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export function takeWhile<T>(items: readonly T[], pred: (x: T) => boolean): T[] {
  const out: T[] = [];
  for (const x of items) {
    if (!pred(x)) break;
    out.push(x);
  }
  return out;
}

export function dropWhile<T>(items: readonly T[], pred: (x: T) => boolean): T[] {
  let i = 0;
  while (i < items.length && pred(items[i]!)) i++;
  return items.slice(i);
}

takeWhile([1, 3, 5, 4, 7], n => n % 2 === 1);   // [1, 3, 5]
dropWhile([1, 3, 5, 4, 7], n => n % 2 === 1);   // [4, 7]