------------------------------------------------------------------------------
--- A universal REPL which can be used on top of a Curry compiler
---
--- @author  Michael Hanus
--- @version March 2023
------------------------------------------------------------------------------

module REPL.Main where

import Control.Monad      ( when, unless )
import Curry.Compiler.Distribution ( installDir )
import Data.Char          ( toLower, toUpper )
import Data.List          ( intercalate, intersperse, isInfixOf, isPrefixOf
                          , maximum, nub, partition, sort, sortBy )
import System.Environment ( getArgs, getEnv )
import System.FilePath    ( (</>), (<.>) )
import System.IO          ( hClose, hFlush, hPutStrLn, isEOF, stdout )

import AbstractCurry.Types hiding (preludeName)
import AbstractCurry.Files
import AbstractCurry.Build ( ioType, stringType, unitType )
import AbstractCurry.Select
import System.CurryPath    ( inCurrySubdir, lookupModuleSource, modNameToPath
                           , stripCurrySuffix )
import System.Directory    ( doesDirectoryExist, doesFileExist, getAbsolutePath
                           , getDirectoryContents, getHomeDirectory
                           , renameFile, setCurrentDirectory )
import System.FilePath     ( searchPathSeparator, splitExtension
                           , splitFileName, splitSearchPath )
import System.FrontendExec
import System.IOExts       ( connectToCommand )
import System.Process      ( exitWith, getPID, system )

import REPL.Compiler
import REPL.RCFile
import REPL.State
import REPL.Utils          ( showMonoTypeExpr, showMonoQualTypeExpr
                           , getTimeCmd, getTimeoutCmd, moduleNameToPath
                           , validModuleName, notNull, removeFileIfExists
                           , strip, writeErrorMsg )

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

--- The main operation to start the REPL. It is parameterized over
--- a description of a Curry compiler.
mainREPL :: CCDescription -> IO ()
mainREPL cd = do
  rcFileDefs <- readRC cd
  args       <- getArgs
  let (nodefargs,defargs) = extractRCArgs args
      (mainargs,rtargs)   = break (=="--") nodefargs
      rcDefs              = updateRCDefs rcFileDefs defargs
      furtherRcDefs       = filter (\da -> fst da `notElem` map fst rcFileDefs)
                                   defargs
  rst   <- initReplState cd
  ipath <- defaultImportPaths rst
  let rst1 = rst { importPaths = ipath
                 , rcVars    = rcDefs
                 , rtsArgs   = if null rtargs then "" else unwords (tail rtargs)
                 }
  if null furtherRcDefs
   then processArgsAndStart
          rst1
          (map strip (words (rcValue (rcVars rst1) "defaultparams")) ++
           mainargs)
   else putStrLn $ "Error: rc property name '" ++ fst (head furtherRcDefs) ++
                   "' not found in rc file!"

processArgsAndStart :: ReplState -> [String] -> IO ()
processArgsAndStart rst []
  | quit rst  = cleanUpAndExitRepl rst
  | otherwise = do
      writeVerboseInfo rst 1 (ccBanner (compiler rst))
      unless (null (usingOption rst)) $ writeVerboseInfo rst 1 $
        "(using " ++ usingOption rst ++ ")\n"
      writeVerboseInfo rst 1 $
        "Type \":h\" for help  (contact: " ++ ccEmail (compiler rst) ++ ")"
      when (currMod rst == "Prelude") $ do
        writeVerboseInfo rst 1 $ "Compiling Prelude..."
        processCompile (reduceVerbose rst) "Prelude" >> return ()
      repLoop rst
processArgsAndStart rst (arg:args)
  -- ignore empty arguments which can be provided by single or double quotes
  | null arg
  = processArgsAndStart rst args
  -- ignore '--nocypm|-n' or '--noreadline'
  -- (since they already processed by separate script to invoke the REPL)
  | arg == "--using" && not (null args)
  = processArgsAndStart rst { usingOption = head args } (tail args)
  | arg `elem` ["-n", "--nocypm", "--noreadline"]
  = processArgsAndStart rst args
  | arg == "-h" || arg == "--help" || arg == "-?"
  = printHelp rst >> cleanUpAndExitRepl rst
  | arg == "-q" || arg == "--quiet"
  = processArgsAndStart rst { verbose = 0 } args
  | arg == "-V" || arg == "--version"
  = do putStrLn (ccBanner (compiler rst))
       processArgsAndStart rst { quit = True} args
  | arg `elem` versionOpts -- process all version options and quit:
  = do let (vopts,mopts) = partition (`elem` versionOpts) args
       if null mopts
         then do system $ unwords (ccExec (compiler rst) : arg : vopts)
                 cleanUpAndExitRepl rst
         else writeErrorMsg ("illegal options: " ++ unwords mopts)
  | isCommand arg = do
    let (cmdargs, more) = break isCommand args
    mbrst <- processCommand rst (tail (unwords (arg:cmdargs)))
    maybe (printHelp rst) (\rst' -> processArgsAndStart rst' more) mbrst
  | otherwise
  = writeErrorMsg ("unknown option: " ++ unwords (arg:args)) >> printHelp rst
 where
  versionOpts = ["--compiler-name", "--numeric-version", "--base-version"]

--- May a `String` be a REPL command?
isCommand :: String -> Bool
isCommand s = case s of
  ':' : _ -> True
  _       -> False

printHelp :: ReplState -> IO ()
printHelp rst = putStrLn $ unlines $
  [ "Invoke interactive environment:"
  , ""
  , "    <repl> <options> [ -- <run-time arguments>]"
  , ""
  , "with options:"
  , ""] ++
  formatVarVals ": "
   (ccMainOpts (compiler rst) ++
    [ ("-h|--help|-?"     , "show this message and quit")
    , ("-V|--version"     , "show version and quit")
    , ("--compiler-name"  , "show the compiler name and quit")
    , ("--numeric-version", "show the compiler version number and quit")
    , ("--base-version   ", "show the version of the base libraries and quit")
    , ("-q|--quiet"       , "work silently")
    , ("--using <s>"      , "set string for 'using' message in banner")
    , ("-Dprop=val"       , "define rc property `prop' as `val'")
    , (":<cmd> <args>"    , "commands of the interactive environment")
    ]) ++
  [ "" ]

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

-- The main read-eval-print loop:
repLoop :: ReplState -> IO ()
repLoop rst = do
  putStr prompt >> hFlush stdout
  eof <- isEOF
  if eof then cleanUpAndExitRepl rst
         else mGetLine >>= maybe (cleanUpAndExitRepl rst) (checkInput . strip)
 where
  prompt = calcPrompt rst

  checkInput inp
    | null inp
    = repLoop rst
    | ord (head inp) == 0 -- indicates sometimes EOF
    = cleanUpAndExitRepl rst
    | otherwise
    = do when (withEcho rst) $ putStrLn $ prompt ++ inp
         processInput rst inp

-- A variant of `Prelude.getLine` which returns `Nothing` if EOF is reached.
mGetLine  :: IO (Maybe String)
mGetLine = do
  eof <- isEOF
  if eof
    then return Nothing
    else do
      c  <- getChar
      if ord c == 0 -- indices EOF in Curry2Go
        then return Nothing
        else if c == '\n'
               then return $ Just []
               else do mGetLine >>= maybe (return Nothing)
                                          (\cs -> return $ Just (c:cs))

-- Calculates the prompt string w.r.t. the currently loaded modules.
calcPrompt :: ReplState -> String
calcPrompt rst =
  substS (unwords (currMod rst : addMods rst)) (prompt rst)

-- Substitute `%s` in a string with a given string (first argument).
substS :: String -> String -> String
substS replacement = sub
 where
  sub []       = []
  sub [c]      = [c]
  sub (c:d:cs) = case c of
    '%' -> case d of
             '%' -> '%' : cs
             's' -> replacement ++ sub cs
             _   -> c : d : sub cs
    _   -> c : sub (d:cs)

