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{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TemplateHaskell #-}
module PPL.Internal
( uniform,
split,
Prob (..),
Meas,
score,
scoreLog,
sample,
randomTree,
samples,
mutateTree,
)
where
import Control.Monad
import Control.Monad.IO.Class
import Control.Monad.Trans.Class
import Control.Monad.Trans.Writer
import Data.Bifunctor
import Data.Monoid
import qualified Language.Haskell.TH.Syntax as TH
import Numeric.Log
import System.Random hiding (split, uniform)
import qualified System.Random as R
-- Reimplementation of the LazyPPL monads to avoid some dependencies
data Tree = Tree !Double [Tree]
split :: Tree -> (Tree, Tree)
split (Tree r (t : ts)) = (t, Tree r ts)
{-# INLINE randomTree #-}
randomTree :: RandomGen g => g -> Tree
randomTree g = let (a, g') = random g in Tree a (randomTrees g')
where
randomTrees g = let (g1, g2) = R.split g in randomTree g1 : randomTrees g2
{-# INLINE mutateTree #-}
mutateTree :: RandomGen g => Double -> Double -> g -> Tree -> Tree
mutateTree p q g (Tree a ts) =
let (r, g1) = random g
(b, g2) = random g1
in if r >= p
then Tree a (mutateTrees p q g1 ts)
else
if r < p * q
then Tree (1 - a) (mutateTrees p q g1 ts)
else Tree b (mutateTrees p q g2 ts)
where
mutateTrees p q g (t : ts) =
let (g1, g2) = R.split g
in mutateTree p q g1 t : mutateTrees p q g2 ts
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 $ \(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
|
