Yang Hui's triangle, Pascal's triangle in F#

yanghui.fs

let rec getNext' (line : int list) result i =
    if i < (List.length line) - 1 then
        getNext' line ((line.[i] + line.[i + 1]) :: result) (i + 1)
    else
        1 :: result

let getNext line =
    getNext' line [1] 0

let rec get' n result i =
    if i = 1 then
        get' n ([1] :: result) (i + 1)
    elif i = 2 then
        get' n ([1; 1] :: result) (i + 1)
    elif i <= n then
        get' n ((getNext (List.head result)) :: result) (i + 1)
    else
        List.rev result

let get n =
    get' n [] 1


// test
printfn "%A" (get 10)
(*
output:
[[1]; [1; 1]; [1; 2; 1]; [1; 3; 3; 1]; [1; 4; 6; 4; 1]; [1; 5; 10; 10; 5; 1];
   [1; 6; 15; 20; 15; 6; 1]; [1; 7; 21; 35; 35; 21; 7; 1];
      [1; 8; 28; 56; 70; 56; 28; 8; 1]; [1; 9; 36; 84; 126; 126; 84; 36; 9; 1]]
*)