Macros

defmacro receives forms at compile time. Quasiquote constructs code; ~ unquotes a form and ~@ splices forms. Use gensym for generated bindings. Expansion runs compiled macro code, including dependency macros: trust them as build-time programs. This macro intentionally repeats its argument, so pass a pure expression; a macro should bind effectful arguments once when single evaluation is required. See syntax §3.16.

(ns main)
(defmacro twice (x) `(+ ~x ~x))
(defun main () -> i64 (do (println (twice 21)) 0))

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