Re: question on assert and retract

[spratt]

On Tuesday, August 27, 2002, at 02:14  PM, address@hidden wrote:

> On Tuesday, August 27, 2002, at 01:31  PM, bruno patin wrote:
>
> > But now, as listing is not an iso-prolog directive how not to add the 
> > same facts two times ?
>
> Perhaps my_assertz:
>
> my_assertz(Term) :-
>      (var(Term)
>        ;
>      copy_term(Term, TermCopy),
>         my_clause(TermCopy) )
>        -> true
>      ;
>      assertz(Term).
>
> my_clause( Term ) :-
>      Term =.. [ (:-), Head, Body]
>        -> clause(Head, Body)
>      ;
>      clause(Term, true).
>
> This only assertz's Term if Term is ground (i.e. contains no unbound 
> variables) and is not unifiable with a clause already in the clause 
> database.

Oops. I changed the code but not the comment--I changed it to use var/1 
instead of checking for groundness, since ground/1 isn't ISO and I'm too 
lazy to go find an implementation of ground/1 right now.
-lindsey