% HiLog: Higher-Order Logic Programming
% Examples demonstrating higher-order syntax in logic programming

% Transitive closure operator - parametric over any binary predicate P
closure(P)(X,Y) <- P(X,Y).
closure(P)(X,Y) <- P(X,Z), closure(P)(Z,Y).

% LISP-like mapping operator - applies binary predicate F element-wise
maplist(F)([], []).
maplist(F)([X|R], [Y|Z]) <- F(X,Y), maplist(F)(R,Z).

% Meta-predicate call expressed naturally in HiLog (without extra-logical features)
call(X) <- X.

% Binary tree traversal using a variable functor
traverse(X(L,R)) <- traverse(L), traverse(R).