How many times you wrote code like this to achieve a simple purpose? Mapping values of an array: foreach ($items as $key => $item) { } Filtering: foreach ($items as $key => $item) {    if (condition($item)) {    } } Or reducing an array to some value: $acc = 0; foreach ($numbers as $number) {    $acc += $number; } The above code samples involve the imperative programming style, which is familiar to everybody. It has a certain flaw: we have to parse the code in our head and go through negligible but required details to understand it. To solve this issue, PHP s