X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Fmain%2FHscTypes.lhs;h=5887e0731bd656949897dc13c5f0d7f3ac441f82;hb=c36b02d9d26fe4050397bdfba60a6f92c7314e8d;hp=498add4732e1b57073c333c3406247e292d975da;hpb=01e0566e61e4222600c7ba0a2d35d6102fd1afb5;p=ghc-hetmet.git diff --git a/ghc/compiler/main/HscTypes.lhs b/ghc/compiler/main/HscTypes.lhs index 498add4..5887e07 100644 --- a/ghc/compiler/main/HscTypes.lhs +++ b/ghc/compiler/main/HscTypes.lhs @@ -5,28 +5,34 @@ \begin{code} module HscTypes ( + GhciMode(..), + ModuleLocation(..), ModDetails(..), ModIface(..), - HomeSymbolTable, PackageTypeEnv, + HomeSymbolTable, emptySymbolTable, + PackageTypeEnv, HomeIfaceTable, PackageIfaceTable, emptyIfaceTable, lookupIface, lookupIfaceByModName, emptyModIface, + InteractiveContext(..), + IfaceDecls, mkIfaceDecls, dcl_tycl, dcl_rules, dcl_insts, - VersionInfo(..), initialVersionInfo, + VersionInfo(..), initialVersionInfo, lookupVersion, - TyThing(..), isTyClThing, + TyThing(..), isTyClThing, implicitTyThingIds, - TypeEnv, lookupType, mkTypeEnv, extendTypeEnvList, - typeEnvClasses, typeEnvTyCons, + TypeEnv, lookupType, mkTypeEnv, emptyTypeEnv, + extendTypeEnvList, extendTypeEnvWithIds, + typeEnvElts, typeEnvClasses, typeEnvTyCons, typeEnvIds, - WhetherHasOrphans, ImportVersion, WhatsImported(..), - PersistentRenamerState(..), IsBootInterface, Avails, DeclsMap, - IfaceInsts, IfaceRules, GatedDecl, - OrigNameEnv(..), OrigNameNameEnv, OrigNameIParamEnv, - AvailEnv, AvailInfo, GenAvailInfo(..), + ImportedModuleInfo, WhetherHasOrphans, ImportVersion, WhatsImported(..), + PersistentRenamerState(..), IsBootInterface, DeclsMap, + IfaceInsts, IfaceRules, GatedDecl, GatedDecls, GateFn, IsExported, + NameSupply(..), OrigNameCache, OrigIParamCache, + Avails, AvailEnv, GenAvailInfo(..), AvailInfo, RdrAvailInfo, PersistentCompilerState(..), Deprecations(..), lookupDeprec, @@ -34,29 +40,32 @@ module HscTypes ( InstEnv, ClsInstEnv, DFunId, PackageInstEnv, PackageRuleBase, - GlobalRdrEnv, RdrAvailInfo, + GlobalRdrEnv, GlobalRdrElt(..), pprGlobalRdrEnv, + LocalRdrEnv, extendLocalRdrEnv, + -- Provenance - Provenance(..), ImportReason(..), PrintUnqualified, + Provenance(..), ImportReason(..), pprNameProvenance, hasBetterProv ) where #include "HsVersions.h" -import RdrName ( RdrNameEnv, emptyRdrEnv ) -import Name ( Name, NamedThing, isLocallyDefined, - getName, nameModule, nameSrcLoc ) -import Name -- Env +import RdrName ( RdrNameEnv, addListToRdrEnv, emptyRdrEnv, mkRdrUnqual, rdrEnvToList ) +import Name ( Name, NamedThing, getName, nameOccName, nameModule, nameSrcLoc ) +import NameEnv import OccName ( OccName ) import Module ( Module, ModuleName, ModuleEnv, lookupModuleEnv, lookupModuleEnvByName, emptyModuleEnv ) import InstEnv ( InstEnv, ClsInstEnv, DFunId ) import Rules ( RuleBase ) +import CoreSyn ( CoreBind ) import Id ( Id ) -import Class ( Class ) -import TyCon ( TyCon ) +import Class ( Class, classSelIds ) +import TyCon ( TyCon, isNewTyCon, tyConGenIds, tyConSelIds, tyConDataConsIfAvailable ) +import DataCon ( dataConId, dataConWrapId ) import BasicTypes ( Version, initialVersion, Fixity ) @@ -68,7 +77,7 @@ import CoreSyn ( IdCoreRule ) import FiniteMap ( FiniteMap ) import Bag ( Bag ) -import Maybes ( seqMaybe ) +import Maybes ( seqMaybe, orElse ) import Outputable import SrcLoc ( SrcLoc, isGoodSrcLoc ) import Util ( thenCmp, sortLt ) @@ -77,6 +86,18 @@ import UniqSupply ( UniqSupply ) %************************************************************************ %* * +\subsection{Which mode we're in +%* * +%************************************************************************ + +\begin{code} +data GhciMode = Batch | Interactive | OneShot + deriving Eq +\end{code} + + +%************************************************************************ +%* * \subsection{Module locations} %* * %************************************************************************ @@ -86,7 +107,7 @@ data ModuleLocation = ModuleLocation { ml_hs_file :: Maybe FilePath, ml_hspp_file :: Maybe FilePath, -- path of preprocessed source - ml_hi_file :: Maybe FilePath, + ml_hi_file :: FilePath, ml_obj_file :: Maybe FilePath } deriving Show @@ -118,26 +139,26 @@ linking; it is the "linked" form of the mi_decls field. \begin{code} data ModIface = ModIface { - mi_module :: Module, -- Complete with package info - mi_version :: VersionInfo, -- Module version number - mi_orphan :: WhetherHasOrphans, -- Whether this module has orphans - mi_boot :: IsBootInterface, -- Whether this interface was read from an hi-boot file + mi_module :: !Module, -- Complete with package info + mi_version :: !VersionInfo, -- Module version number + mi_orphan :: WhetherHasOrphans, -- Whether this module has orphans + mi_boot :: !IsBootInterface, -- read from an hi-boot file? - mi_usages :: [ImportVersion Name], -- Usages; kept sorted so that it's easy - -- to decide whether to write a new iface file - -- (changing usages doesn't affect the version of - -- this module) + mi_usages :: ![ImportVersion Name], + -- Usages; kept sorted so that it's easy to decide + -- whether to write a new iface file (changing usages + -- doesn't affect the version of this module) - mi_exports :: [(ModuleName,Avails)], -- What it exports - -- Kept sorted by (mod,occ), - -- to make version comparisons easier + mi_exports :: ![(ModuleName,Avails)], + -- What it exports Kept sorted by (mod,occ), to make + -- version comparisons easier - mi_globals :: GlobalRdrEnv, -- Its top level environment + mi_globals :: !GlobalRdrEnv, -- Its top level environment - mi_fixities :: NameEnv Fixity, -- Fixities - mi_deprecs :: Deprecations, -- Deprecations + mi_fixities :: !(NameEnv Fixity), -- Fixities + mi_deprecs :: !Deprecations, -- Deprecations - mi_decls :: IfaceDecls -- The RnDecls form of ModDetails + mi_decls :: IfaceDecls -- The RnDecls form of ModDetails } data IfaceDecls = IfaceDecls { dcl_tycl :: [RenamedTyClDecl], -- Sorted @@ -150,24 +171,8 @@ mkIfaceDecls tycls rules insts dcl_rules = sortLt lt_rule rules, dcl_insts = insts } where - d1 `lt_tycl` d2 = nameOccName (tyClDeclName d1) < nameOccName (tyClDeclName d2) - r1 `lt_rule` r2 = nameOccName (ifaceRuleDeclName r1) < nameOccName (ifaceRuleDeclName r2) - - -- I wanted to sort just by the Name, but there's a problem: we are comparing - -- the old version of an interface with the new version. The latter will use - -- local names like 'lvl23' that were constructed not by the renamer but by - -- the simplifier. So the unqiues aren't going to line up. - -- - -- It's ok to compare by OccName because this comparison only drives the - -- computation of new version numbers. - -- - -- Better solutions: Compare in a way that is insensitive to the name used - -- for local things. This would decrease the wobbles due - -- to 'lvl23' changing to 'lvl24'. - -- - -- NB: there's a related comparision on MkIface.diffDecls! - - + d1 `lt_tycl` d2 = tyClDeclName d1 < tyClDeclName d2 + r1 `lt_rule` r2 = ifaceRuleDeclName r1 < ifaceRuleDeclName r2 -- typechecker should only look at this, not ModIface @@ -175,20 +180,47 @@ mkIfaceDecls tycls rules insts data ModDetails = ModDetails { -- The next three fields are created by the typechecker - md_types :: TypeEnv, - md_insts :: [DFunId], -- Dfun-ids for the instances in this module - md_rules :: [IdCoreRule] -- Domain may include Ids from other modules + md_types :: !TypeEnv, + md_insts :: ![DFunId], -- Dfun-ids for the instances in this module + md_rules :: ![IdCoreRule], -- Domain may include Ids from other modules + md_binds :: ![CoreBind] } + +-- The ModDetails takes on several slightly different forms: +-- +-- After typecheck + desugar +-- md_types Contains TyCons, Classes, and implicit Ids +-- md_insts All instances from this module (incl derived ones) +-- md_rules All rules from this module +-- md_binds Desugared bindings +-- +-- After simplification +-- md_types Same as after typecheck +-- md_insts Ditto +-- md_rules Orphan rules only (local ones now attached to binds) +-- md_binds With rules attached +-- +-- After CoreTidy +-- md_types Now contains Ids as well, replete with final IdInfo +-- The Ids are only the ones that are visible from +-- importing modules. Without -O that means only +-- exported Ids, but with -O importing modules may +-- see ids mentioned in unfoldings of exported Ids +-- +-- md_insts Same DFunIds as before, but with final IdInfo, +-- and the unique might have changed; remember that +-- CoreTidy links up the uniques of old and new versions +-- +-- md_rules All rules for exported things, substituted with final Ids +-- +-- md_binds Tidied +-- +-- Passed back to compilation manager +-- Just as after CoreTidy, but with md_binds nuked + \end{code} \begin{code} -emptyModDetails :: ModDetails -emptyModDetails - = ModDetails { md_types = emptyTypeEnv, - md_insts = [], - md_rules = [] - } - emptyModIface :: Module -> ModIface emptyModIface mod = ModIface { mi_module = mod, @@ -215,6 +247,9 @@ type PackageIfaceTable = IfaceTable type HomeSymbolTable = SymbolTable -- Domain = modules in the home package +emptySymbolTable :: SymbolTable +emptySymbolTable = emptyModuleEnv + emptyIfaceTable :: IfaceTable emptyIfaceTable = emptyModuleEnv \end{code} @@ -222,20 +257,37 @@ emptyIfaceTable = emptyModuleEnv Simple lookups in the symbol table. \begin{code} -lookupIface :: HomeIfaceTable -> PackageIfaceTable - -> Module -> Name -- The module is to use for locally-defined names - -> Maybe ModIface +lookupIface :: HomeIfaceTable -> PackageIfaceTable -> Name -> Maybe ModIface -- We often have two IfaceTables, and want to do a lookup -lookupIface hit pit this_mod name - | isLocallyDefined name = lookupModuleEnv hit this_mod - | otherwise = lookupModuleEnv hit mod `seqMaybe` lookupModuleEnv pit mod +lookupIface hit pit name + = lookupModuleEnv hit mod `seqMaybe` lookupModuleEnv pit mod where mod = nameModule name -lookupIfaceByModName :: ModuleEnv a -> ModuleEnv a -> ModuleName -> Maybe a --- We often have two Symbol- or IfaceTables, and want to do a lookup -lookupIfaceByModName ht pt mod - = lookupModuleEnvByName ht mod `seqMaybe` lookupModuleEnvByName pt mod +lookupIfaceByModName :: HomeIfaceTable -> PackageIfaceTable -> ModuleName -> Maybe ModIface +-- We often have two IfaceTables, and want to do a lookup +lookupIfaceByModName hit pit mod + = lookupModuleEnvByName hit mod `seqMaybe` lookupModuleEnvByName pit mod +\end{code} + + +%************************************************************************ +%* * +\subsection{The interactive context} +%* * +%************************************************************************ + +\begin{code} +data InteractiveContext + = InteractiveContext { + ic_module :: Module, -- The current module in which + -- the user is sitting + + ic_rn_env :: LocalRdrEnv, -- Lexical context for variables bound + -- during interaction + + ic_type_env :: TypeEnv -- Ditto for types + } \end{code} @@ -260,9 +312,39 @@ instance NamedThing TyThing where getName (ATyCon tc) = getName tc getName (AClass cl) = getName cl -typeEnvClasses env = [cl | AClass cl <- nameEnvElts env] -typeEnvTyCons env = [tc | ATyCon tc <- nameEnvElts env] +instance Outputable TyThing where + ppr (AnId id) = ptext SLIT("AnId") <+> ppr id + ppr (ATyCon tc) = ptext SLIT("ATyCon") <+> ppr tc + ppr (AClass cl) = ptext SLIT("AClass") <+> ppr cl + + +typeEnvElts :: TypeEnv -> [TyThing] +typeEnvClasses :: TypeEnv -> [Class] +typeEnvTyCons :: TypeEnv -> [TyCon] +typeEnvIds :: TypeEnv -> [Id] +typeEnvElts env = nameEnvElts env +typeEnvClasses env = [cl | AClass cl <- typeEnvElts env] +typeEnvTyCons env = [tc | ATyCon tc <- typeEnvElts env] +typeEnvIds env = [id | AnId id <- typeEnvElts env] + +implicitTyThingIds :: [TyThing] -> [Id] +-- Add the implicit data cons and selectors etc +implicitTyThingIds things + = concat (map go things) + where + go (AnId f) = [] + go (AClass cl) = classSelIds cl + go (ATyCon tc) = tyConGenIds tc ++ + tyConSelIds tc ++ + [ n | dc <- tyConDataConsIfAvailable tc, + n <- implicitConIds tc dc] + -- Synonyms return empty list of constructors and selectors + + implicitConIds tc dc -- Newtypes have a constructor wrapper, + -- but no worker + | isNewTyCon tc = [dataConWrapId dc] + | otherwise = [dataConId dc, dataConWrapId dc] \end{code} @@ -276,17 +358,17 @@ mkTypeEnv things = extendTypeEnvList emptyTypeEnv things extendTypeEnvList :: TypeEnv -> [TyThing] -> TypeEnv extendTypeEnvList env things - = foldl add_thing env things - where - add_thing :: TypeEnv -> TyThing -> TypeEnv - add_thing env thing = extendNameEnv env (getName thing) thing + = extendNameEnvList env [(getName thing, thing) | thing <- things] + +extendTypeEnvWithIds :: TypeEnv -> [Id] -> TypeEnv +extendTypeEnvWithIds env ids + = extendNameEnvList env [(getName id, AnId id) | id <- ids] \end{code} \begin{code} lookupType :: HomeSymbolTable -> PackageTypeEnv -> Name -> Maybe TyThing lookupType hst pte name - = ASSERT2( not (isLocallyDefined name), ppr name ) - case lookupModuleEnv hst (nameModule name) of + = case lookupModuleEnv hst (nameModule name) of Just details -> lookupNameEnv (md_types details) name Nothing -> lookupNameEnv pte name \end{code} @@ -311,13 +393,19 @@ data VersionInfo -- The version of an Id changes if its fixity changes -- Ditto data constructors, class operations, except that the version of -- the parent class/tycon changes + -- + -- If a name isn't in the map, it means 'initialVersion' } initialVersionInfo :: VersionInfo initialVersionInfo = VersionInfo { vers_module = initialVersion, vers_exports = initialVersion, vers_rules = initialVersion, - vers_decls = emptyNameEnv } + vers_decls = emptyNameEnv + } + +lookupVersion :: NameEnv Version -> Name -> Version +lookupVersion env name = lookupNameEnv env name `orElse` initialVersion data Deprecations = NoDeprecs | DeprecAll DeprecTxt -- Whole module deprecated @@ -331,6 +419,13 @@ lookupDeprec (DeprecAll txt) name = Just txt lookupDeprec (DeprecSome env) name = case lookupNameEnv env name of Just (_, txt) -> Just txt Nothing -> Nothing + +instance Eq Deprecations where + -- Used when checking whether we need write a new interface + NoDeprecs == NoDeprecs = True + (DeprecAll t1) == (DeprecAll t2) = t1 == t2 + (DeprecSome e1) == (DeprecSome e2) = nameEnvElts e1 == nameEnvElts e2 + d1 == d2 = False \end{code} @@ -403,6 +498,8 @@ data WhatsImported name = NothingAtAll -- The module is below us in the -- we imported the module without saying exactly what we imported -- We need to recompile if the module exports changes, because we might -- now have a name clash in the importing module. + +type IsExported = Name -> Bool -- True for names that are exported from this module \end{code} @@ -415,20 +512,19 @@ data WhatsImported name = NothingAtAll -- The module is below us in the \begin{code} data PersistentCompilerState = PCS { - pcs_PIT :: PackageIfaceTable, -- Domain = non-home-package modules + pcs_PIT :: !PackageIfaceTable, -- Domain = non-home-package modules -- the mi_decls component is empty - pcs_PTE :: PackageTypeEnv, -- Domain = non-home-package modules + pcs_PTE :: !PackageTypeEnv, -- Domain = non-home-package modules -- except that the InstEnv components is empty - pcs_insts :: PackageInstEnv, -- The total InstEnv accumulated from all + pcs_insts :: !PackageInstEnv, -- The total InstEnv accumulated from all -- the non-home-package modules - pcs_rules :: PackageRuleBase, -- Ditto RuleEnv + pcs_rules :: !PackageRuleBase, -- Ditto RuleEnv - pcs_PRS :: PersistentRenamerState + pcs_PRS :: !PersistentRenamerState } - \end{code} The @PersistentRenamerState@ persists across successive calls to the @@ -458,15 +554,15 @@ type PackageRuleBase = RuleBase type PackageInstEnv = InstEnv data PersistentRenamerState - = PRS { prsOrig :: OrigNameEnv, - prsDecls :: DeclsMap, - prsInsts :: IfaceInsts, - prsRules :: IfaceRules, - prsNS :: UniqSupply + = PRS { prsOrig :: !NameSupply, + prsImpMods :: !ImportedModuleInfo, + prsDecls :: !DeclsMap, + prsInsts :: !IfaceInsts, + prsRules :: !IfaceRules } \end{code} -The OrigNameEnv makes sure that there is just one Unique assigned for +The NameSupply makes sure that there is just one Unique assigned for each original name; i.e. (module-name, occ-name) pair. The Name is always stored as a Global, and has the SrcLoc of its binding location. Actually that's not quite right. When we first encounter the original @@ -479,17 +575,29 @@ encounter the occurrence, we may not know the details of the module, so we just store junk. Then when we find the binding site, we fix it up. \begin{code} -data OrigNameEnv - = Orig { origNames :: OrigNameNameEnv, +data NameSupply + = NameSupply { nsUniqs :: UniqSupply, + -- Supply of uniques + nsNames :: OrigNameCache, -- Ensures that one original name gets one unique - origIParam :: OrigNameIParamEnv + nsIPs :: OrigIParamCache -- Ensures that one implicit parameter name gets one unique } -type OrigNameNameEnv = FiniteMap (ModuleName,OccName) Name -type OrigNameIParamEnv = FiniteMap OccName Name +type OrigNameCache = FiniteMap (ModuleName,OccName) Name +type OrigIParamCache = FiniteMap OccName Name \end{code} +@ImportedModuleInfo@ contains info ONLY about modules that have not yet +been loaded into the iPIT. These modules are mentioned in interfaces we've +already read, so we know a tiny bit about them, but we havn't yet looked +at the interface file for the module itself. It needs to persist across +invocations of the renamer, at least from Rename.checkOldIface to Rename.renameSource. +And there's no harm in it persisting across multiple compilations. + +\begin{code} +type ImportedModuleInfo = FiniteMap ModuleName (WhetherHasOrphans, IsBootInterface) +\end{code} A DeclsMap contains a binding for each Name in the declaration including the constructors of a type decl etc. The Bool is True just @@ -503,7 +611,13 @@ type IfaceInsts = GatedDecls RdrNameInstDecl type IfaceRules = GatedDecls RdrNameRuleDecl type GatedDecls d = (Bag (GatedDecl d), Int) -- The Int says how many have been sucked in -type GatedDecl d = ([Name], (Module, d)) +type GatedDecl d = (GateFn, (Module, d)) +type GateFn = (Name -> Bool) -> Bool -- Returns True <=> gate is open + -- The (Name -> Bool) fn returns True for visible Names + -- For example, suppose this is in an interface file + -- instance C T where ... + -- We want to slurp this decl if both C and T are "visible" in + -- the importing module. See "The