-- Clean resources of REPL and terminate it with exit status.
cleanUpAndExitRepl :: ReplState -> IO ()
cleanUpAndExitRepl rst = do
  terminateSourceProgGUIs rst
  exitWith (exitStatus rst)

processInput :: ReplState -> String -> IO ()
processInput rst g
  | null g      = repLoop rst
  | isCommand g = do mbrst <- processCommand rst (strip (tail g))
                     maybe (repLoop (rst { exitStatus = 1 }))
                           (\rst' -> if quit rst' then cleanUpAndExitRepl rst'
                                                  else repLoop rst')
                           mbrst
  | "let " `isPrefixOf` g
  = getAcyOfExpr rst (g ++ "\n  in ()") >>=
    maybe (repLoop rst)
          (\_ -> repLoop rst { letBinds = letBinds rst ++ [g] })
  | otherwise   = evalExpression rst g >>= repLoop

--- Evaluate an expression w.r.t. currently loaded modules
evalExpression :: ReplState -> String -> IO ReplState
evalExpression rst expr = do
  exst <- compileMainExpression rst expr True
  return rst { exitStatus = exst }

-- Check whether the main module imports an "Unsafe" module.
importUnsafeModule :: ReplState -> IO Bool
importUnsafeModule rst =
  if containsUnsafe (addMods rst)
    then return True
    else do
      let acyMainModFile = acyFileName rst (currMod rst)
          frontendParams = currentFrontendParams rst (verbose rst <= 1)
      catch (do verbCallFrontendWithParams rst ACY frontendParams (currMod rst)
                p <- readAbstractCurryFile acyMainModFile
                return $ containsUnsafe (imports p))
            (\_ -> return (currMod rst /= "Prelude")) -- just to be safe
 where
  containsUnsafe = any ("Unsafe" `isInfixOf`)

-- Compute the front-end parameters for the current state:
currentFrontendParams :: ReplState -> Bool -> FrontendParams
currentFrontendParams rst quiet =
    setQuiet        quiet
  $ setFrontendPath (ccFrontend cc)
  $ setFullPath     (loadPaths rst)
  $ setExtended     (rcValue (rcVars rst) "curryextensions" /= "no")
  $ setOverlapWarn  (rcValue (rcVars rst) "warnoverlapping" /= "no")
  $ setSpecials     (parseOpts rst)
  $ setDefinitions  [("__" ++ map toUpper (ccName cc) ++ "__", maj*100 + min)]
  $ setOutDir       (compilerOutDir rst)
    defaultParams
 where
  cc = compiler rst
  (maj,min,_) = ccVersion cc

-- Computes the directory for auxiliary Curry files w.r.t. the current compiler.
compilerOutDir :: ReplState -> String
compilerOutDir rst =
  ".curry" </> map toLower (ccName cc) ++ "-" ++
  intercalate "." (map show [maj,min,rev])
 where
  cc = compiler rst
  (maj,min,rev) = ccVersion cc

-- Computes the name of the AbstractCurry file for a given module
-- w.r.t. the current compiler
acyFileName :: ReplState -> String -> String
acyFileName rst prog = compilerOutDir rst </> modNameToPath prog <.> "acy"


-- Call the front end and report the call if required by verbosity.
verbCallFrontendWithParams :: ReplState -> FrontendTarget -> FrontendParams
                           -> String -> IO ()
verbCallFrontendWithParams rst target params modpath = do
  when (verbose rst > 1) $ do
    parsecmd <- getFrontendCall target params modpath
    writeVerboseInfo rst 2 $ "Executing: " ++ parsecmd
  callFrontendWithParams target params modpath

-- ---------------------------------------------------------------------------
-- Main expression file stuff
-- ---------------------------------------------------------------------------

writeSimpleMainExpFile :: ReplState -> String -> IO ()
writeSimpleMainExpFile rst exp = writeMainExpFile rst [] Nothing exp

-- write the file with the main exp where necessary imports
-- and possibly a type string is provided:
writeMainExpFile :: ReplState -> [String] -> Maybe String -> String -> IO ()
writeMainExpFile rst imports mtype exp =
  writeFile (mainExpFile rst) $ unlines $
    [noMissingSigs, "module " ++ mainExpMod rst ++ " where"] ++
    map ("import " ++) allImports ++
    maybe [] (\ts -> ["main :: " ++ ts]) mtype ++
    ["main = " ++ concatMap (++ " in\n  ") (letBinds rst)
               ++ qualifyMain (strip exp)]
 where
  allImports = filter (/="Prelude") . nub $ currMod rst : addMods rst ++ imports

  noMissingSigs = "{-# OPTIONS_FRONTEND -W no-missing-signatures #-}"

  -- simple hack to avoid name conflict with "main":
  -- (better solution: pretty print parsed main expression with qualification)
  qualifyMain :: String -> String
  qualifyMain [] = []
  qualifyMain s@(x:xs)
    | "main" `isPrefixOf` s = case drop 3 xs of
                                []  -> currMod rst ++ ".main"
                                c:_ | not (isAlphaNum c)
                                    -> currMod rst ++ ".main" ++ drop 3 xs
                                _ -> x : qualifyMain xs
    | isAlphaNum x          = let (prev, next) = span isAlphaNum xs
                              in x : prev ++ qualifyMain next
    | otherwise             = x : qualifyMain xs

-- Generate, read, and delete .acy file of main expression module.
-- Return Nothing if some error occurred during parsing.
getAcyOfMainExpMod :: ReplState -> IO (Maybe CurryProg)
getAcyOfMainExpMod rst = do
  let acyMainExpFile = acyFileName rst (mainExpMod rst)
      frontendParams  = currentFrontendParams rst (verbose rst <= 1)
  prog <- catch (verbCallFrontendWithParams rst ACY frontendParams
                                            (mainExpMod rst) >>
                 tryReadACYFile acyMainExpFile)
                (\_ -> return Nothing)
  unlessKeepFiles rst $ removeFileIfExists acyMainExpFile
  return prog

getAcyOfExpr :: ReplState -> String -> IO (Maybe CurryProg)
getAcyOfExpr rst expr = do
  writeSimpleMainExpFile rst expr
  mbProg <- getAcyOfMainExpMod rst
  unlessKeepFiles rst $ removeFileIfExists (mainExpFile rst)
  return mbProg

-- Prints the type of an expression w.r.t. main program.
printTypeOfExp :: ReplState -> String -> IO Bool
printTypeOfExp rst exp = do
  mbProg <- getAcyOfExpr rst exp
  maybe (do writeVerboseInfo rst 3 "Cannot read AbstractCurry file"
            return False)
        (\ (CurryProg _ _ _ _ _ _ [CFunc _ _ _ qty _] _) -> do
          putStrLn $ exp ++ " :: " ++ showMonoQualTypeExpr False qty
          return True)
        mbProg

-- Get the module of a function visible in the main program:
getModuleOfFunction :: ReplState -> String -> IO String
getModuleOfFunction rst funname = do
  mbprog <- getAcyOfExpr rst $
    if isAlpha (head funname) then funname else '(' : funname ++ ")"
  return $ maybe ""
                 (\ (CurryProg _ _ _ _  _ _ [CFunc _ _ _ _ mainrules] _) ->
                    modOfMain mainrules)
                 mbprog
 where modOfMain r = case r of
        [CRule [] (CSimpleRhs (CSymbol (m, _)) [])]       -> m
        [CRule [] (CGuardedRhs [(_, CSymbol (m, _))] [])] -> m
        _                                                 -> ""

-- ---------------------------------------------------------------------------
-- Processing of REPL commands
-- ---------------------------------------------------------------------------

