diff --git a/src/main.rs b/src/main.rs
index 328b92c..8a139fa 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -20,6 +20,64 @@ Written by Hatter Jiang
 }
 
 // ---------------------------------------------------------------------------------------------------------
+
+fn walk_dir<FError, FProcess, FFilter>(dir: &Path, 
+        func_read_error: &FError,
+        func_process_file: &FProcess, 
+        func_filter_dir: &FFilter) -> XResult<()>
+        where FError: Fn(&Path, Box<dyn std::error::Error>) -> (),
+              FProcess: Fn(&Path) -> (), 
+              FFilter: Fn(&Path) -> bool {
+    walk_dir_with_depth_check(&mut 0u32, dir, func_read_error, func_process_file, func_filter_dir)
+}
+
+fn walk_dir_with_depth_check<FError, FProcess, FFilter>(depth: &mut u32, dir: &Path, 
+        func_read_error: &FError,
+        func_process_file: &FProcess,
+        func_filter_dir: &FFilter) -> XResult<()>
+        where FError: Fn(&Path, Box<dyn std::error::Error>) -> (),
+              FProcess: Fn(&Path) -> (), 
+              FFilter: Fn(&Path) -> bool {
+    if *depth > 100u32 {
+        return Err(Box::new(std::io::Error::new(std::io::ErrorKind::Other, format!("Depth exceed, depth: {}, path: {:?}", *depth, dir))));
+    }
+    let read_dir = match dir.read_dir() {
+        Err(err) => {
+            func_read_error(&dir, Box::new(err));
+            return Ok(());
+        },
+        Ok(rd) => rd,
+    };
+    for dir_entry_item in read_dir {
+        let dir_entry = match dir_entry_item {
+            Err(err) => {
+                func_read_error(&dir, Box::new(err));
+                continue; // Ok?
+            },
+            Ok(item) => item,
+        };
+
+        let path_buf = dir_entry.path();
+        let sub_dir = path_buf.as_path();
+        if sub_dir.is_file() {
+            func_process_file(&sub_dir);
+        } else if sub_dir.is_dir() {
+            if func_filter_dir(&sub_dir) {
+                *depth += 1;
+                match walk_dir_with_depth_check(depth, &sub_dir, func_read_error, func_process_file, func_filter_dir) {
+                    Err(err) => {
+                        func_read_error(&sub_dir, err);
+                        ()
+                    },
+                    Ok(_) => (),
+                }
+                *depth -= 1;
+            }
+        } // should process else ? not file, dir
+    }
+    Ok(())
+}
+
 fn check_path(path: &Path) {
     //println!("-------------- {:?} {}", path, path.is_dir());
 }