2 % (c) The GRASP Project, Glasgow University, 1992-2002
6 TcRnIf, TcRn, TcM, RnM, IfM, IfL, IfG, -- The monad is opaque outside this module
9 -- The environment types
11 TcGblEnv(..), TcLclEnv(..),
12 IfGblEnv(..), IfLclEnv(..),
16 ImportAvails(..), emptyImportAvails, plusImportAvails,
17 plusAvail, pruneAvails,
18 AvailEnv, emptyAvailEnv, unitAvailEnv, plusAvailEnv,
19 mkAvailEnv, lookupAvailEnv, lookupAvailEnv_maybe, availEnvElts, addAvail,
20 WhereFrom(..), mkModDeps,
23 TcTyThing(..), GadtRefinement,
26 ThStage(..), topStage, topSpliceStage,
27 ThLevel, impLevel, topLevel,
30 ArrowCtxt(..), topArrowCtxt, ProcLevel, topProcLevel,
33 Inst(..), InstOrigin(..), InstLoc(..), pprInstLoc,
34 instLocSrcLoc, instLocSrcSpan,
35 LIE, emptyLIE, unitLIE, plusLIE, consLIE,
36 plusLIEs, mkLIE, isEmptyLIE, lieToList, listToLIE,
39 TcId, TcIdSet, TcDictBinds
42 #include "HsVersions.h"
44 import HsSyn ( PendingSplice, HsOverLit, LRuleDecl, LForeignDecl,
45 ArithSeqInfo, DictBinds, LHsBinds )
46 import HscTypes ( FixityEnv,
47 HscEnv, TypeEnv, TyThing,
48 GenAvailInfo(..), AvailInfo,
49 availName, IsBootInterface, Deprecations )
50 import Packages ( PackageId )
51 import Type ( Type, TvSubstEnv, pprParendType )
52 import TcType ( TcTyVarSet, TcType, TcTauType, TcThetaType, SkolemInfo,
53 TcPredType, TcKind, tcCmpPred, tcCmpType, tcCmpTypes )
54 import InstEnv ( DFunId, InstEnv )
56 import RdrName ( GlobalRdrEnv, LocalRdrEnv )
59 import NameSet ( NameSet, unionNameSets, DefUses )
60 import OccName ( OccEnv )
61 import Var ( Id, TyVar )
62 import VarEnv ( TidyEnv )
64 import SrcLoc ( SrcSpan, SrcLoc, srcSpanStart )
65 import VarSet ( IdSet )
66 import ErrUtils ( Messages, Message )
67 import UniqSupply ( UniqSupply )
68 import BasicTypes ( IPName )
69 import Util ( thenCmp )
72 import Maybe ( mapMaybe )
73 import ListSetOps ( unionLists )
77 %************************************************************************
79 Standard monad definition for TcRn
80 All the combinators for the monad can be found in TcRnMonad
82 %************************************************************************
84 The monad itself has to be defined here, because it is mentioned by ErrCtxt
87 type TcRef a = IORef a
88 type TcId = Id -- Type may be a TcType
90 type TcDictBinds = DictBinds TcId -- Bag of dictionary bindings
94 type TcRnIf a b c = IOEnv (Env a b) c
95 type IfM lcl a = TcRnIf IfGblEnv lcl a -- Iface stuff
96 type IfG a = IfM () a -- Top level
97 type IfL a = IfM IfLclEnv a -- Nested
98 type TcRn a = TcRnIf TcGblEnv TcLclEnv a
99 type RnM a = TcRn a -- Historical
100 type TcM a = TcRn a -- Historical
104 %************************************************************************
106 The main environment types
108 %************************************************************************
111 data Env gbl lcl -- Changes as we move into an expression
113 env_top :: HscEnv, -- Top-level stuff that never changes
114 -- Includes all info about imported things
116 env_us :: TcRef UniqSupply, -- Unique supply for local varibles
118 env_gbl :: gbl, -- Info about things defined at the top level
119 -- of the module being compiled
121 env_lcl :: lcl -- Nested stuff; changes as we go into
125 -- TcGblEnv describes the top-level of the module at the
126 -- point at which the typechecker is finished work.
