Toggle between tabs vs. spaces mode

vimrc

" Return indent (all whitespace at start of a line), converted from
" tabs to spaces if what = 1, or from spaces to tabs otherwise.
" When converting to tabs, result has no redundant spaces.
function! Indenting(indent, what, cols)
  let spccol = repeat(' ', a:cols)
  let result = substitute(a:indent, spccol, '\t', 'g')
  let result = substitute(result, ' \+\ze\t', '', 'g')
  if a:what == 1
    let result = substitute(result, '\t', spccol, 'g')
  endif
  return result
endfunction

" Convert whitespace used for indenting (before first non-whitespace).
" what = 0 (convert spaces to tabs), or 1 (convert tabs to spaces).
" cols = string with number of columns per tab, or empty to use 'tabstop'.
" The cursor position is restored, but the cursor will be in a different
" column when the number of characters in the indent of the line is changed.
function! IndentConvert(line1, line2, what, cols)
  let savepos = getpos('.')
  let cols = empty(a:cols) ? &tabstop : a:cols
  execute a:line1 . ',' . a:line2 . 's/^\s\+/\=Indenting(submatch(0), a:what, cols)/e'
  call histdel('search', -1)
  call setpos('.', savepos)
endfunction
command! -nargs=? -range=% Space2Tab call IndentConvert(<line1>,<line2>,0,<q-args>)
command! -nargs=? -range=% Tab2Space call IndentConvert(<line1>,<line2>,1,<q-args>)
command! -nargs=? -range=% RetabIndent call IndentConvert(<line1>,<line2>,&et,<q-args>)

" allow toggling between tab and spaces mode
function! TabToggle()
  if &expandtab
    set shiftwidth=2
    set softtabstop=0
    set noexpandtab
    retab!
    set list!
    Space2Tab
  else
    set shiftwidth=2
    set softtabstop=2
    set expandtab
    set list
    retab
    Tab2Space
  endif
endfunction
nmap <Leader>ta :call TabToggle()<cr>