Re: question on assert and retract

[Vic Bancroft]

On Mon, 26 Aug 2002, bruno patin wrote:

> is it normal that two identic call to assertz will have a positive 
> answer ? for example :
> 
> assertz(toto(2)).
> assertz(toto(2)).

Yes, assertz does not check for duplicates.  An interesting way to check the
prolog database is,

  | ?- listing.

  toto(2).
  toto(2).

  yes

This is why you have two bindings for X in 

> toto(X).
> X=2
> yes
> X=2
> no

The 1.2.12 version I have here reports this a bit differently, e.g.,

  | ?- toto(X).

  X = 2 ? ;

  X = 2

  yes

> retract(toto(2)).
> 
> toto(X).
> no

It removes all the clauses that would unify with 2.  The 1.2.12 version gives,

  | ?- retract(toto(2)).

  true ? ;

  yes

Why does your version report "no" ?

more,
l8r,

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