Petri net solver in Picat

petrinet.pi

import planner.

lookup(Val, Arr1, Arr2) = Out =>
    nth(I, Arr1, Val),
    nth(I, Arr2, Out).

main =>
    Machine = [{{load1, 1}, {proc1, 0}, {done1, 0}, {load2, 1}, {proc2, 0}, {done2, 0}, {lock,  1}},
               [ {load1, 
                  {{load1, 1}, {lock, 1}},  % Maybe the inner ones should be lists, they're only iterated over
                  {{proc1, 1}}},
                 {load2, {{load2, 1}, {lock, 1}}, {{proc2, 1}}},
                 {proc1, {{proc1, 1}}, {{done1, 1}, {lock, 1}}},
                 {proc2, {{proc2, 1}}, {{done2, 1}, {lock, 1}}}
               ]
              ],
    
    nl,
    
    if plan(Machine, 4, Plan) then
      writeln(Plan),
    else
      writeln(impossible),
    end,
    nl.

final([Nodes, Arcs]) => % Solution is hardcoded, srry
  Nodes = {
    {load1, 0},
    {proc1, 0},  
    {done1, 1},  
    {load2, 0},
    {proc2, 0},
    {done2, 1},
    {lock,  _}
  }.


action(S0, S1, Action, ActionCost) =>
   Action = {fire, ArcId},
   ActionCost = 1,

   Arc = {ArcId, Sources, Sinks},
   member(Arc, S0[2]),

   Nodes = copy_term(S0[1]), % Needed for updates

   % remove dots
   foreach({S, ToRemove} in Sources)
      nth(I, Nodes, {S, D}),
      D >= ToRemove, % Has enough dots
      Nodes[I] :=  {S, D - ToRemove}
    end,

   % add dots
   foreach({S, ToAdd} in Sinks)
      nth(I, Nodes, {S, D}),
      Nodes[I] := {S, D + ToAdd}
    end,
    writeln(Nodes),
    S1 = [Nodes, S0[2]].