module Exam2011

type name = string
type phone = int
type level = int

type description = phone * level
type register = (phone * description) list

let reg = [("Joe",(10101010,4));
           ("Sal",(11111111,2));
           ("Sam",(12121212,7));
           ("Jane",(13131313,1))]

let rec getPhone n r =
  match r with
  | [] -> failwith "Register"
  | (n', (p,_))::xs -> if n = n' then p else getPhone n xs

let delete = function
  | (n,r) -> List.foldBack (fun acc e ->
                              match e with
                              | (n', _) -> if n=n' then acc else e :: acc) r []

let getCandidates le r =
  List.fold
    (fun acc r' ->
      match r' with
      | (n,(p,le')) when abs(le-le') < 3 -> (n,p)::acc
      | _ -> acc) [] r