diff --git a/moon.mod.json b/moon.mod.json
index 7050d65..732e52a 100644
--- a/moon.mod.json
+++ b/moon.mod.json
@@ -1,6 +1,6 @@
 {
   "name": "tiye/cirru-parser",
-  "version": "0.0.9",
+  "version": "0.0.10",
   "deps": {},
   "readme": "README.md",
   "repository": "https://github.com/Cirru/parser.mbt",
diff --git a/src/lib/parser.mbt b/src/lib/parser.mbt
index c8942a8..ebda89f 100644
--- a/src/lib/parser.mbt
+++ b/src/lib/parser.mbt
@@ -1,3 +1,4 @@
+///|
 fn build_exprs(tokens : Array[CirruLexItem]) -> Array[Cirru]!CirruParseError {
   let acc : Array[Cirru] = Array::new()
   let mut idx = 0
@@ -56,7 +57,7 @@ fn build_exprs(tokens : Array[CirruLexItem]) -> Array[Cirru]!CirruParseError {
   }
 }
 
-/// main function to parse Cirru code into syntax tree
+///| main function to parse Cirru code into syntax tree
 pub fn parse(code : String) -> Array[Cirru]!CirruParseError {
   let tokens = resolve_indentations(lex!(code))
   // println("tokens: \{tokens}")
@@ -65,15 +66,17 @@ pub fn parse(code : String) -> Array[Cirru]!CirruParseError {
   resolve_comma(resolve_dollar(tree))
 }
 
+///|
 type! CirruParseError String
 
-/// display Cirru parse error
+///| display Cirru parse error
 pub fn to_string(self : CirruParseError) -> String {
   match self {
     CirruParseError(s) => s
   }
 }
 
+///|
 fn parse_indentation(size : Int) -> CirruLexItem!CirruParseError {
   if size % 2 == 0 {
     CirruLexItem::Indent(size >> 1)
@@ -82,7 +85,7 @@ fn parse_indentation(size : Int) -> CirruLexItem!CirruParseError {
   }
 }
 
-/// lexer is a simpler state machine to tokenize Cirru code
+///| lexer is a simpler state machine to tokenize Cirru code
 fn lex(initial_code : String) -> Array[CirruLexItem]!CirruParseError {
   let acc = []
   let mut state = CirruLexState::Indent
@@ -264,7 +267,7 @@ fn lex(initial_code : String) -> Array[CirruLexItem]!CirruParseError {
   }
 }
 
-/// internal function for figuring out indentations after lexing
+///| internal function for figuring out indentations after lexing
 fn resolve_indentations(tokens : Array[CirruLexItem]) -> Array[CirruLexItem] {
   let size = tokens.length()
   let mut acc : Array[CirruLexItem] = Array::new()
diff --git a/src/lib/parser_test.mbt b/src/lib/parser_test.mbt
index 1a9b46a..bc6be5b 100644
--- a/src/lib/parser_test.mbt
+++ b/src/lib/parser_test.mbt
@@ -1,8 +1,7 @@
 test "parser" {
-  assert_eq!(
-    @lib.parse!("def a"),
-    [@lib.Cirru::List([@lib.Cirru::Leaf("def"), @lib.Cirru::Leaf("a")])],
-  )
+  assert_eq!(@lib.parse!("def a"), [
+    @lib.Cirru::List([@lib.Cirru::Leaf("def"), @lib.Cirru::Leaf("a")]),
+  ])
 }
 
 test "existed demos" {
@@ -18,13 +17,15 @@ test "existed demos" {
     let defined = @json.parse?(json_file).unwrap()
     let defined_str = defined.stringify()
     assert_eq!(tree, defined_str)
-
-    let formatted = @lib.format!(@json.from_json!(defined), {use_inline: false})
+    let formatted = @lib.format!(@json.from_json!(defined), {
+      use_inline: false,
+    })
     let ret = @lib.parse?(formatted).unwrap().to_json().stringify()
     assert_eq!(ret, defined_str)
   }
 }
 
