From 14796663b1d91a1593ee30c221281c635d2d0822 Mon Sep 17 00:00:00 2001
From: Roland Conybeare <rconybeare@gmail.com>
Date: Tue, 2 Jul 2024 16:57:07 -0400
Subject: [PATCH] xo-expression: + binding_path + assoc w/ each Variable

---
 include/xo/expression/Environment.hpp  | 15 +++++++++++++
 include/xo/expression/GlobalEnv.hpp    | 12 +++++++++-
 include/xo/expression/LocalEnv.hpp     |  6 ++++-
 include/xo/expression/Variable.hpp     |  7 +++++-
 include/xo/expression/binding_path.hpp | 29 ++++++++++++++++++++++++
 src/expression/CMakeLists.txt          |  1 +
 src/expression/LocalEnv.cpp            | 31 ++++++++++++++++++++++++++
 src/expression/Variable.cpp            |  7 ++++++
 8 files changed, 105 insertions(+), 3 deletions(-)
 create mode 100644 include/xo/expression/binding_path.hpp
 create mode 100644 src/expression/LocalEnv.cpp

diff --git a/include/xo/expression/Environment.hpp b/include/xo/expression/Environment.hpp
index 6fec9b32..6baded6d 100644
--- a/include/xo/expression/Environment.hpp
+++ b/include/xo/expression/Environment.hpp
@@ -12,6 +12,21 @@ namespace xo {
     namespace ast {
         class Environment : public ref::Refcount {
         public:
+            /** true if this is toplevel (global) environment.
+             *  Toplevel environment doesn't have slot numbers.
+             *
+             *  Variables that bind in the global environment have unique
+             *  names, which we rely on instead of slot numbers.
+             **/
+            virtual bool is_global_env() const = 0;
+
+            /** lookup binding path for @p vname in this environment.
+             *
+             *  Reports ingredients needed to address variable at runtime,
+             *  in runtime analog of this environment
+             **/
+            virtual binding_path lookup_binding(const std::string & vname) const = 0;
+
             /** lookup variable-expression @p vname in this environment.
              *  returns llvm::Value representing code that produces a value for vname
              **/
diff --git a/include/xo/expression/GlobalEnv.hpp b/include/xo/expression/GlobalEnv.hpp
index fbc9ef9c..08eb9355 100644
--- a/include/xo/expression/GlobalEnv.hpp
+++ b/include/xo/expression/GlobalEnv.hpp
@@ -7,6 +7,7 @@
 
 #include "Environment.hpp"
 #include <map>
+#include <string>
 
 namespace xo {
     namespace ast {
@@ -23,7 +24,16 @@ namespace xo {
 
             // ----- Environment -----
 
-            virtual ref::brw<Expression> lookup_var(const std::string & vname) const {
+            virtual bool is_global_env() const override { return true; }
+
+            virtual binding_path lookup_binding(const std::string & vname) const override {
+                /* i_link: -1 for global environment
+                 * j_slot: not used
+                 */
+                return { -1, 0 };
+            }
+
+            virtual ref::brw<Expression> lookup_var(const std::string & vname) const override {
                 auto ix = global_map_.find(vname);
 
                 if (ix == global_map_.end()) {
diff --git a/include/xo/expression/LocalEnv.hpp b/include/xo/expression/LocalEnv.hpp
index 42a36f2e..d8fe2178 100644
--- a/include/xo/expression/LocalEnv.hpp
+++ b/include/xo/expression/LocalEnv.hpp
@@ -47,6 +47,10 @@ namespace xo {
 
             // ----- Environment -----
 
+            virtual bool is_global_env() const override { return false; }
+
+            virtual binding_path lookup_binding(const std::string & vname) const override;
+
             virtual ref::brw<Expression> lookup_var(const std::string & target) const override {
                 for (const auto & arg : argv_) {
                     if (arg->name() == target)
@@ -61,7 +65,7 @@ namespace xo {
 
         private:
             LocalEnv(const std::vector<ref::rp<Variable>> & argv)
-                : argv_(argv) {}
+                : origin_{nullptr}, argv_(argv) {}
 
         private:
             /** Lambnda for which this environment created.
diff --git a/include/xo/expression/Variable.hpp b/include/xo/expression/Variable.hpp
index 471eb873..3f45677e 100644
--- a/include/xo/expression/Variable.hpp
+++ b/include/xo/expression/Variable.hpp
@@ -6,6 +6,7 @@
 #pragma once
 
