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RE: doc on define-minor-mode hook variable(s)

From: Drew Adams
Subject: RE: doc on define-minor-mode hook variable(s)
Date: Mon, 6 Mar 2006 11:10:47 -0800

        > In the past, hook variables were used, and the new notion
        > that a hook need not be associated with a variable should
        > be explained in the doc.

    A hook IS a variable--that is to say, a symbol whose value is used.
    It is a mistake to think that a hook is not a variable.

You quoted me, but I got the idea from Stefan - possibly I misunderstood

IIUC, what Stefan meant was this (he will correct me):

 - What makes a hook a hook is its use: if `run-hooks' uses it, then it's a

 - A symbol used as a hook need not necessarily be bound before it is run.
That is, you can call `run-hooks' on a symbol that has never been bound -
nothing happens.

 - Such an unbound symbol is not a variable. Of course, to do anything
useful as a hook, it must be bound.

 - The way to set up a symbol to serve as a useful hook is to use
`add-hook'. Binding the symbol is not the way to go.

 - For these reasons (I think), Stefan doesn't like to refer to "variable"
in this context: 1) The symbol can be run as an (inert) hook without being
bound. 2) Simply binding a symbol is not the way to make it useful as a

I don't know or care what terminology is used to describe the behavior of
hooks - I'm just learning.

To me, reading the `define-minor-mode' doc about `MODE-hook', I expected to
find existing (bound) variables named `MODE-hook' after calling
`define-minor-mode'. When I searched for them, I found none and I wondered
what the doc really meant.

It turns out (IIUC) that the doc simply meant that the created minor mode
command does (run-hooks 'MODE-hook). And, given an understanding of hooks
(which, in my case was incomplete), this means:

1. IF someone does (add-hook `MODE-hook' <something>) THEN <something> will
be run when the mode is entered and exited.

2. OTHERWISE, nothing will happen, because (run-hooks 'MODE-hook) does
nothing if `MODE-hook' is not bound or is bound to nil. I should say,
instead of speaking of binding, "if either `add-hook' was never called on it
or `remove-hook' was called to remove everything that `add-hook' had added".
I called this an "empty" hook, but Stefan didn't like that term.

IOW, in Stefan's terminology (IIUC): because `run-hooks' runs it, the hook
exists, even though the hook symbol might not be bound (so, no variable).

All this was not clear to me when I read the `define-minor-mode' doc. I
think it would be good if it were explained (using whatever terminology you
like) in the Hooks nodes of the manuals.

Again, I don't claim that my understanding is correct on this. My message
really is that I was confused by the current doc. Do with that feedback what
you will.

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