Controls whether the Lisp printer calls the pretty printer.
If it is false, the pretty printer is not used and a minimum of whitespace_1 is output when printing an expression.
If it is true, the pretty printer is used, and the Lisp printer will endeavor to insert extra whitespace_1 where appropriate to make expressions more readable.
*print-pretty* has an effect even when the value of *print-escape* is false.
(setq *print-pretty* 'nil) ⇒ NIL
(progn (write '(let ((a 1) (b 2) (c 3)) (+ a b c))) nil)
|> (LET ((A 1) (B 2) (C 3)) (+ A B C))
⇒ NIL
(let ((*print-pretty* t))
(progn (write '(let ((a 1) (b 2) (c 3)) (+ a b c))) nil))
|> (LET ((A 1)
|> (B 2)
|> (C 3))
|> (+ A B C))
⇒ NIL
;; Note that the first two expressions printed by this next form
;; differ from the second two only in whether escape characters are printed.
;; In all four cases, extra whitespace is inserted by the pretty printer.
(flet ((test (x)
(let ((*print-pretty* t))
(print x)
(format t "~%~S " x)
(terpri) (princ x) (princ " ")
(format t "~%~A " x))))
(test '#'(lambda () (list "a" #’c #'d))))
|> #'(LAMBDA ()
|> (LIST "a" #’C #'D))
|> #'(LAMBDA ()
|> (LIST "a" #’C #'D))
|> #'(LAMBDA ()
|> (LIST a b 'C #'D))
|> #'(LAMBDA ()
|> (LIST a b 'C #'D))
⇒ NIL