-- Process a command of the REPL.
-- The result is either just a new ReplState or Nothing if an error occurred.
processCommand :: ReplState -> String -> IO (Maybe ReplState)
processCommand rst cmds
  | null cmds        = skipCommand "unknown command"
  | head cmds == '!' = unsafeExec rst $ processSysCall rst (strip $ tail cmds)
  | otherwise        = case matchedCmds of
      []            -> skipCommand $ "unknown command: ':" ++ cmds ++ "'"
      [(fcmd, act)] -> if fcmd `elem` ["eval","load","quit","reload"]
                         then act rst (strip args)
                         else unsafeExec rst $ act rst (strip args)
      (_:_:_)       -> skipCommand $ "ambiguous command: ':" ++ cmds ++ "'"
 where (cmd, args) = break (==' ') cmds
       matchedCmds = filter (isPrefixOf (map toLower cmd) . fst) replCommands

unsafeExec :: ReplState -> IO (Maybe ReplState) -> IO (Maybe ReplState)
unsafeExec rst act =
  if safeExec rst
  then skipCommand "Operation not allowed in safe mode!"
  else act

-- all available REPL commands
replCommands :: [(String, ReplState -> String -> IO (Maybe ReplState))]
replCommands =
  [ ("?"          , processHelp        )
  , ("add"        , processAdd         )
  , ("browse"     , processBrowse      )
  , ("cd"         , processCd          )
  , ("compile"    , processCompile     )
  , ("edit"       , processEdit        )
  , ("eval"       , processEval        )
  , ("fork"       , processFork        )
  , ("help"       , processHelp        )
  , ("interface"  , processInterface   )
  , ("load"       , processLoad        )
  , ("modules"    , processModules     )
  , ("programs"   , processPrograms    )
  , ("reload"     , processReload      )
  , ("quit"       , processQuit        )
  , ("save"       , processSave        )
  , ("set"        , processSetOption   )
  , ("source"     , processSource      )
  , ("show"       , processShow        )
  , ("type"       , processType        )
  , ("usedimports", processUsedImports )
  ]

--- Skip an erroneous command with an error message
skipCommand :: String -> IO (Maybe ReplState)
skipCommand msg = writeErrorMsg msg >> return Nothing

--- Execute a call to a system command
processSysCall :: ReplState -> String -> IO (Maybe ReplState)
processSysCall rst cmd
  | null cmd  = skipCommand "missing system command"
  | otherwise = system cmd >> return (Just rst)

--- Process :add command
processAdd :: ReplState -> String -> IO (Maybe ReplState)
processAdd rst0 args
  | null args = skipCommand "Missing module name"
  | otherwise = Just `fmap` foldIO add rst0 (map stripCurrySuffix (words args))
 where
  add rst m =
    if validModuleName m
      then do
        mbf <- lookupModuleSource (loadPaths rst) m
        case mbf of
          Nothing -> do
            writeErrorMsg $ "Source file of module '" ++ m ++ "' not found"
            return rst
          Just _  ->
            if m `elem` addMods rst
              then return rst
              else compileCurryProgram rst m >>=
                   maybe (return rst)
                         (\rs' -> return rs' { addMods = insM (addMods rs') })
      else do writeErrorMsg $ "Illegal module name (ignored): " ++ m
              return rst
   where
    insM []        = [m]
    insM ms@(n:ns) | m < n     = m : ms
                   | m == n    = ms
                   | otherwise = n : insM ns

  foldIO _ a []     = return a
  foldIO f a (x:xs) = f a x >>= \fax -> foldIO f fax xs

--- Process :browse command
processBrowse :: ReplState -> String -> IO (Maybe ReplState)
processBrowse rst args
  | notNull $ stripCurrySuffix args = skipCommand "superfluous argument"
  | otherwise                       = checkForWish $ do
      writeVerboseInfo rst 1 "Starting Curry Browser in separate window..."
      checkAndCallCpmTool "curry-browse" "currybrowse"
        (\toolexec -> execCommandWithPath rst toolexec [currMod rst])

--- Process :cd command
processCd :: ReplState -> String -> IO (Maybe ReplState)
processCd rst args = do
  dirname <- getAbsolutePath args
  exists  <- doesDirectoryExist dirname
  if exists then setCurrentDirectory dirname >> return (Just rst)
            else skipCommand $ "directory does not exist"

--- Process :compile command
processCompile :: ReplState -> String -> IO (Maybe ReplState)
processCompile rst args = do
  let modname = stripCurrySuffix args
  if null modname
    then skipCommand "missing module name"
    else compileCurryProgram rst modname

--- Process :edit command
processEdit :: ReplState -> String -> IO (Maybe ReplState)
processEdit rst args = do
  modname <- getModuleName rst args
  mbf <- lookupModuleSource (loadPaths rst) modname
  editenv <- getEnv "EDITOR"
  let editcmd  = rcValue (rcVars rst) "editcommand"
      editprog = if null editcmd then editenv else editcmd
  if null editenv && null editcmd
    then skipCommand "no editor defined"
    else maybe (skipCommand "source file not found")
               (\ (_,fn) -> do system (editprog ++ " " ++ fn ++ "& ")
                               return (Just rst))
               mbf

--- Process :eval command
processEval :: ReplState -> String -> IO (Maybe ReplState)
processEval rst args = evalExpression rst args >>= return . Just

--- Process :fork command
processFork :: ReplState -> String -> IO (Maybe ReplState)
processFork rst args
  | currMod rst == preludeName rst
  = skipCommand "no program loaded"
  | otherwise
  = do exst <- compileMainExpression rst (if null args then "main" else args)
                                     False
       if exst == 0
         then do
           pid <- getPID
           let execname = "." </> "MAINFORK" ++ show pid
           renameFile ("." </> mainExpMod rst) execname
           writeVerboseInfo rst 3 $
             "Starting executable '" ++ execname ++ "'..."
           system $ "( " ++ execname ++ " && rm -f " ++ execname ++ ") " ++
                    "> /dev/null 2> /dev/null &"
           return $ Just rst
         else return Nothing

--- Process :help command
processHelp :: ReplState -> String -> IO (Maybe ReplState)
processHelp rst _ = do
  printHelpOnCommands
  return (Just rst)

--- Process :interface command
processInterface :: ReplState -> String -> IO (Maybe ReplState)
processInterface rst args = do
  modname <- getModuleName rst args
  checkAndCallCpmTool "curry-showflat" "showflatcurry"
    (\toolexec -> execCommandWithPath rst toolexec ["-int", modname])

--- Process :load command
processLoad :: ReplState -> String -> IO (Maybe ReplState)
processLoad rst args = do
  rst' <- terminateSourceProgGUIs rst
  let dirmodname = stripCurrySuffix args
  if null dirmodname
    then skipCommand "missing module name"
    else do
      let (dirname, modname) = splitFileName dirmodname
      mbrst <- if (dirname == "./") then return (Just rst')
               else do putStrLn $ "Changing working directory to " ++ dirname
                       processCd rst' dirname
      maybe (return Nothing)
        (\rst2 ->
          lookupModuleSource (loadPaths rst2) modname >>=
          maybe (skipCommand $
                   "source file of module '" ++ dirmodname ++ "' not found")
                (\_ -> loadCurryProgram rst2 { currMod = modname, addMods = [] }
                                        modname)
        )
        mbrst

--- Process :reload command
processReload :: ReplState -> String -> IO (Maybe ReplState)
processReload rst args
  | currMod rst == preludeName rst
  = skipCommand "no program loaded!"
  | null (stripCurrySuffix args)
  = loadCurryProgram rst (currMod rst)
  | otherwise
  = skipCommand "superfluous argument"

--- Process :modules command
processModules :: ReplState -> String -> IO (Maybe ReplState)
processModules rst _ = printAllLoadedModules rst >> return (Just rst)

