Using colon-commands inside ternary expression

Question

I have the following lines in my .vimrc

let g = 0
inoremap <silent> <C-g> <C-o>:let g = !g<CR>
inoremap <expr> <C-_> <C-o>(g == 0 ? :undo : :redo)<CR>

I'm trying to emulate an emacs-like undo/redo feature in insert mode. I'm not sure how to escape or use colon-commands inside a ternary expression. Any help would be greatly appreciated.

Answer 1

inoremap (g == 0 ? :undo : :redo)

You are using an expression mapping, so you must return an expression, e.g. in your case a string describing the command you want Vim to perform. That means your mapping should look like this:

inoremap <expr> <C-_> "\<C-o>".(g == 0 ? ':undo' : ':redo'). "\<CR>"

Or, even slightly simplified:

inoremap <expr> <C-_> "\<c-o>".(g ? ':red' : ':u')."\n"

One thing to note is, that I am not sure, that <C-_> will actually work. This might or might not work, depending on whether you are using a Gui version of vim or whatever type of terminal you use. See also the faq