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
236 tcg_used_rdrnames :: TcRef (Set RdrName),
237 tcg_rn_decls :: Maybe (HsGroup Name),
238 -- ^ Renamed decls, maybe. @Nothing@ <=> Don't retain renamed
241 tcg_binds :: LHsBinds Id, -- Value bindings in this module
242 tcg_warns :: Warnings, -- ...Warnings and deprecations
243 tcg_anns :: [Annotation], -- ...Annotations
244 tcg_insts :: [Instance], -- ...Instances
245 tcg_fam_insts :: [FamInst], -- ...Family instances
246 tcg_rules :: [LRuleDecl Id], -- ...Rules
247 tcg_fords :: [LForeignDecl Id], -- ...Foreign import & exports
249 tcg_doc_hdr :: Maybe LHsDocString, -- ^ Maybe Haddock header docs
250 tcg_hpc :: AnyHpcUsage, -- ^ @True@ if any part of the
251 -- prog uses hpc instrumentation.
253 tcg_main :: Maybe Name -- ^ The Name of the main
254 -- function, if this module is
259 = RecFields (NameEnv [Name]) -- Maps a constructor name *in this module*
260 -- to the fields for that constructor
261 NameSet -- Set of all fields declared *in this module*;
262 -- used to suppress name-shadowing complaints
263 -- when using record wild cards
264 -- E.g. let fld = e in C {..}
265 -- This is used when dealing with ".." notation in record
266 -- construction and pattern matching.
267 -- The FieldEnv deals *only* with constructors defined in *this*
268 -- module. For imported modules, we get the same info from the
272 %************************************************************************
274 The interface environments
275 Used when dealing with IfaceDecls
277 %************************************************************************
282 -- The type environment for the module being compiled,
283 -- in case the interface refers back to it via a reference that
284 -- was originally a hi-boot file.
285 -- We need the module name so we can test when it's appropriate
286 -- to look in this env.
287 if_rec_types :: Maybe (Module, IfG TypeEnv)
288 -- Allows a read effect, so it can be in a mutable
289 -- variable; c.f. handling the external package type env
290 -- Nothing => interactive stuff, no loops possible
295 -- The module for the current IfaceDecl
296 -- So if we see f = \x -> x
297 -- it means M.f = \x -> x, where M is the if_mod
300 -- The field is used only for error reporting
301 -- if (say) there's a Lint error in it
303 -- Where the interface came from:
304 -- .hi file, or GHCi state, or ext core
305 -- plus which bit is currently being examined
307 if_tv_env :: UniqFM TyVar, -- Nested tyvar bindings
308 if_id_env :: UniqFM Id -- Nested id binding
313 %************************************************************************
315 The local typechecker environment
317 %************************************************************************
319 The Global-Env/Local-Env story
320 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
321 During type checking, we keep in the tcg_type_env
322 * All types and classes
323 * All Ids derived from types and classes (constructors, selectors)
325 At the end of type checking, we zonk the local bindings,
326 and as we do so we add to the tcg_type_env
327 * Locally defined top-level Ids
329 Why? Because they are now Ids not TcIds. This final GlobalEnv is
330 a) fed back (via the knot) to typechecking the
331 unfoldings of interface signatures
332 b) used in the ModDetails of this module
335 data TcLclEnv -- Changes as we move inside an expression
336 -- Discarded after typecheck/rename; not passed on to desugarer
338 tcl_loc :: SrcSpan, -- Source span
339 tcl_ctxt :: [ErrCtxt], -- Error context, innermost on top
340 tcl_errs :: TcRef Messages, -- Place to accumulate errors
342 tcl_th_ctxt :: ThStage, -- Template Haskell context
343 tcl_arrow_ctxt :: ArrowCtxt, -- Arrow-notation context
345 tcl_rdr :: LocalRdrEnv, -- Local name envt
346 -- Maintained during renaming, of course, but also during
347 -- type checking, solely so that when renaming a Template-Haskell
348 -- splice we have the right environment for the renamer.
