diff --git a/compiler/erg_compiler/context/compare.rs b/compiler/erg_compiler/context/compare.rs
index 65d114ef..6dfa9127 100644
--- a/compiler/erg_compiler/context/compare.rs
+++ b/compiler/erg_compiler/context/compare.rs
@@ -911,7 +911,7 @@ impl Context {
 
     #[inline]
     fn type_of(&self, p: &TyParam) -> Type {
-        self.get_tp_t(p).unwrap()
+        self.get_tp_t(p).unwrap_or(Type::Obj)
     }
 
     // sup/inf({±∞}) = ±∞ではあるが、Inf/NegInfにはOrdを実装しない
@@ -926,7 +926,7 @@ impl Context {
                             if lhs == &refine.var =>
                         {
                             if let Some(max) = &maybe_max {
-                                if self.try_cmp(rhs, max).unwrap() == Greater {
+                                if self.try_cmp(rhs, max) == Some(Greater) {
                                     maybe_max = Some(rhs.clone());
                                 }
                             } else {
@@ -954,7 +954,7 @@ impl Context {
                             if lhs == &refine.var =>
                         {
                             if let Some(min) = &maybe_min {
-                                if self.try_cmp(rhs, min).unwrap() == Less {
+                                if self.try_cmp(rhs, min) == Some(Less) {
                                     maybe_min = Some(rhs.clone());
                                 }
                             } else {
diff --git a/compiler/erg_compiler/context/initialize/const_func.rs b/compiler/erg_compiler/context/initialize/const_func.rs
index 081984f0..aa5aed54 100644
--- a/compiler/erg_compiler/context/initialize/const_func.rs
+++ b/compiler/erg_compiler/context/initialize/const_func.rs
@@ -3,7 +3,7 @@ use std::mem;
 use erg_common::Str;
 
 use erg_common::astr::AtomicStr;
-use erg_common::color::{RED, RESET};
+use erg_common::color::{RED, RESET, YELLOW};
 use erg_common::error::{ErrorCore, ErrorKind, Location};
 use erg_type::constructors::{and, builtin_mono, mono};
 use erg_type::value::{EvalValueResult, TypeKind, TypeObj, ValueObj};
@@ -18,20 +18,32 @@ pub fn class_func(
     let require = args.remove_left_or_key("Requirement").ok_or_else(|| {
         ErrorCore::new(
             line!() as usize,
-            ErrorKind::KeyError,
+            ErrorKind::TypeError,
             Location::Unknown,
             AtomicStr::from(format!("{RED}Requirement{RESET} is not passed")),
             None,
         )
     })?;
-    let require = require.as_type().unwrap();
+    let require = if let Some(t) = require.as_type() {
+        t
+    } else {
+        return Err(ErrorCore::new(
+            line!() as usize,
+            ErrorKind::TypeError,
+            Location::Unknown,
+            AtomicStr::from(format!(
+                "non-type object {RED}{require}{RESET} is passed to {YELLOW}Requirement{RESET}",
+            )),
+            None,
+        ));
+    };
     let impls = args.remove_left_or_key("Impl");
     let impls = impls.map(|v| v.as_type().unwrap());
     let t = mono(mod_name, __name__.unwrap_or(Str::ever("<Lambda>")));
     Ok(ValueObj::gen_t(TypeKind::Class, t, require, impls, None))
 }
 
-/// Super: Type, Impl := Type, Additional := Type -> ClassType
+/// Super: ClassType, Impl := Type, Additional := Type -> ClassType
 pub fn inherit_func(
     mut args: ValueArgs,
     mod_name: Str,
@@ -46,7 +58,19 @@ pub fn inherit_func(
             None,
         )
     })?;
-    let sup = sup.as_type().unwrap();
+    let sup = if let Some(t) = sup.as_type() {
+        t
+    } else {
+        return Err(ErrorCore::new(
+            line!() as usize,
+            ErrorKind::TypeError,
+            Location::Unknown,
+            AtomicStr::from(format!(
+                "non-class object {RED}{sup}{RESET} is passed to {YELLOW}Super{RESET}",
+            )),
+            None,
+        ));
+    };
     let impls = args.remove_left_or_key("Impl");
     let impls = impls.map(|v| v.as_type().unwrap());
     let additional = args.remove_left_or_key("Additional");
@@ -97,7 +121,7 @@ pub fn inheritable_func(
     }
 }
 
