http://zend-framework-community.634137.n4.nabble.com/Validating-numeric-input-td2237174.html

gistfile1.inc

<?php

// via wiping out possible options of validator
$validate = new Zend_Validate_Callback('is_numeric');
$validate ->setOptions(array());


// via create_function() callback
$callback = create_function('$v', 'return is_numeric($v);');
$validate = new Zend_Validate_Callback($callback);


// via anonymous function callback (for PHP >= 5.3)
$validate = new Zend_Validate_Callback(function($v){
    return is_numeric($v);
});