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alpha-char-p

alpha-char-p Function

Syntax:

alpha-char-p character → generalized-boolean

Arguments and Values:

character—a character .

generalized-boolean—a generalized boolean.

Description:

Returns true if character is an alphabetic1 character ; otherwise, returns false.

Examples:

(alpha-char-p #\a) → true 
(alpha-char-p #\5) → false 
(alpha-char-p #\Newline) → false 
;; This next example presupposes an implementation 
;; in which #\*α* is a defined character. 
(alpha-char-p #\*α*) → implementation-dependent

Affected By:

None. (In particular, the results of this predicate are independent of any special syntax which might have been enabled in the current readtable.)

Exceptional Situations:

Should signal an error of type type-error if character is not a character .

See Also:

alphanumericp, Section 13.1.10 (Documentation of Implementation-Defined Scripts)

Expanded Reference: alpha-char-p​

Basic alphabetic character tests​

alpha-char-p returns true if the character is alphabetic (a letter), and false otherwise.

(alpha-char-p #\a)
=> T
(alpha-char-p #\Z)
=> T
(alpha-char-p #\5)
=> NIL
(alpha-char-p #\+)
=> NIL

Non-graphic and whitespace characters​

Whitespace and non-graphic characters are never alphabetic.

(alpha-char-p #\Space)
=> NIL
(alpha-char-p #\Newline)
=> NIL
(alpha-char-p #\Tab)
=> NIL

Filtering alphabetic characters from a string​

alpha-char-p is commonly used to extract only letter characters from a string.

(remove-if-not #'alpha-char-p "Hello, World! 123")
=> "HelloWorld"

Checking if a string contains only letters​

You can use every with alpha-char-p to test whether a string is purely alphabetic.

(every #'alpha-char-p "Hello")
=> T
(every #'alpha-char-p "Hello!")
=> NIL
(every #'alpha-char-p "abc123")
=> NIL
(every #'alpha-char-p "")
=> T

Relationship with alphanumericp​

alpha-char-p tests for letters only, while alphanumericp also accepts digits.

(alpha-char-p #\7)
=> NIL
(alphanumericp #\7)
=> T
(alpha-char-p #\G)
=> T
(alphanumericp #\G)
=> T