main/GHC.hs

    {-# LANGUAGE CPP, NondecreasingIndentation, ScopedTypeVariables #-}

    -- -----------------------------------------------------------------------------
    --
    -- (c) The University of Glasgow, 2005-2012
    --
    -- The GHC API
    --
    -- -----------------------------------------------------------------------------

    module GHC (
            -- * Initialisation
            defaultErrorHandler,
            defaultCleanupHandler,
            prettyPrintGhcErrors,

            -- * GHC Monad
            Ghc, GhcT, GhcMonad(..), HscEnv,
            runGhc, runGhcT, initGhcMonad,
            gcatch, gbracket, gfinally,
            printException,
            handleSourceError,
            needsTemplateHaskell,

            -- * Flags and settings
            DynFlags(..), GeneralFlag(..), Severity(..), HscTarget(..), gopt,
            GhcMode(..), GhcLink(..), defaultObjectTarget,
            parseDynamicFlags,
            getSessionDynFlags, setSessionDynFlags,
            getProgramDynFlags, setProgramDynFlags,
            getInteractiveDynFlags, setInteractiveDynFlags,
            parseStaticFlags,

            -- * Targets
            Target(..), TargetId(..), Phase,
            setTargets,
            getTargets,
            addTarget,
            removeTarget,
            guessTarget,

            -- * Loading\/compiling the program
            depanal,
            load, LoadHowMuch(..), InteractiveImport(..),
            SuccessFlag(..), succeeded, failed,
            defaultWarnErrLogger, WarnErrLogger,
            workingDirectoryChanged,
            parseModule, typecheckModule, desugarModule, loadModule,
            ParsedModule(..), TypecheckedModule(..), DesugaredModule(..),
            TypecheckedSource, ParsedSource, RenamedSource,   -- ditto
            TypecheckedMod, ParsedMod,
            moduleInfo, renamedSource, typecheckedSource,
            parsedSource, coreModule,

            -- ** Compiling to Core
            CoreModule(..),
            compileToCoreModule, compileToCoreSimplified,

            -- * Inspecting the module structure of the program
            ModuleGraph, ModSummary(..), ms_mod_name, ModLocation(..),
            getModSummary,
            getModuleGraph,
            isLoaded,
            topSortModuleGraph,

            -- * Inspecting modules
            ModuleInfo,
            getModuleInfo,
            modInfoTyThings,
            modInfoTopLevelScope,
            modInfoExports,
            modInfoInstances,
            modInfoIsExportedName,
            modInfoLookupName,
            modInfoIface,
            modInfoSafe,
            lookupGlobalName,
            findGlobalAnns,
            mkPrintUnqualifiedForModule,
            ModIface(..),
            SafeHaskellMode(..),

            -- * Querying the environment
            -- packageDbModules,

            -- * Printing
            PrintUnqualified, alwaysQualify,

            -- * Interactive evaluation
            getBindings, getInsts, getPrintUnqual,
            findModule, lookupModule,
    #ifdef GHCI
            isModuleTrusted,
            moduleTrustReqs,
            setContext, getContext,
            getNamesInScope,
            getRdrNamesInScope,
            getGRE,
            moduleIsInterpreted,
            getInfo,
            exprType,
            typeKind,
            parseName,
            RunResult(..),
            runStmt, runStmtWithLocation, runDecls, runDeclsWithLocation,
            runTcInteractive,   -- Desired by some clients (Trac #8878)
            parseImportDecl, SingleStep(..),
            resume,
            Resume(resumeStmt, resumeThreadId, resumeBreakInfo, resumeSpan,
                   resumeHistory, resumeHistoryIx),
            History(historyBreakInfo, historyEnclosingDecls),
            GHC.getHistorySpan, getHistoryModule,
            getResumeContext,
            abandon, abandonAll,
            InteractiveEval.back,
            InteractiveEval.forward,
            showModule,
            isModuleInterpreted,
            InteractiveEval.compileExpr, HValue, dynCompileExpr,
            GHC.obtainTermFromId, GHC.obtainTermFromVal, reconstructType,
            modInfoModBreaks,
            ModBreaks(..), BreakIndex,
            BreakInfo(breakInfo_number, breakInfo_module),
            BreakArray, setBreakOn, setBreakOff, getBreak,
    #endif
            lookupName,

    #ifdef GHCI
            -- ** EXPERIMENTAL
            setGHCiMonad,
    #endif

            -- * Abstract syntax elements

            -- ** Packages
            PackageKey,

            -- ** Modules
            Module, mkModule, pprModule, moduleName, modulePackageKey,
            ModuleName, mkModuleName, moduleNameString,

            -- ** Names
            Name,
            isExternalName, nameModule, pprParenSymName, nameSrcSpan,
            NamedThing(..),
            RdrName(Qual,Unqual),

            -- ** Identifiers
            Id, idType,
            isImplicitId, isDeadBinder,
            isExportedId, isLocalId, isGlobalId,
            isRecordSelector,
            isPrimOpId, isFCallId, isClassOpId_maybe,
            isDataConWorkId, idDataCon,
            isBottomingId, isDictonaryId,
            recordSelectorFieldLabel,

            -- ** Type constructors
            TyCon,
            tyConTyVars, tyConDataCons, tyConArity,
            isClassTyCon, isTypeSynonymTyCon, isTypeFamilyTyCon, isNewTyCon,
            isPrimTyCon, isFunTyCon,
            isFamilyTyCon, isOpenFamilyTyCon, isOpenTypeFamilyTyCon,
            tyConClass_maybe,
            synTyConRhs_maybe, synTyConDefn_maybe, synTyConResKind,

            -- ** Type variables
            TyVar,
            alphaTyVars,

            -- ** Data constructors
            DataCon,
            dataConSig, dataConType, dataConTyCon, dataConFieldLabels,
            dataConIsInfix, isVanillaDataCon, dataConUserType,
            dataConSrcBangs,
            StrictnessMark(..), isMarkedStrict,

            -- ** Classes
            Class,
            classMethods, classSCTheta, classTvsFds, classATs,
            pprFundeps,

            -- ** Instances
            ClsInst,
            instanceDFunId,
            pprInstance, pprInstanceHdr,
            pprFamInst,

            FamInst,

            -- ** Types and Kinds
            Type, splitForAllTys, funResultTy,
            pprParendType, pprTypeApp,
            Kind,
            PredType,
            ThetaType, pprForAll, pprThetaArrowTy,

            -- ** Entities
            TyThing(..),

            -- ** Syntax
            module HsSyn, -- ToDo: remove extraneous bits

            -- ** Fixities
            FixityDirection(..),
            defaultFixity, maxPrecedence,
            negateFixity,
            compareFixity,

            -- ** Source locations
            SrcLoc(..), RealSrcLoc,
            mkSrcLoc, noSrcLoc,
            srcLocFile, srcLocLine, srcLocCol,
            SrcSpan(..), RealSrcSpan,
            mkSrcSpan, srcLocSpan, isGoodSrcSpan, noSrcSpan,
            srcSpanStart, srcSpanEnd,
            srcSpanFile,
            srcSpanStartLine, srcSpanEndLine,
            srcSpanStartCol, srcSpanEndCol,

            -- ** Located
            GenLocated(..), Located,

            -- *** Constructing Located
            noLoc, mkGeneralLocated,

            -- *** Deconstructing Located
            getLoc, unLoc,

            -- *** Combining and comparing Located values
            eqLocated, cmpLocated, combineLocs, addCLoc,
            leftmost_smallest, leftmost_largest, rightmost,
            spans, isSubspanOf,

