MonadChallenges.hs

--https://mightybyte.github.io/monad-challenges/pages/ex1-4.html

type Gen a = Seed -> (a, Seed)

randPair :: Gen (Char, Integer)
randPair seed = 
  let (c, s0) = randLetter seed in 
    let (i, s1) = rand s0 in
      ((c, i), s1)

generalPair :: Gen a -> Gen b -> Gen (a,b)
generalPair f g = pairValues . applyOnSeed g . f

generalPair' :: Gen a -> Gen b -> Gen (a, b)
generalPair' f g = generalB f g pairValues

generalA :: (a -> b) -> Gen a -> Gen b
generalA f g = applyOnVal f . g

generalB :: Gen a -> Gen b -> ((a, (b, Seed)) -> (c, Seed)) -> Gen c
generalB f g h = h . applyOnSeed g . f

applyOnSeed :: Gen b -> (a, Seed) -> (a, (b, Seed))
applyOnSeed f (x, y) = (x, f y)

applyOnVal :: (a -> b) -> (a, Seed) -> (b, Seed)
applyOnVal f (x, y) = (f x, y)