Cannot use type guard functions created by scanner() in union().

[yona3]

If you pass a type guard function created by scanner() as an argument of union() as follows, it will throw an error and will not work properly.
This is because scanner() is designed to throw an exception instead of returning false usually.

  type Bar = {
    a: string;
    b: Foo | null;
    c: string | null;
  };

  const bar = {
    a: "a",
    b: null,
    c: null,
  };

  const isBar = scanner<Bar>({
    a: string,
    b: union(isFoo, Null), // throw error!
    c: union(string, Null),
  });

[yona3]

This problem can be solved by setting the isUseWithUnion option to true for scanner used in union() like this. This is available in v0.4.0.

  const isFoo = scanner<Foo>(
    {
      a: string,
      b: number,
      c: boolean,
      d: date,
      e: array(string),
      f: optional(string),
      g: list(["a", "b", "c"]),
      h: union(string, Null),
      i: union<string | number>(string, number),
    },
    { isUseWithUnion: true }
  );