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Create convenience commands to load a derivative theme ​

[ NOTE: Users of many Modus derivatives do not need to do anything of what is described herein. Just enable the modus-themes-include-derivatives-mode. ]

In the previous section, we explored the mechanics of the modus-themes-get-themes (Determine what counts as a Modus theme). Independent of that method, developers can use the macro modus-themes-define-derivative-command to define small wrappers for Modus commands that load a theme only for a specific family of Modus derivatives (Build on top of the Modus themes).

The modus-themes-define-derivative-command takes two mandatory arguments:

‘FAMILY’ ​

the family of the Modus themes derivatives, such as ef-themes.

‘SUFFIX’ ​

the suffix of the command-to-be-defined. It is one among the symbols listed in modus-themes-define-derivative-command-known-suffixes.

The suffix is appended to ‘FAMILY’ to derive the symbol of the command. For example, if ‘SUFFIX’ is ‘rotate’ and ‘FAMILY’ is ef-themes, then the symbol is ef-themes-rotate.

Here is how it actually looks in the source code of the Ef themes:

emacs-lisp
;;;###autoload (autoload 'ef-themes-rotate "ef-themes")
(modus-themes-define-derivative-command ef-themes rotate)

This is what the macroexpanded form looks like:

emacs-lisp
(defun ef-themes-rotate ()
  "Like `modus-themes-rotate' but only consider members of the `ef-themes'"
  (interactive)
  (cl-letf (((symbol-function 'modus-themes-get-themes)
             (lambda () (modus-themes-get-all-known-themes 'ef-themes))))
    (call-interactively 'modus-themes-rotate)))

Sometimes, it makes no sense to re-use an existing Modus command (e.g. because the developer wants to introduce a user option to affect what the command is doing), though this approach with the cl-letf can still prove useful.