2 % (c) The University of Glasgow 2006
3 % (c) The GRASP Project, Glasgow University, 1992-2002
7 TcRnIf, TcRn, TcM, RnM, IfM, IfL, IfG, -- The monad is opaque outside this module
10 -- The environment types
12 TcGblEnv(..), TcLclEnv(..),
13 IfGblEnv(..), IfLclEnv(..),
16 ErrCtxt, RecFieldEnv(..),
17 ImportAvails(..), emptyImportAvails, plusImportAvails,
18 WhereFrom(..), mkModDeps,
21 TcTypeEnv, TcTyThing(..), pprTcTyThingCategory,
24 ThStage(..), topStage, topAnnStage, topSpliceStage,
25 ThLevel, impLevel, outerLevel, thLevel,
28 ArrowCtxt(NoArrowCtxt), newArrowScope, escapeArrowScope,
31 Untouchables(..), inTouchableRange, isNoUntouchables,
33 WantedConstraints(..), insolubleWC, emptyWC, isEmptyWC,
34 andWC, addFlats, addImplics, mkFlatWC,
36 EvVarX(..), mkEvVarX, evVarOf, evVarX, evVarOfPred,
37 WantedEvVar, wantedToFlavored,
41 CtLoc(..), ctLocSpan, ctLocOrigin, setCtLocOrigin,
42 CtOrigin(..), EqOrigin(..),
43 WantedLoc, GivenLoc, pushErrCtxt,
47 CtFlavor(..), pprFlavorArising, isWanted, isGiven, isDerived,
51 pprEvVarTheta, pprWantedEvVar, pprWantedsWithLocs,
52 pprEvVars, pprEvVarWithType,
53 pprArising, pprArisingAt,
56 TcId, TcIdSet, TcTyVarBind(..), TcTyVarBinds
60 #include "HsVersions.h"
65 import Class ( Class )
66 import DataCon ( DataCon, dataConUserType )
95 %************************************************************************
97 Standard monad definition for TcRn
98 All the combinators for the monad can be found in TcRnMonad
100 %************************************************************************
102 The monad itself has to be defined here, because it is mentioned by ErrCtxt
105 type TcRef a = IORef a
106 type TcId = Id -- Type may be a TcType DV: WHAT??????????
110 type TcRnIf a b c = IOEnv (Env a b) c
111 type IfM lcl a = TcRnIf IfGblEnv lcl a -- Iface stuff
113 type IfG a = IfM () a -- Top level
114 type IfL a = IfM IfLclEnv a -- Nested
115 type TcRn a = TcRnIf TcGblEnv TcLclEnv a
116 type RnM a = TcRn a -- Historical
117 type TcM a = TcRn a -- Historical
120 Representation of type bindings to uninstantiated meta variables used during
124 data TcTyVarBind = TcTyVarBind TcTyVar TcType
126 type TcTyVarBinds = Bag TcTyVarBind
128 instance Outputable TcTyVarBind where
129 ppr (TcTyVarBind tv ty) = ppr tv <+> text ":=" <+> ppr ty
133 %************************************************************************
135 The main environment types
137 %************************************************************************
140 data Env gbl lcl -- Changes as we move into an expression
142 env_top :: HscEnv, -- Top-level stuff that never changes
143 -- Includes all info about imported things
145 env_us :: {-# UNPACK #-} !(IORef UniqSupply),
146 -- Unique supply for local varibles
148 env_gbl :: gbl, -- Info about things defined at the top level
149 -- of the module being compiled
151 env_lcl :: lcl -- Nested stuff; changes as we go into
154 -- TcGblEnv describes the top-level of the module at the
155 -- point at which the typechecker is finished work.
156 -- It is this structure that is handed on to the desugarer
160 tcg_mod :: Module, -- ^ Module being compiled
161 tcg_src :: HscSource,
162 -- ^ What kind of module (regular Haskell, hs-boot, ext-core)
164 tcg_rdr_env :: GlobalRdrEnv, -- ^ Top level envt; used during renaming
165 tcg_default :: Maybe [Type],
166 -- ^ Types used for defaulting. @Nothing@ => no @default@ decl
168 tcg_fix_env :: FixityEnv, -- ^ Just for things in this module
169 tcg_field_env :: RecFieldEnv, -- ^ Just for things in this module
171 tcg_type_env :: TypeEnv,
172 -- ^ Global type env for the module we are compiling now. All
173 -- TyCons and Classes (for this module) end up in here right away,
174 -- along with their derived constructors, selectors.
176 -- (Ids defined in this module start in the local envt, though they
177 -- move to the global envt during zonking)
179 tcg_type_env_var :: TcRef TypeEnv,
180 -- Used only to initialise the interface-file
181 -- typechecker in initIfaceTcRn, so that it can see stuff
182 -- bound in this module when dealing with hi-boot recursions
183 -- Updated at intervals (e.g. after dealing with types and classes)
185 tcg_inst_env :: InstEnv,
186 -- ^ Instance envt for /home-package/ modules; Includes the dfuns in
188 tcg_fam_inst_env :: FamInstEnv, -- ^ Ditto for family instances
190 -- Now a bunch of things about this module that are simply
191 -- accumulated, but never consulted until the end.
192 -- Nevertheless, it's convenient to accumulate them along
193 -- with the rest of the info from this module.
