Anaphoric macros are extremely useful. There's a hidden anaphor in the
CL loop macro, which binds the value of IT onto a previously-evaluated conditional. In other words, within a loop, you can say something like
(loop
for x in list-of-things
when (find x other-list) collect it)
(defun fn (n)
(let ((x (/ n 3)))
(and (integerp x) x)))
(loop
for x in '(2 3 4 5 6 8 9)
when (fn x) collect it)
(1 2 3)
Gauche Scheme and Racket:
(define (fn n)
(let ((x (/ n 3)))
(and (integer? x) x)))
(filter-map fn '(2 3 4 5 6 8 9))
===>
(1 2 3)
--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)