fn fib(n: int): int {
  if n < 2 {
    return n
  }
  return fib(n - 1) + fib(n - 2)
}

fn int |> twice() |> int {
   var n = 0
   read(&n)
   return n * 2
}

assert(fib(6) == 8)
assert((fib(6) |> twice()) == 16)

fn ...int |> sum() |> int {
  var v: int
  var res = 0
  while read(&v) {
    res += v
  }
  return res
}

fn ...int |> twice_each() |> ...int {
  var n: int
  while read(&n) {
    yield n * 2
  }
}

assert((seq(3) |> sum()) == 6)
assert((seq(3) |> twice_each() |> sum()) == 12)

// Call command by `@command` syntax with pipeline operator
assert(((1, 2) |> @awk('{print $1 + $2}')) == '3')