monad-bayes-1.2.0: models/Sprinkler.hs

module Sprinkler (hard, soft) where

import Control.Monad (when)
import Control.Monad.Bayes.Class

hard :: (MonadMeasure m) => m Bool
hard = do
  rain <- bernoulli 0.3
  sprinkler <- bernoulli $ if rain then 0.1 else 0.4
  wet <- bernoulli $ case (rain, sprinkler) of
    (True, True) -> 0.98
    (True, False) -> 0.8
    (False, True) -> 0.9
    (False, False) -> 0.0
  condition (not wet)
  return rain

soft :: (MonadMeasure m) => m Bool
soft = do
  rain <- bernoulli 0.3
  when rain (factor 0.2)
  sprinkler <- bernoulli $ if rain then 0.1 else 0.4
  when sprinkler (factor 0.1)
  return rain