TypeScript array `partition` utility

partition.ts

/**
 * Takes a predicate and a list of values and returns a a tuple (2-item array),
 *  with each item containing the subset of the list that matches the predicate
 *  and the complement of the predicate respectively
 * 
 * @sig (T -> Boolean, T[]) -> [T[], T[]]
 * 
 * @param {Function} predicate A predicate to determine which side the element belongs to.
 * @param {Array} arr The list to partition
 * 
 * Inspired by the Ramda function of the same name
 * @see https://ramdajs.com/docs/#partition
 *
 * @example
 * 
 *     const isNegative: (n: number) => boolean = n => n < 0
 *     const numbers = [1, 2, -4, -7, 4, 22]
 *     partition(isNegative, numbers)
 *     // => [ [-4, -7], [1, 2, 4, 22] ]
 */
function partition<T> (
    predicate: (val: T) => boolean,
    arr: Array<T>,
): [Array<T>, Array<T>] {
    const partitioned: [Array<T>, Array<T>] = [[], []]
    arr.forEach((val: T) => {
        const partitionIndex: 0 | 1 = predicate(val) ? 0 : 1
        partitioned[partitionIndex].push(val)
    })
    return partitioned
}

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