Btukfyl

Whenever I load the packages breqn and icomma into the same document, the document fails to compile. The order of the packages makes no difference. MWE:

documentclass{article}

usepackage{breqn}

usepackage{icomma}

begin{document}

Look mama, no hands!

end{document}

raises the following cryptic error:

This is pdfTeX, Version 3.14159265-2.6-1.40.18 (TeX Live 2017/Debian) (preloaded format=pdflatex)

 restricted write18 enabled.

entering extended mode

(./test.tex

LaTeX2e <2017-04-15>

Babel <3.18> and hyphenation patterns for 84 language(s) loaded.

(/usr/share/texlive/texmf-dist/tex/latex/base/article.cls

Document Class: article 2014/09/29 v1.4h Standard LaTeX document class

.

.      [lines omitted for brevity]

.

(/usr/share/texlive/texmf-dist/tex/latex/tools/calc.sty))

(/usr/share/texlive/texmf-dist/tex/latex/was/icomma.sty) (./test.aux)

! Bad mathchar (32768).

<to be read again> 

                   mathcode 

l.4 begin{document}



?

but compiles if either of the packages are commented out.

I could not find anyone else with this problem. Does anyone know of a workaround, or if not, who should this bug be reported to (I've never reported a bug to a package manager before)?

It isn't really a bug. breqn by design has to re-implement almost every aspect of math processing and as documented is thus incompatible with more or less any other math mode definitions that are not explicitly written to work with breqn.

Really breqn is an unfinished experiment and sadly its original author died some years ago, and so it is probably not really recommended for use in a production document unless you have very tight control over the input and know it works well on that input, some large but regular output from symbolic computer algebra systems fall in this category.

Basically, breqn makes many characters math active, in order to achieve its goals. Also icomma wants to make the comma math active, assigning it a different definition and this obviously can't work, at least in environments governed by breqn.

You may make the icomma version useable in standard math environments, but I see no real way to sneak it inside dmath or similar environments, where you have to resort to the standard {,} trick.

documentclass{article}

usepackage{breqn}



makeatletter

newifif@breqn

g@addto@macro@dmath@start@hook{@breqntrue}

g@addto@macro@dgroup@start@hook{@breqntrue}



begingroup

catcode`,=active

globalletbreqn@comma=,

gdeficomma@comma{futurelet@let@tokensm@rtcomma}

gdef,{%

  if@breqn

    expandafter@firstoftwo

  else

    expandafter@secondoftwo

  fi

  breqn@commaicomma@comma

}

endgroup

defsm@rtcomma{%

  ifx@let@token@sptoken else

  ifx@let@tokenspace else

    mathordfifi breqn@comma}

makeatother



begin{document}



Look mama, no hands!



$(a, b)=1,2$



begin{dmath}

(a,b)=1{,}2

end{dmath}



end{document}

The same output with siunitx and num.

documentclass{article}

usepackage{breqn}

usepackage{siunitx}



sisetup{output-decimal-marker={,}}



begin{document}



Look mama, no hands!



$(a,b)=num{1,2}$



begin{dmath}

(a,b)=num{1,2}

end{dmath}



end{document}

But follow marmot's advice: don't use breqn if you don't have huge and unreadable formulas generated by some external piece of software that you have no time to break manually.