RE: AW: function hash for prolog terms?

[Daniel Jimenez Gentil]

Thank you very much for your help, but I have a problem when the prolog
term is a variable not unified.

For example:

 :-isinto(X,1,5), hash_term(X,N).

the variable X is not unified, and it returns me an error.

Could you help me?


-----Mensaje original-----
De: Daniel Diaz [mailto:address@hidden 
Enviado el: miercoles, 11 de febrero de 2004 23:43
Para: ibl
CC: Daniel Jimenez Gentil; address@hidden
Asunto: Re: AW: function hash for prolog terms?

Hi,

You'll find as an attachment another Prolog solution to compute a hash 
code from a term.


>>Hello,
>>
>>I am working using the interface of GNU-Prolog for C.
>>
>>I need a function that returns me an unique number for each
>>prolog term. Up
>>to now I am using the following one
>>
>>int hash(PlTerm termino_prolog) {
>>
>>  return abs (Rd_Code (termino_prolog));
>>
>>}
>>
>>But there are cases in those that it stops oneself prolog term it
>>returns me
>>different values.
>>
>>Thank you for your help.
> 
> 
> Daniel,
> 
> while I don't know about the semantics of "Rd_Code", I suspect, that
the
> returned information might be not unique to a specific term.
> 
> For a true hash you need a guaranteed unique function however.
> 
> So I would suggest, that you implement it as follows:
> 
> term_hash(Term,Hash) :-
>       write_canonical_to_atom(CanonicalAtom,Term),
>       my_md5_digest(CanonicalAtom,Hash).
> 
> Of course, this would involve an implementation of "my_md5_digest".
> You can easily wrap a "stock" MD5 function, written in C, to perform
this
> task.
> 
> 
> HTH
> Regards
> Ingo