Robot.hs

module Robot where

import Control.Concurrent.MVar
import Control.Monad.State
import System.Random.Stateful

type Robot    = MVar String
type RunState = [String]

initialState :: RunState
initialState = []

mkRobot :: StateT RunState IO Robot
mkRobot = do
  n <- mkName
  lift (newMVar n)

robotName :: Robot -> IO String
robotName r = do
  n <- takeMVar r
  putMVar r n
  return n

resetName :: Robot -> StateT RunState IO ()
resetName r = do
  n  <- lift (takeMVar r)
  n' <- lift mkName'
  lift (putMVar r n')
  xs <- get
  put (filter (/=n) (n':xs))

mkName :: StateT RunState IO String
mkName = do
  n  <- lift mkName'
  xs <- get
  if n `elem` xs
    then mkName
    else do
      put (n:xs)
      return n

mkName' :: IO String
mkName' = do
  a <- letter
  b <- letter
  c <- digit
  d <- digit
  e <- digit
  return [a,b,c,d,e]
  where
    letter = randomRIO ('A','Z')
    digit  = randomRIO ('0','9')