This Racket package contains a DrRacket tool that displays a list of the unwritten parts of a program, as determined by the macros that implement those unwritten parts, as well as providing opportunities to write the unfinished parts of the program with compiler support.
In particular, when Check Syntax finds a syntax object during expansion with the 'todo syntax property, then it considers that syntax object to be an incomplete program. After expansion, a panel pops up with a list of tasks to be completed. When it finds an object with the 'editing-command property mapped to a description of the editing command, then the editing commands are provided in a DrRacket right-click menu.
An editing command is an instance of the following prefab struct:
(struct command (name module-path function arguments) #:prefab)
The name is a string to be shown to users in a menu, the module-path will be loaded with dynamic-require to find the implementation of the command, and function (which must be provided by the module) will be called with arguments. If it returns a string, then the string is used to replace the region that was clicked on. Additionally, if function accepts the following keyword arguments, then they will be provided as well: #:string contains the string of the region on which the command was placed, #:definitions is the definitions window, #:editor is the text editor object in which the command was called, and #:file the path to the file being edited.
More control over both the contents of TODO items and placement of both TODO list items and editing commands is available for those with advanced needs. For more information, please consult the docs.
This tool is intended for use with cooperating languages, especially statically typed languages and proof assistants. It is inspired by the hole list in the Agda mode for Emacs as well as the ability of users to add interactive commands to Lean's interactions.
If you're interested in adding holes to your own language, then this tool is worth a try. To use it, run rack pkg install -n todo-list in the directory where it is checked out. Then, in DrRacket, open demo.rkt for a demonstration of editing commands and incomplete programs.
I'm interested in feedback from authors of languages with holes on what kinds of customization will make this tool more useful.
The code that interacts with Check Syntax is based on refactoring tool code from an LWC 2016 paper that describes an implementation of a small Java-like language in Racket. I would like to thank Daniel Feltey, Spencer P. Florence, Tim Knutson, Vincent St-Amour, Ryan Culpepper, Matthew Flatt, Robby Findler, and Matthias Felleisen for their great demo of what is possible in Racket!