diff --git a/demos/calc.cpp b/demos/calc.cpp
index df4c6bf..abe235e 100644
--- a/demos/calc.cpp
+++ b/demos/calc.cpp
@@ -5,6 +5,7 @@
 #include "guecs.hpp"
 #include "constants.hpp"
 #include <fmt/xchar.h>
+#include <deque>
 
 #define FSM_DEBUG 1
 #include "fsm.hpp"
@@ -14,94 +15,114 @@ constexpr const int WINDOW_HEIGHT=400;
 
 using std::string, std::wstring;
 
-const std::unordered_map<string, wstring> LABELS {
-    {"readout", L""}, {"clear", L"CLR"}, {"btn0", L"0"}, {"btn1", L"1"},
-    {"btn2", L"2"}, {"btn3", L"3"}, {"btn4", L"4"},
-    {"btn5", L"5"}, {"btn6", L"6"}, {"btn7", L"7"},
-    {"btn8", L"8"}, {"btn9", L"9"}, {"mult", L"*"},
-    {"minus", L"-"}, {"plus", L"+"}, {"neg", L"±"},
-    {"div", L"/"}, {"eq", L"="} };
-
 enum class Event {
   NUMBER, ADD, SUB, MUL,
-  DIV, CLR, NOT, EQ,
+  DIV, CLR, NEG, EQ, PUSH, POP
 };
 
-enum class State {
-  START,
-  CALCULATING,
-  CLEARED,
-  DISPLAYED
-};
-
-
-struct Calculator : DeadSimpleFSM<State, Event> {
+const std::unordered_map<string, wstring> LABELS {
+  {"readout", L""}, {"clear", L"CLR"}, {"btn0", L"0"}, {"btn1", L"1"},
+    {"btn2", L"2"}, {"btn3", L"3"}, {"btn4", L"4"},
+    {"btn5", L"5"}, {"btn6", L"6"}, {"btn7", L"7"},
+    {"btn8", L"8"}, {"btn9", L"9"}, {"mul", L"*"},
+    {"sub", L"-"}, {"add", L"+"}, {"neg", L"±"},
+    {"div", L"/"}, {"eq", L"="},
+    {"push", L"^"}, {"pop", L"v"} };
+
+const std::unordered_map<wchar_t, Event> EVENTS {
+  {L'0', Event::NUMBER}, {L'1', Event::NUMBER},
+    {L'2', Event::NUMBER}, {L'3', Event::NUMBER},
+    {L'4', Event::NUMBER}, {L'5', Event::NUMBER},
+    {L'6', Event::NUMBER}, {L'7', Event::NUMBER},
+    {L'8', Event::NUMBER}, {L'9', Event::NUMBER},
+    {L'*', Event::MUL}, {L'-', Event::SUB},
+    {L'+', Event::ADD}, {L'/', Event::DIV},
+    {L'C', Event::CLR}, {L'^', Event::PUSH},
+    {L'±', Event::NEG}, {L'v', Event::POP},
+    {L'=', Event::EQ} };
+
+
+struct Calculator {
   wstring input;
-  double value = 0.0;
-
-  void event(Event ev, wchar_t op) {
-    switch($state) {
-      FSM_STATE(State, START, ev, op);
-      FSM_STATE(State, CALCULATING, ev, op);
-      FSM_STATE(State, CLEARED, ev, op);
-      FSM_STATE(State, DISPLAYED, ev, op);
+  std::deque<double> stack;
+  double temp = 0.0;
+  double result = 0.0;
+
+  void dump() {
+    fmt::println("STACK: ");
+    for(auto num : stack) {
+      fmt::println("{}", num);
     }
   }
 
-  void START(Event ev, wchar_t op) {
-    if(ev == Event::NUMBER) {
-      input += op;
-      state(State::CALCULATING);
+  void do_op(Event ev) {
+    if(stack.size() < 2) return;
+    using enum Event;
+
+    double left = stack.back();
+    stack.pop_back();
+    double right = stack.back();
+    stack.pop_back();
+
+    switch(ev) {
+      case MUL:
+        temp = left * right;
+        break;
+      case ADD:
+        temp = left + right;
+        break;
+      case SUB:
+        temp = left - right;
+        break;
+      case DIV:
+        temp = left / right;
+        break;
+      default:
+        dbc::sentinel("invalid op passed to op()");
     }
+
+    stack.push_back(temp);
   }
 
