Re: GSOC | Extending Common Lisp support

[Jamison Hope <jrh at theptrgroup dot com>]

On Apr 25, 2012, at 6:42 PM, Charles Turner wrote:

> Sidenote: I'm having trouble logging into Savannah, but I noticed this
> buglet today:
>
> #|kawa:1|# (zero? (define-simple-class))
> java.lang.NullPointerException
> 	at kawa.standard.define_class.rewriteForm(define_class.java:122)
> ...
>
> I've made a note to look into it at some point in the future, but
> NullPointerExceptions aren't good, so maybe if anyone else has time,
> they could look at why that's happening.


(define-simple-class) is a syntax error, of course, but yeah a NPE isn't
very helpful. The cause is that define_class#rewriteForm() does this:

    Declaration decl = null;
    Object form_cdr = form.getCdr(); // form is the list (define- 
simple-class), so form_cdr is ()
    if (form_cdr instanceof Pair)    // and () is not a pair, so we  
skip directly to line 122
      {
        ...
      }
    ClassExp oexp = (ClassExp) decl.getValue(); // here, where decl  
is still null, triggering the NPE


So that if statement should probably have an else clause, something like

    else
    {
      return tr.syntaxError(this.getName() + ": missing class name");
    }

or maybe "else if (form_cdr == EmptyList.emptyList) { ... } else {...}"
so other bad syntax like "(define-simple-class . 42)" can have a  
different
error message.

-J

--
Jamison Hope
The PTR Group
www.theptrgroup.com