php - Twig dynamic functions

The Twig documentation notes the following approach for creating a dynamic function:

$twig->addFunction('*_path', new Twig_Function_Function('twig_path'));

function twig_path($name, $arguments)
{
    // ...
}
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Since I already encapsulate this code within a function, I'd like to avoid creating a function within a function. How can I place 'function twig_path' outside of this scope and still load it?