OCaml piping

piping.ml

type user = int
type task = {
  desc: string;
  priority: int;
  is_finished: bool;
}

let to_string (t : task) : string =
  Printf.sprintf
    "Task { desc: %s; priority: %d; is_finished: %b"
    t.desc
    t.priority
    t.is_finished

let get_user username password : user = 123
let get_tasks user : task list =
  ignore user;
  [
    {desc = "Eat"; priority = 4; is_finished = false};
    {desc = "Sleep"; priority = 6; is_finished = false};
    {desc = "Study"; priority = 2; is_finished = false};
    {desc = "Read"; priority = 2; is_finished = false};
    {desc = "Pay bills"; priority = 3; is_finished = false};
    {desc = "Food shopping"; priority = 1; is_finished = false};
  ]

let rec take n list =
  (* tail call *)
  let rec aux taken remaining n =
    if n = 0 then taken else
      match remaining with
      | [] -> taken
      | hd :: tl -> aux (hd::taken) tl (n-1)
  in
  aux [] list n
  |> List.rev

let get_top_three_ user password =
  let id = get_user user password in
  let tasks = get_tasks id in
  let outstanding = List.filter (fun t -> not t.is_finished) tasks in
  let sorted = List.sort (fun t1 t2 -> if t1.priority > t2.priority then 1 else -1) outstanding in
  let top_three = take 3 sorted in
  top_three

let get_top_three user password =
  get_user user password
  |> get_tasks
  |> List.filter (fun t -> not t.is_finished)
  |> List.sort (fun t1 t2 -> if t1.priority > t2.priority then 1 else -1)
  |> take 3


let () =
  get_top_three_ "user" "password"
  |> List.map to_string
  |> String.concat ", "
  |> print_endline

let () =
  get_top_three "user" "password"
  |> List.map to_string
  |> String.concat ", "
  |> print_endline