Prolog: Access read from parent rule

Question

I want a specific rule for reading user input data in SWI-Prolog, something like:

process( ... ) :-
    % do_stuff
    read_values( ... ),
    % do_more_stuff with X and Y here.

read_values( ... ) :-
    write('Please enter X: '),        
    read(X),
    write('Please enter Y: '),        
    read(Y).

Is that possible?

score 3 · Accepted Answer · answered Sep 27 '12 at 21:40

3

Well you kinda already had the solution:

process :-
    % do_stuff
    read_values(A, B),
    % do_more_stuff with X and Y here
    atom_concat(A, B, C),
    writeln(C).

read_values(X, Y) :-
    write('Please enter X: '),        
    read(X),
    write('Please enter Y: '),        
    read(Y).

Example run:

?- process.
Please enter X: a.
Please enter Y: b.
ab
true.

answered Sep 27 '12 at 21:40

m09

7,490
3
31
58

I'd also made `read_values` non-retractable (or how is that called), but that is a matter of personal preference. – Lyth Sep 27 '12 at 21:43
1

@Lyth: if you mean 'non backtrack able' (or deterministic): read and write are already of that kind – CapelliC Sep 28 '12 at 00:08
Thanks, @Mog. Just had to put the pieces together to realize how to do it. – vmassuchetto Sep 28 '12 at 02:10

Prolog: Access read from parent rule

1 Answers1

Linked