Re: Bug, or at least something wrong

The 'A is X mod 2' requires that X be bound to an integer, but 16.0  
is a float.

You could change the line after  'even(X)' to 'Y is X // 2'. The '//'  
operator guarantees an integer result:

step(X, Y) :-
   X > 1,
   even(X),
   Y is X // 2.

Cheers,
Lindsey Spratt


On Oct 21, 2007, at 3:44 PM, Felipe Ignacio Canas Sabat wrote:

> Hello,
>
> These are the commands I am using:
>
> %%%%%%%%%%%%
> even(X) :-
>   A is X mod 2,
>   A == 0.
>
> odd(X) :-
>   A is X mod 2,
>   A == 1.
>
> step(X,Y) :-
>   X > 1,
>   even(X),
>   Y is X/2.
>
> step(X,Y) :-
>   X > 1,
>   odd(X),
>   Y is 3*X + 1.
> %%%%%%%%%%%%
>
> And this is what I'm running:
>
>   | ?- step(32,X), step(X,Y), step(Y,Z).
>
> And this is the error I get:
>
>   uncaught exception: error(type_error(integer,16.0),(is)/2)
>
> I don't get this error when I run it on SWI-prolog, and I really don't
> see what the error is. This is the trace:
>
>       1    1  Call: step(32,_16) ?
>       2    2  Call: 32>1 ?
>       2    2  Exit: 32>1 ?
>       3    2  Call: even(32) ?
>       4    3  Call: _166 is 32 mod 2 ?
>       4    3  Exit: 0 is 32 mod 2 ?
>       5    3  Call: 0==0 ?
>       5    3  Exit: 0==0 ?
>       3    2  Exit: even(32) ?
>       6    2  Call: _16 is 32/2 ?
>       6    2  Exit: 16.0 is 32/2 ?
>       1    1  Exit: step(32,16.0) ?
>       7    1  Call: step(16.0,_20) ?
>       8    2  Call: 16.0>1 ?
>       8    2  Exit: 16.0>1 ?
>       9    2  Call: even(16.0) ?
> *    10    3  Call: _320 is 16.0 mod 2 ?
> *    10    3  Exception: _332 is 16.0 mod 2 ?
>       9    2  Exception: even(16.0) ?
>       7    1  Exception: step(16.0,_20) ?
>
> I put the asterisks next to the lines where I see something strange
> happening. Namely, it goes from assigning something to _320 to then
> report an exception concerning _332.
>
> What's more, after running the same instruction once more, I get a
> Segmentation Fault. I couldn't figure out how to build a not stripped
> binary, so no backtrace, sorry.
>
> Some required info:
>
> Machine:
> Linux <hostname> 2.6.18-5-686 #1 SMP <date> i686 GNU/Linux
>
> Distro:
> Debian 4.0r1 (Etch)
>
> GNU Prolog version:
> 1.3.0
>
> Hope it helps.
>
> Bye,
> -Felipe
>
>
>
> _______________________________________________
> Bug-prolog mailing list
> [email protected]
> http://lists.gnu.org/mailman/listinfo/bug-prolog