utils.pl

% #################################################
% printFrontier/1 predicate prints any node's
% infos inside the input list.
% #################################################
printFrontier([]).
printFrontier([node(S, ActionsListForS, ActualPathCost, HeuristicCost)|Frontier]) :-
  H is ActualPathCost + HeuristicCost,
  write("\n|Node: "), write(S), write(" | F: "), write(H),
  write("\n| - Actions performed to reach current state: "), write(ActionsListForS),
  write("\n| - Actual path cost "), write(ActualPathCost),
  write("\n| - Heuristic cost: "), write(HeuristicCost),
  write("\n|"),
  printFrontier(Frontier).

% #################################################
% printFrontierWithBound/1 predicate prints any 
% node's infos inside the input list.
% #################################################
printFrontierWithBound([]).
printFrontierWithBound([node(S, ActionsListForS, ActualPathCost, HeuristicCost, DepthOfS)|Frontier]) :-
  H is ActualPathCost + HeuristicCost,
  write("\n|Node: "), write(S), write(" | F: "), write(H),
  write("\n| - Actions performed to reach current state: "), write(ActionsListForS),
  write("\n| - Actual path cost "), write(ActualPathCost),
  write("\n| - Heuristic cost: "), write(HeuristicCost),
  write("\n| - Depth': "), write(DepthOfS),
  write("\n|"),
  printFrontierWithBound(Frontier).

% #################################################
% setElement/1 predicate is self explanatory.
% #################################################
setElement([_|Tail], 0, X, [X|Tail]):-!.
setElement([Head|Tail], Pos, X, [Head|NuovaTail]):-
  Pos1 is Pos-1,
  setElement(Tail, Pos1, X, NuovaTail).

% #################################################
% a_star_comparator/3 predicate provides a comparator
% used to sort A* frontier after each new expansion.
% #################################################
a_star_comparator(R, node(_, _, G_Cost_1, H_Cost_1), node(_, _, G_Cost_2, H_Cost_2)) :-
  F1 is G_Cost_1 + H_Cost_1,
  F2 is G_Cost_2 + H_Cost_2,
  F1 >= F2 -> R = > ; R = < .