194 tcg_exports :: [AvailInfo], -- ^ What is exported
195 tcg_imports :: ImportAvails,
196 -- ^ Information about what was imported from where, including
197 -- things bound in this module.
200 -- ^ What is defined in this module and what is used.
201 -- The latter is used to generate
203 -- (a) version tracking; no need to recompile if these things have
204 -- not changed version stamp
206 -- (b) unused-import info
208 tcg_keep :: TcRef NameSet,
209 -- ^ Locally-defined top-level names to keep alive.
211 -- "Keep alive" means give them an Exported flag, so that the
212 -- simplifier does not discard them as dead code, and so that they
213 -- are exposed in the interface file (but not to export to the
216 -- Some things, like dict-fun Ids and default-method Ids are "born"
217 -- with the Exported flag on, for exactly the above reason, but some
218 -- we only discover as we go. Specifically:
220 -- * The to/from functions for generic data types
222 -- * Top-level variables appearing free in the RHS of an orphan
225 -- * Top-level variables appearing free in a TH bracket
227 tcg_th_used :: TcRef Bool,
228 -- ^ @True@ <=> Template Haskell syntax used.
230 -- We need this so that we can generate a dependency on the
231 -- Template Haskell package, becuase the desugarer is going
232 -- to emit loads of references to TH symbols. The reference
233 -- is implicit rather than explicit, so we have to zap a
236 tcg_dfun_n :: TcRef OccSet,
237 -- ^ Allows us to choose unique DFun names.
239 -- The next fields accumulate the payload of the module
240 -- The binds, rules and foreign-decl fiels are collected
241 -- initially in un-zonked form and are finally zonked in tcRnSrcDecls
243 tcg_rn_exports :: Maybe [Located (IE Name)],
244 tcg_rn_imports :: [LImportDecl Name],
245 -- Keep the renamed imports regardless. They are not
246 -- voluminous and are needed if you want to report unused imports
248 tcg_used_rdrnames :: TcRef (Set RdrName),
249 -- The set of used *imported* (not locally-defined) RdrNames
250 -- Used only to report unused import declarations
252 tcg_rn_decls :: Maybe (HsGroup Name),
253 -- ^ Renamed decls, maybe. @Nothing@ <=> Don't retain renamed
256 tcg_ev_binds :: Bag EvBind, -- Top-level evidence bindings
257 tcg_binds :: LHsBinds Id, -- Value bindings in this module
258 tcg_sigs :: NameSet, -- ...Top-level names that *lack* a signature
259 tcg_imp_specs :: [LTcSpecPrag], -- ...SPECIALISE prags for imported Ids
260 tcg_warns :: Warnings, -- ...Warnings and deprecations
261 tcg_anns :: [Annotation], -- ...Annotations
262 tcg_insts :: [Instance], -- ...Instances
263 tcg_fam_insts :: [FamInst], -- ...Family instances
264 tcg_rules :: [LRuleDecl Id], -- ...Rules
265 tcg_fords :: [LForeignDecl Id], -- ...Foreign import & exports
267 tcg_doc_hdr :: Maybe LHsDocString, -- ^ Maybe Haddock header docs
268 tcg_hpc :: AnyHpcUsage, -- ^ @True@ if any part of the
269 -- prog uses hpc instrumentation.
271 tcg_main :: Maybe Name -- ^ The Name of the main
272 -- function, if this module is
277 = RecFields (NameEnv [Name]) -- Maps a constructor name *in this module*
278 -- to the fields for that constructor
279 NameSet -- Set of all fields declared *in this module*;
280 -- used to suppress name-shadowing complaints
281 -- when using record wild cards
282 -- E.g. let fld = e in C {..}
283 -- This is used when dealing with ".." notation in record
284 -- construction and pattern matching.
285 -- The FieldEnv deals *only* with constructors defined in *this*
286 -- module. For imported modules, we get the same info from the
290 %************************************************************************
292 The interface environments
293 Used when dealing with IfaceDecls
295 %************************************************************************
300 -- The type environment for the module being compiled,
301 -- in case the interface refers back to it via a reference that
302 -- was originally a hi-boot file.
303 -- We need the module name so we can test when it's appropriate
304 -- to look in this env.
305 if_rec_types :: Maybe (Module, IfG TypeEnv)
306 -- Allows a read effect, so it can be in a mutable
307 -- variable; c.f. handling the external package type env
308 -- Nothing => interactive stuff, no loops possible
313 -- The module for the current IfaceDecl
314 -- So if we see f = \x -> x
315 -- it means M.f = \x -> x, where M is the if_mod
318 -- The field is used only for error reporting
319 -- if (say) there's a Lint error in it
321 -- Where the interface came from:
322 -- .hi file, or GHCi state, or ext core
323 -- plus which bit is currently being examined
325 if_tv_env :: UniqFM TyVar, -- Nested tyvar bindings
326 if_id_env :: UniqFM Id -- Nested id binding
331 %************************************************************************
333 The local typechecker environment
335 %************************************************************************
337 The Global-Env/Local-Env story
338 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
339 During type checking, we keep in the tcg_type_env
340 * All types and classes
341 * All Ids derived from types and classes (constructors, selectors)
343 At the end of type checking, we zonk the local bindings,
344 and as we do so we add to the tcg_type_env
345 * Locally defined top-level Ids
347 Why? Because they are now Ids not TcIds. This final GlobalEnv is
348 a) fed back (via the knot) to typechecking the
349 unfoldings of interface signatures
350 b) used in the ModDetails of this module
353 data TcLclEnv -- Changes as we move inside an expression
354 -- Discarded after typecheck/rename; not passed on to desugarer
356 tcl_loc :: SrcSpan, -- Source span
357 tcl_ctxt :: [ErrCtxt], -- Error context, innermost on top
358 tcl_errs :: TcRef Messages, -- Place to accumulate errors
360 tcl_th_ctxt :: ThStage, -- Template Haskell context
361 tcl_arrow_ctxt :: ArrowCtxt, -- Arrow-notation context
363 tcl_rdr :: LocalRdrEnv, -- Local name envt
364 -- Maintained during renaming, of course, but also during
365 -- type checking, solely so that when renaming a Template-Haskell
366 -- splice we have the right environment for the renamer.
