inoremap <C-f> <ESC>:call ReIndent(1)<CR>
function! ReIndent(in_insert_mode)
  let l:col = col(".")
  let l:lnum = line(".")

  " set append = 1, if we're at the end of the line.
  let l:linelen = strlen(getline(l:lnum))
  let l:append = (l:col >= l:linelen)

  let l:indent_ok = 0
  if IndentToParen(l:lnum, 1)
    let l:indent_ok = 1
  elseif IndentToParen(l:lnum, 0)
    let l:indent_ok = 1
  endif

  " Move back to our original position
  let l:linedelta = strlen(getline(l:lnum)) - l:linelen
  call setpos('.', [0, l:lnum, l:col + l:linedelta, 0])

  if l:indent_ok == 0
    "Both indent attempts failed, try using == instead
    normal ==
  endif

  if a:in_insert_mode
    if l:append == 1
      startinsert!
    else
      normal l
      startinsert
    endif
  endif
endfunction

function! IndentToParen(lnum, assume_unclosed)
  " Search for '(' on the previous line
  let l:ret = 1
  let l:lnum = a:lnum
  let l:prevlnum = prevnonblank(l:lnum - 1)
  let l:oldline = getline(l:lnum)

  if a:assume_unclosed
    " insert a ), find what it matches, indent to that open paren?
    call setline(l:lnum, ")")
  else
    call setpos('.', [0, l:prevlnum, 0, 0])
    execute "normal $F)"
  endif

  let [l:slnum, l:scol] = searchpairpos('(', '', ')', 'nbW')

  if a:assume_unclosed
    call setline(l:lnum, l:oldline)
  endif

  if l:slnum[0] != 0
    " Trim leading space/tabs
    call setpos('.', [0, l:lnum, 0, 0])
    s/^[ >]*//

    " Set the line with new indentation
    if a:assume_unclosed == 0
      let l:scol = indent(l:slnum)
    endif
    call setline(l:lnum, repeat(" ", l:scol) . getline(l:lnum))

    " Turn spaces into tabs on this line, if necessary.
    .retab!
  else
    "echo "No match found on IndentToParen " . a:assume_unclosed
    let l:ret = 0
  endif
  return l:ret
endfunction