From 9a1a419aef300afc86cc4bac86590639e81353f3 Mon Sep 17 00:00:00 2001
From: Roland Conybeare <rconybeare@gmail.com>
Date: Tue, 6 Aug 2024 03:20:19 -0400
Subject: [PATCH] xo-exprssion: + DefineExpr

---
 include/xo/expression/DefineExpr.hpp | 128 +++++++++++++++++++++++++++
 src/expression/CMakeLists.txt        |   1 +
 src/expression/DefineExpr.cpp        |  99 +++++++++++++++++++++
 3 files changed, 228 insertions(+)
 create mode 100644 include/xo/expression/DefineExpr.hpp
 create mode 100644 src/expression/DefineExpr.cpp

diff --git a/include/xo/expression/DefineExpr.hpp b/include/xo/expression/DefineExpr.hpp
new file mode 100644
index 00000000..e7ffce65
--- /dev/null
+++ b/include/xo/expression/DefineExpr.hpp
@@ -0,0 +1,128 @@
+/* file DefineExpr.hpp
+ *
+ * author: Roland Conybeare, Jul 2024
+ */
+
+#pragma once
+
+#include "Expression.hpp"
+
+namespace xo {
+    namespace ast {
+        /** @class DefineExpr
+         *  @brief Provide definition for a constant, variable or function
+         *
+         *  At toplevel,  introduces a new global variable.
+         *  In a nested context,
+         *
+         *    def foo = rhsexpr
+         *    body...
+         *
+         *  is equivalent to
+         *
+         *    (lambda (foo) body...)(rhsexpr)
+         **/
+        class DefineExpr : public Expression {
+        public:
+            static rp<DefineExpr> make(std::string name,
+                                       rp<Expression> value);
+
+
+            static ref::brw<DefineExpr> from(ref::brw<Expression> x) {
+                return ref::brw<DefineExpr>::from(x);
+            }
+
+            const std::string & lhs_name() const { return lhs_name_; }
+            const rp<Expression> & rhs() const { return rhs_; }
+
+            std::set<std::string> calc_free_variables() const;
+
+            // ----- Expression -----
+
+            virtual std::set<std::string> get_free_variables() const override {
+                return this->free_var_set_;
+            }
+
+            virtual std::size_t visit_preorder(VisitFn visitor_fn) override {
+                std::size_t n = 1;
+
+                visitor_fn(this);
+
+                n += rhs_->visit_preorder(visitor_fn);
+
+                return n;
+            }
+
+            virtual std::size_t visit_layer(VisitFn visitor_fn) override {
+                std::size_t n = 1;
+
+                visitor_fn(this);
+
+                n += this->rhs_->visit_layer(visitor_fn);
+
+                return n;
+            }
+
+            virtual rp<Expression> xform_layer(TransformFn xform_fn) override {
+                this->rhs_ = this->rhs_->xform_layer(xform_fn);
+
+                return xform_fn(this);
+            }
+
+            virtual void attach_envs(ref::brw<Environment> p) override {
+                rhs_->attach_envs(p);
+            }
+
+            virtual void display(std::ostream & os) const override;
+
+        protected:
+            /**
+             *
+             **/
+            DefineExpr(TypeDescr rhs_valuetype,
+                       std::string lhs_name,
+                       rp<Expression> rhs);
+
+        protected:
+            /** symbol name for this definition **/
+            std::string lhs_name_;
+            /** right-hand side of definition **/
+            rp<Expression> rhs_;
+
+            /** free variables for this definition **/
+            std::set<std::string> free_var_set_;
+        };
+
+        /** @class DefineExprAccess
+         *  @brief DefineExpr with writeable members.
