2 files changed, 33 insertions, 0 deletions
diff --git a/ttwhy/core/concepts.cppm b/ttwhy/core/concepts.cppm
new file mode 100644
index 0000000..f7ac583
--- /dev/null
+++ b/ttwhy/core/concepts.cppm
@@ -0,0 +1,30 @@
+module;
+
+#include <asio.hpp>
+
+#include <concepts>
+#include <span>
+
+export module ttwhy.core:concepts;
+
+namespace ttwhy
+{
+
+  export template<typename Candidate>
+  concept scanner = requires(Candidate a, std::span<char const> buffer) {
+    { a.process(buffer) } -> std::same_as<void>;
+    { a.timeout() } -> std::same_as<void>;
+    { a.is_pending() } -> std::same_as<bool>;
+  };
+
+  export template<typename Candidate, typename Event>
+  concept router = requires(Candidate candidate, Event event) {
+    { candidate.process(event) } -> std::same_as<asio::awaitable<void>>;
+  };
+
+  export template<typename Sink, typename Event>
+  concept event_sink = requires(Sink sink, Event event) {
+    { sink(event) } -> std::same_as<void>;
+  };
+
+}  // namespace ttwhy
diff --git a/ttwhy/core/mod.cppm b/ttwhy/core/mod.cppm
new file mode 100644
index 0000000..a6bf056
--- /dev/null
+++ b/ttwhy/core/mod.cppm
@@ -0,0 +1,3 @@
+export module ttwhy.core;
+
+export import :concepts;