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characterp

characterp Function

Syntax:

characterp object → generalized-boolean

Arguments and Values:

object—an object.

generalized-boolean—a generalized boolean.

Description:

Returns true if object is of type character; otherwise, returns false.

Examples:

(characterp #\a) → true 
(characterp ’a) → false 
(characterp "a") → false 
(characterp 65.) → false 
(characterp #\Newline) → true 
;; This next example presupposes an implementation 
;; in which #\Rubout is an implementation-defined character. 
(characterp #\Rubout) → true


See Also:

character (type and function), typep

Notes:

(characterp object) ≡ (typep object ’character)

Expanded Reference: characterp​

Basic type checking​

characterp returns true if the object is a character, false otherwise.

(characterp #\a)
=> T
(characterp #\Space)
=> T
(characterp #\Newline)
=> T

Non-character objects​

Strings, symbols, and numbers are not characters, even if they represent or contain characters.

(characterp "a")
=> NIL
(characterp 'a)
=> NIL
(characterp 65)
=> NIL
(characterp nil)
=> NIL
(characterp "")
=> NIL

Equivalence with typep​

characterp is equivalent to (typep object 'character).

(eql (characterp #\x) (typep #\x 'character))
=> T
(eql (characterp 42)  (typep 42  'character))
=> T

Using characterp as a predicate​

characterp can be used with higher-order functions to filter or test collections.

(every #'characterp '(#\a #\b #\c))
=> T
(every #'characterp '(#\a "b" #\c))
=> NIL
(remove-if-not #'characterp '(#\a 1 #\b "c"))
=> (#\a #\b)

Characters extracted from strings​

Individual characters extracted from strings via char or aref are always character objects.

(characterp (char "hello" 0))
=> T
(characterp (aref "world" 2))
=> T