--- Process :programs command
processPrograms :: ReplState -> String -> IO (Maybe ReplState)
processPrograms rst _ = printAllLoadPathPrograms rst >> return (Just rst)

--- Process :quit command
processQuit :: ReplState -> String -> IO (Maybe ReplState)
processQuit rst _ = return (Just rst { quit = True })

processSave :: ReplState -> String -> IO (Maybe ReplState)
processSave rst args
  | currMod rst == preludeName rst
  = skipCommand "no program loaded"
  | otherwise
  = do exst <- compileMainExpression rst (if null args then "main" else args)
                                     False
       if exst == 0
         then do renameFile ("." </> mainExpMod rst) (currMod rst)
                 writeVerboseInfo rst 1 $
                   "Executable saved in '" ++ currMod rst ++ "'"
                 return $ Just rst
         else return Nothing

--- Process :show command
processShow :: ReplState -> String -> IO (Maybe ReplState)
processShow rst args = do
  modname <- getModuleName rst args
  mbf <- lookupModuleSource (loadPaths rst) modname
  case mbf of
    Nothing -> skipCommand "source file not found"
    Just (_,fn) -> do
      pager <- getEnv "PAGER"
      let rcshowcmd = rcValue (rcVars rst) "showcommand"
          showprog  = if not (null rcshowcmd)
                        then rcshowcmd
                        else (if null pager then "cat" else pager)
      system $ showprog ++ ' ' : fn
      putStrLn ""
      return (Just rst)

--- Process :source command
processSource :: ReplState -> String -> IO (Maybe ReplState)
processSource rst args
  | null args   = skipCommand "missing function name"
  | null dotfun = do m <- getModuleOfFunction rst args
                     if null m
                       then skipCommand "function not found"
                       else showFunctionInModule rst m args
  | otherwise   = showFunctionInModule rst mod (tail dotfun)
  where (mod, dotfun) = break (== '.') args

--- Process :type command
processType :: ReplState -> String -> IO (Maybe ReplState)
processType rst args = do
  typeok <- printTypeOfExp rst args
  return (if typeok then Just rst else Nothing)

--- Process :usedimports command
processUsedImports :: ReplState -> String -> IO (Maybe ReplState)
processUsedImports rst args = do
  let modname  = if null args then currMod rst else stripCurrySuffix args
  checkAndCallCpmTool "curry-usedimports" "importusage"
    (\toolexec -> execCommandWithPath rst toolexec [modname])

printHelpOnCommands :: IO ()
printHelpOnCommands = putStrLn $ unlines $
  [ "Basic commands (commands can be abbreviated to a prefix if unique):\n" ] ++
  formatVarVals " - "
    [ ("<expr>"          , "evaluate expression <expr>")
    , ("let <p> = <expr>", "add let binding for main expression")
    , (":load <prog>", "load program '<prog>.[l]curry' as main module")
    , (":reload"     , "recompile currently loaded modules")
    , (":add  <m1> .. <mn>",
        "add modules <m1>,...,<mn> to currently loaded modules")
    , (":eval <expr>", "evaluate expression <expr>")
    , (":save <expr>", "save executable with main expression <expr>")
    , (":save"       , "save executable with main expression 'main'")
    , (":type <expr>", "show type of expression <expr>")
    , (":quit"       , "leave the system") ] ++
  [ "\nFurther commands:\n" ] ++
  formatVarVals " - "
    [ (":!<command>"   , "execute <command> in shell")
    , (":browse"       , "browse program and its imported modules")
    , (":cd <dir>"     , "change current directory to <dir>")
    , (":compile <m>"  , "compile module <m> (but do not load it)")
    , (":edit"         , "load source of currently loaded module into editor")
    , (":edit <m>"     , "load source of module <m> into editor")
    , (":fork <expr>"  , "fork new process evaluating <expr>")
    , (":help"         , "show this message")
    , (":interface"    , "show interface of currently loaded module")
    , (":interface <m>", "show interface of module <m>")
    , (":modules"      ,
       "show currently loaded modules with source information")
    , (":programs"     , "show names of Curry modules available in load path")
    , (":set <option>" , "set an option")
    , (":set"          , "see help on options and current options")
    , (":show"         , "show currently loaded source program")
    , (":show <m>"     , "show source of module <m>")
    , (":source <f>"   , "show source of (visible!) function <f>")
    , (":source <m>.<f>   ", "show source of function <f> in module <m>")
    , (":usedimports"  , "show all used imported functions/constructors") ]

--- Print all Curry programs in current load path.
--- Programs found in subdirectories are assumed to be hierarchical.
--- To avoid loops in cyclic directory structure, we put a depth limit
--- on the recursive search.
printAllLoadedModules :: ReplState -> IO ()
printAllLoadedModules rst = do
  putStrLn "Currently loaded modules:"
  let mods = currMod rst : addMods rst
  mapM getSrc mods >>= putStr . unlines . map fmtSrc
 where
  getSrc m = lookupModuleSource (loadPaths rst) m >>=
             return . maybe (m,"???") (\ (_,s) -> (m, s))

  fmtSrc (m,s) = m ++ take (20 - length m) (repeat ' ') ++ " (from " ++ s ++ ")"

--- Print all Curry programs in current load path.
--- Programs found in subdirectories are assumed to be hierarchical.
--- To avoid loops in cyclic directory structure, we put a depth limit
--- on the recursive search.
printAllLoadPathPrograms :: ReplState -> IO ()
printAllLoadPathPrograms rst = mapM_ printDirPrograms (loadPaths rst)
 where
  depthLimit = 10

  printDirPrograms dir = do
    putStrLn $ "Curry programs in directory '" ++ dir ++ "':"
    progs <- getDirPrograms depthLimit "" dir
    putStrLn $ unwords $ sort $ progs
    putStrLn ""

  getDirPrograms dlimit prefix dir = do
    exdir <- doesDirectoryExist dir
    files <- if exdir && dlimit > 0 then getDirectoryContents dir
                                    else return []
    subprogs <- mapM (\d -> getDirPrograms (dlimit - 1) (prefix ++ d ++ ".")
                                           (dir </> d))
                     (filter (\f -> let c = head f in c>='A' && c<='Z') files)
    return $ concat subprogs ++
      concatMap (\f -> let (base, sfx) = splitExtension f
                        in if sfx `elem` [".curry", ".lcurry"] && notNull base
                             then [prefix ++ base]
                             else [])
                files

---------------------------------------------------------------------------
-- Process setting of an option
processSetOption :: ReplState -> String -> IO (Maybe ReplState)
processSetOption rst option
  | null (strip option)
  = printOptions rst >> return (Just rst)
  | otherwise
  = case matched of
      []           -> skipCommand $ "unknown option: '" ++ option ++ "'"
      [(_,act)]    -> act rst (strip args)
      _            -> skipCommand $ "ambiguous option: ':" ++ option ++ "'"
 where
  (opt, args)  = break (==' ') option
  matched      = filter (isPrefixOf (map toLower opt) . fst)
                        (replOptions rst)