            -- * Exceptions
            GhcException(..), showGhcException,

            -- * Token stream manipulations
            Token,
            getTokenStream, getRichTokenStream,
            showRichTokenStream, addSourceToTokens,

            -- * Pure interface to the parser
            parser,

            -- * API Annotations
            ApiAnns,AnnKeywordId(..),AnnotationComment(..),
            getAnnotation, getAndRemoveAnnotation,
            getAnnotationComments, getAndRemoveAnnotationComments,

            -- * Miscellaneous
            --sessionHscEnv,
            cyclicModuleErr,
      ) where

    {-
     ToDo:

      * inline bits of HscMain here to simplify layering: hscTcExpr, hscStmt.
      * what StaticFlags should we expose, if any?
    -}

    #include "HsVersions.h"

    #ifdef GHCI
    import ByteCodeInstr
    import BreakArray
    import InteractiveEval
    import TcRnDriver       ( runTcInteractive )
    #endif

    import PprTyThing       ( pprFamInst )
    import HscMain
    import GhcMake
    import DriverPipeline   ( compileOne' )
    import GhcMonad
    import TcRnMonad        ( finalSafeMode )
    import TcRnTypes
    import Packages
    import NameSet
    import RdrName
    import qualified HsSyn -- hack as we want to reexport the whole module
    import HsSyn
    import Type     hiding( typeKind )
    import Kind             ( synTyConResKind )
    import TcType           hiding( typeKind )
    import Id
    import TysPrim          ( alphaTyVars )
    import TyCon
    import Class
    import DataCon
    import Name             hiding ( varName )
    import Avail
    import InstEnv
    import FamInstEnv ( FamInst )
    import SrcLoc
    import CoreSyn
    import TidyPgm
    import DriverPhases     ( Phase(..), isHaskellSrcFilename )
    import Finder
    import HscTypes
    import DynFlags
    import StaticFlags
    import SysTools
    import Annotations
    import Module
    import UniqFM
    import Panic
    import Platform
    import Bag              ( unitBag )
    import ErrUtils
    import MonadUtils
    import Util
    import StringBuffer
    import Outputable
    import BasicTypes
    import Maybes           ( expectJust )
    import FastString
    import qualified Parser
    import Lexer
    import ApiAnnotation

    import System.Directory ( doesFileExist )
    import Data.Maybe
    import Data.List        ( find )
    import Data.Time
    import Data.Typeable    ( Typeable )
    import Data.Word        ( Word8 )
    import Control.Monad
    import System.Exit      ( exitWith, ExitCode(..) )
    import Exception
    import Data.IORef
    import System.FilePath
    import System.IO
    import Prelude hiding (init)

    -- %************************************************************************
    -- %*                                                                      *
    --             Initialisation: exception handlers
    -- %*                                                                      *
    -- %************************************************************************

    -- | Install some default exception handlers and run the inner computation.
    -- Unless you want to handle exceptions yourself, you should wrap this around
    -- the top level of your program.  The default handlers output the error
    -- message(s) to stderr and exit cleanly.
    defaultErrorHandler :: (ExceptionMonad m, MonadIO m)
                        => FatalMessager -> FlushOut -> m a -> m a
    defaultErrorHandler fm (FlushOut flushOut) inner =
      -- top-level exception handler: any unrecognised exception is a compiler bug.
      ghandle (\exception -> liftIO $ do
               flushOut
               case fromException exception of
                    -- an IO exception probably isn't our fault, so don't panic
                    Just (ioe :: IOException) ->
                      fatalErrorMsg'' fm (show ioe)
                    _ -> case fromException exception of
                         Just UserInterrupt ->
                             -- Important to let this one propagate out so our
                             -- calling process knows we were interrupted by ^C
                             liftIO $ throwIO UserInterrupt
                         Just StackOverflow ->
                             fatalErrorMsg'' fm "stack overflow: use +RTS -K<size> to increase it"
                         _ -> case fromException exception of
                              Just (ex :: ExitCode) -> liftIO $ throwIO ex
                              _ ->
                                  fatalErrorMsg'' fm
                                      (show (Panic (show exception)))
               exitWith (ExitFailure 1)
             ) $

      -- error messages propagated as exceptions
      handleGhcException
                (\ge -> liftIO $ do
                    flushOut
                    case ge of
                         PhaseFailed _ code -> exitWith code
                         Signal _ -> exitWith (ExitFailure 1)
                         _ -> do fatalErrorMsg'' fm (show ge)
                                 exitWith (ExitFailure 1)
                ) $
      inner

    -- | Install a default cleanup handler to remove temporary files deposited by
    -- a GHC run.  This is separate from 'defaultErrorHandler', because you might
    -- want to override the error handling, but still get the ordinary cleanup
    -- behaviour.
    defaultCleanupHandler :: (ExceptionMonad m, MonadIO m) =>
                             DynFlags -> m a -> m a
    defaultCleanupHandler dflags inner =
        -- make sure we clean up after ourselves
        inner `gfinally`
              (liftIO $ do
                  cleanTempFiles dflags
                  cleanTempDirs dflags
              )
              --  exceptions will be blocked while we clean the temporary files,
              -- so there shouldn't be any difficulty if we receive further
              -- signals.

    -- %************************************************************************
    -- %*                                                                      *
    --             The Ghc Monad
    -- %*                                                                      *
    -- %************************************************************************

    -- | Run function for the 'Ghc' monad.
    --
    -- It initialises the GHC session and warnings via 'initGhcMonad'.  Each call
    -- to this function will create a new session which should not be shared among
    -- several threads.
    --
    -- Any errors not handled inside the 'Ghc' action are propagated as IO
    -- exceptions.

    runGhc :: Maybe FilePath  -- ^ See argument to 'initGhcMonad'.
           -> Ghc a           -- ^ The action to perform.
           -> IO a
    runGhc mb_top_dir ghc = do
      ref <- newIORef (panic "empty session")
      let session = Session ref
      flip unGhc session $ do
        initGhcMonad mb_top_dir
        ghc
      -- XXX: unregister interrupt handlers here?

    -- | Run function for 'GhcT' monad transformer.
    --
    -- It initialises the GHC session and warnings via 'initGhcMonad'.  Each call
    -- to this function will create a new session which should not be shared among
    -- several threads.

    runGhcT :: (ExceptionMonad m, Functor m, MonadIO m) =>
               Maybe FilePath  -- ^ See argument to 'initGhcMonad'.
            -> GhcT m a        -- ^ The action to perform.
            -> m a
    runGhcT mb_top_dir ghct = do
      ref <- liftIO $ newIORef (panic "empty session")
      let session = Session ref
      flip unGhcT session $ do
        initGhcMonad mb_top_dir
        ghct

    -- | Initialise a GHC session.
    --
    -- If you implement a custom 'GhcMonad' you must call this function in the
    -- monad run function.  It will initialise the session variable and clear all
    -- warnings.
    --
    -- The first argument should point to the directory where GHC's library files
    -- reside.  More precisely, this should be the output of @ghc --print-libdir@
    -- of the version of GHC the module using this API is compiled with.  For
    -- portability, you should use the @ghc-paths@ package, available at
    -- <http://hackage.haskell.org/package/ghc-paths>.

