An internal DSL written in Racket Scheme. It is the implementation of a DSL for an "algebra of pictures", published by Peter Henderson in 20021. The publication is named "Functional Geometry" and the original version of the paper was published in 19822.
Abstract. An algebra of pictures is described that is sufficiently powerful to denote the structure of a well-known Escher woodcut, Square Limit. A decomposition of the picture that is reasonably faithful to Escher's original design is given. This illustrates how a suitably chosen algebraic specification can be both a clear description and a practical implementation method. It also allows us to address some of the criteria that make a good algebraic description.
[...] computers, computer science and functional programming were all a lot less powerful than they are today. The idea that one could write an algebraic description, embed it in a functional program, and execute it directly was not new. But it was not then considered a practical programming technique. Now we know better and many examples exist of how practical it can be to simply write denotations of what is to be constructed, rather than to write algorithmic descriptions of how to perform the construction. (emphasis mine)