Very basic, very crude ring buffer in haskell

gistfile1.hs

import Prelude hiding (read)
import qualified Data.Map as Map

type SeqCounter = Int
type MaxBound = Int
data Ring a = Ring (Map.Map Int a) SeqCounter MaxBound

newRing :: Int -> Ring a
newRing mb = Ring Map.empty 0 mb

write :: v -> Ring v -> Ring v
write v ring = Ring nm nc m
  where
    (Ring rm c m) = ring
    nc = c + 1
    nm = Map.insert (nc `mod` m) v rm

read :: Ring m -> Int -> Maybe m
read ring n = Map.lookup (n `mod` mb) rm
  where
    (Ring rm _ mb) = ring

main = do
  putStrLn $ show vals
  where
    mb = 10
    fullRing = foldr write (newRing mb) ['z','y'..'a']
    vals = map (read fullRing) [0..mb * 4]