350 -- Does *not* include global name envt; may shadow it
351 -- Includes both ordinary variables and type variables;
352 -- they are kept distinct because tyvar have a different
353 -- occurrence contructor (Name.TvOcc)
354 -- We still need the unsullied global name env so that
355 -- we can look up record field names
357 tcl_env :: NameEnv TcTyThing, -- The local type environment: Ids and
358 -- TyVars defined in this module
360 tcl_tyvars :: TcRef TcTyVarSet, -- The "global tyvars"
361 -- Namely, the in-scope TyVars bound in tcl_env,
362 -- plus the tyvars mentioned in the types of Ids bound
364 -- Why mutable? see notes with tcGetGlobalTyVars
366 tcl_lie :: TcRef LIE, -- Place to accumulate type constraints
368 tcl_tybinds :: TcRef TcTyVarBinds -- Meta and coercion type variable
369 -- bindings accumulated during
370 -- constraint solving
374 {- Note [Given Insts]
376 Because of GADTs, we have to pass inwards the Insts provided by type signatures
377 and existential contexts. Consider
378 data T a where { T1 :: b -> b -> T [b] }
379 f :: Eq a => T a -> Bool
380 f (T1 x y) = [x]==[y]
382 The constructor T1 binds an existential variable 'b', and we need Eq [b].
383 Well, we have it, because Eq a refines to Eq [b], but we can only spot that if we
388 ---------------------------
389 -- Template Haskell stages and levels
390 ---------------------------
392 data ThStage -- See Note [Template Haskell state diagram] in TcSplice
393 = Splice -- Top-level splicing
394 -- This code will be run *at compile time*;
395 -- the result replaces the splice
398 | Comp -- Ordinary Haskell code
401 | Brack -- Inside brackets
402 ThStage -- Binding level = level(stage) + 1
403 (TcRef [PendingSplice]) -- Accumulate pending splices here
404 (TcRef LIE) -- and type constraints here
406 topStage, topAnnStage, topSpliceStage :: ThStage
409 topSpliceStage = Splice
411 instance Outputable ThStage where
412 ppr Splice = text "Splice"
413 ppr Comp = text "Comp"
414 ppr (Brack s _ _) = text "Brack" <> parens (ppr s)
417 -- See Note [Template Haskell levels] in TcSplice
418 -- Incremented when going inside a bracket,
419 -- decremented when going inside a splice
420 -- NB: ThLevel is one greater than the 'n' in Fig 2 of the
421 -- original "Template meta-programming for Haskell" paper
423 impLevel, outerLevel :: ThLevel
424 impLevel = 0 -- Imported things; they can be used inside a top level splice
425 outerLevel = 1 -- Things defined outside brackets
426 -- NB: Things at level 0 are not *necessarily* imported.
427 -- eg $( \b -> ... ) here b is bound at level 0
431 -- g1 = $(map ...) is OK
432 -- g2 = $(f ...) is not OK; because we havn't compiled f yet
434 thLevel :: ThStage -> ThLevel
437 thLevel (Brack s _ _) = thLevel s + 1
439 ---------------------------
440 -- Arrow-notation context
441 ---------------------------
444 In arrow notation, a variable bound by a proc (or enclosed let/kappa)
445 is not in scope to the left of an arrow tail (-<) or the head of (|..|).
