5 ms·

> macros statically evaluate their inputs ie. at compile-time Unless one uses an interpreter. CL-USER 1 > (defmacro my-if (test a b) (print

by lispm 4y ago

> macros statically evaluate their inputs ie. at compile-time Unless one uses an interpreter. CL-USER 1 > (defmacro my-if (test a b) (print "Hi, I'm the executing MY-IF macro") `(if ,test ,a , b)) MY-IF CL-USER 2 > (defun foo (a) (my-if (> a 10) 'big 'small)) FOO CL-USER 3 > (foo 11) "Hi, I'm the executing MY-IF macro" "Hi, I'm the executing MY-IF macro" BIG CL-USER 4 > (foo 2) "Hi, I'm the executing MY-IF macro" "Hi, I'm the executing MY-IF macro" SMALL In this Lisp implementation, the macro even runs twice on each runtime invocations.

tempodox 4y ago
SBCL to the rescue. It compiles everything you enter in the REPL.
- lispm 4y ago
  Unless one uses an interpreter: $ /usr/local/bin/sbcl This is SBCL 2.2.1, an implementation of ANSI Common Lisp. More information about SBCL is available at <http://www.sbcl.org/>. SBCL is free software, provided as is, with absolutely no warranty. It is mostly in the public domain; some portions are provided under BSD-style licenses. See the CREDITS and COPYING files in the distribution for more information. * *evaluator-mode* :COMPILE * (setf *evaluator-mode* :interpret) :INTERPRET * (defmacro my-if (test a b) (print "Hi, I'm the executing MY-IF macro") `(if ,test ,a , b)) MY-IF * (defun foo (a) (my-if (> a 10) 'big 'small)) FOO * (foo 11) (foo 11) "Hi, I'm the executing MY-IF macro" BIG
  - tempodox 4y ago
    Fair enough :) At least the macro is only evaluated once, not twice.
    - lispm 4y ago
      Note that not the generated code ran twice (in LispWorks twice, in the specific SBCL interpreter once), just the code generation. In Common Lisp it's unspecified how often the code generation runs.