Macro hygiene
Macro hygiene is a property of macro expansion that prevents introduced or referenced identifiers from unintentionally conflicting with surrounding code.
Clojure: The Essential Reference
Macro hygiene is the practice of preventing names introduced by macro expansion from unintentionally colliding with names in the surrounding code.
- How it is used
- Prevents accidental symbol capture when macros construct code for a caller’s context.
- How deep it goes
- Explains syntax-quote qualification, auto-gensym, and an escape hatch through expanded examples, but does not implement a purely hygienic macro system.
- Examples
- Compares `foo`, `foo#`, and `~'foo`, then shows a generated `let` binding and generated names in a retry macro.
- What you can do after
- Apply it via Clojure syntax-quote and auto-gensym when introducing names in macros, and inspect expansions with `macroexpand`.
Read how Clojure: The Essential Reference explains macro hygiene →
Write Powerful Rust Macros
Macro hygiene is the property that prevents identifiers introduced or referenced by a macro expansion from unintentionally colliding with identifiers in surrounding code.
- How it is used
- Explains why declarative macros can generate local names without unintentionally capturing symbols from surrounding Rust code.
- How deep it goes
- Defines identifier separation, demonstrates its scope consequence, and stops short of broader macro-expansion internals.
- Examples
- Uses generate_x!(), a generated let binding, an attempted increment, and passing identifiers as macro arguments.
- What you can do after
- Diagnose unresolved macro-related identifiers and pass external names explicitly when generated code must affect surrounding code.
Read how Write Powerful Rust Macros explains macro hygiene →
Related concepts
- declarative macroconfigured by · macro_rules! is Rust syntax for defining declarative macros by matching input token patterns and expanding matching rules into generated source code.
- identifieruses · An identifier is a name or value that denotes or distinguishes an entity or program element within a system.
- syntax-quoteaddressed by · Syntax-quote is Clojure reader syntax that quotes a form while supporting symbol qualification, generated symbols, unquoting, and unquote-splicing.
- gensymhas part · gensym is a Clojure function that generates a unique symbol, typically for avoiding name collisions in macro-generated code.
- macrocontrasts with · A macro is a named construct that expands or transforms source code, commands, or templates before or during execution.
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