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 TcTyThing(..), pprTcTyThingCategory, RefinementVisibility(..),
24 ThStage(..), topStage, topAnnStage, topSpliceStage,
25 ThLevel, impLevel, outerLevel, thLevel,
28 ArrowCtxt(NoArrowCtxt), newArrowScope, escapeArrowScope,
31 Inst(..), EqInstCo, InstOrigin(..), InstLoc(..),
32 pprInstLoc, pprInstArising, instLocSpan, instLocOrigin, setInstLoc,
33 LIE, emptyLIE, unitLIE, plusLIE, consLIE, instLoc, instSpan,
34 plusLIEs, mkLIE, isEmptyLIE, lieToList, listToLIE,
37 TcId, TcIdSet, TcDictBinds, TcTyVarBind(..), TcTyVarBinds
41 #include "HsVersions.h"
43 import HsSyn hiding (LIE)
75 %************************************************************************
77 Standard monad definition for TcRn
78 All the combinators for the monad can be found in TcRnMonad
80 %************************************************************************
82 The monad itself has to be defined here, because it is mentioned by ErrCtxt
85 type TcRef a = IORef a
86 type TcId = Id -- Type may be a TcType
88 type TcDictBinds = DictBinds TcId -- Bag of dictionary bindings
90 type TcRnIf a b c = IOEnv (Env a b) c
91 type IfM lcl a = TcRnIf IfGblEnv lcl a -- Iface stuff
93 type IfG a = IfM () a -- Top level
94 type IfL a = IfM IfLclEnv a -- Nested
95 type TcRn a = TcRnIf TcGblEnv TcLclEnv a
96 type RnM a = TcRn a -- Historical
97 type TcM a = TcRn a -- Historical
100 Representation of type bindings to uninstantiated meta variables used during
104 data TcTyVarBind = TcTyVarBind TcTyVar TcType
106 type TcTyVarBinds = Bag TcTyVarBind
108 instance Outputable TcTyVarBind where
109 ppr (TcTyVarBind tv ty) = ppr tv <+> text ":=" <+> ppr ty
113 %************************************************************************
115 The main environment types
117 %************************************************************************
120 data Env gbl lcl -- Changes as we move into an expression
122 env_top :: HscEnv, -- Top-level stuff that never changes
123 -- Includes all info about imported things
125 env_us :: {-# UNPACK #-} !(IORef UniqSupply),
126 -- Unique supply for local varibles
128 env_gbl :: gbl, -- Info about things defined at the top level
129 -- of the module being compiled
131 env_lcl :: lcl -- Nested stuff; changes as we go into
134 -- TcGblEnv describes the top-level of the module at the
135 -- point at which the typechecker is finished work.
136 -- It is this structure that is handed on to the desugarer
140 tcg_mod :: Module, -- ^ Module being compiled
141 tcg_src :: HscSource,
142 -- ^ What kind of module (regular Haskell, hs-boot, ext-core)
144 tcg_rdr_env :: GlobalRdrEnv, -- ^ Top level envt; used during renaming
145 tcg_default :: Maybe [Type],
146 -- ^ Types used for defaulting. @Nothing@ => no @default@ decl
148 tcg_fix_env :: FixityEnv, -- ^ Just for things in this module
149 tcg_field_env :: RecFieldEnv, -- ^ Just for things in this module
151 tcg_type_env :: TypeEnv,
152 -- ^ Global type env for the module we are compiling now. All
153 -- TyCons and Classes (for this module) end up in here right away,
154 -- along with their derived constructors, selectors.
156 -- (Ids defined in this module start in the local envt, though they
157 -- move to the global envt during zonking)
159 tcg_type_env_var :: TcRef TypeEnv,
160 -- Used only to initialise the interface-file
161 -- typechecker in initIfaceTcRn, so that it can see stuff
162 -- bound in this module when dealing with hi-boot recursions
163 -- Updated at intervals (e.g. after dealing with types and classes)
165 tcg_inst_env :: InstEnv,
166 -- ^ Instance envt for /home-package/ modules; Includes the dfuns in
168 tcg_fam_inst_env :: FamInstEnv, -- ^ Ditto for family instances
170 -- Now a bunch of things about this module that are simply
171 -- accumulated, but never consulted until the end.
172 -- Nevertheless, it's convenient to accumulate them along
173 -- with the rest of the info from this module.
