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
266 tcg_vects :: [LVectDecl Id], -- ...Vectorisation declarations
268 tcg_doc_hdr :: Maybe LHsDocString, -- ^ Maybe Haddock header docs
269 tcg_hpc :: AnyHpcUsage, -- ^ @True@ if any part of the
270 -- prog uses hpc instrumentation.
272 tcg_main :: Maybe Name -- ^ The Name of the main
273 -- function, if this module is
278 = RecFields (NameEnv [Name]) -- Maps a constructor name *in this module*
279 -- to the fields for that constructor
280 NameSet -- Set of all fields declared *in this module*;
281 -- used to suppress name-shadowing complaints
282 -- when using record wild cards
283 -- E.g. let fld = e in C {..}
284 -- This is used when dealing with ".." notation in record
285 -- construction and pattern matching.
286 -- The FieldEnv deals *only* with constructors defined in *this*
287 -- module. For imported modules, we get the same info from the
291 %************************************************************************
293 The interface environments
294 Used when dealing with IfaceDecls
296 %************************************************************************
301 -- The type environment for the module being compiled,
302 -- in case the interface refers back to it via a reference that
303 -- was originally a hi-boot file.
304 -- We need the module name so we can test when it's appropriate
305 -- to look in this env.
306 if_rec_types :: Maybe (Module, IfG TypeEnv)
307 -- Allows a read effect, so it can be in a mutable
308 -- variable; c.f. handling the external package type env
309 -- Nothing => interactive stuff, no loops possible
314 -- The module for the current IfaceDecl
315 -- So if we see f = \x -> x
316 -- it means M.f = \x -> x, where M is the if_mod
319 -- The field is used only for error reporting
320 -- if (say) there's a Lint error in it
322 -- Where the interface came from:
323 -- .hi file, or GHCi state, or ext core
324 -- plus which bit is currently being examined
326 if_tv_env :: UniqFM TyVar, -- Nested tyvar bindings
327 if_id_env :: UniqFM Id -- Nested id binding
332 %************************************************************************
334 The local typechecker environment
336 %************************************************************************
338 The Global-Env/Local-Env story
339 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
340 During type checking, we keep in the tcg_type_env
341 * All types and classes
342 * All Ids derived from types and classes (constructors, selectors)
344 At the end of type checking, we zonk the local bindings,
345 and as we do so we add to the tcg_type_env
346 * Locally defined top-level Ids
348 Why? Because they are now Ids not TcIds. This final GlobalEnv is
349 a) fed back (via the knot) to typechecking the
350 unfoldings of interface signatures
351 b) used in the ModDetails of this module
354 data TcLclEnv -- Changes as we move inside an expression
355 -- Discarded after typecheck/rename; not passed on to desugarer
357 tcl_loc :: SrcSpan, -- Source span
358 tcl_ctxt :: [ErrCtxt], -- Error context, innermost on top
359 tcl_errs :: TcRef Messages, -- Place to accumulate errors
361 tcl_th_ctxt :: ThStage, -- Template Haskell context
362 tcl_arrow_ctxt :: ArrowCtxt, -- Arrow-notation context
364 tcl_rdr :: LocalRdrEnv, -- Local name envt
365 -- Maintained during renaming, of course, but also during
366 -- type checking, solely so that when renaming a Template-Haskell
367 -- splice we have the right environment for the renamer.
