tv is a meta tyvar, and presumably it is
313 -- an *untouchable* meta tyvar, else it'd have been unified
314 | not (k2 `isSubKind` k1) -- Kind error
315 = addErrorReport ctxt $ (kindErrorMsg (mkTyVarTy tv1) ty2)
317 -- Check for skolem escape
318 | (implic:_) <- cec_encl ctxt -- Get the innermost context
319 , let esc_skols = varSetElems (tyVarsOfType ty2 `intersectVarSet` ic_skols implic)
320 implic_loc = ic_loc implic
321 , not (null esc_skols)
322 = setCtLoc implic_loc $ -- Override the error message location from the
323 -- place the equality arose to the implication site
324 do { (env1, env_sigs) <- findGlobals ctxt (unitVarSet tv1)
325 ; let msg = misMatchMsg ty1 ty2
326 esc_doc | isSingleton esc_skols
327 = ptext (sLit "because this skolem type variable would escape:")
329 = ptext (sLit "because these skolem type variables would escape:")
330 extra1 = vcat [ nest 2 $ esc_doc <+> pprQuotedList esc_skols
331 , sep [ (if isSingleton esc_skols
332 then ptext (sLit "This skolem is")
333 else ptext (sLit "These skolems are"))
334 <+> ptext (sLit "bound by")
335 , nest 2 $ pprSkolInfo (ctLocOrigin implic_loc) ] ]
336 ; addErrTcM (env1, msg $$ extra1 $$ mkEnvSigMsg (ppr tv1) env_sigs) }
338 -- Nastiest case: attempt to unify an untouchable variable
339 | (implic:_) <- cec_encl ctxt -- Get the innermost context
340 , let implic_loc = ic_loc implic
341 given = ic_given implic
342 = setCtLoc (ic_loc implic) $
343 do { let (env1, msg) = misMatchMsgWithExtras (cec_tidy ctxt) ty1 ty2
344 extra = vcat [ ptext (sLit "because") <+> ppr tv1 <+> ptext (sLit "is untouchable")
345 , ptext (sLit "inside the constraints") <+> pprEvVarTheta given
346 , nest 2 (ptext (sLit "bound at")
347 <+> pprSkolInfo (ctLocOrigin implic_loc)) ]
348 ; addErrTcM (env1, msg $$ extra) }
350 | otherwise -- I'm not sure how this can happen!
351 = addErrTcM (misMatchMsgWithExtras (cec_tidy ctxt) ty1 ty2)
353 is_meta1 = isMetaTyVar tv1
358 mkTyFunInfoMsg :: TcType -> TcType -> SDoc
359 -- See Note [Non-injective type functions]
360 mkTyFunInfoMsg ty1 ty2
361 | Just (tc1,_) <- tcSplitTyConApp_maybe ty1
362 , Just (tc2,_) <- tcSplitTyConApp_maybe ty2
363 , tc1 == tc2, isSynFamilyTyCon tc1
364 = ptext (sLit "NB:") <+> quotes (ppr tc1)
365 <+> ptext (sLit "is a type function") <> (pp_inj tc1)
368 pp_inj tc | isInjectiveTyCon tc = empty
369 | otherwise = ptext (sLit (", and may not be injective"))
371 misMatchMsgWithExtras :: TidyEnv -> TcType -> TcType -> (TidyEnv, SDoc)
372 -- This version is used by TcSimplify too, which doesn't track the
373 -- expected/acutal thing, so we just have ty1 ty2 here
374 -- NB: The types are already tidied
375 misMatchMsgWithExtras env ty1 ty2
376 = (env2, sep [ misMatchMsg ty1 ty2, nest 2 (extra1 $$ extra2) ])
378 (env1, extra1) = typeExtraInfoMsg env ty1
379 (env2, extra2) = typeExtraInfoMsg env1 ty2
381 misMatchMsg :: TcType -> TcType -> SDoc -- Types are already tidy
382 misMatchMsg ty1 ty2 = sep [ ptext (sLit "Couldn't match type") <+> quotes (ppr ty1)
383 , nest 15 $ ptext (sLit "with") <+> quotes (ppr ty2)]
385 kindErrorMsg :: TcType -> TcType -> SDoc -- Types are already tidy
387 = vcat [ ptext (sLit "Kind incompatibility when matching types:")
388 , nest 2 (vcat [ ppr ty1 <+> dcolon <+> ppr k1
389 , ppr ty2 <+> dcolon <+> ppr k2 ]) ]
394 typeExtraInfoMsg :: TidyEnv -> Type -> (TidyEnv, SDoc)
395 -- Shows a bit of extra info about skolem constants
396 typeExtraInfoMsg env ty
397 | Just tv <- tcGetTyVar_maybe ty
399 , isSkolemTyVar tv || isSigTyVar tv
401 , let (env1, tv1) = tidySkolemTyVar env tv
402 = (env1, pprSkolTvBinding tv1)
404 typeExtraInfoMsg env _ty = (env, empty) -- Normal case
