diff --git a/compiler/erg_common/config.rs b/compiler/erg_common/config.rs
index 104bb1a5..5b7a058c 100644
--- a/compiler/erg_common/config.rs
+++ b/compiler/erg_common/config.rs
@@ -126,6 +126,7 @@ pub struct ErgConfig {
     pub py_server_timeout: u64,
     pub quiet_startup: bool,
     pub input: Input,
+    /// module name to be executed
     pub module: &'static str,
     /// verbosity level for system messages.
     /// * 0: display errors
diff --git a/compiler/erg_compiler/builder.rs b/compiler/erg_compiler/builder.rs
new file mode 100644
index 00000000..297fc388
--- /dev/null
+++ b/compiler/erg_compiler/builder.rs
@@ -0,0 +1,57 @@
+use erg_common::config::{ErgConfig, Input};
+use erg_common::traits::Stream;
+
+use erg_parser::ast::VarName;
+use erg_parser::builder::ASTBuilder;
+
+use crate::error::{CompileError, CompileErrors, TyCheckErrors};
+// use crate::hir::HIR;
+use crate::check::Checker;
+use crate::mod_cache::SharedModuleCache;
+
+#[derive(Debug)]
+pub struct HIRBuilder {
+    checker: Checker,
+    mod_cache: SharedModuleCache,
+}
+
+impl HIRBuilder {
+    fn convert(&self, errs: TyCheckErrors) -> CompileErrors {
+        errs.into_iter()
+            .map(|e| CompileError::new(e.core, self.checker.cfg.input.clone(), e.caused_by))
+            .collect::<Vec<_>>()
+            .into()
+    }
+
+    pub fn new(cfg: ErgConfig, mod_cache: SharedModuleCache) -> Self {
+        Self {
+            checker: Checker::new(cfg, mod_cache.clone()),
+            mod_cache,
+        }
+    }
+
+    pub fn build_and_cache(&mut self, var_name: VarName) -> Result<(), CompileErrors> {
+        let mut ast_builder = ASTBuilder::new(self.checker.cfg.copy());
+        let ast = ast_builder.build()?;
+        let (hir, ctx) = self
+            .checker
+            .check(ast, "exec")
+            .map_err(|errs| self.convert(errs))?;
+        self.mod_cache.register(var_name, Some(hir), ctx);
+        Ok(())
+    }
+
+    pub fn build_and_cache_main(&mut self, src: String, mode: &str) -> Result<(), CompileErrors> {
+        let mut cfg = self.checker.cfg.copy();
+        cfg.input = Input::Str(src);
+        let mut ast_builder = ASTBuilder::new(cfg);
+        let ast = ast_builder.build()?;
+        let (hir, ctx) = self
+            .checker
+            .check(ast, mode)
+            .map_err(|errs| self.convert(errs))?;
+        let name = VarName::from_static("<module>");
+        self.mod_cache.register(name, Some(hir), ctx);
+        Ok(())
+    }
+}
diff --git a/compiler/erg_compiler/checker.rs b/compiler/erg_compiler/check.rs
similarity index 61%
rename from compiler/erg_compiler/checker.rs
rename to compiler/erg_compiler/check.rs
index 9b8f6d2a..551079cc 100644
--- a/compiler/erg_compiler/checker.rs
+++ b/compiler/erg_compiler/check.rs
@@ -5,36 +5,61 @@ use erg_common::traits::Runnable;
 use erg_parser::ast::AST;
 use erg_parser::builder::ASTBuilder;
 
+use crate::context::Context;
 use crate::effectcheck::SideEffectChecker;
 use crate::error::{TyCheckError, TyCheckErrors};
 use crate::hir::HIR;
 use crate::lower::ASTLowerer;
+use crate::mod_cache::SharedModuleCache;
 use crate::ownercheck::OwnershipChecker;
 
 /// Summarize lowering, side-effect checking, and ownership checking
 #[derive(Debug)]
 pub struct Checker {
-    cfg: ErgConfig,
+    pub cfg: ErgConfig,
     lowerer: ASTLowerer,
     ownership_checker: OwnershipChecker,
 }
 
