[This example was created for the 2023 Racket Summer Event.]
The Racket Programming Language has an excellent cross-platform GUI that doesn't get as much attention as it deserves. In this example, I describe one way to implement a drag-and-drop protocol using the Racket GUI. Although not required, it will be helpful to have basic familiarity with the Racket GUI and its classes.
This is a literate program. That means that the source code produces both the program and its documentation using the same files. Racket's literate programming language, called scribble/lp2, separates the code from the documentation and processes each of them appropriately.
To run the program, open the literate-drag-and-drop.scrbl file in DrRacket and click on “Run”. You can also run racket literate-drag-and-drop.scrbl from the command line. To generate HTML documentation, either open the literate-drag-and-drop.scrbl file in DrRacket and click on “Scribble HTML” or run scribble +m literate-drag-and-drop.scrbl from the command line.
For your convenience, the HTML version of the document is available at https://zamora.github.io/literate-drag-and-drop-docs.