AST+Eval: Prevent list copy during core function 'rest'

src/ast.cpp

@@ -22,6 +22,11 @@ Collection::Collection(const std::list<ValuePtr>& nodes)
 {
 }
 
+Collection::Collection(ValueListConstIt begin, ValueListConstIt end)
+	: m_nodes(ValueList(begin, end))
+{
+}
+
 void Collection::add(ValuePtr node)
 {
 	if (node == nullptr) {
@@ -40,6 +45,12 @@ void Collection::addFront(ValuePtr node)
 	m_nodes.push_front(node);
 }
 
+ValueList Collection::rest() const
+{
+	auto start = (m_nodes.size() > 0) ? std::next(m_nodes.begin()) : m_nodes.end();
+	return ValueList(start, m_nodes.end());
+}
+
 // -----------------------------------------
 
 List::List(const std::list<ValuePtr>& nodes)
@@ -47,6 +58,11 @@ List::List(const std::list<ValuePtr>& nodes)
 {
 }
 
+List::List(ValueListConstIt begin, ValueListConstIt end)
+	: Collection(begin, end)
+{
+}
+
 // -----------------------------------------
 
 Vector::Vector(const std::list<ValuePtr>& nodes)
@@ -54,6 +70,11 @@ Vector::Vector(const std::list<ValuePtr>& nodes)
 {
 }
 
+Vector::Vector(ValueListConstIt begin, ValueListConstIt end)
+	: Collection(begin, end)
+{
+}
+
 // -----------------------------------------
 
 HashMap::HashMap(const Elements& elements)

src/ast.h

@@ -67,11 +67,14 @@ public:
 	bool empty() const { return m_nodes.size() == 0; }
 
 	ValuePtr front() const { return m_nodes.front(); }
-	const std::list<ValuePtr>& nodes() const { return m_nodes; }
+	ValueList rest() const;
+
+	const ValueList& nodes() const { return m_nodes; }
 
 protected:
 	Collection() = default;
-	Collection(const std::list<ValuePtr>& nodes);
+	Collection(const ValueList& nodes);
+	Collection(ValueListConstIt begin, ValueListConstIt end);
 
 	template<IsValue... Ts>
 	Collection(std::shared_ptr<Ts>... nodes)
@@ -82,7 +85,7 @@ protected:
 private:
 	virtual bool isCollection() const override { return true; }
 
-	std::list<ValuePtr> m_nodes;
+	ValueList m_nodes;
 };
 
 // -----------------------------------------
@@ -92,6 +95,7 @@ class List final : public Collection {
 public:
 	List() = default;
 	List(const std::list<ValuePtr>& nodes);
+	List(ValueListConstIt begin, ValueListConstIt end);
 
 	template<IsValue... Ts>
 	List(std::shared_ptr<Ts>... nodes)
@@ -112,6 +116,7 @@ class Vector final : public Collection {
 public:
 	Vector() = default;
 	Vector(const std::list<ValuePtr>& nodes);
+	Vector(ValueListConstIt begin, ValueListConstIt end);
 
 	template<IsValue... Ts>
 	Vector(std::shared_ptr<Ts>... nodes)

src/eval.cpp

@@ -79,10 +79,9 @@ ValuePtr Eval::evalImpl()
 		}
 
 		// Special forms
-		auto nodes = list->nodes();
+		if (is<Symbol>(list->front().get())) {
-		if (is<Symbol>(nodes.front().get())) {
+			auto symbol = std::static_pointer_cast<Symbol>(list->front())->symbol();
-			auto symbol = std::static_pointer_cast<Symbol>(nodes.front())->symbol();
+			const auto& nodes = list->rest();
-			nodes.pop_front();
 			if (symbol == "def!") {
 				return evalDef(nodes, env);
 			}
@@ -131,16 +130,11 @@ ValuePtr Eval::evalImpl()
 		}
 
 		// Regular list
-		if (is<Lambda>(evaluated_list->nodes().front().get())) {
+		if (is<Lambda>(evaluated_list->front().get())) {
-			auto evaluated_nodes = evaluated_list->nodes();
+			auto lambda = std::static_pointer_cast<Lambda>(evaluated_list->front());
-
-			// car
-			auto lambda = std::static_pointer_cast<Lambda>(evaluated_nodes.front());
-			// cdr
-			evaluated_nodes.pop_front();
 
 			m_ast_stack.push(lambda->body());
-			m_env_stack.push(Environment::create(lambda, evaluated_nodes));
+			m_env_stack.push(Environment::create(lambda, evaluated_list->rest()));
 			continue; // TCO
 		}
 
@@ -229,13 +223,12 @@ bool Eval::isMacroCall(ValuePtr ast, EnvironmentPtr env)
 ValuePtr Eval::macroExpand(ValuePtr ast, EnvironmentPtr env)
 {
 	while (isMacroCall(ast, env)) {
-		auto nodes = std::static_pointer_cast<List>(ast)->nodes();
+		auto list = std::static_pointer_cast<List>(ast);
-		auto value = env->get(std::static_pointer_cast<Symbol>(nodes.front())->symbol());
+		auto value = env->get(std::static_pointer_cast<Symbol>(list->front())->symbol());
 		auto lambda = std::static_pointer_cast<Lambda>(value);
-		nodes.pop_front();
 
 		m_ast_stack.push(lambda->body());
-		m_env_stack.push(Environment::create(lambda, nodes));
+		m_env_stack.push(Environment::create(lambda, list->rest()));
 		ast = evalImpl();
 	}
 

src/forward.h

@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <list>
 #include <memory> // std::shared_ptr
 
 namespace blaze {
@@ -15,6 +16,9 @@ namespace blaze {
 
 class Value;
 typedef std::shared_ptr<Value> ValuePtr;
+typedef std::list<ValuePtr> ValueList;
+typedef ValueList::iterator ValueListIt;
+typedef ValueList::const_iterator ValueListConstIt;
 
 class Environment;
 typedef std::shared_ptr<Environment> EnvironmentPtr;

src/functions.cpp

@@ -500,12 +500,8 @@ ADD_FUNCTION(
 		}
 
 		VALUE_CAST(collection, Collection, nodes.front());
-		auto collection_nodes = collection->nodes();
-		if (collection_nodes.size() > 0) {
-			collection_nodes.pop_front();
-		}
 
-		return makePtr<List>(collection_nodes);
+		return makePtr<List>(collection->rest());
 	});
 
 // (apply + 1 2 (list 3 4)) -> (+ 1 2 3 4)