-impl Runnable for Checker {
+impl Checker {
+    pub fn new(cfg: ErgConfig, mod_cache: SharedModuleCache) -> Self {
+        Self {
+            cfg,
+            lowerer: ASTLowerer::new(mod_cache),
+            ownership_checker: OwnershipChecker::new(),
+        }
+    }
+
+    pub fn check(&mut self, ast: AST, mode: &str) -> Result<(HIR, Context), TyCheckErrors> {
+        let (hir, ctx, warns) = self.lowerer.lower(ast, mode)?;
+        if self.cfg.verbose >= 2 {
+            warns.fmt_all_stderr();
+        }
+        let effect_checker = SideEffectChecker::new();
+        let hir = effect_checker.check(hir)?;
+        let hir = self.ownership_checker.check(hir)?;
+        Ok((hir, ctx))
+    }
+}
+
+pub struct CheckerRunner {
+    checker: Checker,
+}
+
+impl Runnable for CheckerRunner {
     type Err = TyCheckError;
     type Errs = TyCheckErrors;
     const NAME: &'static str = "Erg type-checker";
 
     fn new(cfg: ErgConfig) -> Self {
         Self {
-            ownership_checker: OwnershipChecker::new(),
-            lowerer: ASTLowerer::new(),
-            cfg,
+            checker: Checker::new(cfg, SharedModuleCache::new()),
         }
     }
 
     #[inline]
     fn cfg(&self) -> &ErgConfig {
-        &self.cfg
+        &self.checker.cfg
     }
 
     #[inline]
@@ -43,30 +68,17 @@ impl Runnable for Checker {
     fn clear(&mut self) {}
 
     fn exec(&mut self) -> Result<(), Self::Errs> {
-        let mut builder = ASTBuilder::new(self.cfg.copy());
+        let mut builder = ASTBuilder::new(self.cfg().copy());
         let ast = builder.build()?;
-        let hir = self.check(ast, "exec")?;
+        let (hir, _) = self.checker.check(ast, "exec")?;
         println!("{hir}");
         Ok(())
     }
 
     fn eval(&mut self, src: String) -> Result<String, TyCheckErrors> {
-        let mut builder = ASTBuilder::new(self.cfg.copy());
-        let ast = builder.build_with_input(src)?;
-        let hir = self.check(ast, "eval")?;
+        let mut builder = ASTBuilder::new(self.cfg().copy());
+        let ast = builder.build_with_str(src)?;
+        let (hir, _) = self.checker.check(ast, "eval")?;
         Ok(hir.to_string())
     }
 }
-
-impl Checker {
-    pub fn check(&mut self, ast: AST, mode: &str) -> Result<HIR, TyCheckErrors> {
-        let (hir, warns) = self.lowerer.lower(ast, mode)?;
-        if self.cfg.verbose >= 2 {
-            warns.fmt_all_stderr();
-        }
-        let effect_checker = SideEffectChecker::new();
-        let hir = effect_checker.check(hir)?;
-        let hir = self.ownership_checker.check(hir)?;
-        Ok(hir)
-    }
-}
diff --git a/compiler/erg_compiler/compile.rs b/compiler/erg_compiler/compile.rs
index f9a65afd..1e411c1b 100644
--- a/compiler/erg_compiler/compile.rs
+++ b/compiler/erg_compiler/compile.rs
@@ -3,16 +3,16 @@
 //! コンパイラーを定義する
 use std::path::Path;
 
-use erg_common::config::{ErgConfig, Input};
+use erg_common::config::ErgConfig;
 use erg_common::log;
 use erg_common::traits::{Runnable, Stream};
 use erg_type::codeobj::CodeObj;
 
-use erg_parser::builder::ASTBuilder;
-
-use crate::checker::Checker;
+use crate::builder::HIRBuilder;
 use crate::codegen::CodeGenerator;
-use crate::error::{CompileError, CompileErrors, TyCheckErrors};
+use crate::error::{CompileError, CompileErrors};
+use crate::link::Linker;
+use crate::mod_cache::SharedModuleCache;
 
 /// * registered as global -> Global
 /// * defined in the toplevel scope (and called in the inner scope) -> Global
@@ -91,7 +91,7 @@ impl AccessKind {
 #[derive(Debug)]
 pub struct Compiler {
     cfg: ErgConfig,
-    checker: Checker,
+    mod_cache: SharedModuleCache,
     code_generator: CodeGenerator,
 }
 
