► |  | Guide: PLT Scheme

1 | Welcome to PLT Scheme
2 | Scheme 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 (Components)
15 | Reflection and Dynamic Evaluation
16 | Macros
17 | Performance
18 | Running and Creating Executables
19 | Compilation and Configuration
20 | More Libraries
21 | Dialects of Scheme
| 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

Version: 4.1.4
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#### 3.5`` Bytes and Byte Strings

A byte is an exact integer between 0 and 255, inclusive. The byte? predicate recognizes numbers that represent bytes.

Examples:
> (byte? 0)
#t
> (byte? 256)
#f

A byte string is similar to a string – see Strings (Unicode) – but its content is a sequence of bytes instead of characters. Byte strings can be used in applications that process pure ASCII instead of Unicode text. The printed form of a byte string supports such uses in particular, because a byte string prints like the ASCII decoding of the byte string, but prefixed with a #. Unprintable ASCII characters or non-ASCII bytes in the byte string are written with octal notation.

Reading Strings in Reference: PLT Scheme documents the fine points of the syntax of byte strings.

Examples:
> #"Apple"
#"Apple"
> (bytes-ref #"Apple" 0)
65
> (make-bytes 3 65)
#"AAA"
> (define b (make-bytes 2 0))
> b
#"\0\0"
> (bytes-set! b 0 1)
> (bytes-set! b 1 255)
> b
#"\1\377"

The display form of a byte string writes its raw bytes to the current output port (see Input and Output). Technically, display of a normal (i.e,. character) string prints the UTF-8 encoding of the string to the current output port, since output is ultimately defined in terms of bytes; display of a byte string, however, writes the raw bytes with no encoding. Along the same lines, when this documentation shows output, it technically shows the UTF-8-decoded form of the output.

Examples:
> (display #"Apple")
Apple
> (display "\316\273") ; same as "Î»"
Î»
> (display #"\316\273") ; UTF-8 encoding of λ
λ

For explicitly converting between strings and byte strings, Scheme supports three kinds of encodings directly: UTF-8, Latin-1, and the current locale’s encoding. General facilities for byte-to-byte conversions (especially to and from UTF-8) fill the gap to support arbitrary string encodings.

Examples:
> (bytes->string/utf-8 #"\316\273")
"λ"
> (bytes->string/latin-1 #"\316\273")
"Î»"

> (parameterize ([current-locale "C"]) ; C locale supports ASCII,
(bytes->string/locale #"\316\273")) ; only, so...

"λ"

> (let ([cvt (bytes-open-converter "cp1253" ; Greek code page
"UTF-8")]
[dest (make-bytes 2)])
(bytes-convert cvt #"\353" 0 1 dest)
(bytes-close-converter cvt)
(bytes->string/utf-8 dest))

bytes-convert: expects type <converter> as 1st argument,
given: #f; other arguments were: #"\353" 0 1 #"\0\0"

Byte Strings in Reference: PLT Scheme provides more on byte strings and byte-string procedures.

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