How can I tell lstlisting to use sans-serif when escaping to math mode?

Question

Title says it all, an example follows:

\lstset{
    mathescape=true,
    basicstyle = \sffamily
}

\begin{lstlisting}
    func($x_0$)
\end{lstlisting}

Where and how can I set the math font used here to be sans-serif italic?

Answer 1

\documentclass[a4paper]{article}
\DeclareMathVersion{sans}
\SetSymbolFont{operators}{sans}{OT1}{cmbr}{m}{n}
\SetSymbolFont{letters}  {sans}{OML}{cmbrm}{m}{it}
\SetSymbolFont{symbols}  {sans}{OMS}{cmbrs}{m}{n}

\usepackage{listings}
\lstnewenvironment{sflisting}[1][]
  {\lstset{#1}\mathversion{sans}}{}

\begin{document}

\lstset{
    mathescape=true,
    basicstyle = \sffamily
}

\begin{sflisting}[caption=Function]
    func($x_0$)
\end{sflisting}
\end{document}

This uses the CMBright fonts, which are mostly compatible with CM Sans.

Answer 2

\documentclass[a4paper]{article}
\usepackage{sansmath}
\usepackage{listings}
\lstnewenvironment{sflisting}[1][]
  {\lstset{mathescape,basicstyle=\sffamily,#1}\sansmath}
  {}
\begin{document}

\begin{sflisting}[caption=Function]
    func($\frac1x \mathrm{d}x$)
\end{sflisting}

\end{document}