407 unifyCtxt :: EqOrigin -> TidyEnv -> TcM (TidyEnv, SDoc)
408 unifyCtxt (UnifyOrigin { uo_actual = act_ty, uo_expected = exp_ty }) tidy_env
409 = do { act_ty' <- zonkTcType act_ty
410 ; exp_ty' <- zonkTcType exp_ty
411 ; let (env1, exp_ty'') = tidyOpenType tidy_env exp_ty'
412 (env2, act_ty'') = tidyOpenType env1 act_ty'
413 ; return (env2, mkExpectedActualMsg act_ty'' exp_ty'') }
415 mkExpectedActualMsg :: Type -> Type -> SDoc
416 mkExpectedActualMsg act_ty exp_ty
417 = vcat [ text "Expected type" <> colon <+> ppr exp_ty
418 , text " Actual type" <> colon <+> ppr act_ty ]
421 Note [Non-injective type functions]
422 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
423 It's very confusing to get a message like
424 Couldn't match expected type `Depend s'
425 against inferred type `Depend s1'
426 so mkTyFunInfoMsg adds:
427 NB: `Depend' is type function, and hence may not be injective
429 Warn of loopy local equalities that were dropped.
432 %************************************************************************
436 %************************************************************************
439 reportDictErrs :: ReportErrCtxt -> [PredType] -> CtOrigin -> TcM ()
440 reportDictErrs ctxt wanteds orig
441 = do { inst_envs <- tcGetInstEnvs
442 ; let (others, overlaps) = partitionWith (check_overlap inst_envs) wanteds
443 ; unless (null others) $
444 addErrorReport ctxt (mk_no_inst_err others)
445 ; mapM_ (addErrorReport ctxt) overlaps }
447 check_overlap :: (InstEnv,InstEnv) -> PredType -> Either PredType SDoc
448 -- Right msg => overlap message
449 -- Left inst => no instance
450 check_overlap inst_envs pred@(ClassP clas tys)
451 = case lookupInstEnv inst_envs clas tys of
452 ([], _) -> Left pred -- No match
453 -- The case of exactly one match and no unifiers means a
454 -- successful lookup. That can't happen here, because dicts
455 -- only end up here if they didn't match in Inst.lookupInst
457 | debugIsOn -> pprPanic "check_overlap" (ppr pred)
458 res -> Right (mk_overlap_msg pred res)
459 check_overlap _ _ = panic "check_overlap"
461 mk_overlap_msg pred (matches, unifiers)
462 = ASSERT( not (null matches) )
463 vcat [ addArising orig (ptext (sLit "Overlapping instances for")
465 , sep [ptext (sLit "Matching instances") <> colon,
466 nest 2 (vcat [pprInstances ispecs, pprInstances unifiers])]
467 , if not (isSingleton matches)
468 then -- Two or more matches
470 else -- One match, plus some unifiers
471 ASSERT( not (null unifiers) )
472 parens (vcat [ptext (sLit "The choice depends on the instantiation of") <+>
473 quotes (pprWithCommas ppr (varSetElems (tyVarsOfPred pred))),
474 ptext (sLit "To pick the first instance above, use -XIncoherentInstances"),
475 ptext (sLit "when compiling the other instance declarations")])]
477 ispecs = [ispec | (ispec, _) <- matches]
479 mk_no_inst_err :: [PredType] -> SDoc
480 mk_no_inst_err wanteds
481 | Just givens <- getUserGivens ctxt
482 = vcat [ addArising orig $ couldNotDeduce givens wanteds
483 , show_fixes (fix1 : fixes2) ]
485 | otherwise -- Top level
486 = vcat [ addArising orig $
487 ptext (sLit "No instance") <> plural wanteds
488 <+> ptext (sLit "for") <+> pprTheta wanteds
489 , show_fixes fixes2 ]
492 fix1 = sep [ ptext (sLit "add") <+> pprTheta wanteds
493 <+> ptext (sLit "to the context of")
494 , nest 2 $ pprErrCtxtLoc ctxt ]
496 fixes2 | null instance_dicts = []
497 | otherwise = [sep [ptext (sLit "add an instance declaration for"),
498 pprTheta instance_dicts]]
499 instance_dicts = filterOut isTyVarClassPred wanteds
500 -- Insts for which it is worth suggesting an adding an
501 -- instance declaration. Exclude tyvar dicts.
