InteractiveUI.hs

{-# OPTIONS -fno-cse #-}
-- -fno-cse is needed for GLOBAL_VAR's to behave properly

{-# OPTIONS_GHC -fno-warn-name-shadowing #-}
-----------------------------------------------------------------------------
--
-- GHC Interactive User Interface
--
-- (c) The GHC Team 2005-2006
--
-----------------------------------------------------------------------------

module InteractiveUI ( interactiveUI, ghciWelcomeMsg ) where

#include "HsVersions.h"

import qualified GhciMonad
import GhciMonad hiding (runStmt)
import GhciTags
import Debugger

-- The GHC interface
import qualified GHC hiding (resume, runStmt)
import GHC              ( LoadHowMuch(..), Target(..),  TargetId(..),
                          TyThing(..), Phase,
                          BreakIndex, Resume, SingleStep,
                          Ghc, handleSourceError )
import PprTyThing
import DynFlags

import Packages
-- import PackageConfig
import UniqFM

import HscTypes ( handleFlagWarnings )
import HsImpExp
import qualified RdrName ( getGRE_NameQualifier_maybes ) -- should this come via GHC?
import RdrName (RdrName)
import Outputable       hiding (printForUser, printForUserPartWay)
import Module           -- for ModuleEnv
import Name
import SrcLoc

-- Other random utilities
import CmdLineParser
import Digraph
import BasicTypes hiding (isTopLevel)
import Panic      hiding (showException)
import Config
import StaticFlags
import Linker
import Util
import NameSet
import Maybes		( orElse, expectJust )
import FastString
import Encoding
import Foreign.C

#ifndef mingw32_HOST_OS
import System.Posix hiding (getEnv)
#else
import qualified System.Win32
#endif

import System.Console.Haskeline as Haskeline
import qualified System.Console.Haskeline.Encoding as Encoding
import Control.Monad.Trans

--import SystemExts

import Exception hiding (catch, block, unblock)

-- import Control.Concurrent

import System.FilePath
import qualified Data.ByteString.Char8 as BS
import Data.List
import Data.Maybe
import System.Cmd
import System.Environment
import System.Exit	( exitWith, ExitCode(..) )
import System.Directory
import System.IO
import System.IO.Error as IO
import Data.Char
import Data.Array
import Control.Monad as Monad
import Text.Printf
import Foreign
import GHC.Exts		( unsafeCoerce# )

#if __GLASGOW_HASKELL__ >= 611
import GHC.IO.Exception	( IOErrorType(InvalidArgument) )
import GHC.IO.Handle    ( hFlushAll )
#else
import GHC.IOBase	( IOErrorType(InvalidArgument) )
#endif

import GHC.TopHandler

import Data.IORef	( IORef, readIORef, writeIORef )

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

ghciWelcomeMsg :: String
ghciWelcomeMsg = "GHCi, version " ++ cProjectVersion ++
                 ": http://www.haskell.org/ghc/  :? for help"

cmdName :: Command -> String
cmdName (n,_,_) = n

GLOBAL_VAR(macros_ref, [], [Command])