    initGhcMonad :: GhcMonad m => Maybe FilePath -> m ()
    initGhcMonad mb_top_dir
      = do { env <- liftIO $
                    do { installSignalHandlers  -- catch ^C
                       ; initStaticOpts
                       ; mySettings <- initSysTools mb_top_dir
                       ; dflags <- initDynFlags (defaultDynFlags mySettings)
                       ; checkBrokenTablesNextToCode dflags
                       ; setUnsafeGlobalDynFlags dflags
                          -- c.f. DynFlags.parseDynamicFlagsFull, which
                          -- creates DynFlags and sets the UnsafeGlobalDynFlags
                       ; newHscEnv dflags }
           ; setSession env }

    -- | The binutils linker on ARM emits unnecessary R_ARM_COPY relocations which
    -- breaks tables-next-to-code in dynamically linked modules. This
    -- check should be more selective but there is currently no released
    -- version where this bug is fixed.
    -- See https://sourceware.org/bugzilla/show_bug.cgi?id=16177 and
    -- https://ghc.haskell.org/trac/ghc/ticket/4210#comment:29
    checkBrokenTablesNextToCode :: MonadIO m => DynFlags -> m ()
    checkBrokenTablesNextToCode dflags
      = do { broken <- checkBrokenTablesNextToCode' dflags
           ; when broken
             $ do { _ <- liftIO $ throwIO $ mkApiErr dflags invalidLdErr
                  ; fail "unsupported linker"
                  }
           }
      where
        invalidLdErr = text "Tables-next-to-code not supported on ARM" <+>
                       text "when using binutils ld (please see:" <+>
                       text "https://sourceware.org/bugzilla/show_bug.cgi?id=16177)"

    checkBrokenTablesNextToCode' :: MonadIO m => DynFlags -> m Bool
    checkBrokenTablesNextToCode' dflags
      | not (isARM arch)              = return False
      | WayDyn `notElem` ways dflags  = return False
      | not (tablesNextToCode dflags) = return False
      | otherwise                     = do
        linkerInfo <- liftIO $ getLinkerInfo dflags
        case linkerInfo of
          GnuLD _  -> return True
          _        -> return False
      where platform = targetPlatform dflags
            arch = platformArch platform

    -- %************************************************************************
    -- %*                                                                      *
    --             Flags & settings
    -- %*                                                                      *
    -- %************************************************************************

    -- $DynFlags
    --
    -- The GHC session maintains two sets of 'DynFlags':
    --
    --   * The "interactive" @DynFlags@, which are used for everything
    --     related to interactive evaluation, including 'runStmt',
    --     'runDecls', 'exprType', 'lookupName' and so on (everything
    --     under \"Interactive evaluation\" in this module).
    --
    --   * The "program" @DynFlags@, which are used when loading
    --     whole modules with 'load'
    --
    -- 'setInteractiveDynFlags', 'getInteractiveDynFlags' work with the
    -- interactive @DynFlags@.
    --
    -- 'setProgramDynFlags', 'getProgramDynFlags' work with the
    -- program @DynFlags@.
    --
    -- 'setSessionDynFlags' sets both @DynFlags@, and 'getSessionDynFlags'
    -- retrieves the program @DynFlags@ (for backwards compatibility).

    -- | Updates both the interactive and program DynFlags in a Session.
    -- This also reads the package database (unless it has already been
    -- read), and prepares the compilers knowledge about packages.  It can
    -- be called again to load new packages: just add new package flags to
    -- (packageFlags dflags).
    --
    -- Returns a list of new packages that may need to be linked in using
    -- the dynamic linker (see 'linkPackages') as a result of new package
    -- flags.  If you are not doing linking or doing static linking, you
    -- can ignore the list of packages returned.
    --
    setSessionDynFlags :: GhcMonad m => DynFlags -> m [PackageKey]
    setSessionDynFlags dflags = do
      dflags' <- checkNewDynFlags dflags
      (dflags'', preload) <- liftIO $ initPackages dflags'
      modifySession $ \h -> h{ hsc_dflags = dflags''
                             , hsc_IC = (hsc_IC h){ ic_dflags = dflags'' } }
      invalidateModSummaryCache
      return preload

    -- | Sets the program 'DynFlags'.
    setProgramDynFlags :: GhcMonad m => DynFlags -> m [PackageKey]
    setProgramDynFlags dflags = do
      dflags' <- checkNewDynFlags dflags
      (dflags'', preload) <- liftIO $ initPackages dflags'
      modifySession $ \h -> h{ hsc_dflags = dflags'' }
      invalidateModSummaryCache
      return preload

    -- When changing the DynFlags, we want the changes to apply to future
    -- loads, but without completely discarding the program.  But the
    -- DynFlags are cached in each ModSummary in the hsc_mod_graph, so
    -- after a change to DynFlags, the changes would apply to new modules
    -- but not existing modules; this seems undesirable.
    --
    -- Furthermore, the GHC API client might expect that changing
    -- log_action would affect future compilation messages, but for those
    -- modules we have cached ModSummaries for, we'll continue to use the
    -- old log_action.  This is definitely wrong (#7478).
    --
    -- Hence, we invalidate the ModSummary cache after changing the
    -- DynFlags.  We do this by tweaking the date on each ModSummary, so
    -- that the next downsweep will think that all the files have changed
    -- and preprocess them again.  This won't necessarily cause everything
    -- to be recompiled, because by the time we check whether we need to
    -- recopmile a module, we'll have re-summarised the module and have a
    -- correct ModSummary.
    --
    invalidateModSummaryCache :: GhcMonad m => m ()
    invalidateModSummaryCache =
      modifySession $ \h -> h { hsc_mod_graph = map inval (hsc_mod_graph h) }
     where
      inval ms = ms { ms_hs_date = addUTCTime (-1) (ms_hs_date ms) }

    -- | Returns the program 'DynFlags'.
    getProgramDynFlags :: GhcMonad m => m DynFlags
    getProgramDynFlags = getSessionDynFlags

    -- | Set the 'DynFlags' used to evaluate interactive expressions.
    -- Note: this cannot be used for changes to packages.  Use
    -- 'setSessionDynFlags', or 'setProgramDynFlags' and then copy the
    -- 'pkgState' into the interactive @DynFlags@.
    setInteractiveDynFlags :: GhcMonad m => DynFlags -> m ()
    setInteractiveDynFlags dflags = do
      dflags' <- checkNewDynFlags dflags
      modifySession $ \h -> h{ hsc_IC = (hsc_IC h) { ic_dflags = dflags' }}

    -- | Get the 'DynFlags' used to evaluate interactive expressions.
    getInteractiveDynFlags :: GhcMonad m => m DynFlags
    getInteractiveDynFlags = withSession $ \h -> return (ic_dflags (hsc_IC h))

    parseDynamicFlags :: MonadIO m =>
                         DynFlags -> [Located String]
                      -> m (DynFlags, [Located String], [Located String])
    parseDynamicFlags = parseDynamicFlagsCmdLine

    {- Note [GHCi and -O]
    ~~~~~~~~~~~~~~~~~~~~~
    When using optimization, the compiler can introduce several things
    (such as unboxed tuples) into the intermediate code, which GHCi later
    chokes on since the bytecode interpreter can't handle this (and while
    this is arguably a bug these aren't handled, there are no plans to fix
    it.)