450 Here, x is not in scope in e1, but it is in scope in e2. This can get
454 proc y -> (proc z -> e1) -< e2
456 Here, x and z are in scope in e1, but y is not. We implement this by
457 recording the environment when passing a proc (using newArrowScope),
458 and returning to that (using escapeArrowScope) on the left of -< and the
464 | ArrowCtxt (Env TcGblEnv TcLclEnv)
466 -- Record the current environment (outside a proc)
467 newArrowScope :: TcM a -> TcM a
470 env { env_lcl = (env_lcl env) { tcl_arrow_ctxt = ArrowCtxt env } }
472 -- Return to the stored environment (from the enclosing proc)
473 escapeArrowScope :: TcM a -> TcM a
475 = updEnv $ \ env -> case tcl_arrow_ctxt (env_lcl env) of
477 ArrowCtxt env' -> env'
479 ---------------------------
481 ---------------------------
484 = AGlobal TyThing -- Used only in the return type of a lookup
486 | ATcId { -- Ids defined in this module; may not be fully zonked
488 tct_co :: RefinementVisibility, -- Previously: Maybe HsWrapper
489 -- Nothing <=> Do not apply a GADT type refinement
490 -- I am wobbly, or have no free
492 -- Just co <=> Apply any type refinement to me,
493 -- and record it in the coercion
494 tct_type :: TcType, -- Type of (coercion applied to id)
495 tct_level :: ThLevel }
497 | ATyVar Name TcType -- The type to which the lexically scoped type vaiable
498 -- is currently refined. We only need the Name
499 -- for error-message purposes
501 | AThing TcKind -- Used temporarily, during kind checking, for the
502 -- tycons and clases in this recursive group
504 data RefinementVisibility
505 = Unrefineable -- Do not apply a GADT refinement
506 -- I have no free variables
508 | Rigid HsWrapper -- Apply any refinement to me
509 -- and record it in the coercion
511 | Wobbly -- Do not apply a GADT refinement
514 | WobblyInvisible -- Wobbly type, not available inside current
517 instance Outputable TcTyThing where -- Debugging only
518 ppr (AGlobal g) = pprTyThing g
519 ppr elt@(ATcId {}) = text "Identifier" <>
520 ifPprDebug (brackets (ppr (tct_id elt) <> dcolon <> ppr (tct_type elt) <> comma
521 <+> ppr (tct_level elt) <+> ppr (tct_co elt)))
522 ppr (ATyVar tv _) = text "Type variable" <+> quotes (ppr tv)
523 ppr (AThing k) = text "AThing" <+> ppr k
525 pprTcTyThingCategory :: TcTyThing -> SDoc
526 pprTcTyThingCategory (AGlobal thing) = pprTyThingCategory thing
527 pprTcTyThingCategory (ATyVar {}) = ptext (sLit "Type variable")
528 pprTcTyThingCategory (ATcId {}) = ptext (sLit "Local identifier")
529 pprTcTyThingCategory (AThing {}) = ptext (sLit "Kinded thing")
531 instance Outputable RefinementVisibility where
532 ppr Unrefineable = ptext (sLit "unrefineable")
533 ppr (Rigid co) = ptext (sLit "rigid") <+> ppr co
534 ppr Wobbly = ptext (sLit "wobbly")
535 ppr WobblyInvisible = ptext (sLit "wobbly-invisible")
540 type ErrCtxt = (Bool, TidyEnv -> TcM (TidyEnv, Message))
541 -- Monadic so that we have a chance
542 -- to deal with bound type variables just before error
543 -- message construction
545 -- Bool: True <=> this is a landmark context; do not
546 -- discard it when trimming for display
550 %************************************************************************
552 Operations over ImportAvails
554 %************************************************************************
557 -- | 'ImportAvails' summarises what was imported from where, irrespective of
558 -- whether the imported things are actually used or not. It is used:
560 -- * when processing the export list,
562 -- * when constructing usage info for the interface file,
564 -- * to identify the list of directly imported modules for initialisation
565 -- purposes and for optimised overlap checking of family instances,
567 -- * when figuring out what things are really unused
571 imp_mods :: ModuleEnv [(ModuleName, Bool, SrcSpan)],
572 -- ^ Domain is all directly-imported modules
573 -- The 'ModuleName' is what the module was imported as, e.g. in
581 -- - @True@ => import was @import Foo ()@
583 -- - @False@ => import was some other form
587 -- (a) to help construct the usage information in the interface
588 -- file; if we import somethign we need to recompile if the
589 -- export version changes
591 -- (b) to specify what child modules to initialise
593 -- We need a full ModuleEnv rather than a ModuleNameEnv here,
594 -- because we might be importing modules of the same name from
595 -- different packages. (currently not the case, but might be in the
598 imp_dep_mods :: ModuleNameEnv (ModuleName, IsBootInterface),
599 -- ^ Home-package modules needed by the module being compiled
601 -- It doesn't matter whether any of these dependencies
602 -- are actually /used/ when compiling the module; they
603 -- are listed if they are below it at all. For
604 -- example, suppose M imports A which imports X. Then
605 -- compiling M might not need to consult X.hi, but X
606 -- is still listed in M's dependencies.
