diff --git a/package/origlang-ast/src/lib.rs b/package/origlang-ast/src/lib.rs
index edd2b88b..52e92188 100644
--- a/package/origlang-ast/src/lib.rs
+++ b/package/origlang-ast/src/lib.rs
@@ -80,7 +80,6 @@ impl Identifier {
     }
 
     #[must_use = "If you don't use it, it will drop entire String"]
-    #[allow(clippy::missing_const_for_fn)] // see https://github.com/rust-lang/rust-clippy/issues/10617
     pub fn name(self) -> String {
         self.0
     }
diff --git a/package/origlang-cli/src/args.rs b/package/origlang-cli/src/args.rs
index bfc3ec1e..87da28d4 100644
--- a/package/origlang-cli/src/args.rs
+++ b/package/origlang-cli/src/args.rs
@@ -1,8 +1,6 @@
 // clap issue?: https://github.com/clap-rs/clap/issues/4733
 #![warn(clippy::almost_swapped)]
 
-use std::fs::File;
-use std::io::{BufReader, Read};
 use std::path::PathBuf;
 use std::string::FromUtf8Error;
 use clap::{Parser, Subcommand};
diff --git a/package/origlang-ir-optimizer/src/ir1.rs b/package/origlang-ir-optimizer/src/ir1.rs
index 3b616b7d..14e7d0aa 100644
--- a/package/origlang-ir-optimizer/src/ir1.rs
+++ b/package/origlang-ir-optimizer/src/ir1.rs
@@ -36,23 +36,6 @@ impl<T: PartialOrd + PartialEq + CastFrom<Ordering>> OutputCompareResultAsSelf f
     }
 }
 
-trait Continue<T> {
-    fn continue_value(self) -> Option<T>;
-}
-
-impl<T> Continue<T> for Option<T> {
-    #[allow(clippy::use_self)]
-    fn continue_value(self) -> Option<T> {
-        self
-    }
-}
-
-impl Continue<Self> for bool {
-    fn continue_value(self) -> Option<Self> {
-        self.then_some(true)
-    }
-}
-
 /// 二項演算子についての定数畳み込みを行う。
 // TODO: 左端以外に畳み込みが行える定数項があっても、それらの項が畳み込まれない。
 //       すなわち、オーバーフローがないものとして`a * 2 / 2`を最適化するとき、`a`に最適化出来ない。
diff --git a/package/origlang-lexer/src/boundary.rs b/package/origlang-lexer/src/boundary.rs
index a559c0d9..be2e9b4c 100644
--- a/package/origlang-lexer/src/boundary.rs
+++ b/package/origlang-lexer/src/boundary.rs
@@ -56,9 +56,3 @@ impl From<char> for Utf8CharStride {
         }
     }
 }
-
-#[derive(Error, Debug)]
-#[error("invalid value for UTF-8 codepoint stride: {given_value}")]
-pub struct InvalidUtf8CharStrideError {
-    given_value: u8
-}
diff --git a/package/origlang-parser/src/parser.rs b/package/origlang-parser/src/parser.rs
index 2f6abcde..7967a189 100644
--- a/package/origlang-parser/src/parser.rs
+++ b/package/origlang-parser/src/parser.rs
@@ -42,7 +42,7 @@ pub enum TokenKind {
 }
 
 impl TokenKind {
-    fn only(token: Token) -> Self {
+    fn only(token: &Token) -> Self {
         Self::Only(token.display())
     }
 }
@@ -142,7 +142,7 @@ impl Parser {
                             unmatch: aliased.data
                 }, aliased.position)) };
 
-                self.read_and_consume_or_report_unexpected_token(Token::SymEq)?;
+                self.read_and_consume_or_report_unexpected_token(&Token::SymEq)?;
                 let Ok(replace_with) = self.lexer.parse_fallible(|| self.parse_type()) else {
                     let p = self.lexer.peek_cloned();
                     return Err(ParserError::new(ParserErrorInner::UnexpectedToken {
@@ -218,7 +218,7 @@ impl Parser {
                     Ok(expr_tuple)
                 } else {
                     let inner_expression = self.parse_lowest_precedence_expression()?;
-                    self.read_and_consume_or_report_unexpected_token(Token::SymRightPar)?;
+                    self.read_and_consume_or_report_unexpected_token(&Token::SymRightPar)?;
                     Ok(inner_expression)
                 }
             }
@@ -582,7 +582,7 @@ impl Parser {
 
                     debug!("type:tuple:accumulator = {vec:?}");
 
