Re: Bug, or at least something wrong

On 2007/10/21, at 20:44, Felipe Ignacio Canas Sabat wrote:

> 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:

There is a bug in your code: you want integer division, not float  
division in the first clause of step/2.. GNU Prolog behavior is  
correct. SWI-Prolog is more forgiving. You may also use arithmetic  
equality (=:=/2) instead of term equality (==/2).

Cheers,

Paulo


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