Add more bolds (or add an option to have them)

[moonTox]

Add more bolds in function definitions and keywords. For example the ef-themes does this

[bbatsov]

In general this makes sense to me, as many themes do it, but it needs to be cleared with the maintainers and we need to agree what exactly could be made bold. (in your example this looks like only font-lock-builtin-face, but boldness is somewhat in other cases as well.

In the mean time you can just tweak theme yourself like this:

(set-face-attribute 'font-lock-builtin-face nil :weight 'bold)

Putting this in your config after the place you load the theme should do the trick.