foop
Version:
interfaces that describe their intentions.
61 lines (56 loc) • 4.65 kB
JavaScript
var curry = require('../../fp/curry')
/**
* The `mapAccum` function behaves like a combination of map and reduce; it
* applies a function to each element of a list, passing an accumulating
* parameter from left to right, and returning a final value of this
* accumulator together with the new list.
*
* The iterator function receives two arguments, *acc* and *value*, and should
* return a tuple *[acc, value]*.
* @since 5.0.0-beta.6
* @memberOf loop
* @alias functionOnEach
*
* @param {Function} fn The function to be called on every element of the input `list`.
* @param {*} acc The accumulator value.
* @param {Array} list The list to iterate over.
* @return {*} The final, accumulated value.
*
* @func
* @fork v0.10.0
* @category List
* @sig (acc -> x -> (acc, y)) -> acc -> [x] -> (acc, [y])
* @symb mapAccum(f, a, [b, c, d]) = [f(f(f(a, b)[0], c)[0], d)[0],
* [
* f(a, b)[1],
* f(f(a, b)[0], c)[1],
* f(f(f(a, b)[0], c)[0], d)[1]
* ]]
*
* @see addIndex, mapAccumRight
*
* @example
*
* var digits = ['1', '2', '3', '4'];
* var appender = (a, b) => [a + b, a + b];
*
* mapAccum(appender, 0, digits);
* //=> ['01234', ['01', '012', '0123', '01234']]
*
*
*/
module.exports = curry(3, function mapAccum(fn, acc, list) {
// nums
var idx = 0
var len = list.length
// arrs
var result = []
var tuple = [acc]
while (idx < len) {
tuple = fn(tuple[0], list[idx])
result[idx] = tuple[1]
idx += 1
}
return [tuple[0], result]
})
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