How to use stan::math::hypergeometric_2F1 in stan?

[MSQ-123]

I was trying to call my stan model by using rstan in R. It seems like stan does not has built-in hypergeometric_2F1 function. This function is only available in stan math. Is there any way to import stan math function directly into stan model? thanks a lot!

[WardBrian]

There is an open issue about exposing this function to the language here: stan-dev/stanc3#1285

Further discussion should be had there. I believe the only thing preventing it was some questions for the implementer @andrjohns.

If you'd like to use it in the mean time, you could likely use RStan's ability to use "external" C++