delay clauses

Dear ECLiPSe Users,

in section 16.9.2 the following program is given:

delay filter(_, Li, Lo) if var(Li), var(Lo).
filter(_, [], []) :- !.
filter(P, [N|LI], LL) :-
        (N mod P =\= 0 ->
                LL = [N|NLI],
                filter(P, LI, NLI)
        ;
                filter(P, LI, LL)
        ).
delay integers(_, List) if var(List).
integers(_, []).
integers(N, [N|Rest]) :-
        N1 is N + 1,
        integers(N1, Rest).

The goal
:- integers(2,L), filter(2,L,[N|R]).
works as expected and produces the result:
L = [2, 3|LI]
N = 3
R = R
 
Delayed goals:
        integers(4, LI)
        filter(2, LI, R)
yes.

But the goal
:- integers(2,L), filter(2,L,[N|R]), R = [M|S].
results in the error message:
instantiation fault in mod(N, 2, _262)

The manual says that the delayed integers goal is woken before the
conditional is executed. Therefore, N should be instantiated to an
integer.

Any comments?

-- 
 Jörg Harm                       jh@informatik.uni-rostock.de
 Fachbereich Informatik, Universität Rostock, D-18051 Rostock
 Telefon: +49-381-4983432                Fax: +49-381-4983426