Re: negative numbers

[michel levy]

Alexandre Saidi wrote:
> Hello all,
> I know that Gprolog does not handle negative intergers.
>
> However, someone could tell me why gprolog rejects vilently this :
>
> ?- fd_domain(I,1,4), fd_element(I,[12, 5, -7,9], X).
>
> Fatal Error: Segmentation Violation
>
> Ok, she does not like my -7.
>
> But with :
> X #= -1.
> I get just (gently)
> no.
>
> PS : the original resuest was :
> ?- fd_domain([S1, S2], 1, 7), S1 #=S2 +X, fd_domain(I,1,4), 
> fd_element(I,[-1,-2,1,2], X), fd_labeling([S1,S2]).
>
> I'm trying to get S1 and S2 (2 days of a week) being two consecutive 
> days or with a difference of 2 .
> An elegant way to this in gprolog (a  short one is wellcome : I'm trying 
> to illustratre CLP power in an introduction).
>
> Thanks.
> Alex
>
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Les variables à domaine finis sont des entiers positifs ou nuls.
Donc en posant cette requête, vous contraignez X à être positif et négatif.

The FD variables are positive or nul integers.
Your request fd_element(I,[12, 5, -7,9], X) constrains X to be positive 
and negative : I am not surprised by this segmentation violation, but in 
the gprolog manual (8.8.2) this case is not referenced.


Another example :
address@hidden ~]$ gprolog
GNU Prolog 1.2.19
By Daniel Diaz
Copyright (C) 1999-2005 Daniel Diaz
| ?- fd_element(1,[-1],X).
Fatal Error: Segmentation Violation

But
| ?- fd_element_var(1,[-1],X).
no

And now let's return to your example
| ?- fd_element_var(I,[12, 5, -7,9], X).
I = _#3(1..2:4)
X = _#71(5:9:12)
yes
| ?- fd_element(I,[12, 5, -7,9], X).
Fatal Error: Segmentation Violation




--
Michel Levy
36 rue George Sand
38400 Saint Martin d'Heres