// The partition function takes a predicate and a list, and returns the pair of lists of elements which do and do not satisfy the predicate
const partition = <T>(predicate: (item: T) => boolean, xs: List<T>): [List<T>, List<T>];

// takeWhile applied to a predicate p and a list xs, returns the longest prefix (possibly empty) of xs of elements that satisfy p.
const takeWhile = <T> (p: (item: T) => boolean, xs: List<T>): List<T>;