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_env :: TcTypeEnv, -- The local type environment: Ids and
376 -- TyVars defined in this module
378 tcl_tyvars :: TcRef TcTyVarSet, -- The "global tyvars"
379 -- Namely, the in-scope TyVars bound in tcl_env,
380 -- plus the tyvars mentioned in the types of Ids bound
382 -- Why mutable? see notes with tcGetGlobalTyVars
384 tcl_lie :: TcRef WantedConstraints, -- Place to accumulate type constraints
387 tcl_meta :: TcRef Unique, -- The next free unique for TcMetaTyVars
388 -- Guaranteed to be allocated linearly
389 tcl_untch :: Unique -- Any TcMetaTyVar with
390 -- unique >= tcl_untch is touchable
391 -- unique < tcl_untch is untouchable
394 type TcTypeEnv = NameEnv TcTyThing
397 {- Note [Given Insts]
399 Because of GADTs, we have to pass inwards the Insts provided by type signatures
400 and existential contexts. Consider
401 data T a where { T1 :: b -> b -> T [b] }
402 f :: Eq a => T a -> Bool
403 f (T1 x y) = [x]==[y]
405 The constructor T1 binds an existential variable 'b', and we need Eq [b].
406 Well, we have it, because Eq a refines to Eq [b], but we can only spot that if we
411 ---------------------------
412 -- Template Haskell stages and levels
413 ---------------------------
415 data ThStage -- See Note [Template Haskell state diagram] in TcSplice
416 = Splice -- Top-level splicing
417 -- This code will be run *at compile time*;
418 -- the result replaces the splice
421 | Comp -- Ordinary Haskell code
424 | Brack -- Inside brackets
425 ThStage -- Binding level = level(stage) + 1
426 (TcRef [PendingSplice]) -- Accumulate pending splices here
427 (TcRef WantedConstraints) -- and type constraints here
429 topStage, topAnnStage, topSpliceStage :: ThStage
432 topSpliceStage = Splice
434 instance Outputable ThStage where
435 ppr Splice = text "Splice"
436 ppr Comp = text "Comp"
437 ppr (Brack s _ _) = text "Brack" <> parens (ppr s)
440 -- See Note [Template Haskell levels] in TcSplice
441 -- Incremented when going inside a bracket,
442 -- decremented when going inside a splice
443 -- NB: ThLevel is one greater than the 'n' in Fig 2 of the
444 -- original "Template meta-programming for Haskell" paper
446 impLevel, outerLevel :: ThLevel
447 impLevel = 0 -- Imported things; they can be used inside a top level splice
448 outerLevel = 1 -- Things defined outside brackets
449 -- NB: Things at level 0 are not *necessarily* imported.
450 -- eg $( \b -> ... ) here b is bound at level 0
454 -- g1 = $(map ...) is OK
455 -- g2 = $(f ...) is not OK; because we havn't compiled f yet
457 thLevel :: ThStage -> ThLevel
460 thLevel (Brack s _ _) = thLevel s + 1
462 ---------------------------
463 -- Arrow-notation context
464 ---------------------------
467 In arrow notation, a variable bound by a proc (or enclosed let/kappa)
468 is not in scope to the left of an arrow tail (-<) or the head of (|..|).