174 tcg_exports :: [AvailInfo], -- ^ What is exported
175 tcg_imports :: ImportAvails,
176 -- ^ Information about what was imported from where, including
177 -- things bound in this module.
180 -- ^ What is defined in this module and what is used.
181 -- The latter is used to generate
183 -- (a) version tracking; no need to recompile if these things have
184 -- not changed version stamp
186 -- (b) unused-import info
188 tcg_keep :: TcRef NameSet,
189 -- ^ Locally-defined top-level names to keep alive.
191 -- "Keep alive" means give them an Exported flag, so that the
192 -- simplifier does not discard them as dead code, and so that they
193 -- are exposed in the interface file (but not to export to the
196 -- Some things, like dict-fun Ids and default-method Ids are "born"
197 -- with the Exported flag on, for exactly the above reason, but some
198 -- we only discover as we go. Specifically:
200 -- * The to/from functions for generic data types
202 -- * Top-level variables appearing free in the RHS of an orphan
205 -- * Top-level variables appearing free in a TH bracket
207 tcg_inst_uses :: TcRef NameSet,
208 -- ^ Home-package Dfuns actually used.
210 -- Used to generate version dependencies This records usages, rather
211 -- like tcg_dus, but it has to be a mutable variable so it can be
212 -- augmented when we look up an instance. These uses of dfuns are
213 -- rather like the free variables of the program, but are implicit
214 -- instead of explicit.
216 tcg_th_used :: TcRef Bool,
217 -- ^ @True@ <=> Template Haskell syntax used.
219 -- We need this so that we can generate a dependency on the Template
220 -- Haskell package, becuase the desugarer is going to emit loads of
221 -- references to TH symbols. It's rather like tcg_inst_uses; the
222 -- reference is implicit rather than explicit, so we have to zap a
225 tcg_dfun_n :: TcRef OccSet,
226 -- ^ Allows us to choose unique DFun names.
228 -- The next fields accumulate the payload of the module
229 -- The binds, rules and foreign-decl fiels are collected
230 -- initially in un-zonked form and are finally zonked in tcRnSrcDecls
232 tcg_rn_exports :: Maybe [Located (IE Name)],
233 tcg_rn_imports :: [LImportDecl Name],
234 -- Keep the renamed imports regardless. They are not
235 -- voluminous and are needed if you want to report unused imports
237 tcg_used_rdrnames :: TcRef (Set RdrName),
238 -- The set of used *imported* (not locally-defined) RdrNames
239 -- Used only to report unused import declarations
241 tcg_rn_decls :: Maybe (HsGroup Name),
242 -- ^ Renamed decls, maybe. @Nothing@ <=> Don't retain renamed
245 tcg_binds :: LHsBinds Id, -- Value bindings in this module
246 tcg_warns :: Warnings, -- ...Warnings and deprecations
247 tcg_anns :: [Annotation], -- ...Annotations
248 tcg_insts :: [Instance], -- ...Instances
249 tcg_fam_insts :: [FamInst], -- ...Family instances
250 tcg_rules :: [LRuleDecl Id], -- ...Rules
251 tcg_fords :: [LForeignDecl Id], -- ...Foreign import & exports
253 tcg_doc_hdr :: Maybe LHsDocString, -- ^ Maybe Haddock header docs
254 tcg_hpc :: AnyHpcUsage, -- ^ @True@ if any part of the
255 -- prog uses hpc instrumentation.
257 tcg_main :: Maybe Name -- ^ The Name of the main
258 -- function, if this module is
263 = RecFields (NameEnv [Name]) -- Maps a constructor name *in this module*
264 -- to the fields for that constructor
265 NameSet -- Set of all fields declared *in this module*;
266 -- used to suppress name-shadowing complaints
267 -- when using record wild cards
268 -- E.g. let fld = e in C {..}
269 -- This is used when dealing with ".." notation in record
270 -- construction and pattern matching.
271 -- The FieldEnv deals *only* with constructors defined in *this*
272 -- module. For imported modules, we get the same info from the
276 %************************************************************************
278 The interface environments
279 Used when dealing with IfaceDecls
281 %************************************************************************
286 -- The type environment for the module being compiled,
287 -- in case the interface refers back to it via a reference that
288 -- was originally a hi-boot file.
289 -- We need the module name so we can test when it's appropriate
290 -- to look in this env.
