Support for Ordered Unions and/or Matchers as types

[HamishWHC]

Request a feature

🤷 Motivation

In a lot of cases, I find myself writing schemas that cause ParseErrors: An unordered union of a type including a morph and a type with overlapping input is indeterminate

I know the input overlaps, but I also have the context of my application and know which schema I was to prioritise. Currently, I do this to shoehorn in an ordered union:

const Thing = type({
	myProp: type.unknown.pipe((v) =>
		match
			.case(TypeA, (v) => v)
			.case(TypeB, (v) => v)
			.default("reject")(v)
	)
})

Playground Link w/ Example

But this has the downside of cutting off errors at the wrong "level" (see playground for comparison of errors this gets, vs what I'd expect).

💡 Solution

I would really like some of kind ordered union option, either by allowing us to drop matchers (i.e. match.case().case()) into a type, or by introducing something like type.firstMatch to make clear the first match behaviour.

[pullfrog]

  ^{｜ Build this ➔ ｜ Make a plan ➔}

[gregg-cbs]

If i do this:

const dateString = type("string").pipe((input, ctx) => {
  return new Date(input);
});

And I extend it like this:

export const ticket = type({some: "string"}).and({
  dates_redeemable: dateString
})

I get the error:
ParseError: An unordered union of a type including a morph and a type with overlapping input is indeterminate:
Left: (In: unknown) => Out
Right: null

Im not sure how to get around this, kind weird that any .pipe will break a merge or and.

[HamishWHC]

@gregg-cbs does the same occur with .merge instead of .and? iirc they are different operations and .merge should not cause a union (and therefore the error).