pascal.sml

structure Pascal =
struct
  local
    fun nextrow row = 
      let
        val (ns, _) =
          foldl
            (fn (x, (acc, prev)) => ((prev + x) :: acc, x))
            ([], 0)
            row
      in
        1 :: ns
      end
  in
    fun triangle 1 = [[1]]
      | triangle n =
          let
            val rows = triangle (n - 1)
          in
            nextrow (hd rows) :: rows
          end

    val row = hd o triangle
  end
end