Biber error with "constants" package

Question

I was trying to run biber (version 2.10; using Texmaker) when this error occurred:

INFO - This is Biber 2.10 INFO - Logfile is 'provabib.blg' ERROR - provabib.bcf is malformed, last biblatex run probably failed. Deleted provabib.bbl INFO - ERRORS: 1

After a few attempts, I found out that the problem was the package constants, which I was using to automatically number the constants I define; removing it, everything works fine. I am definitely not an expert and I have no idea how to fix this, but I guess it's because the package constants is a bit outdated. Do you now any way to avoid this issue? Similar packages doing the same job are welcome too.

Here's a minimal working example:

\documentclass[a4paper,11pt]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel} 
\usepackage[autostyle]{csquotes}
\usepackage[style=alphabetic,backend=biber]{biblatex}
%%\usepackage{constants}        %%<--- this one produces the error
   %% \newconstantfamily{K}{symbol=K}       %% An example
\begin{filecontents*}{\jobname.bib}
   @book{rudin,
   author  = "Rudin, Walter",
   title   = "Real and Complex Analysis",
   year    = "1966",
   publisher = "McGraw-Hill"
 }
\end{filecontents*}
\addbibresource{\jobname.bib}

\begin{document}
   This is a citation: \cite{rudin}. \\
   %% This, instead, an example of use of the ``constants'' package:
   %% \[\Cl[K]{nameconstant}=e^\pi;\]
   %% now here's a new constant of the same family: $\C[K]$, while here I am referring to the first constant defined: $\Cr{nameconstant}$.
   \printbibliography
\end{document}

Answer 1

The constants package inserts throught \AtEndDocument the commands \deadcycles\z@\@@end which end the compilation and so hinders biblatex to finish the bcf-file.

I don't know why the package does this -- it looks like a bad copy of the original code in the kernel -- but it means that the package can break other packages completly and so shouldn't be used.

Answer 2

It turns out that the simple trick described in the first answer of the question Automatically numbering constants does exactly what I want, and avoids that error caused by constants.

In my case, I needed several "epsilons", numbered increasingly, and the possibility to refer to old ones.

The following counter was added in the preamble (notice that hyperref is needed):

\usepackage{hyperref}    
\newcounter{epscnt}                     %% Defines the counter for epsilon
\newcommand{\neweps}{                   %% Used to introduce a new epsilon
    \refstepcounter{epscnt}             %%    with the right subscript
    \ensuremath{\epsilon_\theepscnt}
    }
\newcommand{\oldeps}[1]{\ensuremath{\epsilon_{\ref*{#1}}}}  %% Used to refer to old constants

And here's a (working) example of how it's used (needs probably some improvement, in case other constants are needed):

\documentclass[a4paper,11pt]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel} 
\usepackage[autostyle]{csquotes}
\usepackage[style=alphabetic,backend=biber]{biblatex}
\usepackage{hyperref}
\begin{filecontents*}{\jobname.bib}
     @book{rudin,
     author  = "Rudin, Walter",
     title   = "Real and Complex Analysis",
     year    = "1966",
     publisher = "McGraw-Hill"
     }
     \end{filecontents*}
 \addbibresource{\jobname.bib}

 \newcounter{epscnt}            %% epsilon
 \newcommand{\neweps}{
    \refstepcounter{epscnt}
    \ensuremath{\epsilon_\theepscnt}
    }
 \newcommand{\oldeps}[1]{\ensuremath{\epsilon_{\ref*{#1}}}}

 \newcounter{uckcnt}            %% uppercase K
 \newcommand{\newuck}{
    \refstepcounter{uckcnt}
    \ensuremath{K_\theuckcnt}
    }
 \newcommand{\olduck}[1]{\ensuremath{K_{\ref*{#1}}}}


 \begin{document}
   Here are some numbered constants: $\neweps$, $\neweps$, $\neweps\label{tre}$; now a citation: \cite[99]{rudin}. Finally, new epsilons, old ones and other constants: $\neweps$, $\oldeps{tre}$, $\newuck\label{uno}$, $\newuck$, $\olduck{uno}$.
   \printbibliography
 \end{document}

This looks good to me; if you have suggestions on how to improve it, I'll be glad to hear them.