locutus/esm/elixir/Enum/reduce_while.js

Locutus other languages' standard libraries to JavaScript for fun and educational purposes

function normalizeReduceWhileStep(value) {
    if (Array.isArray(value)) {
        const tag = value[0];
        if ((tag === 'cont' || tag === 'halt') && value.length >= 2) {
            return [tag, value[1]];
        }
    }
    else if (value && typeof value === 'object') {
        const tag = value.tag;
        if (tag === 'cont' || tag === 'halt') {
            return [tag, value.value];
        }
    }
    throw new TypeError("reduce_while(): reducer must return ['cont', value], ['halt', value], or { tag, value }");
}
export function reduce_while(values, initial, reducer) {
    //      discuss at: https://locutus.io/elixir/reduce_while/
    // parity verified: Elixir 1.18
    //     original by: Kevin van Zonneveld (https://kvz.io)
    //          note 1: Mirrors Elixir Enum.reduce_while/3 using ['cont', acc] and ['halt', acc] control tuples.
    //       example 1: reduce_while([1, 2, 3, 4], 0, (acc, value) => (value < 4 ? ['cont', acc + value] : ['halt', acc]))
    //       returns 1: 6
    //       example 2: reduce_while([1, 3, 4, 6], null, (acc, value) => (value % 2 === 0 ? ['halt', value] : ['cont', acc]))
    //       returns 2: 4
    //       example 3: reduce_while([], 'done', (acc, _value) => ['cont', acc])
    //       returns 3: 'done'
    if (typeof reducer !== 'function') {
        throw new TypeError('reduce_while(): reducer must be a function');
    }
    if (!Array.isArray(values) || values.length === 0) {
        return initial;
    }
    let accumulator = initial;
    for (let i = 0; i < values.length; i++) {
        const [tag, nextAccumulator] = normalizeReduceWhileStep(reducer(accumulator, values[i], i, values));
        accumulator = nextAccumulator;
        if (tag === 'halt') {
            break;
        }
    }
    return accumulator;
}