369 -- Does *not* include global name envt; may shadow it
370 -- Includes both ordinary variables and type variables;
371 -- they are kept distinct because tyvar have a different
372 -- occurrence contructor (Name.TvOcc)
373 -- We still need the unsullied global name env so that
374 -- we can look up record field 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 }
514 | ATyVar Name TcType -- The type to which the lexically scoped type vaiable
515 -- is currently refined. We only need the Name
516 -- for error-message purposes; it is the corresponding
517 -- Name in the domain of the envt
519 | AThing TcKind -- Used temporarily, during kind checking, for the
520 -- tycons and clases in this recursive group
522 instance Outputable TcTyThing where -- Debugging only
523 ppr (AGlobal g) = pprTyThing g
524 ppr elt@(ATcId {}) = text "Identifier" <>
525 brackets (ppr (tct_id elt) <> dcolon
526 <> ppr (varType (tct_id elt)) <> comma
527 <+> ppr (tct_level elt))
528 ppr (ATyVar tv _) = text "Type variable" <+> quotes (ppr tv)
529 ppr (AThing k) = text "AThing" <+> ppr k
531 pprTcTyThingCategory :: TcTyThing -> SDoc
532 pprTcTyThingCategory (AGlobal thing) = pprTyThingCategory thing
533 pprTcTyThingCategory (ATyVar {}) = ptext (sLit "Type variable")
534 pprTcTyThingCategory (ATcId {}) = ptext (sLit "Local identifier")
535 pprTcTyThingCategory (AThing {}) = ptext (sLit "Kinded thing")
539 type ErrCtxt = (Bool, TidyEnv -> TcM (TidyEnv, Message))
540 -- Monadic so that we have a chance
541 -- to deal with bound type variables just before error
542 -- message construction
544 -- Bool: True <=> this is a landmark context; do not
545 -- discard it when trimming for display
549 %************************************************************************
551 Operations over ImportAvails
553 %************************************************************************
556 -- | 'ImportAvails' summarises what was imported from where, irrespective of
557 -- whether the imported things are actually used or not. It is used:
559 -- * when processing the export list,
561 -- * when constructing usage info for the interface file,
563 -- * to identify the list of directly imported modules for initialisation
564 -- purposes and for optimised overlap checking of family instances,
566 -- * when figuring out what things are really unused
570 imp_mods :: ModuleEnv [(ModuleName, Bool, SrcSpan)],
571 -- ^ Domain is all directly-imported modules
572 -- The 'ModuleName' is what the module was imported as, e.g. in
580 -- - @True@ => import was @import Foo ()@
582 -- - @False@ => import was some other form
586 -- (a) to help construct the usage information in the interface
587 -- file; if we import somethign we need to recompile if the
588 -- export version changes
590 -- (b) to specify what child modules to initialise
592 -- We need a full ModuleEnv rather than a ModuleNameEnv here,
593 -- because we might be importing modules of the same name from
594 -- different packages. (currently not the case, but might be in the
597 imp_dep_mods :: ModuleNameEnv (ModuleName, IsBootInterface),
598 -- ^ Home-package modules needed by the module being compiled
600 -- It doesn't matter whether any of these dependencies
601 -- are actually /used/ when compiling the module; they
602 -- are listed if they are below it at all. For
603 -- example, suppose M imports A which imports X. Then
604 -- compiling M might not need to consult X.hi, but X
605 -- is still listed in M's dependencies.
607 imp_dep_pkgs :: [PackageId],
608 -- ^ Packages needed by the module being compiled, whether directly,
609 -- or via other modules in this package, or via modules imported
610 -- from other packages.
612 imp_orphs :: [Module],
613 -- ^ Orphan modules below us in the import tree (and maybe including
614 -- us for imported modules)
616 imp_finsts :: [Module]
617 -- ^ Family instance modules below us in the import tree (and maybe
618 -- including us for imported modules)
621 mkModDeps :: [(ModuleName, IsBootInterface)]
622 -> ModuleNameEnv (ModuleName, IsBootInterface)
623 mkModDeps deps = foldl add emptyUFM deps
625 add env elt@(m,_) = addToUFM env m elt
627 emptyImportAvails :: ImportAvails
628 emptyImportAvails = ImportAvails { imp_mods = emptyModuleEnv,
629 imp_dep_mods = emptyUFM,
634 plusImportAvails :: ImportAvails -> ImportAvails -> ImportAvails
636 (ImportAvails { imp_mods = mods1,
637 imp_dep_mods = dmods1, imp_dep_pkgs = dpkgs1,
638 imp_orphs = orphs1, imp_finsts = finsts1 })
639 (ImportAvails { imp_mods = mods2,
640 imp_dep_mods = dmods2, imp_dep_pkgs = dpkgs2,
641 imp_orphs = orphs2, imp_finsts = finsts2 })
642 = ImportAvails { imp_mods = plusModuleEnv_C (++) mods1 mods2,
643 imp_dep_mods = plusUFM_C plus_mod_dep dmods1 dmods2,
644 imp_dep_pkgs = dpkgs1 `unionLists` dpkgs2,
645 imp_orphs = orphs1 `unionLists` orphs2,
646 imp_finsts = finsts1 `unionLists` finsts2 }
648 plus_mod_dep (m1, boot1) (m2, boot2)
649 = WARN( not (m1 == m2), (ppr m1 <+> ppr m2) $$ (ppr boot1 <+> ppr boot2) )
650 -- Check mod-names match
651 (m1, boot1 && boot2) -- If either side can "see" a non-hi-boot interface, use that
654 %************************************************************************
656 \subsection{Where from}
658 %************************************************************************
660 The @WhereFrom@ type controls where the renamer looks for an interface file
664 = ImportByUser IsBootInterface -- Ordinary user import (perhaps {-# SOURCE #-})
665 | ImportBySystem -- Non user import.
