Livt.Base

src/Iteration.lvt

namespace Livt.Iteration

using Livt.Lang

/**
 * Sequential traversal of a caller-owned cursor from its current position.
 * Operations never reset the cursor. Keep exclusive ownership of the cursor
 * and keep its source unchanged until the operation completes.
 */
component Iteration
{
	/**
	 * Returns initial for empty input. Visits values in source order.
	 */
	public static fn Fold<T, TAccumulator>(iterator: IIterator<T>, initial: TAccumulator,
		operation: const fn(accumulator: TAccumulator, value: T) TAccumulator) TAccumulator
	{
		var result = initial

		while (iterator.HasNext()) {
			var value = iterator.Next()
			result = operation(result, value)
		}

		return result
	}

	/**
	 * Stops after consuming the first match. Empty input returns false.
	 */
	public static fn Any<T>(iterator: IIterator<T>, predicate: const fn(value: T) bool) bool
	{
		while (iterator.HasNext()) {
			var value = iterator.Next()

			if (predicate(value)) {
				return true
			}
		}

		return false
	}

	/**
	 * Stops after consuming the first non-match. Empty input returns true.
	 */
	public static fn All<T>(iterator: IIterator<T>, predicate: const fn(value: T) bool) bool
	{
		while (iterator.HasNext()) {
			var value = iterator.Next()

			if (!predicate(value)) {
				return false
			}
		}

		return true
	}

	/**
	 * Counts matching remaining values. The result must fit in int.
	 */
	public static fn CountWhere<T>(iterator: IIterator<T>, predicate: const fn(value: T) bool) int
	{
		var count = 0

		while (iterator.HasNext()) {
			var value = iterator.Next()

			if (predicate(value)) {
				count++
			}
		}

		return count
	}

	/**
	 * Returns an index relative to the starting cursor position, or -1.
	 */
	public static fn FindIndex<T>(iterator: IIterator<T>, predicate: const fn(value: T) bool) int
	{
		var index = 0

		while (iterator.HasNext()) {
			var value = iterator.Next()

			if (predicate(value)) {
				return index
			}

			index++
		}

		return -1
	}
}