+         *
+         *  Convenient when scaffolding a parser,
+         *  e.g. see xo-parser
+         **/
+        class DefineExprAccess : public DefineExpr {
+        public:
+            static rp<DefineExprAccess> make(std::string lhs_name,
+                                             rp<Expression> rhs);
+            static rp<DefineExprAccess> make_empty();
+
+            void assign_lhs_name(const std::string & x) {
+                this->lhs_name_ = x;
+            }
+
+            void assign_rhs(const rp<Expression> & x);
+
+        private:
+            DefineExprAccess(TypeDescr rhs_valuetype,
+                             std::string lhs_name,
+                             rp<Expression> rhs)
+                : DefineExpr(rhs_valuetype,
+                             std::move(lhs_name),
+                             std::move(rhs))
+                {}
+        };
+
+    } /*namespace ast*/
+} /*namespace xo*/
+
+
+/* end DefineExpr.hpp */
diff --git a/src/expression/CMakeLists.txt b/src/expression/CMakeLists.txt
index 50edec01..32520c85 100644
--- a/src/expression/CMakeLists.txt
+++ b/src/expression/CMakeLists.txt
@@ -3,6 +3,7 @@
 set(SELF_LIB xo_expression)
 set(SELF_SRCS
     Expression.cpp
+    DefineExpr.cpp
     Apply.cpp
     Lambda.cpp
     Variable.cpp
diff --git a/src/expression/DefineExpr.cpp b/src/expression/DefineExpr.cpp
new file mode 100644
index 00000000..1c67188c
--- /dev/null
+++ b/src/expression/DefineExpr.cpp
@@ -0,0 +1,99 @@
+/* file DefineExpr.cpp
+ *
+ * author: Roland Conybeare
+ */
+
+#include "DefineExpr.hpp"
+
+namespace xo {
+    namespace ast {
+        rp<DefineExpr>
+        DefineExpr::make(std::string lhs_name,
+                         rp<Expression> rhs)
+        {
+            TypeDescr rhs_valuetype = nullptr;
+
+            if (rhs)
+                rhs_valuetype = rhs->valuetype();
+
+            return new DefineExpr(rhs_valuetype,
+                                  std::move(lhs_name),
+                                  std::move(rhs));
+        } /*make*/
+
+        DefineExpr::DefineExpr(TypeDescr rhs_valuetype,
+                               std::string lhs_name,
+                               rp<Expression> rhs)
+            : Expression(exprtype::define, rhs_valuetype),
+              lhs_name_{std::move(lhs_name)},
+              rhs_{std::move(rhs)}
+        {
+            this->free_var_set_ = this->calc_free_variables();
+        }
+
+        std::set<std::string>
+        DefineExpr::calc_free_variables() const
+        {
+            std::set<std::string> retval;
+
+            if (rhs_)
+                retval = rhs_->get_free_variables();
+
+            /* but remove this variable */
+            if (!this->lhs_name().empty())
+                retval.erase(this->lhs_name());
+
+            return retval;
+        } /*calc_free_variables*/
+
+        void
+        DefineExpr::display(std::ostream & os) const {
+            os << "<Define"
+               << xtag("name", lhs_name_)
+               << xtag("rhs", rhs_)
+               << ">";
+        } /*display*/
+
+        // ----- DefineExprAccess -----
+
+        rp<DefineExprAccess>
+        DefineExprAccess::make(std::string lhs_name,
+                               rp<Expression> rhs)
+        {
+            TypeDescr rhs_valuetype = nullptr;
+
+            if (rhs)
+                rhs_valuetype = rhs->valuetype();
+
+            return new DefineExprAccess(rhs_valuetype,
+                                        std::move(lhs_name),
+                                        std::move(rhs));
+        }
+
+        rp<DefineExprAccess>
+        DefineExprAccess::make_empty()
+        {
+            return new DefineExprAccess(nullptr /*rhs_valuetype*/,
+                                        "" /*lhs_name*/,
+                                        nullptr /*rhs*/);
+        }
+
+        void
+        DefineExprAccess::assign_rhs(const rp<Expression> & x)
+        {
+            assert(x);
+
+            this->rhs_ = x;
+
+            if (x) {
+                this->assign_valuetype(x->valuetype());
+            }
+
+            this->free_var_set_ = this->calc_free_variables();
+        }
+
+    } /*namespace ast*/
+} /*namespace xo*/
+
+
+/* end DefineExpr.cpp */