In a large bowl, sift together the flour, baking powder and salt. In a large bowl, cream the butter with the sugar. Beat in the eggs, 1 at a time, blending thoroughly after each addition. Add the vanilla. Gradually stir in the flour mixture, then fold in the nuts and the chocolate until just blended. Divide the dough into 4 pieces and shape each piece into a 12-inch log. Set the logs on 2 lightly buttered baking sheets and refrigerate until chilled, at least 30 minutes.