.

src/vm/stack.cc

@@ -4,6 +4,11 @@
 
 namespace tyche {
 
+Stack::Stack()
+{
+    fps_.push(0);
+}
+
 void Stack::push(Value const& value)
 {
     stack_.push_back(value);
@@ -11,7 +16,7 @@ void Stack::push(Value const& value)
 
 Value Stack::pop()
 {
-    if (stack_.empty())
+    if (stack_.size() <= fps_.size())
         throw VMStackUnderflow();
 
     Value v = stack_.back();
@@ -22,10 +27,13 @@ Value Stack::pop()
 Value Stack::at(int pos) const
 {
     try {
-        if (pos >= 0)
-            return stack_.at(pos);
-        else
+        if (pos >= 0) {
+            return stack_.at(fps_.top() + pos);
+        } else {
+            if ((int) fps_.top() + (int) stack_.size() + pos < 0)
+                throw VMStackOutOfRange();
             return stack_.at(stack_.size() + pos);
+        }
     } catch (std::out_of_range&) {
         throw VMStackOutOfRange();
     }
@@ -33,7 +41,17 @@ Value Stack::at(int pos) const
 
 size_t Stack::size() const
 {
-    return stack_.size();
+    return stack_.size() - fps_.top();
+}
+
+void Stack::push_fp()
+{
+    fps_.push(stack_.size());
+}
+
+void Stack::pop_fp()
+{
+
 }
 
 } // tyche

src/vm/stack.hh

@@ -1,6 +1,7 @@
 #ifndef TYCHE_STACK_HH
 #define TYCHE_STACK_HH
 
+#include <stack>
 #include <vector>
 
 #include "value.hh"
@@ -9,14 +10,20 @@ namespace tyche {
 
 class Stack {
 public:
+    Stack();
+
     void push(Value const& value);
     Value pop();
 
     [[nodiscard]] Value at(int pos) const;
     [[nodiscard]] size_t size() const;
 
+    void push_fp();
+    void pop_fp();
+
 private:
     std::vector<Value> stack_;
+    std::stack<size_t> fps_;
 };
 
 } // tyche

src/vm/tests.cc

@@ -43,6 +43,31 @@ TEST(Stack, PushPullGet)
     ASSERT_EQ(stack.at(-2).as_integer(), 20);
 }
 
+TEST(Stack, FramePointer)
+{
+    Stack stack;
+    stack.push(Value::CreateInteger(10));
+    stack.push(Value::CreateInteger(20));
+    stack.push_fp();
+    stack.push(Value::CreateInteger(30));
+    stack.push(Value::CreateInteger(40));
+    stack.push(Value::CreateInteger(50));
+
+    ASSERT_EQ(stack.size(), 3);
+    ASSERT_EQ(stack.at(0).as_integer(), 30);
+    ASSERT_EQ(stack.at(1).as_integer(), 40);
+    ASSERT_EQ(stack.at(-1).as_integer(), 50);
+    ASSERT_EQ(stack.at(-2).as_integer(), 40);
+
+    stack.pop_fp();
+
+    ASSERT_EQ(stack.size(), 2);
+    ASSERT_EQ(stack.at(0).as_integer(), 10);
+    ASSERT_EQ(stack.at(1).as_integer(), 20);
+    ASSERT_EQ(stack.at(-1).as_integer(), 20);
+    ASSERT_EQ(stack.at(-2).as_integer(), 10);
+}
+
 int main(int argc, char** argv)
 {
     testing::InitGoogleTest(&argc, argv);