Re: [Sbcl-help] useful code snippet

[Russell M. <rus...@ya...>]

Christophe Rhodes <cs...@ca...> writes:

> Russell McManus <rus...@ya...> writes:
>
>> While writing some code using run-program, I came upon the need for
>> the following:
>>
>> (defmacro with-current-directory ((new-dir) &body body)
>>   (let ((start (gensym)))
>>     `(let ((,start (sb-unix:posix-getcwd)))
>>       (unless (char= #\\ (aref ,start (1- (length ,start))))
>> 	(setf ,start (concatenate 'string ,start "/")))
>>       (setf ,start (parse-namestring ,start))
>>       (unwind-protect
>> 	   (progn
>> 	     (sb-posix:chdir ,new-dir)
>> 	     ,@body)
>> 	(sb-posix:chdir ,start)))))
>>
>> Is there an already existing way to do this sort of thing?
>
> No.  There is at least a plausible argument that RUN-PROGRAM should
> respect *DEFAULT-PATHNAME-DEFAULTS* by chdir()ing to the directory
> component, which would allow the user to request a different directory
> for run-program simply by binding it.  On the other hand, RUN-PROGRAM
> is already a deeply scary mess of options, and adding another doesn't
> really appeal...

I agree about *DEFAULT-PATHNAME-DEFAULTS*, and indeed I tried this
first, hoping that it would "just work".  I would be willing the
change run-program to work in this way: is this of interest?  The
reason I didn't do this first is because I wasn't sure whether there
was an existing way to achieve what I wanted.

I agree that this probably should not be an additional keyword option
to RUN-PROGRAM.

If a patch to RUN-PROGRAM is not desired, then I put the above code in
the public domain, hopefully to be included with sbcl.

-russ