2 % (c) The University of Glasgow, 2000
4 \section[HscTypes]{Types for the per-module compiler}
12 ModDetails(..), ModIface(..),
13 HomeSymbolTable, emptySymbolTable,
15 HomeIfaceTable, PackageIfaceTable, emptyIfaceTable,
16 lookupIface, lookupIfaceByModName,
19 InteractiveContext(..),
21 IfaceDecls, mkIfaceDecls, dcl_tycl, dcl_rules, dcl_insts,
23 VersionInfo(..), initialVersionInfo, lookupVersion,
25 TyThing(..), isTyClThing, implicitTyThingIds,
27 TypeEnv, lookupType, mkTypeEnv, emptyTypeEnv,
28 extendTypeEnvList, extendTypeEnvWithIds,
29 typeEnvElts, typeEnvClasses, typeEnvTyCons, typeEnvIds,
31 ImportedModuleInfo, WhetherHasOrphans, ImportVersion, WhatsImported(..),
32 PersistentRenamerState(..), IsBootInterface, DeclsMap,
33 IfaceInsts, IfaceRules, GatedDecl, GatedDecls, GateFn, IsExported,
34 NameSupply(..), OrigNameCache, OrigIParamCache,
35 Avails, AvailEnv, emptyAvailEnv,
36 GenAvailInfo(..), AvailInfo, RdrAvailInfo,
37 PersistentCompilerState(..),
39 Deprecations(..), lookupDeprec,
41 InstEnv, ClsInstEnv, DFunId,
42 PackageInstEnv, PackageRuleBase,
44 GlobalRdrEnv, GlobalRdrElt(..), pprGlobalRdrEnv,
45 LocalRdrEnv, extendLocalRdrEnv,
49 Provenance(..), ImportReason(..),
50 pprNameProvenance, hasBetterProv
54 #include "HsVersions.h"
56 import RdrName ( RdrName, RdrNameEnv, addListToRdrEnv, emptyRdrEnv,
57 mkRdrUnqual, rdrEnvToList )
58 import Name ( Name, NamedThing, getName, nameOccName, nameModule, nameSrcLoc )
60 import OccName ( OccName )
61 import Module ( Module, ModuleName, ModuleEnv,
62 lookupModuleEnv, lookupModuleEnvByName, emptyModuleEnv
64 import InstEnv ( InstEnv, ClsInstEnv, DFunId )
65 import Rules ( RuleBase )
66 import CoreSyn ( CoreBind )
68 import Class ( Class, classSelIds )
69 import TyCon ( TyCon, isNewTyCon, tyConGenIds, tyConSelIds, tyConDataConsIfAvailable )
70 import DataCon ( dataConId, dataConWrapId )
72 import BasicTypes ( Version, initialVersion, Fixity, IPName )
74 import HsSyn ( DeprecTxt, tyClDeclName, ifaceRuleDeclName )
75 import RdrHsSyn ( RdrNameInstDecl, RdrNameRuleDecl, RdrNameTyClDecl )
76 import RnHsSyn ( RenamedTyClDecl, RenamedRuleDecl, RenamedInstDecl )
78 import CoreSyn ( IdCoreRule )
80 import FiniteMap ( FiniteMap )
82 import Maybes ( seqMaybe, orElse )
84 import SrcLoc ( SrcLoc, isGoodSrcLoc )
85 import Util ( thenCmp, sortLt )
86 import UniqSupply ( UniqSupply )
89 %************************************************************************
91 \subsection{Which mode we're in
93 %************************************************************************
96 data GhciMode = Batch | Interactive | OneShot
101 %************************************************************************
103 \subsection{Module locations}
105 %************************************************************************
110 ml_hs_file :: Maybe FilePath,
111 ml_hspp_file :: Maybe FilePath, -- path of preprocessed source
112 ml_hi_file :: FilePath,
113 ml_obj_file :: Maybe FilePath
117 instance Outputable ModuleLocation where
121 For a module in another package, the hs_file and obj_file
122 components of ModuleLocation are undefined.
124 The locations specified by a ModuleLocation may or may not
125 correspond to actual files yet: for example, even if the object
126 file doesn't exist, the ModuleLocation still contains the path to
127 where the object file will reside if/when it is created.