368 -- Does *not* include global name envt; may shadow it
369 -- Includes both ordinary variables and type variables;
370 -- they are kept distinct because tyvar have a different
371 -- occurrence contructor (Name.TvOcc)
372 -- We still need the unsullied global name env so that
373 -- we can look up record field names
375 tcl_hetMetLevel :: [TyVar], -- The current environment classifier level (list-of-names)
376 tcl_env :: TcTypeEnv, -- The local type environment: Ids and
377 -- TyVars defined in this module
379 tcl_tyvars :: TcRef TcTyVarSet, -- The "global tyvars"
380 -- Namely, the in-scope TyVars bound in tcl_env,
381 -- plus the tyvars mentioned in the types of Ids bound
383 -- Why mutable? see notes with tcGetGlobalTyVars
385 tcl_lie :: TcRef WantedConstraints, -- Place to accumulate type constraints
388 tcl_meta :: TcRef Unique, -- The next free unique for TcMetaTyVars
389 -- Guaranteed to be allocated linearly
390 tcl_untch :: Unique -- Any TcMetaTyVar with
391 -- unique >= tcl_untch is touchable
392 -- unique < tcl_untch is untouchable
395 type TcTypeEnv = NameEnv TcTyThing
398 {- Note [Given Insts]
400 Because of GADTs, we have to pass inwards the Insts provided by type signatures
401 and existential contexts. Consider
402 data T a where { T1 :: b -> b -> T [b] }
403 f :: Eq a => T a -> Bool
404 f (T1 x y) = [x]==[y]
406 The constructor T1 binds an existential variable 'b', and we need Eq [b].
407 Well, we have it, because Eq a refines to Eq [b], but we can only spot that if we
412 ---------------------------
413 -- Template Haskell stages and levels
414 ---------------------------
416 data ThStage -- See Note [Template Haskell state diagram] in TcSplice
417 = Splice -- Top-level splicing
418 -- This code will be run *at compile time*;
419 -- the result replaces the splice
422 | Comp -- Ordinary Haskell code
425 | Brack -- Inside brackets
426 ThStage -- Binding level = level(stage) + 1
427 (TcRef [PendingSplice]) -- Accumulate pending splices here
428 (TcRef WantedConstraints) -- and type constraints here
430 topStage, topAnnStage, topSpliceStage :: ThStage
433 topSpliceStage = Splice
435 instance Outputable ThStage where
436 ppr Splice = text "Splice"
437 ppr Comp = text "Comp"
438 ppr (Brack s _ _) = text "Brack" <> parens (ppr s)
441 -- See Note [Template Haskell levels] in TcSplice
442 -- Incremented when going inside a bracket,
443 -- decremented when going inside a splice
444 -- NB: ThLevel is one greater than the 'n' in Fig 2 of the
445 -- original "Template meta-programming for Haskell" paper
447 impLevel, outerLevel :: ThLevel
448 impLevel = 0 -- Imported things; they can be used inside a top level splice
449 outerLevel = 1 -- Things defined outside brackets
450 -- NB: Things at level 0 are not *necessarily* imported.
451 -- eg $( \b -> ... ) here b is bound at level 0
455 -- g1 = $(map ...) is OK
456 -- g2 = $(f ...) is not OK; because we havn't compiled f yet
458 thLevel :: ThStage -> ThLevel
461 thLevel (Brack s _ _) = thLevel s + 1
463 ---------------------------
464 -- Arrow-notation context
465 ---------------------------
468 In arrow notation, a variable bound by a proc (or enclosed let/kappa)
469 is not in scope to the left of an arrow tail (-<) or the head of (|..|).