    While the driver pipeline always checks for this particular erroneous
    combination when parsing flags, we also need to check when we update
    the flags; this is because API clients may parse flags but update the
    DynFlags afterwords, before finally running code inside a session (see
    T10052 and #10052).
    -}

    -- | Checks the set of new DynFlags for possibly erroneous option
    -- combinations when invoking 'setSessionDynFlags' and friends, and if
    -- found, returns a fixed copy (if possible).
    checkNewDynFlags :: MonadIO m => DynFlags -> m DynFlags
    checkNewDynFlags dflags
      -- See Note [GHCi and -O]
      | Left e <- checkOptLevel (optLevel dflags) dflags
        = do liftIO $ warningMsg dflags (text e)
             return (dflags { optLevel = 0 })
      | otherwise
        = return dflags

    -- %************************************************************************
    -- %*                                                                      *
    --             Setting, getting, and modifying the targets
    -- %*                                                                      *
    -- %************************************************************************

    -- ToDo: think about relative vs. absolute file paths. And what
    -- happens when the current directory changes.

    -- | Sets the targets for this session.  Each target may be a module name
    -- or a filename.  The targets correspond to the set of root modules for
    -- the program\/library.  Unloading the current program is achieved by
    -- setting the current set of targets to be empty, followed by 'load'.
    setTargets :: GhcMonad m => [Target] -> m ()
    setTargets targets = modifySession (\h -> h{ hsc_targets = targets })

    -- | Returns the current set of targets
    getTargets :: GhcMonad m => m [Target]
    getTargets = withSession (return . hsc_targets)

    -- | Add another target.
    addTarget :: GhcMonad m => Target -> m ()
    addTarget target
      = modifySession (\h -> h{ hsc_targets = target : hsc_targets h })

    -- | Remove a target
    removeTarget :: GhcMonad m => TargetId -> m ()
    removeTarget target_id
      = modifySession (\h -> h{ hsc_targets = filter (hsc_targets h) })
      where
       filter targets = [ t | t@(Target id _ _) <- targets, id /= target_id ]

    -- | Attempts to guess what Target a string refers to.  This function
    -- implements the @--make@/GHCi command-line syntax for filenames:
    --
    --   - if the string looks like a Haskell source filename, then interpret it
    --     as such
    --
    --   - if adding a .hs or .lhs suffix yields the name of an existing file,
    --     then use that
    --
    --   - otherwise interpret the string as a module name
    --
    guessTarget :: GhcMonad m => String -> Maybe Phase -> m Target
    guessTarget str (Just phase)
       = return (Target (TargetFile str (Just phase)) True Nothing)
    guessTarget str Nothing
       | isHaskellSrcFilename file
       = return (target (TargetFile file Nothing))
       | otherwise
       = do exists <- liftIO $ doesFileExist hs_file
            if exists
               then return (target (TargetFile hs_file Nothing))
               else do
            exists <- liftIO $ doesFileExist lhs_file
            if exists
               then return (target (TargetFile lhs_file Nothing))
               else do
            if looksLikeModuleName file
               then return (target (TargetModule (mkModuleName file)))
               else do
            dflags <- getDynFlags
            liftIO $ throwGhcExceptionIO
                     (ProgramError (showSDoc dflags $
                     text "target" <+> quotes (text file) <+>
                     text "is not a module name or a source file"))
         where
             (file,obj_allowed)
                    | '*':rest <- str = (rest, False)
                    | otherwise       = (str,  True)

             hs_file  = file <.> "hs"
             lhs_file = file <.> "lhs"

             target tid = Target tid obj_allowed Nothing

    -- | Inform GHC that the working directory has changed.  GHC will flush
    -- its cache of module locations, since it may no longer be valid.
    --
    -- Note: Before changing the working directory make sure all threads running
    -- in the same session have stopped.  If you change the working directory,
    -- you should also unload the current program (set targets to empty,
    -- followed by load).
    workingDirectoryChanged :: GhcMonad m => m ()
    workingDirectoryChanged = withSession $ (liftIO . flushFinderCaches)

    -- %************************************************************************
    -- %*                                                                      *
    --             Running phases one at a time
    -- %*                                                                      *
    -- %************************************************************************

    class ParsedMod m where
      modSummary   :: m -> ModSummary
      parsedSource :: m -> ParsedSource

    class ParsedMod m => TypecheckedMod m where
      renamedSource     :: m -> Maybe RenamedSource
      typecheckedSource :: m -> TypecheckedSource
      moduleInfo        :: m -> ModuleInfo
      tm_internals      :: m -> (TcGblEnv, ModDetails)
            -- ToDo: improvements that could be made here:
            --  if the module succeeded renaming but not typechecking,
            --  we can still get back the GlobalRdrEnv and exports, so
            --  perhaps the ModuleInfo should be split up into separate
            --  fields.

    class TypecheckedMod m => DesugaredMod m where
      coreModule :: m -> ModGuts

    -- | The result of successful parsing.
    data ParsedModule =
      ParsedModule { pm_mod_summary   :: ModSummary
                   , pm_parsed_source :: ParsedSource
                   , pm_extra_src_files :: [FilePath]
                   , pm_annotations :: ApiAnns }
                   -- See Note [Api annotations] in ApiAnnotation.hs

    instance ParsedMod ParsedModule where
      modSummary m    = pm_mod_summary m
      parsedSource m = pm_parsed_source m

    -- | The result of successful typechecking.  It also contains the parser
    --   result.
    data TypecheckedModule =
      TypecheckedModule { tm_parsed_module       :: ParsedModule
                        , tm_renamed_source      :: Maybe RenamedSource
                        , tm_typechecked_source  :: TypecheckedSource
                        , tm_checked_module_info :: ModuleInfo
                        , tm_internals_          :: (TcGblEnv, ModDetails)
                        }

    instance ParsedMod TypecheckedModule where
      modSummary m   = modSummary (tm_parsed_module m)
      parsedSource m = parsedSource (tm_parsed_module m)

    instance TypecheckedMod TypecheckedModule where
      renamedSource m     = tm_renamed_source m
      typecheckedSource m = tm_typechecked_source m
      moduleInfo m        = tm_checked_module_info m
      tm_internals m      = tm_internals_ m

    -- | The result of successful desugaring (i.e., translation to core).  Also
    --  contains all the information of a typechecked module.
    data DesugaredModule =
      DesugaredModule { dm_typechecked_module :: TypecheckedModule
                      , dm_core_module        :: ModGuts
                 }

    instance ParsedMod DesugaredModule where
      modSummary m   = modSummary (dm_typechecked_module m)
      parsedSource m = parsedSource (dm_typechecked_module m)

    instance TypecheckedMod DesugaredModule where
      renamedSource m     = renamedSource (dm_typechecked_module m)
      typecheckedSource m = typecheckedSource (dm_typechecked_module m)
      moduleInfo m        = moduleInfo (dm_typechecked_module m)
      tm_internals m      = tm_internals_ (dm_typechecked_module m)

    instance DesugaredMod DesugaredModule where
      coreModule m = dm_core_module m

    type ParsedSource      = Located (HsModule RdrName)
    type RenamedSource     = (HsGroup Name, [LImportDecl Name], Maybe [LIE Name],
                              Maybe LHsDocString)
    type TypecheckedSource = LHsBinds Id

    -- NOTE:
    --   - things that aren't in the output of the typechecker right now:
    --     - the export list
    --     - the imports
    --     - type signatures
    --     - type/data/newtype declarations
    --     - class declarations
    --     - instances
    --   - extra things in the typechecker's output:
    --     - default methods are turned into top-level decls.
    --     - dictionary bindings

