🚀 go-pugleaf

In article <BxKLHy.Foy@acsu.buffalo.edu>, v104n55k@ubvmsb.cc.buffalo.edu (David I Schwartz) writes:
|> > In article <92316.113830U37956@uicvm.uic.edu>, U37956@uicvm.uic.edu writes...
|> > >Using Sicstus2.1 Prolog, I want to retract some facts (or clauses) which
|> > >were loaded from a file.
|> > >   Suppose in  mfile, there are facts:
|> > >          johnlikes(mary).
|> > >          marylikes(tom).
|> > > 
|> > >After starting prolog, i load the facts in the following way:
|> > >   |- ? [Omfile].
|> > > 
|> > >When I try to remove a fact, such as:
|> > >   |- ? retract((marylikes(tom))).
|> > > 
|> > >I got error message which says static terms can't be retracted.
|> > > 
|> > >How can i retract the facts and how can i made the facts dynamic ?
|> > > 
|> > >Could anyone tell me?
|> > > 
|> > >Thanks in advance.
|> 
|> You can try abolish (ie, abolish(marylikes/1) ) but it is rather extreme.
|> 
|> Dave

All predicates that are dynamic (i.e. that may be asserted or retracted) have
to be declared so. Use

:- dynamic johnlikes/1, marylikes/1.

(The /1 is the arity of the predicate). I think the reason for this is
efficiency reasons, since non-dynamic (static) predicates can be compiled into
som more efficient representation. Hope this helps!

Jostein

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* Jostein Baustad                        * E-mail : baustad@idt.unit.no       *
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