What is conf? If you write a small example that actually compiles, this will be easier to think about.

On Tue, Dec 20, 2022, 11:25 AM PICCA Frederic-Emmanuel <frederic-emmanuel.picca@synchrotron-soleil.fr> wrote:


----- Le 20 Déc 22, à 17:18, David Feuer david.feuer@gmail.com a écrit :

> Please clarify your question. Your code doesn't compile, and I can't tell
> what it's supposed to do.


replace a (Maybe a) value in a data using lens only if the new (Maybe a) is a Just

Is it clearer ?