2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcMonoType]{Typechecking user-specified @MonoTypes@}
7 module TcMonoType ( tcHsType, tcHsSigType, tcHsTypeKind, tcHsTopType, tcHsTopBoxedType, tcHsTopTypeKind,
8 tcContext, tcHsTyVar, kcHsTyVar, kcHsType,
9 tcExtendTyVarScope, tcExtendTopTyVarScope,
10 TcSigInfo(..), tcTySig, mkTcSig, maybeSig,
11 checkSigTyVars, sigCtxt, sigPatCtxt
14 #include "HsVersions.h"
16 import HsSyn ( HsType(..), HsTyVarBndr(..), HsUsageAnn(..),
17 Sig(..), HsPred(..), pprParendHsType, HsTupCon(..) )
18 import RnHsSyn ( RenamedHsType, RenamedContext, RenamedSig )
19 import TcHsSyn ( TcId )
22 import TcEnv ( tcExtendTyVarEnv, tcLookupTy, tcGetValueEnv, tcGetInScopeTyVars,
23 tcExtendUVarEnv, tcLookupUVar,
24 tcGetGlobalTyVars, valueEnvIds, TcTyThing(..)
26 import TcType ( TcType, TcKind, TcTyVar, TcThetaType, TcTauType,
27 typeToTcType, kindToTcKind,
28 newKindVar, tcInstSigVar,
29 zonkTcKindToKind, zonkTcTypeToType, zonkTcTyVars, zonkTcType, zonkTcTyVar
31 import Inst ( Inst, InstOrigin(..), newMethodWithGivenTy, instToIdBndr,
32 instFunDeps, instFunDepsOfTheta )
33 import FunDeps ( tyVarFunDep, oclose )
34 import TcUnify ( unifyKind, unifyKinds, unifyTypeKind )
35 import Type ( Type, PredType(..), ThetaType, UsageAnn(..),
36 mkTyVarTy, mkTyVarTys, mkFunTy, mkSynTy, mkUsgTy,
37 mkUsForAllTy, zipFunTys, hoistForAllTys,
38 mkSigmaTy, mkDictTy, mkPredTy, mkTyConApp,
39 mkAppTys, splitForAllTys, splitRhoTy, mkRhoTy,
40 boxedTypeKind, unboxedTypeKind, tyVarsOfType,
41 mkArrowKinds, getTyVar_maybe, getTyVar,
42 tidyOpenType, tidyOpenTypes, tidyTyVar, tidyTyVars,
43 tyVarsOfType, tyVarsOfTypes, mkForAllTys
45 import PprType ( pprConstraint, pprType )
46 import Subst ( mkTopTyVarSubst, substTy )
47 import Id ( mkVanillaId, idName, idType, idFreeTyVars )
48 import Var ( TyVar, mkTyVar, mkNamedUVar, varName )
51 import Bag ( bagToList )
52 import ErrUtils ( Message )
53 import TyCon ( TyCon )
54 import Name ( Name, OccName, isLocallyDefined )
55 import TysWiredIn ( mkListTy, mkTupleTy )
56 import UniqFM ( elemUFM, foldUFM )
57 import BasicTypes ( Boxity(..) )
58 import SrcLoc ( SrcLoc )
59 import Unique ( Unique, Uniquable(..) )
60 import Util ( mapAccumL, isSingleton, removeDups )
65 %************************************************************************
67 \subsection{Checking types}
69 %************************************************************************
71 tcHsType and tcHsTypeKind
72 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
74 tcHsType checks that the type really is of kind Type!
77 kcHsType :: RenamedHsType -> TcM c ()
78 -- Kind-check the type
79 kcHsType ty = tc_type ty `thenTc_`
82 tcHsSigType :: RenamedHsType -> TcM s TcType
83 -- Used for type sigs written by the programmer
84 -- Hoist any inner for-alls to the top
86 = tcHsType ty `thenTc` \ ty' ->
87 returnTc (hoistForAllTys ty')
89 tcHsType :: RenamedHsType -> TcM s TcType
91 = -- tcAddErrCtxt (typeCtxt ty) $
94 tcHsTypeKind :: RenamedHsType -> TcM s (TcKind, TcType)
96 = -- tcAddErrCtxt (typeCtxt ty) $
99 -- Type-check a type, *and* then lazily zonk it. The important
100 -- point is that this zonks all the uncommitted *kind* variables
101 -- in kinds of any any nested for-all tyvars.
