Hello World

The following program is the “Hello World” of Haskus system:

import Haskus.System

main :: IO ()
main = runSys <| do

   -- Initialize the default terminal
   term <- defaultTerminal

   -- print a string on the standard output
   writeStrLn term "Hello World!"

   -- wait for a key to be pressed
   waitForKey term

   -- shutdown the computer
   powerOff_

It writes the “Hello World” string on the default terminal, then wait for a key to be pressed, and finally it power off the computer.

Note that unlike traditional Unix programs, we don’t use STDIN and STDOUT explicitly: we have to query a terminal and to use it explicitly.