match.ts

type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>

type DiscriminateUnion<Union, TagKey extends keyof Union, TagValue extends Union[TagKey]> =
	Union extends Record<TagKey, TagValue> ? Union : never

type MatchingFunc<A extends { kind: string }, K extends A['kind'], U> = (a: Omit<DiscriminateUnion<A, 'kind', K>, 'kind'>) => U

function match<A extends { kind: string }>(discriminant: A) {
	return <U>(obj:
			{ [K in A['kind']]: MatchingFunc<A, K, U> } |
			(Partial<{ [K in A['kind']]: MatchingFunc<A, K, U> }> & { default(): U }),
	) => {
		const objAny = obj as any

		const caseFn = objAny[discriminant.kind]


		return caseFn
			? caseFn(discriminant) as U
			: objAny.default()

	}
}