builtin_commands :: [Command]
builtin_commands = [
  -- Hugs users are accustomed to :e, so make sure it doesn't overlap
  ("?",         keepGoing help,                 noCompletion),
  ("add",       keepGoingPaths addModule,       completeFilename),
  ("abandon",   keepGoing abandonCmd,           noCompletion),
  ("break",     keepGoing breakCmd,             completeIdentifier),
  ("back",      keepGoing backCmd,              noCompletion),
  ("browse",    keepGoing' (browseCmd False),   completeModule),
  ("browse!",   keepGoing' (browseCmd True),    completeModule),
  ("cd",        keepGoing' changeDirectory,     completeFilename),
  ("check",     keepGoing' checkModule,         completeHomeModule),
  ("continue",  keepGoing continueCmd,          noCompletion),
  ("cmd",       keepGoing cmdCmd,               completeExpression),
  ("ctags",     keepGoing createCTagsWithLineNumbersCmd, completeFilename),
  ("ctags!",    keepGoing createCTagsWithRegExesCmd, completeFilename),
  ("def",       keepGoing (defineMacro False),  completeExpression),
  ("def!",      keepGoing (defineMacro True),   completeExpression),
  ("delete",    keepGoing deleteCmd,            noCompletion),
  ("edit",      keepGoing editFile,             completeFilename),
  ("etags",     keepGoing createETagsFileCmd,   completeFilename),
  ("force",     keepGoing forceCmd,             completeExpression),
  ("forward",   keepGoing forwardCmd,           noCompletion),
  ("help",      keepGoing help,                 noCompletion),
  ("history",   keepGoing historyCmd,           noCompletion),
  ("info",      keepGoing' info,                completeIdentifier),
  ("kind",      keepGoing' kindOfType,          completeIdentifier),
  ("load",      keepGoingPaths loadModule_,     completeHomeModuleOrFile),
  ("list",      keepGoing' listCmd,             noCompletion),
  ("module",    keepGoing setContext,           completeModule),
  ("main",      keepGoing runMain,              completeFilename),
  ("print",     keepGoing printCmd,             completeExpression),
  ("quit",      quit,                           noCompletion),
  ("reload",    keepGoing' reloadModule,        noCompletion),
  ("run",       keepGoing runRun,               completeFilename),
  ("set",       keepGoing setCmd,               completeSetOptions),
  ("show",      keepGoing showCmd,              completeShowOptions),
  ("sprint",    keepGoing sprintCmd,            completeExpression),
  ("step",      keepGoing stepCmd,              completeIdentifier),
  ("steplocal", keepGoing stepLocalCmd,         completeIdentifier),
  ("stepmodule",keepGoing stepModuleCmd,        completeIdentifier),
  ("type",      keepGoing' typeOfExpr,          completeExpression),
  ("trace",     keepGoing traceCmd,             completeExpression),
  ("undef",     keepGoing undefineMacro,        completeMacro),
  ("unset",     keepGoing unsetOptions,         completeSetOptions)
  ]


-- We initialize readline (in the interactiveUI function) to use 
-- word_break_chars as the default set of completion word break characters.
-- This can be overridden for a particular command (for example, filename
-- expansion shouldn't consider '/' to be a word break) by setting the third
-- entry in the Command tuple above.
-- 
-- NOTE: in order for us to override the default correctly, any custom entry
-- must be a SUBSET of word_break_chars.
word_break_chars :: String
word_break_chars = let symbols = "!#$%&*+/<=>?@\\^|-~"
                       specials = "(),;[]`{}"
                       spaces = " \t\n"
                   in spaces ++ specials ++ symbols

flagWordBreakChars :: String
flagWordBreakChars = " \t\n"


keepGoing :: (String -> GHCi ()) -> (String -> InputT GHCi Bool)
keepGoing a str = keepGoing' (lift . a) str

keepGoing' :: Monad m => (String -> m ()) -> String -> m Bool
keepGoing' a str = a str >> return False

keepGoingPaths :: ([FilePath] -> InputT GHCi ()) -> (String -> InputT GHCi Bool)
keepGoingPaths a str
 = do case toArgs str of
          Left err -> Encoding.encode err >>= liftIO . BS.hPutStrLn stderr
          Right args -> a args
      return False

shortHelpText :: String
shortHelpText = "use :? for help.\n"

