2.9 KiB
Strings Unicode
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.
+[missing] in [missing] documents the fine points of the syntax of strings.
The display procedure directly writes the characters of a string to
the current output port see \[missing\], in contrast to the
string-constant syntax used to print a string result.
Examples:
> "Apple"
"Apple"
> "\u03BB"
"λ"
> (display "Apple")
Apple
> (display "a \"quoted\" thing")
a "quoted" thing
> (display "two\nlines")
two
lines
> (display "\u03BB")
λ
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.
Examples:
> (string-ref "Apple" 0)
#\A
> (define s (make-string 5 #\.))
> s
"....."
> (string-set! s 2 #\λ)
> s
"..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.
Examples:
> (string<? "apple" "Banana")
#f
> (string-ci<? "apple" "Banana")
#t
> (string-upcase "Straße")
"STRASSE"
> (parameterize ([current-locale "C"])
(string-locale-upcase "Straße"))
"STRAßE"
For working with plain ASCII, working with raw bytes, or encoding/decoding Unicode strings as bytes, use byte strings.
+[missing] in [missing] provides more on strings and string procedures.