So, my approach to dynamic features, global mutable state, etc... There's this big list of features which have caused me tremendous pain over the years. I am increasingly weary.

Sometimes you want or need them, though. You don't want the same level of strictness for every project (e.g. throwaway scripts or game jams), nor at every stage of a project -- e.g. being forced to specify invariants is something I'd love to be able to enable, but I wouldn't want that on while I'm still figuring out the basic structure of things.

So for game jams I'd put the language into #JAMMODE (which would be short for a bunch of other flags). But the point here is that jam mode should be opt-in, rather than opt-out. You should have to go out of your way to enable the footguns. And a file with #JAMMODE should be a little smelly. You should think, OK I'm actually shipping this thing now, let's get it out of #JAMMODE. (And strict files can't talk to jam files, and we probably want different strictness levels beyond Debug and Release, etc... someone told me with the strictness "zones" that I'm reinventing half of Ada, hahah.)