Re: [Chicken-users] Return value of `system'

[Kon Lovett]

On Mar 14, 2007, at 6:33 PM, Zbigniew wrote:

> On 3/14/07, Kon Lovett <address@hidden> wrote:
> > Zbigniew wrote:
> > > Exit values should be distinguishable from signals (and even from
> > > signals+core dumps).
>
> >    return C_fix(WIFEXITED(n) ? WEXITSTATUS(n) : (WIFSIGNALED(n) ?
> > WTERMSIG(n) : WSTOPSIG(n)));
>
> > I don't always talk thru my hat ;-)
>
> Don't worry, I would expect nothing less from you.  I figured you had
> already checked the code and the return value might be munged.

Please, expect less. That way I can surprise. :-)

> In my experience, on a UNIX box it is imperative that you get the full
> range of information provided by system(), especially since Chicken's
> intent is to be as practical as possible.  My opinion is that (system)
> should return system()'s raw return value-- i.e. C_fix(n) --and that
> accessor functions be provided to tease that information apart, along
> the lines of the C macros.  Since (system) is in unit library and much
> is deliberately left to the vagaries of the system, it may be more
> acceptable to create a new function and accessors in Unit posix. (Or
> in a separate egg so people don't need cutting-edge Chicken?)

Agreed, a better return value is needed.

(I could add a plain substitute for 'system' to the osprocess egg. A  
call that doesn't have the complexity of the current interface.)

What others do:

Chez Scheme 7 'system' returns "unspecified" - one way to get around  
the issue.
MzScheme 'system' returns a boolean.
Gambit-C 'shell-command' returns the C 'system' call return value.

For the library unit 'system' return value:

1) Store the return & exit status for the last call & provide  
accessors, as you suggested. Return the C 'system' call return value.

2) Multi-valued result, a'la 'process-wait'.

3) Return boolean value.

I kinda prefer #3. If the user needs more, use a more complicated  
interface. The posix unit 'process' & 'process*' already have a shell- 
command mode.

Best Wishes,
Kon