def0 Unit : ★ = {tt}

def drop-unit : 0.(A : ★) → Unit → A → A =
  λ A u x ⇒ case u return A of {'tt ⇒ x}

def0 IO : ★ → ★ = λ A ⇒ IOState → A × IOState

def bind : 0.(A B : ★) → IO A → (A → IO B) → IO B =
  λ A B m k s0 ⇒
  case m s0 return B × IOState of { (x, s1) ⇒ k x s1 }

def seq : IO Unit → IO Unit → IO Unit =
  λ a b ⇒ bind Unit Unit a (λ u ⇒ drop-unit (IO Unit) u b)

#[compile-scheme "(lambda (n) (builtin-io (printf \"~d~n\" n) 'tt))"]
postulate print-ℕ : ℕ → IO Unit

#[compile-scheme "(lambda (s) (builtin-io (printf \"~s~n\" s) 'tt))"]
postulate print : String → IO Unit

load "nat.quox"

#[main]
def main : IO Unit =
  let1 sixty-nine = nat.plus 60 9 in
  seq (print-ℕ sixty-nine) (print "(nice)")