    -- | Return the 'ModSummary' of a module with the given name.
    --
    -- The module must be part of the module graph (see 'hsc_mod_graph' and
    -- 'ModuleGraph').  If this is not the case, this function will throw a
    -- 'GhcApiError'.
    --
    -- This function ignores boot modules and requires that there is only one
    -- non-boot module with the given name.
    getModSummary :: GhcMonad m => ModuleName -> m ModSummary
    getModSummary mod = do
       mg <- liftM hsc_mod_graph getSession
       case [ ms | ms <- mg, ms_mod_name ms == mod, not (isBootSummary ms) ] of
         [] -> do dflags <- getDynFlags
                  liftIO $ throwIO $ mkApiErr dflags (text "Module not part of module graph")
         [ms] -> return ms
         multiple -> do dflags <- getDynFlags
                        liftIO $ throwIO $ mkApiErr dflags (text "getModSummary is ambiguous: " <+> ppr multiple)

    -- | Parse a module.
    --
    -- Throws a 'SourceError' on parse error.
    parseModule :: GhcMonad m => ModSummary -> m ParsedModule
    parseModule ms = do
       hsc_env <- getSession
       let hsc_env_tmp = hsc_env { hsc_dflags = ms_hspp_opts ms }
       hpm <- liftIO $ hscParse hsc_env_tmp ms
       return (ParsedModule ms (hpm_module hpm) (hpm_src_files hpm)
                               (hpm_annotations hpm))
                   -- See Note [Api annotations] in ApiAnnotation.hs

    -- | Typecheck and rename a parsed module.
    --
    -- Throws a 'SourceError' if either fails.
    typecheckModule :: GhcMonad m => ParsedModule -> m TypecheckedModule
    typecheckModule pmod = do
     let ms = modSummary pmod
     hsc_env <- getSession
     let hsc_env_tmp = hsc_env { hsc_dflags = ms_hspp_opts ms }
     (tc_gbl_env, rn_info)
           <- liftIO $ hscTypecheckRename hsc_env_tmp ms $
                          HsParsedModule { hpm_module = parsedSource pmod,
                                           hpm_src_files = pm_extra_src_files pmod,
                                           hpm_annotations = pm_annotations pmod }
     details <- liftIO $ makeSimpleDetails hsc_env_tmp tc_gbl_env
     safe    <- liftIO $ finalSafeMode (ms_hspp_opts ms) tc_gbl_env
     return $
         TypecheckedModule {
           tm_internals_          = (tc_gbl_env, details),
           tm_parsed_module       = pmod,
           tm_renamed_source      = rn_info,
           tm_typechecked_source  = tcg_binds tc_gbl_env,
           tm_checked_module_info =
             ModuleInfo {
               minf_type_env  = md_types details,
               minf_exports   = availsToNameSet $ md_exports details,
               minf_rdr_env   = Just (tcg_rdr_env tc_gbl_env),
               minf_instances = md_insts details,
               minf_iface     = Nothing,
               minf_safe      = safe
    #ifdef GHCI
              ,minf_modBreaks = emptyModBreaks
    #endif
             }}

    -- | Desugar a typechecked module.
    desugarModule :: GhcMonad m => TypecheckedModule -> m DesugaredModule
    desugarModule tcm = do
     let ms = modSummary tcm
     let (tcg, _) = tm_internals tcm
     hsc_env <- getSession
     let hsc_env_tmp = hsc_env { hsc_dflags = ms_hspp_opts ms }
     guts <- liftIO $ hscDesugar hsc_env_tmp ms tcg
     return $
         DesugaredModule {
           dm_typechecked_module = tcm,
           dm_core_module        = guts
         }

    -- | Load a module.  Input doesn't need to be desugared.
    --
    -- A module must be loaded before dependent modules can be typechecked.  This
    -- always includes generating a 'ModIface' and, depending on the
    -- 'DynFlags.hscTarget', may also include code generation.
    --
    -- This function will always cause recompilation and will always overwrite
    -- previous compilation results (potentially files on disk).
    --
    loadModule :: (TypecheckedMod mod, GhcMonad m) => mod -> m mod
    loadModule tcm = do
       let ms = modSummary tcm
       let mod = ms_mod_name ms
       let loc = ms_location ms
       let (tcg, _details) = tm_internals tcm

       mb_linkable <- case ms_obj_date ms of
                         Just t | t > ms_hs_date ms  -> do
                             l <- liftIO $ findObjectLinkable (ms_mod ms)
                                                      (ml_obj_file loc) t
                             return (Just l)
                         _otherwise -> return Nothing

       let source_modified | isNothing mb_linkable = SourceModified
                           | otherwise             = SourceUnmodified
                           -- we can't determine stability here

       -- compile doesn't change the session
       hsc_env <- getSession
       mod_info <- liftIO $ compileOne' (Just tcg) Nothing
                                        hsc_env ms 1 1 Nothing mb_linkable
                                        source_modified

       modifySession $ \e -> e{ hsc_HPT = addToUFM (hsc_HPT e) mod mod_info }
       return tcm

    -- %************************************************************************
    -- %*                                                                      *
    --             Dealing with Core
    -- %*                                                                      *
    -- %************************************************************************

    -- | A CoreModule consists of just the fields of a 'ModGuts' that are needed for
    -- the 'GHC.compileToCoreModule' interface.
    data CoreModule
      = CoreModule {
          -- | Module name
          cm_module   :: !Module,
          -- | Type environment for types declared in this module
          cm_types    :: !TypeEnv,
          -- | Declarations
          cm_binds    :: CoreProgram,
          -- | Safe Haskell mode
          cm_safe     :: SafeHaskellMode
        }

    instance Outputable CoreModule where
       ppr (CoreModule {cm_module = mn, cm_types = te, cm_binds = cb,
                        cm_safe = sf})
        = text "%module" <+> ppr mn <+> parens (ppr sf) <+> ppr te
          $$ vcat (map ppr cb)

    -- | This is the way to get access to the Core bindings corresponding
    -- to a module. 'compileToCore' parses, typechecks, and
    -- desugars the module, then returns the resulting Core module (consisting of
    -- the module name, type declarations, and function declarations) if
    -- successful.
    compileToCoreModule :: GhcMonad m => FilePath -> m CoreModule
    compileToCoreModule = compileCore False

    -- | Like compileToCoreModule, but invokes the simplifier, so
    -- as to return simplified and tidied Core.
    compileToCoreSimplified :: GhcMonad m => FilePath -> m CoreModule
    compileToCoreSimplified = compileCore True

    compileCore :: GhcMonad m => Bool -> FilePath -> m CoreModule
    compileCore simplify fn = do
       -- First, set the target to the desired filename
       target <- guessTarget fn Nothing
       addTarget target
       _ <- load LoadAllTargets
       -- Then find dependencies
       modGraph <- depanal [] True
       case find ((== fn) . msHsFilePath) modGraph of
         Just modSummary -> do
           -- Now we have the module name;
           -- parse, typecheck and desugar the module
           mod_guts <- coreModule `fmap`
                          -- TODO: space leaky: call hsc* directly?
                          (desugarModule =<< typecheckModule =<< parseModule modSummary)
           liftM (gutsToCoreModule (mg_safe_haskell mod_guts)) $
             if simplify
              then do
                 -- If simplify is true: simplify (hscSimplify), then tidy
                 -- (tidyProgram).
                 hsc_env <- getSession
                 simpl_guts <- liftIO $ hscSimplify hsc_env mod_guts
                 tidy_guts <- liftIO $ tidyProgram hsc_env simpl_guts
                 return $ Left tidy_guts
              else
                 return $ Right mod_guts