608 imp_dep_pkgs :: [PackageId],
609 -- ^ Packages needed by the module being compiled, whether directly,
610 -- or via other modules in this package, or via modules imported
611 -- from other packages.
613 imp_orphs :: [Module],
614 -- ^ Orphan modules below us in the import tree (and maybe including
615 -- us for imported modules)
617 imp_finsts :: [Module]
618 -- ^ Family instance modules below us in the import tree (and maybe
619 -- including us for imported modules)
622 mkModDeps :: [(ModuleName, IsBootInterface)]
623 -> ModuleNameEnv (ModuleName, IsBootInterface)
624 mkModDeps deps = foldl add emptyUFM deps
626 add env elt@(m,_) = addToUFM env m elt
628 emptyImportAvails :: ImportAvails
629 emptyImportAvails = ImportAvails { imp_mods = emptyModuleEnv,
630 imp_dep_mods = emptyUFM,
635 plusImportAvails :: ImportAvails -> ImportAvails -> ImportAvails
637 (ImportAvails { imp_mods = mods1,
638 imp_dep_mods = dmods1, imp_dep_pkgs = dpkgs1,
639 imp_orphs = orphs1, imp_finsts = finsts1 })
640 (ImportAvails { imp_mods = mods2,
641 imp_dep_mods = dmods2, imp_dep_pkgs = dpkgs2,
642 imp_orphs = orphs2, imp_finsts = finsts2 })
643 = ImportAvails { imp_mods = plusModuleEnv_C (++) mods1 mods2,
644 imp_dep_mods = plusUFM_C plus_mod_dep dmods1 dmods2,
645 imp_dep_pkgs = dpkgs1 `unionLists` dpkgs2,
646 imp_orphs = orphs1 `unionLists` orphs2,
647 imp_finsts = finsts1 `unionLists` finsts2 }
649 plus_mod_dep (m1, boot1) (m2, boot2)
650 = WARN( not (m1 == m2), (ppr m1 <+> ppr m2) $$ (ppr boot1 <+> ppr boot2) )
651 -- Check mod-names match
652 (m1, boot1 && boot2) -- If either side can "see" a non-hi-boot interface, use that
655 %************************************************************************
657 \subsection{Where from}
659 %************************************************************************
661 The @WhereFrom@ type controls where the renamer looks for an interface file
665 = ImportByUser IsBootInterface -- Ordinary user import (perhaps {-# SOURCE #-})
666 | ImportBySystem -- Non user import.
668 instance Outputable WhereFrom where
669 ppr (ImportByUser is_boot) | is_boot = ptext (sLit "{- SOURCE -}")
671 ppr ImportBySystem = ptext (sLit "{- SYSTEM -}")
675 %************************************************************************
677 \subsection[Inst-types]{@Inst@ types}
679 v%************************************************************************
681 An @Inst@ is either a dictionary, an instance of an overloaded
682 literal, or an instance of an overloaded value. We call the latter a
683 ``method'' even though it may not correspond to a class operation.
684 For example, we might have an instance of the @double@ function at
685 type Int, represented by
687 Method 34 doubleId [Int] origin
689 In addition to the basic Haskell variants of 'Inst's, they can now also
690 represent implication constraints 'forall tvs. given => wanted'
691 and equality constraints 'co :: ty1 ~ ty2'.
