What is "with-eval-after-load" in Emacs Lisp

elisp, emacs, macros

Solution

From `etc/NEWS`:

* Lisp Changes in Emacs 24.4
...
** New macro `with-eval-after-load'.
This is like the old `eval-after-load', but better behaved.

Emacs 24.4 was released on 20th October 2014.

`eval-after-load` is considered ill-behaved because it is a function, not a macro, and thus requires the code inside it to be quoted, which means that it cannot be byte-compiled. It also accepts only one form, so if you have more than one, you need to use `progn`. For example:

(eval-after-load "foo"
  '(progn
     (setq foo 42)
     (setq bar 17)))

The equivalent version with `with-eval-after-load` would be:

(with-eval-after-load "foo"
  (setq foo 42)
  (setq bar 17))

As noted by Clément in a comment, one disadvantage of `with-eval-after-load` is that you cannot rely on macros defined in the module in question, while with `eval-after-load` you can be sure that such macros are defined and available to use. This was discussed on emacs-devel.

Problem

I came across the macro `with-eval-after-load` when trying to install `persp-mode` from here. But I am unable to find the macro inside Emacs and/or on Google. Where is it defined? Is it part of standard Emacs Lisp?

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