130 %************************************************************************
132 \subsection{Symbol tables and Module details}
134 %************************************************************************
136 A @ModIface@ plus a @ModDetails@ summarises everything we know
137 about a compiled module. The @ModIface@ is the stuff *before* linking,
138 and can be written out to an interface file. (The @ModDetails@ is after
139 linking; it is the "linked" form of the mi_decls field.)
141 When we *read* an interface file, we also construct a @ModIface@ from it,
142 except that the mi_decls part is empty; when reading we consolidate
143 the declarations into a single indexed map in the @PersistentRenamerState@.
148 mi_module :: !Module, -- Complete with package info
149 mi_version :: !VersionInfo, -- Module version number
150 mi_orphan :: WhetherHasOrphans, -- Whether this module has orphans
151 mi_boot :: !IsBootInterface, -- read from an hi-boot file?
153 mi_usages :: ![ImportVersion Name],
154 -- Usages; kept sorted so that it's easy to decide
155 -- whether to write a new iface file (changing usages
156 -- doesn't affect the version of this module)
158 mi_exports :: ![(ModuleName,Avails)],
159 -- What it exports Kept sorted by (mod,occ), to make
160 -- version comparisons easier
162 mi_globals :: !GlobalRdrEnv, -- Its top level environment
164 mi_fixities :: !(NameEnv Fixity), -- Fixities
165 mi_deprecs :: !Deprecations, -- Deprecations
167 mi_decls :: IfaceDecls -- The RnDecls form of ModDetails
170 data IfaceDecls = IfaceDecls { dcl_tycl :: [RenamedTyClDecl], -- Sorted
171 dcl_rules :: [RenamedRuleDecl], -- Sorted
172 dcl_insts :: [RenamedInstDecl] } -- Unsorted
174 mkIfaceDecls :: [RenamedTyClDecl] -> [RenamedRuleDecl] -> [RenamedInstDecl] -> IfaceDecls
175 mkIfaceDecls tycls rules insts
176 = IfaceDecls { dcl_tycl = sortLt lt_tycl tycls,
177 dcl_rules = sortLt lt_rule rules,
180 d1 `lt_tycl` d2 = tyClDeclName d1 < tyClDeclName d2
181 r1 `lt_rule` r2 = ifaceRuleDeclName r1 < ifaceRuleDeclName r2
184 -- typechecker should only look at this, not ModIface
185 -- Should be able to construct ModDetails from mi_decls in ModIface
188 -- The next three fields are created by the typechecker
189 md_types :: !TypeEnv,
190 md_insts :: ![DFunId], -- Dfun-ids for the instances in this module
191 md_rules :: ![IdCoreRule], -- Domain may include Ids from other modules
192 md_binds :: ![CoreBind]
195 -- The ModDetails takes on several slightly different forms:
197 -- After typecheck + desugar
198 -- md_types Contains TyCons, Classes, and implicit Ids
199 -- md_insts All instances from this module (incl derived ones)
200 -- md_rules All rules from this module
201 -- md_binds Desugared bindings
203 -- After simplification
204 -- md_types Same as after typecheck
206 -- md_rules Orphan rules only (local ones now attached to binds)
207 -- md_binds With rules attached
210 -- md_types Now contains Ids as well, replete with final IdInfo
211 -- The Ids are only the ones that are visible from
212 -- importing modules. Without -O that means only
213 -- exported Ids, but with -O importing modules may
214 -- see ids mentioned in unfoldings of exported Ids
216 -- md_insts Same DFunIds as before, but with final IdInfo,
217 -- and the unique might have changed; remember that
218 -- CoreTidy links up the uniques of old and new versions
220 -- md_rules All rules for exported things, substituted with final Ids
224 -- Passed back to compilation manager
225 -- Just as after CoreTidy, but with md_binds nuked
230 emptyModIface :: Module -> ModIface
232 = ModIface { mi_module = mod,
233 mi_version = initialVersionInfo,
238 mi_fixities = emptyNameEnv,
239 mi_globals = emptyRdrEnv,
240 mi_deprecs = NoDeprecs,
241 mi_decls = panic "emptyModIface: decls"
