Here is a quick way to send a line of text from vim into your favorite REPL. Normal mode only.
Note: I know very little vim; I got this far reading a lot of useless posts and monkeying around.
This recipe requires a named tmux session with the target running, accepting text from stdin. In my case the session is called 'octo'.
Add the following binding to .vimrc:
nnoremap <C-e> :silent! .w !xargs -0 tmux send-keys -t octo:0.0<CR>j:call search('^\s*\S.*', 'W')<CR>
.w ! sends the current line to tmux, via xargs. As a bonus, I advance the cursor to the next non-blank line.
Funny how often I don't need a clunky plugin to do a simple thing.