Eq for literal types

[ingun37]

How can I make Eq for literal types, e.g. Eq<'a'> or Eq<'a'|'b'>?

Documentation of io-ts/Eq says it has literal combinator but it seems not actually implemented.

I'm currently using my own implementation

export const literal: <A extends readonly [string, ...Array<string>]>(
  ...values: A
) => Eq<A[number]> = () => eqStrict;