The Racket Reference

Version: 5.2

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The Racket Reference

Matthew Flatt
and PLT

This manual defines the core Racket language and describes its most prominent libraries. The companion manual The Racket Guide provides a friendlier (though less precise and less complete) overview of the language.

#lang racket/base

Unless otherwise noted, the bindings defined in this manual are exported by the racket/base and racket languages.

The racket/base library is much smaller than the racket library and will typically load faster.
The racket library combines racket/base, racket/bool, racket/bytes, racket/class, racket/cmdline, racket/contract, racket/dict, racket/file, racket/function, racket/future, racket/include, racket/list, racket/local, racket/match, racket/math, racket/path, racket/place, racket/port, racket/pretty, racket/promise, racket/sequence, racket/set, racket/shared, racket/stream, racket/string, racket/system, racket/tcp, racket/udp, racket/unit, and racket/vector.

1 Language Model

1.1 Evaluation Model

1.1.1 Sub-expression Evaluation and Continuations

1.1.2 Tail Position

1.1.3 Multiple Return Values

1.1.4 Top-Level Variables

1.1.5 Objects and Imperative Update

1.1.6 Object Identity and Comparisons

1.1.7 Garbage Collection

1.1.8 Procedure Applications and Local Variables

1.1.9 Variables and Locations

1.1.10 Modules and Module-Level Variables

1.1.10.1 Phases

1.1.10.2 Module Re-declarations

1.1.11 Continuation Frames and Marks

1.1.12 Prompts, Delimited Continuations, and Barriers

1.1.14 Parameters

1.1.15 Exceptions

1.1.16 Custodians

1.2 Syntax Model

1.2.1 Identifiers and Binding

1.2.2 Syntax Objects

1.2.3 Expansion (Parsing)

1.2.3.1 Fully Expanded Programs

1.2.3.2 Expansion Steps

1.2.3.3 Expansion Context

1.2.3.4 Introducing Bindings

1.2.3.5 Transformer Bindings

1.2.3.6 Partial Expansion

1.2.3.7 Internal Definitions

1.2.3.8 Module Phases and Visits

1.2.3.9 Macro-Introduced Bindings

1.2.4 Compilation

1.2.5 Namespaces

1.2.6 Inferred Value Names

1.4 The Printer

2 Syntactic Forms

2.1 Modules: module, ...

2.2 Importing and Exporting: require and provide

2.2.1 Additional require Forms

2.2.2 Additional provide Forms

2.3 Literals: quote and #%datum

2.4 Expression Wrapper: #%expression

2.5 Variable References and #%top

2.6 Locations: #%variable-reference

2.7 Procedure Applications and #%app

2.8 Procedure Expressions: lambda and case-lambda

2.9 Local Binding: let, let*, letrec, ...

2.10 Local Definitions: local

2.11 Constructing Graphs: shared

2.12 Conditionals: if, cond, and, and or

2.13 Dispatch: case

2.14 Definitions: define, define-syntax, ...

2.14.1 require Macros

2.14.2 provide Macros

2.15 Sequencing: begin, begin0, and begin-for-syntax

2.16 Guarded Evaluation: when and unless

2.17 Assignment: set! and set!-values

2.18 Iterations and Comprehensions: for, for/list, ...

2.18.1 Iteration and Comprehension Forms

2.18.2 Deriving New Iteration Forms

2.18.3 Do Loops

2.19 Continuation Marks: with-continuation-mark

2.20 Quasiquoting: quasiquote, unquote, and unquote-splicing

2.21 Syntax Quoting: quote-syntax

2.22 Interaction Wrapper: #%top-interaction

2.23 Limiting Scope: define-package, open-package, ...

2.24 Blocks: block

2.25 Internal-Definition Limiting: #%stratified-body

3.1 Booleans and Equality

3.1.1 Boolean Aliases

3.2.1 Number Types

3.2.2 Generic Numerics

3.2.2.1 Arithmetic

3.2.2.2 Number Comparison

3.2.2.3 Powers and Roots

