Untitled

Creating a compound iterator in F#
seq {
    for y1 = 0 to BOARDSIZE-1 do
        for x1 = 0 to BOARDSIZE-1 do
             for dy = -2 to 2 do
                 for dx = -2 to 2 do
                     let x2 = x1 + dx;
                     let y2 = y1 + dy;
                     let currentMove = new MoveStruct(x1, y1, x2, y2);
                     if (currentMove.SomeCondition = true) then
                             yield currentMove;
   }

let AllCells =
    seq {
        for y=0 to BOARDSIZE-1 do
            for x=0 to BOARDSIZE-1 do
                yield (x,y);
    };

let LegalMovesAround(x1,y1) =
    seq {
      if board.[x1, y1] = WHITE then
        for dy = -2 to 2 do
          for dx = -2 to 2 do
                let x2 = x1 + dx;
                let y2 = y1 + dy;
                let currentMove = new MoveStruct(x1, y1, x2, y2);
                if (currentMove.DetermineMoveType <> MoveType.ILLEGAL
                    && board.[x2, y2] = NONE) then
                        yield currentMove;
     }

let validMoves =
    AllCells
    |> Seq.collect LegalMovesAround
    |> Seq.distinct

let allLegalMoves = seq {
  for cell in AllCells do
    yield! LegalMovesAround cell
}

seq {
    for x,y in Allcells do
        yield! LMA(x,y)
}