Within l3keys, what are the recommended pattern for checking whether some keys have been set? I have an interface where for each term one makes some definitions using key-val. One of these are always required, the others are optional.
@daleif it depends, keys are usually optional; (the major change we made for \includegraphics from the earlier latex209 \epsfig was not having a mandatory file= key and making the filename be a separate argument not part of the keyval) but otherwise if you initialise the internal holding macro to \errorthisshouldbeset then you will get an error when it's used unless it is locally set to a real value by using the key.
@daleif In the model used by l3keys, there's always a value - it might just be empty - other keyval approaches are of course possible (and could be implemented using the lower-level \keyval_parse:nnn)
@JosephWright not quite what I mean. I'm more looking at whether there was a method for checking if a key was set, or if one should just set the keys and then check the holder variables afterward (that is what I currently do)
@daleif What @DavidCarlisle said, but what I was getting at is it really doesn't fit the l3keys model - I would design around empty having some meaning
@JosephWright in this case empty/not set is an error. But the syntax gets clunky if the interface for it is not a key. It's better to check after setting the keys, which is what I do right now.
@UlrikeFischer Hi and good afternoon from Sicily. Please can you help me on this question? Nobody has help me. tex.stackexchange.com/questions/721108/…. Thank you very much.
@Bml People will see new question on the main site. It is not necessary to post them in chat -- and personally I think it is very unfair to all the other users, who will patiently wait until they get an answer to their question, if people advertise their questions here.
@samcarter Sorry, I didn't notice that. I will pay more attention next time and will no longer notify the occurrence of my question in chat (sorry again).
