(lispref.info)Repeated Loading

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Repeated Loading

   You may load a file more than once in an Emacs session.  For
example, after you have rewritten and reinstalled a function definition
by editing it in a buffer, you may wish to return to the original
version; you can do this by reloading the file in which it is located.

   When you load or reload files, bear in mind that the `load' and
`load-library' functions automatically load a byte-compiled file rather
than a non-compiled file of similar name.  If you rewrite a file that
you intend to save and reinstall, remember to byte-compile it if
necessary; otherwise you may find yourself inadvertently reloading the
older, byte-compiled file instead of your newer, non-compiled file!

   When writing the forms in a library, keep in mind that the library
might be loaded more than once.  For example, the choice of `defvar'
vs. `defconst' for defining a variable depends on whether it is
desirable to reinitialize the variable if the library is reloaded:
`defconst' does so, and `defvar' does not.  (Note: Defining

   The simplest way to add an element to an alist is like this:

     (setq minor-mode-alist
           (cons '(leif-mode " Leif") minor-mode-alist))

But this would add multiple elements if the library is reloaded.  To
avoid the problem, write this:

     (or (assq 'leif-mode minor-mode-alist)
         (setq minor-mode-alist
               (cons '(leif-mode " Leif") minor-mode-alist)))

   Occasionally you will want to test explicitly whether a library has
already been loaded; you can do so as follows:

     (if (not (boundp 'foo-was-loaded))
     (setq foo-was-loaded t)

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