helpText :: String
helpText =
 " Commands available from the prompt:\n" ++
 "\n" ++
 "   <statement>                 evaluate/run <statement>\n" ++
 "   :                           repeat last command\n" ++
 "   :{\\n ..lines.. \\n:}\\n       multiline command\n" ++
 "   :add [*]<module> ...        add module(s) to the current target set\n" ++
 "   :browse[!] [[*]<mod>]       display the names defined by module <mod>\n" ++
 "                               (!: more details; *: all top-level names)\n" ++
 "   :cd <dir>                   change directory to <dir>\n" ++
 "   :cmd <expr>                 run the commands returned by <expr>::IO String\n" ++
 "   :ctags[!] [<file>]          create tags file for Vi (default: \"tags\")\n" ++
 "                               (!: use regex instead of line number)\n" ++
 "   :def <cmd> <expr>           define a command :<cmd>\n" ++
 "   :edit <file>                edit file\n" ++
 "   :edit                       edit last module\n" ++
 "   :etags [<file>]             create tags file for Emacs (default: \"TAGS\")\n" ++
 "   :help, :?                   display this list of commands\n" ++
 "   :info [<name> ...]          display information about the given names\n" ++
 "   :kind <type>                show the kind of <type>\n" ++
 "   :load [*]<module> ...       load module(s) and their dependents\n" ++
 "   :main [<arguments> ...]     run the main function with the given arguments\n" ++
 "   :module [+/-] [*]<mod> ...  set the context for expression evaluation\n" ++
 "   :quit                       exit GHCi\n" ++
 "   :reload                     reload the current module set\n" ++
 "   :run function [<arguments> ...] run the function with the given arguments\n" ++
 "   :type <expr>                show the type of <expr>\n" ++
 "   :undef <cmd>                undefine user-defined command :<cmd>\n" ++
 "   :!<command>                 run the shell command <command>\n" ++
 "\n" ++
 " -- Commands for debugging:\n" ++
 "\n" ++
 "   :abandon                    at a breakpoint, abandon current computation\n" ++
 "   :back                       go back in the history (after :trace)\n" ++
 "   :break [<mod>] <l> [<col>]  set a breakpoint at the specified location\n" ++
 "   :break <name>               set a breakpoint on the specified function\n" ++
 "   :continue                   resume after a breakpoint\n" ++
 "   :delete <number>            delete the specified breakpoint\n" ++
 "   :delete *                   delete all breakpoints\n" ++
 "   :force <expr>               print <expr>, forcing unevaluated parts\n" ++
 "   :forward                    go forward in the history (after :back)\n" ++
 "   :history [<n>]              after :trace, show the execution history\n" ++
 "   :list                       show the source code around current breakpoint\n" ++
 "   :list identifier            show the source code for <identifier>\n" ++
 "   :list [<module>] <line>     show the source code around line number <line>\n" ++
 "   :print [<name> ...]         prints a value without forcing its computation\n" ++
 "   :sprint [<name> ...]        simplifed version of :print\n" ++
 "   :step                       single-step after stopping at a breakpoint\n"++
 "   :step <expr>                single-step into <expr>\n"++
 "   :steplocal                  single-step within the current top-level binding\n"++
 "   :stepmodule                 single-step restricted to the current module\n"++
 "   :trace                      trace after stopping at a breakpoint\n"++
 "   :trace <expr>               evaluate <expr> with tracing on (see :history)\n"++

 "\n" ++
 " -- Commands for changing settings:\n" ++
 "\n" ++
 "   :set <option> ...           set options\n" ++
 "   :set args <arg> ...         set the arguments returned by System.getArgs\n" ++
 "   :set prog <progname>        set the value returned by System.getProgName\n" ++
 "   :set prompt <prompt>        set the prompt used in GHCi\n" ++
 "   :set editor <cmd>           set the command used for :edit\n" ++
 "   :set stop [<n>] <cmd>       set the command to run when a breakpoint is hit\n" ++
 "   :unset <option> ...         unset options\n" ++
 "\n" ++
 "  Options for ':set' and ':unset':\n" ++
 "\n" ++
 "    +r            revert top-level expressions after each evaluation\n" ++
 "    +s            print timing/memory stats after each evaluation\n" ++
 "    +t            print type after evaluation\n" ++
 "    -<flags>      most GHC command line flags can also be set here\n" ++
 "                         (eg. -v2, -fglasgow-exts, etc.)\n" ++
 "                    for GHCi-specific flags, see User's Guide,\n"++
 "                    Flag reference, Interactive-mode options\n" ++
 "\n" ++
 " -- Commands for displaying information:\n" ++
 "\n" ++
 "   :show bindings              show the current bindings made at the prompt\n" ++
 "   :show breaks                show the active breakpoints\n" ++
 "   :show context               show the breakpoint context\n" ++
 "   :show modules               show the currently loaded modules\n" ++
 "   :show packages              show the currently active package flags\n" ++
 "   :show languages             show the currently active language flags\n" ++
 "   :show <setting>             show value of <setting>, which is one of\n" ++
 "                                  [args, prog, prompt, editor, stop]\n" ++
 "\n" 

findEditor :: IO String
findEditor = do
  getEnv "EDITOR" 
    `IO.catch` \_ -> do
#if mingw32_HOST_OS
        win <- System.Win32.getWindowsDirectory
        return (win </> "notepad.exe")
#else
        return ""
#endif

foreign import ccall unsafe "rts_isProfiled" isProfiled :: IO CInt

interactiveUI :: [(FilePath, Maybe Phase)] -> Maybe [String]
              -> Ghc ()
interactiveUI srcs maybe_exprs = do
   -- although GHCi compiles with -prof, it is not usable: the byte-code
   -- compiler and interpreter don't work with profiling.  So we check for
   -- this up front and emit a helpful error message (#2197)
   i <- liftIO $ isProfiled
   when (i /= 0) $ 
     ghcError (InstallationError "GHCi cannot be used when compiled with -prof")