-/// Requirement: Type, Impl := Type -> ClassType
+/// Requirement: Type, Impl := Type -> TraitType
 pub fn trait_func(
     mut args: ValueArgs,
     mod_name: Str,
@@ -112,14 +136,26 @@ pub fn trait_func(
             None,
         )
     })?;
-    let require = require.as_type().unwrap();
+    let require = if let Some(t) = require.as_type() {
+        t
+    } else {
+        return Err(ErrorCore::new(
+            line!() as usize,
+            ErrorKind::TypeError,
+            Location::Unknown,
+            AtomicStr::from(format!(
+                "non-type object {RED}{require}{RESET} is passed to {YELLOW}Requirement{RESET}",
+            )),
+            None,
+        ));
+    };
     let impls = args.remove_left_or_key("Impl");
     let impls = impls.map(|v| v.as_type().unwrap());
     let t = mono(mod_name, __name__.unwrap_or(Str::ever("<Lambda>")));
     Ok(ValueObj::gen_t(TypeKind::Trait, t, require, impls, None))
 }
 
-/// Super: Type, Impl := Type, Additional := Type -> ClassType
+/// Super: TraitType, Impl := Type, Additional := Type -> TraitType
 pub fn subsume_func(
     mut args: ValueArgs,
     mod_name: Str,
@@ -134,7 +170,19 @@ pub fn subsume_func(
             None,
         )
     })?;
-    let sup = sup.as_type().unwrap();
+    let sup = if let Some(t) = sup.as_type() {
+        t
+    } else {
+        return Err(ErrorCore::new(
+            line!() as usize,
+            ErrorKind::TypeError,
+            Location::Unknown,
+            AtomicStr::from(format!(
+                "non-trait object {RED}{sup}{RESET} is passed to {YELLOW}Super{RESET}",
+            )),
+            None,
+        ));
+    };
     let impls = args.remove_left_or_key("Impl");
     let impls = impls.map(|v| v.as_type().unwrap());
     let additional = args.remove_left_or_key("Additional");
diff --git a/compiler/erg_compiler/context/inquire.rs b/compiler/erg_compiler/context/inquire.rs
index 3c72ed31..fdf727ea 100644
--- a/compiler/erg_compiler/context/inquire.rs
+++ b/compiler/erg_compiler/context/inquire.rs
@@ -1427,14 +1427,12 @@ impl Context {
                     let insts = self.rec_get_trait_impls(&sup.name());
                     let candidates = insts.into_iter().filter_map(move |inst| {
                         if self.supertype_of(&inst.sup_trait, &sup) {
-                            Some(
-                                self.eval_t_params(
-                                    mono_proj(inst.sub_type, rhs),
-                                    self.level,
-                                    Location::Unknown,
-                                )
-                                .unwrap(),
+                            self.eval_t_params(
+                                mono_proj(inst.sub_type, rhs),
+                                self.level,
+                                Location::Unknown,
                             )
+                            .ok()
                         } else {
                             None
                         }
diff --git a/compiler/erg_compiler/effectcheck.rs b/compiler/erg_compiler/effectcheck.rs
index dd8fa883..1984044b 100644
--- a/compiler/erg_compiler/effectcheck.rs
+++ b/compiler/erg_compiler/effectcheck.rs
@@ -58,7 +58,7 @@ impl SideEffectChecker {
     ///
     /// However, it is not permitted to cause side effects within an instant block in a function
     /// (side effects are allowed in instant blocks in procedures and modules)
-    fn in_context_se_allowed(&self) -> bool {
+    fn in_context_effects_allowed(&self) -> bool {
         // if toplevel
         if self.block_stack.len() == 1 {