-                    self.read_and_consume_or_report_unexpected_token(Token::SymRightPar)?;
+                    self.read_and_consume_or_report_unexpected_token(&Token::SymRightPar)?;
 
                     if vec.len() < 2 {
                         let l = vec.len();
@@ -609,7 +609,7 @@ impl Parser {
 
     fn parse_variable_declaration(&self) -> Result<Statement, ParserError> {
         debug!("decl:var");
-        self.read_and_consume_or_report_unexpected_token(Token::VarKeyword)?;
+        self.read_and_consume_or_report_unexpected_token(&Token::VarKeyword)?;
         let pattern = self.parse_atomic_pattern()?;
 
         // optionally, allow type annotation
@@ -631,7 +631,7 @@ impl Parser {
 
         debug!("decl:var:annotation: {type_annotation:?}");
 
-        self.read_and_consume_or_report_unexpected_token(Token::SymEq)?;
+        self.read_and_consume_or_report_unexpected_token(&Token::SymEq)?;
         debug!("decl:var:expr");
         let expression = self.parse_lowest_precedence_expression()?;
 
@@ -651,7 +651,7 @@ impl Parser {
                     pat: TokenKind::Identifier,
                     unmatch: ident_token.data }, ident_token.position))
         };
-        self.read_and_consume_or_report_unexpected_token(Token::SymEq)?;
+        self.read_and_consume_or_report_unexpected_token(&Token::SymEq)?;
         debug!("assign:var:expr");
         let expression = self.parse_lowest_precedence_expression()?;
         Ok(Statement::VariableAssignment {
@@ -670,9 +670,9 @@ impl Parser {
         if self.lexer.peek().ok_or_else(|| ParserError::new(ParserErrorInner::EndOfFileError, self.lexer.last_position))?.data == Token::KeywordIf {
             self.lexer.next();
             let condition = self.parse_lowest_precedence_expression()?;
-            self.read_and_consume_or_report_unexpected_token(Token::KeywordThen)?;
+            self.read_and_consume_or_report_unexpected_token(&Token::KeywordThen)?;
             let then_clause_value = self.parse_lowest_precedence_expression()?;
-            self.read_and_consume_or_report_unexpected_token(Token::KeywordElse)?;
+            self.read_and_consume_or_report_unexpected_token(&Token::KeywordElse)?;
             let else_clause_value = self.parse_lowest_precedence_expression()?;
             Ok(Expression::If {
                 condition: Box::new(condition),
@@ -686,7 +686,7 @@ impl Parser {
 
     fn parse_block_scope(&self) -> Result<Statement, ParserError> {
         debug!("statement:block");
-        self.read_and_consume_or_report_unexpected_token(Token::KeywordBlock)?;
+        self.read_and_consume_or_report_unexpected_token(&Token::KeywordBlock)?;
         if self.lexer.peek().ok_or_else(|| ParserError::new(ParserErrorInner::EndOfFileError, self.lexer.last_position))?.data == Token::NewLine {
             self.lexer.next();
         }
@@ -695,7 +695,7 @@ impl Parser {
         while let Ok(v) = self.parse_statement() {
             statements.push(v);
         }
-        self.read_and_consume_or_report_unexpected_token(Token::KeywordEnd)?;
+        self.read_and_consume_or_report_unexpected_token(&Token::KeywordEnd)?;
 
         Ok(Statement::Block {
             inner_statements: (statements),
@@ -706,7 +706,7 @@ impl Parser {
         debug!("expr:block");
         if self.lexer.peek().ok_or_else(|| ParserError::new(ParserErrorInner::EndOfFileError, self.lexer.last_position))?.data == Token::KeywordBlock {
             self.lexer.next();
-            self.read_and_consume_or_report_unexpected_token(Token::NewLine)?;
+            self.read_and_consume_or_report_unexpected_token(&Token::NewLine)?;
             let mut statements = vec![];
             while let Ok(v) = self.parse_statement() {
                 statements.push(v);
@@ -715,7 +715,7 @@ impl Parser {
             if self.lexer.peek().ok_or_else(|| ParserError::new(ParserErrorInner::EndOfFileError, self.lexer.last_position))?.data == Token::NewLine {
                 self.lexer.next();
             }
-            self.read_and_consume_or_report_unexpected_token(Token::KeywordEnd)?;
+            self.read_and_consume_or_report_unexpected_token(&Token::KeywordEnd)?;
             Ok(Expression::Block {
                 intermediate_statements: statements,
                 final_expression
@@ -727,7 +727,7 @@ impl Parser {
 
