WISH: map changes to be reported in on-deep-change

[hiiamboris]

Map is not part of series! typeset currently, not it is accepted by modify native, so it is currently impossible to place any reactions on changes in the map. Which limits it's usage a lot.

However I know internally it's just hash!. So this limitation is artificial. Using hash! in place of map! though involves a lot of micromanagement, so not acceptable either.

Ideally I'd like map to be series like @giesse proposes. But it's another topic. For the scope of this wish it would be enough that:

• map keys could be used as sources for reactive relations
• any change could be caught by on-deep-change

[hiiamboris]

Related: #77 #92