THE TEST (entrypoint is then)

main.nix

# https://app.codility.com/programmers/lessons/3-time_complexity/tape_equilibrium/
with builtins;
rec {
  theFn = l:
    theFnRecur l 0;

  theFnRecur = l: i:
  let
    len = length l;
  in if len >= i then
    let
      this = diff l i;
      next = theFnRecur l (i + 1);
    in 
    if this < next 
    then this 
    else next
  else 999999;

  diff = l: i:
  let
    size = length l;
    left = sumUntil l (i - 1);
    right = sumUntil (reverse l) (size - i - 1);
    value = left - right;
  in abs value;
  # assert i < size

  sumUntil = l: i:
  if i <= 0 
  then (head l) 
  else
    (head l) + (sumUntil (tail l) (i - 1));

  reverse = l:
  if (length l) == 0 
  then [] 
  else (reverse (tail l)) ++ [(head l)];

  # assert (theFn [3 1 2 4 3] == 1)
  abs = n: if n < 0 then n * -1 else n;
}