/**
 * Executes a user-supplied "reducer" callback function on each element of the
 * array, in order, passing in the return value from the calculation on the
 * preceding element. The final result of running the reducer across all
 * elements of the array is a single value. Equivalent to
 * `Array.prototype.reduce`.
 *
 * @param data - The items to reduce.
 * @param callbackfn - A function to execute for each element in the array. Its
 * return value becomes the value of the accumulator parameter on the next
 * invocation of callbackFn. For the last invocation, the return value becomes
 * the return value of reduce().
 * @param initialValue - A value to which accumulator is initialized the first
 * time the callback is called. CallbackFn starts executing with the first value
 * in the array as currentValue.
 * @returns The value that results from running the "reducer" callback function
 * to completion over the entire array.
 * @signature
 *    R.reduce(data, callbackfn, initialValue)
 * @example
 *    R.reduce([1, 2, 3, 4, 5], (acc, x) => acc + x, 100) // => 115
 * @dataFirst
 * @category Array
 */
declare function reduce<T, U>(data: ReadonlyArray<T>, callbackfn: (previousValue: U, currentValue: T, currentIndex: number, data: ReadonlyArray<T>) => U, initialValue: U): U;
/**
 * Executes a user-supplied "reducer" callback function on each element of the
 * array, in order, passing in the return value from the calculation on the
 * preceding element. The final result of running the reducer across all
 * elements of the array is a single value. Equivalent to
 * `Array.prototype.reduce`.
 *
 * @param callbackfn - A function to execute for each element in the array. Its
 * return value becomes the value of the accumulator parameter on the next
 * invocation of callbackFn. For the last invocation, the return value becomes
 * the return value of reduce().
 * @param initialValue - A value to which accumulator is initialized the first
 * time the callback is called. CallbackFn starts executing with the first value
 * in the array as currentValue.
 * @returns The value that results from running the "reducer" callback function
 * to completion over the entire array.
 * @signature
 *    R.reduce(fn, initialValue)(array)
 * @example
 *    R.pipe([1, 2, 3, 4, 5], R.reduce((acc, x) => acc + x, 100)) // => 115
 * @dataLast
 * @category Array
 */
declare function reduce<T, U>(callbackfn: (previousValue: U, currentValue: T, currentIndex: number, data: ReadonlyArray<T>) => U, initialValue: U): (data: ReadonlyArray<T>) => U;

export { reduce };