Function operand

src/math-json/utils.ts:160–169

(
  expr: MathJsonExpression | null,
  n: 1 | 2 | 3
)

/** Return the nth operand of a function expression */
export function operand(
  expr: MathJsonExpression | null,
  n: 1 | 2 | 3
): MathJsonExpression | null {
  if (Array.isArray(expr)) return expr[n] ?? null;

  if (expr === null || !isFunctionObject(expr)) return null;

  return expr.fn[n] ?? null;
}

export function nops(expr: MathJsonExpression | null | undefined): number {
  if (expr === null || expr === undefined) return 0;