More Macros and DSLs

Keywords

ver. 1.0.0

Advanced macro techniques: anaphora, compile-time work, macro-generating macros, and building DSLs to raise abstraction and move computation earlier

This unit advances macro programming from adding isolated constructs to designing languages. You revisit macroexpansion basics and then learn to write macros that intentionally introduce bindings (anaphoric macros), create threading-style bindings for intermediate results, move repeated or constant work from runtime to compile time, and even generate new macros. Finally you apply these techniques to design and implement a small domain-specific language (user classification), and learn how to judge when building a DSL is worthwhile.

Full summary

The unit trains you to use macros as tools for raising abstraction and shifting work earlier in the development pipeline. You begin with a compact refresher of macro mechanics (macroexpansion time, unevaluated forms, quoting/unquoting, and macroexpand) so you can proceed without re-deriving basics.

You then learn several concrete, practical macro patterns: - Anaphoric macros that deliberately introduce a binding the caller can use (for example binding the tested value to it), turning what is normally a capture bug into a useful feature. - Threading-style macros that bind each intermediate result so subsequent expressions can refer to those values directly. - Compile-time computation: using macros to perform work once at expansion time (e.g., building lookup tables) so runtime calls avoid repeated setup. - Macro-generating macros: writing a macro whose expansion is itself a defmacro, so macros can produce other macros; this emphasizes careful handling of nested quoting.

These techniques are tied together by a hands-on DSL design exercise. You practice bottom-up decomposition: start from a direct implementation, identify recurring patterns and abstractions, and incrementally build a small declarative language that expresses the problem domain more clearly (the user-classification example). Through this process you learn the design method for domain-specific languages and how metalinguistic abstraction works in practice.

The unit concludes by putting benefits and costs in perspective: language-building can simplify programs and automate repetitive structure, but it also imposes cognitive and maintenance costs on readers who must learn the new language. By the end you’ll be able to recall the macro machinery, write anaphoric and threading macros, perform compile-time computation with macros, generate macros from macros, design and implement a small DSL, and evaluate when creating a DSL is justified.

Materials

Lecture notesThe unit written out, to read at your own paceOpen → SlidesThe deck to present fromOpen →

Source document

Clojure in Action (2nd Edition), A. Rathore and F. Avila, Manning, Dec. 2015 — Link — Page 291-323

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--- title: "More Macros and DSLs" keywords: - ver. 1.0.0 format: html: toc: false --- **Advanced macro techniques: anaphora, compile-time work, macro-generating macros, and building DSLs to raise abstraction and move computation earlier** > This unit advances macro programming from adding isolated constructs to designing languages. You revisit macroexpansion basics and then learn to write macros that intentionally introduce bindings (anaphoric macros), create threading-style bindings for intermediate results, move repeated or constant work from runtime to compile time, and even generate new macros. Finally you apply these techniques to design and implement a small domain-specific language (user classification), and learn how to judge when building a DSL is worthwhile. ::: {.callout-note collapse="true" title="Full summary"} The unit trains you to use macros as tools for raising abstraction and shifting work earlier in the development pipeline. You begin with a compact refresher of macro mechanics (macroexpansion time, unevaluated forms, quoting/unquoting, and macroexpand) so you can proceed without re-deriving basics. You then learn several concrete, practical macro patterns: - Anaphoric macros that deliberately introduce a binding the caller can use (for example binding the tested value to `it`), turning what is normally a capture bug into a useful feature. - Threading-style macros that bind each intermediate result so subsequent expressions can refer to those values directly. - Compile-time computation: using macros to perform work once at expansion time (e.g., building lookup tables) so runtime calls avoid repeated setup. - Macro-generating macros: writing a macro whose expansion is itself a `defmacro`, so macros can produce other macros; this emphasizes careful handling of nested quoting. These techniques are tied together by a hands-on DSL design exercise. You practice bottom-up decomposition: start from a direct implementation, identify recurring patterns and abstractions, and incrementally build a small declarative language that expresses the problem domain more clearly (the user-classification example). Through this process you learn the design method for domain-specific languages and how metalinguistic abstraction works in practice. The unit concludes by putting benefits and costs in perspective: language-building can simplify programs and automate repetitive structure, but it also imposes cognitive and maintenance costs on readers who must learn the new language. By the end you'll be able to recall the macro machinery, write anaphoric and threading macros, perform compile-time computation with macros, generate macros from macros, design and implement a small DSL, and evaluate when creating a DSL is justified. ::: ## Materials ::: {.hg-deck} <a class="hg-card" href="notes.qmd">Lecture notesThe unit written out, to read at your own paceOpen →</a> <a class="hg-card" href="slides.qmd">SlidesThe deck to present fromOpen →</a> ::: ## Source document - Clojure in Action (2nd Edition), _A. Rathore and F. Avila_, Manning, Dec. 2015 — [Link](https://www.manning.com/books/clojure-in-action-second-edition) — Page 291-323 ::: {.hg-nav} [← More on Functional Programming](../8_more_on_functional_programming/index.qmd){.hg-prev} :::