xo-interpreter2 stack: scaffold DClosure, DLocalEnv [WIP]

include/xo/interpreter2/DClosure.hpp

@@ -0,0 +1,49 @@
+/** @file DClosure.hpp
+ *
+ *  @author Roland Conybeare, Feb 2026
+ **/
+
+#include "LocalEnv.hpp"
+#include <xo/expression2/LambdaExpr.hpp>
+
+namespace xo {
+    namespace scm {
+
+        /** @brief runtime representation for a procedure
+         *
+         *  Maintains lambda + captured lexical context
+         **/
+        class DClosure {
+        public:
+            using AAllocator = xo::mm::AAllocator;
+            using size_type = std::int32_t;
+
+        public:
+            DClosure(const DLambdaExpr * lm,
+                     const DLocalEnv * env);
+
+            /** create instance using memory from @p mm
+             *  for lambda @p lm with captured environment @p env.
+             **/
+            static DClosure * make(obj<AAllocator> mm,
+                                   const DLambdaExpr * lm,
+                                   const DLocalEnv * env);
+
+            /** for now, support just fixed-arity procedures **/
+            bool is_nary() const noexcept { return false; }
+            /** number of arguments expected by this procedure (-1 if nary) **/
+            size_type n_args() const noexcept { return lambda_->n_args(); }
+
+        private:
+            /** lambda expression **/
+            const DLambdaExpr * lambda_ = nullptr;
+            /** bindings for captured variables
+             *  (from lexical context where lambda evaluated)
+             **/
+            const DLocalEnv * env_ = nullptr;
+        };
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DClosure.hpp */