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module Data.MemoUgly(memoIO, memo) where
import Control.Concurrent.MVar
import qualified Data.Map as M
import System.IO.Unsafe(unsafePerformIO)
-- | Memoize the given function by allocating a memo table,
-- and then updating the memo table on each function call.
memoIO :: (Ord a)
=> (a -> b) -- ^Function to memoize
-> IO (a -> IO b)
memoIO f = do
v <- newMVar M.empty
let f' x = do
m <- readMVar v
case M.lookup x m of
Nothing -> do let { r = f x }; modifyMVar_ v (return . M.insert x r); return r
Just r -> return r
return f'
-- | The pure version of 'memoIO'.
memo :: (Ord a)
=> (a -> b) -- ^Function to memoize
-> (a -> b)
memo f = let f' = unsafePerformIO (memoIO f) in \ x -> unsafePerformIO (f' x)
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