mapping to enclose symbol under cursor with an expression that contains the symbol (revisited)

Question

@saginaw answered a question I asked a long time ago, in this thread.

Here's a code snippit of his suggestions that illustrates my problem:

function! s:PadMacro(type) abort
    if a:type ==# 'char'
        normal! `[v`]d
    elseif a:type ==# 'line'
        normal! '[V']d
    elseif a:type ==# 'v'
        normal! `<v`>d
    else
        return
    endif
    let string = '\Pad{' . @" . '}'
    silent execute "normal! i\<c-r>=string\r"
endfunction
nnoremap <silent> ;P :set operatorfunc=<sid>PadMacro<cr>g@
vnoremap <silent> ;P :<c-u>call <sid>PadMacro(visualmode())<cr>

a
aaa

Here are @saginaw's instructions

Instructions:
    If you put the previous code in your vimrc, it should do what you want.

    To use it, hit ;P{motion} and the PadMacro() function should enclose the characters covered by {motion} with \Pad{ and }.

The problem I'm having is with the ;P{motion} command: If

(*) on the last line of the snippet I highlight the three aaa's by hitting v and the spacebar, then hit ;P

I get the following error

Error detected while processing function <SNR>7_PaddingFunction:
line   10:
E121: Undefined variable: g:enclosure
E15: Invalid expression: '\' . g:enclosure . '{' . @" . '}'
Press ENTER or type command to continu

HOWEVER, if I first modify the single a in the line above, by putting the cursor over it and then typing ;P (no 'v' then spacebar required), and AFTER DOING SO, repeat the command sequence on the line that begins with (*), the ;P command works as expected.

My ignorant guess is that something needs to be initialized in order for ;P, together with motion, to work properly

Could somebody please advise how to get the (*) command sequence to work the first time? Thanks for any advice.

At @Christian_Brabandt's request I'm posting the output of :scriptnames

1: ~/LOCALSVN/dotFiles/trunk/vimrc
  2: /usr/share/vim/vim74/syntax/syntax.vim
  3: /usr/share/vim/vim74/syntax/synload.vim
  4: /usr/share/vim/vim74/syntax/syncolor.vim
  5: /usr/share/vim/vim74/filetype.vim
  6: ~/LOCALSVN/multiSystem/trunk/vimPlugins/unicode.vim/ftdetect/unicode.vim
  7: /usr/share/vim/vim74/syntax/nosyntax.vim
  8: /usr/share/vim/vim74/colors/delek.vim
  9: ~/LOCALSVN/multiSystem/trunk/vimPlugins/unicode.vim/plugin/unicode.vim
 10: /usr/share/vim/vim74/plugin/getscriptPlugin.vim
 11: /usr/share/vim/vim74/plugin/gzip.vim
 12: /usr/share/vim/vim74/plugin/logiPat.vim
 13: /usr/share/vim/vim74/plugin/matchparen.vim
 14: /usr/share/vim/vim74/plugin/netrwPlugin.vim
 15: /usr/share/vim/vim74/plugin/rrhelper.vim
 16: /usr/share/vim/vim74/plugin/spellfile.vim
 17: /usr/share/vim/vim74/plugin/tarPlugin.vim
 18: /usr/share/vim/vim74/plugin/tohtml.vim
 19: /usr/share/vim/vim74/plugin/vimballPlugin.vim
 20: /usr/share/vim/vim74/plugin/zipPlugin.vim
 21: /usr/share/vim/vim74/scripts.vim

My vimrc file is posted here and a text file that generates the problem is here

Answer 1

This seems like a job for Tim Pope's surround.vim.

Add the following to ~/.vim/after/ftplugin/tex.vim:

let b:surround_{char2nr("P")} = "\\Pad{\r}"

Now you can do ys{motion}P or other surround operations (See :h surround). See :h surround-customizing for more information about customizing surround.vim.

There is also vim-sandwich which is an alternative to surround.vim.