tweak-text: Lisp nesting exceeds `max-lisp-eval-depth

The program should reformat the string like below.

Example: (game-print '(THIS IS A SENTENCE。 WHAT ABOUT THIS？ PROBABLY.))

This is a sentence. What about ths? Probably.

But something is wrong( Lisp nesting exceeds `max-lisp-eval-depth) and i don't know why. This piece of code is actually from the book "Land of lisp" in page 97. The original code is written in common lisp. I want to rewrite it in elisp. The last two argument in tweak-text means captain and literal.

(defun tweak-text (lst caps lit)
  (when lst
    (let ((item (car lst))
          (rest (cdr lst)))
      (cond ((eql item ?\ ) (cons item (tweak-text rest caps lit)))
            ((member item '(?\! ?\? ?\.)) (cons item (tweak-text rest t lit)))
            ((eql item ?\") (tweak-text rest caps (not lit)))
            (lit (cons item (tweak-text rest nil lit)))
            (caps (cons (upcase item) (tweak-text rest nil lit)))
            (t (cons (downcase item) (tweak-text rest nil nil)))))))

(defun game-print (lst)
  (print (coerce (tweak-text (coerce (prin1-to-string lst) 'list) t nil) 'string)))

(game-print '(not only does this sentence have a "comma," it also mentions the "iPad."))

The orignal code written in common lisp.

(defun tweak-text (lst caps lit)
  (when lst
    (let ((item (car lst))
          (rest (cdr lst)))
      (cond ((eql item #\space) (cons item (tweak-text rest caps lit)))
            ((member item '(#\! #\? #\.)) (cons item (tweak-text rest t lit)))
            ((eql item #\") (tweak-text rest caps (not lit)))
            (lit (cons item (tweak-text rest nil lit)))
            (caps (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))

Solution

You are indeed hitting the 'max-lisp-eval-depth' limit when recursing in tweak-text. I don't see anything wrong with the way the code is(I didn't check if its doing what you intend it to do).

You can configure/raise the 'max-lisp-eval-depth' limit. The documentation for that variable states that you can raise it as long as you are confident that you are not going to trip into running out of stack space. The limit is conservatively set to 541 on my machine. Raising it to 600 got the function definition above to work on the input you gave as example.