eAccelerator not compatible with anonymous function/closure under php 5.4.6

Error msg:
PHP Fatal error: Function name must be a string in /usr/local/nginx/html/*******.php on line 168

on that line and some lines above:

    $source_sig_func = function($_var_cookie) {
        return substr(md5("..."), 3, 8);
    };

    $cookie_sig_matched = $cookie_source_sig == $source_sig_func($var_cookie); <= this is the line 168.