474 Here, x is not in scope in e1, but it is in scope in e2. This can get
478 proc y -> (proc z -> e1) -< e2
480 Here, x and z are in scope in e1, but y is not. We implement this by
481 recording the environment when passing a proc (using newArrowScope),
482 and returning to that (using escapeArrowScope) on the left of -< and the
488 | ArrowCtxt (Env TcGblEnv TcLclEnv)
490 -- Record the current environment (outside a proc)
491 newArrowScope :: TcM a -> TcM a
494 env { env_lcl = (env_lcl env) { tcl_arrow_ctxt = ArrowCtxt env } }
496 -- Return to the stored environment (from the enclosing proc)
497 escapeArrowScope :: TcM a -> TcM a
499 = updEnv $ \ env -> case tcl_arrow_ctxt (env_lcl env) of
501 ArrowCtxt env' -> env'
503 ---------------------------
505 ---------------------------
508 = AGlobal TyThing -- Used only in the return type of a lookup
510 | ATcId { -- Ids defined in this module; may not be fully zonked
512 tct_level :: ThLevel,
513 tct_hetMetLevel :: [TyVar]
516 | ATyVar Name TcType -- The type to which the lexically scoped type vaiable
517 -- is currently refined. We only need the Name
518 -- for error-message purposes; it is the corresponding
519 -- Name in the domain of the envt
521 | AThing TcKind -- Used temporarily, during kind checking, for the
522 -- tycons and clases in this recursive group
524 instance Outputable TcTyThing where -- Debugging only
525 ppr (AGlobal g) = pprTyThing g
526 ppr elt@(ATcId {}) = text "Identifier" <>
527 brackets (ppr (tct_id elt) <> dcolon
528 <> ppr (varType (tct_id elt)) <> comma
529 <+> ppr (tct_level elt)
530 <+> ppr (tct_hetMetLevel elt))
531 ppr (ATyVar tv _) = text "Type variable" <+> quotes (ppr tv)
532 ppr (AThing k) = text "AThing" <+> ppr k
534 pprTcTyThingCategory :: TcTyThing -> SDoc
535 pprTcTyThingCategory (AGlobal thing) = pprTyThingCategory thing
536 pprTcTyThingCategory (ATyVar {}) = ptext (sLit "Type variable")
537 pprTcTyThingCategory (ATcId {}) = ptext (sLit "Local identifier")
538 pprTcTyThingCategory (AThing {}) = ptext (sLit "Kinded thing")
542 type ErrCtxt = (Bool, TidyEnv -> TcM (TidyEnv, Message))
543 -- Monadic so that we have a chance
544 -- to deal with bound type variables just before error
545 -- message construction
547 -- Bool: True <=> this is a landmark context; do not
548 -- discard it when trimming for display
552 %************************************************************************
554 Operations over ImportAvails
556 %************************************************************************
559 -- | 'ImportAvails' summarises what was imported from where, irrespective of
560 -- whether the imported things are actually used or not. It is used:
562 -- * when processing the export list,
564 -- * when constructing usage info for the interface file,
566 -- * to identify the list of directly imported modules for initialisation
567 -- purposes and for optimised overlap checking of family instances,
569 -- * when figuring out what things are really unused
573 imp_mods :: ModuleEnv [(ModuleName, Bool, SrcSpan)],
574 -- ^ Domain is all directly-imported modules
575 -- The 'ModuleName' is what the module was imported as, e.g. in
583 -- - @True@ => import was @import Foo ()@
585 -- - @False@ => import was some other form
589 -- (a) to help construct the usage information in the interface
590 -- file; if we import somethign we need to recompile if the
591 -- export version changes
593 -- (b) to specify what child modules to initialise
595 -- We need a full ModuleEnv rather than a ModuleNameEnv here,
596 -- because we might be importing modules of the same name from
597 -- different packages. (currently not the case, but might be in the
600 imp_dep_mods :: ModuleNameEnv (ModuleName, IsBootInterface),
601 -- ^ Home-package modules needed by the module being compiled
603 -- It doesn't matter whether any of these dependencies
604 -- are actually /used/ when compiling the module; they
605 -- are listed if they are below it at all. For
606 -- example, suppose M imports A which imports X. Then
607 -- compiling M might not need to consult X.hi, but X
608 -- is still listed in M's dependencies.
610 imp_dep_pkgs :: [PackageId],
611 -- ^ Packages needed by the module being compiled, whether directly,
612 -- or via other modules in this package, or via modules imported
613 -- from other packages.
615 imp_orphs :: [Module],
616 -- ^ Orphan modules below us in the import tree (and maybe including
617 -- us for imported modules)
619 imp_finsts :: [Module]
620 -- ^ Family instance modules below us in the import tree (and maybe
621 -- including us for imported modules)
624 mkModDeps :: [(ModuleName, IsBootInterface)]
625 -> ModuleNameEnv (ModuleName, IsBootInterface)
626 mkModDeps deps = foldl add emptyUFM deps
628 add env elt@(m,_) = addToUFM env m elt
630 emptyImportAvails :: ImportAvails
631 emptyImportAvails = ImportAvails { imp_mods = emptyModuleEnv,
632 imp_dep_mods = emptyUFM,
637 plusImportAvails :: ImportAvails -> ImportAvails -> ImportAvails
639 (ImportAvails { imp_mods = mods1,
640 imp_dep_mods = dmods1, imp_dep_pkgs = dpkgs1,
641 imp_orphs = orphs1, imp_finsts = finsts1 })
642 (ImportAvails { imp_mods = mods2,
643 imp_dep_mods = dmods2, imp_dep_pkgs = dpkgs2,
644 imp_orphs = orphs2, imp_finsts = finsts2 })
645 = ImportAvails { imp_mods = plusModuleEnv_C (++) mods1 mods2,
646 imp_dep_mods = plusUFM_C plus_mod_dep dmods1 dmods2,
647 imp_dep_pkgs = dpkgs1 `unionLists` dpkgs2,
648 imp_orphs = orphs1 `unionLists` orphs2,
649 imp_finsts = finsts1 `unionLists` finsts2 }
651 plus_mod_dep (m1, boot1) (m2, boot2)
652 = WARN( not (m1 == m2), (ppr m1 <+> ppr m2) $$ (ppr boot1 <+> ppr boot2) )
653 -- Check mod-names match
654 (m1, boot1 && boot2) -- If either side can "see" a non-hi-boot interface, use that
657 %************************************************************************
659 \subsection{Where from}
661 %************************************************************************
663 The @WhereFrom@ type controls where the renamer looks for an interface file
667 = ImportByUser IsBootInterface -- Ordinary user import (perhaps {-# SOURCE #-})
668 | ImportBySystem -- Non user import.