473 Here, x is not in scope in e1, but it is in scope in e2. This can get
477 proc y -> (proc z -> e1) -< e2
479 Here, x and z are in scope in e1, but y is not. We implement this by
480 recording the environment when passing a proc (using newArrowScope),
481 and returning to that (using escapeArrowScope) on the left of -< and the
487 | ArrowCtxt (Env TcGblEnv TcLclEnv)
489 -- Record the current environment (outside a proc)
490 newArrowScope :: TcM a -> TcM a
493 env { env_lcl = (env_lcl env) { tcl_arrow_ctxt = ArrowCtxt env } }
495 -- Return to the stored environment (from the enclosing proc)
496 escapeArrowScope :: TcM a -> TcM a
498 = updEnv $ \ env -> case tcl_arrow_ctxt (env_lcl env) of
500 ArrowCtxt env' -> env'
502 ---------------------------
504 ---------------------------
507 = AGlobal TyThing -- Used only in the return type of a lookup
509 | ATcId { -- Ids defined in this module; may not be fully zonked
511 tct_level :: ThLevel }
513 | ATyVar Name TcType -- The type to which the lexically scoped type vaiable
514 -- is currently refined. We only need the Name
515 -- for error-message purposes; it is the corresponding
516 -- Name in the domain of the envt
518 | AThing TcKind -- Used temporarily, during kind checking, for the
519 -- tycons and clases in this recursive group
521 instance Outputable TcTyThing where -- Debugging only
522 ppr (AGlobal g) = pprTyThing g
523 ppr elt@(ATcId {}) = text "Identifier" <>
524 brackets (ppr (tct_id elt) <> dcolon
525 <> ppr (varType (tct_id elt)) <> comma
526 <+> ppr (tct_level elt))
527 ppr (ATyVar tv _) = text "Type variable" <+> quotes (ppr tv)
528 ppr (AThing k) = text "AThing" <+> ppr k
530 pprTcTyThingCategory :: TcTyThing -> SDoc
531 pprTcTyThingCategory (AGlobal thing) = pprTyThingCategory thing
532 pprTcTyThingCategory (ATyVar {}) = ptext (sLit "Type variable")
533 pprTcTyThingCategory (ATcId {}) = ptext (sLit "Local identifier")
534 pprTcTyThingCategory (AThing {}) = ptext (sLit "Kinded thing")
538 type ErrCtxt = (Bool, TidyEnv -> TcM (TidyEnv, Message))
539 -- Monadic so that we have a chance
540 -- to deal with bound type variables just before error
541 -- message construction
543 -- Bool: True <=> this is a landmark context; do not
544 -- discard it when trimming for display
548 %************************************************************************
550 Operations over ImportAvails
552 %************************************************************************
555 -- | 'ImportAvails' summarises what was imported from where, irrespective of
556 -- whether the imported things are actually used or not. It is used:
558 -- * when processing the export list,
560 -- * when constructing usage info for the interface file,
562 -- * to identify the list of directly imported modules for initialisation
563 -- purposes and for optimised overlap checking of family instances,
565 -- * when figuring out what things are really unused
569 imp_mods :: ModuleEnv [(ModuleName, Bool, SrcSpan)],
570 -- ^ Domain is all directly-imported modules
571 -- The 'ModuleName' is what the module was imported as, e.g. in
579 -- - @True@ => import was @import Foo ()@
581 -- - @False@ => import was some other form
585 -- (a) to help construct the usage information in the interface
586 -- file; if we import somethign we need to recompile if the
587 -- export version changes
589 -- (b) to specify what child modules to initialise
591 -- We need a full ModuleEnv rather than a ModuleNameEnv here,
592 -- because we might be importing modules of the same name from
593 -- different packages. (currently not the case, but might be in the
596 imp_dep_mods :: ModuleNameEnv (ModuleName, IsBootInterface),
597 -- ^ Home-package modules needed by the module being compiled
599 -- It doesn't matter whether any of these dependencies
600 -- are actually /used/ when compiling the module; they
601 -- are listed if they are below it at all. For
602 -- example, suppose M imports A which imports X. Then
603 -- compiling M might not need to consult X.hi, but X
604 -- is still listed in M's dependencies.
606 imp_dep_pkgs :: [PackageId],
607 -- ^ Packages needed by the module being compiled, whether directly,
608 -- or via other modules in this package, or via modules imported
609 -- from other packages.
611 imp_orphs :: [Module],
612 -- ^ Orphan modules below us in the import tree (and maybe including
613 -- us for imported modules)
615 imp_finsts :: [Module]
616 -- ^ Family instance modules below us in the import tree (and maybe
617 -- including us for imported modules)
620 mkModDeps :: [(ModuleName, IsBootInterface)]
621 -> ModuleNameEnv (ModuleName, IsBootInterface)
622 mkModDeps deps = foldl add emptyUFM deps
624 add env elt@(m,_) = addToUFM env m elt
626 emptyImportAvails :: ImportAvails
627 emptyImportAvails = ImportAvails { imp_mods = emptyModuleEnv,
628 imp_dep_mods = emptyUFM,
633 plusImportAvails :: ImportAvails -> ImportAvails -> ImportAvails
635 (ImportAvails { imp_mods = mods1,
636 imp_dep_mods = dmods1, imp_dep_pkgs = dpkgs1,
637 imp_orphs = orphs1, imp_finsts = finsts1 })
638 (ImportAvails { imp_mods = mods2,
639 imp_dep_mods = dmods2, imp_dep_pkgs = dpkgs2,
640 imp_orphs = orphs2, imp_finsts = finsts2 })
641 = ImportAvails { imp_mods = plusModuleEnv_C (++) mods1 mods2,
642 imp_dep_mods = plusUFM_C plus_mod_dep dmods1 dmods2,
643 imp_dep_pkgs = dpkgs1 `unionLists` dpkgs2,
644 imp_orphs = orphs1 `unionLists` orphs2,
645 imp_finsts = finsts1 `unionLists` finsts2 }
647 plus_mod_dep (m1, boot1) (m2, boot2)
648 = WARN( not (m1 == m2), (ppr m1 <+> ppr m2) $$ (ppr boot1 <+> ppr boot2) )
649 -- Check mod-names match
650 (m1, boot1 && boot2) -- If either side can "see" a non-hi-boot interface, use that
653 %************************************************************************
655 \subsection{Where from}
657 %************************************************************************
659 The @WhereFrom@ type controls where the renamer looks for an interface file
663 = ImportByUser IsBootInterface -- Ordinary user import (perhaps {-# SOURCE #-})
664 | ImportBySystem -- Non user import.
