[cl-unification-devel] a simpler example

[Marco Antoniotti]

Thanks Russell,

I think I know where the problem is and I think that, while the  
example works on LW and other Lisps, the problem signaled by SBCL  
should be solved.  I'll definitively look into it.

Cheers

Marco








On Jun 11, 2008, at 21:10 , Russell McManus wrote:

> I tried the attached version, and the problem persists.
>
> Thanks for looking into it,
> -russ
>
> ----- Original Message ----
>> From: Marco Antoniotti <marcoxa at cs.nyu.edu>
>> To: cl-unification-devel at common-lisp.net
>> Cc: Russell McManus <russell_mcmanus at yahoo.com>
>> Sent: Wednesday, June 11, 2008 11:02:56 AM
>> Subject: Re: [cl-unification-devel] a simpler example
>>
>> There may be a misalignment with my version (which works on LW) and
>> the CVS version,  or it may be a problem which SBCL raises due to its
>> version (more strict) of MAKE-LOAD-FORM.
>>
>> I'll look into it.
>>
>> Thanks for raising the issue.
>>
>> Meanwhile try the version attached on SBCL.
>>
>> Cheers
>> --
>> Marco
>>
>>
>>
>>
>>
>>
>> On Jun 11, 2008, at 16:04 , Russell McManus wrote:
>>
>>> I'm pretty sure that I tried repeating the #T before sending my
>>> first email, but it failed with an error.
>>>
>>> I just tried again on sbcl 1.0.10.16 and got the following:
>>>
>>> (unify #T(list ?f #T(list ?s1 ?s2)) '(a (b c)))
>>>
>>>
>>> Cannot unify two different symbols: B MAKE-TEMPLATE.
>>>    [Condition of type CL.EXT.DACF.UNIFICATION::UNIFICATION-FAILURE]
>>>
>>> Restarts:
>>>  0: [ABORT] Return to SLIME's top level.
>>>  1: [TERMINATE-THREAD] Terminate this thread (#
>>> "worker" {1008AB0C91}>)
>>>
>>> Any ideas what I should try next?
>>>
>>> -russ
>>>
>>>
>>>
>>> ----- Original Message ----
>>>> From: Marco Antoniotti
>>>> To: cl-unification-devel at common-lisp.net
>>>> Sent: Tuesday, June 10, 2008 3:51:44 AM
>>>> Subject: Re: [cl-unification-devel] a simpler example
>>>>
>>>>
>>>> On Jun 6, 2008, at 24:38 , Russell McManus wrote:
>>>>
>>>>>
>>>>> Here are some examples:
>>>>>
>>>>> ;; this works
>>>>> (find-variable-value
>>>>>  '?s
>>>>>  (unify #T(list ?f ?s) '(a (b c))))
>>>>
>>>> Yes.
>>>>
>>>>>
>>>>> ;; this works
>>>>> (find-variable-value
>>>>>  '?s1
>>>>>  (unify #T(list ?f (?s1 ?s2)) '(a (b c))))
>>>>
>>>> Yes.
>>>>
>>>>
>>>>>
>>>>> ;; this fails
>>>>> (find-variable-value
>>>>>  '?s1
>>>>>  (unify #T(list ?f (list ?s1 ?s2)) '(a (b c))))
>>>>
>>>> As it should.  What you want is
>>>>
>>>> (unify #T(list ?f #T(list ?s1 ?s2)) '(a (b c)))
>>>>
>>>> In your case you are trying to unify a template of type LIST with a
>>>> variable in FIRST and a list (LIST ?s1 ?s2) in SECOND.  The second
>>>> element cannot unify with (B C), hence the failure.
>>>>
>>>>>
>>>>> I was expecting the meaning of LIST to be the same whether
>>>>> it is encountered at top level in a template, or at a nested  
>>>>> level.
>>>>>
>>>>> Is this a bug, or are my expectations wrong?
>>>>
>>>> Sorry.  It is your expectations.  If you look at the most general
>>>> syntax for templates, you will see that it is #T(.
>>>> ).  This is because it would be a nightmare to do otherwise.
>>>>
>>>>
>>>> Suppose you have a
>>>>
>>>> (unify #T(list 42 (foo)) (list 42 (list 'foo)))
>>>>
>>>> should unify.  But is next you do
>>>>
>>>> (defstruct foo a s d)
>>>>
>>>> then
>>>>
>>>> (unify #T(list 42 (foo)) (list 42 (list 'foo)))
>>>>
>>>> may or may not unify pending interpretation.
>>>>
>>>> Hope this clarifies things.  Let me know if there are other  
>>>> pitfalls
>>>> or bugs in the code.
>>>>
>>>> Cheers
>>>>
>>>> Marco
>>>>
>>>>
>>>>>
>>>>
>>>> --
>>>> Marco Antoniotti
>>>>
>>>>
>>>> _______________________________________________
>>>> cl-unification-devel site list
>>>> cl-unification-devel at common-lisp.net
>>>> http://common-lisp.net/mailman/listinfo/cl-unification-devel
>>>
>>
>> --
>> Marco Antoniotti
>
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--
Marco Antoniotti