Lower bound in tour includes dangers

[som-snytt]

Challenging to fit on a single tour slide, but tries to emphasize that there are two concepts in play: covariance and need for lower bound. The naming of the list example classes may or may not be a distraction.

[julienrf]

Thank you @som-snytt, however, I think it would be better to minimize the changes between the code snippet that does not contain a lower bound and the one that showcases a lower bound, to make it easier for the readers to understand the scope of type bounds. I suggest using Nothing and head and tail from the beginning, instead of doing this change here. What do you think?

[som-snytt]

The suggestion on the linked PR was that the naming of "List" was potentially confusing.

If I'm allowed to muck with the entire example, is it OK to make it look like the familiar List and avoid the nerdy Node terminology?

I was trying avoid changing too much, in case there are pedagogical reasons.

[julienrf]

I am fine with removing the Node terminology.

[julienrf]

Thank you! I have some suggestions.

[julienrf]

Thank you again, sorry for the additional work :) I think this is good to merge, I just left one minor suggestion.

[som-snytt]

@julienrf thanks for making it better