A string is a fixed-length array of characters. It prints using doublequotes, where doublequote and backslash characters within the string are escaped with backslashes. Other common string escapes are supported, including \n for a linefeed, \r for a carriage return, octal escapes using \ followed by up to three octal digits, and hexadecimal escapes with \u (up to four digits). Unprintable characters in a string are normally shown with \u when the string is printed.
A string can be mutable or immutable; strings written directly as expressions are immutable, but most other strings are mutable. The make-string procedure creates a mutable string given a length and optional fill character. The string-ref procedure accesses a character from a string (with 0-based indexing); the string-set! procedure changes a character in a mutable string.
> (string-ref "Apple" 0)
> (define s (make-string 5 #\.))
> (string-set! s 2 #\λ)
String ordering and case operations are generally locale-independent; that is, they work the same for all users. A few locale-dependent operations are provided that allow the way that strings are case-folded and sorted to depend on the end-user’s locale. If you’re sorting strings, for example, use string<? or string-ci<? if the sort result should be consistent across machines and users, but use string-locale<? or string-locale-ci<? if the sort is purely to order strings for an end user.
> (string<? "apple" "Banana")
> (string-ci<? "apple" "Banana")
> (string-upcase "Straße")
> (parameterize ([current-locale "C"]) (string-locale-upcase "Straße"))
For working with plain ASCII, working with raw bytes, or encoding/decoding Unicode strings as bytes, use byte strings.