数据抽象和过程抽象

数据抽象和过程抽象

越来越觉得erlang是个好工具，天生的符号抽象能力，几乎和scheme不相上下

pow(D, N) ->
            pow_iter(normalize(D), D, N).

    pow_iter(R, _, 0) ->
            R;
    pow_iter(R, D, N) ->
            case N rem 2 of
                1 ->
                    pow_iter(mul(R, D), D, N - 1);
                0 ->
                    pow_iter(R, mul(D, D), N div 2)
            end.
    normalize([[_X11, _X12],[_X21, _X22]]) ->
            [[1,0],[0,1]];
    normalize([_X,_Y]) ->
            [1,1];
    normalize(_) ->
            1.
    mul([[X11, X12],[X21, X22]],[[Y11,Y12],[Y21, Y22]]) ->
            [[X11 * Y11 + X12 * Y21, X11 * Y12 + X12 * Y22],
             [X21 * Y11 + X22 * Y21, X21 * Y12 + X22 * Y22]];
    mul([X1,Y1], [X2,Y2]) ->
            X1 * Y2 - X2 * Y1;
    mul(A, B) ->
            A * B.
    fib(N) when N > 0 ->
            [[F,_],[_,_]] = pow([[1,1],[1,0]], N - 1),F;
    fib(_) ->
            0.