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
Bibliography
Index
Version: 4.0.2

 

3.11 Boxes

A box is like a single-element vector. It prints as #& followed by the printed form of the boxed value. A #& form can also be used as an expression, but since the resulting box is constant, it has practically no use.

Examples:

  > (define b (box "apple"))

  > b

  #&"apple"

  > (unbox b)

  "apple"

  > (set-box! b '(banana boat))

  > b

  #&(banana boat)

Boxes in Reference: PLT Scheme provides more on boxes and box procedures.