693 NB: Equalities occur in two flavours:
695 (1) Dict {tci_pred = EqPred ty1 ty2}
696 (2) EqInst {tci_left = ty1, tci_right = ty2, tci_co = coe}
698 The former arises from equalities in contexts, whereas the latter is used
699 whenever the type checker introduces an equality (e.g., during deferring
702 I am not convinced that this duplication is necessary or useful! -=chak
708 tci_pred :: TcPredType, -- Class or implicit parameter only
712 | ImplicInst { -- An implication constraint
713 -- forall tvs. given => wanted
715 tci_tyvars :: [TcTyVar], -- Quantified type variables
716 tci_given :: [Inst], -- Only Dicts and EqInsts
717 -- (no Methods, LitInsts, ImplicInsts)
718 tci_wanted :: [Inst], -- Only Dicts, EqInst, and ImplicInsts
719 -- (no Methods or LitInsts)
723 -- NB: the tci_given are not necessarily rigid
726 tci_id :: TcId, -- The Id for the Inst
728 tci_oid :: TcId, -- The overloaded function
729 -- This function will be a global, local, or ClassOpId;
730 -- inside instance decls (only) it can also be an InstId!
731 -- The id needn't be completely polymorphic.
732 -- You'll probably find its name (for documentation purposes)
733 -- inside the InstOrigin
735 tci_tys :: [TcType], -- The types to which its polymorphic tyvars
736 -- should be instantiated.
737 -- These types must saturate the Id's foralls.
739 tci_theta :: TcThetaType,
740 -- The (types of the) dictionaries to which the function
741 -- must be applied to get the method
745 -- INVARIANT 1: in (Method m f tys theta tau loc)
746 -- type of m = type of (f tys dicts(from theta))
748 -- INVARIANT 2: type of m must not be of form (Pred -> Tau)
749 -- Reason: two methods are considered equal if the
750 -- base Id matches, and the instantiating types
751 -- match. The TcThetaType should then match too.
752 -- This only bites in the call to tcInstClassOp in TcClassDcl.mkMethodBind
756 tci_lit :: HsOverLit Name, -- The literal from the occurrence site
757 -- INVARIANT: never a rebindable-syntax literal
758 -- Reason: tcSyntaxName does unification, and we
759 -- don't want to deal with that during tcSimplify,
760 -- when resolving LitInsts
762 tci_ty :: TcType, -- The type at which the literal is used
766 | EqInst { -- delayed unification of the form
768 tci_left :: TcType, -- ty1 -- both types are...
769 tci_right :: TcType, -- ty2 -- ...free of boxes
770 tci_co :: EqInstCo, -- co
773 tci_name :: Name -- Debugging help only: this makes it easier to
774 -- follow where a constraint is used in a morass
775 -- of trace messages! Unlike other Insts, it
776 -- has no semantic significance whatsoever.
779 type EqInstCo = Either -- Distinguish between given and wanted coercions
780 TcTyVar -- - a wanted equation, with a hole, to be filled
781 -- with a witness for the equality; for equation
782 -- arising from deferring unification, 'ty1' is
783 -- the actual and 'ty2' the expected type
784 Coercion -- - a given equation, with a coercion witnessing
785 -- the equality; a coercion that originates
786 -- from a signature or a GADT is a CoVar, but
787 -- after normalisation of coercions, they can
788 -- be arbitrary Coercions involving constructors
789 -- and pseudo-constructors like sym and trans.
