Munich Clojure Workshop - 09 - Macros

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Transcript

1. Macros Friday, October 11, 13
2. In almost any language worth using, large portions of the language’s functionality is implemented with the language itself. Friday, October 11, 13
3. Macros change the syntax of lisp code Friday, October 11, 13
4. Macros work on parse tree of your program Friday, October 11, 13
5. Only use macros when a function won’t do Friday, October 11, 13
6. Macros are evaluated during compile time Friday, October 11, 13
7. Macros modify / generate Clojure code by means of Clojure code Friday, October 11, 13
8. Clojure code is bootstrapped by several forms such as fn*, if, let*, new, dot and so on... Friday, October 11, 13
9. Simplest macro ever Friday, October 11, 13
10. (defmacro call [sym & params] (cons sym params)) Friday, October 11, 13
11. (call inc 1) '(inc 1) (call + 1 2 3) '(+ 1 2 3) Friday, October 11, 13
12. Macro yields a list of symbols, which are later evaluated Friday, October 11, 13
13. Unquote Friday, October 11, 13
14. (defmacro thrice [form] `(do ~form ~form ~form)) Friday, October 11, 13
15. (thrice (println 'one)) (do (println 'one) (println 'one) (println 'one)) ~form ~form ~form Friday, October 11, 13
16. Forces evaluation Places form one-to-one (for the list of (println 'one) places both elements in as a list) Friday, October 11, 13
17. Splice-unquote Friday, October 11, 13
18. (defmacro my-apply [sym forms] `(~sym ~@forms)) Friday, October 11, 13
19. (my-apply + [1 2 3]) (+ 1 2 3) ~@forms Friday, October 11, 13
20. Forces evaluation Places given collection, removing outer brackets Friday, October 11, 13
21. Gensym Friday, October 11, 13
22. my-sym# G_123143 Friday, October 11, 13
23. Avoid shadowing Auto-generate (unique) symbols on the fly Reuse the name without setting your hair on fire Friday, October 11, 13
24. Quoting Friday, October 11, 13
25. (defmacro a-is-two [& body] `(let [~'a 2] ~@body)) Friday, October 11, 13
26. (a-is-two (println a)) (let [a 2] (println a)) Friday, October 11, 13
27. Useful for generating your own symbols Creating DSLs Chaining/scoping/shadowing Friday, October 11, 13
28. Quote vs Syntax Quote Friday, October 11, 13
29. 'println println `println clojure.core/println Friday, October 11, 13
30. Macroexpansion Friday, October 11, 13
31. macroexpand-1 macroexpand macroexpand-all Friday, October 11, 13