First cut at a replica of the python raycaster. Left side almost works the same but have to sort out math differences.

dbc.cpp

@@ -0,0 +1,40 @@
+#include "dbc.hpp"
+
+void dbc::log(const string &message) {
+  fmt::print("{}\n", message);
+}
+
+void dbc::sentinel(const string &message) {
+  string err = fmt::format("[SENTINEL!] {}\n", message);
+  throw dbc::SentinelError{err};
+}
+
+void dbc::pre(const string &message, bool test) {
+  if(!test) {
+    string err = fmt::format("[PRE!] {}\n", message);
+    throw dbc::PreCondError{err};
+  }
+}
+
+void dbc::pre(const string &message, std::function<bool()> tester) {
+  dbc::pre(message, tester());
+}
+
+void dbc::post(const string &message, bool test) {
+  if(!test) {
+    string err = fmt::format("[POST!] {}\n", message);
+    throw dbc::PostCondError{err};
+  }
+}
+
+void dbc::post(const string &message, std::function<bool()> tester) {
+  dbc::post(message, tester());
+}
+
+void dbc::check(bool test, const string &message) {
+  if(!test) {
+    string err = fmt::format("[CHECK!] {}\n", message);
+    fmt::println("{}", err);
+    throw dbc::CheckError{err};
+  }
+}