Implement ballooneval / bexpr

[ELLIOTTCABLE]

I've tried the following test-file (by Bjorn Winckler, to demonstrate support in MacVim); but I simply get “E518: Unknown option: balooneval / bexpr.”

function! MyBalloonExpr()
    return 'Cursor is at line ' . v:beval_lnum .
            \', column ' . v:beval_col .
            \ ' of file ' .  bufname(v:beval_bufnr) .
            \ ' on word "' . v:beval_text . '"'
endfunction
set bexpr=MyBalloonExpr()
set ballooneval

I'd love to see VimR support ballooneval, for Syntastic error-reporting. (See also: neovim/neovim#2544)

[qvacua]

It seems that neovim will support a text-only version for this in its 0.3.0 release... Let's see who's faster... (probably neovim... 😬)