gistfile1.hs

module Net.LambdaSpider.RollingSum (RollingSum, new, current, add) where

import           Data.Foldable (fold)
import           Data.Monoid
import           Data.Sequence
import           Prelude       hiding (length)

data RollingSum a b = RollingSum Int (Seq a) (a -> Int -> b)

instance Show a => Show (RollingSum a b) where
  show (RollingSum c s n) = show ("rollingsum", c, s)

new :: Monoid a => Int -> (a -> Int -> b) -> RollingSum a b
new capacity divider
  | capacity < 1 = error "oh get stuffed"
  | otherwise    = RollingSum capacity empty divider

current :: Monoid a => RollingSum a b -> b
current (RollingSum _ queue divider) = divider (fold queue)  (length queue)

add :: RollingSum a b -> a -> RollingSum a b
add (RollingSum capacity queue f) el
   | length queue < capacity = RollingSum capacity (el <| queue) f
   | otherwise               = case viewr queue of
     EmptyR          -> error "this can never happen"
     (stripped :> _) -> RollingSum capacity (el <| stripped) f

instance Monoid Int where
 mempty=0
 mappend=(+)