127 -- It is this structure that is handed on to the desugarer
131 tcg_mod :: Module, -- Module being compiled
132 tcg_rdr_env :: GlobalRdrEnv, -- Top level envt; used during renaming
133 tcg_default :: Maybe [Type], -- Types used for defaulting
134 -- Nothing => no 'default' decl
136 tcg_fix_env :: FixityEnv, -- Just for things in this module
138 tcg_type_env :: TypeEnv, -- Global type env for the module we are compiling now
139 -- All TyCons and Classes (for this module) end up in here right away,
140 -- along with their derived constructors, selectors.
142 -- (Ids defined in this module start in the local envt,
143 -- though they move to the global envt during zonking)
145 tcg_type_env_var :: TcRef TypeEnv,
146 -- Used only to initialise the interface-file
147 -- typechecker in initIfaceTcRn, so that it can see stuff
148 -- bound in this module when dealing with hi-boot recursions
149 -- Updated at intervals (e.g. after dealing with types and classes)
151 tcg_inst_env :: InstEnv, -- Instance envt for *home-package* modules
152 -- Includes the dfuns in tcg_insts
153 -- Now a bunch of things about this module that are simply
154 -- accumulated, but never consulted until the end.
155 -- Nevertheless, it's convenient to accumulate them along
156 -- with the rest of the info from this module.
157 tcg_exports :: NameSet, -- What is exported
158 tcg_imports :: ImportAvails, -- Information about what was imported
159 -- from where, including things bound
162 tcg_dus :: DefUses, -- What is defined in this module and what is used.
163 -- The latter is used to generate
164 -- (a) version tracking; no need to recompile if these
165 -- things have not changed version stamp
166 -- (b) unused-import info
168 tcg_keep :: TcRef NameSet, -- Locally-defined top-level names to keep alive
169 -- "Keep alive" means give them an Exported flag, so
170 -- that the simplifier does not discard them as dead
171 -- code, and so that they are exposed in the interface file
172 -- (but not to export to the user).
174 -- Some things, like dict-fun Ids and default-method Ids are
175 -- "born" with the Exported flag on, for exactly the above reason,
176 -- but some we only discover as we go. Specifically:
177 -- * The to/from functions for generic data types
178 -- * Top-level variables appearing free in the RHS of an orphan rule
179 -- * Top-level variables appearing free in a TH bracket
181 tcg_inst_uses :: TcRef NameSet, -- Home-package Dfuns actually used
182 -- Used to generate version dependencies
183 -- This records usages, rather like tcg_dus, but it has to
184 -- be a mutable variable so it can be augmented
185 -- when we look up an instance. These uses of dfuns are
186 -- rather like the free variables of the program, but
187 -- are implicit instead of explicit.
189 tcg_th_used :: TcRef Bool, -- True <=> Template Haskell syntax used
190 -- We need this so that we can generate a dependency on the
191 -- Template Haskell package, becuase the desugarer is going to
192 -- emit loads of references to TH symbols. It's rather like
193 -- tcg_inst_uses; the reference is implicit rather than explicit,
194 -- so we have to zap a mutable variable.
196 -- The next fields accumulate the payload of the module
197 -- The binds, rules and foreign-decl fiels are collected
198 -- initially in un-zonked form and are finally zonked in tcRnSrcDecls
199 tcg_binds :: LHsBinds Id, -- Value bindings in this module
200 tcg_deprecs :: Deprecations, -- ...Deprecations
201 tcg_insts :: [DFunId], -- ...Instances
202 tcg_rules :: [LRuleDecl Id], -- ...Rules
203 tcg_fords :: [LForeignDecl Id] -- ...Foreign import & exports
207 %************************************************************************
209 The interface environments
210 Used when dealing with IfaceDecls
212 %************************************************************************
217 -- The type environment for the module being compiled,
218 -- in case the interface refers back to it via a reference that
219 -- was originally a hi-boot file.
220 -- We need the module name so we can test when it's appropriate
221 -- to look in this env.