666 instance Outputable WhereFrom where
667 ppr (ImportByUser is_boot) | is_boot = ptext (sLit "{- SOURCE -}")
669 ppr ImportBySystem = ptext (sLit "{- SYSTEM -}")
673 %************************************************************************
677 These are forced to be in TcRnTypes because
678 TcLclEnv mentions WantedConstraints
679 WantedConstraint mentions CtLoc
680 CtLoc mentions ErrCtxt
683 v%************************************************************************
686 data WantedConstraints
687 = WC { wc_flat :: Bag WantedEvVar -- Unsolved constraints, all wanted
688 , wc_impl :: Bag Implication
689 , wc_insol :: Bag FlavoredEvVar -- Insoluble constraints, can be
690 -- wanted, given, or derived
691 -- See Note [Insoluble constraints]
694 emptyWC :: WantedConstraints
695 emptyWC = WC { wc_flat = emptyBag, wc_impl = emptyBag, wc_insol = emptyBag }
697 mkFlatWC :: Bag WantedEvVar -> WantedConstraints
698 mkFlatWC wevs = WC { wc_flat = wevs, wc_impl = emptyBag, wc_insol = emptyBag }
700 isEmptyWC :: WantedConstraints -> Bool
701 isEmptyWC (WC { wc_flat = f, wc_impl = i, wc_insol = n })
702 = isEmptyBag f && isEmptyBag i && isEmptyBag n
704 insolubleWC :: WantedConstraints -> Bool
705 -- True if there are any insoluble constraints in the wanted bag
706 insolubleWC wc = not (isEmptyBag (wc_insol wc))
707 || anyBag ic_insol (wc_impl wc)
709 andWC :: WantedConstraints -> WantedConstraints -> WantedConstraints
710 andWC (WC { wc_flat = f1, wc_impl = i1, wc_insol = n1 })
711 (WC { wc_flat = f2, wc_impl = i2, wc_insol = n2 })
712 = WC { wc_flat = f1 `unionBags` f2
713 , wc_impl = i1 `unionBags` i2
714 , wc_insol = n1 `unionBags` n2 }
716 addFlats :: WantedConstraints -> Bag WantedEvVar -> WantedConstraints
717 addFlats wc wevs = wc { wc_flat = wevs `unionBags` wc_flat wc }
719 addImplics :: WantedConstraints -> Bag Implication -> WantedConstraints
720 addImplics wc implic = wc { wc_impl = implic `unionBags` wc_impl wc }
722 instance Outputable WantedConstraints where
723 ppr (WC {wc_flat = f, wc_impl = i, wc_insol = n})
724 = ptext (sLit "WC") <+> braces (vcat
725 [ if isEmptyBag f then empty else
726 ptext (sLit "wc_flat =") <+> pprBag pprWantedEvVar f
727 , if isEmptyBag i then empty else
728 ptext (sLit "wc_impl =") <+> pprBag ppr i
729 , if isEmptyBag n then empty else
730 ptext (sLit "wc_insol =") <+> pprBag ppr n ])
732 pprBag :: (a -> SDoc) -> Bag a -> SDoc
733 pprBag pp b = foldrBag (($$) . pp) empty b
738 data Untouchables = NoUntouchables
742 -- A TcMetaTyvar is *touchable* iff its unique u satisfies
746 instance Outputable Untouchables where
747 ppr NoUntouchables = ptext (sLit "No untouchables")
748 ppr (TouchableRange low high) = ptext (sLit "Touchable range:") <+>
749 ppr low <+> char '-' <+> ppr high
751 isNoUntouchables :: Untouchables -> Bool
752 isNoUntouchables NoUntouchables = True
753 isNoUntouchables (TouchableRange {}) = False
755 inTouchableRange :: Untouchables -> TcTyVar -> Bool
756 inTouchableRange NoUntouchables _ = True