245 Symbol tables map modules to ModDetails:
248 type SymbolTable = ModuleEnv ModDetails
249 type IfaceTable = ModuleEnv ModIface
251 type HomeIfaceTable = IfaceTable
252 type PackageIfaceTable = IfaceTable
254 type HomeSymbolTable = SymbolTable -- Domain = modules in the home package
256 emptySymbolTable :: SymbolTable
257 emptySymbolTable = emptyModuleEnv
259 emptyIfaceTable :: IfaceTable
260 emptyIfaceTable = emptyModuleEnv
263 Simple lookups in the symbol table.
266 lookupIface :: HomeIfaceTable -> PackageIfaceTable -> Name -> Maybe ModIface
267 -- We often have two IfaceTables, and want to do a lookup
268 lookupIface hit pit name
269 = lookupModuleEnv hit mod `seqMaybe` lookupModuleEnv pit mod
271 mod = nameModule name
273 lookupIfaceByModName :: HomeIfaceTable -> PackageIfaceTable -> ModuleName -> Maybe ModIface
274 -- We often have two IfaceTables, and want to do a lookup
275 lookupIfaceByModName hit pit mod
276 = lookupModuleEnvByName hit mod `seqMaybe` lookupModuleEnvByName pit mod
280 %************************************************************************
282 \subsection{The interactive context}
284 %************************************************************************
287 data InteractiveContext
288 = InteractiveContext {
289 ic_module :: Module, -- The current module in which
290 -- the user is sitting
292 ic_rn_env :: LocalRdrEnv, -- Lexical context for variables bound
293 -- during interaction
295 ic_type_env :: TypeEnv -- Ditto for types
300 %************************************************************************
302 \subsection{Type environment stuff}
304 %************************************************************************
307 data TyThing = AnId Id
311 isTyClThing :: TyThing -> Bool
312 isTyClThing (ATyCon _) = True
313 isTyClThing (AClass _) = True
314 isTyClThing (AnId _) = False
316 instance NamedThing TyThing where
317 getName (AnId id) = getName id
318 getName (ATyCon tc) = getName tc
319 getName (AClass cl) = getName cl
321 instance Outputable TyThing where
322 ppr (AnId id) = ptext SLIT("AnId") <+> ppr id
323 ppr (ATyCon tc) = ptext SLIT("ATyCon") <+> ppr tc
324 ppr (AClass cl) = ptext SLIT("AClass") <+> ppr cl
327 typeEnvElts :: TypeEnv -> [TyThing]
328 typeEnvClasses :: TypeEnv -> [Class]
329 typeEnvTyCons :: TypeEnv -> [TyCon]
330 typeEnvIds :: TypeEnv -> [Id]
332 typeEnvElts env = nameEnvElts env
333 typeEnvClasses env = [cl | AClass cl <- typeEnvElts env]
334 typeEnvTyCons env = [tc | ATyCon tc <- typeEnvElts env]
335 typeEnvIds env = [id | AnId id <- typeEnvElts env]
337 implicitTyThingIds :: [TyThing] -> [Id]
338 -- Add the implicit data cons and selectors etc
339 implicitTyThingIds things
340 = concat (map go things)
343 go (AClass cl) = classSelIds cl
344 go (ATyCon tc) = tyConGenIds tc ++
346 [ n | dc <- tyConDataConsIfAvailable tc,
347 n <- implicitConIds tc dc]
348 -- Synonyms return empty list of constructors and selectors
350 implicitConIds tc dc -- Newtypes have a constructor wrapper,
352 | isNewTyCon tc = [dataConWrapId dc]
353 | otherwise = [dataConId dc, dataConWrapId dc]
358 type TypeEnv = NameEnv TyThing
360 emptyTypeEnv = emptyNameEnv
362 mkTypeEnv :: [TyThing] -> TypeEnv
363 mkTypeEnv things = extendTypeEnvList emptyTypeEnv things
365 extendTypeEnvList :: TypeEnv -> [TyThing] -> TypeEnv
366 extendTypeEnvList env things
367 = extendNameEnvList env [(getName thing, thing) | thing <- things]
369 extendTypeEnvWithIds :: TypeEnv -> [Id] -> TypeEnv
370 extendTypeEnvWithIds env ids
371 = extendNameEnvList env [(getName id, AnId id) | id <- ids]
375 lookupType :: HomeSymbolTable -> PackageTypeEnv -> Name -> Maybe TyThing
376 lookupType hst pte name
377 = case lookupModuleEnv hst (nameModule name) of
378 Just details -> lookupNameEnv (md_types details) name
379 Nothing -> lookupNameEnv pte name
382 %************************************************************************
384 \subsection{Auxiliary types}
