Debugging Probabilistic Programs

Many applications compute with estimated and uncertain data. While advances in probabilistic programming help developers build such applications, debugging them remains extremely challenging. New types of errors in probabilistic programs include 1) ignoring dependencies and correlation between random variables and in training data, 2) poorly chosen inference hyper-parameters, and 3) incorrect statistical models. A partial solution to prevent these errors in some languages forbids developers from explicitly invoking inference. While this prevents some dependence errors, it limits composition and control over inference, and does not guarantee absence of other types of errors. This paper presents the FLEXI programming model which supports constructs for invoking inference in the language and reusing the results in other statistical computations. We define a novel formalism for inference with a Decorated Bayesian Network and present a tool, DePP, that analyzes this representation to identify the above errors. We evaluate DePP on a range of prototypical examples to show how it helps developers to detect errors.