Comment by cuddlecake

You can also write the array first, without using enum:

const tokens = ['parenOpen', 'bang', 'plus', 'minus'] as const;

type Token = typeof tokens[number];

type TokenTable<T> = Record<Token, T> // alias for { [key in Token]: T }

const isToken = (t: string): t is Token => tokens.includes(t);

const patterns: TokenTable<RegExp> = { bang: /\+/, // rest }