Make a TypeScript type readonly, recursively

immutable.ts

type AnyFunction = (...args: any[]) => any;
type ImmutablePrimitive = undefined | null | boolean | string | number | AnyFunction;
type Immutable<T> =
  T extends ImmutablePrimitive ? T :
    T extends Map<infer K, infer V> ? ReadonlyMap<Immutable<K>, Immutable<V>> :
      T extends Set<infer E> ? ReadonlySet<Immutable<E>> :
        { readonly [P in keyof T]: Immutable<T[P]> }
  

Taken from this comment, including a fix for tuples