-  void CALCULATING(Event ev, wchar_t op) {
+  void event(Event ev, wchar_t op) {
     using enum Event;
-
     switch(ev) {
       case NUMBER:
         input += op;
         break;
-      case ADD:
-        value += std::stof(input);
-        input = L"";
-        break;
-      case SUB:
-        value -= std::stof(input);
+      case MUL: do_op(MUL); break;
+      case ADD: do_op(ADD); break;
+      case SUB: do_op(SUB); break;
+      case DIV: do_op(DIV); break;
+      case CLR:
         input = L"";
+        stack.clear();
         break;
-      case MUL:
-        value *= std::stof(input);
-        input = L"";
+      case POP:
+        if(!stack.empty()) {
+          temp = stack.back();
+          input = fmt::format(L"{}", temp);
+          stack.pop_back();
+        }
         break;
-      case DIV:
-        value /= std::stof(input);
-        input = L"";
+      case PUSH:
+        if(input.size() > 0) {
+          temp = std::stof(input);
+          input = L"";
+          stack.push_back(temp);
+        }
         break;
-      case NOT:
-        value = std::stof(input) * -1;
-        input = L"";
+      case NEG:
+        if(input.size() > 0) {
+          temp = std::stof(input);
+          input = fmt::format(L"{}", temp * -1);
+        }
         break;
       case EQ:
-        value = std::stof(input);
-        break;
-      case CLR:
-        input = L"";
-        state(State::CLEARED);
         break;
     }
-  }
-
-  void CLEARED(Event ev, wchar_t op) {
-    if(ev == Event::NUMBER) {
-      input += op;
-      state(State::CALCULATING);
-    }
-  }
 
-  void DISPLAYED(Event ev, wchar_t op) {
-    fmt::println(L"ev={}, op={}", (int)ev, op);
-    state(State::CALCULATING);
+    dump();
   }
 };
 
@@ -112,11 +133,13 @@ struct CalculatorUI {
   CalculatorUI() {
     $gui.position(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT);
     $gui.layout(
-        "[*%(400)readout|_|_|_|clear]"
-        "[btn7|btn8|btn9|mult]"
-        "[btn4|btn5|btn6|minus]"
-        "[btn1|btn2|btn3|plus]"
-        "[neg|btn0|eq|div]");
+        "[*%(400)readout|_|_|_]"
+        "[push|pop|clear|eq]"
+        "[add|sub|mul|div]"
+        "[btn7|btn8|btn9]"
+        "[btn4|btn5|btn6]"
+        "[btn1|btn2|btn3]"
+        "[neg|btn0|_]");
   }
 
   void init() {
@@ -133,9 +156,10 @@ struct CalculatorUI {
         $gui.set<guecs::Textual>(id, {L"", 40});
       } else {
         $gui.set<guecs::Label>(id, { label });
+        wchar_t op = label[0];
         $gui.set<guecs::Clickable>(id, {
-            [&, name](auto, auto) { handle_button(label[0]); }
-        });
+            [&, op](auto, auto) { handle_button(op); }
+            });
       }
     }
 
@@ -152,52 +176,13 @@ struct CalculatorUI {
   }
 
   void handle_button(wchar_t op) {
-    using enum Event;
-
-    switch(op) {
-      case L'0':
-      case L'1':
-      case L'2':
-      case L'3':
-      case L'4':
-      case L'5':
-      case L'6':
-      case L'7':
-      case L'8':
-      case L'9':
-        $fsm.event(NUMBER, op);
-        break;
-      case L'*':
-        $fsm.event(MUL, op);
-        break;
-      case L'-':
-        $fsm.event(SUB, op);
-        break;
-      case L'+':
-        $fsm.event(ADD, op);
-        break;
-      case L'/':
-        $fsm.event(DIV, op);
-        break;
-      case L'±':
-        $fsm.event(NOT, op);
-        break;
-      case L'=':
-        $fsm.event(EQ, op);
-        break;
-      case L'C':
-        $fsm.event(CLR, op);
-        break;
-    }
-
+    $fsm.event(EVENTS.at(op), op);
     auto readout = $gui.entity("readout");
     auto& label = $gui.get<guecs::Textual>(readout);
     label.update($fsm.input);
   }
 };
 
-
-
 int main() {
   sound::init();
   shaders::init();