Implements indexing, currently can only be used with strings

src/Evaluator/EvalValues/StringEvalValue.hpp

@@ -32,6 +32,12 @@ public:
     shared_ptr<EvalValue> Clone() final{
         return make_shared<StringEvalValue>(_value);
     }
+
+    EvalValue* IndexValue(EvalValue* val) final{
+        // Porygon is 1-indexed, so we convert to that.
+        auto l = val->EvaluateInteger() - 1;
+        return new StringEvalValue(string(1, _value[l]));
+    }
 };