From d6727ab770263ccad37f6b97498eb4acce3224ac Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@gmail.com>
Date: Sat, 5 Nov 2022 15:40:30 -0700
Subject: [PATCH] advance

---
 day23.cpp                           | 19 ++++++++-----------
 lib/include/intcode/Interpreter.hpp | 28 ++++++++++++++++------------
 2 files changed, 24 insertions(+), 23 deletions(-)

diff --git a/day23.cpp b/day23.cpp
index 73e180d..01fd7f2 100644
--- a/day23.cpp
+++ b/day23.cpp
@@ -25,28 +25,25 @@ auto BuildNetwork(Machine m) -> std::vector<Machine> {
 }
 
 auto Interact(Ethernet & ethernet, Machine & m, std::optional<Packet> p) -> void {
-  while(std::visit(overloaded{
-
-  [&](Input i) {
+  while(Advance(m,
+  [&](auto &i) {
     if (p) {
-      i.pos = p->first;
+      i = p->first;
       StepInput(m, p->second);
       p = {};
       return true;
     }
-    i.pos = -1; // no packet
+    i = -1; // no packet
     return false;
   },
-
-  [&](Output o) {
+  [&](auto d) {
     auto x = StepOutput(m);
     auto y = StepOutput(m);
-    ethernet.push_back({o.val, {x,y}});
+    ethernet.push_back({d, {x,y}});
     return true;
   },
-
-  [](Halt) -> bool { throw std::runtime_error{"unexpected halt"}; },
-  }, Step(m))) {}
+  []() -> bool { throw std::runtime_error{"unexpected halt"}; }
+  )) {}
 }
 
 } // namespace
diff --git a/lib/include/intcode/Interpreter.hpp b/lib/include/intcode/Interpreter.hpp
index 13bc499..2fe2fdd 100644
--- a/lib/include/intcode/Interpreter.hpp
+++ b/lib/include/intcode/Interpreter.hpp
@@ -2,6 +2,7 @@
 #define INTCODE_INTERPRETER_HPP_
 
 #include <variant>
+#include <concepts>
 
 #include <intcode/Machine.hpp>
 #include <Overload.hpp>
@@ -27,19 +28,22 @@ struct BadInstruction : public std::runtime_error {
   explicit BadInstruction(char const* what);
 };
 
-template <class Fin, class Fout>
+template <std::invocable<ValueType&> Fin, std::invocable<ValueType> Fout, std::invocable<> Fhalt>
+auto Advance(Machine & machine, Fin input, Fout output, Fhalt halt) {
+  return std::visit(overloaded{
+    [&](Halt) { return halt(); },
+    [&](Input i) { return input(i.pos); },
+    [&](Output o) { return output(o.val); },
+    }, Step(machine));
+}
+
+template <std::invocable<> Fin, std::invocable<ValueType> Fout>
 auto Run(Machine & machine, Fin input, Fout output) -> void {
-  while (std::visit(overloaded{
-    [](Halt) { return false; },
-    [&](Input arg) {
-      arg.pos = input();
-      return true;
-    },
-    [&](Output arg) {
-      output(arg.val);
-      return true;
-    }},
-    Step(machine)));
+  while (Advance(machine,
+    [&](ValueType &i) { i = input(); return true; },
+    [&](ValueType o) { output(o); return true; },
+    []() { return false; }
+    )) {}
 }
 
 } // namespace