Re: [Kawa-commonlisp-dev] 'NIL != '()

[Per Bothner]

On 08/07/2012 06:18 PM, Charles Turner wrote:
> > Something like, using your repository code:
> >
> >        Object s = LispPackage.currentPackage.get().intern(symname).get(0);
> >        if (s == CommonLisp.NIL_AS_SYMBOL)
> >          s = CommonLisp.FALSE:
> >        return s;
>
> I'm wondering if there's a caveat I'm not seeing to instead just doing
> if (symname == "NIL") return CommonLisp.FALSE
> instead of interning the symbol.

You have to check that LispPackage.currentPackage.get() is the COMMON-LISP
package *or* one that inherits from it.  That seems more complicated
to get right - and most likely slower, at least in the non-NIL case.

> > where CommonLisp.NIL_AS_SYMBOL is CommonLispPackage.getSymbol("NIL").
>
> Due to the way I understand it, it's easier for me to export the
> symbol in CommonLisp, rather than assume it is already an exported
> symbol, so I changed that to:
>
> public static final Symbol NIL =
>        LispPackage.CLNamespace.primExport("NIL");

Well, NIL as a CL value is the same as CommonLis.FALSE, which
is why I used the more verbose NIL_AS_SYMBOL to emphasize this is
not the Lisp value of NIL, but the internal value as a Symbol.
--
        --Per Bothner
address@hidden   http://per.bothner.com/