diff --git a/core/src/api.rs b/core/src/api.rs
index 76cab3e..c8b1553 100644
--- a/core/src/api.rs
+++ b/core/src/api.rs
@@ -2,20 +2,31 @@ use std::collections::HashSet;
 use std::fmt::Debug;
 
 use crate::storage::{
-    frozen_global_storage, Entry, GetOrElse, MultipleVersion, Tree, THREAD_STORAGE,
+    frozen_global_storage, Entry, GetOrElse, MultipleVersion, Params, THREAD_STORAGE,
 };
 use crate::value::{Value, EMPTY};
 use crate::xxh::XXHashable;
 
+/// ParameterScope
+///
+/// `ParameterScope` is a data structure that stores the current set of named parameters
+/// and their values. `ParameterScope` is used to manage the scope of named parameters,
+/// allowing parameters to be defined and used within a specific scope,
+/// and then restored to the previous scope when the scope is exited.
+///
+/// The parameter scope can be used to implement a variety of features, such
+/// as named parameters, default parameter values, and parameter inheritance.
 #[derive(Debug, Clone)]
 pub enum ParamScope {
+    /// No parameters are defined in the current scope.
     Nothing,
-    Just(Tree),
+    /// The current scope contains a set of named parameters stored in `Params`.
+    Just(Params),
 }
 
 impl Default for ParamScope {
     fn default() -> Self {
-        ParamScope::Just(Tree::new())
+        ParamScope::Just(Params::new())
     }
 }
 
@@ -505,3 +516,88 @@ mod tests {
         }
     }
 }
+
+// FILEPATH: /home/reiase/workspace/hyperparameter/core/src/api.rs
+// BEGIN: test_code
+
+#[cfg(test)]
+mod test_param_scope {
+    use super::*;
+    use std::convert::TryInto;
+
+    #[test]
+    fn test_param_scope_default() {
+        let ps = ParamScope::default();
+        match ps {
+            ParamScope::Just(_) => assert!(true),
+            _ => assert!(false, "Default ParamScope should be ParamScope::Just"),
+        }
+    }
+
+    #[test]
+    fn test_param_scope_from_vec() {
+        let vec = vec!["param1=value1", "param2=value2"];
+        let ps: ParamScope = (&vec).into();
+        match ps {
+            ParamScope::Just(params) => {
+                assert_eq!(params.get(&"param1".xxh()).unwrap().value(), &Value::from("value1"));
+                assert_eq!(params.get(&"param2".xxh()).unwrap().value(), &Value::from("value2"));
+            }
+            _ => assert!(false, "ParamScope should be ParamScope::Just"),
+        }
+    }
+
+    #[test]
+    fn test_param_scope_get_with_hash() {
+        let mut ps = ParamScope::default();
+        ps.add("param=value");
+        let value = ps.get_with_hash("param".xxh());
+        assert_eq!(value, Value::from("value"));
+    }
+
+    #[test]
+    fn test_param_scope_get() {
+        let mut ps = ParamScope::default();
+        ps.add("param=value");
+        let value: String = ps.get("param").try_into().unwrap();
+        assert_eq!(value, "value");
+    }
+
+    #[test]
+    fn test_param_scope_add() {
+        let mut ps = ParamScope::default();
+        ps.add("param=value");
+        match ps {
+            ParamScope::Just(params) => {
+                assert_eq!(params.get(&"param".xxh()).unwrap().value(), &Value::from("value"));
+            }
+            _ => assert!(false, "ParamScope should be ParamScope::Just"),
+        }
+    }
+
+    #[test]
+    fn test_param_scope_keys() {
+        let mut ps = ParamScope::default();
+        ps.add("param=value");
+        let keys = ps.keys();
+        assert_eq!(keys, vec!["param"]);
+    }
+
+    #[test]
+    fn test_param_scope_enter_exit() {
+        let mut ps = ParamScope::default();
+        ps.add("param=value");
+        ps.enter();
+        match ps {
+            ParamScope::Nothing => assert!(true),
+            _ => assert!(false, "ParamScope should be ParamScope::Nothing after enter"),
+        }
+        ps.exit();
+        match ps {
+            ParamScope::Just(_) => assert!(true),
+            _ => assert!(false, "ParamScope should be ParamScope::Just after exit"),
+        }
+    }
+}
+
+// END: test_code
\ No newline at end of file
diff --git a/core/src/storage.rs b/core/src/storage.rs
index 84de864..f84ae75 100644
--- a/core/src/storage.rs
+++ b/core/src/storage.rs
@@ -40,7 +40,7 @@ impl Entry {
     }
 }
 
