This is a partial implementation of Sims K. Artificial Evolution for Computer Graphics. Computer Graphics, 25(4), July 1991, pp. 319-328. That is to say, it creates randomly-generated pretty pictures. It comes in three flavors:

• PrettyViewer as a simple standalone macOS application that shows a randomly generated picture. Recycle the process to see a new one.
• pretty-picture is a CLI utility to render a randomly generated or user-specified image expression to PNG.
• pretty-screen is a macOS screen saver.

• Up-to-date macOS, Xcode
• gtest -- check out this repo with --recurse-submodules.
• libpng -- expected to be found in /usr/local/include and /usr/local/lib.