Type of variable used in macro polynomial?

Question

I would like to use polynomial macro, just with the standard way. But the coefficients of the polynom are generated by \FPeval or \pgfmathrandominteger commands => the result of polynomial isn't the expected one ...

\begin{document}
\pgfmathrandominteger{\VRcoeffa}{-5}{-1}
\pgfmathrandominteger{\VRcoeffb}{-5}{-1}
\pgfmathrandominteger{\VRcoeffc}{-5}{-1}
\pgfmathrandominteger{\VRcoeffd}{-5}{-1}

$f(x)=\polynomial[reciprocal]{\VRcoeffa,\VRcoeffb,\VRcoeffc,\VRcoeffd}$\par

\FPeval\VRcoeffa{(0-1)}     \FPclip\VRcoeffa{\VRcoeffa}
\FPeval\VRcoeffb{(0-3)}     \FPclip\VRcoeffb{\VRcoeffb}
\FPeval\VRcoeffc{(0)}       \FPclip\VRcoeffc{\VRcoeffc}
\FPeval\VRcoeffd{(0-12)}    \FPclip\VRcoeffd{\VRcoeffd}
\FPeval\VRcoeffe{(1)}       \FPclip\VRcoeffe{\VRcoeffe}
\FPeval\VRcoefff{(0-1)}     \FPclip\VRcoefff{\VRcoefff}

$f(x)=\polynomial[reciprocal]{%
\VRcoeffa,%
\VRcoeffb,%
\VRcoeffc,%
\VRcoeffd,%
\VRcoeffe,%
\VRcoefff%
}$
\par
$\polynomial[reciprocal]{-1,-3,0,-12,1,-1}$

\end{document}

I suspect a managment of type of variable I've no idea about with LaTeX (I'm not very used to LaTeX ... but I'm trying ;o). Thanks in advance for your help !

**** EDIT ****

This is unrelated to pgfmath. Looks like an expansion issue. Here's a MWE.

\documentclass{article}

\usepackage{polynomial}

\begin{document}

\newcommand{\vl}{-3}

$\polynomial[reciprocal]{1,\vl}$

\end{document}

This produces

instead of $x-3$

Answer 1

As stated in the comments this is a bug due to that the coefficient \vl in the MWE is not expanded before the check of -. Try to include the code from \makeatletter and \makeatother (including these commands) after \usepackage{polynomial} in the preamble as in the modified MWE below. (I also removed the [resiprocal] since it is irrelevant).

Please let me know if this work so I can upload a corrected version to CTAN (after re-learning how to pack it correctly:).

\documentclass{article}

\usepackage{polynomial}
\makeatletter
\def\shpol@getcoeff#1{% Parse the coeffs and store in #1-vars
  \shpol@numcoeff=0%
  \@for\shpol@coeff:=#1\do{%
    \advance\shpol@numcoeff by 1\relax%
    \expandafter\edef\csname shpol@coeff\romannumeral\shpol@numcoeff\endcsname{\shpol@coeff}%
  }%
}
\makeatother

\begin{document}

\newcommand{\vl}{-3}

$\polynomial{1,\vl,-4}$

\end{document}

As pointed out by B.Gravouil there is a problem with passing expanded versions of some commands. For example \dfrac and \tfrac from the Ams-packets does not work with this fix. However, \frac works as expected and a workaround in this case is to use \displaystyle and \textstyle versions of it.

\newcommand{\vl}{-3}
\newcommand{\fl}{\frac{2}{3}}
\begin{document}
\begin{itemize}
\item $\polynomial{1,\vl,\frac{2}{3}}$
\item $\displaystyle\polynomial{1,\vl,\frac{2}{3}}$
\item $\polynomial{1,\vl,\displaystyle\frac{2}{3}}$
\item $\polynomial{1,\fl,\frac{2}{3}}$
\item $\displaystyle\polynomial{1,\fl,\frac{2}{3}}$
\item $\polynomial{1,\fl,\displaystyle\frac{2}{3}}$
\item $\polynomialfrac{1,2,3}{2,\vl,4}$
\end{itemize}