102 -- There won't be any mutable *type* variables at all.
104 -- NOTE the forkNF_Tc. This makes the zonking lazy, which is
105 -- absolutely necessary. During the type-checking of a recursive
106 -- group of tycons/classes (TcTyClsDecls.tcGroup) we use an
107 -- environment in which we aren't allowed to look at the actual
108 -- tycons/classes returned from a lookup. Because tc_app does
109 -- look at the tycon to build the type, we can't look at the type
110 -- either, until we get out of the loop. The fork delays the
111 -- zonking till we've completed the loop. Sigh.
113 tcHsTopType :: RenamedHsType -> TcM s Type
115 = -- tcAddErrCtxt (typeCtxt ty) $
116 tc_type ty `thenTc` \ ty' ->
117 forkNF_Tc (zonkTcTypeToType ty') `thenTc` \ ty'' ->
118 returnTc (hoistForAllTys ty'')
120 tcHsTopBoxedType :: RenamedHsType -> TcM s Type
122 = -- tcAddErrCtxt (typeCtxt ty) $
123 tc_boxed_type ty `thenTc` \ ty' ->
124 forkNF_Tc (zonkTcTypeToType ty') `thenTc` \ ty'' ->
125 returnTc (hoistForAllTys ty'')
127 tcHsTopTypeKind :: RenamedHsType -> TcM s (TcKind, Type)
129 = -- tcAddErrCtxt (typeCtxt ty) $
130 tc_type_kind ty `thenTc` \ (kind, ty') ->
131 forkNF_Tc (zonkTcTypeToType ty') `thenTc` \ zonked_ty ->
132 returnNF_Tc (kind, hoistForAllTys zonked_ty)
140 tc_boxed_type :: RenamedHsType -> TcM s Type
142 = tc_type_kind ty `thenTc` \ (actual_kind, tc_ty) ->
143 tcAddErrCtxt (typeKindCtxt ty)
144 (unifyKind boxedTypeKind actual_kind) `thenTc_`
147 tc_type :: RenamedHsType -> TcM s Type
149 -- The type ty must be a *type*, but it can be boxed
150 -- or unboxed. So we check that is is of form (Type bv)
151 -- using unifyTypeKind
152 = tc_type_kind ty `thenTc` \ (actual_kind, tc_ty) ->
153 tcAddErrCtxt (typeKindCtxt ty)
154 (unifyTypeKind actual_kind) `thenTc_`
157 tc_type_kind :: RenamedHsType -> TcM s (TcKind, Type)
158 tc_type_kind ty@(HsTyVar name)
161 tc_type_kind (HsListTy ty)
162 = tc_boxed_type ty `thenTc` \ tau_ty ->
163 returnTc (boxedTypeKind, mkListTy tau_ty)
165 tc_type_kind (HsTupleTy (HsTupCon _ Boxed) tys)
166 = mapTc tc_boxed_type tys `thenTc` \ tau_tys ->
167 returnTc (boxedTypeKind, mkTupleTy Boxed (length tys) tau_tys)
169 tc_type_kind (HsTupleTy (HsTupCon _ Unboxed) tys)
170 = mapTc tc_type tys `thenTc` \ tau_tys ->
171 returnTc (unboxedTypeKind, mkTupleTy Unboxed (length tys) tau_tys)
173 tc_type_kind (HsFunTy ty1 ty2)
174 = tc_type ty1 `thenTc` \ tau_ty1 ->
175 tc_type ty2 `thenTc` \ tau_ty2 ->
176 returnTc (boxedTypeKind, mkFunTy tau_ty1 tau_ty2)
178 tc_type_kind (HsAppTy ty1 ty2)
181 tc_type_kind (HsPredTy pred)
182 = tcClassAssertion True pred `thenTc` \ pred' ->
183 returnTc (boxedTypeKind, mkPredTy pred')
185 tc_type_kind (HsUsgTy usg ty)
186 = newUsg usg `thenTc` \ usg' ->
187 tc_type_kind ty `thenTc` \ (kind, tc_ty) ->
188 returnTc (kind, mkUsgTy usg' tc_ty)
