Canonical add-hook idiom

Canonical add-hook idiom

[Bob Nelson]

What is the preferred approach given these examples:

    1). (add-hook 'some-mode-hook (lambda () [...]
    2). (add-hook 'some-mode-hook '(lambda () [...]
    3). (add-hook 'some-mode-hook (function (lambda () [...]
    4). None of the above -- please explain.

-- 
=============================================================================
           Bob Nelson -- Dallas, Texas, USA (nelsonbe@earthlink.net)
          http://www.oldradio.com/archives/nelson/open-computing.html
Good engineering is finding the right wrench to pound in the correct screw

Re: Canonical add-hook idiom

[Oliver Scholz]

Bob Nelson <bnelson@nelsonbe.com> writes:

> What is the preferred approach given these examples:
>
>     1). (add-hook 'some-mode-hook (lambda () [...]
>     2). (add-hook 'some-mode-hook '(lambda () [...]
>     3). (add-hook 'some-mode-hook (function (lambda () [...]
>     4). None of the above -- please explain.
[...]

I definitely prefer (1).

Some would prefer #'(lambda () ...), which for the Lisp interpreter
is the same as (3).  But AFAIK this is just a Common Lisp idiom and
it makes no difference in Emacs Lisp.

    Oliver
-- 
25 Brumaire an 212 de la Révolution
Liberté, Egalité, Fraternité!

Re: Canonical add-hook idiom

[Jesper Harder]

Bob Nelson <bnelson@nelsonbe.com> writes:

> What is the preferred approach given these examples:
>
>     1). (add-hook 'some-mode-hook (lambda () [...]
>     2). (add-hook 'some-mode-hook '(lambda () [...]
>     3). (add-hook 'some-mode-hook (function (lambda () [...]
>     4). None of the above -- please explain.

1) or 4).

It's sometimes better to avoid lambda and add a function instead.
This makes it easier to remove it from the hook again:

  (add-hook 'foo-hook 'bar)
  ;; Oops, bar didn't work as expected:
  (remove-hook 'foo-hook 'bar)

Removing isn't quite as easy for lambda's.

Re: Canonical add-hook idiom

[Henrik Enberg]

Oliver Scholz <alkibiades@gmx.de> writes:

> Bob Nelson <bnelson@nelsonbe.com> writes:
>
>> What is the preferred approach given these examples:
>>
>>     1). (add-hook 'some-mode-hook (lambda () [...]
>
> I definitely prefer (1).
>
> Some would prefer #'(lambda () ...), which for the Lisp interpreter
> is the same as (3).  But AFAIK this is just a Common Lisp idiom and
> it makes no difference in Emacs Lisp.

In addition using #'(lambda () ...) or '(lambda () ...) means the lambda
form won't be compiled if the file is.

Re: Canonical add-hook idiom

[Stefan Monnier]

> What is the preferred approach given these examples:
>     1). (add-hook 'some-mode-hook (lambda () [...]
>     2). (add-hook 'some-mode-hook '(lambda () [...]
>     3). (add-hook 'some-mode-hook (function (lambda () [...]
>     4). None of the above -- please explain.

The '(lambda form is to be avoided: the ' says "what follows
is pure data" whereas what follows is actually code, so it's
confusing (I expect humans won't get confused, but byte-compilers
do get confused).

`lambda' is a macro that expands to (function (lambda so the two are
pretty much interchangeable.  As for #'(lambda, it is a shorthand
for (function (lambda.

I thus recommend (lambda since it's the shortest and ask people to stay away
from '(lambda since it poses problems to the byte-compiler (as well as to
other code-walkers such as some fancy CL macros (typically
`lexical-let')).  But if you prefer #(lambda or (function (lambda,
that's OK: you won't burn in hell for it.


        Stefan