pystan2 is so old to install on latest mac

[jiamo]

build and install pystan2 will got

In file included from pystan/stan/lib/stan_math/lib/boost_1.72.0/boost/spirit/home/support/detail/sign.hpp:16:
pystan/stan/lib/stan_math/lib/boost_1.72.0/boost/math/special_functions/sign.hpp:30:22: error: reference to unresolved using declaration
        return (std::signbit)(x) ? 1 : 0;
                     ^

Considering upgrade to pystan3?

[rohanfb]

PRs are welcome :)

[vpasquier]

And as far as i understood pystan3 is not having the right dependency either on httpstan -> https://discourse.mc-stan.org/t/mac-m1-installation-issue-pystan-3/29490, so it needs some manual installs.