190 newUsg usg = case usg of
191 HsUsOnce -> returnTc UsOnce
192 HsUsMany -> returnTc UsMany
193 HsUsVar uv_name -> tcLookupUVar uv_name `thenTc` \ uv ->
196 tc_type_kind (HsUsgForAllTy uv_name ty)
198 uv = mkNamedUVar uv_name
200 tcExtendUVarEnv uv_name uv $
201 tc_type_kind ty `thenTc` \ (kind, tc_ty) ->
202 returnTc (kind, mkUsForAllTy uv tc_ty)
204 tc_type_kind (HsForAllTy (Just tv_names) context ty)
205 = tcExtendTyVarScope tv_names $ \ tyvars ->
206 tcContext context `thenTc` \ theta ->
207 tc_type_kind ty `thenTc` \ (kind, tau) ->
208 tcGetInScopeTyVars `thenTc` \ in_scope_vars ->
210 body_kind | null theta = kind
211 | otherwise = boxedTypeKind
212 -- Context behaves like a function type
213 -- This matters. Return-unboxed-tuple analysis can
214 -- give overloaded functions like
215 -- f :: forall a. Num a => (# a->a, a->a #)
216 -- And we want these to get through the type checker
217 check ct@(Class c tys) | ambiguous = failWithTc (ambigErr (c,tys) tau)
218 where ct_vars = tyVarsOfTypes tys
219 forall_tyvars = map varName in_scope_vars
220 tau_vars = tyVarsOfType tau
221 fds = instFunDepsOfTheta theta
222 tvFundep = tyVarFunDep fds
223 extended_tau_vars = oclose tvFundep tau_vars
224 ambig ct_var = (varName ct_var `elem` forall_tyvars) &&
225 not (ct_var `elemUFM` extended_tau_vars)
226 ambiguous = foldUFM ((||) . ambig) False ct_vars
227 check _ = returnTc ()
229 mapTc check theta `thenTc_`
230 returnTc (body_kind, mkSigmaTy tyvars theta tau)
233 Help functions for type applications
234 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
237 tc_app (HsAppTy ty1 ty2) tys
238 = tc_app ty1 (ty2:tys)
245 = tcAddErrCtxt (appKindCtxt pp_app) $
246 mapAndUnzipTc tc_type_kind tys `thenTc` \ (arg_kinds, arg_tys) ->
247 tc_fun_type ty arg_tys `thenTc` \ (fun_kind, result_ty) ->
249 -- Check argument compatibility
250 newKindVar `thenNF_Tc` \ result_kind ->
251 unifyKind fun_kind (mkArrowKinds arg_kinds result_kind)
253 returnTc (result_kind, result_ty)
255 pp_app = ppr ty <+> sep (map pprParendHsType tys)
257 -- (tc_fun_type ty arg_tys) returns (kind-of ty, mkAppTys ty arg_tys)
258 -- But not quite; for synonyms it checks the correct arity, and builds a SynTy
259 -- hence the rather strange functionality.
261 tc_fun_type (HsTyVar name) arg_tys
262 = tcLookupTy name `thenTc` \ (tycon_kind, thing) ->
264 ATyVar tv -> returnTc (tycon_kind, mkAppTys (mkTyVarTy tv) arg_tys)
265 AClass clas _ -> failWithTc (classAsTyConErr name)
267 ADataTyCon tc -> -- Data or newtype
268 returnTc (tycon_kind, mkTyConApp tc arg_tys)
270 ASynTyCon tc arity -> -- Type synonym
271 checkTc (arity <= n_args) err_msg `thenTc_`
272 returnTc (tycon_kind, result_ty)
274 -- It's OK to have an *over-applied* type synonym
275 -- data Tree a b = ...
276 -- type Foo a = Tree [a]
277 -- f :: Foo a b -> ...
