Reading and outputting from and to a file PROLOG - file-io

Question

I have a programming assignment in one of my classes that is to implement a working binary search tree in Prolog along with a few traversals and other functions. Below is the code I currently have. I cannot figure out how to implement the function readTree, or how to output the integer list given from inorder, preorder, and postorder functions. Any help would be much appreciated!
%testing trees
tree3(node(6, node(4, node(2, nil, nil), node(5, nil, nil)), node(9, node(7, nil, nil), nil))).
tree2(node(8, node(5, nil, node(7, nil, nil)), node(9, nil, node(11, nil, nil)))).
tree1(nil).
%returns true if empty, false otherwise, not working, obviously not the 'prolog' way, but presents the proper outputs, time permitting return to this.
isEmpty(nil) :- write(true).
isEmpty(node(_,_,_)) :- write(false).
%as of now, all traversals must start with an initialization of tree i.e. tree1(T),inorder(T,List).
%inorder traversal of tree
inorder(node(Key,Left,Right), List):-inorder(Left, LL), inorder(Right, LR),
append(LL, [Key|LR], List).
inorder(nil, []).
%preorder traversal of tree
preorder(node(Key,Left,Right), List):-preorder(Left,LL), preorder(Right, LR),
append([Key|LL], LR, List). %, write(List), open(Src, write, File), write(Key), close(File).
preorder(nil, []).
%postorder traversal of tree
postorder(node(Key,Left,Right), List):- postorder(Left,LL), postorder(Right, LR),
append(LL, LR,R1), append(R1, [Key], List).
postorder(nil, []).
%helps all traversal predicates print to file
loop_through_list(File, List) :-
member(Element, List),
write(File, Element),
write(File, ' '),
fail.
write_list_to_file(Filename,List) :-
open(Filename, write, File),
\+ loop_through_list(File, List),
close(File).
%getMin, gets smallest integer in tree
min(node(X, L, _R), Min) :- min_helper(L, X, Min).
min_helper(null, X, X).
min_helper(node(X, L, _R), _X0, Min) :- min_helper(L, X, Min).
%getMax, gets largest integer in tree
%inserting an element into the tree
insert(nil, Key, node(Key, nil, nil)):-
write('Inserted '),
write(Key), nl.
insert(node(Key, Left, Right), Key, node(Key, Left, Right)):-
!, write('Key already in tree\n').
insert(node(Key, Left, Right), Key, node(Key, NewL, Right)):-
Key<Key, !,
insert(Left, Key, NewL).
insert(node(Key, Left, Right), Key, node(Key, Left, NewR)):- insert(Right, Key, NewR).
%delete a key, and shift tree respectively
delete(nil, Key, nil):-
write(Key),
write(' not in tree\n').
delete(node(Key, L, nil), Key, L) :- !. % this clause covers also case for leaf (L=nil)
delete(node(Key, nil, R), Key, R) :- !.
delete(node(Key, L, R), Key, node(Pred, NL, R)) :-
!, get_pred(L, Pred, NL).
delete(node(Key, L, R), Key, node(Key, NL, R)):-
Key<Key, !,
delete(L, Key, NL).
delete(node(Key, L, R), Key, node(Key, L, NR)) :- delete(R, Key, NR).
get_pred(node(Pred, L, nil), Pred, L) :- !.
get_pred(node(Key, L, R), Pred, node(Key, L, NR)) :- get_pred(R, Pred, NR).
%treeRead, not yet implemented
:- debug.