Encode and decode url algorithm

HttpUriEncode.fs

let toHex (c:char) = Convert.ToInt32(c) |> fun i -> i.ToString("X")
let encode s = 
  let parts = s |> Seq.map (fun c -> "%" + (c |> toHex))
  String.Join("", parts)

let (|HexaChar|_|) (s:char list) =
  if s.Length > 0 && s.Head = '%' then
    let chars = s |> Seq.skip 1 |> Seq.take 2 |> Array.ofSeq
    let h = new String(chars)
    let num = Convert.ToInt32(h, 16)
    let tail = s |> Seq.skip (chars.Length+1) |> List.ofSeq
    Some ((Convert.ToChar num), tail)
  else
    None

let toChars (s:string) =
  [for i in [0..s.Length] -> s.[i]]

let urlDecode (text:string) =
  let rec decode s acc = 
    match s with
    | HexaChar (c, t) -> decode t (c :: acc)
    | c :: t          -> decode t (c :: acc)
    | []              -> new string(acc |> List.rev |> Array.ofList)
  decode (text |> toChars) []