impl printing tree of a task

todo.pl

@@ -6,7 +6,11 @@
 all_tasks(L):- findall(X, task(X, _), L).
 all_tasks(L, STATE):- findall(X, task(X, STATE), L).
 
-
+print_task(X):-
+    task(X,ISDONE), 
+    write(ISDONE),
+    write(': '), 
+    write(X). 
 print_task_list([],_).
 print_task_list([H|T],N) :- 
     M is N+1,
@@ -14,10 +18,8 @@ print_task_list([H|T],N) :-
     asserta(idx(N, H)),
     write(N),
     write(". "),
-    task(H,ISDONE), 
-    write(ISDONE),
-    write(': '), 
-    write(H),nl, 
+    print_task(H),
+    nl,
     print_task_list(T, M).
 
 list_all :- all_tasks(L), print_task_list(L,1).
@@ -86,6 +88,24 @@ check(X) :-
     write("no such task as "),
     write(X).
 
+indent(0).
+indent(N):- 
+    write("   "),
+    M is N-1,
+    indent(M).
+
+tree_branch([],_).
+tree_branch([X|T],N):-
+    indent(N),
+    print_task(X),
+    nl,
+    findall(Y, requires(Y,X), L),
+    M is N+1,
+    tree_branch(L,M),
+    tree_branch(T,N).
+tree(X):- task(X,_), tree_branch([X],0).
+tree(X):- idx(X,Y), tree(Y).
+
 uncheck(X) :- idx(X, Task), uncheck(Task).
 uncheck(X):-
     task(X, done),