             return true;
@@ -255,7 +255,7 @@ impl SideEffectChecker {
                         .as_ref()
                         .map(|name| name.is_procedural())
                         .unwrap_or(false))
-                    && !self.in_context_se_allowed()
+                    && !self.in_context_effects_allowed()
                 {
                     self.errs.push(EffectError::has_effect(
                         line!() as usize,
diff --git a/compiler/erg_compiler/error.rs b/compiler/erg_compiler/error.rs
index a993cdac..7be0f54e 100644
--- a/compiler/erg_compiler/error.rs
+++ b/compiler/erg_compiler/error.rs
@@ -995,19 +995,19 @@ passed keyword args:    {RED}{kw_args_len}{RESET}"
                 switch_lang!(
                     "japanese" => format!(
                         "{RED}{name}{RESET}は{}行目ですでに移動されています",
-                        moved_loc.ln_begin().unwrap()
+                        moved_loc.ln_begin().unwrap_or(0)
                     ),
                     "simplified_chinese" => format!(
                         "{RED}{name}{RESET}已移至第{}行",
-                        moved_loc.ln_begin().unwrap()
+                        moved_loc.ln_begin().unwrap_or(0)
                     ),
                     "traditional_chinese" => format!(
                         "{RED}{name}{RESET}已移至第{}行",
-                        moved_loc.ln_begin().unwrap()
+                        moved_loc.ln_begin().unwrap_or(0)
                     ),
                     "english" => format!(
                         "{RED}{name}{RESET} was moved in line {}",
-                        moved_loc.ln_begin().unwrap()
+                        moved_loc.ln_begin().unwrap_or(0)
                     ),
                 ),
                 None,
diff --git a/compiler/erg_compiler/link.rs b/compiler/erg_compiler/link.rs
index dc498f4a..56b54c54 100644
--- a/compiler/erg_compiler/link.rs
+++ b/compiler/erg_compiler/link.rs
@@ -43,7 +43,7 @@ impl Linker {
                         let code = Expr::Code(Block::new(Vec::from(hir.module)));
                         let module_type = Expr::Accessor(Accessor::private_with_line(
                             Str::ever("#ModuleType"),
-                            def.ln_begin().unwrap(),
+                            def.ln_begin().unwrap_or(0),
                         ));
                         let args =
                             Args::new(vec![PosArg::new(mod_name.clone())], None, vec![], None);
@@ -59,7 +59,7 @@ impl Linker {
                         ));
                         let exec = Expr::Accessor(Accessor::public_with_line(
                             Str::ever("exec"),
-                            mod_def.ln_begin().unwrap(),
+                            mod_def.ln_begin().unwrap_or(0),
                         ));
                         let module = Expr::Accessor(Accessor::Ident(def.sig.ident().clone()));
                         let __dict__ = Identifier::public("__dict__");
diff --git a/compiler/erg_type/value.rs b/compiler/erg_type/value.rs
index ae492471..58997796 100644
--- a/compiler/erg_type/value.rs
+++ b/compiler/erg_type/value.rs
@@ -802,8 +802,12 @@ pub mod value_set {
 
     // false -> SyntaxError
     pub fn is_homogeneous(set: &Set<ValueObj>) -> bool {
-        let l_first = set.iter().next().unwrap().class();
-        set.iter().all(|c| c.class() == l_first)
+        if let Some(first) = set.iter().next() {
+            let l_first = first.class();
+            set.iter().all(|c| c.class() == l_first)
+        } else {
+            true
+        }
     }
 
     pub fn inner_class(set: &Set<ValueObj>) -> Type {