670 instance Outputable WhereFrom where
671 ppr (ImportByUser is_boot) | is_boot = ptext (sLit "{- SOURCE -}")
673 ppr ImportBySystem = ptext (sLit "{- SYSTEM -}")
677 %************************************************************************
681 These are forced to be in TcRnTypes because
682 TcLclEnv mentions WantedConstraints
683 WantedConstraint mentions CtLoc
684 CtLoc mentions ErrCtxt
687 v%************************************************************************
690 data WantedConstraints
691 = WC { wc_flat :: Bag WantedEvVar -- Unsolved constraints, all wanted
692 , wc_impl :: Bag Implication
693 , wc_insol :: Bag FlavoredEvVar -- Insoluble constraints, can be
694 -- wanted, given, or derived
695 -- See Note [Insoluble constraints]
698 emptyWC :: WantedConstraints
699 emptyWC = WC { wc_flat = emptyBag, wc_impl = emptyBag, wc_insol = emptyBag }
701 mkFlatWC :: Bag WantedEvVar -> WantedConstraints
702 mkFlatWC wevs = WC { wc_flat = wevs, wc_impl = emptyBag, wc_insol = emptyBag }
704 isEmptyWC :: WantedConstraints -> Bool
705 isEmptyWC (WC { wc_flat = f, wc_impl = i, wc_insol = n })
706 = isEmptyBag f && isEmptyBag i && isEmptyBag n
708 insolubleWC :: WantedConstraints -> Bool
709 -- True if there are any insoluble constraints in the wanted bag
710 insolubleWC wc = not (isEmptyBag (wc_insol wc))
711 || anyBag ic_insol (wc_impl wc)
713 andWC :: WantedConstraints -> WantedConstraints -> WantedConstraints
714 andWC (WC { wc_flat = f1, wc_impl = i1, wc_insol = n1 })
715 (WC { wc_flat = f2, wc_impl = i2, wc_insol = n2 })
716 = WC { wc_flat = f1 `unionBags` f2
717 , wc_impl = i1 `unionBags` i2
718 , wc_insol = n1 `unionBags` n2 }
720 addFlats :: WantedConstraints -> Bag WantedEvVar -> WantedConstraints
721 addFlats wc wevs = wc { wc_flat = wevs `unionBags` wc_flat wc }
723 addImplics :: WantedConstraints -> Bag Implication -> WantedConstraints
724 addImplics wc implic = wc { wc_impl = implic `unionBags` wc_impl wc }
726 instance Outputable WantedConstraints where
727 ppr (WC {wc_flat = f, wc_impl = i, wc_insol = n})
728 = ptext (sLit "WC") <+> braces (vcat
729 [ if isEmptyBag f then empty else
730 ptext (sLit "wc_flat =") <+> pprBag pprWantedEvVar f
731 , if isEmptyBag i then empty else
732 ptext (sLit "wc_impl =") <+> pprBag ppr i
733 , if isEmptyBag n then empty else
734 ptext (sLit "wc_insol =") <+> pprBag ppr n ])
736 pprBag :: (a -> SDoc) -> Bag a -> SDoc
737 pprBag pp b = foldrBag (($$) . pp) empty b
742 data Untouchables = NoUntouchables
746 -- A TcMetaTyvar is *touchable* iff its unique u satisfies
750 instance Outputable Untouchables where
751 ppr NoUntouchables = ptext (sLit "No untouchables")
752 ppr (TouchableRange low high) = ptext (sLit "Touchable range:") <+>
753 ppr low <+> char '-' <+> ppr high
755 isNoUntouchables :: Untouchables -> Bool
756 isNoUntouchables NoUntouchables = True
757 isNoUntouchables (TouchableRange {}) = False
759 inTouchableRange :: Untouchables -> TcTyVar -> Bool
760 inTouchableRange NoUntouchables _ = True
761 inTouchableRange (TouchableRange low high) tv
762 = uniq >= low && uniq < high
766 -- EvVar defined in module Var.lhs:
767 -- Evidence variables include all *quantifiable* constraints
769 -- implicit parameters
770 -- coercion variables
773 %************************************************************************
775 Implication constraints
777 %************************************************************************
782 ic_untch :: Untouchables, -- Untouchables: unification variables
783 -- free in the environment
784 ic_env :: TcTypeEnv, -- The type environment
785 -- Used only when generating error messages
786 -- Generally, ic_untch is a superset of tvsof(ic_env)
787 -- However, we don't zonk ic_env when zonking the Implication
788 -- Instead we do that when generating a skolem-escape error message
790 ic_skols :: TcTyVarSet, -- Introduced skolems
791 -- See Note [Skolems in an implication]
793 ic_given :: [EvVar], -- Given evidence variables
794 -- (order does not matter)
795 ic_loc :: GivenLoc, -- Binding location of the implication,
796 -- which is also the location of all the
797 -- given evidence variables
799 ic_wanted :: WantedConstraints, -- The wanted
800 ic_insol :: Bool, -- True iff insolubleWC ic_wanted is true
802 ic_binds :: EvBindsVar -- Points to the place to fill in the
803 -- abstraction and bindings
806 instance Outputable Implication where
807 ppr (Implic { ic_untch = untch, ic_skols = skols, ic_given = given
809 , ic_binds = binds, ic_loc = loc })
810 = ptext (sLit "Implic") <+> braces
811 (sep [ ptext (sLit "Untouchables = ") <+> ppr untch
812 , ptext (sLit "Skolems = ") <+> ppr skols
813 , ptext (sLit "Given = ") <+> pprEvVars given
814 , ptext (sLit "Wanted = ") <+> ppr wanted
815 , ptext (sLit "Binds = ") <+> ppr binds
816 , pprSkolInfo (ctLocOrigin loc)
817 , ppr (ctLocSpan loc) ])
820 Note [Skolems in an implication]
821 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
822 The skolems in an implication are not there to perform a skolem escape
823 check. That happens because all the environment variables are in the
824 untouchables, and therefore cannot be unified with anything at all,
825 let alone the skolems.