@@ -101,9 +101,10 @@ impl Runnable for Compiler {
     const NAME: &'static str = "Erg compiler";
 
     fn new(cfg: ErgConfig) -> Self {
+        let mod_cache = SharedModuleCache::new();
         Self {
-            checker: Checker::new(cfg.copy()),
             code_generator: CodeGenerator::new(cfg.copy()),
+            mod_cache,
             cfg,
         }
     }
@@ -133,13 +134,6 @@ impl Runnable for Compiler {
 }
 
 impl Compiler {
-    fn convert(&self, errs: TyCheckErrors) -> CompileErrors {
-        errs.into_iter()
-            .map(|e| CompileError::new(e.core, self.input().clone(), e.caused_by))
-            .collect::<Vec<_>>()
-            .into()
-    }
-
     pub fn compile_and_dump_as_pyc<P: AsRef<Path>>(
         &mut self,
         src: String,
@@ -154,14 +148,9 @@ impl Compiler {
 
     pub fn compile(&mut self, src: String, mode: &str) -> Result<CodeObj, CompileErrors> {
         log!(info "the compiling process has started.");
-        let mut cfg = self.cfg.copy();
-        cfg.input = Input::Str(src);
-        let mut ast_builder = ASTBuilder::new(cfg);
-        let ast = ast_builder.build()?;
-        let hir = self
-            .checker
-            .check(ast, mode)
-            .map_err(|errs| self.convert(errs))?;
+        let mut hir_builder = HIRBuilder::new(self.cfg.copy(), self.mod_cache.clone());
+        hir_builder.build_and_cache_main(src, mode)?;
+        let hir = Linker::link(self.mod_cache.clone());
         let codeobj = self.code_generator.emit(hir);
         log!(info "code object:\n{}", codeobj.code_info());
         log!(
diff --git a/compiler/erg_compiler/context/initialize/mod.rs b/compiler/erg_compiler/context/initialize/mod.rs
index 1d2ea802..67e40645 100644
--- a/compiler/erg_compiler/context/initialize/mod.rs
+++ b/compiler/erg_compiler/context/initialize/mod.rs
@@ -1783,13 +1783,13 @@ impl Context {
         ctx
     }
 
-    pub fn new_main_module() -> Self {
+    pub fn new_main_module(mod_cache: SharedModuleCache) -> Self {
         Context::new(
             "<module>".into(),
             ContextKind::Module,
             vec![],
             Some(Context::init_builtins()),
-            Some(SharedModuleCache::new()),
+            Some(mod_cache),
             Context::TOP_LEVEL,
         )
     }
diff --git a/compiler/erg_compiler/context/mod.rs b/compiler/erg_compiler/context/mod.rs
index 5d36221e..c5e38c6d 100644
--- a/compiler/erg_compiler/context/mod.rs
+++ b/compiler/erg_compiler/context/mod.rs
@@ -238,6 +238,7 @@ impl From<DefKind> for ContextKind {
             DefKind::Class | DefKind::Inherit => Self::Class,
             DefKind::Trait | DefKind::Subsume => Self::Trait,
             DefKind::StructuralTrait => Self::StructuralTrait,
+            DefKind::Module => Self::Module,
             DefKind::Other => Self::Instant,
         }
     }
diff --git a/compiler/erg_compiler/context/register.rs b/compiler/erg_compiler/context/register.rs
index d3871ec4..411b98fd 100644
--- a/compiler/erg_compiler/context/register.rs
+++ b/compiler/erg_compiler/context/register.rs
@@ -1,5 +1,7 @@
 use std::option::Option; // conflicting to Type::Option
 
+use erg_common::config::{ErgConfig, Input};
+use erg_common::error::MultiErrorDisplay;
 use erg_common::traits::{Locational, Stream};
 use erg_common::vis::Visibility;
 use erg_common::Str;
@@ -14,11 +16,12 @@ use erg_type::value::{GenTypeObj, TypeKind, TypeObj, ValueObj};
 use erg_type::{HasType, ParamTy, SubrType, TyBound, Type};
 use Type::*;
 
