*print-pretty* (Variable)

Value Type:

a generalized boolean.

Initial Value:

implementation-dependent.

Description:

Controls whether the Lisp printer calls the pretty printer.

If it is false, the pretty printer is not used and a minimum of whitespace₁

is output when printing an expression.

If it is true, the pretty printer is used, and the Lisp printer will endeavor to insert extra whitespace₁ where appropriate to make expressions more readable.

*print-pretty* has an effect even when the value of *print-escape* is false.

Examples:

 (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" #\b 'c #'d))))
▷ #'(LAMBDA ()
▷     (LIST "a" #\b 'C #'D))
▷ #'(LAMBDA ()
▷     (LIST "a" #\b 'C #'D))
▷ #'(LAMBDA ()
▷     (LIST a b 'C #'D))
▷ #'(LAMBDA ()
▷     (LIST a b 'C #'D))
→ NIL

See Also:

write