         Nothing -> panic "compileToCoreModule: target FilePath not found in\
                               module dependency graph"
      where -- two versions, based on whether we simplify (thus run tidyProgram,
            -- which returns a (CgGuts, ModDetails) pair, or not (in which case
            -- we just have a ModGuts.
            gutsToCoreModule :: SafeHaskellMode
                             -> Either (CgGuts, ModDetails) ModGuts
                             -> CoreModule
            gutsToCoreModule safe_mode (Left (cg, md)) = CoreModule {
              cm_module = cg_module cg,
              cm_types  = md_types md,
              cm_binds  = cg_binds cg,
              cm_safe   = safe_mode
            }
            gutsToCoreModule safe_mode (Right mg) = CoreModule {
              cm_module  = mg_module mg,
              cm_types   = typeEnvFromEntities (bindersOfBinds (mg_binds mg))
                                               (mg_tcs mg)
                                               (mg_fam_insts mg),
              cm_binds   = mg_binds mg,
              cm_safe    = safe_mode
             }

    -- %************************************************************************
    -- %*                                                                      *
    --             Inspecting the session
    -- %*                                                                      *
    -- %************************************************************************

    -- | Get the module dependency graph.
    getModuleGraph :: GhcMonad m => m ModuleGraph -- ToDo: DiGraph ModSummary
    getModuleGraph = liftM hsc_mod_graph getSession

    -- | Determines whether a set of modules requires Template Haskell.
    --
    -- Note that if the session's 'DynFlags' enabled Template Haskell when
    -- 'depanal' was called, then each module in the returned module graph will
    -- have Template Haskell enabled whether it is actually needed or not.
    needsTemplateHaskell :: ModuleGraph -> Bool
    needsTemplateHaskell ms =
        any (xopt Opt_TemplateHaskell . ms_hspp_opts) ms

    -- | Return @True@ <==> module is loaded.
    isLoaded :: GhcMonad m => ModuleName -> m Bool
    isLoaded m = withSession $ \hsc_env ->
      return $! isJust (lookupUFM (hsc_HPT hsc_env) m)

    -- | Return the bindings for the current interactive session.
    getBindings :: GhcMonad m => m [TyThing]
    getBindings = withSession $ \hsc_env ->
        return $ icInScopeTTs $ hsc_IC hsc_env

    -- | Return the instances for the current interactive session.
    getInsts :: GhcMonad m => m ([ClsInst], [FamInst])
    getInsts = withSession $ \hsc_env ->
        return $ ic_instances (hsc_IC hsc_env)

    getPrintUnqual :: GhcMonad m => m PrintUnqualified
    getPrintUnqual = withSession $ \hsc_env ->
      return (icPrintUnqual (hsc_dflags hsc_env) (hsc_IC hsc_env))

    -- | Container for information about a 'Module'.
    data ModuleInfo = ModuleInfo {
            minf_type_env  :: TypeEnv,
            minf_exports   :: NameSet, -- ToDo, [AvailInfo] like ModDetails?
            minf_rdr_env   :: Maybe GlobalRdrEnv,   -- Nothing for a compiled/package mod
            minf_instances :: [ClsInst],
            minf_iface     :: Maybe ModIface,
            minf_safe      :: SafeHaskellMode
    #ifdef GHCI
           ,minf_modBreaks :: ModBreaks
    #endif
      }
            -- We don't want HomeModInfo here, because a ModuleInfo applies
            -- to package modules too.

    -- | Request information about a loaded 'Module'
    getModuleInfo :: GhcMonad m => Module -> m (Maybe ModuleInfo)  -- XXX: Maybe X
    getModuleInfo mdl = withSession $ \hsc_env -> do
      let mg = hsc_mod_graph hsc_env
      if mdl `elem` map ms_mod mg
            then liftIO $ getHomeModuleInfo hsc_env mdl
            else do
      {- if isHomeModule (hsc_dflags hsc_env) mdl
            then return Nothing
            else -} liftIO $ getPackageModuleInfo hsc_env mdl
       -- ToDo: we don't understand what the following comment means.
       --    (SDM, 19/7/2011)
       -- getPackageModuleInfo will attempt to find the interface, so
       -- we don't want to call it for a home module, just in case there
       -- was a problem loading the module and the interface doesn't
       -- exist... hence the isHomeModule test here.  (ToDo: reinstate)

    getPackageModuleInfo :: HscEnv -> Module -> IO (Maybe ModuleInfo)
    #ifdef GHCI
    getPackageModuleInfo hsc_env mdl
      = do  eps <- hscEPS hsc_env
            iface <- hscGetModuleInterface hsc_env mdl
            let
                avails = mi_exports iface
                names  = availsToNameSet avails
                pte    = eps_PTE eps
                tys    = [ ty | name <- concatMap availNames avails,
                                Just ty <- [lookupTypeEnv pte name] ]
            --
            return (Just (ModuleInfo {
                            minf_type_env  = mkTypeEnv tys,
                            minf_exports   = names,
                            minf_rdr_env   = Just $! availsToGlobalRdrEnv (moduleName mdl) avails,
                            minf_instances = error "getModuleInfo: instances for package module unimplemented",
                            minf_iface     = Just iface,
                            minf_safe      = getSafeMode $ mi_trust iface,
                            minf_modBreaks = emptyModBreaks
                    }))
    #else
    -- bogusly different for non-GHCI (ToDo)
    getPackageModuleInfo _hsc_env _mdl = do
      return Nothing
    #endif

    getHomeModuleInfo :: HscEnv -> Module -> IO (Maybe ModuleInfo)
    getHomeModuleInfo hsc_env mdl =
      case lookupUFM (hsc_HPT hsc_env) (moduleName mdl) of
        Nothing  -> return Nothing
        Just hmi -> do
          let details = hm_details hmi
              iface   = hm_iface hmi
          return (Just (ModuleInfo {
                            minf_type_env  = md_types details,
                            minf_exports   = availsToNameSet (md_exports details),
                            minf_rdr_env   = mi_globals $! hm_iface hmi,
                            minf_instances = md_insts details,
                            minf_iface     = Just iface,
                            minf_safe      = getSafeMode $ mi_trust iface
    #ifdef GHCI
                           ,minf_modBreaks = getModBreaks hmi
    #endif
                            }))

    -- | The list of top-level entities defined in a module
    modInfoTyThings :: ModuleInfo -> [TyThing]
    modInfoTyThings minf = typeEnvElts (minf_type_env minf)

    modInfoTopLevelScope :: ModuleInfo -> Maybe [Name]
    modInfoTopLevelScope minf
      = fmap (map gre_name . globalRdrEnvElts) (minf_rdr_env minf)

    modInfoExports :: ModuleInfo -> [Name]
    modInfoExports minf = nameSetElems $! minf_exports minf

