RandomWalk.hs

{-# LANGUAGE OverloadedStrings #-}

module Main where

import Control.Monad.Trans (lift)
import Control.Parallel (par, pseq)
import Data.Text.Lazy (pack)
import System.Random (StdGen, newStdGen, random)
import Web.Scotty (get, scotty, text)

randomWalk :: Int -> Int -> StdGen -> Int
randomWalk s 0 _ = s
randomWalk s i r = randomWalk s' (pred i) g
  where (b, g) = random r
        s' = (if b then succ else pred) s

main :: IO ()
main = scotty 3000 $ do
  a <- lift $ newStdGen
  b <- lift $ newStdGen
  get "/" $ do
    let walk = randomWalk 0 10000000
        first = walk a
        second = walk b
    text . pack . show $ first `par` second `pseq` (first + second)