291 if_rec_types :: Maybe (Module, IfG TypeEnv)
292 -- Allows a read effect, so it can be in a mutable
293 -- variable; c.f. handling the external package type env
294 -- Nothing => interactive stuff, no loops possible
299 -- The module for the current IfaceDecl
300 -- So if we see f = \x -> x
301 -- it means M.f = \x -> x, where M is the if_mod
304 -- The field is used only for error reporting
305 -- if (say) there's a Lint error in it
307 -- Where the interface came from:
308 -- .hi file, or GHCi state, or ext core
309 -- plus which bit is currently being examined
311 if_tv_env :: UniqFM TyVar, -- Nested tyvar bindings
312 if_id_env :: UniqFM Id -- Nested id binding
317 %************************************************************************
319 The local typechecker environment
321 %************************************************************************
323 The Global-Env/Local-Env story
324 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
325 During type checking, we keep in the tcg_type_env
326 * All types and classes
327 * All Ids derived from types and classes (constructors, selectors)
329 At the end of type checking, we zonk the local bindings,
330 and as we do so we add to the tcg_type_env
331 * Locally defined top-level Ids
333 Why? Because they are now Ids not TcIds. This final GlobalEnv is
334 a) fed back (via the knot) to typechecking the
335 unfoldings of interface signatures
336 b) used in the ModDetails of this module
339 data TcLclEnv -- Changes as we move inside an expression
340 -- Discarded after typecheck/rename; not passed on to desugarer
342 tcl_loc :: SrcSpan, -- Source span
343 tcl_ctxt :: [ErrCtxt], -- Error context, innermost on top
344 tcl_errs :: TcRef Messages, -- Place to accumulate errors
346 tcl_th_ctxt :: ThStage, -- Template Haskell context
347 tcl_arrow_ctxt :: ArrowCtxt, -- Arrow-notation context
349 tcl_rdr :: LocalRdrEnv, -- Local name envt
350 -- Maintained during renaming, of course, but also during
351 -- type checking, solely so that when renaming a Template-Haskell
352 -- splice we have the right environment for the renamer.
354 -- Does *not* include global name envt; may shadow it
355 -- Includes both ordinary variables and type variables;
356 -- they are kept distinct because tyvar have a different
357 -- occurrence contructor (Name.TvOcc)
358 -- We still need the unsullied global name env so that
359 -- we can look up record field names
361 tcl_env :: NameEnv TcTyThing, -- The local type environment: Ids and
362 -- TyVars defined in this module
364 tcl_tyvars :: TcRef TcTyVarSet, -- The "global tyvars"
365 -- Namely, the in-scope TyVars bound in tcl_env,
366 -- plus the tyvars mentioned in the types of Ids bound
368 -- Why mutable? see notes with tcGetGlobalTyVars
370 tcl_lie :: TcRef LIE, -- Place to accumulate type constraints
372 tcl_tybinds :: TcRef TcTyVarBinds -- Meta and coercion type variable
373 -- bindings accumulated during
374 -- constraint solving
378 {- Note [Given Insts]
380 Because of GADTs, we have to pass inwards the Insts provided by type signatures
381 and existential contexts. Consider
382 data T a where { T1 :: b -> b -> T [b] }
383 f :: Eq a => T a -> Bool
384 f (T1 x y) = [x]==[y]
386 The constructor T1 binds an existential variable 'b', and we need Eq [b].
387 Well, we have it, because Eq a refines to Eq [b], but we can only spot that if we
392 ---------------------------
393 -- Template Haskell stages and levels
394 ---------------------------
396 data ThStage -- See Note [Template Haskell state diagram] in TcSplice
397 = Splice -- Top-level splicing
398 -- This code will be run *at compile time*;
399 -- the result replaces the splice
402 | Comp -- Ordinary Haskell code
405 | Brack -- Inside brackets
406 ThStage -- Binding level = level(stage) + 1
407 (TcRef [PendingSplice]) -- Accumulate pending splices here
408 (TcRef LIE) -- and type constraints here
410 topStage, topAnnStage, topSpliceStage :: ThStage
413 topSpliceStage = Splice
415 instance Outputable ThStage where
416 ppr Splice = text "Splice"
417 ppr Comp = text "Comp"
418 ppr (Brack s _ _) = text "Brack" <> parens (ppr s)
421 -- See Note [Template Haskell levels] in TcSplice
422 -- Incremented when going inside a bracket,
423 -- decremented when going inside a splice
424 -- NB: ThLevel is one greater than the 'n' in Fig 2 of the
425 -- original "Template meta-programming for Haskell" paper
427 impLevel, outerLevel :: ThLevel
428 impLevel = 0 -- Imported things; they can be used inside a top level splice
429 outerLevel = 1 -- Things defined outside brackets
430 -- NB: Things at level 0 are not *necessarily* imported.
