Good question. Disclaimer: I’m in the lab that made Gen & was on the paper, so not impartial :) Anglican is implemented in Clojure, and can be extended (by wri

Good question. Disclaimer: I’m in the lab that made Gen & was on the paper, so not impartial :) Anglican is implemented in Clojure, and can be extended (by writing new Clojure code) to support new general-purpose inference engines. Creating those extensions requires an understanding of both the statistics and the PL concepts used in Anglican’s backend; you are essentially writing a new interpreter for arbitrary Anglican code. Gen provides high level abstractions for writing custom inference algorithms for _specific models/problems_ (not entire general-purpose inference engines). Those abstractions don’t require reasoning about PL concepts like continuation-passing style, nor do they require the user to do any math by hand. Of course, since Gen is just Julia code, you can still reach in and implement new inference engines (just as in Anglican/Clojure) if you’re an expert. But I wouldn’t expect people who are not probabilistic programming researchers to do this (in either Anglican or Gen).