Re: test for presence of library

[Harry Putnam]

pjb@informatimago.com (Pascal J. Bourguignon) writes:

[...]

 Harry wrote:
>> The lisp equivalent of:
>>
>>  if some-lib 
>>  then
>>     (require some-lib)
>>  fi
>
>
> require does the test itself!
>
> C-h f require RET
>
>
> Now, assume that we wrote:
>
> (when (library-exists-p 'some-lib)
>    (require 'some-lib))
>
> and that just after your emacs executed (library-exists-p 'some-lib)
> and returned true, some other process would delete that some-lib.el
> file.  What would happen to your (require 'some-lib)?
>
>
> That is, basically, your above shell script with if [ -f /my/file ] is
> just WRONG!  If you see such tests in scripts, you are allowed to think
> poorly of their authors.

Don't hold back, in this case you are allowed and really forced to
think poorly of the author who admits to having literally hundreds of
such tests scattered thru a 10yr accumulation of various scripts in
various scripting languages. 

I'm a known dimwit... its even ok to use the `R' word... I doubt (Sarah
Palin reads this group)

It's ok, I've learned to live with it.

Now lets assume further that we instead say simply:

   (require 'some-lib)

After patting myself on the back for such a wise solution to getting a
needed library loaded, I move to a different and new machine where I've
carted my every ready .emacs file with me.

I start emacs with `emacs /some/path/file'.... but whoops, since
`some-lib' is not in the path in this environment... my emacs blows up
a bit.  It throws up a confusing buffer full of various leads to
information, but none of it appears to bear directly on the job at
hand. .. Not even any indication of what the problem is.

I finally noticed at the bottom, a place to dismiss this interruption
and get back to work.

I'd like to avoid that even though its not really an earth shaking
problem.

My first thought, being a dunce and all, was to test for the presence
of the library before requiring it, thereby smoothing out the work
flow and interruptions. I wasn't sure how that would be done, hence
the question here.

But looking at the suggested documentation I'm left non the wiser:

 (require FEATURE &optional FILENAME NOERROR)

That isn't going to get it for me.. I've tried a few arrangements but
being an idiot and all, I have no idea how something optional is
introduced into the require.

What do you recommend to a simpleton regarding how to avoid the
interruption?  Just make sure all is perfect before starting emacs?

Or maybe spend a day or two figuring out how to apply the codified
documentation.... again... thats' a hard pull for the intellectually
crippled.