   -- HACK! If we happen to get into an infinite loop (eg the user
   -- types 'let x=x in x' at the prompt), then the thread will block
   -- on a blackhole, and become unreachable during GC.  The GC will
   -- detect that it is unreachable and send it the NonTermination
   -- exception.  However, since the thread is unreachable, everything
   -- it refers to might be finalized, including the standard Handles.
   -- This sounds like a bug, but we don't have a good solution right
   -- now.
   _ <- liftIO $ newStablePtr stdin
   _ <- liftIO $ newStablePtr stdout
   _ <- liftIO $ newStablePtr stderr

    -- Initialise buffering for the *interpreted* I/O system
   initInterpBuffering

   liftIO $ when (isNothing maybe_exprs) $ do
        -- Only for GHCi (not runghc and ghc -e):

        -- Turn buffering off for the compiled program's stdout/stderr
        turnOffBuffering
        -- Turn buffering off for GHCi's stdout
        hFlush stdout
        hSetBuffering stdout NoBuffering
        -- We don't want the cmd line to buffer any input that might be
        -- intended for the program, so unbuffer stdin.
        hSetBuffering stdin NoBuffering
#if defined(mingw32_HOST_OS) && __GLASGOW_HASKELL__ >= 611
        -- On Unix, stdin will use the locale encoding.  The IO library
        -- doesn't do this on Windows (yet), so for now we use UTF-8,
        -- for consistency with GHC 6.10 and to make the tests work.
        hSetEncoding stdin utf8
#endif

   -- initial context is just the Prelude
   prel_mod <- GHC.lookupModule (GHC.mkModuleName "Prelude") Nothing
   GHC.setContext [] [(prel_mod, Nothing)]

   default_editor <- liftIO $ findEditor

   startGHCi (runGHCi srcs maybe_exprs)
        GHCiState{ progname = "<interactive>",
                   args = [],
                   prompt = "%s> ",
                   stop = "",
                   editor = default_editor,
--                   session = session,
                   options = [],
                   prelude = prel_mod,
                   break_ctr = 0,
                   breaks = [],
                   tickarrays = emptyModuleEnv,
                   last_command = Nothing,
                   cmdqueue = [],
                   remembered_ctx = [],
                   ghc_e = isJust maybe_exprs
                 }

   return ()

withGhcAppData :: (FilePath -> IO a) -> IO a -> IO a
withGhcAppData right left = do
   either_dir <- IO.try (getAppUserDataDirectory "ghc")
   case either_dir of
      Right dir -> right dir
      _ -> left

runGHCi :: [(FilePath, Maybe Phase)] -> Maybe [String] -> GHCi ()
runGHCi paths maybe_exprs = do
  let 
   read_dot_files = not opt_IgnoreDotGhci

   current_dir = return (Just ".ghci")

   app_user_dir = io $ withGhcAppData 
                    (\dir -> return (Just (dir </> "ghci.conf")))
                    (return Nothing)

   home_dir = do
    either_dir <- io $ IO.try (getEnv "HOME")
    case either_dir of
      Right home -> return (Just (home </> ".ghci"))
      _ -> return Nothing

   canonicalizePath' :: FilePath -> IO (Maybe FilePath)
   canonicalizePath' fp = liftM Just (canonicalizePath fp)
                `catchIO` \_ -> return Nothing

