Prolog - sum of row in matrix

An n x n matrix can be represented as a list of n lists, each with n elements, the matrix could actually 1 2 3 4 5 6 7 8 9 written as [[1, 2, 3], [4, 5, 6], [7, 8, 9]].

I need to write a Prolog program to add all the values in each ROW. I am new in Prolog, please help. Thanks in advanced!

Below is what I had done, 开发者_如何学JAVAbut it seems like not working....

sum(X):-
    result(X,0,0,Y),!.

result([H|T],I,J,Length):-
    rowTotal([H|T],J,Sum),
    write('Sum of Row: '),
    write(Sum),nl,
    (not(I = Length)) ->
    (NewI is I + 1,
    result([H|T],NewI,0,Length);!).

rowTotal([H|T],J,Sum):-
    rowValue(H,J,Value),
    rowTotal(T,NewSum),
    Sum is Value + NewSum.

rowTotal([],0).

rowValue([H|T],J,Value):-
    (J < 3) ->
    Value = H,
    NewJ is J+1,
    rowValue([H|T],NewJ,Value).

You don't need counters I and J. Simply unpack the lists as you go. Here's a solution for rowTotal:

rowTotal([], 0).
rowTotal([H|T], Sum) :-
    rowTotal(T, SubTotal),
    Sum is H + SubTotal.

The following tail-recursive solution is a little trickier to get your head around, but is more efficient:

rowSum(L, Sum) :-
    rowResult(L, 0, Sum).

rowResult([], Acc, Acc).
rowResult([H|T], Acc, Sum) :-
    S is H + Acc,
    rowResult(T, S, Sum).

Apply the same technique to implement sum and result.