► |  | The Racket Guide

1 | Welcome to Racket
2 | Racket Essentials
3 | Built-In Datatypes
4 | Expressions and Definitions
5 | Programmer-Defined Datatypes
6 | Modules
7 | Contracts
8 | Input and Output
9 | Regular Expressions
10 | Exceptions and Control
11 | Iterations and Comprehensions
12 | Pattern Matching
13 | Classes and Objects
14 | Units
15 | Reflection and Dynamic Evaluation
16 | Macros
17 | Creating Languages
18 | Concurrency and Synchronization
19 | Performance
20 | Parallelism
21 | Running and Creating Executables
22 | More Libraries
23 | Dialects of Racket and Scheme
24 | Command-Line Tools and Your Editor of Choice
| Bibliography
| Index

▼ | 3 | Built-In Datatypes

3.1 | Booleans
3.2 | Numbers
3.3 | Characters
3.4 | Strings (Unicode)
3.5 | Bytes and Byte Strings
3.6 | Symbols
3.7 | Keywords
3.8 | Pairs and Lists
3.9 | Vectors
3.10 | Hash Tables
3.11 | Boxes
3.12 | Void and Undefined

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#### 3.4`` Strings (Unicode)

A string is a fixed-length array of characters. It prints using double quotes, where double quote 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.

> > > Reading Strings in The Racket Reference 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 Input and Output), 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.

> > > Strings in The Racket Reference provides more on strings and string procedures.

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