package examples.turing;

import static examples.turing.Direction.*;

public handler turing {
	constraint delta(
			+Object StateId, char Symbol,                  // input 
			+Object NewStateId, char NewSymbol, Direction  // output
	);
	constraints 
		current_state(+Object Id),
		head(+Object HeadId),
		cell(+Object Id, char Symbol, +Object Left, +Object Right),
		move(Direction, +Object CellId, +Object Left, +Object Right);
		
	rules {
			trans @ delta(S,G,Sp,Gp,Dir) \ current_state(S), head(Cell), 
			                               cell(Cell,G,Left,Right)
			                           <=> current_state(Sp), 
			                               cell(Cell,Gp,Left,Right), 
			                               move(Dir,Cell,Left,Right).

			local +Object L;
			move(LEFT,Cell,null,R), cell(Cell,G,null,R)
			       <=> L = new Object(), cell(Cell,G,L,R), cell(L,'#',null,Cell), head(L).
			move(LEFT,Cell,L,_) <=> L != null | head(L).
			
			local +Object R;
			move(RIGHT,Cell,L,null), cell(Cell,G,_,_)
			       <=> R = new Object(), cell(Cell,G,L,R), cell(R,'#',Cell,null), head(R).
			move(RIGHT,Cell,_,R) <=> R !== null | head(R).
	}
}