-pub type Tree = BTreeMap<u64, Entry>;
+pub type Params = BTreeMap<u64, Entry>;
 
 pub trait MultipleVersion<K> {
     fn update<V: Into<Value>>(&mut self, key: K, val: V);
@@ -48,15 +48,17 @@ pub trait MultipleVersion<K> {
     fn rollback(&mut self, key: K);
 }
 
-impl MultipleVersion<u64> for Tree {
+impl MultipleVersion<u64> for Params {
     fn update<V: Into<Value>>(&mut self, key: u64, val: V) {
-        self.entry(key).and_modify(|e| {
+        if let Some(e) = self.get_mut(&key) {
             e.val.update(val);
-        });
+        }
     }
 
     fn revision<V: Into<Value>>(&mut self, key: u64, val: V) {
-        self.entry(key).and_modify(|e| e.val.revision(val));
+        if let Some(e) = self.get_mut(&key) {
+            e.val.revision(val);
+        }
     }
 
     fn rollback(&mut self, key: u64) {
@@ -75,8 +77,8 @@ thread_local! {
 fn create_thread_storage() -> RefCell<Storage> {
     let ts = RefCell::new(Storage::default());
     ts.borrow_mut()
-        .tree
-        .clone_from(&GLOBAL_STORAGE.lock().unwrap().tree);
+        .params
+        .clone_from(&GLOBAL_STORAGE.lock().unwrap().params);
     ts
 }
 
@@ -89,14 +91,14 @@ pub fn frozen_global_storage() {
         GLOBAL_STORAGE
             .lock()
             .unwrap()
-            .tree
-            .clone_from(&ts.borrow().tree);
+            .params
+            .clone_from(&ts.borrow().params);
     });
 }
 
 #[derive(Debug)]
 pub struct Storage {
-    pub tree: Tree,
+    pub params: Params,
     pub history: Vec<HashSet<u64>>,
 }
 
@@ -105,7 +107,7 @@ unsafe impl Send for Storage {}
 impl Default for Storage {
     fn default() -> Self {
         Storage {
-            tree: Tree::new(),
+            params: Params::new(),
             history: vec![HashSet::new()],
         }
     }
@@ -116,30 +118,30 @@ impl Storage {
         self.history.push(HashSet::new());
     }
 
-    pub fn exit(&mut self) -> Tree {
-        let mut changes = Tree::new();
+    pub fn exit(&mut self) -> Params {
+        let mut changes = Params::new();
         for key in self.history.pop().unwrap() {
-            changes.insert(key, self.tree.get(&key).unwrap().shallow());
-            self.tree.rollback(key);
+            changes.insert(key, self.params.get(&key).unwrap().shallow());
+            self.params.rollback(key);
         }
         changes
     }
 
     pub fn get_entry(&self, key: u64) -> Option<&Entry> {
-        self.tree.get(&key)
+        self.params.get(&key)
     }
 
     pub fn put_entry(&mut self, key: u64, entry: Entry) -> Option<Entry> {
-        self.tree.insert(key, entry)
+        self.params.insert(key, entry)
     }
 
     pub fn del_entry(&mut self, key: u64) {
-        self.tree.remove(&key);
+        self.params.remove(&key);
     }
 
