How do I enhance the '~' command to toggle the "+/-" signs as well?

Question

I need to make a report about investment everyday. It requires a lot of changes of the sign of figures. (from - to + or from + to -)

Is there a simple way to overload (extend) the ~ command (switch case) with such a toggle function?

Answer 1

I would do:

function! ExtendToggle()
  let char = getline(line('.'))[col('.')-1]
  if char == '-'
    return 'r+l'
  elseif char == '+'
    return 'r-l'
  else
    return '~'
  endif
endfunction

nnoremap <expr> ~ ExtendToggle()