Bayesian interpretation of medical tests

medtest.cs

public class TestResult
{
    public TestResult(bool isSick, bool testedPositive, double falsePositiveRate)
    {
        IsSick = isSick;
        Positive = testedPositive;
        FalsePositiveRate = falsePositiveRate;
    }

    public bool IsSick;
    public bool Positive;
    public double FalsePositiveRate;

    public string ShowSick
    {
        get
        {
            if (IsSick) return "Sick";
            return "Not Sick";
        }
    }
}

public void ScenarioA()
{
    var falsePositive = from high in BernoulliF(0.5)
                        select high ? 0.4 : 0.2;

    var test = from isSick in BernoulliF(0.1)
               from fp in falsePositive
               let prPositive = isSick ? 0.9 : fp
               from positiveResult in BernoulliF(prPositive)
               select new TestResult(isSick, positiveResult, fp);

    var testedPositive = test.ConditionHard(t => t.Positive);

    var twoPeople = from p1 in testedPositive
                    from p2 in testedPositive
                    select Pair(p1, p2);

    Debug.WriteLine(twoPeople.Histogram(pair => $"{pair.Item1.ShowSick}/ {pair.Item2.ShowSick}"));
}

public void ScenarioB()
{
    var falsePositive = Func(
        (double prHigh) =>
            from high in BernoulliF(prHigh)
            select high ? 0.4 : 0.2
    );

    var test = Func(
        (double prHigh) =>
            from isSick in BernoulliF(0.1)
            from falsePos in falsePositive(prHigh)
            let prPositive = isSick ? 0.9 : falsePos
            from positiveResult in BernoulliF(prPositive)
            select new TestResult(isSick, positiveResult, falsePos)
     );

    var testedPositive = Func((double prHigh) => test(prHigh).ConditionHard(t => t.Positive));

    var updateTest = Func(
        (FiniteDist<TestResult> dist) =>
            from t1 in dist
            let updatedFP = dist.ProbOf(t => t.FalsePositiveRate == 0.4)
            from t2 in testedPositive(updatedFP.Value)
            select t2
     );

    var firstTest = testedPositive(0.5);

    var twoTests =
        from t1 in firstTest
        from t2 in updateTest(firstTest)
        select Pair(t1, t2);

    Debug.WriteLine(twoTests.Histogram(pair => $"{pair.Item1.ShowSick} / {pair.Item2.ShowSick}"));
}