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*print-right-margin*

∗print-right-margin∗ Variable

Value Type:

a non-negative integer , or nil.

Initial Value:

nil.

Expanded Reference: *print-right-margin*​

Default Behavior (nil)​

When *print-right-margin* is nil, the pretty printer attempts to determine the right margin from the output stream, or uses an implementation-dependent default.

*print-right-margin*
;; => NIL  ; initial value is implementation-dependent

Setting a Specific Right Margin​

Setting *print-right-margin* to an integer specifies the column at which the pretty printer should try to break lines.

(let ((*print-pretty* t)
      (*print-right-margin* 40))
  (write-to-string '(let ((alpha 1) (beta 2) (gamma 3)) (+ alpha beta gamma))))
=> "(LET ((ALPHA 1) (BETA 2) (GAMMA 3))
  (+ ALPHA BETA GAMMA))"

Narrow Right Margin Forces More Line Breaks​

(let ((*print-pretty* t)
      (*print-right-margin* 25))
  (write-to-string '(let ((a 1) (b 2) (c 3)) (+ a b c))))
=> "(LET ((A 1) (B 2) (C 3))
  (+ A B C))"

Wide Right Margin Keeps Things on One Line​

(let ((*print-pretty* t)
      (*print-right-margin* 80))
  (write-to-string '(let ((a 1) (b 2) (c 3)) (+ a b c))))
=> "(LET ((A 1) (B 2) (C 3))
  (+ A B C))"

Only Affects Pretty Printing​

*print-right-margin* has no effect when *print-pretty* is false.

(let ((*print-pretty* nil)
      (*print-right-margin* 10))
  (write-to-string '(a b c d e f g h)))
=> "(A B C D E F G H)"