431 -- eg $( \b -> ... ) here b is bound at level 0
435 -- g1 = $(map ...) is OK
436 -- g2 = $(f ...) is not OK; because we havn't compiled f yet
438 thLevel :: ThStage -> ThLevel
441 thLevel (Brack s _ _) = thLevel s + 1
443 ---------------------------
444 -- Arrow-notation context
445 ---------------------------
448 In arrow notation, a variable bound by a proc (or enclosed let/kappa)
449 is not in scope to the left of an arrow tail (-<) or the head of (|..|).
454 Here, x is not in scope in e1, but it is in scope in e2. This can get
458 proc y -> (proc z -> e1) -< e2
460 Here, x and z are in scope in e1, but y is not. We implement this by
461 recording the environment when passing a proc (using newArrowScope),
462 and returning to that (using escapeArrowScope) on the left of -< and the
468 | ArrowCtxt (Env TcGblEnv TcLclEnv)
470 -- Record the current environment (outside a proc)
471 newArrowScope :: TcM a -> TcM a
474 env { env_lcl = (env_lcl env) { tcl_arrow_ctxt = ArrowCtxt env } }
476 -- Return to the stored environment (from the enclosing proc)
477 escapeArrowScope :: TcM a -> TcM a
479 = updEnv $ \ env -> case tcl_arrow_ctxt (env_lcl env) of
481 ArrowCtxt env' -> env'
483 ---------------------------
485 ---------------------------
488 = AGlobal TyThing -- Used only in the return type of a lookup
490 | ATcId { -- Ids defined in this module; may not be fully zonked
492 tct_co :: RefinementVisibility, -- Previously: Maybe HsWrapper
493 -- Nothing <=> Do not apply a GADT type refinement
494 -- I am wobbly, or have no free
496 -- Just co <=> Apply any type refinement to me,
497 -- and record it in the coercion
498 tct_type :: TcType, -- Type of (coercion applied to id)
499 tct_level :: ThLevel }
501 | ATyVar Name TcType -- The type to which the lexically scoped type vaiable
502 -- is currently refined. We only need the Name
503 -- for error-message purposes
505 | AThing TcKind -- Used temporarily, during kind checking, for the
506 -- tycons and clases in this recursive group
508 data RefinementVisibility
509 = Unrefineable -- Do not apply a GADT refinement
510 -- I have no free variables
512 | Rigid HsWrapper -- Apply any refinement to me
513 -- and record it in the coercion
515 | Wobbly -- Do not apply a GADT refinement
518 | WobblyInvisible -- Wobbly type, not available inside current
521 instance Outputable TcTyThing where -- Debugging only
522 ppr (AGlobal g) = pprTyThing g
523 ppr elt@(ATcId {}) = text "Identifier" <>
524 ifPprDebug (brackets (ppr (tct_id elt) <> dcolon <> ppr (tct_type elt) <> comma
525 <+> ppr (tct_level elt) <+> ppr (tct_co elt)))
526 ppr (ATyVar tv _) = text "Type variable" <+> quotes (ppr tv)
527 ppr (AThing k) = text "AThing" <+> ppr k
529 pprTcTyThingCategory :: TcTyThing -> SDoc
530 pprTcTyThingCategory (AGlobal thing) = pprTyThingCategory thing
531 pprTcTyThingCategory (ATyVar {}) = ptext (sLit "Type variable")
532 pprTcTyThingCategory (ATcId {}) = ptext (sLit "Local identifier")
533 pprTcTyThingCategory (AThing {}) = ptext (sLit "Kinded thing")
535 instance Outputable RefinementVisibility where
536 ppr Unrefineable = ptext (sLit "unrefineable")
537 ppr (Rigid co) = ptext (sLit "rigid") <+> ppr co
538 ppr Wobbly = ptext (sLit "wobbly")
539 ppr WobblyInvisible = ptext (sLit "wobbly-invisible")
544 type ErrCtxt = (Bool, TidyEnv -> TcM (TidyEnv, Message))
545 -- Monadic so that we have a chance
546 -- to deal with bound type variables just before error
547 -- message construction
549 -- Bool: True <=> this is a landmark context; do not
550 -- discard it when trimming for display
554 %************************************************************************
556 Operations over ImportAvails
558 %************************************************************************
561 -- | 'ImportAvails' summarises what was imported from where, irrespective of
562 -- whether the imported things are actually used or not. It is used:
564 -- * when processing the export list,