222 if_rec_types :: Maybe (Module, IfG TypeEnv)
223 -- Allows a read effect, so it can be in a mutable
224 -- variable; c.f. handling the external package type env
225 -- Nothing => interactive stuff, no loops possible
230 -- The module for the current IfaceDecl
231 -- So if we see f = \x -> x
232 -- it means M.f = \x -> x, where M is the if_mod
235 if_tv_env :: OccEnv TyVar, -- Nested tyvar bindings
236 if_id_env :: OccEnv Id -- Nested id binding
241 %************************************************************************
243 The local typechecker environment
245 %************************************************************************
247 The Global-Env/Local-Env story
248 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
249 During type checking, we keep in the tcg_type_env
250 * All types and classes
251 * All Ids derived from types and classes (constructors, selectors)
253 At the end of type checking, we zonk the local bindings,
254 and as we do so we add to the tcg_type_env
255 * Locally defined top-level Ids
257 Why? Because they are now Ids not TcIds. This final GlobalEnv is
258 a) fed back (via the knot) to typechecking the
259 unfoldings of interface signatures
260 b) used in the ModDetails of this module
263 data TcLclEnv -- Changes as we move inside an expression
264 -- Discarded after typecheck/rename; not passed on to desugarer
266 tcl_loc :: SrcSpan, -- Source span
267 tcl_ctxt :: ErrCtxt, -- Error context
268 tcl_errs :: TcRef Messages, -- Place to accumulate errors
270 tcl_th_ctxt :: ThStage, -- Template Haskell context
271 tcl_arrow_ctxt :: ArrowCtxt, -- Arrow-notation context
273 tcl_rdr :: LocalRdrEnv, -- Local name envt
274 -- Maintained during renaming, of course, but also during
275 -- type checking, solely so that when renaming a Template-Haskell
276 -- splice we have the right environment for the renamer.
278 -- Does *not* include global name envt; may shadow it
279 -- Includes both ordinary variables and type variables;
280 -- they are kept distinct because tyvar have a different
281 -- occurrence contructor (Name.TvOcc)
282 -- We still need the unsullied global name env so that
283 -- we can look up record field names
285 tcl_env :: NameEnv TcTyThing, -- The local type environment: Ids and TyVars
286 -- defined in this module
288 tcl_tyvars :: TcRef TcTyVarSet, -- The "global tyvars"
289 -- Namely, the in-scope TyVars bound in tcl_env,
290 -- plus the tyvars mentioned in the types of Ids bound in tcl_lenv
291 -- Why mutable? see notes with tcGetGlobalTyVars
293 tcl_lie :: TcRef LIE, -- Place to accumulate type constraints
294 tcl_gadt :: GadtRefinement -- The current type refinement for GADTs
296 -----------------------------------------------------------
297 -- Not yet; it's a new complication and I want to see whether it bites
298 -- tcl_given :: [Inst] -- Insts available in the current context (see Note [Given Insts])
299 -----------------------------------------------------------
302 type GadtRefinement = TvSubstEnv -- Binds rigid type variables to their refinements
304 {- Note [Given Insts]
306 Because of GADTs, we have to pass inwards the Insts provided by type signatures
307 and existential contexts. Consider
308 data T a where { T1 :: b -> b -> T [b] }
309 f :: Eq a => T a -> Bool
310 f (T1 x y) = [x]==[y]
312 The constructor T1 binds an existential variable 'b', and we need Eq [b].
313 Well, we have it, because Eq a refines to Eq [b], but we can only spot that if we
318 ---------------------------
319 -- Template Haskell levels
320 ---------------------------
323 -- Indicates how many levels of brackets we are inside
325 -- Incremented when going inside a bracket,
326 -- decremented when going inside a splice
328 impLevel, topLevel :: ThLevel
329 topLevel = 1 -- Things defined at top level of this module
330 impLevel = 0 -- Imported things; they can be used inside a top level splice
334 -- g1 = $(map ...) is OK
335 -- g2 = $(f ...) is not OK; because we havn't compiled f yet
339 = Comp -- Ordinary compiling, at level topLevel
340 | Splice ThLevel -- Inside a splice
341 | Brack ThLevel -- Inside brackets;
342 (TcRef [PendingSplice]) -- accumulate pending splices here
343 (TcRef LIE) -- and type constraints here
344 topStage, topSpliceStage :: ThStage
346 topSpliceStage = Splice (topLevel - 1) -- Stage for the body of a top-level splice
349 ---------------------------
350 -- Arrow-notation stages
351 ---------------------------
353 -- In arrow notation, a variable bound by a proc (or enclosed let/kappa)
354 -- is not in scope to the left of an arrow tail (-<). For example
356 -- proc x -> (e1 -< e2)
358 -- Here, x is not in scope in e1, but it is in scope in e2. This can get
359 -- a bit complicated:
362 -- prox y -> (proc z -> e1) -< e2
364 -- Here, x and z are in scope in e1, but y is not. Here's how we track this:
365 -- a) Assign an "proc level" to each proc, being the number of
366 -- lexically-enclosing procs + 1.
