After trying a few SFM libraries I found they're just too much for what I need, so here's the start of a simple one I can use.

fsmtest.cpp

@@ -0,0 +1,62 @@
+#include <fmt/core.h>
+
+using namespace fmt;
+
+template<typename S, typename E>
+class DeadSimpleFSM {
+protected:
+  S _state = S::START;
+
+public:
+  virtual void event(E event) = 0;
+
+  void state(S next_state) {
+    _state = next_state;
+  }
+};
+
+#define T(S, F) case S: F(); break
+
+enum MyState {
+  START, RUNNING, END
+};
+
+enum MyEvent {
+  STARTED, PUSH, QUIT
+};
+
+class MyFSM : DeadSimpleFSM<MyState, MyEvent> {
+public:
+  void event(MyEvent ev) override {
+    switch(ev) {
+      T(STARTED, start);
+      T(PUSH, push);
+      T(QUIT, stop);
+    }
+  }
+
+  void start() {
+    println("<<< START");
+    state(RUNNING);
+  }
+
+  void push() {
+    println("<<< RUN");
+    state(RUNNING);
+  }
+
+  void quit() {
+    println("<<< STOP");
+    state(END);
+  }
+};
+
+int main() {
+  MyFSM fsm;
+
+  fsm.event(STARTED);
+  fsm.event(PUSH);
+  fsm.event(PUSH);
+  fsm.event(PUSH);
+  fsm.event(QUIT);
+}

meson.build

@@ -11,9 +11,9 @@ opts.add_cmake_defines({
   'BUILD_TESTS': false,
   })
 libgit2_proj = cmake.subproject('libgit2', options: opts)
-libgit2package_dep = libgit2_proj.dependency('libgit2package')
+libgit2package = libgit2_proj.dependency('libgit2package')
 
-efsw_dep = dependency('efsw')
+efsw = dependency('efsw')
 fmt = dependency('fmt')
 catch2 = dependency('catch2-with-main')
 sfml = dependency('sfml')
@@ -21,7 +21,7 @@ json = dependency('nlohmann_json')
 imgui = dependency('imgui-sfml')
 
 dependencies = [
-  fmt, libgit2package_dep, efsw_dep,
+  fmt, libgit2package, efsw,
   sfml, imgui, json
 ]
 
@@ -46,6 +46,9 @@ executable('jsontest', 'jsontest.cpp',
 executable('threadtest', 'threadtest.cpp',
   dependencies: dependencies)
 
+executable('fsmtest', 'fsmtest.cpp',
+  dependencies: dependencies)
+
 executable('badref', 'badref.cpp',
   dependencies: dependencies)