sample.ml

(* This is the original function. It works fine, but makes extra calls to check_left and check_right. *)
let sorting_hat id =
  if not (base_case id) then Dead
  else
    begin
      if check_left id && check_right id then Central
      else if check_left id then Left
      else if check_right id then Right
      else Dead
    end

(* 
   One technique that OCaml newbies often overlook is using pattern matching against the components of a 
   tuple to test multiple values at once.  This can give you the ability to convert many long "else if" 
   chains to elegant match expressions. This function is a good candidate for this approach, since it's
   really just a case analysis over the results of check_left and check_right.
   
   Here's a version that uses this technique.  The code only evaluates check_left and check_right once.
   As a bonus, the mutually exclusive case analysis jumps right out at you.
 *)
let sorting_hat id =
  if not (base_case id) then Dead
  else match (check_left id), (check_right id) with
    | true, true -> Central
    | true, false -> Left
    | false, true -> Right
    | _ -> Dead