+use crate::builder::HIRBuilder;
 use crate::context::{ClassDefType, Context, DefaultInfo, RegistrationMode, TraitInstance};
 use crate::error::readable_name;
 use crate::error::{TyCheckError, TyCheckResult};
 use crate::hir;
-use crate::mod_cache::ModuleEntry;
+use crate::mod_cache::SharedModuleCache;
 use crate::varinfo::{Mutability, ParamIdx, VarInfo, VarKind};
 use Mutability::*;
 use RegistrationMode::*;
@@ -763,56 +766,55 @@ impl Context {
         match mod_name {
             hir::Expr::Lit(lit) => {
                 if self.subtype_of(&lit.value.class(), &Str) {
-                    let name = enum_unwrap!(lit.value.clone(), ValueObj::Str);
-                    if let Some(mod_cache) = self.mod_cache.as_mut() {
-                        match &name[..] {
+                    let __name__ = enum_unwrap!(lit.value.clone(), ValueObj::Str);
+                    if let Some(mod_cache) = self.mod_cache.as_ref() {
+                        match &__name__[..] {
                             "importlib" => {
                                 mod_cache.register(
                                     var_name.clone(),
-                                    ModuleEntry::builtin(Self::init_py_importlib_mod()),
+                                    None,
+                                    Self::init_py_importlib_mod(),
                                 );
                             }
                             "io" => {
-                                mod_cache.register(
-                                    var_name.clone(),
-                                    ModuleEntry::builtin(Self::init_py_io_mod()),
-                                );
+                                mod_cache.register(var_name.clone(), None, Self::init_py_io_mod());
                             }
                             "math" => {
                                 mod_cache.register(
                                     var_name.clone(),
-                                    ModuleEntry::builtin(Self::init_py_math_mod()),
+                                    None,
+                                    Self::init_py_math_mod(),
                                 );
                             }
                             "random" => {
                                 mod_cache.register(
                                     var_name.clone(),
-                                    ModuleEntry::builtin(Self::init_py_random_mod()),
+                                    None,
+                                    Self::init_py_random_mod(),
                                 );
                             }
                             "socket" => {
                                 mod_cache.register(
                                     var_name.clone(),
-                                    ModuleEntry::builtin(Self::init_py_socket_mod()),
+                                    None,
+                                    Self::init_py_socket_mod(),
                                 );
                             }
                             "sys" => {
-                                mod_cache.register(
-                                    var_name.clone(),
-                                    ModuleEntry::builtin(Self::init_py_sys_mod()),
-                                );
+                                mod_cache.register(var_name.clone(), None, Self::init_py_sys_mod());
                             }
                             "time" => {
                                 mod_cache.register(
                                     var_name.clone(),
-                                    ModuleEntry::builtin(Self::init_py_time_mod()),
+                                    None,
+                                    Self::init_py_time_mod(),
                                 );
                             }
-                            other => todo!("importing {other}"),
+                            _ => self.import_user_module(var_name, __name__, mod_cache),
                         }
                     } else {
                         // maybe unreachable
-                        todo!("importing {name} in the builtin module")
+                        todo!("importing {__name__} in the builtin module")
                     }
                 } else {
                     return Err(TyCheckError::type_mismatch_error(
@@ -839,6 +841,17 @@ impl Context {
         Ok(())
     }
 
+    fn import_user_module(&self, var_name: &VarName, __name__: Str, mod_cache: &SharedModuleCache) {
+        let cfg = ErgConfig {
+            input: Input::File(format!("{__name__}.er")),
+            ..ErgConfig::default()
+        };
+        let mut hir_builder = HIRBuilder::new(cfg, mod_cache.clone());
+        if let Err(errs) = hir_builder.build_and_cache(var_name.clone()) {
+            errs.fmt_all_stderr();
+        }
+    }
+
     pub(crate) fn _push_subtype_bound(&mut self, sub: Type, sup: Type) {
         self.bounds.push(TyBound::subtype_of(sub, sup));
     }
diff --git a/compiler/erg_compiler/hir.rs b/compiler/erg_compiler/hir.rs
index 244eb059..a041a595 100644
--- a/compiler/erg_compiler/hir.rs
+++ b/compiler/erg_compiler/hir.rs
@@ -1332,6 +1332,7 @@ impl Def {
                         DefKind::Other
                     }
                 }
+                Some("import") => DefKind::Module,
                 _ => DefKind::Other,
             },
             _ => DefKind::Other,
diff --git a/compiler/erg_compiler/lib.rs b/compiler/erg_compiler/lib.rs
index 795219c4..71b29231 100644
--- a/compiler/erg_compiler/lib.rs
+++ b/compiler/erg_compiler/lib.rs
@@ -3,7 +3,8 @@
 extern crate erg_common;
 pub extern crate erg_parser;
 
