primes :: [Int]
primes = mapMaybe log2 $ fractran prog 2
  where
    prog =
      [ 17 % 91
      , 78 % 85
      , 19 % 51
      , 23 % 38
      , 29 % 33
      , 77 % 29
      , 95 % 23
      , 77 % 19
      , 1 % 17
      , 11 % 13
      , 13 % 11
      , 15 % 14
      , 15 % 2
      , 55 % 1
      ]
    log2 = fmap succ . elemIndex 2 . takeWhile even . iterate (`div` 2)