autocomplete without typing first character

Question

When typing LaTeX one often needs to type a \ to invoke a command such as \omega. One of the nicer features of LaTeX is the ability to define your own commands, which can then be detected by Vim if 'define' is properly set. This will allow completion of these commands with <c-x><c-d>. I would like to avoid typing the \ too often as it is located rather awkwardly on my keyboard. Therefore I would like to be able to type ome<c-x><c-d> and have vim complete that to \omega. In other words, I want to be able to complete a word of which I never typed the first character. Is this even possible using the vim completion function or do I need something more capable?

Just to be clear, I will of course be remapping <c-x><c-d> in this case, as this is still an awkward combination.

Answer 1

Mapping

As recommended by @statox in the comments of the question, this mapping seems to solve your problem

inoremap <c-x><c-d> <esc>bi\<esc>ea<c-x><c-d>

I have tested this mapping. It adds the backslash to the beginning of the word, and then shows you recommended completions (you would then need to select the desired completion manually).

As a frequent LaTeX user myself, I would opt for the following instead:

inoremap <c-x><c-d> <esc>bi\<esc>ea<C-n>

This does the same thing as the original mapping but automatically selects the first completion. I like this solution the best and have added this particular mapping to my own ftplugin/tex.vim file. (I have, however, replaced <c-x><c-d> with <C-l>.)

UltiSnips

I would recommend you check out UltiSnips. This plugin is overkill if you are only looking to use one or two mappings, but if you're open to a small time investment in exchange for a much more powerful solution, this is probably what your looking for.

You'll have to refer to the official documentation for all of the nitty-gritty details.

Basically, after you install the plugin, create a file called ~/.vim/my-snippets/UltiSnips/tex.snippet containing the following lines:

snippet ome "\omega"
\omega
endsnippet

Now, when editing a .tex file, you should be able to type ome followed by a <tab> and it will expand to \omega.

Given that it only saves you two keystrokes, this is a waste of a mapping if you ask me. But to each his own I guess.

Alternative Snippet: (as mentioned in the comments)

snippet cmd "\<command>"
\\${1:command}
endsnippet