367 -- b) Assign to each local variable the proc-level of its lexically
369 -- c) Keep a list of out-of-scope procs. When moving to the left of
370 -- an arrow-tail, add the proc-level of the immediately enclosing
372 -- d) When looking up a variable, complain if its proc-level is in
375 type ProcLevel = Int -- Always >= 0
376 topProcLevel = 0 -- Not inside any proc
378 data ArrowCtxt = ArrCtxt { proc_level :: ProcLevel, -- Current level
379 proc_banned :: [ProcLevel] } -- Out of scope proc-levels
381 topArrowCtxt = ArrCtxt { proc_level = topProcLevel, proc_banned = [] }
383 ---------------------------
385 ---------------------------
388 = AGlobal TyThing -- Used only in the return type of a lookup
390 | ATcId TcId ThLevel ProcLevel -- Ids defined in this module; may not be fully zonked
392 | ATyVar TyVar TcType -- Type variables; tv -> type. It can't just be a TyVar
393 -- that is mutated to point to the type it is bound to,
394 -- because that would make it a wobbly type, and we
395 -- want pattern-bound lexically-scoped type variables to
396 -- be able to stand for rigid types
398 | AThing TcKind -- Used temporarily, during kind checking, for the
399 -- tycons and clases in this recursive group
401 instance Outputable TcTyThing where -- Debugging only
402 ppr (AGlobal g) = text "AGlobal" <+> ppr g
403 ppr (ATcId g tl pl) = text "ATcId" <+> ppr g <+> ppr tl <+> ppr pl
404 ppr (ATyVar tv ty) = text "ATyVar" <+> ppr tv <+> pprParendType ty
405 ppr (AThing k) = text "AThing" <+> ppr k
409 type ErrCtxt = [TidyEnv -> TcM (TidyEnv, Message)]
410 -- Innermost first. Monadic so that we have a chance
411 -- to deal with bound type variables just before error
412 -- message construction
416 %************************************************************************
418 Operations over ImportAvails
420 %************************************************************************
422 ImportAvails summarises what was imported from where, irrespective
423 of whether the imported things are actually used or not
424 It is used * when processing the export list
425 * when constructing usage info for the inteface file
426 * to identify the list of directly imported modules
427 for initialisation purposes
428 * when figuring out what things are really unused
433 imp_env :: ModuleEnv NameSet,
434 -- All the things imported, classified by
435 -- the *module qualifier* for its import
436 -- e.g. import List as Foo
437 -- would add a binding Foo |-> ...stuff from List...
440 -- We need to classify them like this so that we can figure out
441 -- "module M" export specifiers in an export list
442 -- (see 1.4 Report Section 5.1.1). Ultimately, we want to find
443 -- everything that is unambiguously in scope as 'M.x'
444 -- and where plain 'x' is (perhaps ambiguously) in scope.
445 -- So the starting point is all things that are in scope as 'M.x',
446 -- which is what this field tells us.
448 imp_mods :: ModuleEnv (Module, Maybe Bool, SrcSpan),
449 -- Domain is all directly-imported modules
450 -- Maybe value answers the question "is the import restricted?"
451 -- Nothing => unrestricted import (e.g., "import Foo")
452 -- Just True => restricted import, at least one entity (e.g., "import Foo(x)")
453 -- Just False => fully restricted import (e.g., "import Foo ()")
455 -- A distinction is made between the first and the third in order
456 -- to more precisely emit warnings about unused imports.
