diff --git a/Cargo.lock b/Cargo.lock
index dff8e1c..c18c3b5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -88,7 +88,6 @@ dependencies = [
  "heck",
  "itertools",
  "log",
- "prettyplease",
  "proc-macro2",
  "quote",
  "roxmltree",
@@ -164,16 +163,6 @@ version = "1.20.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1261fe7e33c73b354eab43b1273a57c8f967d0391e80353e51f764ac02cf6775"
 
-[[package]]
-name = "prettyplease"
-version = "0.2.29"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6924ced06e1f7dfe3fa48d57b9f74f55d8915f5036121bef647ef4b204895fac"
-dependencies = [
- "proc-macro2",
- "syn",
-]
-
 [[package]]
 name = "proc-macro2"
 version = "1.0.93"
diff --git a/Cargo.toml b/Cargo.toml
index 6bd8bcc..755bd1c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -17,7 +17,6 @@ env_logger = "0.11.6"
 heck = "0.5"
 itertools = "0.14"
 log = "0.4"
-prettyplease = "0.2"
 proc-macro2 = "1.0.93"
 quote = "1.0"
 roxmltree = "0.20"
diff --git a/src/generator.rs b/src/generator.rs
index a4c6d95..2ab6d5c 100644
--- a/src/generator.rs
+++ b/src/generator.rs
@@ -1,9 +1,9 @@
 //! Generate register interface rust code from types in [`crate::types`].
 //!
-//! root: [`Module::generate_code`]
+//! root: [`CodeGen`]
 //!
-//! # For developers
-//! Pass `--document-private-items` to see non-public items.
+//! # TODO
+//! add docs (especially fields and registers)
 
 use std::{
     collections::HashMap,
@@ -15,14 +15,13 @@ use crate::{
     types::{Block, Module, ModuleBlockElements, Register},
 };
 use heck::{ToSnakeCase, ToUpperCamelCase};
-use itertools::Itertools;
 use quote::quote;
 use thiserror::Error;
 
 #[derive(Debug, Error)]
 pub enum CodeGenError {
-    #[error("tokenization(syn) error: {0}")]
-    SynError(#[from] syn::Error),
+    #[error("tokenization error: {0}")]
+    TokenizeError(#[from] syn::Error),
     #[error("failed to create file: {0}")]
     FilePathError(String),
     #[error("parent is required for {module}")]
@@ -121,22 +120,7 @@ mod util {
     }
 }
 
-impl Module {
-    pub fn generate_code(self) -> Result<HashMap<path::PathBuf, syn::File>, CodeGenError> {
-        let files = self.generate_register_interface(None, None, HashMap::new())?;
-        Ok(files
-            .into_iter()
-            .map(
-                |(path, tokens)| -> Result<(PathBuf, syn::File), syn::Error> {
-                    let file: syn::File = syn::parse2(tokens)?;
-                    Ok((path, file))
-                },
-            )
-            .process_results(|kv| HashMap::from_iter(kv))?)
-    }
-}
-
-trait CodeGen {
+pub trait CodeGen {
     /// `parent_name` in UpperCamelCase.
     fn generate_register_interface(
         self,
diff --git a/src/io.rs b/src/io.rs
deleted file mode 100644
index 2f345da..0000000
--- a/src/io.rs
+++ /dev/null
@@ -1,27 +0,0 @@
-//! File IO for generated codes.
-
-use std::{collections::HashMap, fs, io, path};
-
-/// Write formatted codes generated with [`Module::generate_code`](crate::types::Module::generate_code).
-pub fn write_to_files(
-    files: HashMap<path::PathBuf, syn::File>,
-    out_path: &path::Path,
-) -> io::Result<()> {
-    if !out_path.is_dir() {
-        return Err(io::Error::from(io::ErrorKind::NotADirectory));
-    }
-    if fs::read_dir(out_path)?.next().is_some() {
-        return Err(io::Error::new(
-            io::ErrorKind::AlreadyExists,
-            "out path is not empty",
-        ));
-    }
-    for (file_path, code) in files {
-        fs::DirBuilder::new()
-            .recursive(true)
-            .create(out_path.join(&file_path).parent().unwrap())?;
-
-        fs::write(out_path.join(&file_path), prettyplease::unparse(&code))?;
-    }
-    Ok(())
-}
diff --git a/src/lib.rs b/src/lib.rs
index 4129c60..49b6578 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,27 +1,4 @@
-//! Generate register interface software from register map in XML.
-//!
-//! # Example
-//!
-//! Here's a typical usage:
-//! ```no_run
-//! use endcap_sl_software_ri_generator::types;
-//!
-//! let xmlfile = std::fs::read_to_string("./csr.xml")?;
-//! let doc = roxmltree::Document::parse_with_options(
-//!     &xmlfile,
-//!     roxmltree::ParsingOptions {
-//!         allow_dtd: true,
-//!         nodes_limit: u32::MAX,
-//!     },
-//! )?;
-//!
-//! let register_map = types::Module::from_xml_dom(doc.root_element())?;
-//!
-//! let files = register_map.generate_code()?;
-//! endcap_sl_software_ri_generator::write_to_files(files, &std::path::PathBuf::from("out"))?;
-//!
-//! # Ok::<(), anyhow::Error>(())
-//! ```
+//! Root document [`types::Module::from_xml_dom`]
 //!
 //! # Overview
 //!
@@ -32,15 +9,13 @@
 //!
 //! # modules
 //! - [`types`]: type definitions of internal register map representation
+//! - [`type_traits`]: supplemental traits for types in [`types`]
+//! - [`parser`]: supplemental parser (string to custom types)
 //! - [`converter`]: DOM to internal representation
 //! - [`generator`]: internal representation to rust code
-//! - [`io`]: formatting and printing
 
