oneliner map to fold all / unfold all

Question

I'm trying to optimize this solution I came up with.

---

The code bellow do works fine. So feel free to use it as a valid solution to this question.

nnoremap <F2> :call ToogleFold()<CR>

function! ToogleFold()
     if &foldlevel >= 20
         "normal! zM<CR> (folds all)
         set foldlevel=0
     else
         "normal! zR<CR> (unfolds everything)
         set foldlevel=20
     endif
 endfunction

---

But I believe we can do it all in a single line without the use of functions.

I've tried some strange combinations here, attempting to get it right. So, to inspire your creativity, here the wrong codes:

nnoremap <F2> @=(foldlevel('.')?'zM':'zR')<CR>
nnoremap <F2> :exe 'if &foldlevel>=20' \ <ESC>zM \ else <ESC>zR'
nnoremap <F2> :exe &foldlevel>=20? <ESC>zM : <ESC>zR
nnoremap <F2> :exe '&foldlevel>=20?' <ESC>zM : <ESC>zR'

In the and, what I'm trying to achieve is the use of zM and zR in normal mode depending on the value of a setting variable foldlevel.

I believe this solution may be very useful to other similar cases (other variables)

Answer 1

So you want to toggle between all lines folded and no lines folded.

Does this mapping do what you want?

:nnoremap <expr> <f2> &foldlevel ? 'zM' :'zR'

Answer 2

I wrote a similar function in Lua for those using Neovim:

local key = vim.keymap.set
local silent = { noremap = true, silent = true }

-- Toggle all folds
key('n', "<Leader><Tab>",
    function()
        local get_opt = vim.api.nvim_win_get_option
        local set_opt = vim.api.nvim_win_set_option

        if get_opt(0, "foldlevel") >= 20 then
            set_opt(0, "foldlevel", 0)
        else
            set_opt(0, "foldlevel", 20)
        end
    end,
silent)