Imperial Prolog assessed Cwk

crossings.pro

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%                                                  %
%         276 Introduction to Prolog               %
%                                                  %
%         Coursework 2013-14 (crossings)           %
%                                                  %
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%% ------------  (utilities) DO NOT EDIT

fees(2,3).   

forall(P,Q) :- \+ (P, \+ Q).

app_remove(X,List,Remainder) :-
  append(Front, [X|Back], List),
  append(Front, Back, Remainder).

% solutions for testing 
solution([f(g),f,f(w),f(g),f(c),f,f(b),f,f(g)]).
solution([f(g),f,f(c),f(g),f(w),f,f(b),f,f(g)]).
solution([f(g),f,f(b),f,f(w),f(g),f(c),f,f(g)]).
solution([f(g),f,f(b),f,f(c),f(g),f(w),f,f(g)]).

%% --------- END (utilities)
%% ------ Add your code to this file here.

safe(Bank) :-
  ([H | _ ] = Bank, H = f);
  \+ ((member(w, Bank), member(g, Bank));
      (member(g, Bank), member(c, Bank))).

safe_state(N-S) :-
  safe(N), safe(S).

sorted_state(N-S, SN-SS) :-
  sort(N, SN), sort(S, SS).

equiv(S1, S2) :-
  sorted_state(S1, SS1), 
  sorted_state(S2, SS2), 
  SS1 = SS2.

goal(S) :-
  equiv(S, []-[f,b,c,g,w]).

visited(State, History) :-
  setof(S, (member(S,History), equiv(State,S)), EquivStates),
  \+ (EquivStates = []).

remove(X, [H | T], Remainder) :-
  X = H,
  Remainder = T;
  \+ (T = [])
  -> remove(X, T, SubRemainder),
  Remainder = [H|SubRemainder].

% move(Start, Move, Result)
move(B1-[ f | Rem ], Move, F1-F2) :-
  move([f|Rem]-B1, Move, F2-F1).
move([ f | B1 ]-B2, f, F1-F2) :-
  F1 = B1, F2 = [ f | B2 ].
move([ f | B1 ]-B2, f(X), F1-F2) :-
  remove(X, B1, F1),
  F2 = [ f | [X | B2 ] ].

crossing(Start, Move, Finish) :-
  safe_state(Start),
  move(Start, Move, Finish),
  safe_state(Finish).

journey(Crrt, History, Sequence) :-
  goal(Crrt)
->Sequence = [];
  crossing(Crrt, Move, Next),
  \+ visited(Next, History),
  journey(Next, [Next | History], SubSequence),
  Sequence = [Move | SubSequence].

succeeds(Sequence) :-
  journey([f,w,g,c,b]-[], [], Sequence).

journey_cost_helper([], 0).
journey_cost_helper([Move | Rem], Cost) :-
  fees(Farmer,Accomp),
  journey_cost_helper(Rem, SubCost),
  (Move = f -> Cost is Farmer + SubCost;
              Cost is Accomp + SubCost).

journey_cost(Sequence, Cost) :-
  succeeds(Sequence),
  journey_cost_helper(Sequence, Cost).