566 -- * when constructing usage info for the interface file,
568 -- * to identify the list of directly imported modules for initialisation
569 -- purposes and for optimised overlap checking of family instances,
571 -- * when figuring out what things are really unused
575 imp_mods :: ModuleEnv [(ModuleName, Bool, SrcSpan)],
576 -- ^ Domain is all directly-imported modules
577 -- The 'ModuleName' is what the module was imported as, e.g. in
585 -- - @True@ => import was @import Foo ()@
587 -- - @False@ => import was some other form
591 -- (a) to help construct the usage information in the interface
592 -- file; if we import somethign we need to recompile if the
593 -- export version changes
595 -- (b) to specify what child modules to initialise
597 -- We need a full ModuleEnv rather than a ModuleNameEnv here,
598 -- because we might be importing modules of the same name from
599 -- different packages. (currently not the case, but might be in the
602 imp_dep_mods :: ModuleNameEnv (ModuleName, IsBootInterface),
603 -- ^ Home-package modules needed by the module being compiled
605 -- It doesn't matter whether any of these dependencies
606 -- are actually /used/ when compiling the module; they
607 -- are listed if they are below it at all. For
608 -- example, suppose M imports A which imports X. Then
609 -- compiling M might not need to consult X.hi, but X
610 -- is still listed in M's dependencies.
612 imp_dep_pkgs :: [PackageId],
613 -- ^ Packages needed by the module being compiled, whether directly,
614 -- or via other modules in this package, or via modules imported
615 -- from other packages.
617 imp_orphs :: [Module],
618 -- ^ Orphan modules below us in the import tree (and maybe including
619 -- us for imported modules)
621 imp_finsts :: [Module]
622 -- ^ Family instance modules below us in the import tree (and maybe
623 -- including us for imported modules)
626 mkModDeps :: [(ModuleName, IsBootInterface)]
627 -> ModuleNameEnv (ModuleName, IsBootInterface)
628 mkModDeps deps = foldl add emptyUFM deps
630 add env elt@(m,_) = addToUFM env m elt
632 emptyImportAvails :: ImportAvails
633 emptyImportAvails = ImportAvails { imp_mods = emptyModuleEnv,
634 imp_dep_mods = emptyUFM,
639 plusImportAvails :: ImportAvails -> ImportAvails -> ImportAvails
641 (ImportAvails { imp_mods = mods1,
642 imp_dep_mods = dmods1, imp_dep_pkgs = dpkgs1,
643 imp_orphs = orphs1, imp_finsts = finsts1 })
644 (ImportAvails { imp_mods = mods2,
645 imp_dep_mods = dmods2, imp_dep_pkgs = dpkgs2,
646 imp_orphs = orphs2, imp_finsts = finsts2 })
647 = ImportAvails { imp_mods = plusModuleEnv_C (++) mods1 mods2,
648 imp_dep_mods = plusUFM_C plus_mod_dep dmods1 dmods2,
649 imp_dep_pkgs = dpkgs1 `unionLists` dpkgs2,
650 imp_orphs = orphs1 `unionLists` orphs2,
651 imp_finsts = finsts1 `unionLists` finsts2 }
653 plus_mod_dep (m1, boot1) (m2, boot2)
654 = WARN( not (m1 == m2), (ppr m1 <+> ppr m2) $$ (ppr boot1 <+> ppr boot2) )
655 -- Check mod-names match
656 (m1, boot1 && boot2) -- If either side can "see" a non-hi-boot interface, use that
659 %************************************************************************
661 \subsection{Where from}
663 %************************************************************************
665 The @WhereFrom@ type controls where the renamer looks for an interface file
669 = ImportByUser IsBootInterface -- Ordinary user import (perhaps {-# SOURCE #-})
670 | ImportBySystem -- Non user import.
672 instance Outputable WhereFrom where
673 ppr (ImportByUser is_boot) | is_boot = ptext (sLit "{- SOURCE -}")
675 ppr ImportBySystem = ptext (sLit "{- SYSTEM -}")
679 %************************************************************************
681 \subsection[Inst-types]{@Inst@ types}
683 v%************************************************************************
685 An @Inst@ is either a dictionary, an instance of an overloaded
686 literal, or an instance of an overloaded value. We call the latter a
687 ``method'' even though it may not correspond to a class operation.
