xo-reader2 xo-expresion2: work on define-expressions [WIP]

include/xo/expression2/DDefineExpr.hpp

@@ -0,0 +1,75 @@
+/** @file DDefineExpr.hpp
+*
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#pragma once
+
+#include "Expression.hpp"
+#include "DVariable.hpp"
+#include <xo/alloc2/Allocator.hpp>
+
+namespace xo {
+    namespace scm {
+        class DUniqueString; // see DUniqueString.hpp
+
+        /** @class DDefineExpr
+         *  @brief an expression that introduces a variable.
+         *
+         *  Variable may optionally be declared with a type,
+         *  and may come with an expression specifying an initial value
+         **/
+        class DDefineExpr {
+        public:
+            using AAllocator = xo::mm::AAllocator;
+            using TypeDescr = xo::reflect::TypeDescr;
+
+        public:
+            /** create instance: define-expr using memory from @p mm
+             *  with lhs name @p lhs_name and rhs expression @p rhs_expr
+             **/
+            static DDefineExpr * make(obj<AAllocator> mm,
+                                      const DUniqueString * lhs_name,
+                                      obj<AExpression> rhs_expr);
+            /** create empty skeleton. Rely on this for parsing
+             **/
+            static DDefineExpr * make_empty(obj<AAllocator> mm);
+
+            DVariable * lhs() const { return lhs_var_; }
+            obj<AExpression> rhs() const noexcept { return rhs_; }
+
+            const DUniqueString * name() const noexcept;
+
+            void assign_lhs_name(const DUniqueString * name);
+            /** CONCESSION.  will use DUniqueString* once we have StringTable **/
+            void assign_lhs_name(std::string_view name);
+
+            /** @defgroup scm-defineexpr-expression-facet **/
+            ///@{
+
+            exprtype extype() const noexcept { return exprtype::define; }
+            TypeRef typeref() const noexcept { return lhs_var_->typeref(); }
+            TypeDescr valuetype() const noexcept { return lhs_var_->typeref().td(); }
+            void assign_valuetype(TypeDescr td) noexcept;
+
+            ///@}
+
+        private:
+            DDefineExpr(DVariable * lhs_var,
+                        obj<AExpression> rhs);
+
+        private:
+            /** variable being defined by this expression.
+             **/
+            DVariable * lhs_var_ = nullptr;
+
+            /** expression for initial value of this expression
+             **/
+            obj<AExpression> rhs_;
+
+            // std::set<std::string> free_var_set_;
+        };
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DDefineExpr.hpp */