Haskell MPI example

gistfile1.hs

-- Below is a small but complete MPI program. Process 1 sends the message "Hello World"
-- to process 0, which in turn receives the message and prints it to standard output.
-- All other processes, if there are any, do nothing. 
--                                                    -- http://hackage.haskell.org/package/haskell-mpi

module Main where

import Control.Parallel.MPI.Simple (mpiWorld, commWorld, unitTag, send, recv)

main :: IO ()
main = mpiWorld $ \size rank ->
   if size < 2
      then putStrLn "At least two processes are needed"
      else case rank of
         0 -> do (msg, _status) <- recv commWorld 1 unitTag
                 putStrLn msg
         1 -> send commWorld 0 unitTag "Hello World"
         _ -> return ()