688 For example, we might have an instance of the @double@ function at
689 type Int, represented by
691 Method 34 doubleId [Int] origin
693 In addition to the basic Haskell variants of 'Inst's, they can now also
694 represent implication constraints 'forall tvs. given => wanted'
695 and equality constraints 'co :: ty1 ~ ty2'.
697 NB: Equalities occur in two flavours:
699 (1) Dict {tci_pred = EqPred ty1 ty2}
700 (2) EqInst {tci_left = ty1, tci_right = ty2, tci_co = coe}
702 The former arises from equalities in contexts, whereas the latter is used
703 whenever the type checker introduces an equality (e.g., during deferring
706 I am not convinced that this duplication is necessary or useful! -=chak
712 tci_pred :: TcPredType, -- Class or implicit parameter only
716 | ImplicInst { -- An implication constraint
717 -- forall tvs. given => wanted
719 tci_tyvars :: [TcTyVar], -- Quantified type variables
720 tci_given :: [Inst], -- Only Dicts and EqInsts
721 -- (no Methods, LitInsts, ImplicInsts)
722 tci_wanted :: [Inst], -- Only Dicts, EqInst, and ImplicInsts
723 -- (no Methods or LitInsts)
727 -- NB: the tci_given are not necessarily rigid
730 tci_id :: TcId, -- The Id for the Inst
732 tci_oid :: TcId, -- The overloaded function
733 -- This function will be a global, local, or ClassOpId;
734 -- inside instance decls (only) it can also be an InstId!
735 -- The id needn't be completely polymorphic.
736 -- You'll probably find its name (for documentation purposes)
737 -- inside the InstOrigin
739 tci_tys :: [TcType], -- The types to which its polymorphic tyvars
740 -- should be instantiated.
741 -- These types must saturate the Id's foralls.
743 tci_theta :: TcThetaType,
744 -- The (types of the) dictionaries to which the function
745 -- must be applied to get the method
749 -- INVARIANT 1: in (Method m f tys theta tau loc)
750 -- type of m = type of (f tys dicts(from theta))
752 -- INVARIANT 2: type of m must not be of form (Pred -> Tau)
753 -- Reason: two methods are considered equal if the
754 -- base Id matches, and the instantiating types
755 -- match. The TcThetaType should then match too.
756 -- This only bites in the call to tcInstClassOp in TcClassDcl.mkMethodBind
760 tci_lit :: HsOverLit Name, -- The literal from the occurrence site
761 -- INVARIANT: never a rebindable-syntax literal
762 -- Reason: tcSyntaxName does unification, and we
763 -- don't want to deal with that during tcSimplify,
764 -- when resolving LitInsts
766 tci_ty :: TcType, -- The type at which the literal is used
770 | EqInst { -- delayed unification of the form
772 tci_left :: TcType, -- ty1 -- both types are...
773 tci_right :: TcType, -- ty2 -- ...free of boxes
774 tci_co :: EqInstCo, -- co
777 tci_name :: Name -- Debugging help only: this makes it easier to
778 -- follow where a constraint is used in a morass
779 -- of trace messages! Unlike other Insts, it
780 -- has no semantic significance whatsoever.
783 type EqInstCo = Either -- Distinguish between given and wanted coercions
784 TcTyVar -- - a wanted equation, with a hole, to be filled
785 -- with a witness for the equality; for equation
786 -- arising from deferring unification, 'ty1' is
787 -- the actual and 'ty2' the expected type
788 Coercion -- - a given equation, with a coercion witnessing
789 -- the equality; a coercion that originates
790 -- from a signature or a GADT is a CoVar, but
791 -- after normalisation of coercions, they can
792 -- be arbitrary Coercions involving constructors
793 -- and pseudo-constructors like sym and trans.
