Thank you all so much for your comments (the resulting discussion was also
entertaining and unexpected).

If I were to implement path auto-completion, would it be useful if it
wasn’t integrated into DrRacket? I am not precisely sure what I would be
adding this functionality to if not DrRacket.

On Sunday, October 22, 2017, Neil Van Dyke <> wrote:

> I could be missing something, but I think a filename completion procedure
> (not the DrRacket integration part) might be a doable exercise for a
> budding Racket programmer, so long as they already have a basic familiarity
> with using the filesystem and shell as a normal user.
> Point them to the "Paths" and "Filesystem" sections of the Racket
> Reference, and tell them they just need a few procedures from each
> (probably including `split-path` and `directory-list`).
> They might want to first make a procedure like this:
> (path-completions path-or-string?)
> ==> (listof completion-string)
> And then make a second procedure, which uses the first procedure, then
> adds an additional step, to let it return two values instead of one:
> (path-completion-prefix-and-suffixes path-or-string?)
> ==> (values prefix-string-shared-by-all-completions
>             (listof completion-remainder-after-any-shared-prefix-string))
> Then, when a user is interactively doing completion (like when they hit
> the Tab key in a shell), the first value returned by that second procedure
> is what would get added automatically to the path.  The second value is the
> list of possible completions following that shared prefix.
> There are a few special cases to consider, but most should be easy to
> recognize and work through, just by thinking methodically about each point
> in your code.  For example, what do you do when the input path is relative,
> or when when there are no completions, or when the path is invalid or
> nonexistent or permissions-inaccessible, or when your path is already
> complete.  One case that's not obvious from the code: if the path is
> already complete and is a directory, a shell usually completes a directory
> separator, so consider whether you want to do that.
> To make unit tests for these, they'll have to also look at more of the
> "Filesystem" section of the Racket Reference, to create and remove files
> and directories.
> (I think wrapping a shell process, robustly, is much more difficult.)
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