792 @Insts@ are ordered by their class/type info, rather than by their
793 unique. This allows the context-reduction mechanism to use standard finite
794 maps to do their stuff. It's horrible that this code is here, rather
795 than with the Avails handling stuff in TcSimplify
798 instance Ord Inst where
800 -- Used *only* for AvailEnv in TcSimplify
802 instance Eq Inst where
803 (==) i1 i2 = case i1 `cmpInst` i2 of
807 cmpInst :: Inst -> Inst -> Ordering
808 cmpInst d1@(Dict {}) d2@(Dict {}) = tci_pred d1 `tcCmpPred` tci_pred d2
809 cmpInst (Dict {}) _ = LT
811 cmpInst (Method {}) (Dict {}) = GT
812 cmpInst m1@(Method {}) m2@(Method {}) = (tci_oid m1 `compare` tci_oid m2) `thenCmp`
813 (tci_tys m1 `tcCmpTypes` tci_tys m2)
814 cmpInst (Method {}) _ = LT
816 cmpInst (LitInst {}) (Dict {}) = GT
817 cmpInst (LitInst {}) (Method {}) = GT
818 cmpInst l1@(LitInst {}) l2@(LitInst {}) = (tci_lit l1 `compare` tci_lit l2) `thenCmp`
819 (tci_ty l1 `tcCmpType` tci_ty l2)
820 cmpInst (LitInst {}) _ = LT
822 -- Implication constraints are compared by *name*
823 -- not by type; that is, we make no attempt to do CSE on them
824 cmpInst (ImplicInst {}) (Dict {}) = GT
825 cmpInst (ImplicInst {}) (Method {}) = GT
826 cmpInst (ImplicInst {}) (LitInst {}) = GT
827 cmpInst i1@(ImplicInst {}) i2@(ImplicInst {}) = tci_name i1 `compare` tci_name i2
828 cmpInst (ImplicInst {}) _ = LT
830 -- same for Equality constraints
831 cmpInst (EqInst {}) (Dict {}) = GT
832 cmpInst (EqInst {}) (Method {}) = GT
833 cmpInst (EqInst {}) (LitInst {}) = GT
834 cmpInst (EqInst {}) (ImplicInst {}) = GT
835 cmpInst i1@(EqInst {}) i2@(EqInst {}) = (tci_left i1 `tcCmpType` tci_left i2) `thenCmp`
836 (tci_right i1 `tcCmpType` tci_right i2)
840 %************************************************************************
842 \subsection[Inst-collections]{LIE: a collection of Insts}
844 %************************************************************************
847 -- FIXME: Rename this. It clashes with (Located (IE ...))
850 isEmptyLIE :: LIE -> Bool
851 isEmptyLIE = isEmptyBag
856 unitLIE :: Inst -> LIE
857 unitLIE inst = unitBag inst
859 mkLIE :: [Inst] -> LIE
860 mkLIE insts = listToBag insts
862 plusLIE :: LIE -> LIE -> LIE
863 plusLIE lie1 lie2 = lie1 `unionBags` lie2
865 plusLIEs :: [LIE] -> LIE
866 plusLIEs lies = unionManyBags lies
868 lieToList :: LIE -> [Inst]
869 lieToList = bagToList
871 listToLIE :: [Inst] -> LIE
872 listToLIE = listToBag
874 consLIE :: Inst -> LIE -> LIE
875 consLIE inst lie = lie `snocBag` inst
876 -- Putting the new Inst at the *end* of the bag is a half-hearted attempt
877 -- to ensure that we tend to report the *leftmost* type-constraint error
880 -- we'd like to complain about the '1', not the '3'.
882 -- "Half-hearted" because the rest of the type checker makes no great
883 -- claims for retaining order in the constraint set. Still, this
884 -- seems to improve matters slightly. Exampes: mdofail001, tcfail015
888 %************************************************************************
890 \subsection[Inst-origin]{The @InstOrigin@ type}
892 %************************************************************************
894 The @InstOrigin@ type gives information about where a dictionary came from.
895 This is important for decent error message reporting because dictionaries
896 don't appear in the original source code. Doubtless this type will evolve...
898 It appears in TcMonad because there are a couple of error-message-generation
899 functions that deal with it.