     fn parse_tuple_destruct_pattern(&self) -> Result<AtomicPattern, ParserError> {
         debug!("pattern:tuple");
-        self.read_and_consume_or_report_unexpected_token(Token::SymLeftPar)?;
+        self.read_and_consume_or_report_unexpected_token(&Token::SymLeftPar)?;
 
         let mut v = vec![];
 
@@ -740,10 +740,10 @@ impl Parser {
                 break
             }
 
-            self.read_and_consume_or_report_unexpected_token(Token::SymComma)?;
+            self.read_and_consume_or_report_unexpected_token(&Token::SymComma)?;
         }
 
-        self.read_and_consume_or_report_unexpected_token(Token::SymRightPar)?;
+        self.read_and_consume_or_report_unexpected_token(&Token::SymRightPar)?;
 
         Ok(AtomicPattern::Tuple(v))
     }
@@ -774,11 +774,11 @@ impl Parser {
     }
 
     /// 現在のトークンが指定されたトークンならそのトークンをそのまま返した上でレキサーを1個進める。そうではないなら[`ParseError::UnexpectedToken`]を返す。
-    fn read_and_consume_or_report_unexpected_token(&self, token: Token) -> Result<Token, ParserError> {
+    fn read_and_consume_or_report_unexpected_token(&self, token: &Token) -> Result<(), ParserError> {
         let peek = self.lexer.peek().ok_or_else(|| ParserError::new(ParserErrorInner::EndOfFileError, self.lexer.last_position))?;
-        if peek.data == token {
+        if &peek.data == token {
             self.lexer.next();
-            Ok(token)
+            Ok(())
         } else {
             Err(ParserError::new(ParserErrorInner::UnexpectedToken {
                     pat: TokenKind::only(token),
diff --git a/package/origlang-runtime/src/lib.rs b/package/origlang-runtime/src/lib.rs
index 07d319ea..ba0a3a85 100644
--- a/package/origlang-runtime/src/lib.rs
+++ b/package/origlang-runtime/src/lib.rs
@@ -192,7 +192,6 @@ impl Runtime {
     }
 
     /// Start runtime. Never returns until execution is completed.
-    #[allow(dead_code)]
     pub fn start<'s: 'o, 'o>(&'s self, seq: &[IR2]) -> &'o RefCell<dyn OutputAccumulator> {
         // info!("{ast:?}", ast = &ast);
         let x = seq;
@@ -342,6 +341,49 @@ macro_rules! indicate_type_checker_bug {
     };
 }
 
