# FUNCTIONS
# =========
fun double(n)
  return n * 2
end

assert double(4) == 8
assert 8 == double(4)

assert (double(4) == 10) == false
assert (9 == double(4)) == false

assert double(double(double(3))) == 24

fun a()
  return 45
end

assert a() == 45

fun b()
  return 27
  return 32
end

assert b() == 27

fun max(m, n)
  if m > n then
    return m
  end
  return n
end

assert max(7, 3) == 7
assert max(7, 9) == 9

# RECURSIVITY
# ===========
fun fac(n)
  if n == 0 then
    return 1
  end

  return n * fac(n - 1)
end

assert fac(5) == 120

fun fib(n)
  if n == 0 or n == 1 then
    return 1
  end

  return fib(n - 2) + fib(n - 1)
end

assert fib(6) == 13

# HIGH ORDER FUNCTIONS
# ====================
fun fi(n)
  return n + 1
end

fun fd(n)
  return n * 2
end

fun twice(f, x)
  return f(f(x))
end

assert twice(fi, 27) == 29
assert twice(fd, 12) == 48

# CLOSURES
# ========
fun make()
  let counter = 0

  fun inner()
    counter = counter + 1
    return counter - 1
  end

  return inner
end

let c = make()

assert c() == 0
assert c() == 1
assert c() == 2

fun make_val(init)
  let counter = init

  fun inner()
    counter = counter + 1
    return counter - 1
  end

  return inner
end

let d = make_val(7)
let e = make_val(3)

assert d() == 7
assert e() == 3
assert d() == 8
assert e() == 4
assert d() == 9
assert e() == 5