:- use_module(library(lists), [member/2]).

exit(Exit) :-
	Walls = [],
	BeenTheres = [],
	StartPoint = (1,1),
	once(walk(StartPoint,Walls,BeenTheres,Exit)).

walk(Point,    _,         _,Point) :- at_exit.
walk(Point,Walls,BeenTheres,Exit) :-
	next_point(Point,NextPoint),
	\+ member(NextPoint,BeenTheres),
	Wall = wall(Point,NextPoint),
	\+ member(Wall,Walls),
	( move(NextPoint) ->
	    (
	      walk(NextPoint,Walls,[NextPoint|BeenTheres],Exit)
	    ;
	      move(Point),
	      fail
	    )
	;
	    walk((1,1),[Wall|Walls],[],Exit)
	).

move((I,J)) :- move(I,J).

next_point((I,J),(NextI,NextJ)) :- NextI = I, NextJ is J + 1.
next_point((I,J),(NextI,NextJ)) :- NextI = I, NextJ is J - 1.
next_point((I,J),(NextI,NextJ)) :- NextJ = J, NextI is I + 1.
next_point((I,J),(NextI,NextJ)) :- NextJ = J, NextI is I - 1.