Pisano Period in Haskell

pisano_period.hs

-- https://en.wikipedia.org/wiki/Pisano_period

fibs :: [Integer]
fibs = 0 : 1 : zipWith (+) fibs (tail fibs)

pisanoPeriod :: Integer -> Int
pisanoPeriod m = length $ 0 : 1 : helper (drop 2 fibs)
  where
    helper (x:y:xs)=
      if a == 0 && b == 1
        then []
        else a : helper (y:xs)
        where
          a = x `mod` m
          b = y `mod` m