Vim function toggle replace character under cursor - vim

Question

I'm trying to change "X" to " " and vice versa to mark a checkbox in a markdown file in normal mode:
- [X] Zucchini
- [ ] Nutmeg
Here's what I've tried:
First
function! ToggleComplete()
if getline('.')[col('.')-1] == 'X'
return ' '
else
return 'X'
endif
endfunction
nnoremap <C-x> :call ToggleComplete()<CR>
Second
function! ToggleComplete()
if getline('.')[col('.')-1] == 'X'
return '\r\<Space>'
else
return '\rX'
endif
endfunction
nnoremap <C-x> :call ToggleComplete()<CR>

Answer 1

It really can't work like this; the main reason is how you use the return statement : your function returns a space or an X char, but the returned value is never used, and is lost when you use call ToggleComplete(). Actually there's nothing in your code that changes the content of your buffer.
A secondary point: your if test is very restrictive; it requires your cursor to be exactly on the right char in the line, in order to work (because of [col('.')-1]). Maybe it's what you want, but you may also add some flexibility by using a test which works without depending on the cursor column.
The following is one possibility of doing what you want:
function! ToggleComplete()
" Get current line:
let l:line = getline('.')
" Get the char to test with the help of a pattern, ' ' or 'X':
" \zs and \ze lets you retrieve only the part between themselves:
let l:char = matchstr(l:line, '\[\zs.\ze]')
" Invert the value:
if l:char == 'X'
let l:char = ' '
else
let l:char = 'X'
endif
" Replace the current line with a new one, with the right
" char substituted:
call setline(line('.'), substitute(l:line, '\[\zs.\ze]', l:char, ''))
" Please note that this last line is doing the desired job. There is
" no need to return anything
endfunction