Write FAIL at the sld tree leafs with no solutions

Question

I have this piece of code posted below. Now I'd like to implement function which prints FAIL at the leafs which fails in this prolog tree. This is basically meta-interpreter which makes whole sld tree in DOT format to file.

prove_d(true,Goal,N,_):-!,
    gv_answer(N,Goal). %writtes TRUE at the end of leaf
prove_d(_,_Goal,N,D):-
    D=0, !, gv_stop(N). %writes ending brackets and closes file
prove_d((A,B),Goal,N,D):-!,
    D>0, D1 is D-1,
    resolve(A,C),
    conj_append(C,B,E),
    gv_node(N,(?-E),N1), %writes node and connects with parent node
    prove_d(E,Goal,N1,D1).
prove_d(_,_Goal,N,D):- % HL
    D=0, !, gv_stop(N).
prove_d(A,Goal,N,D):-
    D>0, D1 is D-1,
    resolve(A,B),
    gv_node(N,(?-B),N1),
    prove_d(B,Goal,N1,D1).

resolve(!, true):-
    !, (true ; throw(cut)).
resolve(A,true):-
    predicate_property(A,built_in),!,
    call(A).
resolve(A,B):-
    clause(A,B).

gv_fail(N0):- %where to place this?
    gv_id(N), %gets id for parent node
    writes([N,' [label="fail", shape=plaintext];']),
    writes([N0,' -> ',N,' [style=dotted, length=0];']).

The closest to solution is

prove_d((A,B),Goal,N,D):-!,
    D>0, D1 is D-1,
    resolve(A,C),
    conj_append(C,B,E),
    gv_node(N,(?-E),N1),
    (prove_d(E,Goal,N1,D1) ; gv_fail(N1)).

but this prints fail at the end of every leaf even with true at the end of the leaf.

I use swi-prolog.

EDIT: Because this code is little longer, here is complete program.http://pastebin.com/bQKD1Cyi

It works like this. You consult this file at start-up of prolog. Then in other file is program you want to visualise, so you call why/3, then it makes DOT output to separate file. You can use this website to visualise DOT output - http://webgraphviz.com/

EDIT2: Here is my program I test it on:

v(X):-p(X), s(X).
v(n).

p(a).
p(b).

s(a).
s(c).

the only solutions are v(n) and s(a), yet at goal s(a) it writes true and fail at the end of the leaf when only true should be there.

First, [consider this](http://stackoverflow.com/questions/27390236/execution-tree-meta-interpreting#comment-43228494) — false, Mar 10 '15 at 14:16
@false I considered my previous question. I found out, after examining the trace, that I seem to somehow prevent backtracking in this one. I tried several solutions like throwing exceptions and catching them, cuts or add another predicate `prove_d/3` at the end but still it does print `fail` where should not be. — Đrakenus, Mar 10 '15 at 18:06
Hey, right now, i need a prolog meta-interpreter which generates the SLD-Tree of a query. I found this post, when I was about to create one of my own. I wanted to ask if your interpreter is finished by now, and if it would be possible for me to use it. — Uzaku, May 27 '15 at 17:12
My meta-interpreter is bugged. The cut-handling is very bad, some leafs produces 2 fails per leaf and sometimes the leaf ends without true of false. Still interested? — Đrakenus, Jun 01 '15 at 20:14
Hey, I am still interested, that is way better than everything I have ^^ — Uzaku, Aug 01 '15 at 09:22

Yasel · Answer 1 · 2015-03-10T01:09:47.420

The program is incomplete. Without the predicates gv_answer/2, gv_stop/1, gv_node/3, and so many others no included in your code, I can only give a partial answer, based in my appreciation of what is missing in your code. I think that you need a new clause in your prove_d/3 predicate, the last one, that will succeed in case the other fails. Also, you must modify the last clause prove_d/3, to avoid backtracking for the new clause. So, the predicate prove_d/3, will go like this:

prove_d(true,Goal,N,_):-!,
    gv_answer(N,Goal). %writtes TRUE at the end of leaf
prove_d(_,_Goal,N,D):-
    D=0, !, gv_stop(N). %writes ending brackets and closes file
prove_d((A,B),Goal,N,D):-!,
    D>0, D1 is D-1,
    resolve(A,C),
    conj_append(C,B,E),
    gv_node(N,(?-E),N1), %writes node and connects with parent node
    prove_d(E,Goal,N1,D1).
prove_d(_,_Goal,N,D):- % HL
    D=0, !, gv_stop(N).
prove_d(A,Goal,N,D):-
    D>0,!, D1 is D-1,
    resolve(A,B),
    gv_node(N,(?-B),N1),
    prove_d(B,Goal,N1,D1).
prove_d(_,_,N,_):- gv_fail(N).

I tried this predicate (saved in the file multiply.pl):

%Multiply members of a list
multiply([X], X):-!.
multiply([H|T], X):-multiply(T, M), X is M *H.

and this goal:

?- why(multiply([1,2,3],X), './sldtree.pl', './multiply.pl').

And the SLD tree looks ok to me. There is only one success and the leafs that show fails is because Prolog fails to do backtracking on those conditions. Maybe the issues is in your input program, or the SLD tree generated exceeds the default depth (10 levels), in that case you will never see the succeed.

I edited my question. I was thinking about something simillar but it does not works maybe due to `sld/4`'s fail driven looping. It simply puts Fail to almost every leaf. — Đrakenus, Mar 09 '15 at 21:20
@Đrakenus I test the program with a simple program and it looks ok. I added some details at the end of my answer, so you can use the same example. — Yasel, Mar 10 '15 at 00:59
Thank you, I really appreciate your work. Maybe I dont understand how to make SLD trees. But what I try to do is that it should write only fail at the end of leafs that are not true. So in your multiply/2 there should not be any fails. — Đrakenus, Mar 10 '15 at 10:47

Write FAIL at the sld tree leafs with no solutions

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