def main (xs : List String) : IO Unit :=
do
let bs := [1, 2, 3].toByteArray,
IO.println bs,
let bs := bs.push 4,
let bs := bs.set 1 20,
IO.println bs,
let bs₁ := bs.set 2 30,
IO.println bs₁,
IO.println bs,
IO.println bs.size,
pure ()