-mod checker;
+mod builder;
+mod check;
 mod compile;
 pub use compile::*;
 mod codegen;
@@ -11,8 +12,10 @@ pub mod context;
 pub mod effectcheck;
 pub mod error;
 pub mod hir;
+pub mod link;
 pub mod lower;
 pub mod mod_cache;
+// pub mod name_resolve;
 pub mod optimize;
 pub mod ownercheck;
 pub mod varinfo;
diff --git a/compiler/erg_compiler/link.rs b/compiler/erg_compiler/link.rs
new file mode 100644
index 00000000..14564a09
--- /dev/null
+++ b/compiler/erg_compiler/link.rs
@@ -0,0 +1,19 @@
+use erg_common::traits::Stream;
+
+use crate::hir::{Expr, HIR};
+use crate::mod_cache::SharedModuleCache;
+
+pub struct Linker {}
+
+impl Linker {
+    pub fn link(mod_cache: SharedModuleCache) -> HIR {
+        let mut main_mod_hir = mod_cache.remove("<module>").unwrap().hir.unwrap();
+        for chunk in main_mod_hir.module.iter_mut() {
+            match chunk {
+                Expr::Def(def) if def.def_kind().is_module() => {}
+                _ => {}
+            }
+        }
+        main_mod_hir
+    }
+}
diff --git a/compiler/erg_compiler/lower.rs b/compiler/erg_compiler/lower.rs
index 857b85e7..bff3b3fc 100644
--- a/compiler/erg_compiler/lower.rs
+++ b/compiler/erg_compiler/lower.rs
@@ -27,6 +27,7 @@ use crate::error::{
 };
 use crate::hir;
 use crate::hir::HIR;
+use crate::mod_cache::SharedModuleCache;
 use crate::varinfo::VarKind;
 use Visibility::*;
 
@@ -48,7 +49,7 @@ impl Runnable for ASTLowererRunner {
     fn new(cfg: ErgConfig) -> Self {
         Self {
             cfg,
-            lowerer: ASTLowerer::new(),
+            lowerer: ASTLowerer::new(SharedModuleCache::new()),
         }
     }
 
@@ -63,7 +64,7 @@ impl Runnable for ASTLowererRunner {
     fn exec(&mut self) -> Result<(), Self::Errs> {
         let mut ast_builder = ASTBuilder::new(self.cfg.copy());
         let ast = ast_builder.build()?;
-        let (hir, warns) = self
+        let (hir, _, warns) = self
             .lowerer
             .lower(ast, "exec")
             .map_err(|errs| self.convert(errs))?;
@@ -77,8 +78,8 @@ impl Runnable for ASTLowererRunner {
 
     fn eval(&mut self, src: String) -> Result<String, CompileErrors> {
         let mut ast_builder = ASTBuilder::new(self.cfg.copy());
-        let ast = ast_builder.build_with_input(src)?;
-        let (hir, _) = self
+        let ast = ast_builder.build_with_str(src)?;
+        let (hir, ..) = self
             .lowerer
             .lower(ast, "eval")
             .map_err(|errs| self.convert(errs))?;
@@ -105,14 +106,14 @@ pub struct ASTLowerer {
 
 impl Default for ASTLowerer {
     fn default() -> Self {
-        Self::new()
+        Self::new(SharedModuleCache::new())
     }
 }
 
 impl ASTLowerer {
-    pub fn new() -> Self {
+    pub fn new(mod_cache: SharedModuleCache) -> Self {
         Self {
-            ctx: Context::new_main_module(),
+            ctx: Context::new_main_module(mod_cache),
             errs: LowerErrors::empty(),
             warns: LowerWarnings::empty(),
         }
@@ -1008,7 +1009,11 @@ impl ASTLowerer {
         Ok(hir::Block::new(hir_block))
     }
 