 #include "Expression.hpp"
+#include "binding_path.hpp"
 
 namespace xo {
     namespace ast {
@@ -42,7 +43,7 @@ namespace xo {
                 return 1;
             }
 
-            virtual void attach_envs(ref::brw<Environment> /*p*/) override {}
+            virtual void attach_envs(ref::brw<Environment> /*p*/) override;
 
             virtual void display(std::ostream & os) const override;
 
@@ -55,6 +56,10 @@ namespace xo {
         private:
             /** variable name **/
             std::string name_;
+            /** navigate environment via this path to find runtime memory
+             *  location for this variable
+             **/
+            binding_path path_;
         }; /*Variable*/
 
         inline ref::rp<Variable>
diff --git a/include/xo/expression/binding_path.hpp b/include/xo/expression/binding_path.hpp
new file mode 100644
index 00000000..a3692ed1
--- /dev/null
+++ b/include/xo/expression/binding_path.hpp
@@ -0,0 +1,29 @@
+/* file binding_path.hpp
+ *
+ * author: Roland Conybeare, Jul 2024
+ */
+
+#pragma once
+
+namespace xo {
+    namespace ast {
+        /** @class path
+         *
+         *  @brief path from the *use* of a variable to the environment
+         *  providing its location.
+         **/
+        struct binding_path {
+            /** @of parent links to traverse.  -1 if global **/
+            int i_link_ = -1;
+            /** for variables bound in some local environment:
+             *  slot# within that environment.
+             *
+             *  Ignored if @ref i_link_ is -1
+             **/
+            int j_slot_ = 0;
+        }; /*binding_path*/
+    } /*namespace ast*/
+} /*namespace xo*/
+
+
+/* end binding_path.hpp */
diff --git a/src/expression/CMakeLists.txt b/src/expression/CMakeLists.txt
index ef5cf6f2..50edec01 100644
--- a/src/expression/CMakeLists.txt
+++ b/src/expression/CMakeLists.txt
@@ -7,6 +7,7 @@ set(SELF_SRCS
     Lambda.cpp
     Variable.cpp
     IfExpr.cpp
+    LocalEnv.cpp
 )
 
 xo_add_shared_library4(${SELF_LIB} ${PROJECT_NAME}Targets ${PROJECT_VERSION} 1 ${SELF_SRCS})
diff --git a/src/expression/LocalEnv.cpp b/src/expression/LocalEnv.cpp
new file mode 100644
index 00000000..fb724aeb
--- /dev/null
+++ b/src/expression/LocalEnv.cpp
@@ -0,0 +1,31 @@
+/* file LocalEnv.cpp
+ *
+ * author: Roland Conybeare
+ */
+
+#include "LocalEnv.hpp"
+
+namespace xo {
+    namespace ast {
+        binding_path
+        LocalEnv::lookup_binding(const std::string & vname) const
+        {
+            int j_slot = 0;
+            for (const auto & arg : argv_) {
+                if (arg->name() == vname)
+                    return { 0 /*i_link*/, j_slot };
+                ++j_slot;
+            }
+
+            auto tmp = parent_env_->lookup_binding(vname);
+
+            if (tmp.i_link_ == -1)
+                return tmp;
+            else
+                return { tmp.i_link_ + 1, tmp.j_slot_ };
+        } /*lookup_binding*/
+    } /*namespace ast*/
+} /*namespace xo*/
+
+
+/* end LocalEnv.cpp */
diff --git a/src/expression/Variable.cpp b/src/expression/Variable.cpp
index 52890ccc..71d47655 100644
--- a/src/expression/Variable.cpp
+++ b/src/expression/Variable.cpp
@@ -1,9 +1,16 @@
 /* @file Variable.cpp */
 
 #include "Variable.hpp"
+#include "Environment.hpp"
 
 namespace xo {
     namespace ast {
+        void
+        Variable::attach_envs(ref::brw<Environment> e) {
+            /** e makes accessible all enclosing lexical scopes **/
+            this->path_ = e->lookup_binding(this->name_);
+        } /*attach_envs*/
+
         void
         Variable::display(std::ostream & os) const {
             os << "<Variable"