+fn evaluate_bin_op(runtime: &Runtime, lhs: &CompiledTypedExpression, rhs: &CompiledTypedExpression, operator: &BinaryOperatorKind) -> EvaluateResult {
+    let lhs = lhs.evaluate(runtime)?;
+    let rhs = rhs.evaluate(runtime)?;
+    if matches!(operator, BinaryOperatorKind::Equal | BinaryOperatorKind::NotEqual) {
+        return if lhs.get_type() == rhs.get_type() {
+            let ret = match operator {
+                BinaryOperatorKind::Equal => lhs == rhs,
+                BinaryOperatorKind::NotEqual => lhs != rhs,
+                _ => unreachable!(),
+            };
+            Ok(ret.into())
+        } else {
+            indicate_type_checker_bug!(context = "type checker must deny equality check between different types")
+        }
+    }
+
+    match (lhs, rhs) {
+        (TypeBox::NonCoercedInteger(lhs), TypeBox::NonCoercedInteger(rhs)) => {
+            f!(lhs, operator, rhs as NonCoerced)
+        },
+        (TypeBox::Int8(lhs), TypeBox::Int8(rhs)) => {
+            f!(lhs, operator, rhs)
+        },
+        (TypeBox::Int16(lhs), TypeBox::Int16(rhs)) => {
+            f!(lhs, operator, rhs)
+        },
+        (TypeBox::Int32(lhs), TypeBox::Int32(rhs)) => {
+            f!(lhs, operator, rhs)
+        },
+        (TypeBox::Int64(lhs), TypeBox::Int64(rhs)) => {
+            f!(lhs, operator, rhs as Coerced)
+        },
+        (TypeBox::String(lhs), TypeBox::String(rhs)) => {
+            let mut ret = lhs;
+            // give hint to compiler
+            ret.reserve_exact(rhs.len());
+            ret += rhs.as_str();
+            Ok(ret.into())
+        }
+        _ => indicate_type_checker_bug!(context = "type checker must deny operator application between different type")
+    }
+}
+
 impl CanBeEvaluated for CompiledTypedExpression {
     fn evaluate(&self, runtime: &Runtime) -> EvaluateResult {
         match self {
@@ -361,46 +403,7 @@ impl CanBeEvaluated for CompiledTypedExpression {
                     .ok_or(RuntimeError::UndefinedVariable { identifier: ident.clone() })
             },
             Self::BinaryOperator { lhs, rhs, operator, return_type: _ } => {
-                let lhs = lhs.as_ref().evaluate(runtime)?;
-                let rhs = rhs.as_ref().evaluate(runtime)?;
-                if matches!(operator, BinaryOperatorKind::Equal | BinaryOperatorKind::NotEqual) {
-                    return if lhs.get_type() == rhs.get_type() {
-                        let ret = match operator {
-                            BinaryOperatorKind::Equal => lhs == rhs,
-                            BinaryOperatorKind::NotEqual => lhs != rhs,
-                            _ => unreachable!(),
-                        };
-                        Ok(ret.into())
-                    } else {
-                        indicate_type_checker_bug!(context = "type checker must deny equality check between different types")
-                    }
-                }
-
-                return match (lhs, rhs) {
-                    (TypeBox::NonCoercedInteger(lhs), TypeBox::NonCoercedInteger(rhs)) => {
-                        f!(lhs, operator, rhs as NonCoerced)
-                    },
-                    (TypeBox::Int8(lhs), TypeBox::Int8(rhs)) => {
-                        f!(lhs, operator, rhs)
-                    },
-                    (TypeBox::Int16(lhs), TypeBox::Int16(rhs)) => {
-                        f!(lhs, operator, rhs)
-                    },
-                    (TypeBox::Int32(lhs), TypeBox::Int32(rhs)) => {
-                        f!(lhs, operator, rhs)
-                    },
-                    (TypeBox::Int64(lhs), TypeBox::Int64(rhs)) => {
-                        f!(lhs, operator, rhs as Coerced)
-                    },
-                    (TypeBox::String(lhs), TypeBox::String(rhs)) => {
-                        let mut ret = lhs;
-                        // give hint to compiler
-                        ret.reserve_exact(rhs.len());
-                        ret += rhs.as_str();
-                        Ok(ret.into())
-                    }
-                    _ => indicate_type_checker_bug!(context = "type checker must deny operator application between different type")
-                };
+                evaluate_bin_op(runtime, lhs, rhs, operator)
             }
             Self::If { condition, then: then_clause_value, els: else_clause_value, return_type: _ } => {
                 let ret = condition.as_ref().evaluate(runtime)?;
diff --git a/package/origlang-typecheck/src/lib.rs b/package/origlang-typecheck/src/lib.rs
index c8b770ce..1b3436e2 100644
--- a/package/origlang-typecheck/src/lib.rs
+++ b/package/origlang-typecheck/src/lib.rs
@@ -1,18 +1,5 @@
 #![deny(clippy::all)]
 #![warn(clippy::pedantic, clippy::nursery)]
-pub mod type_check;
-
-pub fn add(left: usize, right: usize) -> usize {
-    left + right
-}
 
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn it_works() {
-        let result = add(2, 2);
-        assert_eq!(result, 4);
-    }
-}
+// TODO: lift up
+pub mod type_check;
diff --git a/package/origlang-typecheck/src/type_check.rs b/package/origlang-typecheck/src/type_check.rs
index 7ee91c09..6a9940cd 100644
--- a/package/origlang-typecheck/src/type_check.rs
+++ b/package/origlang-typecheck/src/type_check.rs
@@ -493,6 +493,8 @@ impl TypeChecker {
         }
     }
 
+    #[must_use]
+    #[allow(clippy::missing_panics_doc)] // do not panic
     pub fn make_fresh_identifier(&self) -> Identifier {
         // TODO: this implementation is poor. choice more elegant algorithm.
         let hello = RandomState::new().hash_one(());