At present Fns are completely opaque, when they don't have to be.
[ ] Be able to determine implemented arities from a Fn instance. This includes type hints. Could later be used to implement specialized static call sites.
[ ] Be able to determine supported the source as a list at least of the fully macroexpanded form.
[ ] Be able to determine the call set of a Fn. Note that the reach set cannot be statically determined because Vars are the only linkage.
At present Fns are completely opaque, when they don't have to be.
Prior art: https://github.com/mikera/kiss/blob/master/src/main/java/kiss/lang/impl/ATypedFn.java