Add ls

Change-Id: I86f799ff9577940c7df8e01cda6c6b7867de8e7e
diff --git a/src/interpreter.hpp b/src/interpreter.hpp
index 64cc0e9..8acf8bd 100644
--- a/src/interpreter.hpp
+++ b/src/interpreter.hpp
@@ -18,6 +18,7 @@
     void operator()(const cd_&) const;
     void operator()(const create_&) const;
     void operator()(const delete_&) const;
+    void operator()(const ls_&) const;
 
 private:
     Parser& m_parser;