add racket-pcomplete

[suzzvv]

When you use eshell-mode or shell-mode as your main shell, racket and raco command completion is convenient. Emacs use pcomplete for command completion, so I add this.

For now, I just add pcomplete/raco. If you think the code should be merged, I will add pcomplete/racket.

[greghendershott]

Thank you very much for this pull request. I like the idea of providing shell completion.

Before I merge, may I ask about another idea, how to do this?

It would be elegant to discover all the raco commands and their options, programmatically. That way, as users install more tools, and/or the tools add more options, it would be correct automatically (compared to updating the static list).

How to find the tools? It looks like the following returns a list of information about all installed tools:

(require raco/all-tools)
(all-tools)

How about the command-line options for each tool? This is trickier. Two ideas:

1. Probably most tools use the command-line form. It might not be too difficult to find that in the tool's source? (Weak point: Not all tools use command-line at all. Some use it only via some fancy macros, which I think is the case for raco pkg.)
2. Run the tools with the -h flag and parse the text output. Weak point: Parsing text is a bit kludgy. Good point: It works for all tools that provide help. If they use command-line, the help format is very consistent.

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However. Maybe I'm over-thinking this. If you think this idea is too complicated or too difficult, then I should simply merge the PR as-is. :)

[suzzvv]

Hi.
Thanks your advices.
I came to racket recently, and I can't get the big picture of racket now. For me now, it's not convenient to type in eshell when there is no completion.
I will make the code better when I get family with it.