757 inTouchableRange (TouchableRange low high) tv
758 = uniq >= low && uniq < high
762 -- EvVar defined in module Var.lhs:
763 -- Evidence variables include all *quantifiable* constraints
765 -- implicit parameters
766 -- coercion variables
769 %************************************************************************
771 Implication constraints
773 %************************************************************************
778 ic_untch :: Untouchables, -- Untouchables: unification variables
779 -- free in the environment
780 ic_env :: TcTypeEnv, -- The type environment
781 -- Used only when generating error messages
782 -- Generally, ic_untch is a superset of tvsof(ic_env)
783 -- However, we don't zonk ic_env when zonking the Implication
784 -- Instead we do that when generating a skolem-escape error message
786 ic_skols :: TcTyVarSet, -- Introduced skolems
787 -- See Note [Skolems in an implication]
789 ic_given :: [EvVar], -- Given evidence variables
790 -- (order does not matter)
791 ic_loc :: GivenLoc, -- Binding location of the implication,
792 -- which is also the location of all the
793 -- given evidence variables
795 ic_wanted :: WantedConstraints, -- The wanted
796 ic_insol :: Bool, -- True iff insolubleWC ic_wantted is true
798 ic_binds :: EvBindsVar -- Points to the place to fill in the
799 -- abstraction and bindings
802 instance Outputable Implication where
803 ppr (Implic { ic_untch = untch, ic_skols = skols, ic_given = given
805 , ic_binds = binds, ic_loc = loc })
806 = ptext (sLit "Implic") <+> braces
807 (sep [ ptext (sLit "Untouchables = ") <+> ppr untch
808 , ptext (sLit "Skolems = ") <+> ppr skols
809 , ptext (sLit "Given = ") <+> pprEvVars given
810 , ptext (sLit "Wanted = ") <+> ppr wanted
811 , ptext (sLit "Binds = ") <+> ppr binds
812 , pprSkolInfo (ctLocOrigin loc)
813 , ppr (ctLocSpan loc) ])
816 Note [Skolems in an implication]
817 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
818 The skolems in an implication are not there to perform a skolem escape
819 check. That happens because all the environment variables are in the
820 untouchables, and therefore cannot be unified with anything at all,
821 let alone the skolems.
823 Instead, ic_skols is used only when considering floating a constraint
824 outside the implication in TcSimplify.floatEqualities or
825 TcSimplify.approximateImplications
827 Note [Insoluble constraints]
828 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
829 Some of the errors that we get during canonicalization are best
830 reported when all constraints have been simplified as much as
831 possible. For instance, assume that during simplification the
832 following constraints arise:
834 [Wanted] F alpha ~ uf1
835 [Wanted] beta ~ uf1 beta
837 When canonicalizing the wanted (beta ~ uf1 beta), if we eagerly fail
838 we will simply see a message:
839 'Can't construct the infinite type beta ~ uf1 beta'
840 and the user has no idea what the uf1 variable is.