    -- | Returns the instances defined by the specified module.
    -- Warning: currently unimplemented for package modules.
    modInfoInstances :: ModuleInfo -> [ClsInst]
    modInfoInstances = minf_instances

    modInfoIsExportedName :: ModuleInfo -> Name -> Bool
    modInfoIsExportedName minf name = elemNameSet name (minf_exports minf)

    mkPrintUnqualifiedForModule :: GhcMonad m =>
                                   ModuleInfo
                                -> m (Maybe PrintUnqualified) -- XXX: returns a Maybe X
    mkPrintUnqualifiedForModule minf = withSession $ \hsc_env -> do
      return (fmap (mkPrintUnqualified (hsc_dflags hsc_env)) (minf_rdr_env minf))

    modInfoLookupName :: GhcMonad m =>
                         ModuleInfo -> Name
                      -> m (Maybe TyThing) -- XXX: returns a Maybe X
    modInfoLookupName minf name = withSession $ \hsc_env -> do
       case lookupTypeEnv (minf_type_env minf) name of
         Just tyThing -> return (Just tyThing)
         Nothing      -> do
           eps <- liftIO $ readIORef (hsc_EPS hsc_env)
           return $! lookupType (hsc_dflags hsc_env)
                                (hsc_HPT hsc_env) (eps_PTE eps) name

    modInfoIface :: ModuleInfo -> Maybe ModIface
    modInfoIface = minf_iface

    -- | Retrieve module safe haskell mode
    modInfoSafe :: ModuleInfo -> SafeHaskellMode
    modInfoSafe = minf_safe

    #ifdef GHCI
    modInfoModBreaks :: ModuleInfo -> ModBreaks
    modInfoModBreaks = minf_modBreaks
    #endif

    isDictonaryId :: Id -> Bool
    isDictonaryId id
      = case tcSplitSigmaTy (idType id) of { (_tvs, _theta, tau) -> isDictTy tau }

    -- | Looks up a global name: that is, any top-level name in any
    -- visible module.  Unlike 'lookupName', lookupGlobalName does not use
    -- the interactive context, and therefore does not require a preceding
    -- 'setContext'.
    lookupGlobalName :: GhcMonad m => Name -> m (Maybe TyThing)
    lookupGlobalName name = withSession $ \hsc_env -> do
       liftIO $ lookupTypeHscEnv hsc_env name

    findGlobalAnns :: (GhcMonad m, Typeable a) => ([Word8] -> a) -> AnnTarget Name -> m [a]
    findGlobalAnns deserialize target = withSession $ \hsc_env -> do
        ann_env <- liftIO $ prepareAnnotations hsc_env Nothing
        return (findAnns deserialize ann_env target)

    #ifdef GHCI
    -- | get the GlobalRdrEnv for a session
    getGRE :: GhcMonad m => m GlobalRdrEnv
    getGRE = withSession $ \hsc_env-> return $ ic_rn_gbl_env (hsc_IC hsc_env)
    #endif

    -- -----------------------------------------------------------------------------

    {- ToDo: Move the primary logic here to compiler/main/Packages.lhs
    -- | Return all /external/ modules available in the package database.
    -- Modules from the current session (i.e., from the 'HomePackageTable') are
    -- not included.  This includes module names which are reexported by packages.
    packageDbModules :: GhcMonad m =>
                        Bool  -- ^ Only consider exposed packages.
                     -> m [Module]
    packageDbModules only_exposed = do
       dflags <- getSessionDynFlags
       let pkgs = eltsUFM (pkgIdMap (pkgState dflags))
       return $
         [ mkModule pid modname
         | p <- pkgs
         , not only_exposed || exposed p
         , let pid = packageConfigId p
         , modname <- exposedModules p
                   ++ map exportName (reexportedModules p) ]
                   -}

    -- -----------------------------------------------------------------------------
    -- Misc exported utils

    dataConType :: DataCon -> Type
    dataConType dc = idType (dataConWrapId dc)

    -- | print a 'NamedThing', adding parentheses if the name is an operator.
    pprParenSymName :: NamedThing a => a -> SDoc
    pprParenSymName a = parenSymOcc (getOccName a) (ppr (getName a))

    -- ----------------------------------------------------------------------------

    #if 0

    -- ToDo:
    --   - Data and Typeable instances for HsSyn.

    -- ToDo: check for small transformations that happen to the syntax in
    -- the typechecker (eg. -e ==> negate e, perhaps for fromIntegral)

    -- ToDo: maybe use TH syntax instead of IfaceSyn?  There's already a way
    -- to get from TyCons, Ids etc. to TH syntax (reify).

    -- :browse will use either lm_toplev or inspect lm_interface, depending
    -- on whether the module is interpreted or not.

    #endif

    -- Extract the filename, stringbuffer content and dynflags associed to a module
    --
    -- XXX: Explain pre-conditions
    getModuleSourceAndFlags :: GhcMonad m => Module -> m (String, StringBuffer, DynFlags)
    getModuleSourceAndFlags mod = do
      m <- getModSummary (moduleName mod)
      case ml_hs_file $ ms_location m of
        Nothing -> do dflags <- getDynFlags
                      liftIO $ throwIO $ mkApiErr dflags (text "No source available for module " <+> ppr mod)
        Just sourceFile -> do
            source <- liftIO $ hGetStringBuffer sourceFile
            return (sourceFile, source, ms_hspp_opts m)

    -- | Return module source as token stream, including comments.
    --
    -- The module must be in the module graph and its source must be available.
    -- Throws a 'HscTypes.SourceError' on parse error.
    getTokenStream :: GhcMonad m => Module -> m [Located Token]
    getTokenStream mod = do
      (sourceFile, source, flags) <- getModuleSourceAndFlags mod
      let startLoc = mkRealSrcLoc (mkFastString sourceFile) 1 1
      case lexTokenStream source startLoc flags of
        POk _ ts  -> return ts
        PFailed span err ->
            do dflags <- getDynFlags
               liftIO $ throwIO $ mkSrcErr (unitBag $ mkPlainErrMsg dflags span err)

    -- | Give even more information on the source than 'getTokenStream'
    -- This function allows reconstructing the source completely with
    -- 'showRichTokenStream'.
    getRichTokenStream :: GhcMonad m => Module -> m [(Located Token, String)]
    getRichTokenStream mod = do
      (sourceFile, source, flags) <- getModuleSourceAndFlags mod
      let startLoc = mkRealSrcLoc (mkFastString sourceFile) 1 1
      case lexTokenStream source startLoc flags of
        POk _ ts -> return $ addSourceToTokens startLoc source ts
        PFailed span err ->
            do dflags <- getDynFlags
               liftIO $ throwIO $ mkSrcErr (unitBag $ mkPlainErrMsg dflags span err)

    -- | Given a source location and a StringBuffer corresponding to this
    -- location, return a rich token stream with the source associated to the
    -- tokens.
    addSourceToTokens :: RealSrcLoc -> StringBuffer -> [Located Token]
                      -> [(Located Token, String)]
    addSourceToTokens _ _ [] = []
    addSourceToTokens loc buf (t@(L span _) : ts)
        = case span of
          UnhelpfulSpan _ -> (t,"") : addSourceToTokens loc buf ts
          RealSrcSpan s   -> (t,str) : addSourceToTokens newLoc newBuf ts
            where
              (newLoc, newBuf, str) = go "" loc buf
              start = realSrcSpanStart s
              end = realSrcSpanEnd s
              go acc loc buf | loc < start = go acc nLoc nBuf
                             | start <= loc && loc < end = go (ch:acc) nLoc nBuf
                             | otherwise = (loc, buf, reverse acc)
                  where (ch, nBuf) = nextChar buf
                        nLoc = advanceSrcLoc loc ch

