[cl-unification-devel] copy-env

[Marco Antoniotti]

On Dec 4, 2005, at 6:25 AM, Gavin Mendel-Gleason wrote:

> Hello,
>
> I had the same problem and I don't think it was intentional.   I think
> it is because it is mostly used for deterministic code.

I had not given too much thought indeed to non-determinism.  As per the 
actual copy operations, if people are  interested in deep copy 
operations then they can be added, but I would keep them alongside the 
shallow copy operations.


>
> You don't really need to copy everything anyhow if you are using a
> standard unification algorithm since changes should be monotonic.  You
> just need to branch.  You can effect this with the following change:
>
> (defun make-shared-environment (env)
>   (make-environment :frames (environment-frames env)))
>
> =>
>
> (defun make-shared-environment (env)
>   (make-environment :frames (cons
>                              (make-frame)
>                              (environment-frames env))))
>
> Or some alteration that is similar that branches the environments at
> choice points.


MAKE-SHARED-ENVIRONMENT was provided as is because the augmentation of 
the environment (branches) was supposed to be done by other functions.  
But maybe ensuring that the extra frame is there is a good idea.

Cheers
--
Marco







>

> On 12/4/05, norman werner <norman.werner at web.de> wrote:
>> Hello
>>
>> While writing  a library with prolog like capabilities on top of 
>> cl-unification and a home brewn nondeterministic library
>> I need a way to copy environments.
>>
>> There is a (internal) function copy-env in cl-unification. So I 
>> exported it.
>> The problem is that this function returns a new environment which 
>> actually still shares
>> objects with its original argument.
>>
>> Is this intentional?
>> If not I propose the following (code will certainly contain bug, 
>> because i write it from memory only)
>>
>> (defun copy-env (e)
>>   (make-environment :frames (mapcar #'copy-frame (frames e))))
>>
>> (defun copy-frame (f)
>>   (make-frame :bindings (mapcar #'copy-binding (binding f))))
>>
>> (defun copy-binding (b)
>>    (mapcar #'(lambda (cell) (cons (car cell)
>>                                                     (cdr cell))) b))
>>
>>
>>
>> Norman
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--
Marco Antoniotti					http://bioinformatics.nyu.edu/~marcoxa
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