827 Instead, ic_skols is used only when considering floating a constraint
828 outside the implication in TcSimplify.floatEqualities or
829 TcSimplify.approximateImplications
831 Note [Insoluble constraints]
832 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
833 Some of the errors that we get during canonicalization are best
834 reported when all constraints have been simplified as much as
835 possible. For instance, assume that during simplification the
836 following constraints arise:
838 [Wanted] F alpha ~ uf1
839 [Wanted] beta ~ uf1 beta
841 When canonicalizing the wanted (beta ~ uf1 beta), if we eagerly fail
842 we will simply see a message:
843 'Can't construct the infinite type beta ~ uf1 beta'
844 and the user has no idea what the uf1 variable is.
846 Instead our plan is that we will NOT fail immediately, but:
847 (1) Record the "frozen" error in the ic_insols field
848 (2) Isolate the offending constraint from the rest of the inerts
849 (3) Keep on simplifying/canonicalizing
851 At the end, we will hopefully have substituted uf1 := F alpha, and we
852 will be able to report a more informative error:
853 'Can't construct the infinite type beta ~ F alpha beta'
855 %************************************************************************
857 EvVarX, WantedEvVar, FlavoredEvVar
859 %************************************************************************
862 data EvVarX a = EvVarX EvVar a
863 -- An evidence variable with accompanying info
865 type WantedEvVar = EvVarX WantedLoc -- The location where it arose
866 type FlavoredEvVar = EvVarX CtFlavor
868 instance Outputable (EvVarX a) where
869 ppr (EvVarX ev _) = pprEvVarWithType ev
870 -- If you want to see the associated info,
871 -- use a more specific printing function
873 mkEvVarX :: EvVar -> a -> EvVarX a
876 evVarOf :: EvVarX a -> EvVar
877 evVarOf (EvVarX ev _) = ev
879 evVarX :: EvVarX a -> a
880 evVarX (EvVarX _ a) = a
882 evVarOfPred :: EvVarX a -> PredType
883 evVarOfPred wev = evVarPred (evVarOf wev)
885 wantedToFlavored :: WantedEvVar -> FlavoredEvVar
886 wantedToFlavored (EvVarX v wl) = EvVarX v (Wanted wl)
888 keepWanted :: Bag FlavoredEvVar -> Bag WantedEvVar
890 = foldlBag keep_wanted emptyBag flevs
892 keep_wanted :: Bag WantedEvVar -> FlavoredEvVar -> Bag WantedEvVar
893 keep_wanted r (EvVarX ev (Wanted wloc)) = consBag (EvVarX ev wloc) r
899 pprEvVars :: [EvVar] -> SDoc -- Print with their types
900 pprEvVars ev_vars = vcat (map pprEvVarWithType ev_vars)
902 pprEvVarTheta :: [EvVar] -> SDoc
903 pprEvVarTheta ev_vars = pprTheta (map evVarPred ev_vars)
905 pprEvVarWithType :: EvVar -> SDoc
906 pprEvVarWithType v = ppr v <+> dcolon <+> pprPred (evVarPred v)
908 pprWantedsWithLocs :: WantedConstraints -> SDoc
909 pprWantedsWithLocs wcs
910 = vcat [ pprBag pprWantedEvVarWithLoc (wc_flat wcs)
911 , pprBag ppr (wc_impl wcs)
912 , pprBag ppr (wc_insol wcs) ]
914 pprWantedEvVarWithLoc, pprWantedEvVar :: WantedEvVar -> SDoc
915 pprWantedEvVarWithLoc (EvVarX v loc) = hang (pprEvVarWithType v)
917 pprWantedEvVar (EvVarX v _) = pprEvVarWithType v
920 %************************************************************************
924 %************************************************************************
928 = Given GivenLoc -- We have evidence for this constraint in TcEvBinds
930 -- We have evidence for this constraint in TcEvBinds;
931 -- *however* this evidence can contain wanteds, so
932 -- it's valid only provisionally to the solution of
934 | Wanted WantedLoc -- We have no evidence bindings for this constraint.
