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6.2 Selecting String Components

procedure: string? object

Returns #t if object is a string; otherwise returns #f.

(string? "Hi")                  ⇒  #t
(string? 'Hi)                   ⇒  #f
procedure: string-length string

Returns the length of string as an exact non-negative integer.

(string-length "")              ⇒  0
(string-length "The length")    ⇒  10
procedure: string-null? string

Returns #t if string has zero length; otherwise returns #f.

(string-null? "")               ⇒  #t
(string-null? "Hi")             ⇒  #f
procedure: string-ref string k

Returns character k of string. K must be a valid index of string.

(string-ref "Hello" 1)          ⇒  #\e
(string-ref "Hello" 5)          error→ 5 not in correct range
procedure: string-set! string k char

Stores char in element k of string and returns an unspecified value. K must be a valid index of string, and char must satisfy the predicate char-ascii?.

(define str "Dog")              ⇒  unspecified
(string-set! str 0 #\L)         ⇒  unspecified
str                             ⇒  "Log"
(string-set! str 3 #\t)         error→ 3 not in correct range