Yeah, I just can't stop thinking about envs / dynamic binding when someone brings up the other.

Speaking of using both direct and dynamic arguments, a common pattern in (Common) Lisp is using dynamically-bound variables (so-called "special" variables) to provide default values. Since default values in (Common) Lisp can be given as any expression, which gets evaluated at function-call time, I can write this:

  (defun function (&key (some-keyword-arg *some-special*))
    ...)

And then, if I call this function with no arguments, i.e (some-function), the some-keyword-arg will pull its value from current dynamic value of some-special. In process land, this would be equivalent to having command line parser use values in environment variables as defaults for arguments that were not provided.