   sourceConfigFile :: FilePath -> GHCi ()
   sourceConfigFile file = do
     exists <- io $ doesFileExist file
     when exists $ do
       dir_ok  <- io $ checkPerms (getDirectory file)
       file_ok <- io $ checkPerms file
       when (dir_ok && file_ok) $ do
         either_hdl <- io $ IO.try (openFile file ReadMode)
         case either_hdl of
           Left _e   -> return ()
           -- NOTE: this assumes that runInputT won't affect the terminal;
           -- can we assume this will always be the case?
           -- This would be a good place for runFileInputT.
           Right hdl -> runInputTWithPrefs defaultPrefs defaultSettings $ do
                            runCommands $ fileLoop hdl
     where
      getDirectory f = case takeDirectory f of "" -> "."; d -> d

  when (read_dot_files) $ do
    mcfgs0 <- sequence [ current_dir, app_user_dir, home_dir ]
    mcfgs <- io $ mapM canonicalizePath' (catMaybes mcfgs0)
    mapM_ sourceConfigFile $ nub $ catMaybes mcfgs
        -- nub, because we don't want to read .ghci twice if the
        -- CWD is $HOME.

  -- Perform a :load for files given on the GHCi command line
  -- When in -e mode, if the load fails then we want to stop
  -- immediately rather than going on to evaluate the expression.
  when (not (null paths)) $ do
     ok <- ghciHandle (\e -> do showException e; return Failed) $
                -- TODO: this is a hack.
                runInputTWithPrefs defaultPrefs defaultSettings $ do
                    let (filePaths, phases) = unzip paths
                    filePaths' <- mapM (Encoding.decode . BS.pack) filePaths
                    loadModule (zip filePaths' phases)
     when (isJust maybe_exprs && failed ok) $
        io (exitWith (ExitFailure 1))

  -- if verbosity is greater than 0, or we are connected to a
  -- terminal, display the prompt in the interactive loop.
  is_tty <- io (hIsTerminalDevice stdin)
  dflags <- getDynFlags
  let show_prompt = verbosity dflags > 0 || is_tty

  case maybe_exprs of
        Nothing ->
          do
            -- enter the interactive loop
            runGHCiInput $ runCommands $ nextInputLine show_prompt is_tty
        Just exprs -> do
            -- just evaluate the expression we were given
            enqueueCommands exprs
            let handle e = do st <- getGHCiState
                              -- flush the interpreter's stdout/stderr on exit (#3890)
                              flushInterpBuffers
                                   -- Jump through some hoops to get the
                                   -- current progname in the exception text:
                                   -- <progname>: <exception>
                              io $ withProgName (progname st)
                                   -- this used to be topHandlerFastExit, see #2228
                                 $ topHandler e
            runInputTWithPrefs defaultPrefs defaultSettings $ do
                runCommands' handle (return Nothing)

  -- and finally, exit
  io $ do when (verbosity dflags > 0) $ putStrLn "Leaving GHCi."

runGHCiInput :: InputT GHCi a -> GHCi a
runGHCiInput f = do
    histFile <- io $ withGhcAppData (\dir -> return (Just (dir </> "ghci_history")))
                        (return Nothing)
    let settings = setComplete ghciCompleteWord
                    $ defaultSettings {historyFile = histFile}
    runInputT settings f

nextInputLine :: Bool -> Bool -> InputT GHCi (Maybe String)
nextInputLine show_prompt is_tty
  | is_tty = do
    prompt <- if show_prompt then lift mkPrompt else return ""
    getInputLine prompt
  | otherwise = do
    when show_prompt $ lift mkPrompt >>= liftIO . putStr
    fileLoop stdin

-- NOTE: We only read .ghci files if they are owned by the current user,
-- and aren't world writable.  Otherwise, we could be accidentally 
-- running code planted by a malicious third party.

-- Furthermore, We only read ./.ghci if . is owned by the current user
-- and isn't writable by anyone else.  I think this is sufficient: we
-- don't need to check .. and ../.. etc. because "."  always refers to
-- the same directory while a process is running.