667 instance Outputable WhereFrom where
668 ppr (ImportByUser is_boot) | is_boot = ptext (sLit "{- SOURCE -}")
670 ppr ImportBySystem = ptext (sLit "{- SYSTEM -}")
674 %************************************************************************
678 These are forced to be in TcRnTypes because
679 TcLclEnv mentions WantedConstraints
680 WantedConstraint mentions CtLoc
681 CtLoc mentions ErrCtxt
684 v%************************************************************************
687 data WantedConstraints
688 = WC { wc_flat :: Bag WantedEvVar -- Unsolved constraints, all wanted
689 , wc_impl :: Bag Implication
690 , wc_insol :: Bag FlavoredEvVar -- Insoluble constraints, can be
691 -- wanted, given, or derived
692 -- See Note [Insoluble constraints]
695 emptyWC :: WantedConstraints
696 emptyWC = WC { wc_flat = emptyBag, wc_impl = emptyBag, wc_insol = emptyBag }
698 mkFlatWC :: Bag WantedEvVar -> WantedConstraints
699 mkFlatWC wevs = WC { wc_flat = wevs, wc_impl = emptyBag, wc_insol = emptyBag }
701 isEmptyWC :: WantedConstraints -> Bool
702 isEmptyWC (WC { wc_flat = f, wc_impl = i, wc_insol = n })
703 = isEmptyBag f && isEmptyBag i && isEmptyBag n
705 insolubleWC :: WantedConstraints -> Bool
706 -- True if there are any insoluble constraints in the wanted bag
707 insolubleWC wc = not (isEmptyBag (wc_insol wc))
708 || anyBag ic_insol (wc_impl wc)
710 andWC :: WantedConstraints -> WantedConstraints -> WantedConstraints
711 andWC (WC { wc_flat = f1, wc_impl = i1, wc_insol = n1 })
712 (WC { wc_flat = f2, wc_impl = i2, wc_insol = n2 })
713 = WC { wc_flat = f1 `unionBags` f2
714 , wc_impl = i1 `unionBags` i2
715 , wc_insol = n1 `unionBags` n2 }
717 addFlats :: WantedConstraints -> Bag WantedEvVar -> WantedConstraints
718 addFlats wc wevs = wc { wc_flat = wc_flat wc `unionBags` wevs }
720 addImplics :: WantedConstraints -> Bag Implication -> WantedConstraints
721 addImplics wc implic = wc { wc_impl = wc_impl wc `unionBags` implic }
723 instance Outputable WantedConstraints where
724 ppr (WC {wc_flat = f, wc_impl = i, wc_insol = n})
725 = ptext (sLit "WC") <+> braces (vcat
726 [ if isEmptyBag f then empty else
727 ptext (sLit "wc_flat =") <+> pprBag pprWantedEvVar f
728 , if isEmptyBag i then empty else
729 ptext (sLit "wc_impl =") <+> pprBag ppr i
730 , if isEmptyBag n then empty else
731 ptext (sLit "wc_insol =") <+> pprBag ppr n ])
733 pprBag :: (a -> SDoc) -> Bag a -> SDoc
734 pprBag pp b = foldrBag (($$) . pp) empty b
739 data Untouchables = NoUntouchables
743 -- A TcMetaTyvar is *touchable* iff its unique u satisfies
747 instance Outputable Untouchables where
748 ppr NoUntouchables = ptext (sLit "No untouchables")
749 ppr (TouchableRange low high) = ptext (sLit "Touchable range:") <+>
750 ppr low <+> char '-' <+> ppr high
752 isNoUntouchables :: Untouchables -> Bool
753 isNoUntouchables NoUntouchables = True
754 isNoUntouchables (TouchableRange {}) = False
756 inTouchableRange :: Untouchables -> TcTyVar -> Bool
757 inTouchableRange NoUntouchables _ = True
758 inTouchableRange (TouchableRange low high) tv
759 = uniq >= low && uniq < high
763 -- EvVar defined in module Var.lhs:
764 -- Evidence variables include all *quantifiable* constraints
766 -- implicit parameters
767 -- coercion variables
770 %************************************************************************
772 Implication constraints
774 %************************************************************************
779 ic_untch :: Untouchables, -- Untouchables: unification variables
780 -- free in the environment
781 ic_env :: TcTypeEnv, -- The type environment
782 -- Used only when generating error messages
783 -- Generally, ic_untch is a superset of tvsof(ic_env)
784 -- However, we don't zonk ic_env when zonking the Implication
