CustomREPL

(defun game-repl ()
 (let ((cmd (game-read)))
 (unless (eq (car cmd) 'quit)
 (game-print (game-eval cmd))
 (game-repl))))
 
(defun game-read ()
 (let ((cmd (read-from-string
 (concatenate 'string "(" (read-line) ")"))))
 (flet ((quote-it (x)
 (list 'quote x)))
 (cons (car cmd) (mapcar #'quote-it (cdr cmd))))))

(defparameter *allowed-commands* '(look walk pickup inventory))

(defun game-eval (sexp)
 (if (member (car sexp) *allowed-commands*)
 (eval sexp)
 '(I do not know that command.)))

(defun tweak-text (lst caps lit)
 (when lst
 (let ((item (car lst))
 (rest (cdr lst)))
 (cond ((eq item #\space) (cons item (tweak-text rest caps lit)))
 ((member item '(#\! #\? #\.)) (cons item (tweak-text rest t lit)))
 ((eq item #\") (tweak-text rest caps (not lit)))
 (lit (cons item (tweak-text rest nil lit)))
 ((or caps lit) (cons (char-upcase item) (tweak-text rest nil lit)))
 (t (cons (char-downcase item) (tweak-text rest nil nil)))))))
 
(defun game-print (lst)
 (princ (coerce (tweak-text (coerce (string-trim "() "
 (prin1-to-string lst))
 'list)
 t
 nil)
 'string))
 (fresh-line))