842 Instead our plan is that we will NOT fail immediately, but:
843 (1) Record the "frozen" error in the ic_insols field
844 (2) Isolate the offending constraint from the rest of the inerts
845 (3) Keep on simplifying/canonicalizing
847 At the end, we will hopefully have substituted uf1 := F alpha, and we
848 will be able to report a more informative error:
849 'Can't construct the infinite type beta ~ F alpha beta'
851 %************************************************************************
853 EvVarX, WantedEvVar, FlavoredEvVar
855 %************************************************************************
858 data EvVarX a = EvVarX EvVar a
859 -- An evidence variable with accompanying info
861 type WantedEvVar = EvVarX WantedLoc -- The location where it arose
862 type FlavoredEvVar = EvVarX CtFlavor
864 instance Outputable (EvVarX a) where
865 ppr (EvVarX ev _) = pprEvVarWithType ev
866 -- If you want to see the associated info,
867 -- use a more specific printing function
869 mkEvVarX :: EvVar -> a -> EvVarX a
872 evVarOf :: EvVarX a -> EvVar
873 evVarOf (EvVarX ev _) = ev
875 evVarX :: EvVarX a -> a
876 evVarX (EvVarX _ a) = a
878 evVarOfPred :: EvVarX a -> PredType
879 evVarOfPred wev = evVarPred (evVarOf wev)
881 wantedToFlavored :: WantedEvVar -> FlavoredEvVar
882 wantedToFlavored (EvVarX v wl) = EvVarX v (Wanted wl)
884 keepWanted :: Bag FlavoredEvVar -> Bag WantedEvVar
886 = foldlBag keep_wanted emptyBag flevs
888 keep_wanted :: Bag WantedEvVar -> FlavoredEvVar -> Bag WantedEvVar
889 keep_wanted r (EvVarX ev (Wanted wloc)) = consBag (EvVarX ev wloc) r
895 pprEvVars :: [EvVar] -> SDoc -- Print with their types
896 pprEvVars ev_vars = vcat (map pprEvVarWithType ev_vars)
898 pprEvVarTheta :: [EvVar] -> SDoc
899 pprEvVarTheta ev_vars = pprTheta (map evVarPred ev_vars)
901 pprEvVarWithType :: EvVar -> SDoc
902 pprEvVarWithType v = ppr v <+> dcolon <+> pprPred (evVarPred v)
904 pprWantedsWithLocs :: WantedConstraints -> SDoc
905 pprWantedsWithLocs wcs
906 = vcat [ pprBag pprWantedEvVarWithLoc (wc_flat wcs)
907 , pprBag ppr (wc_impl wcs)
908 , pprBag ppr (wc_insol wcs) ]
910 pprWantedEvVarWithLoc, pprWantedEvVar :: WantedEvVar -> SDoc
911 pprWantedEvVarWithLoc (EvVarX v loc) = hang (pprEvVarWithType v)
913 pprWantedEvVar (EvVarX v _) = pprEvVarWithType v
916 %************************************************************************
920 %************************************************************************
924 = Given GivenLoc -- We have evidence for this constraint in TcEvBinds
926 -- We have evidence for this constraint in TcEvBinds;
927 -- *however* this evidence can contain wanteds, so
928 -- it's valid only provisionally to the solution of
930 | Wanted WantedLoc -- We have no evidence bindings for this constraint.
932 -- data DerivedOrig = DerSC | DerInst | DerSelf
933 -- Deriveds are either superclasses of other wanteds or deriveds, or partially
934 -- solved wanteds from instances, or 'self' dictionaries containing yet wanted
937 instance Outputable CtFlavor where
938 ppr (Given _) = ptext (sLit "[Given]")
939 ppr (Wanted _) = ptext (sLit "[Wanted]")
940 ppr (Derived {}) = ptext (sLit "[Derived]")
942 pprFlavorArising :: CtFlavor -> SDoc
943 pprFlavorArising (Derived wl ) = pprArisingAt wl
944 pprFlavorArising (Wanted wl) = pprArisingAt wl
945 pprFlavorArising (Given gl) = pprArisingAt gl
947 isWanted :: CtFlavor -> Bool
948 isWanted (Wanted {}) = True
951 isGiven :: CtFlavor -> Bool
952 isGiven (Given {}) = True
955 isDerived :: CtFlavor -> Bool
956 isDerived (Derived {}) = True
960 %************************************************************************
964 %************************************************************************
966 The 'CtLoc' gives information about where a constraint came from.
967 This is important for decent error message reporting because
968 dictionaries don't appear in the original source code.