785 -- Instead we do that when generating a skolem-escape error message
787 ic_skols :: TcTyVarSet, -- Introduced skolems
788 -- See Note [Skolems in an implication]
790 ic_given :: [EvVar], -- Given evidence variables
791 -- (order does not matter)
792 ic_loc :: GivenLoc, -- Binding location of the implication,
793 -- which is also the location of all the
794 -- given evidence variables
796 ic_wanted :: WantedConstraints, -- The wanted
797 ic_insol :: Bool, -- True iff insolubleWC ic_wanted is true
799 ic_binds :: EvBindsVar -- Points to the place to fill in the
800 -- abstraction and bindings
803 instance Outputable Implication where
804 ppr (Implic { ic_untch = untch, ic_skols = skols, ic_given = given
806 , ic_binds = binds, ic_loc = loc })
807 = ptext (sLit "Implic") <+> braces
808 (sep [ ptext (sLit "Untouchables = ") <+> ppr untch
809 , ptext (sLit "Skolems = ") <+> ppr skols
810 , ptext (sLit "Given = ") <+> pprEvVars given
811 , ptext (sLit "Wanted = ") <+> ppr wanted
812 , ptext (sLit "Binds = ") <+> ppr binds
813 , pprSkolInfo (ctLocOrigin loc)
814 , ppr (ctLocSpan loc) ])
817 Note [Skolems in an implication]
818 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
819 The skolems in an implication are not there to perform a skolem escape
820 check. That happens because all the environment variables are in the
821 untouchables, and therefore cannot be unified with anything at all,
822 let alone the skolems.
824 Instead, ic_skols is used only when considering floating a constraint
825 outside the implication in TcSimplify.floatEqualities or
826 TcSimplify.approximateImplications
828 Note [Insoluble constraints]
829 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
830 Some of the errors that we get during canonicalization are best
831 reported when all constraints have been simplified as much as
832 possible. For instance, assume that during simplification the
833 following constraints arise:
835 [Wanted] F alpha ~ uf1
836 [Wanted] beta ~ uf1 beta
838 When canonicalizing the wanted (beta ~ uf1 beta), if we eagerly fail
839 we will simply see a message:
840 'Can't construct the infinite type beta ~ uf1 beta'
841 and the user has no idea what the uf1 variable is.
843 Instead our plan is that we will NOT fail immediately, but:
844 (1) Record the "frozen" error in the ic_insols field
845 (2) Isolate the offending constraint from the rest of the inerts
846 (3) Keep on simplifying/canonicalizing
848 At the end, we will hopefully have substituted uf1 := F alpha, and we
849 will be able to report a more informative error:
850 'Can't construct the infinite type beta ~ F alpha beta'
852 %************************************************************************
854 EvVarX, WantedEvVar, FlavoredEvVar
856 %************************************************************************
859 data EvVarX a = EvVarX EvVar a
860 -- An evidence variable with accompanying info
862 type WantedEvVar = EvVarX WantedLoc -- The location where it arose
863 type FlavoredEvVar = EvVarX CtFlavor
865 instance Outputable (EvVarX a) where
866 ppr (EvVarX ev _) = pprEvVarWithType ev
867 -- If you want to see the associated info,
868 -- use a more specific printing function
870 mkEvVarX :: EvVar -> a -> EvVarX a
873 evVarOf :: EvVarX a -> EvVar
874 evVarOf (EvVarX ev _) = ev
876 evVarX :: EvVarX a -> a
877 evVarX (EvVarX _ a) = a
879 evVarOfPred :: EvVarX a -> PredType
880 evVarOfPred wev = evVarPred (evVarOf wev)
882 wantedToFlavored :: WantedEvVar -> FlavoredEvVar
883 wantedToFlavored (EvVarX v wl) = EvVarX v (Wanted wl)
885 keepWanted :: Bag FlavoredEvVar -> Bag WantedEvVar
887 = foldrBag keep_wanted emptyBag flevs
888 -- Important: use fold*r*Bag to preserve the order of the evidence variables.
