Or with more Python-esque syntax: (let ((files (coerce "ABCDEFGH" 'list)) (ranks (loop for r from 1 to 9 collect r))) [(format nil "~a~a" f

Or with more Python-esque syntax: (let ((files (coerce "ABCDEFGH" 'list)) (ranks (loop for r from 1 to 9 collect r))) [(format nil "~a~a" file rank) (file <- files) (rank <- ranks)]) Based on the list comprehension macro from 1991 in https://3e8.org/pub/scheme/doc/lisp-pointers/v4i2/p16-lapalme.pdf https://3e8.org/pub/scheme/doc/lisp-pointers/v4i2/p16-lapalm... that still works. (defmacro comp ((e &rest qs) l2) (if (null qs) `(cons ,e ,l2) ; rule A (let ((q1 (car qs)) (q (cdr qs))) (if (not (eq (cadr q1) '<-)) ; a generator? `(if ,q1 (comp (,e ,@q) ,l2) ,l2) ; rule B (let ((v (car q1)) ; rule C (l1 (third q1)) (h (gentemp "H-")) (us (gentemp "US-")) (us1 (gentemp "US1-"))) `(labels ((,h (,us) ; corresponds to a letrec (if (null ,us) ,l2 (let ((,v (car ,us)) (,us1 (cdr ,us))) (comp (,e ,@q) (,h ,us1)))))) (,h ,l1))))))) (defun open-bracket (stream ch) (do ((l nil) (c (read stream t nil t)(read stream t nil t))) ((eq c '|]|) `(comp ,(reverse l) ())) (push c l))) (defun closing-bracket (stream ch) '|]|) (set-macro-character #\[ #'open-bracket) (set-macro-character #\] #'closing-bracket) Supports filtering too, e.g. (let ((xs '(1 2 3 4)) (ys '(1 2 3 4))) [(+ x y) (x <- xs) (y <- ys) (evenp x) (oddp y)]) ; -> (3 5 5 7)