Fixing Inference about inference chapter -- partial debugging and workaround about probmods2

[daphnab]

I think the answer may be that the broken Inference about Inference examples should use cache instead of mem. This seems to produce the right behaviour (second example):

///fold:
var getProbs = function(vector) {
  return map(function(i) {return T.get(vector,i)}, _.range(vector.length))
}

var chooseAction = function(goalSatisfied, transition, state) {
  return Infer({method: 'rejection', samples: 1}, function() {
    var action = actionPrior()
    condition(goalSatisfied(transition(state, action)))
    return action;
  })
}
///
var actionPrior = function() {
  return flip(.7) ? ['a'] : ['a'].concat(actionPrior());
}

var goalPosterior = Infer({method: 'rejection', samples: 5000}, function() {
  var buttonsToOutcomeProbs = cache(function(buttons) {return getProbs(dirichlet(ones([2,1])))})
  
  var vendingMachine = function(state, action) {
    return categorical({vs: ['bagel', 'cookie'], ps: buttonsToOutcomeProbs(action)});
  }
  
  var goal = categorical({vs: ['bagel', 'cookie'], ps: [.5, .5]})
  var goalSatisfied = function(outcome) {return outcome == goal};
  var actionDist = chooseAction(goalSatisfied, vendingMachine, 'state');

  var chosenAction = sample(chooseAction(goalSatisfied, vendingMachine, 'state'));

//corrected condition
  condition(vendingMachine('state', ['a', 'a']) == 'cookie' &&
             _.isEqual(chosenAction, ['a', 'a']))
  
  return {goal: goal, 
          once: buttonsToOutcomeProbs(['a'])[1],
          twice: buttonsToOutcomeProbs(['a', 'a'])[1]}
})

print("probability of actions giving a cookie")
viz.marginals(goalPosterior);

[ngoodman]

thanks for all of these suggestions! most were incorporated long ago (forgot to close the issue), but i've also just cleaned this up, and all seem to be working!