Substitute characters in text-mode with their math equivalent

Question

I'm looking for a TeXway to substitute - (or other characters) while in text-mode with their math equivalent (i.e. $-$) in one environment/group. I'm looking for a 'switch' (\foo # and not \foo{#}).

The code below does essentially what I want, but only works in math-mode.

\def\foo{%
  \bgroup\uccode`\~\expandafter`\string-%
  \uppercase{\egroup\edef~{\noexpand\text{$-$\relax}}}%
  \mathcode\expandafter`\string-"8000 }
\def\textsymbols{\foo}

I've been unable to come up with a solution. The closest I've come is the following command that takes one argument (which I don't want) and it does not work with $-$ (but $+$ works).

\begingroup
\catcode`-=\active\gdef\foo{%
 \begingroup\catcode`-=\active\gdef-{$+$}%
 \fooaux
 }\gdef\fooaux#1{\endgroup #1}
\endgroup

A usecase would be:

\begin{table}
\foo
- is now set in math.
\end{table}

Answer 1

You should use a non active - in the replacement text:

\def\foo{\catcode`\-=\active
  \begingroup\lccode`~=`-
    \lowercase{\endgroup\def~}{$-$}%
}


\begingroup\foo
This is a - sign and not a hyphen.
\endgroup

Now - is a hyphen.

\bye

In a LaTeX context you probably want to use \ensuremath{-} instead of $-$.