+///|
 pub extern "js" fn fsReadSync(path : String) -> String =
   #|(path) => {
   #|  const fs = require("node:fs");
diff --git a/src/lib/primes.mbt b/src/lib/primes.mbt
index 34e7c95..25b964e 100644
--- a/src/lib/primes.mbt
+++ b/src/lib/primes.mbt
@@ -70,7 +70,7 @@ fn Cirru::default() -> Cirru {
 }
 
 ///|
-pub fn output(self : Cirru, logger : Logger) -> Unit {
+pub fn output(self : Cirru, logger : &Logger) -> Unit {
   logger.write_string(self.to_string())
 }
 
@@ -176,7 +176,7 @@ enum CirruLexItem {
 }
 
 ///|
-fn output(self : CirruLexItem, logger : Logger) -> Unit {
+fn output(self : CirruLexItem, logger : &Logger) -> Unit {
   logger.write_string(self.to_string())
 }
 
diff --git a/src/lib/s_expr.mbt b/src/lib/s_expr.mbt
index a1679d9..1687799 100644
--- a/src/lib/s_expr.mbt
+++ b/src/lib/s_expr.mbt
@@ -1,6 +1,7 @@
+///|
 type! FormatError String
 
-/// format program to Cirru to Lisp-like code
+///| format program to Cirru to Lisp-like code
 pub fn format_to_lisp(xs : Array[Cirru]) -> String!FormatError {
   let mut content : String = "\n"
   for expr in xs {
@@ -9,7 +10,7 @@ pub fn format_to_lisp(xs : Array[Cirru]) -> String!FormatError {
   content
 }
 
-/// format single expression to Lisp-like code
+///| format single expression to Lisp-like code
 fn format_lispy_expr(self : Cirru, indent : Int) -> String!FormatError {
   let emptySpace = " "
   match self {
@@ -62,6 +63,7 @@ fn format_lispy_expr(self : Cirru, indent : Int) -> String!FormatError {
   }
 }
 
+///|
 fn ends_with_newline(s : String) -> Bool {
   for c in s.rev() {
     if c == 'c' {
@@ -74,6 +76,7 @@ fn ends_with_newline(s : String) -> Bool {
   false
 }
 
+///|
 fn gen_newline(n : Int) -> String {
   let mut chunk : String = ""
   chunk = "\{chunk}\n"
@@ -83,7 +86,7 @@ fn gen_newline(n : Int) -> String {
   chunk
 }
 
-/// `.escape_default()` in Rust
+///| `.escape_default()` in Rust
 fn escape_string(s : String) -> String {
   let mut chunk : String = ""
   for c in s {
diff --git a/src/lib/tree.mbt b/src/lib/tree.mbt
index 60d8c0c..6634d39 100644
--- a/src/lib/tree.mbt
+++ b/src/lib/tree.mbt
@@ -1,3 +1,4 @@
+///|
 fn resolve_comma(xs : Array[Cirru]) -> Array[Cirru] {
   if xs.is_empty() {
     []
@@ -6,6 +7,7 @@ fn resolve_comma(xs : Array[Cirru]) -> Array[Cirru] {
   }
 }
 
+///|
 fn comma_helper(initial_after : Array[Cirru]) -> Array[Cirru] {
   let before : Array[Cirru] = []
   let after : Array[Cirru] = initial_after
@@ -35,6 +37,7 @@ fn comma_helper(initial_after : Array[Cirru]) -> Array[Cirru] {
   }
 }
 
+///|
 fn resolve_dollar(xs : Array[Cirru]) -> Array[Cirru] {
   if xs.is_empty() {
     []
@@ -43,6 +46,7 @@ fn resolve_dollar(xs : Array[Cirru]) -> Array[Cirru] {
   }
 }
 
+///|
 fn dollar_helper(initial_after : Array[Cirru]) -> Array[Cirru] {
   let before : Array[Cirru] = []
   let after : Array[Cirru] = initial_after
diff --git a/src/lib/writer.mbt b/src/lib/writer.mbt
index bc8efc3..c397bd1 100644
--- a/src/lib/writer.mbt
+++ b/src/lib/writer.mbt
@@ -1,3 +1,4 @@
+///|
 enum WriterNode {
   Nil
   Leaf
@@ -6,18 +7,23 @@ enum WriterNode {
   Expr
 } derive(Eq)
 
