Is it possible in Stan now, or a feature that might be added, to let a function be passed into a user-defined Stan function?

I am thinking I have functions P and Q defined in the functions block, along with some other function R:

`functions{

real P(real X){

real Z;

Z=X+1;

return Z;

}

real Q(real X){

real Z;

Z=X+2;

return Z;

}

real R(function S, real X){

real Z;

Z=S(X);

return Z;

}

}`

and then have something like:

`model{ real Y[2] Y[1] = S(P,X); Y[2] = S(Q,X); }`

In this example code, it a rather useless request, but in the project I’m working on it would reduce a bunch of code replication.