890 keep_wanted :: FlavoredEvVar -> Bag WantedEvVar -> Bag WantedEvVar
891 keep_wanted (EvVarX ev (Wanted wloc)) r = consBag (EvVarX ev wloc) r
897 pprEvVars :: [EvVar] -> SDoc -- Print with their types
898 pprEvVars ev_vars = vcat (map pprEvVarWithType ev_vars)
900 pprEvVarTheta :: [EvVar] -> SDoc
901 pprEvVarTheta ev_vars = pprTheta (map evVarPred ev_vars)
903 pprEvVarWithType :: EvVar -> SDoc
904 pprEvVarWithType v = ppr v <+> dcolon <+> pprPred (evVarPred v)
906 pprWantedsWithLocs :: WantedConstraints -> SDoc
907 pprWantedsWithLocs wcs
908 = vcat [ pprBag pprWantedEvVarWithLoc (wc_flat wcs)
909 , pprBag ppr (wc_impl wcs)
910 , pprBag ppr (wc_insol wcs) ]
912 pprWantedEvVarWithLoc, pprWantedEvVar :: WantedEvVar -> SDoc
913 pprWantedEvVarWithLoc (EvVarX v loc) = hang (pprEvVarWithType v)
915 pprWantedEvVar (EvVarX v _) = pprEvVarWithType v
918 %************************************************************************
922 %************************************************************************
926 = Given GivenLoc -- We have evidence for this constraint in TcEvBinds
928 -- We have evidence for this constraint in TcEvBinds;
929 -- *however* this evidence can contain wanteds, so
930 -- it's valid only provisionally to the solution of
932 | Wanted WantedLoc -- We have no evidence bindings for this constraint.
934 -- data DerivedOrig = DerSC | DerInst | DerSelf
935 -- Deriveds are either superclasses of other wanteds or deriveds, or partially
936 -- solved wanteds from instances, or 'self' dictionaries containing yet wanted
939 instance Outputable CtFlavor where
940 ppr (Given {}) = ptext (sLit "[G]")
941 ppr (Wanted {}) = ptext (sLit "[W]")
942 ppr (Derived {}) = ptext (sLit "[D]")
943 pprFlavorArising :: CtFlavor -> SDoc
944 pprFlavorArising (Derived wl ) = pprArisingAt wl
945 pprFlavorArising (Wanted wl) = pprArisingAt wl
946 pprFlavorArising (Given gl) = pprArisingAt gl
948 isWanted :: CtFlavor -> Bool
949 isWanted (Wanted {}) = True
952 isGiven :: CtFlavor -> Bool
953 isGiven (Given {}) = True
956 isDerived :: CtFlavor -> Bool
957 isDerived (Derived {}) = True
961 %************************************************************************
965 %************************************************************************
967 The 'CtLoc' gives information about where a constraint came from.
968 This is important for decent error message reporting because
969 dictionaries don't appear in the original source code.
