[Ecls-list] unbound-variable handler

[Dustin Long]

That's interesting....

This works in clisp:

(handler-bind ((unbound-variable (lambda (e) (invoke-restart 'use-value 
nil)))) (format t "value is [~s]~%" x))

but not in ECL. Does anyone know if unbound-variable is supposed to 
establish the use-value restart? Or is that optional and implementation 
dependent? I can't find any information about the portability of such 
things.

Dustin

Dean O'Connor wrote:
> thanks a lot. That got me much further. This exits cleanly, but I need 
> it to continue executing the nested expressions, using value NIL for the 
> unbound variable.
>
> The aim was that if a scripts said something like:
>
>     (when VAR1
>           (print "yep"))
>
> Then if VAR1 was never bound by a SETQ or whatever, then VAR1's value 
> would simply returned as NIL (by a handler) instead of entering debug.
>
> I am trying to RTFM to see if I can sort of continue, but if anyone has 
> the answer handy, I would much appreciate it.
>
> cheers
> deano
>
>
> Pierre THIERRY wrote:
>   
>> Scribit Dean O'Connor dies 19/06/2007 hora 03:03:
>>   
>>     
>>> I am trying to setup a handler to catch "unbound-variable".
>>>     
>>>       
>> The thing is, if I understand the condition system correctly, you need
>> to setup a restart around the expression that might be unbound:
>>
>> (handler-bind
>>     ((unbound-variable (lambda (c)
>> 			 (declare (ignore c))
>> 			 (invoke-restart 'use-nil))))
>>   (not (restart-case
>> 	   not-yet-bound-variable
>> 	 (use-nil () nil))))
>>
>> Works in SBCL and ECL (yields t).
>>
>> Quickly,
>> Pierre
>>   
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