 pub mod converter;
 pub mod generator;
-pub mod io;
-mod parser;
-mod type_traits;
+pub mod parser;
+pub mod type_traits;
 pub mod types;
-
-pub use io::write_to_files;
diff --git a/src/main.rs b/src/main.rs
index a3a63bf..9b443de 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,13 +1,15 @@
-use std::fs;
+use std::fs::DirBuilder;
+use std::io::Write;
+use std::{collections::HashMap, fs, io::BufWriter};
 
-use anyhow::Result;
-use endcap_sl_software_ri_generator::types;
+use anyhow::{anyhow, Context, Result};
+use endcap_sl_software_ri_generator::{generator::CodeGen, types};
 use itertools::Itertools;
 
 fn main() -> Result<()> {
     env_logger::init();
-    log::debug!("logger enabled");
 
+    println!("Hello, world!");
     let xmlfile = fs::read_to_string("./csr.xml")?;
     let doc = roxmltree::Document::parse_with_options(
         &xmlfile,
@@ -16,26 +18,39 @@ fn main() -> Result<()> {
             nodes_limit: u32::MAX,
         },
     )?;
-    log::debug!("Parsed: {:#?}", doc);
+    // println!("Parsed: {:#?}", doc);
+    // println!("Root: {:?}", doc.root_element());
 
     let register_map = types::Module::from_xml_dom(doc.root_element())?;
-    log::info!("read: {:?}", register_map);
-    log::debug!("read: {:#?}", register_map);
+    println!("read: {:#?}", register_map);
 
-    let files = register_map.generate_code()?;
-    if log::log_enabled!(log::Level::Debug) {
-        for (path, code) in &files {
-            log::debug!("path: {:?}", path);
-            log::debug!("{}", prettyplease::unparse(code));
-        }
-    }
-    if log::log_enabled!(log::Level::Info) {
-        for filepath in files.keys().sorted() {
-            log::info!("{}", filepath.display());
-        }
-    }
+    println!("===========================================");
 
-    endcap_sl_software_ri_generator::write_to_files(files, &std::path::PathBuf::from("out"))?;
+    let files = register_map.generate_register_interface(None, None, HashMap::new())?;
+    // println!("{:#?}", files);
+    for filepath in files.keys().sorted() {
+        println!("{}", filepath.display());
+    }
+    if !std::fs::read_dir("register_interface")
+        .context("register_interface not found")?
+        .collect_vec()
+        .is_empty()
+    {
+        return Err(anyhow!("dir register_interface is not empty"));
+    };
+    for (file, code) in files {
+        DirBuilder::new()
+            .recursive(true)
+            .create(file.parent().context("no parent")?)?;
+        let file = fs::OpenOptions::new()
+            .create(true)
+            .truncate(true)
+            .write(true)
+            .open(file)
+            .context("opening file")?;
+        let mut writer = BufWriter::new(file);
+        write!(writer, "{}", code)?;
+    }
 
     Ok(())
 }