278 result_ty = mkAppTys (mkSynTy tc (take arity arg_tys))
280 err_msg = arityErr "type synonym" name arity n_args
281 n_args = length arg_tys
283 tc_fun_type ty arg_tys
284 = tc_type_kind ty `thenTc` \ (fun_kind, fun_ty) ->
285 returnTc (fun_kind, mkAppTys fun_ty arg_tys)
293 tcContext :: RenamedContext -> TcM s ThetaType
294 tcContext context = mapTc (tcClassAssertion False) context
296 tcClassAssertion ccall_ok assn@(HsPClass class_name tys)
297 = tcAddErrCtxt (appKindCtxt (ppr assn)) $
298 mapAndUnzipTc tc_type_kind tys `thenTc` \ (arg_kinds, arg_tys) ->
299 tcLookupTy class_name `thenTc` \ (kind, thing) ->
302 -- Check with kind mis-match
303 checkTc (arity == n_tys) err `thenTc_`
304 unifyKind kind (mkArrowKinds arg_kinds boxedTypeKind) `thenTc_`
305 returnTc (Class clas arg_tys)
308 err = arityErr "Class" class_name arity n_tys
309 other -> failWithTc (tyVarAsClassErr class_name)
311 tcClassAssertion ccall_ok assn@(HsPIParam name ty)
312 = tcAddErrCtxt (appKindCtxt (ppr assn)) $
313 tc_type_kind ty `thenTc` \ (arg_kind, arg_ty) ->
314 returnTc (IParam name arg_ty)
318 %************************************************************************
320 \subsection{Type variables, with knot tying!}
322 %************************************************************************
325 tcExtendTopTyVarScope :: TcKind -> [HsTyVarBndr Name]
326 -> ([TcTyVar] -> TcKind -> TcM s a)
328 tcExtendTopTyVarScope kind tyvar_names thing_inside
330 (tyvars_w_kinds, result_kind) = zipFunTys tyvar_names kind
331 tyvars = map mk_tv tyvars_w_kinds
333 tcExtendTyVarEnv tyvars (thing_inside tyvars result_kind)
335 mk_tv (UserTyVar name, kind) = mkTyVar name kind
336 mk_tv (IfaceTyVar name _, kind) = mkTyVar name kind
337 -- NB: immutable tyvars, but perhaps with mutable kinds
339 tcExtendTyVarScope :: [HsTyVarBndr Name]
340 -> ([TcTyVar] -> TcM s a) -> TcM s a
341 tcExtendTyVarScope tv_names thing_inside
342 = mapNF_Tc tcHsTyVar tv_names `thenNF_Tc` \ tyvars ->
343 tcExtendTyVarEnv tyvars $
346 tcHsTyVar :: HsTyVarBndr Name -> NF_TcM s TcTyVar
347 tcHsTyVar (UserTyVar name) = newKindVar `thenNF_Tc` \ kind ->
348 tcNewMutTyVar name kind
349 -- NB: mutable kind => mutable tyvar, so that zonking can bind
350 -- the tyvar to its immutable form
352 tcHsTyVar (IfaceTyVar name kind) = returnNF_Tc (mkTyVar name (kindToTcKind kind))
354 kcHsTyVar :: HsTyVarBndr name -> NF_TcM s TcKind
355 kcHsTyVar (UserTyVar name) = newKindVar
356 kcHsTyVar (IfaceTyVar name kind) = returnNF_Tc (kindToTcKind kind)
360 %************************************************************************
362 \subsection{Signatures}
364 %************************************************************************
366 @tcSigs@ checks the signatures for validity, and returns a list of
367 {\em freshly-instantiated} signatures. That is, the types are already
368 split up, and have fresh type variables installed. All non-type-signature
369 "RenamedSigs" are ignored.
