module SWCache(Cache, mkCache, cache, findC) where

-- XXX make sure list gets trimmed

import Graphics.UI.WX

data Cache a b = C Int (Var [(a, b)])

mkCache :: Int -> IO (Cache a b)
mkCache size = do
    vcache <- varCreate []
    return (C size vcache)

cache :: a -> b -> Cache a b -> IO ()
cache a b (C size vcache) = do
    l <- varGet vcache
    varSet vcache (take size ((a, b) : l))

findC :: (Eq a) => a -> Cache a b -> IO (Maybe b)
findC a (C _ vcache) = do
    l <- varGet vcache
    let (r, l') = look a l []
    varSet vcache l'
    return r

-- Find a value and move entry to front if found.
look a [] xs = (Nothing, reverse xs)
look a (ab@(a',b):abs) xs =
    if a == a' then
	(Just b, ab : reverse xs ++ abs)
    else
	look a abs (ab:xs)