Add 'xo-expression/' from commit '5ac3c03a0c'

git-subtree-dir: xo-expression
git-subtree-mainline: d0f5ccc1ce
git-subtree-split: 5ac3c03a0c

xo-expression/include/xo/expression/Variable.hpp

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+/** @file Variable.hpp
+ *
+ *  Author: Roland Conybeare
+ **/
+
+#pragma once
+
+#include "Expression.hpp"
+#include "binding_path.hpp"
+
+namespace xo {
+    namespace ast {
+
+        /** @class Variable
+         *  @brief syntax for a variable reference
+         **/
+        class Variable : public Expression {
+        public:
+            /** create expression representing a variable
+             *  identified by @p name,  that can take on values
+             *  described by @p var_type.
+             **/
+            static rp<Variable> make(const std::string & name,
+                                     TypeDescr var_type) {
+                return new Variable(name, var_type);
+            }
+
+            /** return copy of x:  same var, different object identity **/
+            static rp<Variable> copy(ref::brw<Variable> x) {
+                return new Variable(x->name(), x->valuetype());
+            }
+
+            /** downcast from Expression **/
+            static ref::brw<Variable> from(ref::brw<Expression> x) {
+                return ref::brw<Variable>::from(x);
+            }
+
+            const std::string & name() const { return name_; }
+
+            virtual std::set<std::string> get_free_variables() const override {
+                std::set<std::string> retval;
+                retval.insert(this->name_);
+                return retval;
+            }
+
+            virtual std::size_t visit_preorder(VisitFn visitor_fn) override {
+                visitor_fn(this);
+                return 1;
+            }
+
+            virtual std::size_t visit_layer(VisitFn visitor_fn) override {
+                visitor_fn(this);
+                return 1;
+            }
+
+            virtual rp<Expression> xform_layer(TransformFn xform_fn) override {
+                return xform_fn(this);
+            }
+
+            virtual void attach_envs(ref::brw<Environment> /*p*/) override;
+
+            virtual void display(std::ostream & os) const override;
+
+        private:
+            Variable(const std::string & name,
+                     TypeDescr var_type)
+                : Expression(exprtype::variable, var_type),
+                  name_{name} {}
+
+        private:
+            /** variable name **/
+            std::string name_;
+            /** navigate environment via this path to find runtime memory
+             *  location for this variable
+             **/
+            binding_path path_;
+        }; /*Variable*/
+
+        inline rp<Variable>
+        make_var(const std::string & name,
+                 reflect::TypeDescr var_type) {
+            return Variable::make(name, var_type);
+        }
+    } /*namespace ast*/
+} /*namespace xo*/
+
+
+/** end Variable.hpp **/