diff --git a/crates/erg_compiler/context/initialize/mod.rs b/crates/erg_compiler/context/initialize/mod.rs
index 4e4254de..5009ea19 100644
--- a/crates/erg_compiler/context/initialize/mod.rs
+++ b/crates/erg_compiler/context/initialize/mod.rs
@@ -92,6 +92,10 @@ const PROC_WRITE: &str = "write!";
 const FILE_LIKE: &str = "FileLike";
 const MUTABLE_FILE_LIKE: &str = "FileLike!";
 const SHOW: &str = "Show";
+const TO_BOOL: &str = "ToBool";
+const TO_INT: &str = "ToInt";
+const TO_FLOAT: &str = "ToFloat";
+const ROUND: &str = "Round";
 const INPUT: &str = "Input";
 const OUTPUT: &str = "Output";
 const POW_OUTPUT: &str = "PowOutput";
@@ -494,6 +498,7 @@ const FUNC_SLICE: &str = "slice";
 const FUNC_SORTED: &str = "sorted";
 const FUNC_STATICMETHOD: &str = "staticmethod";
 const FUNC_SUM: &str = "sum";
+const FUNC_VARS: &str = "vars";
 const FUNC_IF: &str = "if";
 const FUNC_IF__: &str = "if__";
 const FUNC_DISCARD: &str = "discard";
@@ -571,9 +576,15 @@ const FUNDAMENTAL_CALL: &str = "__call__";
 const FUNDAMENTAL_NAME: &str = "__name__";
 const FUNDAMENTAL_FILE: &str = "__file__";
 const FUNDAMENTAL_PACKAGE: &str = "__package__";
-const FUNDAMENTAL_STR: &str = "__str__";
 const FUNDAMENTAL_HASH: &str = "__hash__";
+const FUNDAMENTAL_STR: &str = "__str__";
 const FUNDAMENTAL_INT: &str = "__int__";
+const FUNDAMENTAL_BOOL: &str = "__bool__";
+const FUNDAMENTAL_FLOAT: &str = "__float__";
+const FUNDAMENTAL_ROUND: &str = "__round__";
+const FUNDAMENTAL_TRUNC: &str = "__trunc__";
+const FUNDAMENTAL_CEIL: &str = "__ceil__";
+const FUNDAMENTAL_FLOOR: &str = "__floor__";
 const FUNDAMENTAL_ITER: &str = "__iter__";
 const FUNDAMENTAL_NEXT: &str = "__next__";
 const FUNDAMENTAL_MODULE: &str = "__module__";
@@ -708,6 +719,7 @@ const KW_OTHER: &str = "other";
 const KW_CONFLICT_RESOLVER: &str = "conflict_resolver";
 const KW_EPSILON: &str = "epsilon";
 const KW_PATH: &str = "Path";
+const KW_NDIGITS: &str = "ndigits";
 
 pub fn builtins_path() -> PathBuf {
     erg_pystd_path().join("builtins.d.er")
diff --git a/crates/erg_compiler/context/initialize/traits.rs b/crates/erg_compiler/context/initialize/traits.rs
index ad2d51da..cb3f2af9 100644
--- a/crates/erg_compiler/context/initialize/traits.rs
+++ b/crates/erg_compiler/context/initialize/traits.rs
@@ -445,6 +445,41 @@ impl Context {
         num.register_superclass(poly(ADD, vec![]), &add);
         num.register_superclass(poly(SUB, vec![]), &sub);
         num.register_superclass(poly(MUL, vec![]), &mul);
+        /* ToBool */
+        let mut to_bool = Self::builtin_mono_trait(TO_BOOL, 2);
+        let _Slf = mono_q(SELF, subtypeof(mono(TO_BOOL)));
+        let op_t = fn0_met(_Slf.clone(), Bool).quantify();
+        to_bool.register_builtin_erg_decl(FUNDAMENTAL_BOOL, op_t, Visibility::BUILTIN_PUBLIC);
+        /* ToInt */
+        let mut to_int = Self::builtin_mono_trait(TO_INT, 2);
+        let _Slf = mono_q(SELF, subtypeof(mono(TO_INT)));
+        let op_t = fn0_met(_Slf.clone(), Int).quantify();
+        to_int.register_builtin_erg_decl(FUNDAMENTAL_INT, op_t, Visibility::BUILTIN_PUBLIC);
+        /* ToFloat */
+        let mut to_float = Self::builtin_mono_trait(TO_FLOAT, 2);
+        let _Slf = mono_q(SELF, subtypeof(mono(TO_FLOAT)));
+        let op_t = fn0_met(_Slf.clone(), Float).quantify();
+        to_float.register_builtin_erg_decl(FUNDAMENTAL_FLOAT, op_t, Visibility::BUILTIN_PUBLIC);
+        /* Round */
+        let mut round = Self::builtin_mono_trait(ROUND, 2);
+        let _Slf = mono_q(SELF, subtypeof(mono(ROUND)));
+        // TODO: Output <: Integral = Int # (default)
+        let op_t = fn_met(
+            _Slf.clone(),
+            vec![],
+            None,
+            vec![kw_default(KW_NDIGITS, Nat, Nat)],
+            None,
+            Int,
+        )
+        .quantify();
+        round.register_builtin_erg_decl(FUNDAMENTAL_ROUND, op_t, Visibility::BUILTIN_PUBLIC);
+        let op_t = fn0_met(_Slf.clone(), Int).quantify();
+        round.register_builtin_erg_decl(FUNDAMENTAL_TRUNC, op_t, Visibility::BUILTIN_PUBLIC);
+        let op_t = fn0_met(_Slf.clone(), Int).quantify();
+        round.register_builtin_erg_decl(FUNDAMENTAL_FLOOR, op_t, Visibility::BUILTIN_PUBLIC);
+        let op_t = fn0_met(_Slf.clone(), Int).quantify();
+        round.register_builtin_erg_decl(FUNDAMENTAL_CEIL, op_t, Visibility::BUILTIN_PUBLIC);
         self.register_builtin_type(mono(UNPACK), unpack, vis.clone(), Const, None);
         self.register_builtin_type(
             mono(INHERITABLE_TYPE),
@@ -511,6 +546,10 @@ impl Context {
         self.register_builtin_type(mono(PARTIAL_ORD), partial_ord, vis.clone(), Const, None);
         self.register_builtin_type(mono(ORD), ord, vis.clone(), Const, None);
         self.register_builtin_type(mono(NUM), num, vis.clone(), Const, None);
+        self.register_builtin_type(mono(TO_BOOL), to_bool, vis.clone(), Const, None);
+        self.register_builtin_type(mono(TO_INT), to_int, vis.clone(), Const, None);
+        self.register_builtin_type(mono(TO_FLOAT), to_float, vis.clone(), Const, None);
+        self.register_builtin_type(mono(ROUND), round, vis.clone(), Const, None);
         self.register_builtin_type(
             poly(SEQUENCE, vec![ty_tp(T.clone())]),
             sequence,