Issues with Best-first Search on Bratko's book

Hi all,
I'm following Ivan Bratko's book second edition.
There's an example that shows how to solve an eight puzzle problem
using Best-first search.
(Page 282 and 289).

Here's the complete code, I'm having a problem with the line with the
bagof. I'm getting an error saying Syntax Error: Operator Expected.
I'm using swi-prolog. I have checked it several times and it's not a
misswriting error, any idea on how to solve this?

Regards
Sebastian

% Figure 12.3 A best-first search program.
% bestfirst( Start, Solution): Solution is a path from Start to a goal

bestfirst( Start, Solution) :-
expand( [], l( Start, 0/0), 9999, _, yes, Solution).

% Assume 9999 is greater than any f-value
% expand( Path, Tree, Bound, Tree1, Solved, Solution):
% Path is path between start node of search and subtree Tree,
% Tree1 is Tree expanded within Bound,
% if goal found then Solution is solution path and Solved = yes

% Case 1: goal leaf-node, construct a solution path
expand( P, l( N, _), _, _, yes, [N|P]) :-
goal(N).

% Case 2: leaf-node, f-value less than Bound
% Generate successors and expand them within Bound.

expand( P, l(N,F/G), Bound, Tree1, Solved, Sol) :-
F =< Bound,
(bagof( M/C, ( s(N,M,C), not member(M,P)), Succ),
!, % Node N has
successors
succlist( G, Succ, Ts), % Make
subtrees Ts
bestf( Ts, F1), % f-value of
best successor
expand( P, t(N,F1/G,Ts), Bound, Tree1, Solved, Sol)
;
Solved = never % N has no
successors - dead end
).


% Case 3: non-leaf, f-value less than Bound
% Expand the most promising subtree; depending on
% results, procedure continue will decide how to proceed

expand( P, t(N,F/G,[T|Ts]), Bound, Tree1, Solved, Sol) :-
F =< Bound,
bestf( Ts, BF), min( Bound, BF, Bound1), % Bound1 =
min(Bound,BF)
expand( [N|P], T, Bound1, T1, Solved1, Sol),
continue( P, t(N,F/G,[T1|Ts]), Bound, Tree1, Solved1, Solved,
Sol).

% Case 4: non-leaf with empty subtrees
% This is a dead end which will never be solved

expand( _, t(_,_,[]), _, _, never, _) :- !.


% Case 5: f-value greater than Bound
% Tree may not grow.

expand( _, Tree, Bound, Tree, no, _) :-
f( Tree, F), F > Bound.


% continue( Path, Tree, Bound, NewTree, SubtreeSolved, TreeSolved,
Solution)

continue( _, _, _, _, yes, yes, Sol).
continue( P, t(N,F/G,[T1|Ts]), Bound, Tree1, no, Solved, Sol) :-
insert( T1, Ts, NTs),
bestf( NTs, F1),
expand( P, t(N,F1/G,NTs), Bound, Tree1, Solved, Sol).
continue( P, t(N,F/G,[_|Ts]), Bound, Tree1, never, Solved, Sol) :-
bestf( Ts, F1),
expand( P, t(N,F1/G,Ts), Bound, Tree1, Solved, Sol).


% succlist( G0, [ Node1/Cost1, ...], [ l(BestNode,BestF/G), ...]):
% make list of search leaves ordered by their F-values
succlist( _, [], []).
succlist( G0, [N/C | NCs], Ts) :-
G is G0 + C,
h( N, H), % Heuristic term h(N)
F is G + H,
succlist( G0, NCs, Ts1),
insert( l(N,F/G), Ts1, Ts).

% Insert T into list of trees Ts preserving order w.r.t. f-values
insert( T, Ts, [T | Ts]) :-
f( T, F), bestf( Ts, F1),
F =< F1, !.

insert( T, [T1 | Ts], [T1 | Ts1]) :-
insert( T, Ts, Ts1).

% Extract f-value
f( l(_,F/_), F). % f-value of a leaf
f( t(_,F/_,_), F). % f-value of a tree

bestf( [T|_], F) :- % Best f-value of a list of trees
f( T, F).
bestf( [], 9999). % No trees: bad f-value

min( X, Y, X) :-
X =< Y, !.
min( X, Y, Y).














% s(Node,successorNode,Cost)
s([Empty|Tiles],[Tile|Tiles1],1):- % all arc
cost are 1
swap(Empty,Tile,Tiles,Tiles1). % Swap Empty
and Tile in Tiles

swap(Empty,Tile,[Tile|Ts],[Empty|Ts]):-
mandist(Empty,Tile,1).

swap(Empty,Tile,[T1,Ts],[T1|Ts1]):-
swap(Empty,Tile,Ts,Ts1).

mandist(X/Y,X1/Y1,D):- % Dis
Manh Dist between 2 sqares
diff(X,X1,DX),
diff(Y,Y1,DY),
D is DX + DY.

diff(A,B,D):-
D is A-B, D>=0,!;
D is B-A.

% Heuristic estimate h is the sum of distance of each tile
% from its home sqare plus 3 times sequence score

h([Empty|Tiles],H):-
goal([Empty|GoalSqares]),
toddist(Tiles,GoalSqares, D),
seq(Tiles,S),
H is D + 3 * S.
totdist([],[],0).
totdist([Tile|Tiles],[Square|Squares],D):-
mandist(Tile,Square,D1),
totdist(Tiles,Squares,D2),
D is D1 + D2.

% seq(TilePosition,Score):-squence score
seq([First|OtherTiles],S):-
seq([First|OtherTiles],First,S).

seq([Tile1,Tile2|Tiles],First,S):-
score(Tile1,Tile2,S1),
seq([Tile2|Tiles],First,S2),
S is S1 + S2.

seq([Last],First,S):-
score(Last,First,S).
score(2/2,_,1):-!.

score(1/3,2/3,0):- !.
score(2/3,3/3,0):- !.
score(3/3,3/2,0):- !.
score(3/2,3/1,0):- !.
score(3/1,2/1,0):- !.
score(2/1,1/1,0):- !.
score(1/1,1/2,0):- !.
score(1/2,1/3,0):- !.

score(_,_,2).
goal([2/2,1/3,2/3,3/3,3/2,3/1,2/1,1/1,1/2]).

showsol([]).

showsol([P|L]):-
showsol(L),
nl, write('---'),
showpos(P).

showpos([S0,S1,S2,S3,S4,S5,S6,S7,S8]):-
member(Y,[3,2,1]),nl,
member(X,[1,2,3]),
member(Tile-X|Y,[''-S0,1-S1,2-
S2,3-S3,4-S4,5-S5,6-S6,7-S7,8-S8]),
write(Tile),
fail
;
true.

start1([2/2,1/3,3/2,2/3,3/3,3/1,2/1,1/1,1/2]).
start2([2/1,1/2,1/3,3/3,3/2,3/1,2/2,1/1,2/3]).
start3([2/2,2/3,1/3,3/1,1/2,2/1,3/3,1/1,3/2]).

% example goal: start1(Pos),bestfirst(Pos,Sol),showsol(Sol).

.