gistfile1.elm

import Random as R

main = (\(_,_,stuff,msgs) -> flow down (asText stuff :: map plainText msgs)) <~ 
  foldp stepFSM 
        (("Waiting",0),("Waiting",0),(0,0),[])
        (R.floatList ((fps 1) `sampleOn` constant 3))

stepFSM rnds ((stateA,seqA),(stateB,seqB),(recA,recB),messages) = 
  let rs = map (\n -> floor (n*10.0)) rnds
      ra = head rs
      rb = head <| drop 1 rs
      rc = head <| drop 2 rs
      msgA = host "'A'" ra (stateA,seqA) recA
      msgB = host "'B'" rb (stateB,seqB) recB
      recA' = if ra == 0 && seqA > recA then recA + 1 else recA
      recB' = if rb == 0 && seqB > recB then recB + 1 else recB
      msgs = msgA ++ msgB ++ messages
      stateC = if recA <= recB then "Routing A" else "Routing B" in
  case stateC of
    "Routing A" -> case rc of
      0 -> (("Sending",recA+1),(stateB,seqB),(recA',recB'),
        ("'A' received ACK from 'C' for packet #" ++ show (recA+1)) :: msgs)
      1 -> ((stateA,seqA),(stateB,seqB),(recA',recB'),
        "An ACK going from 'C' to 'A' never made it or was corrupted." :: msgs)
      _ -> ((stateA,seqA),(stateB,seqB),(recA',recB'),msgs)
    "Routing B" -> case rc of
      0 -> ((stateA,seqA),("Sending",recB+1),(recA',recB'),
        ("'B' received ACK from 'C' for packet #" ++ show (recB+1)) :: msgs)
      1 -> ((stateA,seqA),(stateB,seqB),(recA',recB'),
        "An ACK going from 'C' to 'B' never made it or was corrupted." :: msgs)
      _ -> ((stateA,seqA),(stateB,seqB),(recA',recB'),msgs)
      

host name r (state,seq) rec = case state of
  "Sending" -> case r of
    0 -> if rec >= seq
         then [name ++ " successfully sent packet " ++ show seq ++ ". 'C' already has it and will ignore it."]
         else [name ++ " successfully sent packet " ++ show seq ++ "."]
    1 -> ["A packet going from" ++ name ++ " to 'C' never made it or was corrupted."]
    _ -> []
  "Waiting" -> []