string-set! - modify a string element

(import (rnrs mutable-strings))     ;R6RS
(import (scheme r5rs))              ;R7RS
(import (scheme base))              ;R7RS

(string-set! string k char)

Stores char in element k of string.

R6RS

Implementors should make string-ref(3scm) run in constant time, which may mean that this procedure will also run in constant time.

R7RS

There is no requirement for this procedure to execute in constant time.

(define (f) (make-string 3 #\*))
(define (g) "***")
(string-set! (f) 0 #\?)       => unspecified
(string-set! (g) 0 #\?)       => unspecified
             ; should raise &assertion exception

This procedure is rarely used to modify existing strings. It is sometimes used to build up new strings, but a better option is often to use an output string created by open-string-output-port(3scm), which have the benefit that the output length does not need to be known in advance.

This procedure works the same everywhere. Whether a string literal is truly immutable depends on the implementation (but they should not be mutated either way).

This procedure can raise exceptions with the following condition types:

&assertion (R6RS)

The wrong number of arguments was passed or an argument was outside its domain. In particular, k must be a valid index of string, which in turn must be a mutable string.

R7RS

The assertions described above are errors. Implementations may signal an error, extend the procedure's domain of definition to include such arguments, or fail catastrophically.

Unsupported characters (R7RS)

It is an error to store a character which the implementation does not support. 7-bit ASCII (except #\null) must be supported. Any other character is optional and potentially an error (as described above). You can use the full-unicode feature identifier in cond-expand(3scm) to check if all of Unicode 6.0 is supported.

open-string-output-port(3scm)

R4RS, IEEE Scheme, R5RS, R6RS, R7RS

The first Scheme report to include this procedure was R2RS. In R6RS this procedure was moved to its own library which is normally not imported.

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