(* ****** ****** *)
//
#include
"share/atspre_define.hats" // defines some names
#include
"share/atspre_staload.hats" // for targeting C
#include
"share/HATS/atspre_staload_libats_ML.hats" // for ...
//
(* ****** ****** *)
//
extern
fun
Zig_zag_matrix(n: int): void
//
(* ****** ****** *)

fun max(a: int, b: int): int =
  if a > b then a else b

fun movex(n: int, x: int, y: int): int =
  if y < n-1 then max(0, x-1) else x+1

fun movey(n: int, x: int, y: int): int =
  if y < n-1 then y+1 else y

fun zigzag(n: int, i: int, row: int, x: int, y: int): void =
  if i = n*n then ()
  else
    let
      val () = (if x = row then begin print i; print ','; end else ())
      //val () = (begin print x; print ' '; print y; print ' '; print i; print ' '; end)
      val nextX: int = if ((x+y) % 2) = 0 then movex(n, x, y) else movey(n, y, x)
      val nextY: int = if ((x+y) % 2) = 0 then movey(n, x, y) else movex(n, y, x)
    in
      zigzag(n, i+1, row, nextX, nextY)
    end

implement
Zig_zag_matrix(n) =
  let
    fun loop(row: int): void =
      if row = n then () else
        let
          val () = zigzag(n, 0, row, 0, 0)
          val () = println!(" ")
        in
          loop(row + 1)
        end
  in
    loop(0)
  end

(* ****** ****** *)

implement
main0() = () where
{
  val () = Zig_zag_matrix(5)
} (* end of [main0] *)

(* ****** ****** *)