PHP sample iterating over an array or hash with efficient special processing on first and last element

iterate-list-example.php

<?php
    # Iterates through the supplied hash or array with optional special processing on first and last element.
    # PARAMETERS:
    #   $list:    the hash or array to iterate over
    #   $fnMain:  function($listElement) which should process the list elements
    #   $fnFirst: function($listElement) which should process the FIRST element in the list
    #             if null, no special processing is done, and the first element will be processed with $fnMain
    #   $fnLast:  function($listElement) which should process the LAST element in the list
    #             if null, no special processing is done, and the last element will be processed with $fnMain
    function iterateList($list, $fnMain, $fnFirst, $fnLast) {
        $arr = array_keys($list);
        $numItems = count($arr);
        if ($numItems == 0) {
            return;
        };
        $i=0;
        if (is_callable($fnFirst)) {
            $firstItem=$list[$arr[0]];
            call_user_func($fnFirst, $firstItem);
            $i++;
        }
        
        while($i<$numItems-1){
            $someItem=$list[$arr[$i]];
            call_user_func($fnMain, $someItem);
            $i++;
        }
        
        $lastItem=$list[$arr[$i]];
        call_user_func((is_callable($fnLast) ? $fnLast : $fnMain), $lastItem);
        $i++;    
    }
    ######### END FUNCTION ###########
    
    # EXAMPLE USAGE
    $handleItem = function($item) {
        echo("<div>".$item."</div>");
    };
    $handleFirst = function($item) {
        echo("<div>FIRST: ".$item."</div>");
    };
    $handleLast = function($item) {
        echo("<div>LAST: ".$item."</div><br/>");
    };

    $objarr = array('one' => "1 1 1", 4 => 'Four', 9 => 9, 8 => 'Eight');
    
    iterateList($objarr, $handleItem, $handleFirst, $handleLast);
    iterateList([4, 3, 2, 1], $handleItem, null, $handleLast);
    iterateList($objarr, $handleItem, $handleFirst, null);
?>