973 data CtLoc orig = CtLoc orig SrcSpan [ErrCtxt]
975 type WantedLoc = CtLoc CtOrigin -- Instantiation for wanted constraints
976 type GivenLoc = CtLoc SkolemInfo -- Instantiation for given constraints
978 ctLocSpan :: CtLoc o -> SrcSpan
979 ctLocSpan (CtLoc _ s _) = s
981 ctLocOrigin :: CtLoc o -> o
982 ctLocOrigin (CtLoc o _ _) = o
984 setCtLocOrigin :: CtLoc o -> o' -> CtLoc o'
985 setCtLocOrigin (CtLoc _ s c) o = CtLoc o s c
987 pushErrCtxt :: orig -> ErrCtxt -> CtLoc orig -> CtLoc orig
988 pushErrCtxt o err (CtLoc _ s errs) = CtLoc o s (err:errs)
990 pprArising :: CtOrigin -> SDoc
991 -- Used for the main, top-level error message
992 -- We've done special processing for TypeEq and FunDep origins
993 pprArising (TypeEqOrigin {}) = empty
994 pprArising FunDepOrigin = empty
995 pprArising orig = text "arising from" <+> ppr orig
997 pprArisingAt :: Outputable o => CtLoc o -> SDoc
998 pprArisingAt (CtLoc o s _) = sep [ text "arising from" <+> ppr o
999 , text "at" <+> ppr s]
1002 %************************************************************************
1006 %************************************************************************
1009 -- SkolemInfo gives the origin of *given* constraints
1010 -- a) type variables are skolemised
1011 -- b) an implication constraint is generated
1013 = SigSkol UserTypeCtxt -- A skolem that is created by instantiating
1014 Type -- a programmer-supplied type signature
1015 -- Location of the binding site is on the TyVar
1017 -- The rest are for non-scoped skolems
1018 | ClsSkol Class -- Bound at a class decl
1019 | InstSkol -- Bound at an instance decl
1020 | DataSkol -- Bound at a data type declaration
1021 | FamInstSkol -- Bound at a family instance decl
1022 | PatSkol -- An existential type variable bound by a pattern for
1023 DataCon -- a data constructor with an existential type.
1024 (HsMatchContext Name)
1025 -- e.g. data T = forall a. Eq a => MkT a
1027 -- The pattern MkT x will allocate an existential type
1028 -- variable for 'a'.
1030 | ArrowSkol -- An arrow form (see TcArrows)
1032 | IPSkol [IPName Name] -- Binding site of an implicit parameter
1034 | RuleSkol RuleName -- The LHS of a RULE
1036 | InferSkol [(Name,TcType)]
1037 -- We have inferred a type for these (mutually-recursivive)
1038 -- polymorphic Ids, and are now checking that their RHS
1039 -- constraints are satisfied.
1041 | BracketSkol -- Template Haskell bracket
1043 | UnkSkol -- Unhelpful info (until I improve it)
1045 instance Outputable SkolemInfo where
1048 pprSkolInfo :: SkolemInfo -> SDoc
1049 -- Complete the sentence "is a rigid type variable bound by..."
1050 pprSkolInfo (SigSkol (FunSigCtxt f) ty)
1051 = hang (ptext (sLit "the type signature for"))
1052 2 (ppr f <+> dcolon <+> ppr ty)
1053 pprSkolInfo (SigSkol cx ty) = hang (pprUserTypeCtxt cx <> colon)
1055 pprSkolInfo (IPSkol ips) = ptext (sLit "the implicit-parameter bindings for")
1056 <+> pprWithCommas ppr ips
1057 pprSkolInfo (ClsSkol cls) = ptext (sLit "the class declaration for") <+> quotes (ppr cls)
1058 pprSkolInfo InstSkol = ptext (sLit "the instance declaration")
1059 pprSkolInfo DataSkol = ptext (sLit "the data type declaration")
1060 pprSkolInfo FamInstSkol = ptext (sLit "the family instance declaration")
1061 pprSkolInfo BracketSkol = ptext (sLit "a Template Haskell bracket")
1062 pprSkolInfo (RuleSkol name) = ptext (sLit "the RULE") <+> doubleQuotes (ftext name)
1063 pprSkolInfo ArrowSkol = ptext (sLit "the arrow form")
1064 pprSkolInfo (PatSkol dc mc) = sep [ ptext (sLit "a pattern with constructor")
1065 , nest 2 $ ppr dc <+> dcolon
1066 <+> ppr (dataConUserType dc) <> comma
1067 , ptext (sLit "in") <+> pprMatchContext mc ]
1068 pprSkolInfo (InferSkol ids) = sep [ ptext (sLit "the inferred type of")
1069 , vcat [ ppr name <+> dcolon <+> ppr ty
1070 | (name,ty) <- ids ]]
1073 -- For type variables the others are dealt with by pprSkolTvBinding.
