xduce
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Composable algorithmic transformations library for JavaScript
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JavaScript
/*
* Copyright (c) 2017 Thomas Otterson
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
* the Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
/**
* Basic functions necessary across transducers, along with a number of transducers that don't belong in other
* categories.
*
* @module core
* @private
*/
const { protocols } = require('../modules/protocol');
const { sequence } = require('../modules/transformation');
const { isIterable } = require('../modules/iteration');
const { isNumber } = require('../modules/util');
const { isCompleted, complete, reduce } = require('../modules/reduction');
const p = protocols;
/**
* Defines equality per the definition of SameValueZero in the JS spec, This is the comparison used in similar
* situations by Lodash and other libraries. It's the same as `===` in JavaScript, except that `NaN` is equal to itself.
*
* @private
*
* @param {number} a The first number.
* @param {number} b The second number.
* @return {boolean} Either `true` if the numbers are equal per `===` or if both numbers are `NaN`, or `false`
* otherwise.
*/
function sameValueZero(a, b) {
return a === b || (isNaN(a) && isNaN(b));
}
/**
* A transducer function that is returned by the `{@link module:xduce.transducers.identity|identity}` transducer.
*
* @private
*
* @param {module:xduce~transducerObject} xform The transducer object that the new one should be chained to.
* @return {module:xduce~transducerObject} A new transducer object, performing no transformation and chaining to the
* provided transducer object.
*/
function identityTransducer(xform) {
return {
[p.init]() {
return xform[p.init]();
},
[p.step](acc, input) {
return xform[p.step](acc, input);
},
[p.result](value) {
return xform[p.result](value);
}
};
}
/**
* **Returns exactly the same collection sent to it.**
*
* This is generally a function used when a transducer function is required but there is no desire to do an actual
* transformation. The "transformation" implemented here is to pass each element through exactly as it is.
*
* If no collection is provided, a function is returned that can be passed to `{@link module:xduce.sequence|sequence}`,
* et al.
*
* ```
* const result = identity([1, 2, 3, 4, 5]);
* // result = [1, 2, 3, 4, 5]
* ```
*
* @memberof module:xduce.transducers
*
* @param {*} [collection] An optional input collection that is to be transduced.
* @return {(*|module:xduce~transducerFunction)} If a collection is supplied, then the function returns a new
* collection of the same type with all of the elements of the input collection untouched. If no collection is
* supplied, a transducer function, suitable for passing to `{@link module:xduce.sequence|sequence}`,
* `{@link module:xduce.into|into}`, etc. is returned.
*/
function identity(collection) {
return collection ? sequence(collection, identity()) : xform => identityTransducer(xform);
}
/**
* A transducer function that is returned by the `{@link module:xduce.transducers.flatten|flatten}` transducer.
*
* @private
*
* @param {module:xduce~transducerObject} xform The transducer object that the new one should be chained to.
* @return {module:xduce~transducerObject} A new transducer object chained to the provided transducer object.
*/
function flattenTransducer(xform) {
return {
[p.init]() {
return xform[p.init]();
},
[p.step](acc, input) {
const subXform = {
[p.init]() {
return xform[p.init]();
},
[p.step](acc, input) {
const v = xform[p.step](acc, input);
return isCompleted(v) ? complete(v) : v;
},
[p.result](value) {
return xform[p.result](value);
}
};
return isIterable(input) ? reduce(input, subXform, acc) : subXform[p.step](acc, input);
},
[p.result](value) {
return xform[p.result](value);
}
};
}
/**
* **Flattens a collection by merging elements in any sub-collection into the main collection.**
*
* Elements of the main collection that are not collections themselves are not changed. It's fine to have a combination
* of the two, some elements that are collections and some that are not.
*
* Since there aren't sub-collections in objects, strings, or iterators, `flatten` doesn't make sense with those types
* of collections.
*
* If no collection is provided, a function is returned that can be passed to `{@link module:xduce.sequence|sequence}`,
* et al.
*
* ```
* const result = flatten([[1, 2], [3, 4, 5], 6, [7]]);
* // result = [1, 2, 3, 4, 5, 6, 7]
* ```
*
* @memberof module:xduce.transducers
*
* @param {*} [collection] An optional input collection that is to be transduced.
* @return {(*|module:xduce~transducerFunction)} If a collection is supplied, then the function returns a new
* collection of the same type with all of the elements of the input collection flattened. If no collection is
* supplied, a transducer function, suitable for passing to `{@link module:xduce.sequence|sequence}`,
* `{@link module:xduce.into|into}`, etc. is returned.
*/
function flatten(collection) {
return collection ? sequence(collection, flatten()) : xform => flattenTransducer(xform);
}
/**
* A transducer function that is returned by the `{@link module:xduce.transducers.flatten|flatten}` transducer.
*
* @private
*
* @param {number} n The number of times that each element should be repeated in the output collection.
* @param {module:xduce~transducerObject} xform The transducer object that the new one should be chained to.
* @return {module:xduce~transducerObject} A new transducer object chained to the provided transducer object.
*/
function repeatTransducer(n, xform) {
return {
[p.init]() {
return xform[p.init]();
},
[p.step](acc, input) {
let result = acc;
for (let i = 0; i < n; ++i) {
result = xform[p.step](result, input);
if (isCompleted(result)) {
break;
}
}
return result;
},
[p.result](value) {
return xform[p.result](value);
}
};
}
/**
* **Repeats each element from the input collection `n` times in the output collection.**
*
* These elements are put into the main output collection, not into subcollections. In other words, each input element
* creates `n` output elements.
*
* If no collection is provided, a function is returned that can be passed to `{@link module:xduce.sequence|sequence}`,
* et al.
*
* ```
* const result = repeat([1, 2, 3, 4, 5], 3);
* // result = [1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5]
* ```
*
* @memberof module:xduce.transducers
*
* @param {*} [collection] An optional input collection that is to be transduced.
* @param {number} n The number of times that each element from the input collection should be repeated in the output
* collection.
* @return {(*|module:xduce~transducerFunction)} If a collection is supplied, then the function returns a new
* collection of the same type with all of the elements of the input collection repeated. If no collection is
* supplied, a transducer function, suitable for passing to `{@link module:xduce.sequence|sequence}`,
* `{@link module:xduce.into|into}`, etc. is returned.
*/
function repeat(collection, n) {
const [col, num] = isNumber(collection) ? [null, collection] : [collection, n];
return col ? sequence(col, repeat(num)) : xform => repeatTransducer(num, xform);
}
module.exports = {
sameValueZero,
identity,
flatten,
repeat
};