checkPerms :: String -> IO Bool
#ifdef mingw32_HOST_OS
checkPerms _ =
  return True
#else
checkPerms name =
  handleIO (\_ -> return False) $ do
     st <- getFileStatus name
     me <- getRealUserID
     if fileOwner st /= me then do
   	putStrLn $ "WARNING: " ++ name ++ " is owned by someone else, IGNORING!"
   	return False
      else do
   	let mode =  fileMode st
   	if (groupWriteMode == (mode `intersectFileModes` groupWriteMode))
   	   || (otherWriteMode == (mode `intersectFileModes` otherWriteMode)) 
   	   then do
   	       putStrLn $ "*** WARNING: " ++ name ++ 
   			  " is writable by someone else, IGNORING!"
   	       return False
   	  else return True
#endif

fileLoop :: MonadIO m => Handle -> InputT m (Maybe String)
fileLoop hdl = do
   l <- liftIO $ IO.try $ hGetLine hdl
   case l of
        Left e | isEOFError e              -> return Nothing
               | InvalidArgument <- etype  -> return Nothing
               | otherwise                 -> liftIO $ ioError e
                where etype = ioeGetErrorType e
                -- treat InvalidArgument in the same way as EOF:
                -- this can happen if the user closed stdin, or
                -- perhaps did getContents which closes stdin at
                -- EOF.
        Right l -> return (Just l)

mkPrompt :: GHCi String
mkPrompt = do
  (toplevs,exports) <- GHC.getContext
  resumes <- GHC.getResumeContext
  -- st <- getGHCiState

  context_bit <-
        case resumes of
            [] -> return empty
            r:_ -> do
                let ix = GHC.resumeHistoryIx r
                if ix == 0
                   then return (brackets (ppr (GHC.resumeSpan r)) <> space)
                   else do
                        let hist = GHC.resumeHistory r !! (ix-1)
                        span <- GHC.getHistorySpan hist
                        return (brackets (ppr (negate ix) <> char ':' 
                                          <+> ppr span) <> space)
  let
        dots | _:rs <- resumes, not (null rs) = text "... "
             | otherwise = empty

        modules_bit = 
       -- ToDo: maybe...
       --  let (btoplevs, bexports) = fromMaybe ([],[]) (remembered_ctx st) in
       --  hsep (map (\m -> text "!*" <> ppr (GHC.moduleName m)) btoplevs) <+>
       --  hsep (map (\m -> char '!'  <> ppr (GHC.moduleName m)) bexports) <+>
             hsep (map (\m -> char '*'  <> ppr (GHC.moduleName m)) toplevs) <+>
             hsep (map (ppr . GHC.moduleName) (nub (map fst exports)))

        deflt_prompt = dots <> context_bit <> modules_bit

        f ('%':'s':xs) = deflt_prompt <> f xs
        f ('%':'%':xs) = char '%' <> f xs
        f (x:xs) = char x <> f xs
        f [] = empty
   --
  st <- getGHCiState
  return (showSDoc (f (prompt st)))


queryQueue :: GHCi (Maybe String)
queryQueue = do
  st <- getGHCiState
  case cmdqueue st of
    []   -> return Nothing
    c:cs -> do setGHCiState st{ cmdqueue = cs }
               return (Just c)

runCommands :: InputT GHCi (Maybe String) -> InputT GHCi ()
runCommands = runCommands' handler

runCommands' :: (SomeException -> GHCi Bool) -- Exception handler
             -> InputT GHCi (Maybe String) -> InputT GHCi ()
runCommands' eh getCmd = do
    b <- ghandle (\e -> case fromException e of
                          Just UserInterrupt -> return False
                          _ -> case fromException e of
                                 Just ghc_e ->
                                   do liftIO (print (ghc_e :: GhcException))
                                      return True
                                 _other ->
                                   liftIO (Exception.throwIO e))
            (runOneCommand eh getCmd)
    if b then return () else runCommands' eh getCmd

runOneCommand :: (SomeException -> GHCi Bool) -> InputT GHCi (Maybe String)
            -> InputT GHCi Bool
runOneCommand eh getCmd = do
  mb_cmd <- noSpace (lift queryQueue)
  mb_cmd <- maybe (noSpace getCmd) (return . Just) mb_cmd
  case mb_cmd of
    Nothing -> return True
    Just c  -> ghciHandle (lift . eh) $
             handleSourceError printErrorAndKeepGoing
               (doCommand c)
  where
    printErrorAndKeepGoing err = do
        GHC.printExceptionAndWarnings err
        return False

