module Test.Control.Monad.State where

import Test.QuickCheck (TestGroup(..), TestResult, quickCheck1)
import Prelude (IO, Unit, bind, discard, (+), (-), (==))
import Control.Monad.State (State, evalState, execState, get, gets, put, modify)

fib :: Integer -> State (Integer, Integer) Integer
fib 0 = gets (\(a, b) -> b)
fib n = do
  modify (\(a, b) -> (b, a + b))
  fib (n - 1)

plus :: State Integer ()
plus = do
  a <- get
  put (a + 1)

test :: TestGroup (Integer -> IO TestResult)
test = Exe [
  quickCheck1 "fib" (evalState (fib 7) (0, 1) == 21),
  quickCheck1 "plus" (execState plus 2 == 3)
]