let str_join = module{
    sep=" ",
    list=NULL,
} => {
    let joiner = macro(acc, item) => {
        result = select (acc.out == ""), NULL, {
            true = acc{
                out="@@" % (acc.out,item),
            },
            false = acc{
                out="@@@" % (acc.out, acc.sep, item),
            },
        },
    };

    let result = (reduce joiner.result {sep=mod.sep, out=""}, (mod.list)).out;
};

let len = module{
    list = NULL,
} => {
    let counter = macro(acc, item) => {
        result = acc + 1,
    };

    let result = reduce counter.result 0, (mod.list);
};

let reverse = module{
    list = NULL,
} => {
    let reducer = macro(acc, item) => {
        result = [item] + acc,
    };

    let result = reduce reducer.result [], (mod.list); 
};

let enumerate = module{
    start = 0,
    step = 1,
    list = NULL,
} => {
    let reducer = macro(acc, item) => {
        result = acc{count = acc.count + acc.step, list=acc.list + [[acc.count, item]]},
    };

    let acc = {count=mod.start, list=[], step=mod.step};

    let enumerated = reduce reducer.result acc, (mod.list);
    let result = enumerated.list;
};

let zip = module{
    list1 = NULL,
    list2 = NULL,
} => {
    let counter = macro(acc, item) => {
        result = acc + 1,
    };

    let len1 = reduce counter.result 0, (mod.list1);
    let len2 = reduce counter.result 0, (mod.list2);

    let rng = select (len1 >= len2), NULL, {
        true = 0:(len1 - 1),
        false = 0:(len2 - 1),
    };

    let reducer = macro(acc, item) => {
        result = acc{
            result = acc.result + [[acc.list1.(item), acc.list2.(item)]],
            idxs = acc.idxs + [item]
        },
    };

    let acc = {
        list1 = mod.list1,
        list2 = mod.list2,
        result = [],
        idxs = [],
    };

    let result = (reduce reducer.result acc, rng).result;
};