require a package only if present

require a package only if present

[Andrei Alexandrescu]

I am trying to use the same copy of .emacs across various machines. 
Some, however, don't have certain packages. So I need to replace lines like:

(require 'tex-site)

with code that checks whether tex-site is present and only loads it if 
there. How can I do that? Any pointers welcome.


Thanks,

Andrei

Re: require a package only if present

[Edward O'Connor]

> I am trying to use the same copy of .emacs across various machines.  
> Some, however, don't have certain packages. So I need to replace  
> lines like:
>
> (require 'tex-site)
>
> with code that checks whether tex-site is present and only loads it  
> if there. How can I do that? Any pointers welcome.

(require 'tex-site nil t)

Re: require a package only if present

[Andrei Alexandrescu]

Edward O'Connor wrote:
> 
>> I am trying to use the same copy of .emacs across various machines. 
>> Some, however, don't have certain packages. So I need to replace lines 
>> like:
>>
>> (require 'tex-site)
>>
>> with code that checks whether tex-site is present and only loads it if 
>> there. How can I do that? Any pointers welcome.
> 
> (require 'tex-site nil t)

Many thanks!

Andrei

Re: require a package only if present

[Will Parsons]

Edward O'Connor wrote:
>
>> I am trying to use the same copy of .emacs across various machines.  
>> Some, however, don't have certain packages. So I need to replace  
>> lines like:
>>
>> (require 'tex-site)
>>
>> with code that checks whether tex-site is present and only loads it  
>> if there. How can I do that? Any pointers welcome.
>
> (require 'tex-site nil t)

I don't believe that works for XEmacs (which may be irrelevant for the OP),
so I use instead:

(when (locate-library "lib-name")
  (require 'lib-name))

-- 
Will

Re: require a package only if present

[Fabrice Niessen]

Hello,

Will Parsons wrote:
> Edward O'Connor wrote:
>>> I am trying to use the same copy of .emacs across various machines. Some,
>>> however, don't have certain packages. So I need to replace lines like:
>>>
>>> (require 'tex-site)
>>>
>>> with code that checks whether tex-site is present and only loads it if
>>> there. How can I do that? Any pointers welcome.
>>
>> (require 'tex-site nil t)
>
> I don't believe that works for XEmacs (which may be irrelevant for the OP),
> so I use instead:
>
> (when (locate-library "lib-name")
>   (require 'lib-name))

I'm using the following code, both compatible with GNU Emacs and XEmacs:

--8<---------------cut here---------------start------------->8---
(defvar missing-packages-list nil
  "List of packages that `try-require' can't find.")

;; attempt to load a feature/library, failing silently
(defun try-require (feature)
  "Attempt to load a library or module. Return true if the
library given as argument is successfully loaded. If not, instead
of an error, just add the package to a list of missing packages."
  (condition-case err
      ;; protected form
      (progn
        (message "Checking for library `%s'..." feature)
        (if (stringp feature)
            (load-library feature)
          (require feature))
        (message "Checking for library `%s'... Found" feature))
    ;; error handler
    (file-error  ; condition
     (progn
       (message "Checking for library `%s'... Missing" feature)
       (add-to-list 'missing-packages-list feature))
     nil)))
--8<---------------cut here---------------end--------------->8---

and, for every package I wanna load if present:

--8<---------------cut here---------------start------------->8---
(try-require 'tex-site)
--8<---------------cut here---------------end--------------->8---

(for example).

See http://www.mygooglest.com/fni/dot-emacs.html for more examples.

Fabrice

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Fabrice Niessen
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