16 Macros

► |  | 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

▼ | 16 | Macros

16.1 | Pattern-Based Macros
16.2 | General Macro Transformers
16.3 | Module Instantiations and Visits

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## 16 Macros🔗ℹ

A macro is a syntactic form with an associated transformer that expands the original form into existing forms. To put it another way, a macro is an extension to the Racket compiler. Most of the syntactic forms of racket/base and racket are actually macros that expand into a small set of core constructs.

Like many languages, Racket provides pattern-based macros that make simple transformations easy to implement and reliable to use. Racket also supports arbitrary macro transformers that are implemented in Racket—or in a macro-extended variant of Racket.

This chapter provides an introduction to Racket macros, but see Fear of Macros for an introduction from a different perspective.

Racket includes additional support for macro development: A macro debugger to make it easier for experienced programmers to debug their macros and for novices to study their behavior, and of macros. And the syntax/parse library for writing macros and specifying syntax that automatically validates macro uses and reports syntax errors.

16.1 Pattern-Based Macros
16.1.1 define-syntax-rule
16.1.2 Lexical Scope
16.1.3 define-syntax and syntax-rules
16.1.4 Matching Sequences
16.1.5 Identifier Macros
16.1.6 set! Transformers
16.1.7 Macro-Generating Macros
16.1.8 Extended Example: Call-by-Reference Functions
16.2 General Macro Transformers
16.2.1 Syntax Objects
16.2.2 Macro Transformer Procedures
16.2.3 Mixing Patterns and Expressions: syntax-case
16.2.4 with-syntax and generate-temporaries
16.2.5 Compile and Run-Time Phases
16.2.6 General Phase Levels
16.2.6.1 Phases and Bindings
16.2.6.2 Phases and Modules
16.2.7 Tainted Syntax
16.3 Module Instantiations and Visits
16.3.1 Declaration versus Instantiation
16.3.2 Compile-Time Instantiation
16.3.3 Visiting Modules
16.3.4 Lazy Visits via Available Modules

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