xo-expression2 xo-gc: DSequenceExpr builds [WIP]

include/xo/expression2/DSequenceExpr.hpp

@@ -0,0 +1,83 @@
+/** @file DSequenceExpr.hpp
+ *
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#pragma once
+
+#include "Expression.hpp"
+#include "TypeRef.hpp"
+#include <xo/object2/DArray.hpp>
+
+namespace xo {
+    namespace scm {
+
+        /** syntax for a sequence of expressions
+         *   {
+         *      expr(1);
+         *      expr(2);
+         *      ...
+         *      expr(n);
+         *   }
+         **/
+        class DSequenceExpr {
+        public:
+            using AAllocator = xo::mm::AAllocator;
+            using TypeDescr = xo::reflect::TypeDescr;
+            using size_type = DArray::size_type;
+            using ppindentinfo = xo::print::ppindentinfo;
+
+        public:
+            DSequenceExpr() = default;
+            DSequenceExpr(DArray * xv) : expr_v_{xv} {}
+
+            /** create empty sequence using memory from @p mm **/
+            static obj<AExpression,DSequenceExpr> make_empty(obj<AAllocator> mm);
+
+            /** create empty sequence expression using mmeory from @p mm **/
+            static DSequenceExpr * _make_empty(obj<AAllocator> mm);
+
+            size_type size() const noexcept;
+            obj<AExpression> operator[](std::size_t i) const;
+
+            /** append @p expr to the end of this sequence;
+             *  use memory from @p mm if need to expand storage
+             **/
+            void push_back(obj<AAllocator> mm,
+                           obj<AExpression> expr);
+
+            // get_free_variables();
+            // visit_preorder();
+            // visit_layer();
+            // xform_layer()
+            // attach_envs()
+
+            /** @defgroup scm-ifelseexpr-expression-facets **/
+            ///@{
+
+            exprtype extype() const noexcept { return exprtype::sequence; }
+            TypeRef typeref() const noexcept { return typeref_; }
+            TypeDescr valuetype() const noexcept { return typeref_.td(); }
+            void assign_valuetype(TypeDescr td) noexcept;
+
+            ///@}
+            /** @defgroup scm-sequenceexpr-printable-facet printable facet methods **/
+            ///@{
+
+            /** pretty-printing driver; combine layout+printing **/
+            bool pretty(const ppindentinfo & ppii) const;
+
+            ///@}
+
+        private:
+            /** expression value always has type consistent with this description
+             **/
+            TypeRef typeref_;
+            /** array of expressions **/
+            DArray * expr_v_ = nullptr;
+        };
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DSequenceExpr.hpp */