Function isEmptySequence

src/math-json/utils.ts:451–457

(
  expr: MathJsonExpression | null | undefined
)

/** `Nothing` or the empty sequence (`["Sequence"]`) */
export function isEmptySequence(
  expr: MathJsonExpression | null | undefined
): expr is null | undefined {
  if (expr === null || expr === undefined) return true;
  if (expr === 'Nothing') return true;
  return operator(expr) === 'Sequence' && nops(expr) === 0;
}

export function missingIfEmpty(
  expr: MathJsonExpression | null | undefined