Create a gist now

Instantly share code, notes, and snippets.

anonymous /database.lgt
Created Nov 9, 2011

What would you like to do?
Meta-Programming in Prolog - Part 2
:- object(database).
:- public(rule/2).
nat(zero) :- true.
nat(s(X)) :- nat(X).
add(zero, Y, Y) :- true.
add(s(X), Y, s(Z)) :-
add(X, Y, Z).
append([_X], Ys, Ys) :- true.
append([X|Xs], Ys, [X|Zs]) :-
append(Xs, Ys, Zs).
prove(G) :-
prove1([G]).
prove1([]) :- true.
prove1([G|Gs]) :-
rule(G, B),
prove1(B),
prove1(Gs).
length([], 0) :- true.
length([_|Xs], N) :-
length(Xs, N1),
N is N1 + 1.
:- end_object.
:- object(debugging).
%Based on source code from The Art of Prolog.
:- public(false_solution/2).
false_solution(G, Clause) :-
interpreter::prove(G, T),
false_goal(T, Clause).
false_goal((A :- B), Clause) :-
( false_conjunction(B, Clause) ->
true
; Clause = (A :- B1),
extract_body(B, B1)
).
false_conjunction(((A :- B), _Bs), Clause) :-
query_goal(A, false),
!,
false_goal((A :- B), Clause).
%Almost the same as above, but with only one element.
false_conjunction((A :- B), Clause) :-
query_goal(A, false),
!,
false_goal((A :- B), Clause).
false_conjunction((_A, As), Clause) :-
%A is implicitly true.
false_conjunction(As, Clause).
extract_body(true, true).
extract_body((A :- _B), A).
extract_body(((A :- _B), Bs), (A, As)) :-
extract_body(Bs, As).
query_goal(G, Answer) :-
write('Is the goal '),
write(G),
write(' true?'),
nl,
read(Answer).
:- end_object.
:- object(interpreter).
:- public(prove/1).
:- public(prove/2).
%Initialize the goal list with G.
prove(G) :-
prove1([G]).
prove1([]).
prove1([G|Gs]) :-
rule(G, B),
prove1(B),
prove1(Gs).
prove(G, T) :-
prove1([G], T0),
filter(T0, T).
prove1([], true).
prove1([G|Gs], ((G :- T1), T2)) :-
rule(G, B),
prove1(B, T1),
prove1(Gs, T2).
filter(true, true).
filter((T0, true), T) :-
filter(T0, T).
filter((T1, T2), (T3, T4)) :-
T2 \= true,
filter(T1, T3),
filter(T2, T4).
filter((A :- B0), A :- B) :-
filter(B0, B).
rule(rule(A, B), []) :- rule(A, B).
rule((X is Y), []) :- X is Y.
rule(G, B) :-
database::rule(G, B).
:- end_object.
:- initialization((
logtalk_load(library(metapredicates_loader)),
logtalk_load(library(types_loader)),
logtalk_load(rule_expansion),
logtalk_load(database, [hook(rule_expansion)]),
logtalk_load(interpreter),
logtalk_load(debugging))).
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment