elisp: Wrong Time
13.5.1 Wrong Time
-----------------
The most common problem in writing macros is doing some of the real work
prematurely—while expanding the macro, rather than in the expansion
itself. For instance, one real package had this macro definition:
(defmacro my-set-buffer-multibyte (arg)
(if (fboundp 'set-buffer-multibyte)
(set-buffer-multibyte arg)))
With this erroneous macro definition, the program worked fine when
interpreted but failed when compiled. This macro definition called
‘set-buffer-multibyte’ during compilation, which was wrong, and then did
nothing when the compiled package was run. The definition that the
programmer really wanted was this:
(defmacro my-set-buffer-multibyte (arg)
(if (fboundp 'set-buffer-multibyte)
`(set-buffer-multibyte ,arg)))
This macro expands, if appropriate, into a call to
‘set-buffer-multibyte’ that will be executed when the compiled program
is actually run.
Info Catalog
elisp: Problems with Macros
elisp: Argument Evaluation