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{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TemplateHaskell #-}
module PPL.Internal
( uniform,
Prob (..),
Meas,
score,
scoreLog,
sample,
samples,
newTree,
HashMap,
Tree (..),
)
where
import Control.Monad
import Control.Monad.Trans.Class
import Control.Monad.Trans.Writer
import Data.Bifunctor
import Data.Bits
import Data.IORef
import Data.Monoid
import qualified Data.Vector.Hashtables as H
import qualified Data.Vector.Unboxed.Mutable as UM
import Data.Word
import qualified Language.Haskell.TH.Syntax as TH
import Numeric.Log
import System.IO.Unsafe
import System.Random hiding (split, uniform)
import qualified System.Random as R
type HashMap k v = H.Dictionary (H.PrimState IO) UM.MVector k UM.MVector v
-- Simple hashing scheme into 64-bit space based on mzHash64
data Hash = Hash {unhash :: Word64} deriving (Eq, Ord, Show)
pushbit :: Bool -> Hash -> Hash
pushbit b (Hash state) = Hash $ (0xB2DEEF07CB4ACD43 * fromBool b) `xor` (state `shiftL` 2) `xor` (state `shiftR` 2)
where
fromBool True = 1
fromBool False = 0
initHash :: Hash
initHash = Hash 0xE297DA430DB2DF1A
-- Reimplementation of the LazyPPL monads to avoid some dependencies
data Tree = Tree
{ draw :: !Double,
split :: (Tree, Tree)
}
{-# INLINE newTree #-}
newTree :: IORef (HashMap Word64 Double, StdGen) -> Tree
newTree s = go initHash
where
go :: Hash -> Tree
go id =
Tree
( unsafePerformIO $ do
(m, g) <- readIORef s
H.lookup m (unhash id) >>= \case
Nothing -> do
let (x, g') = R.random g
H.insert m (unhash id) x
writeIORef s (m, g')
pure x
Just x -> pure x
)
(go (pushbit False id), go (pushbit True id))
newtype Prob a = Prob {runProb :: Tree -> a}
instance Monad Prob where
Prob f >>= g = Prob $ \t ->
let (t1, t2) = split t
(Prob g') = g (f t1)
in g' t2
instance Functor Prob where fmap = liftM
instance Applicative Prob where pure = Prob . const; (<*>) = ap
uniform :: Prob Double
uniform = Prob $ \(Tree r _) -> r
newtype Meas a = Meas (WriterT (Product (Log Double)) Prob a)
deriving (Functor, Applicative, Monad)
{-# INLINE score #-}
score :: Double -> Meas ()
score = scoreLog . Exp . log . max eps
where
eps = $(TH.lift (2 * until ((== 1) . (1 +)) (/ 2) (1 :: Double))) -- machine epsilon, force compile time eval
{-# INLINE scoreLog #-}
scoreLog :: Log Double -> Meas ()
scoreLog = Meas . tell . Product
{-# INLINE sample #-}
sample :: Prob a -> Meas a
sample = Meas . lift
{-# INLINE samples #-}
samples :: forall a. Meas a -> Tree -> [(a, Log Double)]
samples (Meas m) = map (second getProduct) . runProb f
where
f = runWriterT m >>= \x -> (x :) <$> f
|
