webppl example

example.wppl

var g0 = 'Hello, World!'
var g1 = 'Howdy, universe!'
var g2 = 'Oh no, not again!'

var greeting = function(sunny) {
  return function() {
    var greetingChoice =  sunny ? flip(0.6) : flip(0.2)
    var altAnswer = sunny ?  g1 : g2
    return greetingChoice ? g0 : altAnswer
  }
}
var predictGreeting = function(sunnyDist) {
  return function() {
    var x = sample(sunnyDist);
    return greeting(x)()
  }
}

var sunnyTomorrow = function(sunnyToday) {
  return function() {
    var pSunny = sample(sunnyToday) ? 0.8 : 0.05
    return flip(pSunny)
  }
}

var predictGreetingToday = function () {
  var sunnyToday = flip(0.2)
  return greeting(sunnyToday)()
}

var inferWeatherToday = function (observedGreeting) {
  return function() {
    var sunnyToday = flip(0.2);
    var greet = greeting(sunnyToday)
    condition(greet() == observedGreeting)
    return sunnyToday
  }
}

var LearnandPredict = function (observedGreeting) {
  return function() {
    // Infer today's weather
    var sunnyToday = Infer({method: 'rejection', samples: 1000}, 
                            inferWeatherToday(observedGreeting))
    // Predict tomorrow's weather
    var sTomorrow = Infer({method: 'forward', samples: 1000},
                          sunnyTomorrow(sunnyToday))
    // Predict tomorrow's greeting
    var gTomorrow = Infer({method: 'forward', samples:1000},
                           predictGreeting(sTomorrow))
    return gTomorrow
  }
}
// Predict today's greeting
viz(repeat(100, predictGreetingToday))

var g_obs = g2
// Infer today's weather based on an observed greeting
viz(Infer({method: 'rejection', samples: 1000}, inferWeatherToday(g_obs)))

// Predict tomorrow's weather based on an observed greeting
viz(LearnandPredict(g_obs)())