[tmtvl]

The usual argument I've seen in favour of Lisp-2 (I personally don't care as much about the function namespace as I do about the type namespace, which I find much more important) is that you can name an argument a conflicting name with a function without the conflict interfering with the code you would write:

  (defun merge-sort (list before?)
    (declare (type List list)
             (type Function before?))
    (flet ((merge-2 (a b)
             (declare (type List a b)
             (merge 'List a b before?)))
      (unless (null list)
        (reduce #'merge-2 list :key #'list))))

  (merge-sort '(1 9 8 2 3 4 7 6 5)
              #'<)

Instead of having to name lists 'lst' or something. Which is pretty much personal preference anyway.

[xigoi]

Isn’t this only a problem if the language is case-insensitive?

[tmtvl]

Okay, let me give a simpler example:

  (defun first-two (list)
    (assert (>= (length list)
                2))
    (list (first list)
          (second list)))

In a language which doesn't normalise the case of symbols you could in theory work around that by capitalising or upper-casing either the function or the variable, but that's still not a particularly elegant solution.