Use motion in normal mapping calling a function

Question

I have this function which displays line numbers. I want it to be called in different ways:

• from a command, specifying the lines as arguments
• with a visual selection, printing the first and last line numbers of the selection
• with a motion, printing the current line and the line at the end of the motion

So far I have the first two ones:

command! -nargs=* PL :call PrintLines('command',<f-args>)
vnoremap <silent> P :<C-U>call PrintLines('visual')<CR>

function! PrintLines(type,...)

  " Get the lines to fold around
  if a:type == 'command'
    let l:line_before = a:000[0]
    let l:line_after = a:000[1]
  elseif a:type == 'visual'
    let l:line_before = line("'<")
    let l:line_after = line("'>")
  endif

  echo l:line_before
  echo l:line_after

endfunction

But I can't figure out the way to use this with a motion. Ideally it would be possible to do something like:

 nnoremap P{motion} :<C-U>call('normal')<CR>

And use it like this:

 Pib

Answer 1

You'll nee to use the g@ feature (see :h g@) This operator allow to specify a motion after a function call and position the marks '[ and '] at the beginning and the end of the text selected by the motion.

When calling a function this way the mode of selection (line-wise, character-wise, block-wise) is passed as the first argument of the function.

With this method you can use line("'[") and line("']") to get the number of the lines. Your function should look like this:

function! PrintLines(type,...)

    " Get the lines to fold around
    if a:type == 'command'
        let l:line_before  = a:000[0]
        let l:line_after   = a:000[1]
    elseif a:type == 'visual'
        let l:line_before  = line("'<")
        let l:line_after   = line("'>")
    elseif a:type =~ 'line\|char\|block'
        " Test the different mode that g@ can pass as argument
        " and get the corresponding lines
        let l:line_before  = line("'[")
        let l:line_after   = line("']")
    endif

    echomsg l:line_before.' '.l:line_after

endfunction

Now about the mapping it should look like this (largely inspired from the example of the doc):

nnoremap <silent> P :set opfunc=PrintLines<CR>g@

You can then use your mapping P and Vim will wait for a motion input (like } or 5j) to call the function correctly.