371 The @TcSigInfo@ contains @TcTypes@ because they are unified with
372 the variable's type, and after that checked to see whether they've
378 Name -- N, the Name in corresponding binding
380 TcId -- *Polymorphic* binder for this value...
387 TcId -- *Monomorphic* binder for this value
388 -- Does *not* have name = N
391 [Inst] -- Empty if theta is null, or
392 -- (method mono_id) otherwise
394 SrcLoc -- Of the signature
396 instance Outputable TcSigInfo where
397 ppr (TySigInfo nm id tyvars theta tau _ inst loc) =
398 ppr nm <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
400 maybeSig :: [TcSigInfo] -> Name -> Maybe (TcSigInfo)
401 -- Search for a particular signature
402 maybeSig [] name = Nothing
403 maybeSig (sig@(TySigInfo sig_name _ _ _ _ _ _ _) : sigs) name
404 | name == sig_name = Just sig
405 | otherwise = maybeSig sigs name
410 tcTySig :: RenamedSig -> TcM s TcSigInfo
412 tcTySig (Sig v ty src_loc)
413 = tcAddSrcLoc src_loc $
414 tcHsSigType ty `thenTc` \ sigma_tc_ty ->
415 mkTcSig (mkVanillaId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig ->
418 mkTcSig :: TcId -> SrcLoc -> NF_TcM s TcSigInfo
419 mkTcSig poly_id src_loc
420 = -- Instantiate this type
421 -- It's important to do this even though in the error-free case
422 -- we could just split the sigma_tc_ty (since the tyvars don't
423 -- unified with anything). But in the case of an error, when
424 -- the tyvars *do* get unified with something, we want to carry on
425 -- typechecking the rest of the program with the function bound
426 -- to a pristine type, namely sigma_tc_ty
428 (tyvars, rho) = splitForAllTys (idType poly_id)
430 mapNF_Tc tcInstSigVar tyvars `thenNF_Tc` \ tyvars' ->
431 -- Make *signature* type variables
434 tyvar_tys' = mkTyVarTys tyvars'
435 rho' = substTy (mkTopTyVarSubst tyvars tyvar_tys') rho
436 -- mkTopTyVarSubst because the tyvars' are fresh
437 (theta', tau') = splitRhoTy rho'
438 -- This splitRhoTy tries hard to make sure that tau' is a type synonym
439 -- wherever possible, which can improve interface files.
441 newMethodWithGivenTy SignatureOrigin
444 theta' tau' `thenNF_Tc` \ inst ->
445 -- We make a Method even if it's not overloaded; no harm
446 instFunDeps SignatureOrigin theta' `thenNF_Tc` \ fds ->
448 returnNF_Tc (TySigInfo name poly_id tyvars' theta' tau' (instToIdBndr inst) (inst : fds) src_loc)
450 name = idName poly_id
455 %************************************************************************
457 \subsection{Checking signature type variables}
459 %************************************************************************
461 @checkSigTyVars@ is used after the type in a type signature has been unified with
462 the actual type found. It then checks that the type variables of the type signature
464 (a) Still all type variables
465 eg matching signature [a] against inferred type [(p,q)]
466 [then a will be unified to a non-type variable]
468 (b) Still all distinct
469 eg matching signature [(a,b)] against inferred type [(p,p)]
470 [then a and b will be unified together]
472 (c) Not mentioned in the environment
473 eg the signature for f in this:
479 Here, f is forced to be monorphic by the free occurence of x.
481 (d) Not (unified with another type variable that is) in scope.
482 eg f x :: (r->r) = (\y->y) :: forall a. a->r
483 when checking the expression type signature, we find that
484 even though there is nothing in scope whose type mentions r,
485 nevertheless the type signature for the expression isn't right.
487 Another example is in a class or instance declaration:
489 op :: forall b. a -> b
491 Here, b gets unified with a
493 Before doing this, the substitution is applied to the signature type variable.
495 We used to have the notion of a "DontBind" type variable, which would
496 only be bound to itself or nothing. Then points (a) and (b) were
497 self-checking. But it gave rise to bogus consequential error messages.
500 f = (*) -- Monomorphic
505 Here, we get a complaint when checking the type signature for g,
506 that g isn't polymorphic enough; but then we get another one when
507 dealing with the (Num x) context arising from f's definition;
508 we try to unify x with Int (to default it), but find that x has already
509 been unified with the DontBind variable "a" from g's signature.
510 This is really a problem with side-effecting unification; we'd like to
511 undo g's effects when its type signature fails, but unification is done
512 by side effect, so we can't (easily).
514 So we revert to ordinary type variables for signatures, and try to
515 give a helpful message in checkSigTyVars.
