Re: setof question

On Sat, Mar 15, 2014 at 10:54:27 +0000, Roelof Wobben wrote:
> Im now experimenting with setof.

You probably shouldn't. You still seem to lack basic understanding of things
that you should understand before moving on to things like setof/3, which
behave in weird non-logical ways unlike most of the rest of the language.

That said...
 
> setof(X, parents(X,Y), X) 
>  
> Can I somehow print out both. 
> So the output will be something like this:
>  
> x = father  y=mother. 

This variant will try all bindings for X *separately* for each binding of Y:

?- setof(X, parents(X, Y), Parents).
Y = bob,
Parents = [alice] ;
Y = eve,
Parents = [adam] ;
Y = sally,
Parents = [harry].

You can change this behavior by saying that the X bindings for all bindings
of Y should be collected:

?- setof(X, Y^parents(X, Y), Parents).
Parents = [adam, alice, harry].

You can make pairs by using any two-place functor such as the popular -/2:

?- setof(X-Y, parents(X, Y), Parents).
Parents = [adam-eve, alice-bob, harry-sally].

Or construct any term of your liking:

?- setof(my_term(one_parent=X, other_parent=Y), parents(X, Y), Parents).
Parents = [my_term(one_parent=adam, other_parent=eve),
           my_term(one_parent=alice, other_parent=bob),
           my_term(one_parent=harry, other_parent=sally)].

(You are still using a term parents/2 without any indication which argument
is the father and which is the mother. Don't.)

-- 
Gergö Barany, research assistant                 [email protected]
Institute of Computer Languages      http://www.complang.tuwien.ac.at/gergo/
Vienna University of Technology                       Tel: +43-1-58801-58522
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