gating story" in RnIfaces for details. \end{code} @@ -513,13 +627,32 @@ type GatedDecl d = ([Name], (Module, d)) %* * %************************************************************************ +A LocalRdrEnv is used for local bindings (let, where, lambda, case) + +\begin{code} +type LocalRdrEnv = RdrNameEnv Name + +extendLocalRdrEnv :: LocalRdrEnv -> [Name] -> LocalRdrEnv +extendLocalRdrEnv env names + = addListToRdrEnv env [(mkRdrUnqual (nameOccName n), n) | n <- names] +\end{code} + The GlobalRdrEnv gives maps RdrNames to Names. There is a separate one for each module, corresponding to that module's top-level scope. \begin{code} -type GlobalRdrEnv = RdrNameEnv [(Name,Provenance)] -- The list is because there may be name clashes - -- These only get reported on lookup, - -- not on construction +type GlobalRdrEnv = RdrNameEnv [GlobalRdrElt] + -- The list is because there may be name clashes + -- These only get reported on lookup, not on construction + +data GlobalRdrElt = GRE Name Provenance (Maybe DeprecTxt) + -- The Maybe DeprecTxt tells whether this name is deprecated + +pprGlobalRdrEnv env + = vcat (map pp (rdrEnvToList env)) + where + pp (rn, nps) = ppr rn <> colon <+> + vcat [ppr n <+> pprNameProvenance n p | (GRE n p _) <- nps] \end{code} The "provenance" of something says how it came to be in scope. @@ -530,7 +663,6 @@ data Provenance | NonLocalDef -- Defined non-locally ImportReason - PrintUnqualified -- Just used for grouping error messages (in RnEnv.warnUnusedBinds) instance Eq Provenance where @@ -541,10 +673,10 @@ instance Eq ImportReason where instance Ord Provenance where compare LocalDef LocalDef = EQ - compare LocalDef (NonLocalDef _ _) = LT - compare (NonLocalDef _ _) LocalDef = GT + compare LocalDef (NonLocalDef _) = LT + compare (NonLocalDef _) LocalDef = GT - compare (NonLocalDef reason1 _) (NonLocalDef reason2 _) + compare (NonLocalDef reason1) (NonLocalDef reason2) = compare reason1 reason2 instance Ord ImportReason where @@ -568,11 +700,6 @@ data ImportReason -- This info is used when warning of unused names. | ImplicitImport -- Imported implicitly for some other reason - - -type PrintUnqualified = Bool -- True <=> the unqualified name of this thing is - -- in scope in this module, so print it - -- unqualified in error messages \end{code} \begin{code} @@ -581,19 +708,18 @@ hasBetterProv :: Provenance -> Provenance -> Bool -- a local thing over an imported thing -- a user-imported thing over a non-user-imported thing -- an explicitly-imported thing over an implicitly imported thing -hasBetterProv LocalDef _ = True -hasBetterProv (NonLocalDef (UserImport _ _ True) _) _ = True -hasBetterProv (NonLocalDef (UserImport _ _ _ ) _) (NonLocalDef ImplicitImport _) = True -hasBetterProv _ _ = False +hasBetterProv LocalDef _ = True +hasBetterProv (NonLocalDef (UserImport _ _ _ )) (NonLocalDef ImplicitImport) = True +hasBetterProv _ _ = False pprNameProvenance :: Name -> Provenance -> SDoc -pprNameProvenance name LocalDef = ptext SLIT("defined at") <+> ppr (nameSrcLoc name) -pprNameProvenance name (NonLocalDef why _) = sep [ppr_reason why, - nest 2 (parens (ppr_defn (nameSrcLoc name)))] +pprNameProvenance name LocalDef = ptext SLIT("defined at") <+> ppr (nameSrcLoc name) +pprNameProvenance name (NonLocalDef why) = sep [ppr_reason why, + nest 2 (ppr_defn (nameSrcLoc name))] ppr_reason ImplicitImport = ptext SLIT("implicitly imported") ppr_reason (UserImport mod loc _) = ptext SLIT("imported from") <+> ppr mod <+> ptext SLIT("at") <+> ppr loc -ppr_defn loc | isGoodSrcLoc loc = ptext SLIT("at") <+> ppr loc +ppr_defn loc | isGoodSrcLoc loc = parens (ptext SLIT("at") <+> ppr loc) | otherwise = empty \end{code}