square-brackets.lisp

(set-macro-character #\[
  (lambda (stream char)
    (declare (ignore char))
    (let ((result (read-delimited-list #\] stream t)))
      `(,@result))))

(set-macro-character #\]
  (lambda (stream char)
    (declare (ignore stream char))
    (error "Unmatched closing bracket: ]")))

(let ([a "It Works with square brackets!"])
  (print a))