Made it possible to access variables down the stack

Advanced Software Engineering/Advanced Software Engineering/Verbs/Value/ValueStorage.cs

@@ -16,8 +16,9 @@ namespace Advanced_Software_Engineering.Verbs.Value {
             SetStack(0);
         }
 
-        public void SetStack(int stack) {
-            currentStack = stack < 0 ? 0 : stack;
+        private void SetStack(int stack) {
+            if (stack < 0) throw new Exception("Stack cannot be less than 0");
+
             if (!Variables.ContainsKey(stack)) Variables.Add(currentStack, new Dictionary<string, IValue>());
         }
 
@@ -34,36 +35,42 @@ namespace Advanced_Software_Engineering.Verbs.Value {
             }
         }
 
-        public void SetVariable(string name, int stack, IValue value) {
-            if (stack == 0) Variables[stack][name] = value;
-            else {
-                if (CheckVariableExists(name, stack)) Variables[stack][name] = value;
-                else if (CheckVariableExists(name, 0)) Variables[0][name] = value;
-                else Variables[stack][name] = value;
+        private void SetVariable(string name, int stack, IValue value) {
+            for (int internalStack = stack; internalStack >= 0; internalStack--) {
+                if (value == null || CheckVariableExists(name, internalStack)) {
+                    Variables[internalStack][name] = value;
+                    return;
+                }
             }
+            Variables[stack][name] = value;
         }
 
         public void SetVariable(string name, IValue value) {
             SetVariable(name, currentStack, value);
         }
 
-        public IValue GetVariable(string name, int stack) {
+        private IValue GetVariable(string name, int stack) {
             return Variables[stack][name];
         }
 
         public IValue GetVariable(string name) {
-            if (currentStack > 0 && CheckVariableExists(name, currentStack)) return GetVariable(name, currentStack);
-            else if (CheckVariableExists(name, 0)) return GetVariable(name, 0);
-            else throw new Exception("Cannot find variable " + name);
+            for (int stack = currentStack; stack >= 0; stack--) {
+                if (CheckVariableExists(name, stack)) return GetVariable(name, stack);
+            }
+            throw new Exception("Cannot find variable " + name);
         }
 
-        public bool CheckVariableExists(string name, int stack) {
+        private bool CheckVariableExists(string name, int stack) {
             if (name == null) return false;
             return Variables[stack].ContainsKey(name);
         }
 
         public bool CheckVariableExists(string name) {
-            return CheckVariableExists(name, currentStack) || CheckVariableExists(name, 0);
+            if (name == null) return false;
+            for (int stack = currentStack; stack >= 0; stack--) {
+                if (CheckVariableExists(name, stack)) return true;
+            }
+            return false;
         }
     }
 }