IT WORKS =====D

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+implementation module StdIOMonad

+

+import StdBool

+import StdEnum

+import StdFile

+import StdList

+import StdMaybe

+import StdMisc

+import StdMonad

+import StdOverloaded

+import StdString

+import StdTuple

+

+:: IO a = IO (*W -> *(a, *W))

+:: *W :== *(*World, *[*(Filehandle, *File)])

+:: Filemode = Lees | Schrijf

+:: Filenaam :== String

+:: Filehandle :== String

+

+instance toInt Filemode where

+	toInt Lees = FReadText

+	toInt Schrijf = FWriteText

+

+//voer monadische I/O actie uit op de wereld:

+doIO:: (IO a) *World -> *(a, *W)

+doIO (IO f) w = f (w, [])

+

+unIO:: (IO a) -> *W -> *(a, *W)

+unIO (IO f) = f 

+

+//  IO is een monad:

+instance return IO where

+	return x = IO (\w -> (x, w))

+instance >>=    IO where

+	(>>=) (IO f) g = IO (\w = let (a, w1) = f w in unIO (g a) w1)

+

+read:: IO String

+read = IO read`

+	where

+		read`:: *W -> *(String, *W)

+		read` (world, s)

+		# (io, world) = stdio world

+		# (line, io) = freadline io

+		# (_, world) = fclose io world

+		= (line, (world, s))

+

+//	schrijf regel naar de console:

+write		:: String -> IO Void

+write s = IO (write` s)

+	where

+		write`:: String *W -> *(Void, *W)

+		write` line (world, s)

+		# (io, world) = stdio world

+		# io = io <<< line

+		# (_, world) = fclose io world

+		= (Void, (world, s))

+

+//	open de file met gegeven filenaam en mode:

+find:: Filehandle *[*(Filehandle, *File)] -> (Maybe *(Filehandle, *File), *[*(Filehandle, *File)]) 

+find fh fs

+# (fhs, fis) = unzip fs

+# fhsC = zip2 [0..length fhs] fhs

+# index = [(i, h) \\ (i, h) <- fhsC | h == fh]

+| length index == 0 = (Nothing, zip2 fhs fis)

+# index = fst (hd index)

+# (fis1, fis2) = splitAt index fis

+# (fhs1, fhs2) = splitAt index fhs

+# (thefile, fis2) = splitAt 1 fis2

+# (thehandle, fhs2) = splitAt 1 fhs2

+= (Just (hd thehandle, hd thefile), zip2 (fhs1 ++ fhs2) (fis1 ++ fis2))

+

+

+open:: Filenaam Filemode -> IO (Maybe Filehandle)

+open s m = IO (open` s m)

+	where

+		open`:: String Filemode *W -> *(Maybe Filehandle, *W)

+		open` fp m (world, fs)

+		| any (\l = fp == fst l) fs = (Nothing, (world, fs))

+		# (ok, file, world) = fopen fp (toInt m) world

+		= (Just fp, (world, [(fp, file):fs]))

+

+//	sluit de file met gegeven filenaam:

+close:: Filehandle -> IO Bool

+close fh = IO (close` fh)

+	where

+		close`:: Filehandle *W -> *(Bool, *W)

+		close` fp (world, fs)

+		# (currentfiletuple, fs) = find fp fs

+		| isNothing currentfiletuple = (False, (world, fs))

+		# (currentfh, currentfile) = fromJust currentfiletuple

+		# (ok, world) = fclose currentfile world

+		| not ok = abort "File can't be closed"

+		| otherwise = (True, (world, fs))

+		

+

+//	bepaal of het lezen van de file klaar is:

+eof			:: Filehandle -> IO Bool

+eof fh = IO (eof` fh)

+	where 

+		eof`:: Filehandle *W -> *(Bool, *W)

+		eof` fp (world, fs)

+		# (currentfiletuple, fs) = find fp fs

+		| isNothing currentfiletuple = abort "Can't do eof on non-existing file"

+		# (currentfh, currentfile) = fromJust currentfiletuple

+		# (ok, file) = fend currentfile

+		= (ok, (world, [(currentfh, file):fs]))

+

+//	lees een regel van een file:

+readline	:: Filehandle -> IO (Maybe String)

+readline fh = IO (readline` fh)

+	where

+		readline` :: Filehandle *W -> *(Maybe String, *W)

+		readline` fh (world, fs)

+		# (currentfiletuple, fs) = find fh fs

+		| isNothing currentfiletuple = (Nothing, (world, fs))

+		# (currentfh, currentfile) = fromJust currentfiletuple

+		# (s, currentfile) = freadline currentfile

+		= (Just s, (world, [(currentfh, currentfile):fs]))

+

+//	schrijf een regel naar een file:

+writeline	:: String Filehandle -> IO Bool

+writeline s fh = IO (writeline` s fh)

+	where

+		writeline` :: String Filehandle *W -> *(Bool, *W)

+		writeline` s fh (world, fs)

+		# (currentfiletuple, fs) = find fh fs

+		| isNothing currentfiletuple = (True, (world, fs))

+		# (currentfh, currentfile) = fromJust currentfiletuple

+		# currentfile = fwrites (s +++ "\n") currentfile

+		= (True, (world, [(currentfh, currentfile):fs]))