better_collections.php

better_collections.php

<?php

function take(Iterator $it, int $n) {
    for ($i = 0; $i < $n && $it->valid(); $i++, $it->next()) {
        yield $it->current();
    }
}

function filter(Iterator $it, callable $f) {
    foreach ($it as $item) {
        if ($f($item)) {
            yield $item;
        }
    }
}

function map(Iterator $it, callable $f) {
    foreach ($it as $item) {
        yield $f($item);
    }
}

function flat_map(Iterator $it, callable $f) {
    foreach ($it as $item) {
        yield from $f($item);
    }
}

function skip(Iterator $it, int $n) {
    for ($i = 0; $i < $n && $it->valid(); $i++, $it->next());
    
    for (; $it->valid(); $it->next()) {
        yield $it->current();
    }
}

function skip_while(Iterator $it, callable $f) {
    for (; $it->valid() && $f($it->current()); $it->next());

    for (; $it->valid(); $it->next()) {
        yield $it->current();
    }
}

function paginate(Iterator $it, int $n) {
    while($it->valid()) {
        yield take($it, $n);
    }
}

function take_while(Iterator $it, callable $f) {
    for (; $it->valid() && $f($it->current()); $it->next()) {
        yield $it->current();
    }
}

function slice(Iterator $it, int $offset, int $length) {
    return take(skip($it, $offset), $length);
}

function scan(Iterator $it, $initial, callable $f) {
    $carry = $initial;
    foreach($it as $item) {
        $carry = $f($carry, $item);
        yield $carry;
    }
}

function fold(Iterator $it, $acc, callable $f) {
    foreach ($it as $value) {
        $acc = $f($acc, $value);
    }

    return $acc;
}

function zip(Iterator $left, Iterator $right) {
    for (; $left->valid() && $right->valid(); $left->next(), $right->next()) {
        yield [$left->current(), $right->current()];
    }
}

function groupBy(Iterator $it, callable $f) {
    while($it->valid()){
        $current = $it->current();
        yield take_while($it, function($item) use ($f, $current) {
            return $f($current, $item);
        });
    }
}