3.2.2.4 Trignometric Functions

3.2.2.5 Complex Numbers

3.2.2.6 Bitwise Operations

3.2.2.7 Random Numbers

3.2.2.8 Number–String Conversions

3.2.2.9 Extra Constants and Functions

3.2.3.1 Flonum Arithmetic

3.2.3.2 Flonum Vectors

3.2.4.1 Fixnum Arithmetic

3.2.4.2 Fixnum Vectors

3.3.1 String Constructors, Selectors, and Mutators

3.3.2 String Comparisons

3.3.3 String Conversions

3.3.4 Locale-Specific String Operations

3.3.5 Additional String Functions

3.4 Byte Strings

3.4.1 Byte String Constructors, Selectors, and Mutators

3.4.2 Byte String Comparisons

3.4.3 Bytes to/from Characters, Decoding and Encoding

3.4.4 Bytes to Bytes Encoding Conversion

3.4.5 Additional Byte String Functions

3.5.1 Characters and Scalar Values

3.5.2 Character Comparisons

3.5.3 Classifications

3.5.4 Character Conversions

3.7 Regular Expressions

3.7.1 Regexp Syntax

3.7.2 Additional Syntactic Constraints

3.7.3 Regexp Constructors

3.7.4 Regexp Matching

3.7.5 Regexp Splitting

3.7.6 Regexp Substitution

3.9 Pairs and Lists

3.9.1 Pair Constructors and Selectors

3.9.2 List Operations

3.9.3 List Iteration

3.9.4 List Filtering

3.9.5 List Searching

3.9.6 Pair Accessor Shorthands

3.9.7 Additional List Functions and Synonyms

3.9.8 Immutable Cyclic Data

3.10 Mutable Pairs and Lists

3.10.1 Mutable Pair Constructors and Selectors

3.10.2 Mutable List Functions

3.11.1 Additional Vector Functions

3.13 Hash Tables

3.14 Sequences and Streams

3.14.1 Sequences

3.14.1.1 Sequence Predicate and Constructors

3.14.1.2 Sequence Conversion

3.14.1.3 Sequence Combinations

3.14.3 Generators

3.15 Dictionaries

3.17 Procedures

3.17.1 Keywords and Arity

3.17.2 Reflecting on Primitives

3.17.3 Additional Higher-Order Functions

3.18 Void and Undefined

4.1 Defining Structure Types: struct

4.2 Creating Structure Types

4.3 Structure Type Properties

4.4 Copying and Updating Structures

4.5 Structure Utilities

4.6 Structure Type Transformer Binding

5 Classes and Objects

5.1 Creating Interfaces

5.2 Creating Classes

5.2.1 Initialization Variables

5.2.3.1 Method Definitions

5.2.3.2 Inherited and Superclass Methods

5.2.3.3 Internal and External Names

5.3 Creating Objects

5.4 Field and Method Access

5.7 Object and Class Contracts

5.8 Object Equality and Hashing

5.9 Object Serialization

5.10 Object Printing

5.11 Object, Class, and Interface Utilities

5.12 Surrogates

6.1 Creating Units

6.2 Invoking Units

6.3 Linking Units and Creating Compound Units

6.4 Inferred Linking

6.5 Generating A Unit from Context

6.6 Structural Matching

6.7 Extending the Syntax of Signatures

6.8 Unit Utilities

6.9 Unit Contracts

6.10 Single-Unit Modules

6.11 Single-Signature Modules

6.12 Transformer Helpers

7.1 Data-structure Contracts

7.2 Function Contracts

7.3 Parametric Contracts

7.4 Lazy Data-structure Contracts

7.5 Attaching Contracts to Values

7.5.1 Nested Contract Boundaries

7.5.2 Low-level Contract Boundaries

7.6 Building New Contract Combinators

7.6.1 Blame Objects

7.6.2 Contracts as structs

7.6.3 Obligation Information in Check Syntax

7.6.4 Utilities for Building New Combinators

7.7 Contract Utilities

7.8 Legacy Contracts

8 Pattern Matching

8.1 Additional Matching Forms

8.2 Extending match

8.3 Library Extensions

9.1 Multiple Values

9.2.1 Raising Exceptions

9.2.2 Handling Exceptions

9.2.3 Configuring Default Handling

9.2.4 Built-in Exception Types

9.3 Delayed Evaluation

9.3.1 Additional Promise Kinds

9.4 Continuations