386 %************************************************************************
388 These types are defined here because they are mentioned in ModDetails,
389 but they are mostly elaborated elsewhere
394 vers_module :: Version, -- Changes when anything changes
395 vers_exports :: Version, -- Changes when export list changes
396 vers_rules :: Version, -- Changes when any rule changes
397 vers_decls :: NameEnv Version
398 -- Versions for "big" names only (not data constructors, class ops)
399 -- The version of an Id changes if its fixity changes
400 -- Ditto data constructors, class operations, except that the version of
401 -- the parent class/tycon changes
403 -- If a name isn't in the map, it means 'initialVersion'
406 initialVersionInfo :: VersionInfo
407 initialVersionInfo = VersionInfo { vers_module = initialVersion,
408 vers_exports = initialVersion,
409 vers_rules = initialVersion,
410 vers_decls = emptyNameEnv
413 lookupVersion :: NameEnv Version -> Name -> Version
414 lookupVersion env name = lookupNameEnv env name `orElse` initialVersion
416 data Deprecations = NoDeprecs
417 | DeprecAll DeprecTxt -- Whole module deprecated
418 | DeprecSome (NameEnv (Name,DeprecTxt)) -- Some things deprecated
420 -- We keep the Name in the range, so we can print them out
422 lookupDeprec :: Deprecations -> Name -> Maybe DeprecTxt
423 lookupDeprec NoDeprecs name = Nothing
424 lookupDeprec (DeprecAll txt) name = Just txt
425 lookupDeprec (DeprecSome env) name = case lookupNameEnv env name of
426 Just (_, txt) -> Just txt
429 instance Eq Deprecations where
430 -- Used when checking whether we need write a new interface
431 NoDeprecs == NoDeprecs = True
432 (DeprecAll t1) == (DeprecAll t2) = t1 == t2
433 (DeprecSome e1) == (DeprecSome e2) = nameEnvElts e1 == nameEnvElts e2
439 type Avails = [AvailInfo]
440 type AvailInfo = GenAvailInfo Name
441 type RdrAvailInfo = GenAvailInfo OccName
443 data GenAvailInfo name = Avail name -- An ordinary identifier
444 | AvailTC name -- The name of the type or class
445 [name] -- The available pieces of type/class.
446 -- NB: If the type or class is itself
447 -- to be in scope, it must be in this list.
448 -- Thus, typically: AvailTC Eq [Eq, ==, /=]
450 -- Equality used when deciding if the interface has changed
452 type AvailEnv = NameEnv AvailInfo -- Maps a Name to the AvailInfo that contains it
454 emptyAvailEnv :: AvailEnv
455 emptyAvailEnv = emptyNameEnv
457 instance Outputable n => Outputable (GenAvailInfo n) where
460 pprAvail :: Outputable n => GenAvailInfo n -> SDoc
461 pprAvail (AvailTC n ns) = ppr n <> case {- filter (/= n) -} ns of
463 ns' -> braces (hsep (punctuate comma (map ppr ns')))
465 pprAvail (Avail n) = ppr n
469 %************************************************************************
471 \subsection{ModIface}
473 %************************************************************************
476 type WhetherHasOrphans = Bool
478 -- * an instance decl in a module other than the defn module for
479 -- one of the tycons or classes in the instance head
480 -- * a transformation rule in a module other than the one defining
481 -- the function in the head of the rule.
483 type IsBootInterface = Bool
485 type ImportVersion name = (ModuleName, WhetherHasOrphans, IsBootInterface, WhatsImported name)
487 data WhatsImported name = NothingAtAll -- The module is below us in the
488 -- hierarchy, but we import nothing
490 | Everything Version -- Used for modules from other packages;
491 -- we record only the module's version number
494 Version -- Module version
495 (Maybe Version) -- Export-list version, if we depend on it
496 [(name,Version)] -- List guaranteed non-empty
497 Version -- Rules version
500 -- 'Specifically' doesn't let you say "I imported f but none of the rules in
501 -- the module". If you use anything in the module you get its rule version
502 -- So if the rules change, you'll recompile, even if you don't use them.
