From 4b0a2cff2a7413c1662ec8d3d20404347d107538 Mon Sep 17 00:00:00 2001
From: Roland Conybeare <rconybeare@gmail.com>
Date: Wed, 3 Jul 2024 16:20:18 -0400
Subject: [PATCH] xo-expression: + Lambda::nested_lambda_map

---
 include/xo/expression/GlobalEnv.hpp    |  2 +-
 include/xo/expression/Lambda.hpp       |  3 +++
 include/xo/expression/binding_path.hpp |  4 ++--
 src/expression/Lambda.cpp              | 21 ++++++++++++++++++++-
 src/expression/Variable.cpp            |  6 +++++-
 5 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/include/xo/expression/GlobalEnv.hpp b/include/xo/expression/GlobalEnv.hpp
index 08eb9355..010dc296 100644
--- a/include/xo/expression/GlobalEnv.hpp
+++ b/include/xo/expression/GlobalEnv.hpp
@@ -26,7 +26,7 @@ namespace xo {
 
             virtual bool is_global_env() const override { return true; }
 
-            virtual binding_path lookup_binding(const std::string & vname) const override {
+            virtual binding_path lookup_binding(const std::string & /*vname*/) const override {
                 /* i_link: -1 for global environment
                  * j_slot: not used
                  */
diff --git a/include/xo/expression/Lambda.hpp b/include/xo/expression/Lambda.hpp
index 3a3de6ac..91366ca9 100644
--- a/include/xo/expression/Lambda.hpp
+++ b/include/xo/expression/Lambda.hpp
@@ -135,6 +135,9 @@ namespace xo {
              **/
             std::map<std::string, ref::rp<Variable>> layer_var_map_;
 
+            /** all lambdas nested once inside this lambda's body **/
+            std::map<std::string, ref::brw<Lambda>> nested_lambda_map_;
+
             /** established (once) by @ref attach_envs.
              *
              * @note data dependency on ancestor expressions that don't exist yet
diff --git a/include/xo/expression/binding_path.hpp b/include/xo/expression/binding_path.hpp
index a3692ed1..7aef8c51 100644
--- a/include/xo/expression/binding_path.hpp
+++ b/include/xo/expression/binding_path.hpp
@@ -13,8 +13,8 @@ namespace xo {
          *  providing its location.
          **/
         struct binding_path {
-            /** @of parent links to traverse.  -1 if global **/
-            int i_link_ = -1;
+            /** @of parent links to traverse.  -1 if global. -2 if sentinel **/
+            int i_link_ = -2;
             /** for variables bound in some local environment:
              *  slot# within that environment.
              *
diff --git a/src/expression/Lambda.cpp b/src/expression/Lambda.cpp
index fba94694..320e1eda 100644
--- a/src/expression/Lambda.cpp
+++ b/src/expression/Lambda.cpp
@@ -83,7 +83,7 @@ namespace xo {
              * Motivation is to unify Variables that would use the same
              * binding_path to resolve their runtime location.
              */
-            std::map<std::string, rp<Variable>> var_map;
+            std::map<std::string, ref::rp<Variable>> var_map;
 
             for (const auto & arg : local_env_->argv()) {
                 /* each arg name can appear at most once
@@ -148,6 +148,24 @@ namespace xo {
 
             this->free_var_set_ = this->calc_free_variables();
 
+            std::map<std::string, ref::brw<Lambda>> nested_lambda_map;
+
+            this->body_->visit_layer
+                ([&nested_lambda_map]
+                 (ref::brw<Expression> expr)
+                    {
+                        if (expr->extype() == exprtype::lambda) {
+                            ref::brw<Lambda> lm = Lambda::from(expr);
+
+                            nested_lambda_map[lm->name()] = lm.get();
+                        }
+                    });
+
+            this->nested_lambda_map_ = std::move(nested_lambda_map);
+
+            /* in particular:
+             * - establish binding path for each variable
+             */
             this->body_->attach_envs(local_env_);
         } /*ctor*/
 
@@ -155,6 +173,7 @@ namespace xo {
         Lambda::attach_envs(ref::brw<Environment> p) {
             local_env_->assign_parent(p);
 
+            /** establish a binding path for each variable **/
         }
 
         void
diff --git a/src/expression/Variable.cpp b/src/expression/Variable.cpp
index 71d47655..766e0c67 100644
--- a/src/expression/Variable.cpp
+++ b/src/expression/Variable.cpp
@@ -8,7 +8,11 @@ namespace xo {
         void
         Variable::attach_envs(ref::brw<Environment> e) {
             /** e makes accessible all enclosing lexical scopes **/
-            this->path_ = e->lookup_binding(this->name_);
+            if (this->path_.i_link_ == -2 /*sentinel*/) {
+                this->path_ = e->lookup_binding(this->name_);
+            } else {
+                /* have already established binding for this Variable */
+            }
         } /*attach_envs*/
 
         void