Function interp_make_active_binding 

fn interp_make_active_binding(
    positional: &[RValue],
    _named: &[(String, RValue)],
    _context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Create an active binding.

Active bindings call a function every time they are accessed. The function fun is stored in the environment and re-evaluated on every read of sym.

@param sym name for the binding (character string) @param fun zero-argument function to call on access @param env environment in which to create the binding @return NULL (invisibly)