=================================================================
Logtalk - Object oriented extension to Prolog
Release 2.21.1

Copyright (c) 1998-2004 Paulo Moura.  All Rights Reserved.
=================================================================


% start by loading the example:

| ?- logtalk_load(loader).
...


% solver - a simple meta-interpreter for pure Prolog:

| ?- solver::assertz(member_of(H, [H| _])).

H = _G178 
yes

| ?- solver::assertz((member_of(H, [_| T]) :- member_of(H, T))).

H = _G181
T = _G179 
yes

| ?- solver::solve(member_of(2, [1,2,3])).

yes

| ?- solver::solve(member_of(X, [1,2,3])).

X = 1 ;
X = 2 ;
X = 3
yes


% proof_tree - a simple meta-interpreter for pure Prolog that 
% construct a proof tree:

| ?- proof_tree::assertz(member_of(H, [H| _])).

H = _G178 
yes

| ?- proof_tree::assertz((member_of(H, [_| T]) :- member_of(H, T))).

H = _G181
T = _G179 
yes

| ?- proof_tree::solve(member_of(2, [1,2,3]), Tree).

Tree = member_of(2, [1, 2, 3]):- (member_of(2, [2, 3]):-true) 
yes


% tracer - a simple meta-interpreter for tracing goal proofs 
% using pure Prolog:


| ?- tracer::assertz(member_of(H, [H| _])).

H = _G178 
yes

| ?- tracer::assertz((member_of(H, [_| T]) :- member_of(H, T))).

H = _G181
T = _G179 
yes

| ?- tracer::trace(member_of(3, [1,2,3])).

1 call: member_of(3, [1, 2, 3])
2 call: member_of(3, [2, 3])
3 call: member_of(3, [3])
3 exit: member_of(3, [3])
2 exit: member_of(3, [2, 3])
1 exit: member_of(3, [1, 2, 3])
yes

| ?- tracer::trace(member_of(X, [1,2,3])).

1 call: member_of(_G187, [1, 2, 3])
1 exit: member_of(1, [1, 2, 3])

X = 1 ;
1 redo: member_of(1, [1, 2, 3])
2 call: member_of(_G187, [2, 3])
2 exit: member_of(2, [2, 3])
1 exit: member_of(2, [1, 2, 3])

X = 2 ;
1 redo: member_of(2, [1, 2, 3])
2 redo: member_of(2, [2, 3])
3 call: member_of(_G187, [3])
3 exit: member_of(3, [3])
2 exit: member_of(3, [2, 3])
1 exit: member_of(3, [1, 2, 3])

X = 3 ;
1 redo: member_of(3, [1, 2, 3])
2 redo: member_of(3, [2, 3])
3 redo: member_of(3, [3])
4 call: member_of(_G187, [])
4 fail: member_of(_G187, [])
3 fail: member_of(_G187, [3])
2 fail: member_of(_G187, [2, 3])
1 fail: member_of(_G187, [1, 2, 3])
no