Do a network call at random intervals using a Poisson progression

randomCall.hs

import Network.HTTP
import Network.URI (parseURI)
import System.Random
import Control.Concurrent


typicalDelayInSecs = fromIntegral 5

rate = recip typicalDelayInSecs

poissonDelay rate x = - (log x) / rate

poissonProcess g r = map (poissonDelay r) (randoms g :: [Float])


doThenWait stuff delayInSecs = do
  stuff
  threadDelay delay
  where
    delay = 1000000 * delayInSecs

uri = case parseURI "http://requestb.in/uactskua" of
       Just u -> u

mkPostRq body = Request { rqURI = uri
                  , rqMethod = POST
                  , rqHeaders = [ mkHeader HdrContentType "application/json"
                                , mkHeader HdrContentLength $ show . length $ body]
                  , rqBody = body
                  }


showStatus (2,_,_) = print "OK"
showStatus (_,_,_) = print "Fail"

makeCall = do
  status <- simpleHTTP (mkPostRq "{}")
            >>= getResponseCode
  showStatus status

poissonSequenceInSecs g = map round $ poissonProcess g rate

callThenSleep = doThenWait makeCall

main:: IO ()
main = do
  g <- newStdGen
  let delays = poissonSequenceInSecs g
  mapM_ callThenSleep delays