How can I have <C-E> and <C-Y>'s normal mode functionalities also work in insert mode?

Question

Once I've asked a general question about special characters, but I've not really pulled anything out of it.

So now I'm asking a very specific question.

I want to have Ctrl+e and Ctrl+y behave in insert mode as they do in normal mode.

(Yes, I have looked at :help i_CTRL-E and :help i_CTRL-Y, but I have no idea when such a functionality will ever be useful to me, so I'd happily drop it in favour of normal mode CTRL-E and CTRL-Y.)

Here's my main failed attempt:

inoremap <c-e> <esc>:<c-u>exe "normal \<c-e>"<cr>a

but clearly there are a few variations of it where I've tried to more \, or to insert Ctrl+e by hitting it after Ctrl+v.

And even if the above command worked, I think it would have the problem of screwing up the undo sequence because it exits insert mode and then re-enters it.

Answer 1

EDIT

As @D.BenKnoble pointed out this is the simplest way:

inoremap <C-E> <C-O><C-E>

Original answer

Try using <cmd>...<cr> instead:

inoremap <c-e> <cmd>exe "normal! \<c-e>"<cr>

:h <cmd> excerpt:

*<Cmd>* *:map-cmd*

The special text <Cmd> begins a "command mapping", it executes the command
directly without changing modes.  Where you might use ":...<CR>" in the
{rhs} of a mapping, you can instead use "<Cmd>...<CR>".
Example: 
    noremap x <Cmd>echo mode(1)<CR>

This is more flexible than `:<C-U>` in Visual and Operator-pending mode, or
`<C-O>:` in Insert mode, because the commands are executed directly in the
current mode, instead of always going to Normal mode.  Visual mode is
preserved, so tricks with |gv| are not needed.

PS,

Your mapping could be also written as

inoremap <c-e> <c-o>:exe "normal \<lt>c-e>"<cr>

Where you change < to a <lt> as otherwise \<c-e> is literally interpreted by a command line your are in when mapping is in effect. (and <C-e> is goto end of cmdline)