► |  | The Racket Reference

1 | Language Model
2 | Syntactic Forms
3 | Datatypes
4 | Structures
5 | Classes and Objects
6 | Units
7 | Contracts
8 | Pattern Matching
9 | Control Flow
10 | Concurrency and Parallelism
11 | Macros
12 | Input and Output
13 | Reflection and Security
14 | Operating System
15 | Memory Management
16 | Unsafe Operations
17 | Running Racket
| Bibliography
| Index

▼ | 3 | Datatypes

3.1 | Booleans and Equality
3.2 | Numbers
3.3 | Strings
3.4 | Byte Strings
3.5 | Characters
3.6 | Symbols
3.7 | Regular Expressions
3.8 | Keywords
3.9 | Pairs and Lists
3.10 | Mutable Pairs and Lists
3.11 | Vectors
3.12 | Boxes
3.13 | Hash Tables
3.14 | Sequences and Streams
3.15 | Dictionaries
3.16 | Sets
3.17 | Procedures
3.18 | Void and Undefined

On this page:

void?
void

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#### 3.18`` Void and Undefined

The constant #<void> is returned by most forms and procedures that have a side-effect and no useful result. The constant #<undefined> is used as the initial value for letrec bindings.

The #<void> value is always eq? to itself, and the #<undefined> value is also eq? to itself.

> > procedure

> > (void? v) → void?

> v : any/c

Returns #t if v is the constant #<void>, #f otherwise.

> > procedure

> > (void v ...) → void?

> v : any/c

Returns the constant #<void>. Each v argument is ignored.
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