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).
@@ -28,33 +30,129 @@ list_done :- all_tasks(L, done), print_task_list(L,1).
 print_list([]).
 print_list([H|T]) :- write(H),nl, print_list(T).
 
+new(X) :- 
+    task(X, todo), 
+    write("task already exist"),
+    !.
 new(X) :- 
     asserta(task(X, todo)), 
     write("added task "), 
     write(X).
+new(X,Y) :- idx(Y, Task), new(X, Task).
+new(X,Y) :- 
+    asserta(task(X, todo)), 
+    asserta(requires(X, Y)),
+    uncheck(X), 
+    write("added task "), 
+    write(X),
+    write(" as a subtask for "), 
+    write(X).
+depend(X,Y) :- idx(X, Task), depend(Task, Y).
+depend(X,Y) :- idx(Y, Task), depend(X, Task).
+depend(X,Y) :- 
+    task(X, todo),
+    task(Y, _),
+    asserta(requires(X, Y)).
+depend(X,Y) :- 
+    task(X, done),
+    task(Y, todo),
+    uncheck(X).
+depend(X,Y) :- 
+    task(X, done),
+    task(Y, done).
+
+check(X) :- idx(X, Task), check(Task).
 check(X) :- 
     task(X, todo), 
+    \+ (requires(Y, X), task(Y,todo)),
     asserta(task(X, done)), 
     retractall(task(X, todo)), 
     write("marked "), 
     write(X), 
-    write(" as done").
-check(X) :- idx(X, Task), check(Task).
+    write(" as done"),
+    !.
+check(X) :- 
+    task(X, todo), 
+    (requires(Y, X), task(Y,todo)),
+    write("you need to do "), 
+    write(Y), 
+    write(" before doing "),
+    write(X), 
+    !.
+check(X) :- 
+    task(X, done),
+    write("the task is already done "),
+    !.
+check(X) :- 
+    \+ task(X, todo),
+    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),
+    retractall(task(X, done)),
+    asserta(task(X, todo)), 
+    write("unchecked task: "),
+    write(X),
+    nl,
+    findall(Parent, requires(X, Parent), L),
+    uncheck_list(L).
+uncheck_list([]).
+uncheck_list([H|T]):-
+    task(H, todo),
+    uncheck_list(T).
+uncheck_list([H|T]):-
+    uncheck(H),
+    uncheck_list(T).
+
+save_requirement(T1, T2, Stream) :-
+    requires(T1, T2),
+    write_canonical(Stream, requires(T1,T2)),
+    write(Stream, '.\n').
+save_requirement_list(T2, [T1], Stream) :- 
+    save_requirement(T1, T2, Stream).
+save_requirement_list(T2,[H|T], Stream) :- 
+    save_requirement(H, T2, Stream),
+    save_requirement_list(T2, T, Stream).
+save_task_requirements(Task, Stream) :- 
+    findall(X, requires(X, Task), L),
+    save_requirement_list(Task, L, Stream).
+save_task_requirements(Task, _) :- \+ requires(_, Task).
 
 
 save_task(Task, Stream) :-
     task(Task, State),
     write_canonical(Stream, task(Task, State)),
-    write(Stream, '.').
+    write(Stream, '.\n'),
+    save_task_requirements(Task, Stream).
 
 save_task_list([Task], Stream) :- 
     save_task(Task, Stream).
-
 save_task_list([H|T], Stream) :- 
     save_task(H, Stream),
-    write(Stream, '\n'),
     save_task_list(T, Stream).
 
+
+
 save :-
     all_tasks(L), 
     open('data.pl', write, Stream),