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implementation module StdIOMonad
//Deze module verpakt StdFile in een monadische jas
import StdFile
import StdMonad
import StdMaybeMonad
:: IO a = IO (*World Filehandle -> *(a, *World, Filehandle))
:: Void = Void
:: Filemode = Lees | Schrijf
:: Filenaam :== String
:: *Filehandle = None | FH *(Bool, Filemode, *File)
toInt :: Filemode -> Int
toInt Lees = FReadText
toInt Schrijf = FWriteText
Start world = read
////voer monadische I/O actie uit op de wereld:
//doIO :: (IO a) *World -> *(a,*World)
//doIO (IO f) world = f (world, Closed)
// IO is een monad:
instance return IO where
return x = IO (\w fh = (x, w, fh))
//instance >>= IO where
// (>>=) (IO f) g = IO(\w = let (a, w1) = f w in doIO (g a) w1)
//lees regel van de console:
read:: IO String
read = IO (\w fh -> ("", w, fh))
/*//schrijf regel naar de console:
write:: String -> IO Void
write s = IO (\w = (Void, write` s w))
where
write`:: String *World -> *World
write` s world
# (io, world) = stdio world
# io = fwrites s world
# (_, world) = fclose io
= world
//open de file met gegeven filenaam en mode:
open:: Filenaam Filemode -> IO (Maybe Filehandle)
open s m = IO (\w = let (f1, w1) = openfh` s m w in (f1, (w1, f1)))
where
openfh`:: Filenaam Filemode *World -> (Maybe Filehandle, *World)
openfh` s m world
# (ok, file, world) = fopen s (toInt m) world
| ok = (Just (Open (m, file)), world)
| otherwise = (Nothing, world)
//sluit de file met gegeven filenaam:
close:: Filehandle -> IO Bool
close fh = IO (\w = let (b1, w1) = close` fh w in (b1, (w1, Closed)))
where
close`:: Filehandle *World -> (Bool, *World)
close` Closed world = (False, world)
close` (Open (_, file)) world = fclose file world
//bepaal of het lezen van de file klaar is:
eof:: Filehandle -> IO Bool
eof fh = IO (\w = let (b1, w1) = eof` fh w in (b1, (w1, Closed)))
where
eof`:: Filehandle *World -> (Bool, *World)
eof` Closed world = (world, False)
eaf`(Open (_, file)) world = fclose file
//lees een regel van een file:
readline:: Filehandle -> IO (Maybe String)
readline fh = IO (\w = let r1 = readline` fh w in r1)
where
readline`:: Filehandle *World -> (Maybe String, (*World, Filehandle))
readline` Closed world = (world, Nothing)
readline` (Open (Schrijf, _)) world = (world, Nothing)
readline` (Open (Lees, file)) world
# (line, file) = sfreadline file
= (Just line, (world, Open (Lees, file)))
//schrijf een regel naar een file:
writeline:: String Filehandle -> IO Bool
writeline s fh = IO (\w = let r1 = writeline` s fh w in r1)
where
writeline`:: String Filehandle *World -> (Bool, (*World, Filehandle))
writeline` line Closed world = (False, (world, Closed))
writeline` line (Open (Lees, file)) world = (False, (world, (Open (Lees, file))))
writeline` line (Open (Schrijf, file)) world
# file = fwrites line file
= (True, (world, file))*/
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