Hi all, is it possible to change a Buffer reference in a genexpr function? If yes, how?

In the attached patch I created three gen~ patches: the first one is a simple patch which plays the content of an external buffer, and it works. In the second patch I used a codebox with the same algorithm, and it still works. In the third patch I enclosed the algorithm into a function, then called the function, and it doesn't work: that is because the buffer declaration is inside the function and cannot (apparently) be redirect from the 'outside'. I tried to pass the buffer name as a parameter but without success.

Is there a way to make it work? Thanks!