Prolog extra task

print_expression([]).
print_expression([A|B]) :-
  write(A),
  print_expression(B).

num_length(N, R) :-
    ( N >= 1,N < 10 ) ->  R is 1;
    ( N >= 10,N < 100 ) ->  R is 2;
    ( N >= 100,N < 1000 ) ->  R is 3.

solve(Digit, Total, CurNum, SignCount, Expr, A, B, Goal) :-
    BA is B - A,
    ( BA > 50 ) ->  (   B2 is div(B-A, 2)+A, Goal1 is div(Goal, 2), Goal2 is Goal - Goal1, D2 is B2 + 1,
                    solve(Digit, 0, CurNum, 0, [], A, B2, Goal1),
                    solve(D2, 0, B2, 0, [], B2, B, Goal2));(
    Digit >= A, Digit =< B,D1 is Digit+1,
    number_string(CurNum, Str),
    num_length(Digit, P),
    (
        T1 is Total + CurNum, CurNum1 is Digit, C1 is SignCount+1,  append(Expr, ["+", Str], Expr1);
        T1 is Total - CurNum, CurNum1 is Digit, C1 is SignCount+1, append(Expr, ["-", Str], Expr1);
        CurNum1 is CurNum * (10 ** P) + Digit, T1 is Total, C1 is SignCount,  Expr1 = Expr
    ),
    (
        (
               ( Digit == B,CurNum1 == B,T1 == Goal ) ->   print_expression(Expr1),write("="),writeln(Goal); false
        );
        solve(D1, T1, CurNum1, C1, Expr1, A, B, Goal)
    )
 ).