503 -- This is easy to implement, and it's safer: you might not have used the rules last
504 -- time round, but if someone has added a new rule you might need it this time
506 -- The export list field is (Just v) if we depend on the export list:
507 -- we imported the module without saying exactly what we imported
508 -- We need to recompile if the module exports changes, because we might
509 -- now have a name clash in the importing module.
511 type IsExported = Name -> Bool -- True for names that are exported from this module
515 %************************************************************************
517 \subsection{The persistent compiler state}
519 %************************************************************************
521 The @PersistentCompilerState@ persists across successive calls to the
524 * A ModIface for each non-home-package module
526 * An accumulated TypeEnv from all the modules in imported packages
528 * An accumulated InstEnv from all the modules in imported packages
529 The point is that we don't want to keep recreating it whenever
530 we compile a new module. The InstEnv component of pcPST is empty.
531 (This means we might "see" instances that we shouldn't "really" see;
532 but the Haskell Report is vague on what is meant to be visible,
533 so we just take the easy road here.)
537 * The persistent renamer state
540 data PersistentCompilerState
542 pcs_PIT :: !PackageIfaceTable, -- Domain = non-home-package modules
543 -- the mi_decls component is empty
545 pcs_PTE :: !PackageTypeEnv, -- Domain = non-home-package modules
546 -- except that the InstEnv components is empty
548 pcs_insts :: !PackageInstEnv, -- The total InstEnv accumulated from all
549 -- the non-home-package modules
551 pcs_rules :: !PackageRuleBase, -- Ditto RuleEnv
553 pcs_PRS :: !PersistentRenamerState
558 The persistent renamer state contains:
560 * A name supply, which deals with allocating unique names to
561 (Module,OccName) original names,
563 * A "holding pen" for declarations that have been read out of
564 interface files but not yet sucked in, renamed, and typechecked
567 type PackageTypeEnv = TypeEnv
568 type PackageRuleBase = RuleBase
569 type PackageInstEnv = InstEnv
571 data PersistentRenamerState
572 = PRS { prsOrig :: !NameSupply,
573 prsImpMods :: !ImportedModuleInfo,
575 -- Holding pens for stuff that has been read in
576 -- but not yet slurped into the renamer
577 prsDecls :: !DeclsMap,
578 prsInsts :: !IfaceInsts,
579 prsRules :: !IfaceRules
583 The NameSupply makes sure that there is just one Unique assigned for
584 each original name; i.e. (module-name, occ-name) pair. The Name is
585 always stored as a Global, and has the SrcLoc of its binding location.
586 Actually that's not quite right. When we first encounter the original
587 name, we might not be at its binding site (e.g. we are reading an
588 interface file); so we give it 'noSrcLoc' then. Later, when we find
589 its binding site, we fix it up.
591 Exactly the same is true of the Module stored in the Name. When we first
592 encounter the occurrence, we may not know the details of the module, so
593 we just store junk. Then when we find the binding site, we fix it up.
597 = NameSupply { nsUniqs :: UniqSupply,
599 nsNames :: OrigNameCache,
600 -- Ensures that one original name gets one unique
601 nsIPs :: OrigIParamCache
602 -- Ensures that one implicit parameter name gets one unique
605 type OrigNameCache = FiniteMap (ModuleName,OccName) Name
606 type OrigIParamCache = FiniteMap (IPName RdrName) (IPName Name)
609 @ImportedModuleInfo@ contains info ONLY about modules that have not yet
610 been loaded into the iPIT. These modules are mentioned in interfaces we've
611 already read, so we know a tiny bit about them, but we havn't yet looked
612 at the interface file for the module itself. It needs to persist across
613 invocations of the renamer, at least from Rename.checkOldIface to Rename.renameSource.
614 And there's no harm in it persisting across multiple compilations.
617 type ImportedModuleInfo = FiniteMap ModuleName (WhetherHasOrphans, IsBootInterface)
620 A DeclsMap contains a binding for each Name in the declaration
621 including the constructors of a type decl etc. The Bool is True just
625 type DeclsMap = (NameEnv (AvailInfo, Bool, (Module, RdrNameTyClDecl)), Int)
626 -- The Int says how many have been sucked in
628 type IfaceInsts = GatedDecls RdrNameInstDecl
629 type IfaceRules = GatedDecls RdrNameRuleDecl
631 type GatedDecls d = (Bag (GatedDecl d), Int) -- The Int says how many have been sucked in
632 type GatedDecl d = (GateFn, (Module, d))
633 type GateFn = (Name -> Bool) -> Bool -- Returns True <=> gate is open
634 -- The (Name -> Bool) fn returns True for visible Names
635 -- For example, suppose this is in an interface file
636 -- instance C T where ...
