Re: a suggested solution for better external' completion in certain emacs modes

[Nic Ferrier <nferrier@tapsellferrier.co.uk>]

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Richard Stallman <rms@gnu.org> writes:

>     - Readline advertises to Emacs the functions the current program
>       supports  by writing the information (a sexp?) to the stream
>
> I am not quite sure what this means.  What questions would this
> information answer?  Could you give an example?

Sure.

Let's imagine I want to start psql (the PostgreSQL command line
client) in Emacs. This is what might happen, given my suggestion:

Emacs does:  READLINE_CTRL=API psql somedb

This opens the normal stream between the two programs, but puts
libreadline into 'api' mode


psql/Readline sends: (readline-api rl_insert_text 
                                   rl_delete_text
                                   rl_copy_text
                                   rl_kill_text
                                   rl_complete  
                                   rl_possible_completions
                                   rl_insert_completions)


This tells Emacs what function calls the readline program can accept.

The next step is that the user gives some input to emacs:

   select * from 

and then she presses C-TAB (the completion key). Emacs doesn't know
how to complete the line but it does know that psql/Readline supports
rl_complete so:

Emacs sends: (rl_complete "select * from ")

psql/Readline accepts the command, performs it and then:

psql/Readline sends: ("invoices" "orders" "expenses" "users")

and Emacs can display the completion list. The user types an "i" and
presses C-TAB so now....

Emacs sends: (rl_complete "select * from i")

and psql/Readline responds with: ("nvoices")

so now there is only one completion item Emacs can display the line:

    select * from invoices

At some point the user presses enter and Emacs passes the line to
psql/Readline again in some form that causes psql/Readline to execute
the line and send the output to the stream.



This would be a very cool way to solve the problem of getting at
completion services provided by, in particular, Readline enabled
programs.

It would require quite a lot of work to make Readline do it though.


-- 
Nic Ferrier
http://www.tapsellferrier.co.uk