    -- | Take a rich token stream such as produced from 'getRichTokenStream' and
    -- return source code almost identical to the original code (except for
    -- insignificant whitespace.)
    showRichTokenStream :: [(Located Token, String)] -> String
    showRichTokenStream ts = go startLoc ts ""
        where sourceFile = getFile $ map (getLoc . fst) ts
              getFile [] = panic "showRichTokenStream: No source file found"
              getFile (UnhelpfulSpan _ : xs) = getFile xs
              getFile (RealSrcSpan s : _) = srcSpanFile s
              startLoc = mkRealSrcLoc sourceFile 1 1
              go _ [] = id
              go loc ((L span _, str):ts)
                  = case span of
                    UnhelpfulSpan _ -> go loc ts
                    RealSrcSpan s
                     | locLine == tokLine -> ((replicate (tokCol - locCol) ' ') ++)
                                           . (str ++)
                                           . go tokEnd ts
                     | otherwise -> ((replicate (tokLine - locLine) '\n') ++)
                                   . ((replicate (tokCol - 1) ' ') ++)
                                  . (str ++)
                                  . go tokEnd ts
                      where (locLine, locCol) = (srcLocLine loc, srcLocCol loc)
                            (tokLine, tokCol) = (srcSpanStartLine s, srcSpanStartCol s)
                            tokEnd = realSrcSpanEnd s

    -- -----------------------------------------------------------------------------
    -- Interactive evaluation

    -- | Takes a 'ModuleName' and possibly a 'PackageKey', and consults the
    -- filesystem and package database to find the corresponding 'Module',
    -- using the algorithm that is used for an @import@ declaration.
    findModule :: GhcMonad m => ModuleName -> Maybe FastString -> m Module
    findModule mod_name maybe_pkg = withSession $ \hsc_env -> do
      let
        dflags   = hsc_dflags hsc_env
        this_pkg = thisPackage dflags
      --
      case maybe_pkg of
        Just pkg | fsToPackageKey pkg /= this_pkg && pkg /= fsLit "this" -> liftIO $ do
          res <- findImportedModule hsc_env mod_name maybe_pkg
          case res of
            Found _ m -> return m
            err       -> throwOneError $ noModError dflags noSrcSpan mod_name err
        _otherwise -> do
          home <- lookupLoadedHomeModule mod_name
          case home of
            Just m  -> return m
            Nothing -> liftIO $ do
               res <- findImportedModule hsc_env mod_name maybe_pkg
               case res of
                 Found loc m | modulePackageKey m /= this_pkg -> return m
                             | otherwise -> modNotLoadedError dflags m loc
                 err -> throwOneError $ noModError dflags noSrcSpan mod_name err

    modNotLoadedError :: DynFlags -> Module -> ModLocation -> IO a
    modNotLoadedError dflags m loc = throwGhcExceptionIO $ CmdLineError $ showSDoc dflags $
       text "module is not loaded:" <+>
       quotes (ppr (moduleName m)) <+>
       parens (text (expectJust "modNotLoadedError" (ml_hs_file loc)))

    -- | Like 'findModule', but differs slightly when the module refers to
    -- a source file, and the file has not been loaded via 'load'.  In
    -- this case, 'findModule' will throw an error (module not loaded),
    -- but 'lookupModule' will check to see whether the module can also be
    -- found in a package, and if so, that package 'Module' will be
    -- returned.  If not, the usual module-not-found error will be thrown.
    --
    lookupModule :: GhcMonad m => ModuleName -> Maybe FastString -> m Module
    lookupModule mod_name (Just pkg) = findModule mod_name (Just pkg)
    lookupModule mod_name Nothing = withSession $ \hsc_env -> do
      home <- lookupLoadedHomeModule mod_name
      case home of
        Just m  -> return m
        Nothing -> liftIO $ do
          res <- findExposedPackageModule hsc_env mod_name Nothing
          case res of
            Found _ m -> return m
            err       -> throwOneError $ noModError (hsc_dflags hsc_env) noSrcSpan mod_name err

    lookupLoadedHomeModule :: GhcMonad m => ModuleName -> m (Maybe Module)
    lookupLoadedHomeModule mod_name = withSession $ \hsc_env ->
      case lookupUFM (hsc_HPT hsc_env) mod_name of
        Just mod_info      -> return (Just (mi_module (hm_iface mod_info)))
        _not_a_home_module -> return Nothing

    #ifdef GHCI
    -- | Check that a module is safe to import (according to Safe Haskell).
    --
    -- We return True to indicate the import is safe and False otherwise
    -- although in the False case an error may be thrown first.
    isModuleTrusted :: GhcMonad m => Module -> m Bool
    isModuleTrusted m = withSession $ \hsc_env ->
        liftIO $ hscCheckSafe hsc_env m noSrcSpan

    -- | Return if a module is trusted and the pkgs it depends on to be trusted.
    moduleTrustReqs :: GhcMonad m => Module -> m (Bool, [PackageKey])
    moduleTrustReqs m = withSession $ \hsc_env ->
        liftIO $ hscGetSafe hsc_env m noSrcSpan

    -- | EXPERIMENTAL: DO NOT USE.
    --
    -- Set the monad GHCi lifts user statements into.
    --
    -- Checks that a type (in string form) is an instance of the
    -- @GHC.GHCi.GHCiSandboxIO@ type class. Sets it to be the GHCi monad if it is,
    -- throws an error otherwise.
    {-# WARNING setGHCiMonad "This is experimental! Don't use." #-}
    setGHCiMonad :: GhcMonad m => String -> m ()
    setGHCiMonad name = withSession $ \hsc_env -> do
        ty <- liftIO $ hscIsGHCiMonad hsc_env name
        modifySession $ \s ->
            let ic = (hsc_IC s) { ic_monad = ty }
            in s { hsc_IC = ic }

    getHistorySpan :: GhcMonad m => History -> m SrcSpan
    getHistorySpan h = withSession $ \hsc_env ->
        return $ InteractiveEval.getHistorySpan hsc_env h

    obtainTermFromVal :: GhcMonad m => Int ->  Bool -> Type -> a -> m Term
    obtainTermFromVal bound force ty a = withSession $ \hsc_env ->
        liftIO $ InteractiveEval.obtainTermFromVal hsc_env bound force ty a

    obtainTermFromId :: GhcMonad m => Int -> Bool -> Id -> m Term
    obtainTermFromId bound force id = withSession $ \hsc_env ->
        liftIO $ InteractiveEval.obtainTermFromId hsc_env bound force id

    #endif

    -- | Returns the 'TyThing' for a 'Name'.  The 'Name' may refer to any
    -- entity known to GHC, including 'Name's defined using 'runStmt'.
    lookupName :: GhcMonad m => Name -> m (Maybe TyThing)
    lookupName name =
         withSession $ \hsc_env ->
           liftIO $ hscTcRcLookupName hsc_env name

    -- -----------------------------------------------------------------------------
    -- Pure API

    -- | A pure interface to the module parser.
    --
    parser :: String         -- ^ Haskell module source text (full Unicode is supported)
           -> DynFlags       -- ^ the flags
           -> FilePath       -- ^ the filename (for source locations)
           -> Either ErrorMessages (WarningMessages, Located (HsModule RdrName))

    parser str dflags filename =
       let
           loc  = mkRealSrcLoc (mkFastString filename) 1 1
           buf  = stringToStringBuffer str
       in
       case unP Parser.parseModule (mkPState dflags buf loc) of

         PFailed span err   ->
             Left (unitBag (mkPlainErrMsg dflags span err))

         POk pst rdr_module ->
             let (warns,_) = getMessages pst in
             Right (warns, rdr_module)