972 data CtLoc orig = CtLoc orig SrcSpan [ErrCtxt]
974 type WantedLoc = CtLoc CtOrigin -- Instantiation for wanted constraints
975 type GivenLoc = CtLoc SkolemInfo -- Instantiation for given constraints
977 ctLocSpan :: CtLoc o -> SrcSpan
978 ctLocSpan (CtLoc _ s _) = s
980 ctLocOrigin :: CtLoc o -> o
981 ctLocOrigin (CtLoc o _ _) = o
983 setCtLocOrigin :: CtLoc o -> o' -> CtLoc o'
984 setCtLocOrigin (CtLoc _ s c) o = CtLoc o s c
986 pushErrCtxt :: orig -> ErrCtxt -> CtLoc orig -> CtLoc orig
987 pushErrCtxt o err (CtLoc _ s errs) = CtLoc o s (err:errs)
989 pprArising :: CtOrigin -> SDoc
990 -- Used for the main, top-level error message
991 -- We've done special processing for TypeEq and FunDep origins
992 pprArising (TypeEqOrigin {}) = empty
993 pprArising FunDepOrigin = empty
994 pprArising orig = text "arising from" <+> ppr orig
996 pprArisingAt :: Outputable o => CtLoc o -> SDoc
997 pprArisingAt (CtLoc o s _) = sep [ text "arising from" <+> ppr o
998 , text "at" <+> ppr s]
1001 %************************************************************************
1005 %************************************************************************
1008 -- SkolemInfo gives the origin of *given* constraints
1009 -- a) type variables are skolemised
1010 -- b) an implication constraint is generated
1012 = SigSkol UserTypeCtxt -- A skolem that is created by instantiating
1013 Type -- a programmer-supplied type signature
1014 -- Location of the binding site is on the TyVar
1016 -- The rest are for non-scoped skolems
1017 | ClsSkol Class -- Bound at a class decl
1018 | InstSkol -- Bound at an instance decl
1019 | DataSkol -- Bound at a data type declaration
1020 | FamInstSkol -- Bound at a family instance decl
1021 | PatSkol -- An existential type variable bound by a pattern for
1022 DataCon -- a data constructor with an existential type.
1023 (HsMatchContext Name)
1024 -- e.g. data T = forall a. Eq a => MkT a
1026 -- The pattern MkT x will allocate an existential type
1027 -- variable for 'a'.
1029 | ArrowSkol -- An arrow form (see TcArrows)
1031 | IPSkol [IPName Name] -- Binding site of an implicit parameter
1033 | RuleSkol RuleName -- The LHS of a RULE
1035 | InferSkol [(Name,TcType)]
1036 -- We have inferred a type for these (mutually-recursivive)
1037 -- polymorphic Ids, and are now checking that their RHS
1038 -- constraints are satisfied.
1040 | RuntimeUnkSkol -- a type variable used to represent an unknown
1041 -- runtime type (used in the GHCi debugger)
1043 | BracketSkol -- Template Haskell bracket
1045 | UnkSkol -- Unhelpful info (until I improve it)
1047 instance Outputable SkolemInfo where
1050 pprSkolInfo :: SkolemInfo -> SDoc
1051 -- Complete the sentence "is a rigid type variable bound by..."
1052 pprSkolInfo (SigSkol (FunSigCtxt f) ty)
1053 = hang (ptext (sLit "the type signature for"))
1054 2 (ppr f <+> dcolon <+> ppr ty)
1055 pprSkolInfo (SigSkol cx ty) = hang (pprUserTypeCtxt cx <> colon)
1057 pprSkolInfo (IPSkol ips) = ptext (sLit "the implicit-parameter bindings for")
1058 <+> pprWithCommas ppr ips
1059 pprSkolInfo (ClsSkol cls) = ptext (sLit "the class declaration for") <+> quotes (ppr cls)
1060 pprSkolInfo InstSkol = ptext (sLit "the instance declaration")
1061 pprSkolInfo DataSkol = ptext (sLit "the data type declaration")
1062 pprSkolInfo FamInstSkol = ptext (sLit "the family instance declaration")
1063 pprSkolInfo BracketSkol = ptext (sLit "a Template Haskell bracket")
1064 pprSkolInfo (RuleSkol name) = ptext (sLit "the RULE") <+> doubleQuotes (ftext name)
1065 pprSkolInfo ArrowSkol = ptext (sLit "the arrow form")
1066 pprSkolInfo (PatSkol dc mc) = sep [ ptext (sLit "a pattern with constructor")
1067 , nest 2 $ ppr dc <+> dcolon
1068 <+> ppr (dataConUserType dc) <> comma
1069 , ptext (sLit "in") <+> pprMatchContext mc ]
1070 pprSkolInfo (InferSkol ids) = sep [ ptext (sLit "the inferred type of")
1071 , vcat [ ppr name <+> dcolon <+> ppr ty
1072 | (name,ty) <- ids ]]
1075 -- For type variables the others are dealt with by pprSkolTvBinding.