503 show_fixes :: [SDoc] -> SDoc
504 show_fixes [] = empty
505 show_fixes (f:fs) = sep [ptext (sLit "Possible fix:"),
506 nest 2 (vcat (f : map (ptext (sLit "or") <+>) fs))]
508 reportAmbigErrs :: ReportErrCtxt -> TcTyVarSet -> [WantedEvVar] -> TcM ()
509 reportAmbigErrs ctxt skols ambigs
510 -- Divide into groups that share a common set of ambiguous tyvars
511 = mapM_ report (equivClasses cmp ambigs_w_tvs)
513 ambigs_w_tvs = [ (d, varSetElems (tyVarsOfWantedEvVar d `minusVarSet` skols))
515 cmp (_,tvs1) (_,tvs2) = tvs1 `compare` tvs2
517 report :: [(WantedEvVar, [TcTyVar])] -> TcM ()
520 do { let main_msg = sep [ text "Ambiguous type variable" <> plural tvs
521 <+> pprQuotedList tvs
522 <+> text "in the constraint" <> plural pairs <> colon
523 , nest 2 pp_wanteds ]
524 ; (tidy_env, mono_msg) <- mkMonomorphismMsg ctxt tvs
525 ; addErrTcM (tidy_env, main_msg $$ mono_msg) }
528 (loc, pp_wanteds) = pprWithArising (map fst pairs)
530 mkMonomorphismMsg :: ReportErrCtxt -> [TcTyVar] -> TcM (TidyEnv, SDoc)
531 -- There's an error with these Insts; if they have free type variables
532 -- it's probably caused by the monomorphism restriction.
533 -- Try to identify the offending variable
534 -- ASSUMPTION: the Insts are fully zonked
535 mkMonomorphismMsg ctxt inst_tvs
536 = do { dflags <- getDOpts
537 ; (tidy_env, docs) <- findGlobals ctxt (mkVarSet inst_tvs)
538 ; return (tidy_env, mk_msg dflags docs) }
540 mk_msg _ _ | any isRuntimeUnk inst_tvs
541 = vcat [ptext (sLit "Cannot resolve unknown runtime types:") <+>
542 (pprWithCommas ppr inst_tvs),
543 ptext (sLit "Use :print or :force to determine these types")]
544 mk_msg _ [] = ptext (sLit "Probable fix: add a type signature that fixes these type variable(s)")
545 -- This happens in things like
546 -- f x = show (read "foo")
547 -- where monomorphism doesn't play any role
549 = vcat [ptext (sLit "Possible cause: the monomorphism restriction applied to the following:"),
551 monomorphism_fix dflags]
553 monomorphism_fix :: DynFlags -> SDoc
554 monomorphism_fix dflags
555 = ptext (sLit "Probable fix:") <+> vcat
556 [ptext (sLit "give these definition(s) an explicit type signature"),
557 if xopt Opt_MonomorphismRestriction dflags
558 then ptext (sLit "or use -XNoMonomorphismRestriction")
559 else empty] -- Only suggest adding "-XNoMonomorphismRestriction"
560 -- if it is not already set!
563 -----------------------
564 -- findGlobals looks at the value environment and finds values whose
565 -- types mention any of the offending type variables. It has to be
566 -- careful to zonk the Id's type first, so it has to be in the monad.
567 -- We must be careful to pass it a zonked type variable, too.
