fp2/week2/mart/StdIOMonad.icl

   1 module StdIOMonad
   2
   3 import StdEnv, StdMaybe, StdMonad, StdFile
   4
   5 :: IO a = IO (*World -> *(a, *World))
   6
   7 read :: *World -> (IO String, *World)
   8 read world
   9 # (io, world) = stdio world
  10 # (line, io) = freadline io
  11 # (ok, world) = fclose io
  12 | not ok = abort "Couldn't close console"
  13 | otherwise = line
  14
  15 instance return IO where
  16         return x = IO (\w = (x, w))
  17
  18 instance >>= IO where
  19         >>= (IO f) g = (IO f)
  20
  21 Start :: *World -> (IO String, *World)
  22 Start world = read