basic haskell randoms and io

gistfile1.txt

module Main( main ) where

import System.Environment
import System.Random
import Text.Printf
import Control.Monad

data Player = PlayerA | PlayerB
  deriving (Show, Eq)

main :: IO ()
main = do
    let noOfRounds = 100
    let n = 10
    gen <- newStdGen
    let rnds = randoms gen :: [Int]
    rnds2 <- rands

    rs1 <- sequence [playRound 0 0 | _ <- [1 .. noOfRounds] ]
    printf "PlayRound: noOfRounds %d \n" (noOfRounds)
    let noOfPlayerAWins = count playerAPred rs1
    printf "Player A wins: %d \n" (noOfPlayerAWins)
    print rs1

    print "Replicated (pure)"
    rs2 <- replicateM noOfRounds (playRound2 rnds2 0 0)
    print rs2

    x <- replicateM 3 (rollDice 6)
    print "Dice Rolls:"
    print x


playerAPred x = x == PlayerA

count pred = length . filter pred

playRound :: Int -> Int -> IO Player
playRound xLast yLast = do
  x <- randomRIO (1 :: Int, 6)
  y <- randomRIO (1 :: Int, 6)
  if x < xLast then
    return PlayerB
  else if y < yLast then
    return PlayerA
  else playRound x y

playRound2 :: [Int] -> Int -> Int -> IO Player
playRound2 (x : y : rs) xLast yLast =
  if x < xLast then
    return PlayerB
  else if y < yLast then
    return PlayerA
  else playRound2 rs x y

rollDice :: Int => IO Int
rollDice n = getStdRandom (randomR (1, n))

rands :: () => IO [Int]
rands = do
    g <- newStdGen
    let rnds = randoms g :: [Int]
    return rnds