    noSpace q = q >>= maybe (return Nothing)
                            (\c->case removeSpaces c of 
                                   ""   -> noSpace q
                                   ":{" -> multiLineCmd q
                                   c    -> return (Just c) )
    multiLineCmd q = do
      st <- lift getGHCiState
      let p = prompt st
      lift $ setGHCiState st{ prompt = "%s| " }
      mb_cmd <- collectCommand q ""
      lift $ getGHCiState >>= \st->setGHCiState st{ prompt = p }
      return mb_cmd
    -- we can't use removeSpaces for the sublines here, so 
    -- multiline commands are somewhat more brittle against
    -- fileformat errors (such as \r in dos input on unix), 
    -- we get rid of any extra spaces for the ":}" test; 
    -- we also avoid silent failure if ":}" is not found;
    -- and since there is no (?) valid occurrence of \r (as 
    -- opposed to its String representation, "\r") inside a
    -- ghci command, we replace any such with ' ' (argh:-(
    collectCommand q c = q >>= 
      maybe (liftIO (ioError collectError))
            (\l->if removeSpaces l == ":}" 
                 then return (Just $ removeSpaces c) 
                 else collectCommand q (c ++ "\n" ++ map normSpace l))
      where normSpace '\r' = ' '
            normSpace   c  = c
    -- QUESTION: is userError the one to use here?
    collectError = userError "unterminated multiline command :{ .. :}"
    doCommand (':' : cmd) = specialCommand cmd
    doCommand stmt        = do _ <- timeIt $ lift $ runStmt stmt GHC.RunToCompletion
                               return False

enqueueCommands :: [String] -> GHCi ()
enqueueCommands cmds = do
  st <- getGHCiState
  setGHCiState st{ cmdqueue = cmds ++ cmdqueue st }


runStmt :: String -> SingleStep -> GHCi Bool
runStmt stmt step
 | null (filter (not.isSpace) stmt)
 = return False
 | "import " `isPrefixOf` stmt
 = do newContextCmd (Import stmt); return False
 | otherwise
 = do
#if __GLASGOW_HASKELL__ >= 611
      -- In the new IO library, read handles buffer data even if the Handle
      -- is set to NoBuffering.  This causes problems for GHCi where there
      -- are really two stdin Handles.  So we flush any bufferred data in
      -- GHCi's stdin Handle here (only relevant if stdin is attached to
      -- a file, otherwise the read buffer can't be flushed).
      _ <- liftIO $ IO.try $ hFlushAll stdin
#endif
      result <- GhciMonad.runStmt stmt step
      afterRunStmt (const True) result

--afterRunStmt :: GHC.RunResult -> GHCi Bool
                                 -- False <=> the statement failed to compile
afterRunStmt :: (SrcSpan -> Bool) -> GHC.RunResult -> GHCi Bool
afterRunStmt _ (GHC.RunException e) = throw e
afterRunStmt step_here run_result = do
  resumes <- GHC.getResumeContext
  case run_result of
     GHC.RunOk names -> do
        show_types <- isOptionSet ShowType
        when show_types $ printTypeOfNames names
     GHC.RunBreak _ names mb_info
         | isNothing  mb_info ||
           step_here (GHC.resumeSpan $ head resumes) -> do
               mb_id_loc <- toBreakIdAndLocation mb_info
               let breakCmd = maybe "" ( \(_,l) -> onBreakCmd l ) mb_id_loc
               if (null breakCmd)
                 then printStoppedAtBreakInfo (head resumes) names
                 else enqueueCommands [breakCmd]
               -- run the command set with ":set stop <cmd>"
               st <- getGHCiState
               enqueueCommands [stop st]
               return ()
         | otherwise -> resume step_here GHC.SingleStep >>=
                        afterRunStmt step_here >> return ()
     _ -> return ()

  flushInterpBuffers
  io installSignalHandlers
  b <- isOptionSet RevertCAFs
  when b revertCAFs

  return (case run_result of GHC.RunOk _ -> True; _ -> False)

toBreakIdAndLocation ::
  Maybe GHC.BreakInfo -> GHCi (Maybe (Int, BreakLocation))
toBreakIdAndLocation Nothing = return Nothing
toBreakIdAndLocation (Just info) = do
  let mod = GHC.breakInfo_module info
      nm  = GHC.breakInfo_number info
  st <- getGHCiState
  return $ listToMaybe [ id_loc | id_loc@(_,loc) <- breaks st,
                                  breakModule loc == mod,
                                  breakTick loc == nm ]

