Using the unicode prime character outside math mode with unicode-math and newunicodechar

Question

I am trying to use unicode-math, newunicodechar and LuaLaTeX/XeLaTeX to write my LaTeX code making use of unicode characters in the source text.

This works fine, except for the prime character; if I try to use \newunicodechar for it, it introduces errors if the prime is outside math mode.

\documentclass{article}

\usepackage{unicode-math}
\setmathfont{XITS Math}
\usepackage{newunicodechar}
\newunicodechar{′}{any replacement character}

\begin{document}
This prime causes “Missing \$ inserted”: ′
\end{document}

Unfortunately, I can't restrict my use of the prime character to just math mode; I am writing literate Agda and wish to use the prime character in my code, and the LaTeX source produced by Agda is not in math mode.

Is there any workaround for this problem? As it stands, my only solutions seem to be avoiding prime in my code or running a script to replace instances of prime in the Agda generated LaTeX source.

Answer 1

Note that (as mentioned by Ulrike in the comments) if you just want to typeset a prime outside of maths mode all you need to do is load a font that contains that glyph:

\documentclass{article}
\usepackage{unicode-math}
\setmainfont{texgyrepagella-regular.otf}
\begin{document}
This prime: ′
\end{document}

Answer 2

As @egreg pointed out, unicode-math redefines the prime character at begin document, so wrapping the \newunicodechar invocation in \AtBeginDocument solves the issue.

An important note is that while I usually use the form

\newunicodechar{α}{\ensuremath{\mathrm{α}}}

for defining unicode characters, doing so with prime causes a crash. So make sure to use a single quote instead.

\documentclass{article}

\usepackage{unicode-math}
\setmathfont{XITS Math}
\usepackage{newunicodechar}
\AtBeginDocument{\newunicodechar{′}{\ensuremath{\mathrm{'}}}}
\AtBeginDocument{\newunicodechar{″}{\ensuremath{\mathrm{''}}}}

\begin{document}
Now I can write a prime: A′.

Double prime had the same problem, and is resolved the same way: A″.
\end{document}