936 -- data DerivedOrig = DerSC | DerInst | DerSelf
937 -- Deriveds are either superclasses of other wanteds or deriveds, or partially
938 -- solved wanteds from instances, or 'self' dictionaries containing yet wanted
941 instance Outputable CtFlavor where
942 ppr (Given _) = ptext (sLit "[Given]")
943 ppr (Wanted _) = ptext (sLit "[Wanted]")
944 ppr (Derived {}) = ptext (sLit "[Derived]")
946 pprFlavorArising :: CtFlavor -> SDoc
947 pprFlavorArising (Derived wl ) = pprArisingAt wl
948 pprFlavorArising (Wanted wl) = pprArisingAt wl
949 pprFlavorArising (Given gl) = pprArisingAt gl
951 isWanted :: CtFlavor -> Bool
952 isWanted (Wanted {}) = True
955 isGiven :: CtFlavor -> Bool
956 isGiven (Given {}) = True
959 isDerived :: CtFlavor -> Bool
960 isDerived (Derived {}) = True
964 %************************************************************************
968 %************************************************************************
970 The 'CtLoc' gives information about where a constraint came from.
971 This is important for decent error message reporting because
972 dictionaries don't appear in the original source code.
976 data CtLoc orig = CtLoc orig SrcSpan [ErrCtxt]
978 type WantedLoc = CtLoc CtOrigin -- Instantiation for wanted constraints
979 type GivenLoc = CtLoc SkolemInfo -- Instantiation for given constraints
981 ctLocSpan :: CtLoc o -> SrcSpan
982 ctLocSpan (CtLoc _ s _) = s
984 ctLocOrigin :: CtLoc o -> o
985 ctLocOrigin (CtLoc o _ _) = o
987 setCtLocOrigin :: CtLoc o -> o' -> CtLoc o'
988 setCtLocOrigin (CtLoc _ s c) o = CtLoc o s c
990 pushErrCtxt :: orig -> ErrCtxt -> CtLoc orig -> CtLoc orig
991 pushErrCtxt o err (CtLoc _ s errs) = CtLoc o s (err:errs)
993 pprArising :: CtOrigin -> SDoc
994 -- Used for the main, top-level error message
995 -- We've done special processing for TypeEq and FunDep origins
996 pprArising (TypeEqOrigin {}) = empty
997 pprArising FunDepOrigin = empty
998 pprArising orig = text "arising from" <+> ppr orig
1000 pprArisingAt :: Outputable o => CtLoc o -> SDoc
1001 pprArisingAt (CtLoc o s _) = sep [ text "arising from" <+> ppr o
1002 , text "at" <+> ppr s]
1005 %************************************************************************
1009 %************************************************************************
1012 -- SkolemInfo gives the origin of *given* constraints
1013 -- a) type variables are skolemised
1014 -- b) an implication constraint is generated
1016 = SigSkol UserTypeCtxt -- A skolem that is created by instantiating
1017 Type -- a programmer-supplied type signature
1018 -- Location of the binding site is on the TyVar
1020 -- The rest are for non-scoped skolems
1021 | ClsSkol Class -- Bound at a class decl
1022 | InstSkol -- Bound at an instance decl
1023 | DataSkol -- Bound at a data type declaration
1024 | FamInstSkol -- Bound at a family instance decl
1025 | PatSkol -- An existential type variable bound by a pattern for
1026 DataCon -- a data constructor with an existential type.
1027 (HsMatchContext Name)
1028 -- e.g. data T = forall a. Eq a => MkT a
1030 -- The pattern MkT x will allocate an existential type
1031 -- variable for 'a'.
1033 | ArrowSkol -- An arrow form (see TcArrows)
1035 | IPSkol [IPName Name] -- Binding site of an implicit parameter
1037 | RuleSkol RuleName -- The LHS of a RULE
1039 | InferSkol [(Name,TcType)]
1040 -- We have inferred a type for these (mutually-recursivive)
1041 -- polymorphic Ids, and are now checking that their RHS
1042 -- constraints are satisfied.
1044 | RuntimeUnkSkol -- a type variable used to represent an unknown
1045 -- runtime type (used in the GHCi debugger)
1047 | BracketSkol -- Template Haskell bracket
1049 | UnkSkol -- Unhelpful info (until I improve it)
1051 instance Outputable SkolemInfo where
1054 pprSkolInfo :: SkolemInfo -> SDoc
1055 -- Complete the sentence "is a rigid type variable bound by..."
1056 pprSkolInfo (SigSkol (FunSigCtxt f) ty)
1057 = hang (ptext (sLit "the type signature for"))
1058 2 (ppr f <+> dcolon <+> ppr ty)
1059 pprSkolInfo (SigSkol cx ty) = hang (pprUserTypeCtxt cx <> colon)
1061 pprSkolInfo (IPSkol ips) = ptext (sLit "the implicit-parameter bindings for")
1062 <+> pprWithCommas ppr ips
1063 pprSkolInfo (ClsSkol cls) = ptext (sLit "the class declaration for") <+> quotes (ppr cls)
1064 pprSkolInfo InstSkol = ptext (sLit "the instance declaration")
1065 pprSkolInfo DataSkol = ptext (sLit "the data type declaration")
1066 pprSkolInfo FamInstSkol = ptext (sLit "the family instance declaration")
1067 pprSkolInfo BracketSkol = ptext (sLit "a Template Haskell bracket")
1068 pprSkolInfo (RuleSkol name) = ptext (sLit "the RULE") <+> doubleQuotes (ftext name)
1069 pprSkolInfo ArrowSkol = ptext (sLit "the arrow form")
1070 pprSkolInfo (PatSkol dc mc) = sep [ ptext (sLit "a pattern with constructor")
1071 , nest 2 $ ppr dc <+> dcolon
1072 <+> ppr (dataConUserType dc) <> comma
1073 , ptext (sLit "in") <+> pprMatchContext mc ]
1074 pprSkolInfo (InferSkol ids) = sep [ ptext (sLit "the inferred type of")
1075 , vcat [ ppr name <+> dcolon <+> ppr ty
1076 | (name,ty) <- ids ]]
1079 -- For type variables the others are dealt with by pprSkolTvBinding.
