diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index 9d4af94..19d0bf5 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -16,4 +16,5 @@ jobs:
         with:
           toolchain: stable
 
-      - run: cargo run
+      - run: cargo run examples/hello.cirru
+      - run: cargo run examples/sum.cirru
diff --git a/Cargo.toml b/Cargo.toml
index 070e207..4cae47a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,6 +10,7 @@ edition = "2018"
 cirru_parser = "0.1.1"
 regex = "1"
 lazy_static = "1.4.0"
+clap = "3.0.0-beta.4"
 
 [profile.release]
 debug = true
\ No newline at end of file
diff --git a/README.md b/README.md
index 1b21f57..f58becd 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,18 @@
 
 ### Usages
 
-TODO
+```bash
+cargo install calx-vm
+calx hello.cirru
+```
+
+it starts with a `main` function:
+
+```cirru
+fn main ()
+  const "|hello world"
+  echo
+```
 
 ### Instructions
 
diff --git a/examples/hello.cirru b/examples/hello.cirru
new file mode 100644
index 0000000..b68cadb
--- /dev/null
+++ b/examples/hello.cirru
@@ -0,0 +1,4 @@
+
+fn main ()
+  const "|hello world"
+  echo
diff --git a/examples/demo.cirru b/examples/sum.cirru
similarity index 97%
rename from examples/demo.cirru
rename to examples/sum.cirru
index 0609ee0..0c33ade 100644
--- a/examples/demo.cirru
+++ b/examples/sum.cirru
@@ -17,7 +17,7 @@ fn demo (-> i64)
     const 0
     local.set 0
     const 0
-    loop (i64 -> i64)
+    loop (i64)
       const 1
       i.add
       dup
diff --git a/src/bin/calx.rs b/src/bin/calx.rs
index 5aa5b38..0db1577 100644
--- a/src/bin/calx.rs
+++ b/src/bin/calx.rs
@@ -3,16 +3,35 @@ use std::fs;
 use std::time::Instant;
 
 use cirru_parser::{parse, Cirru};
+use clap::{App, Arg};
 
 use calx_vm::{parse_function, Calx, CalxFunc, CalxImportsDict, CalxVM};
 
-fn log2_calx_value(xs: Vec<Calx>) -> Result<Calx, String> {
-  println!("log: {:?}", xs);
-  Ok(Calx::Nil)
-}
-
 fn main() -> Result<(), String> {
-  let contents = fs::read_to_string("examples/demo.cirru").expect("Cirru file for instructions");
+  let matches = App::new("Calx VM")
+    .version("0.1.0")
+    .author("Jon Chen <jiyinyiyong@gmail.com>")
+    .about("A toy VM")
+    .arg(
+      Arg::new("SHOW_CODE")
+        .short('S')
+        .long("show-code")
+        .value_name("show-code")
+        .about("Sets a custom config file")
+        .takes_value(false),
+    )
+    .arg(
+      Arg::new("SOURCE")
+        .about("A *.cirru file for loading code")
+        .required(true)
+        .index(1),
+    )
+    .get_matches();
+
+  let source = matches.value_of("SOURCE").unwrap();
+  let show_code = matches.is_present("SHOW_CODE");
+
+  let contents = fs::read_to_string(source).expect("Cirru file for instructions");
   let code = parse(&contents).expect("Some Cirru content");
 
   if let Cirru::List(xs) = code {
@@ -30,10 +49,11 @@ fn main() -> Result<(), String> {
     imports.insert(String::from("log2"), (log2_calx_value, 2));
 
     let mut vm = CalxVM::new(fns, vec![], imports);
-
-    // for func in vm.funcs.to_owned() {
-    //   println!("loaded fn: {}", func);
-    // }
+    if show_code {
+      for func in vm.funcs.to_owned() {
+        println!("loaded fn: {}", func);
+      }
+    }
     let now = Instant::now();
 
     match vm.run() {
@@ -53,3 +73,8 @@ fn main() -> Result<(), String> {
     Err(String::from("TODO not cirru code"))
   }
 }
+
+fn log2_calx_value(xs: Vec<Calx>) -> Result<Calx, String> {
+  println!("log: {:?}", xs);
+  Ok(Calx::Nil)
+}
diff --git a/src/parser.rs b/src/parser.rs
index 7bc1d61..ae9d218 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -327,6 +327,11 @@ pub fn parse_block(ptr_base: usize, xs: &[Cirru], looped: bool) -> Result<Vec<Ca
     }
   }
   chunk.push(CalxInstr::BlockEnd);
+
+  if looped && !ret_types.is_empty() {
+    println!("return types for loop actuall not checked: {:?}", ret_types);
+  }
+
   chunk.insert(
     0,
     CalxInstr::Block {
diff --git a/src/vm.rs b/src/vm.rs
index 6cabd67..45a90f0 100644
--- a/src/vm.rs
+++ b/src/vm.rs
@@ -61,15 +61,7 @@ impl CalxVM {
       }
       match self.top_frame.instrs[self.top_frame.pointer].to_owned() {
         CalxInstr::Br(size) => {
-          if self.top_frame.blocks_track.len() <= size {
-            return Err(format!(
-              "stack size {} eq/smaller than br size {}",
-              self.top_frame.blocks_track.len(),
-              size
-            ));
-          }
-
-          self.shrink_blocks_by(size);
+          self.shrink_blocks_by(size)?;
 
           let last_idx = self.top_frame.blocks_track.len() - 1;
           if self.top_frame.blocks_track[last_idx].looped {
@@ -83,15 +75,7 @@ impl CalxVM {
         CalxInstr::BrIf(size) => {
           let v = self.stack_pop()?;
           if v == Calx::Bool(true) || v == Calx::I64(1) {
-            if self.top_frame.blocks_track.len() <= size {
-              return Err(format!(
-                "stack size {} eq/smaller than br size {}",
-                self.top_frame.blocks_track.len(),
-                size
-              ));
-            }
-
-            self.shrink_blocks_by(size);
+            self.shrink_blocks_by(size)?;
 
             let last_idx = self.top_frame.blocks_track.len() - 1;
             if self.top_frame.blocks_track[last_idx].looped {
@@ -514,12 +498,22 @@ impl CalxVM {
 
   /// assumed that the size already checked
   #[inline(always)]
-  fn shrink_blocks_by(&mut self, size: usize) {
+  fn shrink_blocks_by(&mut self, size: usize) -> Result<(), String> {
+    if self.top_frame.blocks_track.len() <= size {
+      return Err(format!(
+        "stack size {} eq/smaller than br size {}",
+        self.top_frame.blocks_track.len(),
+        size
+      ));
+    }
+
     let mut i = size;
     while i > 0 {
       self.top_frame.blocks_track.pop();
       i -= 1;
     }
+
+    Ok(())
   }
 }