switch toggle function - background

Question

I'm trying to assign a key toggle to switch between dark or light background. I wrote this function:

function ToggleBG()
    let l:bg='set background?'
    if l:bg==dark
        :set background=light
    elseif l:bg==light
        :set background=dark
    endif    
endfunction

nmap <F6> :call ToggleBG()<cr>

It doesn't work, error,

E121: Undefined variable: dark  
E15: Invalid expression: l:bg==dark

The logic is, retrieve current bg setting set background?, put it in a local variable, l:bg; if it's dark switch it to light and vice versa.
Assign the function to F6 key.

Using Vim 8.1 and Neovim. Any ideas how will this work?

Answer 1

Try to execute several times in a command line:

:let &bg=(&bg=='light'?'dark':'light')

It will change background from light to dark to light...

Then map it to F6:

nnoremap <F6> :let &bg=(&bg=='light'?'dark':'light')<cr>

Check

• :help :let-& -- on how to access option values in vimscript.
• :help trinary -- for expr ? expr : expr description