1080 -- For Insts, these cases should not happen
1081 pprSkolInfo UnkSkol = WARN( True, text "pprSkolInfo: UnkSkol" ) ptext (sLit "UnkSkol")
1082 pprSkolInfo RuntimeUnkSkol = WARN( True, text "pprSkolInfo: RuntimeUnkSkol" ) ptext (sLit "RuntimeUnkSkol")
1086 %************************************************************************
1090 %************************************************************************
1093 -- CtOrigin gives the origin of *wanted* constraints
1095 = OccurrenceOf Name -- Occurrence of an overloaded identifier
1096 | AppOrigin -- An application of some kind
1098 | SpecPragOrigin Name -- Specialisation pragma for identifier
1100 | TypeEqOrigin EqOrigin
1102 | IPOccOrigin (IPName Name) -- Occurrence of an implicit parameter
1104 | LiteralOrigin (HsOverLit Name) -- Occurrence of a literal
1105 | NegateOrigin -- Occurrence of syntactic negation
1107 | ArithSeqOrigin (ArithSeqInfo Name) -- [x..], [x..y] etc
1108 | PArrSeqOrigin (ArithSeqInfo Name) -- [:x..y:] and [:x,y..z:]
1110 | TupleOrigin -- (..,..)
1111 | ExprSigOrigin -- e :: ty
1112 | PatSigOrigin -- p :: ty
1113 | PatOrigin -- Instantiating a polytyped pattern at a constructor
1117 | ScOrigin -- Typechecking superclasses of an instance declaration
1118 | DerivOrigin -- Typechecking deriving
1119 | StandAloneDerivOrigin -- Typechecking stand-alone deriving
1120 | DefaultOrigin -- Typechecking a default decl
1121 | DoOrigin -- Arising from a do expression
1122 | IfOrigin -- Arising from an if statement
1123 | ProcOrigin -- Arising from a proc expression
1124 | AnnOrigin -- An annotation
1129 { uo_actual :: TcType
1130 , uo_expected :: TcType }
1132 instance Outputable CtOrigin where
1133 ppr orig = pprO orig
1135 pprO :: CtOrigin -> SDoc
1136 pprO (OccurrenceOf name) = hsep [ptext (sLit "a use of"), quotes (ppr name)]
1137 pprO AppOrigin = ptext (sLit "an application")
1138 pprO (SpecPragOrigin name) = hsep [ptext (sLit "a specialisation pragma for"), quotes (ppr name)]
1139 pprO (IPOccOrigin name) = hsep [ptext (sLit "a use of implicit parameter"), quotes (ppr name)]
1140 pprO RecordUpdOrigin = ptext (sLit "a record update")
1141 pprO ExprSigOrigin = ptext (sLit "an expression type signature")
1142 pprO PatSigOrigin = ptext (sLit "a pattern type signature")
1143 pprO PatOrigin = ptext (sLit "a pattern")
1144 pprO ViewPatOrigin = ptext (sLit "a view pattern")
1145 pprO IfOrigin = ptext (sLit "an if statement")
1146 pprO (LiteralOrigin lit) = hsep [ptext (sLit "the literal"), quotes (ppr lit)]
1147 pprO (ArithSeqOrigin seq) = hsep [ptext (sLit "the arithmetic sequence"), quotes (ppr seq)]
1148 pprO (PArrSeqOrigin seq) = hsep [ptext (sLit "the parallel array sequence"), quotes (ppr seq)]
1149 pprO SectionOrigin = ptext (sLit "an operator section")
1150 pprO TupleOrigin = ptext (sLit "a tuple")
1151 pprO NegateOrigin = ptext (sLit "a use of syntactic negation")
1152 pprO ScOrigin = ptext (sLit "the superclasses of an instance declaration")
1153 pprO DerivOrigin = ptext (sLit "the 'deriving' clause of a data type declaration")
1154 pprO StandAloneDerivOrigin = ptext (sLit "a 'deriving' declaration")
1155 pprO DefaultOrigin = ptext (sLit "a 'default' declaration")
1156 pprO DoOrigin = ptext (sLit "a do statement")
1157 pprO ProcOrigin = ptext (sLit "a proc expression")
1158 pprO (TypeEqOrigin eq) = ptext (sLit "an equality") <+> ppr eq
1159 pprO AnnOrigin = ptext (sLit "an annotation")
1160 pprO FunDepOrigin = ptext (sLit "a functional dependency")
1162 instance Outputable EqOrigin where
1163 ppr (UnifyOrigin t1 t2) = ppr t1 <+> char '~' <+> ppr t2