mathfont not working: for xelatex, mathspec package is required

[njbart]

Using the mathfont variable leads to a latex error:

pandoc -V mathfont="Minion Pro" --template=default.latex --latex-engine=xelatex -o file.pdf file.txt

gives

pandoc: Error producing PDF from TeX source.
! Undefined control sequence.
l.20     \setmathfont

Reason:
\setmathfont is a command from the mathspec package not contained in the fontspec package.

I’d suggest replacing fontspec by mathspec – for xelatex only, however; apparently mathspec does not work with lualatex.

With xelatex, I have had good results using a template with

\usepackage{mathspec}
...
$if(mainfont)$
    \setallmainfonts[Numbers=OldStyle]{$mainfont$}
$endif$
$if(sansfont)$
    \setsansfont[Numbers=OldStyle]{$sansfont$}
$endif$
$if(monofont)$
    \setmonofont{$monofont$}
$endif$
$if(mathfont)$
    \setmathsfont(Digits,Latin,Greek)
    [Numbers={Lining,Proportional}]{$mathfont$}
$endif$

Setting math fonts in lualatex seems possible too. I have never used lualatex, but http://tex.stackexchange.com/questions/34855/selecting-main-math-font-in-luatex has suggestions.