$.post() callback executed no data passed

$.post() callback executed no data passed

hello everyone. here is my server side code:

$arr = array ('a'=>1,'b'=>2,'c'=>3,'d'=>4,'e'=>5);
echo json_encode($arr);

here is my javascript:

$.post($SERVER, {op:"one", test:"two"} ,HandleJSON(), "json");
}

function HandleJSON(data)
{
alert("being called");
alert(data);
return;
}

when i call alert(data), it says it is "undefined". i am new to jQuery, but this appears to mean that no data is being passed to the callback function even though i know the $.post() executed properly (the server side code is executing, and the other alert() tells me that it had a successful result and the callback is being made.

any ideas?