eval-when-compile

[Achim Gratz]

[I hope this is the correct list for asking this question.]

I've been trying to use eval-when-compile to switch between alternate
versions of code based on a compile-time decision.  However it seems
that either I don't understand the documentation or something doesn't
quite work.

Compiling this source file:

--8<---------------cut here---------------start------------->8---
(eval-when-compile
  (if t
      (defvar unquoted-t "true")
    (defvar unquoted-nil "false")))
(eval-when-compile
  (if nil
      '(defvar quoted-t "true")
    '(defvar quoted-nil "false")))
--8<---------------cut here---------------end--------------->8---

results in an empty (except the header of course) byte-compiled file.  I
expected the quoted version to compile

`(defvar quoted-nil "false")´

which is what that form evaluates to.  When I wrap a defmacro around it
and call that macro outside the eval-when-compile:

--8<---------------cut here---------------start------------->8---
(eval-when-compile
  (defmacro ewc-macro (&rest body)
    (if nil
        '(defvar macro-t "true")
      '(defvar macro-nil "false"))))
(ewc-macro)
--8<---------------cut here---------------end--------------->8---

then I get the expected output in the byte-compiled file, but it seems
there must be an easier way to do that.  The eval-when-compile in this
version suppresses the macro definition itself being byte-compiled of
course.


Regards,
Achim.
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