This is a toy probabilistic programming system written in beautiful racket, which is by no means efficient or even safe. The goal is to gain more insight in the mechanics of step-by-step probabilistic computation, with language constructs for sampling and bayesian inversion.
Install docker on your machine if not running Linux. The system has been tested on Debian (bullseye) and Arch Linux.
Make sure you have installed git, racket, and sqlite3.
Also install beautiful-racket by executing the following command:
$ raco pkg install beautiful-racket
After cloning this repository and changing the working directory to it, run
$ raco pkg install
to install the programming system.
After cloning this repository, build a docker image by executing the following command within the local repository:
$ docker build -t debian:simpl .
If successful, the docker image you just installed shows up in the list of images:
$ docker image list
REPOSITORY TAG IMAGE ID ...
debian simpl N ...
You can run the image in an interactive container by doing
$ docker run -it N
Run the unit tests with
$ raco test tests
Note that in some test cases, sampled values are checked to be within a certain range, and may fail with some low but nonzero probability. This is to be expected.
There are some examples available in the directory examples.
The file normal-sampling.rkt, for example, samples 1000 times from a normal(100,20) distribution and calculates the sample mean and sample variance.
$ racket examples/normal-sampling.rkt
The result should be approximately (100 20).
The first line of normal-sampling.rkt is
#lang simpl
This tells racket that it is supposed to interpret the rest of the file as the simple imperative minimalist programming language that is this tool.
The file gender-height.rkt contains a probabilistic model for a simple Bayesian inference procedure on the Bernoulli distributed random variable for the gender of a person, conditioned on the fact that we observe a height of 190 cm.
$ racket examples/gender-height.rkt
The first line contains #lang simpl/sybex, which tells racket to do symbolic execution, rather than concrete.
The result will thus (always) be
(list
(end-config 1 9.684491216181099e-5 '((< X_0 0.496)))
(end-config 0 0.008598284478336488 '((not (< X_0 0.496)))))
The structures end-config contain respectively the return value (1 and 0 here), the likelihood of the outcome, and the path condition.
The path condition is expressed using symbolic random variables, in this case X_0.