pub fn for(
  iterator: Iterator(a, return, next),
  fun: fn(a) -> any,
) -> Nil

pub fn new(
  next: fn(option.Option(next)) -> iterator_result.IteratorResult(
    a,
    return,
  ),
) -> Iterator(a, return, next)

pub fn next(
  iterator: Iterator(a, return, next),
) -> iterator_result.IteratorResult(a, return)

pub fn next_with(
  iterator: Iterator(a, return, next),
  value: next,
) -> iterator_result.IteratorResult(a, return)

pub fn return(
  iterator: Iterator(a, return, next),
) -> Result(iterator_result.IteratorResult(a, return), Nil)

pub fn return_with(
  iterator: Iterator(a, return, next),
  value: return,
) -> Result(iterator_result.IteratorResult(a, return), Nil)

pub fn throw(
  iterator: Iterator(a, return, next),
  e: e,
) -> Result(iterator_result.IteratorResult(a, return), Nil)

pub fn with_return(
  iterator: Iterator(a, return, next),
  return: fn(option.Option(return)) -> iterator_result.IteratorResult(
    a,
    return,
  ),
) -> Iterator(a, return, next)

pub fn with_throw(
  iterator: Iterator(a, return, next),
  throw: fn(e) -> iterator_result.IteratorResult(a, return),
) -> Iterator(a, return, next)