Adding Non-breaking space after single character in text mode

Question

Is it possible in LaTeX (2e) to create macro or other processing command that will add non-breaking space after single character in text mode?

Example:

A new example here will add a "tilde", after single letter, but will skip math mode.
$12 \times A = 128$

should produce:

A~new example here will add a~"tilde", after single letter, but will skip math mode.
$12 \times A = 128$

I know that I can use regular expresion like: s/\(\<[a-z]\>\)[ ]/\1\~/g, but this one will also change text in math mode and listing/verbatim mode.

Answer 1

It would be a bit fragile to do that in TeX: I'd do the replace with a regex in the editor as you suggest. (If you just wanted to make a ~ in text and a normal space in math that would be easier, but having it work in listings and verbatim would be harder)

For example given

\documentclass{article}

\usepackage{amsmath}

\begin{document}

A new example here will add a "tilde", after single letter, but will skip math mode.
$12 \times A = 128$
\[ a b c = 123\]
and a bit nore text
\begin{align}
a &= b\\
x & = y 
\end{align}

\begin{verbatim}
A new example here will add a "tilde", after single letter,
but will skip math mode.
$12 \times A = 128$
\[ a b c = 123\]
and a bit nore text
\begin{align}
a &= b\\
x & = y 
\end{align}
\end{verbatim}


A new example here will add a "tilde", after single letter, but will skip math mode.
$12 \times A = 128$
\[ a b c = 123\]
and a bit nore text
\begin{align}
a &= b\\
x & = y 
\end{align}

\begin{verbatim}
A new example here will add a "tilde", after single letter,
but will skip math mode.
$12 \times A = 128$
\[ a b c = 123\]
and a bit nore text
\begin{align}
a &= b\\
x & = y 
\end{align}
\end{verbatim}

\end{document}

The command M-x addtilde in emacs produces

\documentclass{article}

\usepackage{amsmath}

\begin{document}

A~new example here will add a~"tilde", after single letter, but will skip math mode.
$12 \times A = 128$
\[ a b c = 123\]
and a~bit nore text
\begin{align}
a &= b\\
x & = y 
\end{align}

\begin{verbatim}
A new example here will add a "tilde", after single letter,
but will skip math mode.
$12 \times A = 128$
\[ a b c = 123\]
and a bit nore text
\begin{align}
a &= b\\
x & = y 
\end{align}
\end{verbatim}


A~new example here will add a~"tilde", after single letter, but will skip math mode.
$12 \times A = 128$
\[ a b c = 123\]
and a~bit nore text
\begin{align}
a &= b\\
x & = y 
\end{align}

\begin{verbatim}
A new example here will add a "tilde", after single letter,
but will skip math mode.
$12 \times A = 128$
\[ a b c = 123\]
and a bit nore text
\begin{align}
a &= b\\
x & = y 
\end{align}
\end{verbatim}

\end{document}

where addtilde is defined by

(defun hidespaceenv (e)
  (goto-char (point-min))
  (while (re-search-forward 
      (if (string-equal e "[") "\\\\\\["
        (if (string-equal e "$") "\\$"
          (concat "\\\\begin{" e "}")))
      nil 1)
    (while (re-search-forward "\\([a-zA-Z]\\)\\(\\s-+\\)\\|\\(\\\\begin\\)" (save-excursion(re-search-forward 
                                  (if (string-equal e "[") "\\\\\\]"
                                    (if (string-equal e "$") "\\$"
                                      (concat "\\\\end{" e "}")))
                                  nil 1) (point)) 1)
      (replace-match "\\1SPACE@@\\2\\3@@" t))))

(defun addtilde ()
  (interactive)
  (mapcar `hidespaceenv (list "verbatim" "align" "equation" "[" "$"))
  (goto-char (point-min))
  (while (re-search-forward "\\(\\(^\\|\\s-+\\)[a-zA-Z]\\)\\s-+" nil 1)
    (replace-match "\\1~"))
  (goto-char (point-min))
  (while (re-search-forward "SPACE@@\\(\\s-+\\|\\\\begin\\)@@" nil 1)
    (replace-match "\\1")))