purescript-0.5.4.1: examples/passing/Fib.purs

module Main where

import Prelude
import Control.Monad.Eff
import Control.Monad.ST

main = runST (do
  n1 <- newSTRef 1
  n2 <- newSTRef 1
  whileE ((>) 1000 <$> readSTRef n1) $ do
    n1' <- readSTRef n1
    n2' <- readSTRef n2
    writeSTRef n2 $ n1' + n2'
    writeSTRef n1 n2'
    Debug.Trace.print n2')