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{- |
Module : Sample.Memo
Copyright : (c) Eduard Sergeev 2013
License : BSD-style (see the file LICENSE)
Maintainer : eduard.sergeev@gmail.com
Stability : experimental
Portability : non-portable
More advanced examples
-}
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances,
TypeFamilies, TypeSynonymInstances #-}
module Example.Customisation.Vector
(
-- * Custom `VectorMemo`
-- $UnboxedTupleVector
BoolInt,
evalFibSTUV,
runFibSTUV,
evalFibIOUV,
runFibIOUV
) where
import Control.Monad
import Control.Monad.ST
import Control.Monad.Primitive
import qualified Data.Vector.Unboxed as UV
import qualified Data.Vector.Unboxed.Mutable as UM
import Data.MaybeLike
import Control.Monad.Memo.Class
import Control.Monad.Trans.Memo.ReaderCache
import Control.Monad.Memo.Vector
fibm 0 = return 0
fibm 1 = return 1
fibm n = liftM2 (+) (memo fibm (n-1)) (memo fibm (n-2))
{- $UnboxedTupleVector
New custom types, not handled by "Control.Monad.Trans.Memo.Vector.Instances", can be used inside `VectorCache` if necessary.
For example if we need a full range of `Int` (including `minBound` and `maxBound`) we can represent `Maybelike` `Int` as a pair @(Bool,Int)@ with `nothing` indicated by the @False@ value of its first element. `Data.Vector.Unboxed.Mutable.MVector` can store such pair efficiently (internally as a pair of unboxed arrays) so all we have to do then is to define `MaybeLike` and `VectorMemo` instances for our product-type.
-}
-- | Unboxed `Int` which can memoize entire range of `Int` values
-- by indicating `nothing` values by setting its first element to @False@
type BoolInt = (Bool,Int)
-- | MaybeLike instance for our unboxed Int
instance MaybeLike BoolInt Int where
nothing = (False,0)
isNothing (b,_) = not b
just a = (True,a)
fromJust (True,a) = a
-- | UVectorMemo instance will allow us to use all @eval*@ and @run*@ functions
-- from unboxed part of "Control.Monad.Trans.Memo.Vector" module
instance UVectorMemo Int BoolInt
-- | Use standard function once we defined the instance for `VectorMemo`
evalFibSTUV :: Int -> Int
evalFibSTUV n = runST $ evalUVectorMemo (fibm n) (n+1)
runFibSTUV :: Int -> (Int, UV.Vector (Bool,Int))
runFibSTUV n = runST $ do
(a,vec) <- runUVectorMemo (fibm n) (n+1)
ivec <- UV.unsafeFreeze vec
return (a, ivec)
evalFibIOUV :: Int -> IO Int
evalFibIOUV n = evalUVectorMemo (fibm n) (n+1)
runFibIOUV :: Int -> IO (Int, UV.Vector (Bool,Int))
runFibIOUV n = do
(a, vec) <- runUVectorMemo (fibm n) (n+1)
ivec <- UV.unsafeFreeze vec
return (a, ivec)
|