printStoppedAtBreakInfo :: Resume -> [Name] -> GHCi ()
printStoppedAtBreakInfo resume names = do
  printForUser $ ptext (sLit "Stopped at") <+>
    ppr (GHC.resumeSpan resume)
  --  printTypeOfNames session names
  let namesSorted = sortBy compareNames names
  tythings <- catMaybes `liftM` mapM GHC.lookupName namesSorted
  docs <- pprTypeAndContents [id | AnId id <- tythings]
  printForUserPartWay docs

printTypeOfNames :: [Name] -> GHCi ()
printTypeOfNames names
 = mapM_ (printTypeOfName ) $ sortBy compareNames names

compareNames :: Name -> Name -> Ordering
n1 `compareNames` n2 = compareWith n1 `compare` compareWith n2
    where compareWith n = (getOccString n, getSrcSpan n)

printTypeOfName :: Name -> GHCi ()
printTypeOfName n
   = do maybe_tything <- GHC.lookupName n
        case maybe_tything of
            Nothing    -> return ()
            Just thing -> printTyThing thing


data MaybeCommand = GotCommand Command | BadCommand | NoLastCommand

specialCommand :: String -> InputT GHCi Bool
specialCommand ('!':str) = lift $ shellEscape (dropWhile isSpace str)
specialCommand str = do
  let (cmd,rest) = break isSpace str
  maybe_cmd <- lift $ lookupCommand cmd
  case maybe_cmd of
    GotCommand (_,f,_) -> f (dropWhile isSpace rest)
    BadCommand ->
      do liftIO $ hPutStr stdout ("unknown command ':" ++ cmd ++ "'\n"
                           ++ shortHelpText)
         return False
    NoLastCommand ->
      do liftIO $ hPutStr stdout ("there is no last command to perform\n"
                           ++ shortHelpText)
         return False

lookupCommand :: String -> GHCi (MaybeCommand)
lookupCommand "" = do
  st <- getGHCiState
  case last_command st of
      Just c -> return $ GotCommand c
      Nothing -> return NoLastCommand
lookupCommand str = do
  mc <- io $ lookupCommand' str
  st <- getGHCiState
  setGHCiState st{ last_command = mc }
  return $ case mc of
           Just c -> GotCommand c
           Nothing -> BadCommand

lookupCommand' :: String -> IO (Maybe Command)
lookupCommand' ":" = return Nothing
lookupCommand' str' = do
  macros <- readIORef macros_ref
  let{ (str, cmds) = case str' of
      ':' : rest -> (rest, builtin_commands)
      _ -> (str', macros ++ builtin_commands) }
  -- look for exact match first, then the first prefix match
  return $ case [ c | c <- cmds, str == cmdName c ] of
           c:_ -> Just c
           [] -> case [ c | c@(s,_,_) <- cmds, str `isPrefixOf` s ] of
                 [] -> Nothing
                 c:_ -> Just c

getCurrentBreakSpan :: GHCi (Maybe SrcSpan)
getCurrentBreakSpan = do
  resumes <- GHC.getResumeContext
  case resumes of
    [] -> return Nothing
    (r:_) -> do
        let ix = GHC.resumeHistoryIx r
        if ix == 0
           then return (Just (GHC.resumeSpan r))
           else do
                let hist = GHC.resumeHistory r !! (ix-1)
                span <- GHC.getHistorySpan hist
                return (Just span)

getCurrentBreakModule :: GHCi (Maybe Module)
getCurrentBreakModule = do
  resumes <- GHC.getResumeContext
  case resumes of
    [] -> return Nothing
    (r:_) -> do
        let ix = GHC.resumeHistoryIx r
        if ix == 0
           then return (GHC.breakInfo_module `liftM` GHC.resumeBreakInfo r)
           else do
                let hist = GHC.resumeHistory r !! (ix-1)
                return $ Just $ GHC.getHistoryModule  hist

-----------------------------------------------------------------------------
-- Commands

noArgs :: GHCi () -> String -> GHCi ()
noArgs m "" = m
noArgs _ _  = io $ putStrLn "This command takes no arguments"

help :: String -> GHCi ()
help _ = io (putStr helpText)

info :: String -> InputT GHCi ()