A macro transforms unevaluated source forms before evaluation. In Clojure, a macro is a regular function invoked by the compiler: it receives its arguments as implicitly quoted data and returns a valid Clojure expression for runtime evaluation. section 4.0
Macros are useful when ordinary functions cannot express the desired syntax or evaluation flow:
- Reduce repeated code and express operations more concisely. section 4.0
- Alter normal evaluation flow, as threading macros do when describing processing pipelines. section 2.5 section 2.0
- Support complex domain-specific languages or embedded compilers. section 4.0
Creating and inspecting a macro
Use defmacro as the main definition entry point. Use quote when a form must remain unevaluated, and macroexpand to inspect the expression produced by a macro without executing it. Use gensym when generated code needs unique symbol names. section 4.0 section 4.9
Macro programming combines code and data: the macro receives forms, constructs a replacement form, and leaves that result for runtime evaluation. Its power comes with special syntax that can initially make macros harder to understand. section 4.0 section 4.9
