Piet is a programming language in which programs look like abstract paintings. The language is named after Piet Mondrian, who pioneered the field of geometric abstract art. I would have liked to call the language Mondrian, but someone beat me to it with a rather mundane-looking scripting language.

I wrote the Piet specification a long time ago, and the language has taken on a bit of a life of its own, with a small community of coders writing Piet programs, interpreters, IDEs, and even compilers. I have not written any "authoritative" interpreter, and the different ones available sometimes interpret the specification slightly differently.

Piet uses a stack for storage of all data values. Data values exist only as integers, though they may be read in or printed as Unicode character values with appropriate commands. The stack is notionally infinitely deep, but implementations may elect to provide a finite maximum stack size. If a finite stack overflows, it should be treated as a runtime error, and handling this will be implementation dependent.