@lumino/algorithm/src/range.ts

Lumino Algorithms and Iterators

// Copyright (c) Jupyter Development Team.
// Distributed under the terms of the Modified BSD License.
/*-----------------------------------------------------------------------------
| Copyright (c) 2014-2017, PhosphorJS Contributors
|
| Distributed under the terms of the BSD 3-Clause License.
|
| The full license is in the file LICENSE, distributed with this software.
|----------------------------------------------------------------------------*/
/**
 * Create an iterator of evenly spaced values.
 *
 * @param start - The starting value for the range, inclusive.
 *
 * @param stop - The stopping value for the range, exclusive.
 *
 * @param step - The distance between each value.
 *
 * @returns An iterator which produces evenly spaced values.
 *
 * #### Notes
 * In the single argument form of `range(stop)`, `start` defaults to
 * `0` and `step` defaults to `1`.
 *
 * In the two argument form of `range(start, stop)`, `step` defaults
 * to `1`.
 *
 * #### Example
 * ```typescript
 * import { range } from '@lumino/algorithm';
 *
 * let stream = range(2, 4);
 *
 * Array.from(stream);  // [2, 3]
 * ```
 */
export function* range(
  start: number,
  stop?: number,
  step?: number
): IterableIterator<number> {
  if (stop === undefined) {
    stop = start;
    start = 0;
    step = 1;
  } else if (step === undefined) {
    step = 1;
  }
  const length = Private.rangeLength(start, stop, step);
  for (let index = 0; index < length; index++) {
    yield start + step * index;
  }
}

/**
 * The namespace for the module implementation details.
 */
namespace Private {
  /**
   * Compute the effective length of a range.
   *
   * @param start - The starting value for the range, inclusive.
   *
   * @param stop - The stopping value for the range, exclusive.
   *
   * @param step - The distance between each value.
   *
   * @returns The number of steps need to traverse the range.
   */
  export function rangeLength(
    start: number,
    stop: number,
    step: number
  ): number {
    if (step === 0) {
      return Infinity;
    }
    if (start > stop && step > 0) {
      return 0;
    }
    if (start < stop && step < 0) {
      return 0;
    }
    return Math.ceil((stop - start) / step);
  }
}