(***********************)
(* The Pipe Combinator *)
(***********************)

let (|>) x f = f x ;;

(************************)
(* The Pair Combinators *)
(************************)

let both   f (x,y) = (f x, f y);;
let do_fst f (x,y) = (f x,   y);;
let do_snd f (x,y) = (  x, f y);;

(**************************)
(* Pipelines:  An Example *)
(**************************)

let even x = (x/2)*2 == x;;

let process (p : float * float) =
  p |> both int_of_float	(* convert to float *)
    |> do_fst ((/) 3)		(* divide fst by 3  *)
    |> do_snd ((/) 2)		(* divice snd by 2  *)
    |> both even		(* test for even    *)
    |> fun (x,y) -> x && y	(* both even	    *)
;;

(********************)
(* Grade Processing *)
(********************)

type student = {first: string; last: string; assign: float list; final: float};;

let students : student list =
  [{first="Sarah"; last="Jones"; assign=[7.0;8.0;10.0;9.0];final=8.5};
   {first="Qian"; last="Xi"; assign=[7.3;8.1;3.1;9.0];final=6.5};
   {first="Naga"; last="Katta"; assign=[7.3;8.1;3.5;9.0];final=7.0}
  ]
;;

(* Task:  Create a function display that does the following:
 * for each student, print the following:
 * last name, first name: score
 *
 * where score is computed by averaging the assignments and giving the
 * assignment average 1/2 the weight of the final
 *
 * the students are sorted by score and displayed
 *)

let compute_score {first=f; last=l; assign=grades; final=exam} =
  let score grades exam = 
    List.fold_right 
      (fun x (number,total) -> (number+1,total+.x)) grades (0,0.0)
  in  
  let (number, total) = score grades exam in
  (f, l, total /. float_of_int number)
;;

let student_compare (_,_,score1) (_,_,score2) =
  if score1 < score2 then 1
  else if score1 > score2 then -1
  else 0
;;

let stringify (first, last, score) = 
  last ^ ", " ^ first ^ ": " ^ string_of_float score;;

let display (ss : student list) : unit =
  ss |> List.map compute_score
     |> List.sort student_compare
     |> List.map stringify 
     |> List.iter print_endline
;;