569 mkEnvSigMsg :: SDoc -> [SDoc] -> SDoc
570 mkEnvSigMsg what env_sigs
571 | null env_sigs = empty
572 | otherwise = vcat [ ptext (sLit "The following variables have types that mention") <+> what
573 , nest 2 (vcat env_sigs) ]
575 findGlobals :: ReportErrCtxt
577 -> TcM (TidyEnv, [SDoc])
580 = do { lcl_ty_env <- case cec_encl ctxt of
582 (i:_) -> return (ic_env i)
583 ; go (cec_tidy ctxt) [] (nameEnvElts lcl_ty_env) }
585 go tidy_env acc [] = return (tidy_env, acc)
586 go tidy_env acc (thing : things) = do
587 (tidy_env1, maybe_doc) <- find_thing tidy_env ignore_it thing
589 Just d -> go tidy_env1 (d:acc) things
590 Nothing -> go tidy_env1 acc things
592 ignore_it ty = tvs `disjointVarSet` tyVarsOfType ty
594 -----------------------
595 find_thing :: TidyEnv -> (TcType -> Bool)
596 -> TcTyThing -> TcM (TidyEnv, Maybe SDoc)
597 find_thing tidy_env ignore_it (ATcId { tct_id = id })
598 = do { id_ty <- zonkTcType (idType id)
599 ; if ignore_it id_ty then
600 return (tidy_env, Nothing)
602 { let (tidy_env', tidy_ty) = tidyOpenType tidy_env id_ty
603 msg = sep [ ppr id <+> dcolon <+> ppr tidy_ty
604 , nest 2 (parens (ptext (sLit "bound at") <+>
605 ppr (getSrcLoc id)))]
606 ; return (tidy_env', Just msg) } }
608 find_thing tidy_env ignore_it (ATyVar tv ty)
609 = do { tv_ty <- zonkTcType ty
610 ; if ignore_it tv_ty then
611 return (tidy_env, Nothing)
613 { let -- The name tv is scoped, so we don't need to tidy it
614 (tidy_env1, tidy_ty) = tidyOpenType tidy_env tv_ty
615 msg = sep [ ptext (sLit "Scoped type variable") <+> quotes (ppr tv) <+> eq_stuff
618 eq_stuff | Just tv' <- tcGetTyVar_maybe tv_ty
619 , getOccName tv == getOccName tv' = empty
620 | otherwise = equals <+> ppr tidy_ty
621 -- It's ok to use Type.getTyVar_maybe because ty is zonked by now
622 bound_at = parens $ ptext (sLit "bound at:") <+> ppr (getSrcLoc tv)
624 ; return (tidy_env1, Just msg) } }
626 find_thing _ _ thing = pprPanic "find_thing" (ppr thing)
628 warnDefaulting :: [WantedEvVar] -> Type -> TcM ()
629 warnDefaulting wanteds default_ty
630 = do { warn_default <- doptM Opt_WarnTypeDefaults
631 ; setCtLoc loc $ warnTc warn_default warn_msg }
634 warn_msg = vcat [ ptext (sLit "Defaulting the following constraint(s) to type") <+>
635 quotes (ppr default_ty),
637 (loc, ppr_wanteds) = pprWithArising wanteds
640 %************************************************************************
642 Error from the canonicaliser
643 These ones are called *during* constraint simplification
645 %************************************************************************
648 kindErrorTcS :: CtFlavor -> TcType -> TcType -> TcS ()
649 -- If there's a kind error, we don't want to blindly say "kind error"
650 -- We might, say, be unifying a skolem 'a' with a type 'Int',
651 -- in which case that's the error to report. So we set things
652 -- up to call reportEqErr, which does the business properly
653 kindErrorTcS fl ty1 ty2
654 = wrapEqErrTcS fl ty1 ty2 $ \ env0 ty1 ty2 extra ->
655 do { let ctxt = CEC { cec_encl = []
658 ; reportEqErr ctxt ty1 ty2 }
660 misMatchErrorTcS :: CtFlavor -> TcType -> TcType -> TcS a
661 misMatchErrorTcS fl ty1 ty2
662 = wrapEqErrTcS fl ty1 ty2 $ \ env0 ty1 ty2 extra ->
663 do { let (env1, msg) = misMatchMsgWithExtras env0 ty1 ty2
664 ; failWithTcM (env1, inaccessible_msg $$ msg $$ extra) }
668 Given loc -> hang (ptext (sLit "Inaccessible code in"))
672 = case ctLocOrigin loc of
673 PatSkol dc mc -> sep [ ptext (sLit "a pattern with constructor")
674 <+> quotes (ppr dc) <> comma
675 , ptext (sLit "in") <+> pprMatchContext mc ]
676 other_skol -> pprSkolInfo other_skol
678 occursCheckErrorTcS :: CtFlavor -> TcTyVar -> TcType -> TcS a
679 occursCheckErrorTcS fl tv ty
680 = wrapEqErrTcS fl (mkTyVarTy tv) ty $ \ env0 ty1 ty2 extra2 ->
681 do { let extra1 = sep [ppr ty1, char '=', ppr ty2]
682 ; failWithTcM (env0, hang msg 2 (extra1 $$ extra2)) }