-- Returns a list of pairs of option names and the corresponding
-- action to set the option with a given parameter in the state.
replOptions :: ReplState
            -> [(String, ReplState -> String -> IO (Maybe ReplState))]
replOptions rst =
  [ ("v0"           , \r _ -> return (Just r { verbose      = 0     }))
  , ("v1"           , \r _ -> return (Just r { verbose      = 1     }))
  , ("v2"           , \r _ -> return (Just r { verbose      = 2     }))
  , ("v3"           , \r _ -> return (Just r { verbose      = 3     }))
  , ("v4"           , \r _ -> return (Just r { verbose      = 4     }))
  , ("path"         , setOptionPath                                   )
  , ("prompt"       , setPrompt                                       )
  , ("safe"         , \r _ -> return (Just r { safeExec     = True  }))
  , ("parser"       , \r a -> return (Just r { parseOpts    = a     }))
  , ("timeout"      , setTimeout                                      )
  , ("args"         , \r a -> return (Just r { rtsArgs      = a     }))
  -- , ("prelude"      , \r a -> return (Just r { preludeName  = a     }))
  , ("+bindings"    , \r _ -> return (Just r { showBindings = True  }))
  , ("-bindings"    , \r _ -> return (Just r { showBindings = False }))
  , ("+echo"        , \r _ -> return (Just r { withEcho     = True  }))
  , ("-echo"        , \r _ -> return (Just r { withEcho     = False }))
  , ("+show"        , \r _ -> return (Just r { withShow     = True  }))
  , ("-show"        , \r _ -> return (Just r { withShow     = False }))
  , ("+time"        , \r _ -> return (Just r { showTime     = True  }))
  , ("-time"        , \r _ -> return (Just r { showTime     = False }))
  ] ++
  concatMap setCmpOpt ccopts
 where
  ccopts = ccOpts (compiler rst)

  setCmpOpt (CCOption _ _ tags) = map setOptTag tags

  setOptTag opt@(ConstOpt tag _) =
    (tag,
     \r _ -> return (Just r { cmpOpts = map (replaceCompilerOption ccopts opt)
                                            (cmpOpts r) }))
  setOptTag (ArgOpt tag _ fo) = (tag, checkArg)
   where
    checkArg r a =
      maybe (skipCommand "Illegal option argument!")
            (\_ -> return (Just r { cmpOpts = map (replaceCompilerOption ccopts
                                                     (ArgOpt tag a fo))
                                                  (cmpOpts r) }))
            (fo a)

setPrompt :: ReplState -> String -> IO (Maybe ReplState)
setPrompt rst p
  | null rawPrompt = skipCommand "no prompt specified"
  | otherwise      = case head rawPrompt of
    '"' -> case reads rawPrompt of
      [(strPrompt, [])] -> return (Just rst { prompt = strPrompt })
      _                 -> skipCommand "could not parse prompt"
    _   -> return (Just rst { prompt = rawPrompt })
 where rawPrompt = strip p

setTimeout :: ReplState -> String -> IO (Maybe ReplState)
setTimeout rst rawopt
  | null opts  = skipCommand "no value for timeout given"
  | otherwise  = case reads opts of
      [(n, [])] -> return (Just rst { timeOut = if n<0 then 0 else n })
      _         -> skipCommand "illegal timeout parameter (no integer)"
 where opts = strip rawopt

------------------------------------------------------------------------------
-- Show help on options and current settings.
printOptions :: ReplState -> IO ()
printOptions rst = putStrLn $ unlines $ filter notNull
  [ "Options for ':set' command:" ] ++
  formatVarVals " - "
    ([ ("v<n>", "verbosity level\n" ++
                "0: quiet (errors and warnings only)\n" ++
                "1: show status messages (default)\n" ++
                "2: show commands\n" ++
                "3: show intermediate infos\n" ++
                "4: show all details")
     , ("path <paths>"   , "set additional search paths for imported modules")
     , ("prompt <prompt>", "set the user prompt")
     , ("safe"           , "safe execution mode without I/O actions")
     , ("parser  <opts>" , "additional options passed to parser (front end)")
     , ("timeout <n>"    ,
        "timeout (in seconds) for main evaluation (0 = unlimited)")
     , ("args    <args>" , "run-time arguments passed to main program") ] ++
     sort
       ([ ("+/-time"   , "show compilation and execution time")
        , ("+/-echo"   , "turn on/off echoing of commands")
        , ("+/-show"   , "use 'Prelude.show' to show evaluation results")
        , ("+/-bindings", "show bindings of free variables in initial goal")
        ] ++ map showCompilerOptionDescr (ccOpts (compiler rst)))) ++
  [ showCurrentOptions rst ]

showCurrentOptions :: ReplState -> String
showCurrentOptions rst = intercalate "\n" $ filter notNull
  [ "\nCurrent settings:" ] ++
  formatVarVals ": "
    [ ("import paths      ", intercalate [searchPathSeparator] (loadPaths rst))
    , ("parser options    ", parseOpts rst)
    , ("timeout           ", show (timeOut rst))
    , ("run-time arguments", rtsArgs rst)
    , ("verbosity         ", show (verbose rst))
    , ("prompt            ", show (prompt rst))
    , ("let bindings      ", unlines (letBinds rst))
    , ("...............and"
      , unwordsOpts $ sortBy (\f1 f2 -> setFlag f1 <= setFlag f2) $
          [ showOnOff (showBindings rst) ++ "bindings"
          , showOnOff (withEcho     rst) ++ "echo"
          , showOnOff (withShow     rst) ++ "show"
          , showOnOff (showTime     rst) ++ "time"
          ] ++ map showCompilerOption (cmpOpts rst)) ] ++
  (if verbose rst > 2
     then [ "\nProperties from rc file:" ] ++
          formatVarVals " = " (rcVars rst) ++
          [ "\nREPL configuration:" ] ++
          formatVarVals ": "
            [ ("prelude name"       , preludeName rst)
            , ("main exp module"    , mainExpMod  rst)
            , ("parser executable"  , ccFrontend ccdesc)
            , ("parser option"      , ccParseOpt ccdesc "OPTS")
            , ("compiler home dir"  , ccHome     ccdesc)
            , ("compiler executable", ccExec     ccdesc)
            , ("verbosity option"   , ccVerbOpt  ccdesc "VERB")
            , ("compile option"     , ccCmplOpt  ccdesc "MOD")
            , ("executable option"  , ccExecOpt  ccdesc "MOD")
            , ("clean command"      , ccCleanCmd ccdesc "MOD") ]
     else [])
 where
  ccdesc = compiler rst

  unwordsOpts xs = let s = unwords xs
                   in if length s >= 60 then unlines (unwordsN 5 xs)
                                        else s

  unwordsN n xs = let (ns,ms) = splitAt n xs
                  in unwords ns : if null ms then [] else unwordsN n ms

  setFlag []     = []
  setFlag (c:cs) = if c `elem` "+-" then '~':cs else c:cs

  showOnOff b = if b then "+" else "-"

-- Format a list of variable/value string pairs and put the first argument
-- between these strings.
formatVarVals :: String -> [(String,String)] -> [String]
formatVarVals sep vvs =
  map (\ (var,val) -> var ++ blanks (maxvar - length var) ++ sep ++
           intercalate ('\n' : blanks (maxvar + length sep)) (lines val))
      vvs
 where
  blanks n = take n (repeat ' ')

  maxvar = maximum (map (length . fst) vvs)

---------------------------------------------------------------------------
--- The default import paths of the Curry compiler.
--- It consists of the path defined by the environment variable CURRYPATH,
--- and the "libraries" property defined in ~/.<compiler>rc
defaultImportPaths :: ReplState -> IO [String]
defaultImportPaths rst = do
  currypath <- getEnv "CURRYPATH"
  let rclibs = rcValue (rcVars rst) "libraries"
  return $ filter (/= ".") $ splitSearchPath currypath ++ splitSearchPath rclibs

defaultImportPathsWith :: ReplState -> String -> IO [String]
defaultImportPathsWith rst dirs = do
  defipath <- defaultImportPaths rst
  adirs    <- mapM getAbsolutePath (splitSearchPath dirs)
  return (adirs ++ defipath)

setOptionPath :: ReplState -> String -> IO (Maybe ReplState)
setOptionPath rst args = do
  ipath <- if null args then defaultImportPaths rst
                        else defaultImportPathsWith rst args
  return (Just rst { importPaths = ipath })

