triangleWorker n lastval = let current = n + lastval
                           in [current] ++ triangleWorker (n + 1) current
triangleWorker n lastval = let current = n + lastval
                           in [current] ++ triangleWorker (n + 1) current
triangleWorker n lastval = let current = n + lastval
                           in [current] ++ triangleWorker (n + 1) current