Commit 5ce3af69 authored by Hans-Peter Deifel's avatar Hans-Peter Deifel 🐢
Browse files

wta: Don't use floats for probability 

This switches from floats to a sort of arbitrary precision base10 floating point
implementation where we can easily generate uniform random numbers.

The problem with floats is that they aren't distributed equally across the whole
range and thus a random number in [0, 1) is not uniform.
parent bb0d6c9b

copar.cabal

+1 −0
Original line number Diff line number Diff line
@@ -289,6 +289,7 @@ executable random-wta 
  other-modules:       Types

                     , Generator

                     , Output

                     , Probability

  default-language:    Haskell2010

  default-extensions:  OverloadedStrings

                     , LambdaCase

src/random-wta/Generator.hs

+3 −4
Original line number Diff line number Diff line
@@ -13,10 +13,11 @@ import Data.Maybe 
import           Data.Foldable



import           Types hiding (spec)

import           Probability



data GeneratorConfig m = GeneratorConfig

   { spec :: WTASpec m

   , zeroFreq :: Double

   , zeroFreq :: Probability

   }



type Generator m = ReaderT (GeneratorConfig m) IO
@@ -42,9 +43,7 @@ aritySummand arity = do 


decideZero :: Generator m Bool

decideZero = do

  freq <- asks zeroFreq

  randomValue :: Double <- liftIO (randomRIO (0.0, 1.0))

  return $ randomValue < freq

  asks zeroFreq >>= liftIO . decide



-- Generates Nothing, when it decides that a zero value would be in order

genTransition :: Int -> Int -> [State] -> Generator m (Maybe (Transition m))

src/random-wta/Main.hs

+4 −3
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ import System.IO 
import           Types

import           Generator

import           Output

import           Probability



data SomeMonoid = forall m. SomeMonoid (MonoidType m)
@@ -29,7 +30,7 @@ data Opts = Opts 
  { optMonoid :: SomeMonoid

  , optStates :: Int

  , optSymbols :: SymbolSpec

  , optZeroFrequency :: Double

  , optZeroFrequency :: Probability

  , optRandomState :: Maybe StdGen

  }
@@ -82,10 +83,10 @@ parseOpts = 
               "Comma separated list of symbols per arity. E.g. 2,0,1 means two symbols with arity 0, non with arity 1 and one with arity two"

          )

    <*> Options.option

          Options.auto

          (Options.eitherReader readProbability)

          (  Options.long "zero-frequency"

          <> Options.showDefault

          <> Options.value 0.7

          <> Options.value (Probability 7 1)

          <> Options.metavar "FREQ"

          <> Options.help

               "Frequency of edges with zero weight as number between 0 and 1."

src/random-wta/Probability.hs

0 → 100644
+31 −0
Original line number Diff line number Diff line 
{-# LANGUAGE GeneralizedNewtypeDeriving #-}



module Probability (Probability(..), readProbability, decide) where



import           System.Random

import           Text.Printf



data Probability = Probability Integer Int



readProbability :: String -> Either String Probability

readProbability input = case input of

  "0" -> Right (Probability 0 0)

  ('0':'.':rest) -> case reads rest of

    [(digits, "")] -> Right (Probability digits (length rest))

    _ -> failure

  "1" -> Right (Probability 1 0)

  ('1':'.':rest)

    | all (=='0') rest -> Right (Probability 1 0)

    | otherwise -> failure

  _ -> failure



  where failure = Left "Could not parse probability"



instance Show Probability where

  show (Probability digits 0) = show digits

  show (Probability digits exp) = "0." ++ printf "%0*d" exp digits



decide :: Probability -> IO Bool

decide (Probability digits exp) = do

  randomNumber <- randomRIO (0, (10^exp)-1)

  return $ randomNumber < digits