684 msg = text $ "Occurs check: cannot construct the infinite type:"
686 solverDepthErrorTcS :: Int -> [CanonicalCt] -> TcS a
687 solverDepthErrorTcS depth stack
688 | null stack -- Shouldn't happen unless you say -fcontext-stack=0
689 = wrapErrTcS $ failWith msg
692 setCtFlavorLoc (cc_flavor top_item) $
693 do { env0 <- tcInitTidyEnv
694 ; let ev_vars = map cc_id stack
695 env1 = tidyFreeTyVars env0 free_tvs
696 free_tvs = foldr (unionVarSet . tyVarsOfEvVar) emptyVarSet ev_vars
697 extra = pprEvVars (map (tidyEvVar env1) ev_vars)
698 ; failWithTcM (env1, hang msg 2 extra) }
700 top_item = head stack
701 msg = vcat [ ptext (sLit "Context reduction stack overflow; size =") <+> int depth
702 , ptext (sLit "Use -fcontext-stack=N to increase stack size to N") ]
704 flattenForAllErrorTcS :: CtFlavor -> TcType -> Bag CanonicalCt -> TcS a
705 flattenForAllErrorTcS fl ty _bad_eqs
708 do { env0 <- tcInitTidyEnv
709 ; let (env1, ty') = tidyOpenType env0 ty
710 msg = sep [ ptext (sLit "Cannot deal with a type function under a forall type:")
712 ; failWithTcM (env1, msg) }
715 %************************************************************************
719 %************************************************************************
722 setCtFlavorLoc :: CtFlavor -> TcM a -> TcM a
723 setCtFlavorLoc (Wanted loc) thing = setCtLoc loc thing
724 setCtFlavorLoc (Derived loc) thing = setCtLoc loc thing
725 setCtFlavorLoc (Given loc) thing = setCtLoc loc thing
727 wrapEqErrTcS :: CtFlavor -> TcType -> TcType
728 -> (TidyEnv -> TcType -> TcType -> SDoc -> TcM a)
730 wrapEqErrTcS fl ty1 ty2 thing_inside
731 = do { ty_binds_var <- getTcSTyBinds
732 ; wrapErrTcS $ setCtFlavorLoc fl $
733 do { -- Apply the current substitition
734 -- and zonk to get rid of flatten-skolems
735 ; ty_binds_map <- readTcRef ty_binds_var
736 ; let subst = mkOpenTvSubst (mapVarEnv snd ty_binds_map)
737 ; env0 <- tcInitTidyEnv
738 ; (env1, ty1) <- zonkSubstTidy env0 subst ty1
739 ; (env2, ty2) <- zonkSubstTidy env1 subst ty2
740 ; let do_wanted loc = do { (env3, extra) <- getWantedEqExtra subst env2
741 (ctLocOrigin loc) ty1 ty2
742 ; thing_inside env3 ty1 ty2 extra }
744 Wanted loc -> do_wanted loc
745 Derived loc -> do_wanted loc
746 Given {} -> thing_inside env2 ty1 ty2 empty
747 -- We could print more info, but it
748 -- seems to be coming out already
752 getWantedEqExtra :: TvSubst -> TidyEnv -> CtOrigin -> TcType -> TcType
753 -> TcM (TidyEnv, SDoc)
754 getWantedEqExtra subst env0 (TypeEqOrigin item) ty1 ty2
755 -- If the types in the error message are the same
756 -- as the types we are unifying (remember to zonk the latter)
757 -- don't add the extra expected/actual message
759 -- The complication is that the types in the TypeEqOrigin must
761 -- (b) have any TcS-monad pending equalities applied to them
762 -- (hence the passed-in substitution)
763 = do { (env1, act) <- zonkSubstTidy env0 subst (uo_actual item)
764 ; (env2, exp) <- zonkSubstTidy env1 subst (uo_expected item)
765 ; if (act `tcEqType` ty1 && exp `tcEqType` ty2)
766 || (exp `tcEqType` ty1 && act `tcEqType` ty2)
770 return (env2, mkExpectedActualMsg act exp) }
772 getWantedEqExtra _ env0 orig _ _
773 = return (env0, pprArising orig)
775 zonkSubstTidy :: TidyEnv -> TvSubst -> TcType -> TcM (TidyEnv, TcType)
776 -- In general, becore printing a type, we want to
777 -- a) Zonk it. Even during constraint simplification this is
778 -- is important, to un-flatten the flatten skolems in a type
779 -- b) Substitute any solved unification variables. This is
780 -- only important *during* solving, becuase after solving
781 -- the substitution is expressed in the mutable type variables
782 -- But during solving there may be constraint (F xi ~ ty)
783 -- where the substitution has not been applied to the RHS
784 zonkSubstTidy env subst ty
785 = do { ty' <- zonkTcTypeAndSubst subst ty
786 ; return (tidyOpenType env ty') }