Fast word count function in Vim

Question

I am trying to display a live word count in the vim statusline. I do this by setting my status line in my .vimrc and inserting a function into it. The idea of this function

Answer 1

In case someone else is coming here from Google, I modified Abslom Daak's answer to work with Airline. I saved the following as

~/.vim/bundle/vim-airline/autoload/airline/extensions/pandoc.vim

and added

call airline#extensions#pandoc#init(s:ext)

to extensions.vim

let s:spc = g:airline_symbols.space

function! airline#extensions#pandoc#word_count()
if mode() == "s"
    return 0
else
    let s:old_status = v:statusmsg
    let position = getpos(".")
    let s:word_count = 0
    exe ":silent normal g\"
    let stat = v:statusmsg
    let s:word_count = 0
    if stat != '--No lines in buffer--'
        let s:word_count = str2nr(split(v:statusmsg)[11])
        let v:statusmsg = s:old_status
    end
    call setpos('.', position)
    return s:word_count 
end
endfunction

function! airline#extensions#pandoc#apply(...)
if &ft == "pandoc"
    let w:airline_section_x = "%{airline#extensions#pandoc#word_count()} Words"
endif
endfunction

function! airline#extensions#pandoc#init(ext)
call a:ext.add_statusline_func('airline#extensions#pandoc#apply')
endfunction