Selecting String Components - MIT/GNU Scheme 9.1
Description: MIT/GNU Scheme 9.1

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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