9.4.1 Classical Control Operators

9.5 Continuation Marks

10 Concurrency and Parallelism

10.1.1 Creating Threads

10.1.2 Suspending, Resuming, and Killing Threads

10.1.3 Synchronizing Thread State

10.1.4 Thread Mailboxes

10.2 Synchronization

10.2.2 Channels

10.2.3 Semaphores

10.2.4 Buffered Asynchronous Channels

10.3 Thread-Local Storage

10.3.1 Thread Cells

10.3.2 Parameters

10.4.1 Future Performance Logging

11.1 Pattern-Based Syntax Matching

11.2 Syntax Object Content

11.3 Syntax Object Bindings

11.4 Syntax Transformers

11.4.1 require Transformers

11.4.2 provide Transformers

11.5 Syntax Parameters

11.5.1 Syntax Parameter Inspection

11.6 Local Binding with Splicing Body

11.7 Syntax Object Properties

11.8 Syntax Taints

11.9 Expanding Top-Level Forms

11.9.1 Information on Expanded Modules

11.10 File Inclusion

11.11 Syntax Utilities

11.11.1 Creating formatted identifiers

11.11.2 Pattern variables

11.11.3 Error reporting

11.11.4 Recording disappeared uses

11.11.5 Miscellaneous utilities

12 Input and Output

12.1.1 Encodings and Locales

12.1.2 Managing Ports

12.1.3 Port Buffers and Positions

12.1.4 Counting Positions, Lines, and Columns

12.1.5 File Ports

12.1.6 String Ports

12.1.8 Structures as Ports

12.1.9 Custom Ports

12.1.10 More Port Constructors, Procedures, and Events

12.1.10.1 Port String and List Conversions

12.1.10.2 Creating Ports

12.1.10.3 Port Events

12.1.10.4 Copying Streams

12.2 Byte and String Input

12.3 Byte and String Output

12.6 Pretty Printing

12.6.1 Basic Pretty-Print Options

12.6.2 Per-Symbol Special Printing

12.6.3 Line-Output Hook

12.6.4 Value Output Hook

12.6.5 Additional Custom-Output Support

12.7 Reader Extension

12.7.1 Readtables

12.7.2 Reader-Extension Procedures

12.7.3 Special Comments

12.8 Printer Extension

12.9 Serialization

12.10 Fast-Load Serialization

13 Reflection and Security

13.1 Namespaces

13.2 Evaluation and Compilation

13.3 The racket/load Language

13.4 Module Names and Loading

13.4.1 Resolving Module Names

13.4.2 Compiled Modules and References

13.4.3 Dynamic Module Access

13.5 Impersonators and Chaperones

13.5.1 Impersonator Constructors

13.5.2 Chaperone Constructors

13.5.3 Impersonator Properties

13.6 Security Guards

13.7 Custodians

13.8 Thread Groups

13.9 Structure Inspectors

13.10 Code Inspectors

13.11 Sandboxed Evaluation

13.11.1 Customizing Evaluators

13.11.2 Interacting with Evaluators

13.11.3 Miscellaneous

14 Operating System

14.1.1 Manipulating Paths

14.1.2 More Path Utilities

14.1.3 Unix and Mac OS X Paths

14.1.4 Windows Path Conventions

14.2 Filesystem

14.2.1 Locating Paths

14.2.3 Directories

14.2.4 Declaring Paths Needed at Run Time

14.2.5 More File and Directory Utilities

14.3 Networking

14.4.1 Simple Subprocesses

14.5.1 Creating Loggers

14.5.2 Logging Events

14.5.3 Receiving Logged Events

14.6.1 Date Utilities

14.7 Environment and Runtime Information

14.8 Command-Line Parsing

15 Memory Management

15.1 Weak Boxes

15.2 Ephemerons

15.3 Wills and Executors

15.4 Garbage Collection

16 Unsafe Operations

16.1 Unsafe Numeric Operations

16.2 Unsafe Data Extraction

17 Running Racket

17.1 Running Racket or GRacket

17.1.1 Initialization

17.1.2 Exit Status

17.1.3 Init Libraries

17.1.4 Command Line

17.1.5 Language Run-Time Configuration

17.2 Libraries and Collections

17.2.1 Collection Links

17.3 Interactive Help

17.4 Interactive Module Loading

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