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*print-escape*

∗print-escape∗ Variable

Value Type:

a generalized boolean.

Initial Value:

true.

Description:

If false, escape characters and package prefixes are not output when an expression is printed.

If true, an attempt is made to print an expression in such a way that it can be read again to produce an equal expression. (This is only a guideline; not a requirement. See *print-readably*.)

For more specific details of how the value of *print-escape* affects the printing of certain types, see Section 22.1.3 (Default Print-Object Methods).

Examples:

(let ((\*print-escape\* t)) (write #\a)) 

▷ #\a 
→ #\a 
(let ((\*print-escape\* nil)) (write #\a)) 
▷ a 
→ #\a

Affected By:

princ, prin1, format

See Also:

write, readtable-case

Notes:

princ effectively binds *print-escape* to false. prin1 effectively binds *print-escape* to true.

Expanded Reference: *print-escape*​

Default Behavior (true)​

When *print-escape* is true (the default), objects are printed with escape characters so they can be read back by read.

(let ((*print-escape* t))
  (write-to-string "hello"))
=> "\"hello\""

(let ((*print-escape* t))
  (write-to-string #\Space))
=> "#\\ "

(let ((*print-escape* t))
  (write-to-string 'foo))
=> "FOO"

When Set to NIL​

When *print-escape* is false, escape characters and package prefixes are omitted. Output looks "nice" but may not be readable by read.

(let ((*print-escape* nil))
  (write-to-string "hello"))
=> "hello"

(let ((*print-escape* nil))
  (write-to-string #\Space))
=> " "

Relationship to prin1 and princ​

prin1 binds *print-escape* to true; princ binds it to false. This is the key difference between the two functions.

;; prin1 uses escape characters
(prin1-to-string "She said \"hi\"")
=> "\"She said \\\"hi\\\"\""

;; princ suppresses escape characters
(princ-to-string "She said \"hi\"")
=> "She said \"hi\""

Effect on Symbols with Special Characters​

(let ((*print-escape* t))
  (write-to-string '|hello world|))
=> "|hello world|"

(let ((*print-escape* nil))
  (write-to-string '|hello world|))
=> "hello world"