458 -- We need the Module in the range because we can't get
459 -- the keys of a ModuleEnv
461 -- (a) to help construct the usage information in
462 -- the interface file; if we import everything we
463 -- need to recompile if the module version changes
464 -- (b) to specify what child modules to initialise
466 imp_dep_mods :: ModuleEnv (Module, IsBootInterface),
467 -- Home-package modules needed by the module being compiled
469 -- It doesn't matter whether any of these dependencies
470 -- are actually *used* when compiling the module; they
471 -- are listed if they are below it at all. For
472 -- example, suppose M imports A which imports X. Then
473 -- compiling M might not need to consult X.hi, but X
474 -- is still listed in M's dependencies.
476 imp_dep_pkgs :: [PackageId],
477 -- Packages needed by the module being compiled, whether
478 -- directly, or via other modules in this package, or via
479 -- modules imported from other packages.
481 imp_orphs :: [Module]
482 -- Orphan modules below us in the import tree
485 mkModDeps :: [(Module, IsBootInterface)]
486 -> ModuleEnv (Module, IsBootInterface)
487 mkModDeps deps = foldl add emptyModuleEnv deps
489 add env elt@(m,_) = extendModuleEnv env m elt
491 emptyImportAvails :: ImportAvails
492 emptyImportAvails = ImportAvails { imp_env = emptyModuleEnv,
493 imp_mods = emptyModuleEnv,
494 imp_dep_mods = emptyModuleEnv,
498 plusImportAvails :: ImportAvails -> ImportAvails -> ImportAvails
500 (ImportAvails { imp_env = env1, imp_mods = mods1,
501 imp_dep_mods = dmods1, imp_dep_pkgs = dpkgs1, imp_orphs = orphs1 })
502 (ImportAvails { imp_env = env2, imp_mods = mods2,
503 imp_dep_mods = dmods2, imp_dep_pkgs = dpkgs2, imp_orphs = orphs2 })
504 = ImportAvails { imp_env = plusModuleEnv_C unionNameSets env1 env2,
505 imp_mods = mods1 `plusModuleEnv` mods2,
506 imp_dep_mods = plusModuleEnv_C plus_mod_dep dmods1 dmods2,
507 imp_dep_pkgs = dpkgs1 `unionLists` dpkgs2,
508 imp_orphs = orphs1 `unionLists` orphs2 }
510 plus_mod_dep (m1, boot1) (m2, boot2)
511 = WARN( not (m1 == m2), (ppr m1 <+> ppr m2) $$ (ppr boot1 <+> ppr boot2) )
512 -- Check mod-names match
513 (m1, boot1 && boot2) -- If either side can "see" a non-hi-boot interface, use that
516 %************************************************************************
518 Avails, AvailEnv, etc
520 v%************************************************************************
523 plusAvail (Avail n1) (Avail n2) = Avail n1
524 plusAvail (AvailTC n1 ns1) (AvailTC n2 ns2) = AvailTC n2 (ns1 `unionLists` ns2)
527 plusAvail a1 a2 = pprPanic "RnEnv.plusAvail" (hsep [ppr a1,ppr a2])
530 -------------------------
531 pruneAvails :: (Name -> Bool) -- Keep if this is True
534 pruneAvails keep avails
535 = mapMaybe del avails
537 del :: AvailInfo -> Maybe AvailInfo -- Nothing => nothing left!
538 del (Avail n) | keep n = Just (Avail n)
539 | otherwise = Nothing
540 del (AvailTC n ns) | null ns' = Nothing
541 | otherwise = Just (AvailTC n ns')
546 ---------------------------------------
548 ---------------------------------------
551 type AvailEnv = NameEnv AvailInfo -- Maps a Name to the AvailInfo that contains it
553 emptyAvailEnv :: AvailEnv
554 emptyAvailEnv = emptyNameEnv
556 unitAvailEnv :: AvailInfo -> AvailEnv
557 unitAvailEnv a = unitNameEnv (availName a) a
559 plusAvailEnv :: AvailEnv -> AvailEnv -> AvailEnv
560 plusAvailEnv = plusNameEnv_C plusAvail
562 lookupAvailEnv_maybe :: AvailEnv -> Name -> Maybe AvailInfo
563 lookupAvailEnv_maybe = lookupNameEnv
565 lookupAvailEnv :: AvailEnv -> Name -> AvailInfo
566 lookupAvailEnv env n = case lookupNameEnv env n of
568 Nothing -> pprPanic "lookupAvailEnv" (ppr n)
570 availEnvElts = nameEnvElts
572 addAvail :: AvailEnv -> AvailInfo -> AvailEnv
573 addAvail avails avail = extendNameEnv_C plusAvail avails (availName avail) avail
575 mkAvailEnv :: [AvailInfo] -> AvailEnv
576 -- 'avails' may have several items with the same availName
577 -- E.g import Ix( Ix(..), index )
578 -- will give Ix(Ix,index,range) and Ix(index)
579 -- We want to combine these; addAvail does that
580 mkAvailEnv avails = foldl addAvail emptyAvailEnv avails
583 %************************************************************************
585 \subsection{Where from}
587 %************************************************************************
589 The @WhereFrom@ type controls where the renamer looks for an interface file
593 = ImportByUser IsBootInterface -- Ordinary user import (perhaps {-# SOURCE #-})
594 | ImportBySystem -- Non user import.
