Vimのバッファでカウンターを実装するサンプル

counter.vim

function! s:State(bufid) abort
  let l:counter = 0
  let l:bufid   = a:bufid

  function! Inc() closure
    let l:counter += 1
    call Flash()
  endfunction

  function! Dec() closure
    let l:counter -= 1
    call Flash()
  endfunction

  function! Flash() closure
    call setbufline(l:bufid, 1, string(l:counter))
  endfunction

  return #{
    \Inc: funcref('Inc'),
    \Dec: funcref('Dec'),
    \Flash: funcref('Flash'),
  \}
endfunction

function! g:NewBuffer() abort
  execute 'new' fnameescape("Counter")
  setlocal modifiable
  silent %delete _
  setlocal nomodified
  setlocal buftype=nofile bufhidden=wipe

  let b:state = s:State(bufnr())
  nnoremap <buffer>k <cmd>call b:state.Inc()<CR>
  nnoremap <buffer>j <cmd>call b:state.Dec()<CR>
  call setline(2, "j/k to up/down counter")
  call b:state.Flash()
endfunction

call g:NewBuffer()