Listing inside align environment doesn't work

Question

I found a very specific formatting error: when I use lstinline[mathescape] inside an align environment, some of the basic math formatting like subscripting stops working. It does however work in e.g., an equation environment. The strange thing is that when I don't load the syntax package, this bug does not occur.

A complete minimal example that reproduces the problem:

\documentclass{article}

\usepackage{amsmath}
\usepackage{listings}
\usepackage{syntax}

\begin{document}

\begin{align*}
e_1 \mapsto \lstinline[mathescape]|Stream.of($e_1$)|
\end{align*}

\begin{equation*}
e_1 \mapsto \lstinline[mathescape]|Stream.of($e_1$)|
\end{equation*}

\end{document}

As you can see, the subscription inside the align envirnoment doesn't work.

Is there a way to resolve this error cleanly? What is causing it?

---

EDIT Based on @UlrikFisher's comment, I could find a workaround specifically for the underscore. Unfortunately, this workaround does not work for other macros. Here is a more complete example:

\documentclass{article}

\usepackage{amsmath}
\usepackage{listings}
\usepackage[nounderscore]{syntax}
\usepackage[shorthand]{semantic}

\begin{document}

\begin{align*}
e_1 \mapsto \lstinline[mathescape]+Stream.of($|[e_1|]$)+
\end{align*}

\begin{equation*}
e_1 \mapsto \lstinline[mathescape]+Stream.of($|[e_1|]$)+
\end{equation*}

\end{document}

Answer 1

The body of an AMS alignment is essentially the argument of an internal command (so the body can be used twice as part of the alignment measuring) This means that no verb-like commands work.

Sometimes you get lucky and the argument to lstinline doesn't need any special catcode changes so that the command appears to work, but basically it can not work in this setting.

Loading teh syntax package apparently globally redefined _ with a catcode 13 definition and listings can not revert this inside an align

You can set the text in a box before starting the alignment

\documentclass{article}

\usepackage{amsmath}
\usepackage{listings}
\usepackage{syntax}

\newbox\mybox
\begin{document}


\setbox\mybox\hbox{{\lstinline[mathescape]|Stream.of($e_1$)|}}
\begin{align*}
e_1 \mapsto \usebox{\mybox}
\end{align*}

\begin{equation*}
e_1 \mapsto \lstinline[mathescape]|Stream.of($e_1$)|
\end{equation*}

\end{document}