637 -- We want to slurp this decl if both C and T are "visible" in
638 -- the importing module. See "The gating story" in RnIfaces for details.
642 %************************************************************************
644 \subsection{Provenance and export info}
646 %************************************************************************
648 A LocalRdrEnv is used for local bindings (let, where, lambda, case)
651 type LocalRdrEnv = RdrNameEnv Name
653 extendLocalRdrEnv :: LocalRdrEnv -> [Name] -> LocalRdrEnv
654 extendLocalRdrEnv env names
655 = addListToRdrEnv env [(mkRdrUnqual (nameOccName n), n) | n <- names]
658 The GlobalRdrEnv gives maps RdrNames to Names. There is a separate
659 one for each module, corresponding to that module's top-level scope.
662 type GlobalRdrEnv = RdrNameEnv [GlobalRdrElt]
663 -- The list is because there may be name clashes
664 -- These only get reported on lookup, not on construction
666 data GlobalRdrElt = GRE Name Provenance (Maybe DeprecTxt)
667 -- The Maybe DeprecTxt tells whether this name is deprecated
670 = vcat (map pp (rdrEnvToList env))
672 pp (rn, nps) = ppr rn <> colon <+>
673 vcat [ppr n <+> pprNameProvenance n p | (GRE n p _) <- nps]
676 The "provenance" of something says how it came to be in scope.
680 = LocalDef -- Defined locally
682 | NonLocalDef -- Defined non-locally
685 -- Just used for grouping error messages (in RnEnv.warnUnusedBinds)
686 instance Eq Provenance where
687 p1 == p2 = case p1 `compare` p2 of EQ -> True; _ -> False
689 instance Eq ImportReason where
690 p1 == p2 = case p1 `compare` p2 of EQ -> True; _ -> False
692 instance Ord Provenance where
693 compare LocalDef LocalDef = EQ
694 compare LocalDef (NonLocalDef _) = LT
695 compare (NonLocalDef _) LocalDef = GT
697 compare (NonLocalDef reason1) (NonLocalDef reason2)
698 = compare reason1 reason2
700 instance Ord ImportReason where
701 compare ImplicitImport ImplicitImport = EQ
702 compare ImplicitImport (UserImport _ _ _) = LT
703 compare (UserImport _ _ _) ImplicitImport = GT
704 compare (UserImport m1 loc1 _) (UserImport m2 loc2 _)
705 = (m1 `compare` m2) `thenCmp` (loc1 `compare` loc2)
709 = UserImport Module SrcLoc Bool -- Imported from module M on line L
710 -- Note the M may well not be the defining module
712 -- The Bool is true iff the thing was named *explicitly* in the import spec,
713 -- rather than being imported as part of a group; e.g.
716 -- Here, everything imported by B, and the constructors of T
717 -- are not named explicitly; only T is named explicitly.
718 -- This info is used when warning of unused names.
720 | ImplicitImport -- Imported implicitly for some other reason
724 hasBetterProv :: Provenance -> Provenance -> Bool
726 -- a local thing over an imported thing
727 -- a user-imported thing over a non-user-imported thing
728 -- an explicitly-imported thing over an implicitly imported thing
729 hasBetterProv LocalDef _ = True
730 hasBetterProv (NonLocalDef (UserImport _ _ _ )) (NonLocalDef ImplicitImport) = True
731 hasBetterProv _ _ = False
733 pprNameProvenance :: Name -> Provenance -> SDoc
734 pprNameProvenance name LocalDef = ptext SLIT("defined at") <+> ppr (nameSrcLoc name)
735 pprNameProvenance name (NonLocalDef why) = sep [ppr_reason why,
736 nest 2 (ppr_defn (nameSrcLoc name))]
738 ppr_reason ImplicitImport = ptext SLIT("implicitly imported")
739 ppr_reason (UserImport mod loc _) = ptext SLIT("imported from") <+> ppr mod <+> ptext SLIT("at") <+> ppr loc
741 ppr_defn loc | isGoodSrcLoc loc = parens (ptext SLIT("at") <+> ppr loc)