1074 -- For Insts, these cases should not happen
1075 pprSkolInfo UnkSkol = WARN( True, text "pprSkolInfo: UnkSkol" ) ptext (sLit "UnkSkol")
1079 %************************************************************************
1083 %************************************************************************
1086 -- CtOrigin gives the origin of *wanted* constraints
1088 = OccurrenceOf Name -- Occurrence of an overloaded identifier
1089 | AppOrigin -- An application of some kind
1091 | SpecPragOrigin Name -- Specialisation pragma for identifier
1093 | TypeEqOrigin EqOrigin
1095 | IPOccOrigin (IPName Name) -- Occurrence of an implicit parameter
1097 | LiteralOrigin (HsOverLit Name) -- Occurrence of a literal
1098 | NegateOrigin -- Occurrence of syntactic negation
1100 | ArithSeqOrigin (ArithSeqInfo Name) -- [x..], [x..y] etc
1101 | PArrSeqOrigin (ArithSeqInfo Name) -- [:x..y:] and [:x,y..z:]
1103 | TupleOrigin -- (..,..)
1104 | ExprSigOrigin -- e :: ty
1105 | PatSigOrigin -- p :: ty
1106 | PatOrigin -- Instantiating a polytyped pattern at a constructor
1110 | ScOrigin -- Typechecking superclasses of an instance declaration
1111 | DerivOrigin -- Typechecking deriving
1112 | StandAloneDerivOrigin -- Typechecking stand-alone deriving
1113 | DefaultOrigin -- Typechecking a default decl
1114 | DoOrigin -- Arising from a do expression
1115 | MCompOrigin -- Arising from a monad comprehension
1116 | IfOrigin -- Arising from an if statement
1117 | ProcOrigin -- Arising from a proc expression
1118 | AnnOrigin -- An annotation
1123 { uo_actual :: TcType
1124 , uo_expected :: TcType }
1126 instance Outputable CtOrigin where
1127 ppr orig = pprO orig
1129 pprO :: CtOrigin -> SDoc
1130 pprO (OccurrenceOf name) = hsep [ptext (sLit "a use of"), quotes (ppr name)]
1131 pprO AppOrigin = ptext (sLit "an application")
1132 pprO (SpecPragOrigin name) = hsep [ptext (sLit "a specialisation pragma for"), quotes (ppr name)]
1133 pprO (IPOccOrigin name) = hsep [ptext (sLit "a use of implicit parameter"), quotes (ppr name)]
1134 pprO RecordUpdOrigin = ptext (sLit "a record update")
1135 pprO ExprSigOrigin = ptext (sLit "an expression type signature")
1136 pprO PatSigOrigin = ptext (sLit "a pattern type signature")
1137 pprO PatOrigin = ptext (sLit "a pattern")
1138 pprO ViewPatOrigin = ptext (sLit "a view pattern")
1139 pprO IfOrigin = ptext (sLit "an if statement")
1140 pprO (LiteralOrigin lit) = hsep [ptext (sLit "the literal"), quotes (ppr lit)]
1141 pprO (ArithSeqOrigin seq) = hsep [ptext (sLit "the arithmetic sequence"), quotes (ppr seq)]
1142 pprO (PArrSeqOrigin seq) = hsep [ptext (sLit "the parallel array sequence"), quotes (ppr seq)]
1143 pprO SectionOrigin = ptext (sLit "an operator section")
1144 pprO TupleOrigin = ptext (sLit "a tuple")
1145 pprO NegateOrigin = ptext (sLit "a use of syntactic negation")
1146 pprO ScOrigin = ptext (sLit "the superclasses of an instance declaration")
1147 pprO DerivOrigin = ptext (sLit "the 'deriving' clause of a data type declaration")
1148 pprO StandAloneDerivOrigin = ptext (sLit "a 'deriving' declaration")
1149 pprO DefaultOrigin = ptext (sLit "a 'default' declaration")
1150 pprO DoOrigin = ptext (sLit "a do statement")
1151 pprO MCompOrigin = ptext (sLit "a statement in a monad comprehension")
1152 pprO ProcOrigin = ptext (sLit "a proc expression")
1153 pprO (TypeEqOrigin eq) = ptext (sLit "an equality") <+> ppr eq
1154 pprO AnnOrigin = ptext (sLit "an annotation")
1155 pprO FunDepOrigin = ptext (sLit "a functional dependency")
1157 instance Outputable EqOrigin where
1158 ppr (UnifyOrigin t1 t2) = ppr t1 <+> char '~' <+> ppr t2