Majority Element Algorithm implemented in Haskell

majority.hs

module Majority
( isMajority
, majority
, occurrences
) where

majority :: Eq a => [a] -> Maybe a
majority [] = Nothing
majority  xs'@(x: xs) = if isMajority majority' xs' then Just majority' else Nothing
  where
    -- Find unique candidate for the majority
    (majority', _) = foldr majAcc (x, 1) xs

-- Accumulator function for finding a candidate majority element using foldr
majAcc :: (Eq t, Eq a, Num a) => t -> (t, a) -> (t, a)
majAcc elt (maj, num)
  | elt == maj = (maj, num + 1)
  | num == 0   = (elt, 1)
  | otherwise  = (maj, num - 1)

isMajority :: Eq a => a -> [a] -> Bool
isMajority maj l = (occurrences maj l) > (length l) `div` 2

occurrences :: (Eq a, Num b) => a -> [a] -> b
occurrences a = foldr (\x acc -> if x == a then acc + 1 else acc) 0

main :: IO ()
main = print $ majority [1,1,1,3,1,5]

The general goal here (which may or may not be apparent) was just to use foldr a lot.