-    pub fn lower(&mut self, ast: AST, mode: &str) -> Result<(HIR, LowerWarnings), LowerErrors> {
+    pub fn lower(
+        &mut self,
+        ast: AST,
+        mode: &str,
+    ) -> Result<(HIR, Context, LowerWarnings), LowerErrors> {
         log!(info "the AST lowering process has started.");
         log!(info "the type-checking process has started.");
         let mut module = hir::Module::with_capacity(ast.module.len());
@@ -1035,7 +1040,11 @@ impl ASTLowerer {
         if self.errs.is_empty() {
             log!(info "HIR:\n{hir}");
             log!(info "the AST lowering process has completed.");
-            Ok((hir, LowerWarnings::from(self.warns.take_all())))
+            Ok((
+                hir,
+                self.ctx.pop()?,
+                LowerWarnings::from(self.warns.take_all()),
+            ))
         } else {
             log!(err "the AST lowering process has failed.");
             Err(LowerErrors::from(self.errs.take_all()))
diff --git a/compiler/erg_compiler/mod_cache.rs b/compiler/erg_compiler/mod_cache.rs
index 25499462..5e490860 100644
--- a/compiler/erg_compiler/mod_cache.rs
+++ b/compiler/erg_compiler/mod_cache.rs
@@ -27,24 +27,24 @@ impl ModId {
 
 #[derive(Debug)]
 pub struct ModuleEntry {
-    _id: ModId, // builtin == 0, __main__ == 1
-    _hir: Option<HIR>,
+    id: ModId, // builtin == 0, __main__ == 1
+    pub hir: Option<HIR>,
     ctx: Rc<Context>,
 }
 
 impl ModuleEntry {
     pub fn new(id: ModId, hir: Option<HIR>, ctx: Context) -> Self {
         Self {
-            _id: id,
-            _hir: hir,
+            id,
+            hir,
             ctx: Rc::new(ctx),
         }
     }
 
     pub fn builtin(ctx: Context) -> Self {
         Self {
-            _id: ModId::builtin(),
-            _hir: None,
+            id: ModId::builtin(),
+            hir: None,
             ctx: Rc::new(ctx),
         }
     }
@@ -53,11 +53,15 @@ impl ModuleEntry {
 #[derive(Debug, Default)]
 pub struct ModuleCache {
     cache: Dict<VarName, ModuleEntry>,
+    last_id: usize,
 }
 
 impl ModuleCache {
     pub fn new() -> Self {
-        Self { cache: Dict::new() }
+        Self {
+            cache: Dict::new(),
+            last_id: 0,
+        }
     }
 
     pub fn get<Q: Eq + Hash + ?Sized>(&self, name: &Q) -> Option<&ModuleEntry>
@@ -67,7 +71,10 @@ impl ModuleCache {
         self.cache.get(name)
     }
 
-    pub fn register(&mut self, name: VarName, entry: ModuleEntry) {
+    pub fn register(&mut self, name: VarName, hir: Option<HIR>, ctx: Context) {
+        self.last_id += 1;
+        let id = ModId::new(self.last_id);
+        let entry = ModuleEntry::new(id, hir, ctx);
         self.cache.insert(name, entry);
     }
 
@@ -77,6 +84,20 @@ impl ModuleCache {
     {
         self.cache.remove(name)
     }
+
+    pub fn remove_by_id(&mut self, id: ModId) -> Option<ModuleEntry> {
+        if let Some(name) = self.cache.iter().find_map(|(name, ent)| {
+            if ent.id == id {
+                Some(name.clone())
+            } else {
+                None
+            }
+        }) {
+            self.remove(&name)
+        } else {
+            None
+        }
+    }
 }
 
 #[derive(Debug, Clone, Default)]
@@ -102,14 +123,18 @@ impl SharedModuleCache {
         ref_.get(name).map(|entry| entry.ctx.as_ref())
     }
 
