Re: exit value

[Anthony Green <green@cygnus.com>]

>   Which one is the right value for -1?

Both! And neither!

>   guile> (system "guile -c \"(exit -1)\"")
>   65280
>
>   szi@olivia:/home/szi$ make -f make-test 
>   guile -c "(exit -1)"
>   make: *** [all] Error 255

There are a couple of problems here. Under unix at least, the argument
to exit muct be an integer value between 0 and 255. Anything else
results in undefined behaviour. You should never exit with -1.

What's happening in your second example is that the -1 (binary
11111111111111111111111111111111) is being truncated to an 8 bit
value, 11111111, or 255. This result is encoded and returned to make,
which decodes the value and presents 255.

The same thing is happening in your first example, except that guile
isn't decoding the result for you. If you were to call system() from
C, then you would use the WEXITSTATUS macro to decode the result. On
your machine, this would shift the result to the right by 8 bits.
65280 >> 8 == 255. You need to do this yourself in
Guile. Unfortunately, this isn't portable.

As long as Guile is providing 'system', it should provide some support
for extracting the results properly. Hmmm.. now that I think about it,
'system' isn't very schemey, is it? I think we should trash it in
favour of something that actually returns a decoded exit code, and
does some kind of appropriate throw otherwise.

AG

-- 
Anthony Green                                               Cygnus Solutions
                                                       Sunnyvale, California