Re: How to define a (derived) minor mode inaccessible to the user

[Stefan Monnier <monnier@iro.umontreal.ca>]

> I'd like to define a special-purpose major mode, derived from
> `special-mode', in such a way that the user cannot set it using M-x.

Can you explain why?

> (It is to be called via another command.)

That doesn't explain why it would be harmful to also expose the actual
major mode command.

E.g. You can do `M-x comint-mode` even though it likely won't do you
much good since `comint-mode` needs to be used together with a process
and is hence normally enabled by the command that launches the process.

> It seems that `define-derived-mode' always sets the mode as
> `interactive'.

Indeed.

> M-: (symbol-plist 'my--mode)
> expecting an `interactive-form' entry on the plist

The `interactive-form` property is virtually never used.  Instead, the
interactive form is traditionally stored within the function.

If you *really* care about hiding the major mode from the user
I suggest you use an "obscure" or "scary" name.

> What's going on?  Is it possible to define a (derived) major mode so
> that it can't be called interactively?

Of course it is:

    (define-derived-mode my-mode "My" "My doc.")
    (defconst my-mode (symbol-function 'my-mode))
    (fmakunbound 'my-mode)

and then you can enable the mode with `(funcall my-mode)`.


        Stefan