-    pub fn register(&self, name: VarName, entry: ModuleEntry) {
-        self.0.borrow_mut().register(name, entry);
+    pub fn register(&self, name: VarName, hir: Option<HIR>, ctx: Context) {
+        self.0.borrow_mut().register(name, hir, ctx);
     }
 
-    pub fn remove<Q: Eq + Hash + ?Sized>(&mut self, name: &Q) -> Option<ModuleEntry>
+    pub fn remove<Q: Eq + Hash + ?Sized>(&self, name: &Q) -> Option<ModuleEntry>
     where
         VarName: Borrow<Q>,
     {
         self.0.borrow_mut().remove(name)
     }
+
+    pub fn remove_by_id(&self, id: ModId) -> Option<ModuleEntry> {
+        self.0.borrow_mut().remove_by_id(id)
+    }
 }
diff --git a/compiler/erg_parser/reorder.rs b/compiler/erg_compiler/reorder.rs
similarity index 100%
rename from compiler/erg_parser/reorder.rs
rename to compiler/erg_compiler/reorder.rs
diff --git a/compiler/erg_compiler/tests/test.rs b/compiler/erg_compiler/tests/test.rs
index a137e2eb..fa286655 100644
--- a/compiler/erg_compiler/tests/test.rs
+++ b/compiler/erg_compiler/tests/test.rs
@@ -1,15 +1,16 @@
 use erg_compiler::context::Context;
+use erg_compiler::mod_cache::SharedModuleCache;
 
 #[test]
 fn test_subtyping() -> Result<(), ()> {
-    let context = Context::new_main_module();
+    let context = Context::new_main_module(SharedModuleCache::new());
     context.test_refinement_subtyping()?;
     Ok(())
 }
 
 #[test]
 fn test_instantiation_and_generalization() -> Result<(), ()> {
-    let context = Context::new_main_module();
+    let context = Context::new_main_module(SharedModuleCache::new());
     context.test_instantiation_and_generalization()?;
     Ok(())
 }
diff --git a/compiler/erg_parser/ast.rs b/compiler/erg_parser/ast.rs
index d5f1b4be..dc1cc275 100644
--- a/compiler/erg_parser/ast.rs
+++ b/compiler/erg_parser/ast.rs
@@ -2839,6 +2839,7 @@ pub enum DefKind {
     Trait,
     Subsume,
     StructuralTrait,
+    Module,
     Other,
 }
 
@@ -2846,6 +2847,10 @@ impl DefKind {
     pub const fn is_trait(&self) -> bool {
         matches!(self, Self::Trait | Self::Subsume | Self::StructuralTrait)
     }
+
+    pub fn is_module(&self) -> bool {
+        matches!(self, Self::Module)
+    }
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
diff --git a/compiler/erg_parser/builder.rs b/compiler/erg_parser/builder.rs
index 3659863f..bd7c24c9 100644
--- a/compiler/erg_parser/builder.rs
+++ b/compiler/erg_parser/builder.rs
@@ -6,9 +6,8 @@ use crate::ast::AST;
 use crate::desugar::Desugarer;
 use crate::error::ParserRunnerErrors;
 use crate::parse::ParserRunner;
-use crate::reorder::Reorderer;
 
-/// Summarize parsing, desugaring, and reordering
+/// Summarize parsing and desugaring
 pub struct ASTBuilder {
     runner: ParserRunner,
 }
@@ -27,24 +26,16 @@ impl ASTBuilder {
         let mut desugarer = Desugarer::new();
         let module = desugarer.desugar(module);
         let ast = AST::new(Str::ever(self.runner.cfg().module), module);
-        let reorderer = Reorderer::new();
-        let ast = reorderer
-            .reorder(ast)
-            .map_err(|errs| ParserRunnerErrors::convert(self.runner.input(), errs))?;
         Ok(ast)
     }
 
