Editing Macro (computer science) (section)

=== Hygienic macros ===
{{Main article|Hygienic macro}}

In the mid-eighties, a number of papers<ref>{{cite conference |last1=Kohlbecker |first1=Eugene |last2=Friedman |first2=Daniel |last3=Felleisen |first3=Matthias |last4=Duba |first4=Bruce |book-title=LFP '86: Proceedings of the 1986 ACM conference on LISP and functional programming |title=Hygienic Macro Expansion |year=1986 |pages=151–161 |doi=10.1145/319838.319859 |isbn=0897912004}}</ref><ref>[http://portal.acm.org/citation.cfm?id=99583.99607] Clinger, Rees. "Macros that Work"</ref> introduced the notion of [[hygienic macro]] expansion (<CODE>syntax-rules</CODE>), a pattern-based system where the syntactic environments of the macro definition and the macro use are distinct, allowing macro definers and users not to worry about inadvertent variable capture (cf. [[referential transparency]]). Hygienic macros have been standardized for Scheme in the [[R5RS]], [[R6RS]], and [[R7RS]] standards. A number of competing implementations of hygienic macros exist such as <code>syntax-rules</code>, <code>syntax-case</code>, explicit renaming, and syntactic closures. Both <code>syntax-rules</code> and <code>syntax-case</code> have been standardized in the Scheme standards.

Recently, [[Racket (programming language)|Racket]] has combined the notions of hygienic macros with a "[[tower of evaluators]]", so that the syntactic expansion time of one macro system is the ordinary runtime of another block of code,<ref>{{cite news | last1 = Flatt | first1 = Matthew | title = Composable and compilable macros: you want it when? |url=http://www.cs.utah.edu/plt/publications/macromod.pdf}}</ref> and showed how to apply interleaved expansion and parsing in a non-parenthesized language.<ref>{{cite news | last1 = Rafkind | first1 = Jon | last2 = Flatt | first2 = Matthew | title = Honu: Syntactic Extension for Algebraic Notation through Enforestation |url=http://www.cs.utah.edu/plt/publications/gpce12-rf.pdf}}</ref>

A number of languages other than Scheme either implement hygienic macros or implement partially hygienic systems. Examples include [[Scala (programming language)|Scala]], [[Rust (programming language)|Rust]], [[Elixir (programming language)|Elixir]], [[Julia (programming language)|Julia]], [[Dylan (programming language)|Dylan]], [[Nim (programming language)|Nim]], and [[Nemerle]].