<?php

function is_sequential (array $array, bool $strict = false) {
    return array_filter($array, "is_int", ARRAY_FILTER_USE_KEY) == ($strict ? $array : true);
}

$array = ["foo", "baz", "bar"];

if (is_sequential($array, true)) {
    for ($i = 0; $i < count($array); $i++) {
        echo $array[$i], PHP_EOL;
    }
}

$array = ["foo", "baz" => "bar"];

if (is_sequential($array, true)) {
    for ($i = 0; $i < count($array); $i++) {
        echo $array[$i], PHP_EOL;
    }
}