diff --git a/moon.mod.json b/moon.mod.json
index ca0a064..8bbd6df 100644
--- a/moon.mod.json
+++ b/moon.mod.json
@@ -1,11 +1,12 @@
 {
   "name": "tiye/cirru-parser",
-  "version": "0.1.0",
+  "version": "0.1.1",
   "deps": {},
   "readme": "README.md",
   "repository": "https://github.com/Cirru/parser.mbt",
   "license": "Apache-2.0",
   "keywords": ["Cirru"],
   "source": "src",
+  "preferred-target": "js",
   "description": "parser for Cirru Syntax"
 }
diff --git a/src/lib/parser_test.mbt b/src/lib/parser_test.mbt
index b70b01f..d540957 100644
--- a/src/lib/parser_test.mbt
+++ b/src/lib/parser_test.mbt
@@ -16,14 +16,14 @@ test "existed demos" {
   for demo in demos {
     let demo_file = fsReadSync("./test/cirru/\{demo}.cirru")
     let json_file = fsReadSync("./test/data/\{demo}.json")
-    let tree = Cirru::parse?(demo_file).unwrap().to_json().stringify()
-    let defined = @json.parse?(json_file).unwrap()
+    let tree = (try? Cirru::parse(demo_file)).unwrap().to_json().stringify()
+    let defined = (try? @json.parse(json_file)).unwrap()
     let defined_str = defined.stringify()
     assert_eq(tree, defined_str)
     let formatted = Cirru::format(@json.from_json(defined), {
       use_inline: false,
     })
-    let ret = Cirru::parse?(formatted).unwrap().to_json().stringify()
+    let ret = (try? Cirru::parse(formatted)).unwrap().to_json().stringify()
     assert_eq(ret, defined_str)
   }
 }
diff --git a/src/lib/primes.mbt b/src/lib/primes.mbt
index cf0a9b0..ba67bca 100644
--- a/src/lib/primes.mbt
+++ b/src/lib/primes.mbt
@@ -65,11 +65,6 @@ pub impl @json.FromJson for Cirru with from_json(json, path) {
   }
 }
 
-///|
-impl Default for Cirru with default() -> Cirru {
-  List(Array::new())
-}
-
 ///|
 pub impl Show for Cirru with output(self : Cirru, logger : &Logger) -> Unit {
   match self {
@@ -98,7 +93,7 @@ pub impl Compare for Cirru with compare(self, other) -> Int {
   match (self, other) {
     (Leaf(a), Leaf(b)) => a.compare(b)
     (List(xs), List(ys)) => {
-      let size = @math.minimum(xs.length(), ys.length())
+      let size = @cmp.minimum(xs.length(), ys.length())
       for i = 0; i < size; i = i + 1 {
         let x = xs[i]
         let y = ys[i]
@@ -149,7 +144,7 @@ pub fn Cirru::is_nested(self : Cirru) -> Bool {
 ///|
 pub fn Cirru::is_comment(self : Cirru) -> Bool {
   match self {
-    Leaf(s) => s.char_at(0) == ';'
+    Leaf(s) => s.length() > 0 && s[0] == ';'
     _ => false
   }
 }
@@ -167,7 +162,7 @@ priv enum CirruLexState {
   Indent
   /// Working on a string
   Str
-} derive(Show)
+}
 
 ///|
 /// lexer is a simpler state machine to tokenize Cirru code
@@ -201,7 +196,7 @@ fn CirruLexItem::is_normal_str(tok : String) -> Bool {
   }
   let mut i = 0
   while i < size {
-    let c = tok.char_at(i)
+    let c = tok[i]
     match c {
       'A'..='Z' => ()
       'a'..='z' => ()
@@ -239,7 +234,7 @@ fn escape_cirru_leaf(s : String) -> String {
     let size = s.length()
     let mut i = 0
     while i < size {
-      let c = s.char_at(i)
+      let c = s[i]
       match c {
         '\n' => out += "\\n"
         '\t' => out += "\\t"
diff --git a/src/lib/s_expr.mbt b/src/lib/s_expr.mbt
index ff98cc6..e9bbe05 100644
--- a/src/lib/s_expr.mbt
+++ b/src/lib/s_expr.mbt
@@ -51,7 +51,7 @@ fn format_lispy_expr(self : Cirru, indent : Int) -> String raise FormatError {
       if token.is_empty() {
         raise FormatError("empty string is invalid")
       } else {
-        let s0 = token.char_at(0)
+        let s0 = token[0]
         if s0 == '|' || s0 == '"' {
           "\"" + escape_string(token.substring(start=1)) + "\""
         } else if token.contains(" ") ||
diff --git a/src/main/main.mbt b/src/main/main.mbt
index 046a915..b59d073 100644
--- a/src/main/main.mbt
+++ b/src/main/main.mbt
@@ -13,11 +13,11 @@ pub fn main_parser() -> Unit {
 
   let demo_file = fsReadSync("./test/cirru/unfolding.cirru")
   let json_file = fsReadSync("./test/data/unfolding.json")
-  let tree = Cirru::parse?(demo_file)
+  let tree = try? Cirru::parse(demo_file)
   match tree {
     Ok(tree) => {
       println(tree.to_json().stringify())
-      match @json.parse?(json_file) {
+      match (try? @json.parse(json_file)) {
         Ok(json) => println(json.stringify())
         Err(err) => println(err.to_string())
       }
@@ -32,13 +32,13 @@ pub fn main_writer() -> Unit {
   let demo = "unfolding"
   let demo_file = fsReadSync("./test/cirru/\{demo}.cirru")
   let json_file = fsReadSync("./test/data/\{demo}.json")
-  let defined = @json.parse?(json_file).unwrap()
-  let tree : Array[Cirru] = @json.from_json?(defined).unwrap()
+  let defined = (try? @json.parse(json_file)).unwrap()
+  let tree : Array[Cirru] = (try? @json.from_json(defined)).unwrap()
   println("TREE:")
   for item in tree {
     println(item.to_json().stringify())
   }
-  let ret = Cirru::format?(tree, { use_inline: false }).unwrap()
+  let ret = (try? Cirru::format(tree, { use_inline: false })).unwrap()
   println("Generated:")
   println(ret)
   println("Expected:")