     pub fn get<T: XXHashable>(&self, key: T) -> &Value {
         let hkey = key.xxh();
-        if let Some(e) = self.tree.get(&hkey) {
+        if let Some(e) = self.params.get(&hkey) {
             e.value()
         } else {
             &EMPTY
@@ -150,15 +152,15 @@ impl Storage {
         let hkey = key.xxh();
         let key: String = key.into();
         if self.history.last().unwrap().contains(&hkey) {
-            self.tree.update(hkey, val);
+            self.params.update(hkey, val);
         } else {
-            if let std::collections::btree_map::Entry::Vacant(e) = self.tree.entry(hkey) {
+            if let std::collections::btree_map::Entry::Vacant(e) = self.params.entry(hkey) {
                 e.insert(Entry {
                     key,
                     val: VersionedValue::from(val.into()),
                 });
             } else {
-                self.tree.revision(hkey, val);
+                self.params.revision(hkey, val);
             }
             self.history.last_mut().unwrap().insert(hkey);
         }
@@ -167,15 +169,15 @@ impl Storage {
     pub fn del<T: XXHashable>(&mut self, key: T) {
         let hkey = key.xxh();
         if self.history.last().unwrap().contains(&hkey) {
-            self.tree.update(hkey, None::<i32>);
+            self.params.update(hkey, None::<i32>);
         } else {
-            self.tree.revision(hkey, None::<i32>);
+            self.params.revision(hkey, None::<i32>);
             self.history.last_mut().unwrap().insert(hkey);
         }
     }
 
     pub fn keys(&self) -> Vec<String> {
-        self.tree
+        self.params
             .values()
             .filter(|x| !matches!(x.value(), Value::Empty))
             .map(|x| x.key.clone())
@@ -202,7 +204,7 @@ where
     T: Into<Value> + TryFrom<Value> + for<'a> TryFrom<&'a Value>,
 {
     fn get_or_else(&self, key: u64, dval: T) -> T {
-        if let Some(val) = self.tree.get(&key) {
+        if let Some(val) = self.params.get(&key) {
             match val.value().try_into() {
                 Ok(v) => v,
                 Err(_) => dval,
diff --git a/core/src/value.rs b/core/src/value.rs
index 540a57c..46120c4 100644
--- a/core/src/value.rs
+++ b/core/src/value.rs
@@ -39,13 +39,7 @@ pub const EMPTY: Value = Value::Empty;
 
 impl<T: Into<Value>> From<Option<T>> for Value {
     fn from(value: Option<T>) -> Self {
-        match value {
-            Some(x) => {
-                let y: Value = x.into();
-                y
-            }
-            None => Value::Empty,
-        }
+        value.map_or(Value::Empty, |x| x.into())
     }
 }
 
@@ -63,7 +57,7 @@ impl From<i64> for Value {
 
 impl From<f32> for Value {
     fn from(value: f32) -> Self {
-        Value::Float(value.into())
+        Value::Float(value as f64)
     }
 }
 
@@ -81,7 +75,7 @@ impl From<String> for Value {
 
 impl From<&String> for Value {
     fn from(value: &String) -> Self {
-        Value::Text(value.clone())
+        Value::Text(value.to_string())
     }
 }
 
diff --git a/core/src/xxh.rs b/core/src/xxh.rs
index 69c4436..8ac78ca 100644
--- a/core/src/xxh.rs
+++ b/core/src/xxh.rs
@@ -29,15 +29,13 @@ impl XXHashable for &str {
 
 impl XXHashable for CStr {
     fn xxh(&self) -> u64 {
-        let bs = self.to_bytes();
-        xxhash(bs)
+        xxhash(self.to_bytes())
     }
 }
 
 impl XXHashable for CString {
     fn xxh(&self) -> u64 {
-        let bs = self.to_bytes();
-        xxhash(bs)
+        xxhash(self.to_bytes())
     }
 }