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

-- Compiles a main expression by creating a "main" module.
-- If the third argument is `True`, the generated executable is
-- invoked and then removed.
compileMainExpression :: ReplState -> String -> Bool -> IO Int
compileMainExpression rst exp runrmexec = do
  if safeExec rst
    then do -- check for imports of Unsafe
      unsafeused <- importUnsafeModule rst
      if unsafeused
        then do writeErrorMsg "Import of 'Unsafe' not allowed in safe mode!"
                return 1
        else compileProgExp
    else compileProgExp
 where
  compileProgExp = do
    (ecg, freevars) <- generateMainExpFile
    let mainexpmod = mainExpMod rst
    if ecg /= 0
      then do cleanModule rst mainexpmod
              return ecg
      else do
        when (verbose rst > 3) $ do
          putStrLn "GENERATED MAIN MODULE:"
          readFile (mainExpFile rst) >>= putStrLn
        let compilecmd = curryCompilerCommand (reduceVerbose rst) freevars ++
                         " " ++ (ccExecOpt (compiler rst)) mainexpmod
        timecompilecmd <- getTimeCmd rst "Compilation" compilecmd
        if ccCurryPath (compiler rst)
          then execCommandWithPath rst timecompilecmd [] >> return ()
          else do writeVerboseInfo rst 2 $ "Executing: " ++ timecompilecmd
                  system timecompilecmd >> return ()
        cleanModule rst mainexpmod
        if runrmexec
          then do
            timecmd <- getTimeCmd rst "Execution"
                         (unwords ["./" ++ mainexpmod, rtsArgs rst])
            getTimeoutCmd rst timecmd >>= execAndRemove rst mainexpmod
          else return 0

  generateMainExpFile = do
    unlessKeepFiles rst $ removeFileIfExists $ acyFileName rst (mainExpMod rst)
    writeSimpleMainExpFile rst exp
    getAcyOfMainExpMod rst >>=
      maybe (return (1, []))
            (\cprog -> makeMainExpMonomorphic rst cprog exp >>=
                       maybe
                         (return (1, []))
                         (\ (mprog,mexp) ->
                             insertFreeVarsShowInMainExp rst mprog mexp >>=
                             maybe (return (1, []))
                                   (\ (_,_,freevars) -> return (0, freevars))))

-- Invokes a command (third argument) and removes the executable (second
-- argument) after execution (unless `keepfiles` option is set).
-- In order to support the deletion of the executable event after Ctrl-C,
-- the execution is wrapped into a shell which traps interrupts.
execAndRemove :: ReplState -> String -> String -> IO Int
execAndRemove rst executable execcmd = do
  writeVerboseInfo rst 2 $ "Executing: " ++ execcmd
  let scriptfile = executable ++ ".sh"
  let shellscript = shellScript scriptfile
  writeFile scriptfile shellscript
  writeVerboseInfo rst 3 $ "...with shell script:\n" ++ shellscript
  ecx <- system $ "/bin/sh " ++ scriptfile
  unless (ecx == 0) $ writeVerboseInfo rst 1 $
    "Execution terminated with exit status: " ++ show ecx
  unlessKeepFiles rst $ do
    removeFileIfExists scriptfile
    removeFileIfExists executable
  return ecx
 where
  shellScript scriptfile = unlines
    [ "#!/bin/sh"
    , "cleanup_mainfiles() {"
    , "  ECODE=$?"
    , "  # change exit code 130 (Ctrl-C) to 1 to avoid exit of REPL:"
    , "  if [ $ECODE -eq 130 ] ; then ECODE=1 ; fi"
    , (if keepFiles rst
         then ""
         else "  /bin/rm -f " ++ executable ++ " " ++ scriptfile ++ " && ")
      ++ "  exit $ECODE"
    , "}"
    , "trap 'cleanup_mainfiles' 1 2 3 6"
    , execcmd
    , "######################## end of script ###################"
    ]


-- Removes a Curry module and intermediate files.
cleanModule :: ReplState -> String -> IO ()
cleanModule rst mainmod = unlessKeepFiles rst $ do
  writeVerboseInfo rst 2 $ "Executing: " ++ cleancmd
  system cleancmd
  return ()
 where
  cleancmd  = ccCleanCmd (compiler rst) mainmod

-- Executes an I/O action if the RC values `keepfiles` is not `yes`.
unlessKeepFiles :: ReplState -> IO () -> IO ()
unlessKeepFiles rst act = unless (keepFiles rst) act

-- Returns `True` if RC value `keepfiles` is set to `yes`.
keepFiles :: ReplState -> Bool
keepFiles rst = rcValue (rcVars rst) "keepfiles" == "yes"

---------------------------------------------------------------------------
-- Transforming main expression into appropriate form.

-- In LegacyFreeMode:
-- Insert free variables occurring in the main expressions
-- as components of the main expression so that their bindings are shown.
-- The arguments are the AbstractCurry program of the main expression
-- and the main expression as a string.
-- Also adds show/print if desired.
-- The result is Nothing (if some error occurred) or the transformed
-- AbstractCurry program, expression and any free variables.
-- If not in LegacyFreeMode:
-- Only add show/print if desired,
-- the rest is done by the respective compiler.
-- The result structure is the same as in LegacyFreeMode.
insertFreeVarsShowInMainExp :: ReplState -> CurryProg -> String
                            -> IO (Maybe (CurryProg, String, [String]))
insertFreeVarsShowInMainExp rst (CurryProg _ _ _ _ _ _ fdecls _) mainexp = do
  let [mfunc@(CFunc _ _ _ (CQualType _ ty) _)] = fdecls
  let freevars           = freeVarsInFuncRule mfunc
      (exp, whereclause) = breakWhereFreeClause mainexp
  if safeExec rst && isIOType ty
    then do writeErrorMsg "Operation not allowed in safe mode!"
            return Nothing
    else
      if null freevars
          || not (showBindings rst)
          || ((not (withShow rst) && isLegacyFreeMode (freeMode rst))
                && length freevars > 10) -- due to tuple limit
          || null whereclause
        then do
          let freevarexp = addPrintShow exp ty ++ whereclause
          writeVerboseInfo rst 2 "Adding show/print to expression"
          writeVerboseInfo rst 3 $ "New expression: " ++ freevarexp
          writeSimpleMainExpFile rst freevarexp
          getAcyOfMainExpMod rst >>=
            maybe (return Nothing)
                  (\p -> return $ Just (p,freevarexp,[]))
        else if isLegacyFreeMode (freeMode rst)
          then do
            let freevarexp = addFreeShowLegacy exp freevars whereclause ty
            writeVerboseInfo rst 2 $
              "Adding printing of bindings for free variables: " ++
                intercalate "," freevars
            writeVerboseInfo rst 3 $ "New expression: " ++ freevarexp
            writeSimpleMainExpFile rst freevarexp
            getAcyOfMainExpMod rst >>=
              maybe (return Nothing)
                    (\p -> return $ Just (p,freevarexp, []))
          else do
            let freevarexp = addFreeShowCmdLine exp whereclause ty
            writeVerboseInfo rst 2 "Adding show/print to expression"
            writeVerboseInfo rst 3 $ "New expression: " ++ freevarexp
            writeSimpleMainExpFile rst freevarexp
            getAcyOfMainExpMod rst >>=
              maybe (return Nothing)
                    (\p -> return $ Just (p,freevarexp,freevars))
 where
  addPrintShow exp ty
    | withShow rst && isIOReturnType ty = exp ++ " Prelude.>>= Prelude.print"
    | withShow rst && not (isIOType ty) = "show (" ++ exp ++ ")"
    | otherwise                         = exp

  addFreeShowLegacy exp freevars whereclause ty = unwords $
    if withShow rst
      then if null freevars || isIOReturnType ty
        then [addPrintShow exp ty, whereclause]
        else
             ["((\"{\""] ++
             intersperse ("++ \", \" ")
               (map (\v-> "++ \"" ++ v ++ " = \" ++ show " ++ v) freevars) ++
             ["++ \"} \") ++) $!! "] ++ [addPrintShow exp ty] ++ [whereclause]
      else ["(", exp] ++
           map (\v-> ", \"" ++ v ++ ":\", " ++ v) freevars ++
           [")"] ++ [whereclause]

  addFreeShowCmdLine exp whereclause ty = unwords $
    if withShow rst
      then [addPrintShow exp ty, whereclause]
      else [exp, whereclause]

  freeVarsInFuncRule f = case f of
    CFunc _ _ _ _ (CRule _ rhs : _) -> freeVarsInRhs rhs
    _ -> error "REPL.insertFreeVarsShowInMainGoal.freeVarsInFuncRule"

  freeVarsInRhs rhs = case rhs of
    CSimpleRhs  _ ldecls -> concatMap lvarName ldecls
    CGuardedRhs _ ldecls -> concatMap lvarName ldecls

  lvarName ldecl = case ldecl of CLocalVars vs -> map snd vs
                                 _             -> []

