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Re: gEDA-dev: some suggestions

On Fri, 15 Dec 2006, Carlos Nieves Ónega wrote:

> Hi Peter,
>
> El jue, 14-12-2006 a las 22:25 +0000, Peter TB Brett escribió:
> [snip]
>> I think that a more elegant way to do it would be for:
>>
>>   (define default-titleblock nil)
>>
>> to disable the titleblock[1], and
>>
>>   (define default-titleblock "")
>>
>> to give a warning as before.
>>
>> I'd submit a revised patch myself, but I think you'd be able to change it
>> faster than I could find the right piece of code. ;)
>>
>> Cheers,
>>
>> Peter
>>
>> [1] Am I right in thinking that 'nil' in Scheme has the same meaning as in
>> ANSI Lisp, i.e. null?
>
> I'm not sure about it. It seems that in guile, null? checks for an empty
> list, and nil is used for lisp compatibility.
>
> I wouldn't like to use null for this issue, because the component name
> is not a list.
>
> The piece of code doing that kind of work seems to be:
>  if (SCM_NFALSEP(scm_eq_p(scm_comp_name, SCM_NIL))) {
>    return SCM_BOOL_F;
>  }
> SCM_NIL doesn't exist. Anyone knows a way to do it?

I think you might want
 	if(SCM_NILP(scm_comp_name)) {



At a higher design level though, it does appear that "nil" in scheme is 
only present for compatibility with other lisps.  It definitely is not 
equal to the empty list or to #f (boolean false).

I don't know for sure what the properly schemey tradition would suggest 
using here, but (null? comp_name) to test for the empty list might be 
considered better by the purists.

In C, that's
 	if(SCM_NULLP(scm_comp_name))
(which is very different a C NULL pointer)


Steve



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