May be used to make keyword, a loop keyword (such as
for), into a Lisp macro which may introduce a loop form.
For example, after evaluating
(define-loop-macro for),
one may now write an iteration as
(for i from 1 below n do ...)
This facility exists primarily for diehard users of a
predecessor of loop. Its unconstrained use is not recommended,
as it tends to decrease the transportability of the code and
needlessly uses up a function name.