Assign a function to a variable, and invoke it

Assign a function to a variable, and invoke it

[troelskn]

I'm trying to assign an existing function to a variable, so I can call
that variable, rather than the actual function directly. The aim is to
have a single point, where I can change behaviour for my module. The
code I have so far is:

(defvar my-browse-url 'browse-url)
...
(my-browse-url "http://example.com")

I suppose that functions and variables have different namespaces in
elisp? How do I invoke the function, which my-browse-url points to?

Re: Assign a function to a variable, and invoke it

[troelskn]

On Jul 31, 12:22 am, troelskn <troel...@gmail.com> wrote:
> I'm trying to assign an existing function to a variable, so I can call
> that variable, rather than the actual function directly. The aim is to
> have a single point, where I can change behaviour for my module. The
> code I have so far is:
>
> (defvar my-browse-url 'browse-url)
> ...
> (my-browse-url "http://example.com")
>
> I suppose that functions and variables have different namespaces in
> elisp? How do I invoke the function, which my-browse-url points to?

I figured it out. I need to use funcall

http://www.delorie.com/gnu/docs/elisp-manual-21/elisp_168.html

RE: Assign a function to a variable, and invoke it

[Drew Adams]

> (defvar my-browse-url 'browse-url)
> ...
> (my-browse-url "http://example.com")
>
> I suppose that functions and variables have different namespaces in
> elisp? How do I invoke the function, which my-browse-url points to?

Invoke the function using `funcall' or `apply': (funcall my-browse-url).

A symbol, such as `my-browse-url' or `browse-url', has a value cell and a
function cell, so the same symbol can act as a function (via its function
cell) and as a variable (via its value cell).

When evaluated, the symbol's value is returned (from its value cell). In a
function call, as in (browse-url), its function cell is used. When you do
(funcall my-browse-url), the symbol `my-browse-url' is evaluated (value
cell) to the symbol `browse-url', and then the function in the function cell
of that symbol, `browse-url', is called (by `funcall').

See the Elisp manual in Emacs (C-h i) for a better and more complete
explanation of all of this - it is your friend.

Re: Assign a function to a variable, and invoke it

[Joost Kremers]

troelskn wrote:
> On Jul 31, 12:22 am, troelskn <troel...@gmail.com> wrote:
>> I'm trying to assign an existing function to a variable, so I can call
>> that variable, rather than the actual function directly. The aim is to
>> have a single point, where I can change behaviour for my module. The
>> code I have so far is:
>>
>> (defvar my-browse-url 'browse-url)
>> ...
>> (my-browse-url "http://example.com")
>>
>> I suppose that functions and variables have different namespaces in
>> elisp?

yup.

> How do I invoke the function, which my-browse-url points to?
>
> I figured it out. I need to use funcall

or perhaps use fset or defalias?


-- 
Joost Kremers                                      joostkremers@yahoo.com
Selbst in die Unterwelt dringt durch Spalten Licht
EN:SiS(9)