Is there an easy way to mimic generics with an accept method of a visitor pattern?

[Mina via Digitalmars-d-learn]

I'm following along with the crafting interpreters book 
(https://craftinginterpreters.com) and it goes into implementing 
a visitor pattern that returns generic types, so implementing it 
in D came down to the accept method causing undefined symbol 
error that goes away when changing it to returning a concrete 
type, so here's what I've got working 
(https://github.com/MKamelll/dlox/blob/main/source/loxast.d) and 
here's the book's implementation 
(https://github.com/munificent/craftinginterpreters/blob/master/java/com/craftinginterpreters/lox/Expr.java).

Thanks.