596 instance Outputable WhereFrom where
597 ppr (ImportByUser is_boot) | is_boot = ptext SLIT("{- SOURCE -}")
599 ppr ImportBySystem = ptext SLIT("{- SYSTEM -}")
603 %************************************************************************
605 \subsection[Inst-types]{@Inst@ types}
607 v%************************************************************************
609 An @Inst@ is either a dictionary, an instance of an overloaded
610 literal, or an instance of an overloaded value. We call the latter a
611 ``method'' even though it may not correspond to a class operation.
612 For example, we might have an instance of the @double@ function at
613 type Int, represented by
615 Method 34 doubleId [Int] origin
627 TcId -- The overloaded function
628 -- This function will be a global, local, or ClassOpId;
629 -- inside instance decls (only) it can also be an InstId!
630 -- The id needn't be completely polymorphic.
631 -- You'll probably find its name (for documentation purposes)
632 -- inside the InstOrigin
634 [TcType] -- The types to which its polymorphic tyvars
635 -- should be instantiated.
636 -- These types must saturate the Id's foralls.
638 TcThetaType -- The (types of the) dictionaries to which the function
639 -- must be applied to get the method
641 TcTauType -- The tau-type of the method
645 -- INVARIANT 1: in (Method u f tys theta tau loc)
646 -- type of (f tys dicts(from theta)) = tau
648 -- INVARIANT 2: tau must not be of form (Pred -> Tau)
649 -- Reason: two methods are considered equal if the
650 -- base Id matches, and the instantiating types
651 -- match. The TcThetaType should then match too.
652 -- This only bites in the call to tcInstClassOp in TcClassDcl.mkMethodBind
656 HsOverLit -- The literal from the occurrence site
657 -- INVARIANT: never a rebindable-syntax literal
658 -- Reason: tcSyntaxName does unification, and we
659 -- don't want to deal with that during tcSimplify
660 TcType -- The type at which the literal is used
664 @Insts@ are ordered by their class/type info, rather than by their
665 unique. This allows the context-reduction mechanism to use standard finite
666 maps to do their stuff.
669 instance Ord Inst where
672 instance Eq Inst where
673 (==) i1 i2 = case i1 `cmpInst` i2 of
677 cmpInst (Dict _ pred1 _) (Dict _ pred2 _) = pred1 `tcCmpPred` pred2
678 cmpInst (Dict _ _ _) other = LT
680 cmpInst (Method _ _ _ _ _ _) (Dict _ _ _) = GT
681 cmpInst (Method _ id1 tys1 _ _ _) (Method _ id2 tys2 _ _ _) = (id1 `compare` id2) `thenCmp` (tys1 `tcCmpTypes` tys2)
682 cmpInst (Method _ _ _ _ _ _) other = LT
684 cmpInst (LitInst _ _ _ _) (Dict _ _ _) = GT
685 cmpInst (LitInst _ _ _ _) (Method _ _ _ _ _ _) = GT
686 cmpInst (LitInst _ lit1 ty1 _) (LitInst _ lit2 ty2 _) = (lit1 `compare` lit2) `thenCmp` (ty1 `tcCmpType` ty2)
