🚀 go-pugleaf

You should look at Sebastian Kremer's "[La]TeX name completion package", 
containing:    README tex-complete.el latex-names.el tex-names.el
I use it quite successfully with the usual latex-mode.

Part of the README shows off the interface:

    Example of name completion in an Emacs TeX/LaTeX buffer:

	TeX:        Type 'C-\' and 'c e TAB RET' to insert '\centerline'
		    Type 'C-\' and 'h e TAB RET' to insert '\heartsuit'

	LaTeX:      Type 'C-\' and 'c e TAB RET' to insert '\centering'

		    Type 'C-c C-m' and 'a b TAB RET' to make an
		    `abstract' environment

		    Type 'C-c i' and 'a b TAB RET' to insert the beginning
		    of an `abstract' environment

I imagine it has been archived (Dave Sill: care to supply citation?).
Sebastion posted it 20 Jun 90.

Of course, just using an existing package won't lead you into deeper wisdom
about the wheres and wayfors of elisp.   ;-)

- Pres
- -------
->        David L. Presberg, Compass, Inc.                           <-
->Domain: presberg@compass.com                                       <-
-> .5&.5: compass!presberg@think.com                                 <-
->uucp:   {think,bu.edu,cvbnet}!compass!presberg                     <-
->Nicname:    Pres                                                   <-