Why the partial derivative example gives wrong answer?

Question

I tried this example from the site: https://cadabra.science/manual/PartialDerivative.html

\tau::Coordinate;
\partial{#}::Derivative(\tau);
f::Depends(\tau);
ex:= \partial{f g};
unwrap(ex);

It returns 0 instead of g∂f

Answer 1

The above works fine with the current version on github. If it does not for you, either upgrade, or say explicitly that the derivative is with respect to $\tau$,

  ex:= \partial_{\tau}{ f g};

or make $f$ depend on \partial:

 f::Depends(\partial{#}).

Otherwise the 'old' version of Cadabra which you use does not know how to figure out that \partial is a $\tau$-derivative.