796 @Insts@ are ordered by their class/type info, rather than by their
797 unique. This allows the context-reduction mechanism to use standard finite
798 maps to do their stuff. It's horrible that this code is here, rather
799 than with the Avails handling stuff in TcSimplify
802 instance Ord Inst where
804 -- Used *only* for AvailEnv in TcSimplify
806 instance Eq Inst where
807 (==) i1 i2 = case i1 `cmpInst` i2 of
811 cmpInst :: Inst -> Inst -> Ordering
812 cmpInst d1@(Dict {}) d2@(Dict {}) = tci_pred d1 `tcCmpPred` tci_pred d2
813 cmpInst (Dict {}) _ = LT
815 cmpInst (Method {}) (Dict {}) = GT
816 cmpInst m1@(Method {}) m2@(Method {}) = (tci_oid m1 `compare` tci_oid m2) `thenCmp`
817 (tci_tys m1 `tcCmpTypes` tci_tys m2)
818 cmpInst (Method {}) _ = LT
820 cmpInst (LitInst {}) (Dict {}) = GT
821 cmpInst (LitInst {}) (Method {}) = GT
822 cmpInst l1@(LitInst {}) l2@(LitInst {}) = (tci_lit l1 `compare` tci_lit l2) `thenCmp`
823 (tci_ty l1 `tcCmpType` tci_ty l2)
824 cmpInst (LitInst {}) _ = LT
826 -- Implication constraints are compared by *name*
827 -- not by type; that is, we make no attempt to do CSE on them
828 cmpInst (ImplicInst {}) (Dict {}) = GT
829 cmpInst (ImplicInst {}) (Method {}) = GT
830 cmpInst (ImplicInst {}) (LitInst {}) = GT
831 cmpInst i1@(ImplicInst {}) i2@(ImplicInst {}) = tci_name i1 `compare` tci_name i2
832 cmpInst (ImplicInst {}) _ = LT
834 -- same for Equality constraints
835 cmpInst (EqInst {}) (Dict {}) = GT
836 cmpInst (EqInst {}) (Method {}) = GT
837 cmpInst (EqInst {}) (LitInst {}) = GT
838 cmpInst (EqInst {}) (ImplicInst {}) = GT
839 cmpInst i1@(EqInst {}) i2@(EqInst {}) = (tci_left i1 `tcCmpType` tci_left i2) `thenCmp`
840 (tci_right i1 `tcCmpType` tci_right i2)
844 %************************************************************************
846 \subsection[Inst-collections]{LIE: a collection of Insts}
848 %************************************************************************
851 -- FIXME: Rename this. It clashes with (Located (IE ...))
854 isEmptyLIE :: LIE -> Bool
855 isEmptyLIE = isEmptyBag
860 unitLIE :: Inst -> LIE
861 unitLIE inst = unitBag inst
863 mkLIE :: [Inst] -> LIE
864 mkLIE insts = listToBag insts
866 plusLIE :: LIE -> LIE -> LIE
867 plusLIE lie1 lie2 = lie1 `unionBags` lie2
869 plusLIEs :: [LIE] -> LIE
870 plusLIEs lies = unionManyBags lies
872 lieToList :: LIE -> [Inst]
873 lieToList = bagToList
875 listToLIE :: [Inst] -> LIE
876 listToLIE = listToBag
878 consLIE :: Inst -> LIE -> LIE
879 consLIE inst lie = lie `snocBag` inst
880 -- Putting the new Inst at the *end* of the bag is a half-hearted attempt
881 -- to ensure that we tend to report the *leftmost* type-constraint error
884 -- we'd like to complain about the '1', not the '3'.
886 -- "Half-hearted" because the rest of the type checker makes no great
887 -- claims for retaining order in the constraint set. Still, this
888 -- seems to improve matters slightly. Exampes: mdofail001, tcfail015
892 %************************************************************************
894 \subsection[Inst-origin]{The @InstOrigin@ type}
896 %************************************************************************
898 The @InstOrigin@ type gives information about where a dictionary came from.
899 This is important for decent error message reporting because dictionaries
900 don't appear in the original source code. Doubtless this type will evolve...
902 It appears in TcMonad because there are a couple of error-message-generation
903 functions that deal with it.