+///|
 let char_close : Char = ')'
 
+///|
 let char_open : Char = '('
 
+///|
 let allowed_chars : String = "$-:<>[]{}*=+.,\\/!?~_@#&%^|;'"
 
+///|
 fn is_a_digit(c : Char) -> Bool {
   let n = c.to_int()
   // ascii table https://tool.oschina.net/commons?type=4
   n >= 48 && n <= 57
 }
 
+///|
 fn is_a_letter(c : Char) -> Bool {
   let n = c.to_int()
   if n >= 65 && n <= 90 {
@@ -29,6 +35,7 @@ fn is_a_letter(c : Char) -> Bool {
   false
 }
 
+///|
 fn is_simple_expr(ys : Array[Cirru]) -> Bool {
   for y in ys {
     match y {
@@ -39,6 +46,7 @@ fn is_simple_expr(ys : Array[Cirru]) -> Bool {
   true
 }
 
+///|
 fn is_boxed(ys : Array[Cirru]) -> Bool {
   for y in ys {
     match y {
@@ -49,10 +57,12 @@ fn is_boxed(ys : Array[Cirru]) -> Bool {
   true
 }
 
+///|
 fn is_simple_char(x : Char) -> Bool {
   is_a_letter(x) || is_a_digit(x)
 }
 
+///|
 fn is_char_allowed(x : Char) -> Bool {
   if is_simple_char(x) {
     return true
@@ -60,6 +70,7 @@ fn is_char_allowed(x : Char) -> Bool {
   allowed_chars.contains_char(x)
 }
 
+///|
 fn generate_leaf(s : String) -> String {
   let mut all_allowed = true
   for x in s {
@@ -89,10 +100,12 @@ fn generate_leaf(s : String) -> String {
   }
 }
 
+///|
 fn generate_empty_expr() -> String {
   "()"
 }
 
+///|
 fn generate_inline_expr(xs : Array[Cirru]) -> String {
   let mut result = char_open.to_string()
   for idx, x in xs {
@@ -109,7 +122,7 @@ fn generate_inline_expr(xs : Array[Cirru]) -> String {
   result
 }
 
-/// by 2 spaces
+///| by 2 spaces
 fn push_spaces(buf : String, n : Int) -> String {
   let mut ret = buf
   // for _ in 0..n {
@@ -121,6 +134,7 @@ fn push_spaces(buf : String, n : Int) -> String {
   return ret
 }
 
+///|
 fn render_newline(n : Int) -> String {
   let mut ret = ""
   ret = ret + "\n"
@@ -128,12 +142,12 @@ fn render_newline(n : Int) -> String {
   ret
 }
 
-/// options for writer, `use_inline` for more compact format.
+///| options for writer, `use_inline` for more compact format.
 pub(all) struct CirruWriterOptions {
   use_inline : Bool
 }
 
-/// kind for writer nodes
+///| kind for writer nodes
 fn get_node_kind(self : Cirru) -> WriterNode {
   match self {
     Cirru::Leaf(_) => WriterNode::Leaf
@@ -150,14 +164,17 @@ fn get_node_kind(self : Cirru) -> WriterNode {
   }
 }
 
+///|
 pub(all) type! FormatCirruError String
 
+///|
 pub fn to_string(self : FormatCirruError) -> String {
   match self {
     FormatCirruError(s) => s
   }
 }
 
+///|
 fn generate_tree(
   xs : Array[Cirru],
   insist_head : Bool,
@@ -291,6 +308,7 @@ fn generate_tree(
   result
 }
 
+///|
 fn generate_statements(
   ys : Array[Cirru],
   options : CirruWriterOptions
@@ -309,7 +327,7 @@ fn generate_statements(
   zs
 }
 
-/// format Cirru code, use options to control `use_inline` option
+///| format Cirru code, use options to control `use_inline` option
 pub fn format(
   xs : Array[Cirru],
   options : CirruWriterOptions