Recursive cond fn in typescript

cond.ts

type Predicate<T> = (val: T) => boolean;
type Mapper<T, R> = (val: T) => R;
type CondTuple<T, R> = [Predicate<T>, Mapper<T, R>];

function cond<T, R>(clauses: CondTuple<T, R>[] = []) {
	const [[pred, mapr] = [undefined, undefined], ...rest] = clauses;

	return (val: T): R | undefined => {
		// base case: pred is undefined - exit the recursion
		if (pred === undefined || mapr === undefined) {
			return undefined;
		}
		// When applying the pred fn to val returns true, exit the recursion
		// by returning the application of the mapr fn to val. otherwise recurse
		return pred(val) ? mapr(val) : cond(rest)(val);
	};
}