pub fn get(cell: @internal Cell(a)) -> a

pub fn make(value: a) -> @internal Cell(a)

pub fn set(cell: @internal Cell(a), value: a) -> Nil

pub fn subscribe(
  cell: @internal Cell(a),
  callback: fn(a) -> Nil,
) -> fn() -> Nil

pub fn update(cell: @internal Cell(a), updater: fn(a) -> a) -> a