1076 -- For Insts, these cases should not happen
1077 pprSkolInfo UnkSkol = WARN( True, text "pprSkolInfo: UnkSkol" ) ptext (sLit "UnkSkol")
1078 pprSkolInfo RuntimeUnkSkol = WARN( True, text "pprSkolInfo: RuntimeUnkSkol" ) ptext (sLit "RuntimeUnkSkol")
1082 %************************************************************************
1086 %************************************************************************
1089 -- CtOrigin gives the origin of *wanted* constraints
1091 = OccurrenceOf Name -- Occurrence of an overloaded identifier
1092 | AppOrigin -- An application of some kind
1094 | SpecPragOrigin Name -- Specialisation pragma for identifier
1096 | TypeEqOrigin EqOrigin
1098 | IPOccOrigin (IPName Name) -- Occurrence of an implicit parameter
1100 | LiteralOrigin (HsOverLit Name) -- Occurrence of a literal
1101 | NegateOrigin -- Occurrence of syntactic negation
1103 | ArithSeqOrigin (ArithSeqInfo Name) -- [x..], [x..y] etc
1104 | PArrSeqOrigin (ArithSeqInfo Name) -- [:x..y:] and [:x,y..z:]
1106 | TupleOrigin -- (..,..)
1107 | ExprSigOrigin -- e :: ty
1108 | PatSigOrigin -- p :: ty
1109 | PatOrigin -- Instantiating a polytyped pattern at a constructor
1113 | ScOrigin -- Typechecking superclasses of an instance declaration
1114 | DerivOrigin -- Typechecking deriving
1115 | StandAloneDerivOrigin -- Typechecking stand-alone deriving
1116 | DefaultOrigin -- Typechecking a default decl
1117 | DoOrigin -- Arising from a do expression
1118 | IfOrigin -- Arising from an if statement
1119 | ProcOrigin -- Arising from a proc expression
1120 | AnnOrigin -- An annotation
1125 { uo_actual :: TcType
1126 , uo_expected :: TcType }
1128 instance Outputable CtOrigin where
1129 ppr orig = pprO orig
1131 pprO :: CtOrigin -> SDoc
1132 pprO (OccurrenceOf name) = hsep [ptext (sLit "a use of"), quotes (ppr name)]
1133 pprO AppOrigin = ptext (sLit "an application")
1134 pprO (SpecPragOrigin name) = hsep [ptext (sLit "a specialisation pragma for"), quotes (ppr name)]
1135 pprO (IPOccOrigin name) = hsep [ptext (sLit "a use of implicit parameter"), quotes (ppr name)]
1136 pprO RecordUpdOrigin = ptext (sLit "a record update")
1137 pprO ExprSigOrigin = ptext (sLit "an expression type signature")
1138 pprO PatSigOrigin = ptext (sLit "a pattern type signature")
1139 pprO PatOrigin = ptext (sLit "a pattern")
1140 pprO ViewPatOrigin = ptext (sLit "a view pattern")
1141 pprO IfOrigin = ptext (sLit "an if statement")
1142 pprO (LiteralOrigin lit) = hsep [ptext (sLit "the literal"), quotes (ppr lit)]
1143 pprO (ArithSeqOrigin seq) = hsep [ptext (sLit "the arithmetic sequence"), quotes (ppr seq)]
1144 pprO (PArrSeqOrigin seq) = hsep [ptext (sLit "the parallel array sequence"), quotes (ppr seq)]
1145 pprO SectionOrigin = ptext (sLit "an operator section")
1146 pprO TupleOrigin = ptext (sLit "a tuple")
1147 pprO NegateOrigin = ptext (sLit "a use of syntactic negation")
1148 pprO ScOrigin = ptext (sLit "the superclasses of an instance declaration")
1149 pprO DerivOrigin = ptext (sLit "the 'deriving' clause of a data type declaration")
1150 pprO StandAloneDerivOrigin = ptext (sLit "a 'deriving' declaration")
1151 pprO DefaultOrigin = ptext (sLit "a 'default' declaration")
1152 pprO DoOrigin = ptext (sLit "a do statement")
1153 pprO ProcOrigin = ptext (sLit "a proc expression")
1154 pprO (TypeEqOrigin eq) = ptext (sLit "an equality") <+> ppr eq
1155 pprO AnnOrigin = ptext (sLit "an annotation")
1156 pprO FunDepOrigin = ptext (sLit "a functional dependency")
1158 instance Outputable EqOrigin where
1159 ppr (UnifyOrigin t1 t2) = ppr t1 <+> char '~' <+> ppr t2