-    pub fn build_with_input(&mut self, src: String) -> Result<AST, ParserRunnerErrors> {
-        let module = self.runner.parse_with_input(src)?;
+    pub fn build_with_str(&mut self, src: String) -> Result<AST, ParserRunnerErrors> {
+        let module = self.runner.parse_with_str(src)?;
         let mut desugarer = Desugarer::new();
         let module = desugarer.desugar(module);
         let mut desugarer = Desugarer::new();
         let module = desugarer.desugar(module);
         let ast = AST::new(Str::ever(self.runner.cfg().module), module);
-        let reorderer = Reorderer::new();
-        let ast = reorderer
-            .reorder(ast)
-            .map_err(|errs| ParserRunnerErrors::convert(self.runner.input(), errs))?;
         Ok(ast)
     }
 }
diff --git a/compiler/erg_parser/lib.rs b/compiler/erg_parser/lib.rs
index e2fcd877..731424cf 100644
--- a/compiler/erg_parser/lib.rs
+++ b/compiler/erg_parser/lib.rs
@@ -9,7 +9,6 @@ pub mod desugar;
 pub mod error;
 pub mod lex;
 pub mod parse;
-pub mod reorder;
 pub mod token;
 
 pub use parse::{Parser, ParserRunner};
diff --git a/compiler/erg_parser/parse.rs b/compiler/erg_parser/parse.rs
index f11cbdfd..92d76591 100644
--- a/compiler/erg_parser/parse.rs
+++ b/compiler/erg_parser/parse.rs
@@ -193,7 +193,7 @@ impl Runnable for ParserRunner {
     }
 
     fn eval(&mut self, src: String) -> Result<String, ParserRunnerErrors> {
-        let ast = self.parse_with_input(src)?;
+        let ast = self.parse_with_str(src)?;
         Ok(format!("{ast}"))
     }
 }
@@ -212,7 +212,6 @@ impl ParserRunner {
         self.parse_token_stream(ts)
     }
 
-    /// Parses with default configuration
     pub fn parse_with_default_config(input: Input) -> Result<Module, ParserRunnerErrors> {
         let cfg = ErgConfig {
             input,
@@ -222,7 +221,7 @@ impl ParserRunner {
         self_.parse()
     }
 
-    pub fn parse_with_input(&mut self, src: String) -> Result<Module, ParserRunnerErrors> {
+    pub fn parse_with_str(&mut self, src: String) -> Result<Module, ParserRunnerErrors> {
         let ts = Lexer::new(Input::Str(src))
             .lex()
             .map_err(|errs| ParserRunnerErrors::convert(self.input(), errs))?;
diff --git a/doc/JA/compiler/architecture.md b/doc/JA/compiler/architecture.md
index abafdcef..0e4a7f8e 100644
--- a/doc/JA/compiler/architecture.md
+++ b/doc/JA/compiler/architecture.md
@@ -16,15 +16,22 @@
 * `Parser` は `Lexer` と同様に `Parser::new` と `Parser::from_str` の 2 つのコンストラクタを持ち、`Parser::parse` は `AST` を返す。
 * `AST`は`Vec<Expr>`のラッパー型で、「抽象構文木」を表す。
 
-### 2.5 `AST`の脱糖
+### 2.1 `AST`の脱糖
 
 * ネストされた変数を展開 (`Desugarer::desugar_nest_vars_pattern`)
 * 複数パターン定義構文をmatchへ変換 (`Desugarer::desugar_multiple_pattern_def`)
 
-## 3. 型チェックと推論、 `AST` -> `HIR` を変換 (compiler/lower.rs)
+## 3. `AST` -> `HIR`  (compiler/lower.rs)
+
+## 3.1 名前解決
+
+* 型推論の前に全てのAST(importされたモジュール含む)を走査し、名前解決を行う
+* 定数の循環検査や並び替えなどが行われるほか、型推論のためのContextが作成される(ただし、このContextに登録された変数の情報ははまだ殆どが未確定)
+
+### 3.2 型チェックと推論 (compiler/lower.rs)
 
 * `HIR` は、すべての変数の型情報を持っており、「高レベルの中間表現」を表す。
-* `ASTLowerer は Parser や Lexer と同じように構築できる。
+* `ASTLowerer` は Parser や Lexer と同じように構築できる。
 * `ASTLowerer::lower` は、エラーが発生しなければ、`HIR` と `CompileWarnings` のタプルを出力する。
 * `ASTLowerer` は `Compiler` によって所有されている。 `ASTLowerer` は従来の構造体とは異なり、文脈を保持し、1 回限りの使い捨てではない。
 * 型推論の結果が不完全な場合(未知の型変数がある場合)、名前解決時にエラーが発生する。