518 checkSigTyVars :: [TcTyVar] -- Universally-quantified type variables in the signature
519 -> TcTyVarSet -- Tyvars that are free in the type signature
520 -- These should *already* be in the global-var set, and are
521 -- used here only to improve the error message
522 -> TcM s [TcTyVar] -- Zonked signature type variables
524 checkSigTyVars [] free = returnTc []
526 checkSigTyVars sig_tyvars free_tyvars
527 = zonkTcTyVars sig_tyvars `thenNF_Tc` \ sig_tys ->
528 tcGetGlobalTyVars `thenNF_Tc` \ globals ->
530 checkTcM (all_ok sig_tys globals)
531 (complain sig_tys globals) `thenTc_`
533 returnTc (map (getTyVar "checkSigTyVars") sig_tys)
537 all_ok (ty:tys) acc = case getTyVar_maybe ty of
538 Nothing -> False -- Point (a)
539 Just tv | tv `elemVarSet` acc -> False -- Point (b) or (c)
540 | otherwise -> all_ok tys (acc `extendVarSet` tv)
543 complain sig_tys globals
544 = -- For the in-scope ones, zonk them and construct a map
545 -- from the zonked tyvar to the in-scope one
546 -- If any of the in-scope tyvars zonk to a type, then ignore them;
547 -- that'll be caught later when we back up to their type sig
548 tcGetInScopeTyVars `thenNF_Tc` \ in_scope_tvs ->
549 zonkTcTyVars in_scope_tvs `thenNF_Tc` \ in_scope_tys ->
551 in_scope_assoc = [ (zonked_tv, in_scope_tv)
552 | (z_ty, in_scope_tv) <- in_scope_tys `zip` in_scope_tvs,
553 Just zonked_tv <- [getTyVar_maybe z_ty]
555 in_scope_env = mkVarEnv in_scope_assoc
558 -- "check" checks each sig tyvar in turn
560 (env2, in_scope_env, [])
561 (tidy_tvs `zip` tidy_tys) `thenNF_Tc` \ (env3, _, msgs) ->
563 failWithTcM (env3, main_msg $$ nest 4 (vcat msgs))
565 (env1, tidy_tvs) = mapAccumL tidyTyVar emptyTidyEnv sig_tyvars
566 (env2, tidy_tys) = tidyOpenTypes env1 sig_tys
568 main_msg = ptext SLIT("Inferred type is less polymorphic than expected")
570 check (env, acc, msgs) (sig_tyvar,ty)
571 -- sig_tyvar is from the signature;
572 -- ty is what you get if you zonk sig_tyvar and then tidy it
574 -- acc maps a zonked type variable back to a signature type variable
575 = case getTyVar_maybe ty of {
576 Nothing -> -- Error (a)!
577 returnNF_Tc (env, acc, unify_msg sig_tyvar (ppr ty) : msgs) ;
581 case lookupVarEnv acc tv of {
582 Just sig_tyvar' -> -- Error (b) or (d)!
583 returnNF_Tc (env, acc, unify_msg sig_tyvar (ppr sig_tyvar') : msgs) ;
587 if tv `elemVarSet` globals -- Error (c)! Type variable escapes
588 -- The least comprehensible, so put it last
589 then tcGetValueEnv `thenNF_Tc` \ ve ->
590 find_globals tv env [] (valueEnvIds ve) `thenNF_Tc` \ (env1, globs) ->
591 find_frees tv env1 [] (varSetElems free_tyvars) `thenNF_Tc` \ (env2, frees) ->
592 returnNF_Tc (env2, acc, escape_msg sig_tyvar tv globs frees : msgs)
595 returnNF_Tc (env, extendVarEnv acc tv sig_tyvar, msgs)
598 -- find_globals looks at the value environment and finds values
599 -- whose types mention the offending type variable. It has to be
600 -- careful to zonk the Id's type first, so it has to be in the monad.
601 -- We must be careful to pass it a zonked type variable, too.