906 -------------------------------------------
907 data InstLoc = InstLoc InstOrigin SrcSpan [ErrCtxt]
909 instLoc :: Inst -> InstLoc
910 instLoc inst = tci_loc inst
912 setInstLoc :: Inst -> InstLoc -> Inst
913 setInstLoc inst new_loc = inst { tci_loc = new_loc }
915 instSpan :: Inst -> SrcSpan
916 instSpan wanted = instLocSpan (instLoc wanted)
918 instLocSpan :: InstLoc -> SrcSpan
919 instLocSpan (InstLoc _ s _) = s
921 instLocOrigin :: InstLoc -> InstOrigin
922 instLocOrigin (InstLoc o _ _) = o
924 pprInstArising :: Inst -> SDoc
925 pprInstArising loc = ptext (sLit "arising from") <+> pprInstLoc (tci_loc loc)
927 pprInstLoc :: InstLoc -> SDoc
928 pprInstLoc (InstLoc orig span _) = sep [ppr orig, text "at" <+> ppr span]
930 -------------------------------------------
932 = SigOrigin SkolemInfo -- Pattern, class decl, inst decl etc;
933 -- Places that bind type variables and introduce
934 -- available constraints
936 | IPBindOrigin (IPName Name) -- Binding site of an implicit parameter
938 -------------------------------------------------------
939 -- The rest are all occurrences: Insts that are 'wanted'
940 -------------------------------------------------------
941 | OccurrenceOf Name -- Occurrence of an overloaded identifier
942 | SpecPragOrigin Name -- Specialisation pragma for identifier
944 | IPOccOrigin (IPName Name) -- Occurrence of an implicit parameter
946 | LiteralOrigin (HsOverLit Name) -- Occurrence of a literal
947 | NegateOrigin -- Occurrence of syntactic negation
949 | ArithSeqOrigin (ArithSeqInfo Name) -- [x..], [x..y] etc
950 | PArrSeqOrigin (ArithSeqInfo Name) -- [:x..y:] and [:x,y..z:]
951 | TupleOrigin -- (..,..)
953 | InstSigOrigin -- A dict occurrence arising from instantiating
954 -- a polymorphic type during a subsumption check
956 | ExprSigOrigin -- e :: ty
960 | InstScOrigin -- Typechecking superclasses of an instance declaration
962 | NoScOrigin -- A very special hack; see TcSimplify,
963 -- Note [Recursive instances and superclases]
966 | DerivOrigin -- Typechecking deriving
967 | StandAloneDerivOrigin -- Typechecking stand-alone deriving
968 | DefaultOrigin -- Typechecking a default decl
969 | DoOrigin -- Arising from a do expression
970 | ProcOrigin -- Arising from a proc expression
971 | ImplicOrigin SDoc -- An implication constraint
972 | EqOrigin -- A type equality
973 | AnnOrigin -- An annotation
975 instance Outputable InstOrigin where
976 ppr (OccurrenceOf name) = hsep [ptext (sLit "a use of"), quotes (ppr name)]
977 ppr (SpecPragOrigin name) = hsep [ptext (sLit "a specialisation pragma for"), quotes (ppr name)]
978 ppr (IPOccOrigin name) = hsep [ptext (sLit "a use of implicit parameter"), quotes (ppr name)]
979 ppr (IPBindOrigin name) = hsep [ptext (sLit "a binding for implicit parameter"), quotes (ppr name)]
980 ppr RecordUpdOrigin = ptext (sLit "a record update")
981 ppr ExprSigOrigin = ptext (sLit "an expression type signature")
982 ppr ViewPatOrigin = ptext (sLit "a view pattern")
983 ppr (LiteralOrigin lit) = hsep [ptext (sLit "the literal"), quotes (ppr lit)]
984 ppr (ArithSeqOrigin seq) = hsep [ptext (sLit "the arithmetic sequence"), quotes (ppr seq)]
985 ppr (PArrSeqOrigin seq) = hsep [ptext (sLit "the parallel array sequence"), quotes (ppr seq)]
986 ppr TupleOrigin = ptext (sLit "a tuple")
987 ppr NegateOrigin = ptext (sLit "a use of syntactic negation")
988 ppr InstScOrigin = ptext (sLit "the superclasses of an instance declaration")
989 ppr NoScOrigin = ptext (sLit "an instance declaration")
990 ppr DerivOrigin = ptext (sLit "the 'deriving' clause of a data type declaration")
991 ppr StandAloneDerivOrigin = ptext (sLit "a 'deriving' declaration")
992 ppr DefaultOrigin = ptext (sLit "a 'default' declaration")
993 ppr DoOrigin = ptext (sLit "a do statement")
994 ppr ProcOrigin = ptext (sLit "a proc expression")
995 ppr (ImplicOrigin doc) = doc
996 ppr (SigOrigin info) = pprSkolInfo info
997 ppr EqOrigin = ptext (sLit "a type equality")
998 ppr InstSigOrigin = panic "ppr InstSigOrigin"
999 ppr AnnOrigin = ptext (sLit "an annotation")