902 -------------------------------------------
903 data InstLoc = InstLoc InstOrigin SrcSpan [ErrCtxt]
905 instLoc :: Inst -> InstLoc
906 instLoc inst = tci_loc inst
908 setInstLoc :: Inst -> InstLoc -> Inst
909 setInstLoc inst new_loc = inst { tci_loc = new_loc }
911 instSpan :: Inst -> SrcSpan
912 instSpan wanted = instLocSpan (instLoc wanted)
914 instLocSpan :: InstLoc -> SrcSpan
915 instLocSpan (InstLoc _ s _) = s
917 instLocOrigin :: InstLoc -> InstOrigin
918 instLocOrigin (InstLoc o _ _) = o
920 pprInstArising :: Inst -> SDoc
921 pprInstArising loc = ptext (sLit "arising from") <+> pprInstLoc (tci_loc loc)
923 pprInstLoc :: InstLoc -> SDoc
924 pprInstLoc (InstLoc orig span _) = sep [ppr orig, text "at" <+> ppr span]
926 -------------------------------------------
928 = SigOrigin SkolemInfo -- Pattern, class decl, inst decl etc;
929 -- Places that bind type variables and introduce
930 -- available constraints
932 | IPBindOrigin (IPName Name) -- Binding site of an implicit parameter
934 -------------------------------------------------------
935 -- The rest are all occurrences: Insts that are 'wanted'
936 -------------------------------------------------------
937 | OccurrenceOf Name -- Occurrence of an overloaded identifier
938 | SpecPragOrigin Name -- Specialisation pragma for identifier
940 | IPOccOrigin (IPName Name) -- Occurrence of an implicit parameter
942 | LiteralOrigin (HsOverLit Name) -- Occurrence of a literal
943 | NegateOrigin -- Occurrence of syntactic negation
945 | ArithSeqOrigin (ArithSeqInfo Name) -- [x..], [x..y] etc
946 | PArrSeqOrigin (ArithSeqInfo Name) -- [:x..y:] and [:x,y..z:]
947 | TupleOrigin -- (..,..)
949 | InstSigOrigin -- A dict occurrence arising from instantiating
950 -- a polymorphic type during a subsumption check
952 | ExprSigOrigin -- e :: ty
956 | InstScOrigin -- Typechecking superclasses of an instance declaration
958 | NoScOrigin -- A very special hack; see TcSimplify,
959 -- Note [Recursive instances and superclases]
962 | DerivOrigin -- Typechecking deriving
963 | StandAloneDerivOrigin -- Typechecking stand-alone deriving
964 | DefaultOrigin -- Typechecking a default decl
965 | DoOrigin -- Arising from a do expression
966 | ProcOrigin -- Arising from a proc expression
967 | ImplicOrigin SDoc -- An implication constraint
968 | EqOrigin -- A type equality
969 | AnnOrigin -- An annotation
971 instance Outputable InstOrigin where
972 ppr (OccurrenceOf name) = hsep [ptext (sLit "a use of"), quotes (ppr name)]
973 ppr (SpecPragOrigin name) = hsep [ptext (sLit "a specialisation pragma for"), quotes (ppr name)]
974 ppr (IPOccOrigin name) = hsep [ptext (sLit "a use of implicit parameter"), quotes (ppr name)]
975 ppr (IPBindOrigin name) = hsep [ptext (sLit "a binding for implicit parameter"), quotes (ppr name)]
976 ppr RecordUpdOrigin = ptext (sLit "a record update")
977 ppr ExprSigOrigin = ptext (sLit "an expression type signature")
978 ppr ViewPatOrigin = ptext (sLit "a view pattern")
979 ppr (LiteralOrigin lit) = hsep [ptext (sLit "the literal"), quotes (ppr lit)]
980 ppr (ArithSeqOrigin seq) = hsep [ptext (sLit "the arithmetic sequence"), quotes (ppr seq)]
981 ppr (PArrSeqOrigin seq) = hsep [ptext (sLit "the parallel array sequence"), quotes (ppr seq)]
982 ppr TupleOrigin = ptext (sLit "a tuple")
983 ppr NegateOrigin = ptext (sLit "a use of syntactic negation")
984 ppr InstScOrigin = ptext (sLit "the superclasses of an instance declaration")
985 ppr NoScOrigin = ptext (sLit "an instance declaration")
986 ppr DerivOrigin = ptext (sLit "the 'deriving' clause of a data type declaration")
987 ppr StandAloneDerivOrigin = ptext (sLit "a 'deriving' declaration")
988 ppr DefaultOrigin = ptext (sLit "a 'default' declaration")
989 ppr DoOrigin = ptext (sLit "a do statement")
990 ppr ProcOrigin = ptext (sLit "a proc expression")
991 ppr (ImplicOrigin doc) = doc
992 ppr (SigOrigin info) = pprSkolInfo info
993 ppr EqOrigin = ptext (sLit "a type equality")
994 ppr InstSigOrigin = panic "ppr InstSigOrigin"
995 ppr AnnOrigin = ptext (sLit "an annotation")