690 %************************************************************************
692 \subsection[Inst-collections]{LIE: a collection of Insts}
694 %************************************************************************
699 isEmptyLIE = isEmptyBag
701 unitLIE inst = unitBag inst
702 mkLIE insts = listToBag insts
703 plusLIE lie1 lie2 = lie1 `unionBags` lie2
704 consLIE inst lie = inst `consBag` lie
705 plusLIEs lies = unionManyBags lies
706 lieToList = bagToList
707 listToLIE = listToBag
711 %************************************************************************
713 \subsection[Inst-origin]{The @InstOrigin@ type}
715 %************************************************************************
717 The @InstOrigin@ type gives information about where a dictionary came from.
718 This is important for decent error message reporting because dictionaries
719 don't appear in the original source code. Doubtless this type will evolve...
721 It appears in TcMonad because there are a couple of error-message-generation
722 functions that deal with it.
725 data InstLoc = InstLoc InstOrigin SrcSpan ErrCtxt
727 instLocSrcLoc :: InstLoc -> SrcLoc
728 instLocSrcLoc (InstLoc _ src_span _) = srcSpanStart src_span
730 instLocSrcSpan :: InstLoc -> SrcSpan
731 instLocSrcSpan (InstLoc _ src_span _) = src_span
734 = SigOrigin SkolemInfo -- Pattern, class decl, inst decl etc;
735 -- Places that bind type variables and introduce
736 -- available constraints
738 | IPBindOrigin (IPName Name) -- Binding site of an implicit parameter
740 -------------------------------------------------------
741 -- The rest are all occurrences: Insts that are 'wanted'
742 -------------------------------------------------------
743 | OccurrenceOf Name -- Occurrence of an overloaded identifier
745 | IPOccOrigin (IPName Name) -- Occurrence of an implicit parameter
747 | LiteralOrigin HsOverLit -- Occurrence of a literal
749 | ArithSeqOrigin (ArithSeqInfo Name) -- [x..], [x..y] etc
750 | PArrSeqOrigin (ArithSeqInfo Name) -- [:x..y:] and [:x,y..z:]
752 | InstSigOrigin -- A dict occurrence arising from instantiating
753 -- a polymorphic type during a subsumption check
756 | InstScOrigin -- Typechecking superclasses of an instance declaration
757 | DerivOrigin -- Typechecking deriving
758 | DefaultOrigin -- Typechecking a default decl
759 | DoOrigin -- Arising from a do expression
760 | ProcOrigin -- Arising from a proc expression
764 pprInstLoc :: InstLoc -> SDoc
765 pprInstLoc (InstLoc (SigOrigin info) locn _)
766 = text "arising from" <+> ppr info -- I don't think this happens much, if at all
767 pprInstLoc (InstLoc orig locn _)
768 = hsep [text "arising from", pp_orig orig, text "at", ppr locn]
770 pp_orig (OccurrenceOf name) = hsep [ptext SLIT("use of"), quotes (ppr name)]
771 pp_orig (IPOccOrigin name) = hsep [ptext SLIT("use of implicit parameter"), quotes (ppr name)]
772 pp_orig (IPBindOrigin name) = hsep [ptext SLIT("binding for implicit parameter"), quotes (ppr name)]
773 pp_orig RecordUpdOrigin = ptext SLIT("a record update")
774 pp_orig (LiteralOrigin lit) = hsep [ptext SLIT("the literal"), quotes (ppr lit)]
775 pp_orig (ArithSeqOrigin seq) = hsep [ptext SLIT("the arithmetic sequence"), quotes (ppr seq)]
776 pp_orig (PArrSeqOrigin seq) = hsep [ptext SLIT("the parallel array sequence"), quotes (ppr seq)]
777 pp_orig InstSigOrigin = ptext SLIT("instantiating a type signature")
778 pp_orig InstScOrigin = ptext SLIT("the superclasses of an instance declaration")
779 pp_orig DerivOrigin = ptext SLIT("the 'deriving' clause of a data type declaration")
780 pp_orig DefaultOrigin = ptext SLIT("a 'default' declaration")
781 pp_orig DoOrigin = ptext SLIT("a do statement")
782 pp_orig ProcOrigin = ptext SLIT("a proc expression")
783 pp_orig (SigOrigin info) = ppr info