Implemented SymTable optimization for efficient variable updates

src/config.rs

@@ -40,6 +40,7 @@ pub fn configure(filename: String, syms: &mut SymTable) -> Result<(), String> {
 
     default value: false".to_string(),
             value: ValueType::VarForm(Box::new(Ctr::Bool(false))),
+            ..Default::default()
         },
     );
 
@@ -56,6 +57,7 @@ checked at shell startup by configuration daemon. not used afterwards.
 default value: 1 (set)
 ".to_string(),
             value: ValueType::VarForm(Box::new(Ctr::Bool(true))),
+            ..Default::default()
         },
     );
 
@@ -69,6 +71,7 @@ default value: 1 (set)
 default value (<lambda>)"
                 .to_string(),
             value: ValueType::Internal(Rc::new(prompt_default_callback)),
+            ..Default::default()
         },
     );