Haxe GADTs for API endpoints

Test.hx

class Test {
  static function main() {
    var req = makeRequest(Foo, r -> trace(r.foo));
    req.send();
    
    var req2 = makeRequest(Bar(42), r -> trace(r.answer));
    req2.send();
  }
  
  static function makeRequest<T>(endpoint:Endpoint<T>, handler:T->Void) {
    return {
      // Replace this with a proper server call
      send: () -> handler(switch (endpoint) {
      	case Foo: {foo: "bar"};
    		case Bar(v): {answer: v};
    	})
  	};
  }
}

enum Endpoint<TResponse> {
  Foo:Endpoint<FooResponse>;
  Bar(v:Int):Endpoint<BarResponse>;
}
  
typedef FooResponse = {foo:String}
typedef BarResponse = {answer:Int}

https://try.haxe.org/#deDe2396