I'm trying to implement an interpreter in D as a class project. Having already written the the parser and interpreter in Racket, I'm having trouble figuring out if dlang has a way for me to create a union object that can be one of many object and have it be a first-class object, ie it can be the return type of functions. Is this something dlang supports? If not, is there a better way of implementing this?
Below is some rudimentary code I wrote to test this:
import std.stdio;
import std.string;
alias string = immutable(char)[];
union Value {real realV; bool booV; string stringV; primV prim;};

struct primV{
    real function(int, int) doer;
}
real add (int a, int b){
    real sum = a+b;
    return cast(real)sum;
}
void main(){
        writeln("Beginning Interp");
        primV adder = primV(&add);
        real x = adder.doer(5,6);
        writeln(x);
        }

On Sunday, 26 May 2019 at 17:59:21 UTC, Dhruv Singal wrote:
> I'm having trouble figuring out if dlang has a way for me to create a union object that can be one of many object and have it be a first-class object, ie it can be the return type of functions. Is this something dlang supports?

Structs and unions can be returned in D. You can implement a tagged union [1] yourself with them, or use an existing library solution. The standard library has std.variant [2], but I'd recommend the sumtype package [3] (see the 'Features' section in the package description).

[1] https://en.wikipedia.org/wiki/Tagged_union
[2] https://dlang.org/phobos/std_variant.html
[3] http://code.dlang.org/packages/sumtype