-- Breaks a main expression into an expression and a where...free clause.
-- If the where clause is not present, the `where` part is empty.
breakWhereFreeClause :: String -> (String,String)
breakWhereFreeClause exp =
  let revexp = reverse exp
  in if take 4 revexp == "eerf"
       then let woWhere = findWhere (drop 4 revexp)
            in if null woWhere
                 then (exp,"")
                 else (reverse woWhere, drop (length woWhere) exp)
       else (exp,"")
 where
  findWhere [] = []
  findWhere (c:cs) | isSpace c && take 6 cs == "erehw " = drop 6 cs
                   | otherwise                          = findWhere cs


--- If the main expression is polymorphic, make it monomorphic by adding
--- a type declaration where type variables are replaced by type `()`.
--- Before, type variables with a numeric constraint like `Num`/`Integral` or
--- `Fractional`/`Floating` are defaulted to the types `Int` or `Float`,
--- respectively. The type of the main expression is only allowed to contain
--- numeric constraints.
--- If the main exp has type `IO t` where t is monomorphic and not a function,
--- t /= (), and `withShow` is `True`, then `>>= print` is added
--- to the expression to print the computed value.
--- Otherwise (if the main exp has type `IO t`), `>>= return` is added
--- in order to support raising non-determinism errors during the
--- monadic bind operation.
--- The arguments are the AbstractCurry program of the main expression
--- and the main expression as a string.
--- The result is Nothing (if some error occurred) or the transformed
--- AbstractCurry program and expression.
makeMainExpMonomorphic :: ReplState -> CurryProg -> String
                       -> IO (Maybe (CurryProg, String))
makeMainExpMonomorphic rst prog exp = case prog of
  CurryProg _ _ _ _ _ _ [CFunc _ _ _ qty _] _ -> makeMonoType qty
  _ -> error "REPL.makeMainExpMonomorphic"
 where
  makeMonoType qty@(CQualType _ ty)
    | isFunctionalType ty
    = do writeErrorMsg "expression is of functional type"
         return Nothing
    | isPolyType ty
    = case defaultQualTypeExpr qty of
        CQualType (CContext []) defTy -> do
          when (defTy /= ty) $ writeVerboseInfo rst 2 $
            "Defaulted type of main expression: " ++
            showMonoTypeExpr False defTy
          let (nwexp, whereclause) = breakWhereFreeClause exp
              nwexpR               = addReturn nwexp defTy
              mtype = showMonoTypeExpr True defTy
              mexp  = "(" ++ nwexpR ++ " :: " ++ mtype ++ ") " ++ whereclause
          writeMainExpFile rst (modsOfType defTy) (Just mtype) mexp
          writeVerboseInfo rst 3 $ "New expression: " ++ mexp
          when (isPolyType defTy) $ writeVerboseInfo rst 2 $
            "Type of main expression \"" ++ showMonoTypeExpr False defTy
            ++ "\" made monomorphic by replacing type variables by \"()\""
          getAcyOfMainExpMod rst >>=
            maybe (return Nothing)
                  (\p -> return $ Just (p,mexp))
        _ -> do writeErrorMsg $
                  "cannot handle overloaded top-level expression of type: " ++
                  showMonoQualTypeExpr False qty
                return Nothing
    | otherwise
    = if newexp == exp
        then return $ Just (prog,exp)
        else do writeSimpleMainExpFile rst newexp
                getAcyOfMainExpMod rst >>=
                  maybe (return Nothing)
                        (\p -> return $ Just (p,newexp))
   where
    newexp = let (nwexp, whereclause) = breakWhereFreeClause exp
                 nwexpR               = addReturn nwexp ty
             in nwexpR ++ whereclause

    -- raise ND-in-IO Errors
    addReturn e te = if isIOType te
                       then '(' : e ++ ") Prelude.>>= Prelude.return"
                       else e

-- Defaults type variables with a numeric constraint like `Num`/`Integral` or
-- `Fractional`/`Floating` to the types `Int` or `Float`, respectively.
-- Moreover, existing `Data`, `Eq`, `Ord`, `Read`, and `Show` constraints
-- for the same type variable are removed.
-- Finally, remaining type variables with `Data` and `Monad` constraints are
-- defaulted to `Prelude.Bool` and `Prelude.IO`, respectively.
defaultQualTypeExpr :: CQualTypeExpr -> CQualTypeExpr
defaultQualTypeExpr (CQualType (CContext ctxt) cty) =
  defaultMonad $ defaultData $ defaultTExp ctxt (CQualType (CContext []) cty)
 where
  defaultData qty@(CQualType (CContext dctxt) dcty) = case dctxt of
    [] -> qty
    (qtcons, CTVar tv) : cs | qtcons == pre "Data"
      -> defaultData (CQualType (CContext cs)
                        (substTypeVar tv (CTCons (pre "Bool")) dcty))
    _ -> qty

  defaultMonad qty@(CQualType (CContext dctxt) dcty) = case dctxt of
    [] -> qty
    (qtcons, CTVar tv) : cs | qtcons `elem` map pre ["Monad","MonadFail"]
      -> defaultMonad (CQualType (CContext cs)
                         (substTypeVar tv (CTCons (pre "IO")) dcty))
    _ -> qty

  defaultTExp :: [CConstraint] -> CQualTypeExpr -> CQualTypeExpr
  defaultTExp []     qty                           = qty
  defaultTExp (c:cs) (CQualType (CContext cs2) ty) = case c of
    (("Prelude", ptype), CTVar tv) ->
      if ptype `elem` ["Num", "Integral", "Fractional", "Floating"]
        then let defptype = if ptype `elem` ["Fractional", "Floating"]
                              then "Float"
                              else "Int"
             in defaultTExp
                  (removeConstraints tv defptype cs)
                  (CQualType (CContext (removeConstraints tv defptype cs2))
                     (substTypeVar tv (CTCons (pre  defptype)) ty))
        else defaultTExp cs (CQualType (CContext (cs2 ++ [c])) ty)
    _ -> defaultTExp cs (CQualType (CContext (cs2 ++ [c])) ty)

  removeConstraints _  _        []       = []
  removeConstraints tv dflttype (c3:cs3) = case c3 of
    (("Prelude", cls), CTVar tv2)
      | tv == tv2 && cls `elem` ["Data", "Eq", "Ord", "Read", "Show"]
      -> removeConstraints tv dflttype cs3
      | tv == tv2 && dflttype == "Int" && cls == "Enum"
      -> removeConstraints tv dflttype cs3
    _ -> c3 : removeConstraints tv dflttype cs3

