Try tail recursion

day23.cpp

@@ -6,6 +6,7 @@
 #include <utility>
 #include <variant>
 #include <vector>
+#include <fstream>
 
 #include <intcode/intcode.hpp>
 using namespace intcode;
@@ -25,25 +26,23 @@ auto BuildNetwork(Machine m) -> std::vector<Machine> {
 }
 
 auto Interact(Ethernet & ethernet, Machine & m, std::optional<Packet> p) -> void {
-  while(Advance(m,
-  [&](auto &i) {
+  std::visit(overloaded{
+  [&](Input i) {
     if (p) {
-      i = p->first;
+      i.pos = p->first;
       StepInput(m, p->second);
-      p = {};
-      return true;
+      Interact(ethernet, m, {});
     }
-    i = -1; // no packet
-    return false;
+    i.pos = -1; // no packet
   },
-  [&](auto d) {
+  [&](Output d) {
     auto x = StepOutput(m);
     auto y = StepOutput(m);
-    ethernet.push_back({d, {x,y}});
-    return true;
+    ethernet.push_back({d.val, {x,y}});
+    Interact(ethernet, m, p);
   },
-  []() -> bool { throw std::runtime_error{"unexpected halt"}; }
-  )) {}
+  [](Halt) -> void { throw std::runtime_error{"unexpected halt"}; },
+  }, Step(m));
 }
 
 } // namespace