test.php

<?php
$arrResult = [
    'R' => ['1', '2'],
    'A' => ['1', '2', '3'],
    'M' => ['1', '2'],
];
//R1A1M1

foreach ($arrResult['R'] as $item1){
    foreach ($arrResult['A'] as $item2) {
        foreach ($arrResult['M'] as $item3) {
            echo 'R' . $item1 . 'A' . $item2 . 'M' . $item3;
            echo '<br>';
        }
    }
}
//foreach ($arrResult as $key => $value) {
//    foreach ($value as $item) {
//        echo $key . $item;
//    }
//}
/*function saeed($asli, $arr, $key, $counter)
{
    foreach ($arr as $item) {
        echo $key . $item;
        if (count($asli) > $counter) {
            $counter++;
            saeed($asli, next($asli), key($asli), $counter);
        }
        echo '<br>';
    }
}

foreach ($arrResult as $key => $values) {
    echo $key;
    foreach ($values as $value) {
        echo $value;
        foreach ($arrResult as $key => $values) {
            echo $key;
            foreach ($values as $value) {
                echo $value;
                echo "<br>";
            }
        }
    }
}

saeed($arrResult, current($arrResult), key($arrResult), 0);*/
//array_walk($arrResult, 'saeed');
//function asghar($value, $key){
//    return $value;
//}
//function saeed($value, $key)
//{
//    if(is_array($value)){
//        return $key . ' ' . array_walk($value, 'asghar');
//    }
//    print "$key  <br>\n";
//}