-- Replaces a type variable with a type expression.
substTypeVar :: CTVarIName -> CTypeExpr -> CTypeExpr -> CTypeExpr
substTypeVar tv def te@(CTVar      tv2) = if tv == tv2 then def else te
substTypeVar _  _   te@(CTCons       _) = te
substTypeVar tv def (CFuncType te1 te2) =
  CFuncType (substTypeVar tv def te1) (substTypeVar tv def te2)
substTypeVar tv def (CTApply   te1 te2) =
  CTApply (substTypeVar tv def te1) (substTypeVar tv def te2)

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

-- Parse a Curry program to detect errors (for load/reload command):
parseCurryProgram :: ReplState -> String -> Bool -> IO (Maybe ReplState)
parseCurryProgram rst curryprog tfcy = do
  let frontendparams = currentFrontendParams rst (verbose rst == 0)
      target         = if tfcy then TFCY else FCY
  catch (verbCallFrontendWithParams rst target frontendparams curryprog
           >> return (Just rst))
        (\_ -> return Nothing)

-- Load a Curry program (parse only or compile it):
loadCurryProgram :: ReplState -> String -> IO (Maybe ReplState)
loadCurryProgram rst0 curryprog = do
  let rst = rst0 { letBinds = [] }
  maybe (compileCurryProgram rst curryprog)
        (parseCurryProgram rst curryprog)
        (ccTypedFC (compiler rst))

-- Compile a Curry program with the Curry compiler:
compileCurryProgram :: ReplState -> String -> IO (Maybe ReplState)
compileCurryProgram rst curryprog = do
  let compilecmd = curryCompilerCommand rst [] ++ " " ++
                   (ccCmplOpt (compiler rst)) curryprog
  timecompilecmd <- getTimeCmd rst "Compilation" compilecmd
  if ccCurryPath (compiler rst)
    then execCommandWithPath rst timecompilecmd []
    else do writeVerboseInfo rst 2 $ "Executing: " ++ timecompilecmd
            es <- system timecompilecmd
            return $ if es == 0 then Just rst else Nothing

-- Generate the base command to call the Curry compiler:
curryCompilerCommand :: ReplState -> [String] -> String
curryCompilerCommand rst vs = unwords [ccExec (compiler rst), cmpopts]
 where
  cmpopts = unwords $
    [ -- pass current value of "bindingoptimization" property to compiler:
      -- "-Dbindingoptimization=" ++ rcValue (rcVars rst) "bindingoptimization"
      (ccVerbOpt (compiler rst)) (show (verbose rst))
    ] ++
    (if ccCurryPath (compiler rst)
       then []
       else map ("-i" ++) (loadPaths rst)) ++
    filter notNull (map mapCompilerOption (cmpOpts rst)) ++
    (if null (parseOpts rst)
      then []
      else [(ccParseOpt (compiler rst)) (parseOpts rst)]) ++
    (case freeMode rst of
      LegacyFreeMode            -> []
      CommandLineFreeMode trans -> [trans (zip vs [1..])] ++
                                   [ "-B" | showBindings rst])

--- Extract a module name, possibly prefixed by a path, from an argument,
--- or return the current module name if the argument is the empty string.
getModuleName :: ReplState -> String -> IO String
getModuleName rst args =
  if null args
  then return (currMod rst)
  else let (dirname, mname) = splitFileName (stripCurrySuffix args)
        in if dirname == "./"
           then return mname
           else getAbsolutePath (stripCurrySuffix args)

-- Reduce verbosity in the REPL state.
reduceVerbose :: ReplState -> ReplState
reduceVerbose rst = rst { verbose = redVerb (verbose rst) }
 where
  redVerb n | n == 0    = 0
            | otherwise = n - 1

---------------------------------------------------------------------------
-- Operations to call auxiliary tools.

-- Showing source code of functions via SourcProgGUI tool.
-- If necessary, open a new connection and remember it in the repl state.
showFunctionInModule :: ReplState -> String -> String -> IO (Maybe ReplState)
showFunctionInModule rst mod fun =
  checkForWish $
  checkAndCallCpmTool "curry-showsource" "sourceproggui" $ \spgui -> do
    writeVerboseInfo rst 1 $
      "Showing source code of function '" ++ mod ++ "." ++ fun ++
      "' in separate window..."
    let spguicmd = "CURRYPATH=" ++
                   intercalate [searchPathSeparator] (loadPaths rst) ++
                   " && export CURRYPATH && " ++ spgui ++ " " ++ mod
    writeVerboseInfo rst 2 $ "Executing: " ++ spguicmd
    (rst',h') <- maybe (do h <- connectToCommand spguicmd
                           return (rst {sourceguis = (mod,(fun,h))
                                                     : sourceguis rst }, h))
                       (\ (f,h) -> do
                           hPutStrLn h ('-':f)
                           hFlush h
                           return (rst {sourceguis = updateFun (sourceguis rst)
                                                               mod fun }, h))
                       (lookup mod (sourceguis rst))
    hPutStrLn h' ('+':fun)
    hFlush h'
    return (Just rst')
 where
  updateFun []                _  _  = []
  updateFun ((m,(f,h)):sguis) md fn =
    if m==md then (m,(fn,h)):sguis
             else (m,(f,h)) : updateFun sguis md fn

-- Check whether some CPM tool is available, i.e., either in the current
-- path or in the CPM bin directory. If it is not available,
-- skip the command with an error message how to install the tool from
-- the package (specified in the second argument). Otherwise, continue with
-- the last argument by passing the name of the CPM tool.
checkAndCallCpmTool :: String -> String -> (String -> IO (Maybe ReplState))
                    -> IO (Maybe ReplState)
checkAndCallCpmTool tool package continue = do
  excmd <- system $ "which " ++ tool ++ " > /dev/null"
  if excmd == 0
    then continue tool
    else do homedir <- getHomeDirectory
            let cpmtoolfile = homedir </> ".cpm" </> "bin" </> tool
            excpm <- doesFileExist cpmtoolfile
            if excpm
              then continue cpmtoolfile
              else skipCommand errmsg
 where
  errmsg = "'" ++ tool ++ "' not found. Install it by: 'cypm install " ++
           package ++ "'!"

-- Execute some command (first argument) with some arguments (second argument).
-- The current load path is exported to the command via the environment
-- variable CURRYPATH.
execCommandWithPath :: ReplState -> String -> [String]
                    -> IO (Maybe ReplState)
execCommandWithPath rst cmd args = do
  let setpath = "CURRYPATH=" ++
                intercalate [searchPathSeparator] (loadPaths rst) ++
                " && export CURRYPATH && "
      syscmd = setpath ++ cmd ++ ' ' : unwords args
  writeVerboseInfo rst 2 $ "Executing: " ++ syscmd
  system syscmd >> return (Just rst)

-- Check whether some system command is available. If it is not available,
-- skip the command with the given error message, otherwise continue with
-- the last argument.
checkForCommand :: String -> String -> IO (Maybe ReplState)
                -> IO (Maybe ReplState)
checkForCommand cmd errmsg continue = do
  excmd <- system $ "which " ++ cmd ++ " > /dev/null"
  if (excmd>0) then skipCommand errmsg
               else continue

-- Check whether the windowing shell "wish" is available.
checkForWish :: IO (Maybe ReplState) -> IO (Maybe ReplState)
checkForWish =
  checkForCommand "wish"
    "Windowing shell `wish' not found. Please install package `tk'!"

-- Terminate all open SourceProgGUIs
terminateSourceProgGUIs :: ReplState -> IO ReplState
terminateSourceProgGUIs rst
  | null sguis = return rst
  | otherwise  = do
      writeVerboseInfo rst 1 "Terminating source program GUIs..."
      catch (mapM_ (\ (_,(_,h)) -> hPutStrLn h "q" >> hFlush h >> hClose h)
                   sguis)
            (\_ -> return ())
      return rst { sourceguis = [] }
 where sguis = sourceguis rst

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