602 find_globals tv tidy_env acc []
603 = returnNF_Tc (tidy_env, acc)
605 find_globals tv tidy_env acc (id:ids)
606 | not (isLocallyDefined id) ||
607 isEmptyVarSet (idFreeTyVars id)
608 = find_globals tv tidy_env acc ids
611 = zonkTcType (idType id) `thenNF_Tc` \ id_ty ->
612 if tv `elemVarSet` tyVarsOfType id_ty then
614 (tidy_env', id_ty') = tidyOpenType tidy_env id_ty
615 acc' = (idName id, id_ty') : acc
617 find_globals tv tidy_env' acc' ids
619 find_globals tv tidy_env acc ids
621 find_frees tv tidy_env acc []
622 = returnNF_Tc (tidy_env, acc)
623 find_frees tv tidy_env acc (ftv:ftvs)
624 = zonkTcTyVar ftv `thenNF_Tc` \ ty ->
625 if tv `elemVarSet` tyVarsOfType ty then
627 (tidy_env', ftv') = tidyTyVar tidy_env ftv
629 find_frees tv tidy_env' (ftv':acc) ftvs
631 find_frees tv tidy_env acc ftvs
634 escape_msg sig_tv tv globs frees
635 = mk_msg sig_tv <+> ptext SLIT("escapes") $$
636 if not (null globs) then
637 vcat [pp_it <+> ptext SLIT("is mentioned in the environment"),
638 ptext SLIT("The following variables in the environment mention") <+> quotes (ppr tv),
639 nest 2 (vcat_first 10 [ppr name <+> dcolon <+> ppr ty | (name,ty) <- globs])
641 else if not (null frees) then
642 vcat [ptext SLIT("It is reachable from the type variable(s)") <+> pprQuotedList frees,
643 nest 2 (ptext SLIT("which") <+> is_are <+> ptext SLIT("free in the signature"))
646 empty -- Sigh. It's really hard to give a good error message
647 -- all the time. One bad case is an existential pattern match
649 is_are | isSingleton frees = ptext SLIT("is")
650 | otherwise = ptext SLIT("are")
651 pp_it | sig_tv /= tv = ptext SLIT("It unifies with") <+> quotes (ppr tv) <> comma <+> ptext SLIT("which")
652 | otherwise = ptext SLIT("It")
654 vcat_first :: Int -> [SDoc] -> SDoc
655 vcat_first n [] = empty
656 vcat_first 0 (x:xs) = text "...others omitted..."
657 vcat_first n (x:xs) = x $$ vcat_first (n-1) xs
659 unify_msg tv thing = mk_msg tv <+> ptext SLIT("is unified with") <+> quotes thing
660 mk_msg tv = ptext SLIT("Quantified type variable") <+> quotes (ppr tv)
663 These two context are used with checkSigTyVars
666 sigCtxt :: Message -> [TcTyVar] -> TcThetaType -> TcTauType
667 -> TidyEnv -> NF_TcM s (TidyEnv, Message)
668 sigCtxt when sig_tyvars sig_theta sig_tau tidy_env
669 = zonkTcType sig_tau `thenNF_Tc` \ actual_tau ->
671 (env1, tidy_sig_tyvars) = tidyTyVars tidy_env sig_tyvars
672 (env2, tidy_sig_rho) = tidyOpenType env1 (mkRhoTy sig_theta sig_tau)
673 (env3, tidy_actual_tau) = tidyOpenType env1 actual_tau
674 msg = vcat [ptext SLIT("Signature type: ") <+> pprType (mkForAllTys tidy_sig_tyvars tidy_sig_rho),
675 ptext SLIT("Type to generalise:") <+> pprType tidy_actual_tau,
679 returnNF_Tc (env3, msg)
681 sigPatCtxt bound_tvs bound_ids tidy_env
683 sep [ptext SLIT("When checking a pattern that binds"),
684 nest 4 (vcat (zipWith ppr_id show_ids tidy_tys))])
686 show_ids = filter is_interesting bound_ids
687 is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs
689 (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
690 ppr_id id ty = ppr id <+> dcolon <+> ppr ty
691 -- Don't zonk the types so we get the separate, un-unified versions
695 %************************************************************************
697 \subsection{Errors and contexts}
699 %************************************************************************
702 typeCtxt ty = ptext SLIT("In the type") <+> quotes (ppr ty)
704 typeKindCtxt :: RenamedHsType -> Message
705 typeKindCtxt ty = sep [ptext SLIT("When checking that"),
706 nest 2 (quotes (ppr ty)),
707 ptext SLIT("is a type")]
709 appKindCtxt :: SDoc -> Message
710 appKindCtxt pp = ptext SLIT("When checking kinds in") <+> quotes pp
713 = ptext SLIT("Class used as a type constructor:") <+> ppr name
716 = ptext SLIT("Type constructor used as a class:") <+> ppr name
719 = ptext SLIT("Type variable used as a class:") <+> ppr name
722 = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprConstraint c ts),
723 nest 4 (ptext SLIT("for the type:") <+> ppr ty),
724 nest 4 (ptext SLIT("Each forall'd type variable mentioned by the constraint must appear after the =>"))]