diff --git a/nac3artiq/src/symbol_resolver.rs b/nac3artiq/src/symbol_resolver.rs
index e420bd808..165250969 100644
--- a/nac3artiq/src/symbol_resolver.rs
+++ b/nac3artiq/src/symbol_resolver.rs
@@ -2,7 +2,7 @@ use inkwell::{types::BasicType, values::BasicValueEnum, AddressSpace};
 use nac3core::{
     codegen::CodeGenContext,
     location::Location,
-    symbol_resolver::SymbolResolver,
+    symbol_resolver::{SymbolResolver, SymbolValue},
     toplevel::{DefinitionId, TopLevelDef},
     typecheck::{
         type_inferencer::PrimitiveStore,
@@ -14,7 +14,7 @@ use pyo3::{
     types::{PyList, PyModule, PyTuple},
     PyAny, PyObject, PyResult, Python,
 };
-use nac3parser::ast::StrRef;
+use nac3parser::ast::{self, StrRef};
 use std::{
     cell::RefCell,
     collections::{HashMap, HashSet},
@@ -399,9 +399,86 @@ impl Resolver {
             }
         }
     }
+
+    fn get_default_param_obj_value(&self, obj: &PyAny, helper: &PythonHelper) -> PyResult<Result<SymbolValue, String>> {
+        let ty_id: u64 = helper
+            .id_fn
+            .call1((helper.type_fn.call1((obj,))?,))?
+            .extract()?;
+        Ok(
+            if ty_id == self.primitive_ids.int || ty_id == self.primitive_ids.int32 {
+                let val: i32 = obj.extract()?;
+                Ok(SymbolValue::I32(val))
+            } else if ty_id == self.primitive_ids.int64 {
+                let val: i64 = obj.extract()?;
+                Ok(SymbolValue::I64(val))
+            } else if ty_id == self.primitive_ids.bool {
+                let val: bool = obj.extract()?;
+                Ok(SymbolValue::Bool(val))
+            } else if ty_id == self.primitive_ids.float {
+                let val: f64 = obj.extract()?;
+                Ok(SymbolValue::Double(val))
+            } else if ty_id == self.primitive_ids.tuple {
+                let elements: &PyTuple = obj.cast_as()?;
+                let elements: Result<Result<Vec<_>, String>, _> = elements
+                    .iter()
+                    .map(|elem| {
+                        self.get_default_param_obj_value(
+                            elem,
+                            helper
+                        )
+                    })
+                    .collect();
+                let elements = match elements? {
+                    Ok(el) => el,
+                    Err(err) => return Ok(Err(err))
+                };
+                Ok(SymbolValue::Tuple(elements))
+            } else {
+                Err("only primitives values and tuple can be default parameter value".into())
+            }
+        )
+    }
 }
 
 impl SymbolResolver for Resolver {
+    fn get_default_param_value(
+        &self,
+        expr: &ast::Expr
+    ) -> Option<SymbolValue> {
+        match &expr.node {
+            ast::ExprKind::Name { id, .. } => {
+                Python::with_gil(
+                    |py| -> PyResult<Option<SymbolValue>> {
+                        let obj: &PyAny = self.module.extract(py)?;
+                        let members: &PyList = PyModule::import(py, "inspect")?
+                            .getattr("getmembers")?
+                            .call1((obj,))?
+                            .cast_as()?;
+                        let mut sym_value = None;
+                        for member in members.iter() {
+                            let key: &str = member.get_item(0)?.extract()?;
+                            let val = member.get_item(1)?;
+                            if key == id.to_string() {
+                                let builtins = PyModule::import(py, "builtins")?;
+                                let helper = PythonHelper {
+                                    id_fn: builtins.getattr("id").unwrap(),
+                                    len_fn: builtins.getattr("len").unwrap(),
+                                    type_fn: builtins.getattr("type").unwrap(),
+                                };
+                                sym_value = Some(self.get_default_param_obj_value(val, &helper).unwrap().unwrap());
+                                break;
+                            }
+                        }
+                        Ok(sym_value)
+                    }
+                )
+                .unwrap()
+            }
+            _ => unimplemented!("other type of expr not supported at {}", expr.location)
+        }
+    }
+
     fn get_symbol_type(
         &self,
         unifier: &mut Unifier,
diff --git a/nac3core/src/codegen/test.rs b/nac3core/src/codegen/test.rs
index ce958ff32..f9e2810ff 100644
--- a/nac3core/src/codegen/test.rs
+++ b/nac3core/src/codegen/test.rs
@@ -37,6 +37,10 @@ impl Resolver {
 }
 
 impl SymbolResolver for Resolver {
+    fn get_default_param_value(&self, _: &nac3parser::ast::Expr) -> Option<crate::symbol_resolver::SymbolValue> {
+        unimplemented!()
+    }
+    
     fn get_symbol_type(
         &self,
         _: &mut Unifier,
diff --git a/nac3core/src/symbol_resolver.rs b/nac3core/src/symbol_resolver.rs
index 161d78a92..e8d594da6 100644
--- a/nac3core/src/symbol_resolver.rs
+++ b/nac3core/src/symbol_resolver.rs
@@ -44,6 +44,7 @@ pub trait SymbolResolver {
         ctx: &mut CodeGenContext<'ctx, 'a>,
     ) -> Option<BasicValueEnum<'ctx>>;
     fn get_symbol_location(&self, str: StrRef) -> Option<Location>;
+    fn get_default_param_value(&self, expr: &nac3parser::ast::Expr) -> Option<SymbolValue>;
     // handle function call etc.
 }
 
diff --git a/nac3core/src/toplevel/composer.rs b/nac3core/src/toplevel/composer.rs
index e7c17cd05..b0afaf263 100644
--- a/nac3core/src/toplevel/composer.rs
+++ b/nac3core/src/toplevel/composer.rs
@@ -1066,10 +1066,23 @@ impl TopLevelComposer {
                             and names thould not be the same as the keywords"
                                 .into());
                         }
-
-                        args.args
+                        
+                        let arg_with_default: Vec<(&ast::Located<ast::ArgData<()>>, Option<&ast::Expr>)> = args
+                            .args
                             .iter()
-                            .map(|x| -> Result<FuncArg, String> {
+                            .rev()
+                            .zip(args
+                                .defaults
+                                .iter()
+                                .rev()
+                                .map(|x| -> Option<&ast::Expr> { Some(x) })
+                                .chain(std::iter::repeat(None))
+                            ).collect_vec();
+
+                        arg_with_default
+                            .iter()
+                            .rev()
+                            .map(|(x, default)| -> Result<FuncArg, String> {
                                 let annotation = x
                                     .node
                                     .annotation
@@ -1121,7 +1134,19 @@ impl TopLevelComposer {
                                 Ok(FuncArg {
                                     name: x.node.arg,
                                     ty,
-                                    default_value: Default::default(),
+                                    default_value: match default {
+                                        None => None,
+                                        Some(default) => Some({
+                                            let v = Self::parse_parameter_default_value(default, resolver)?;
+                                            Self::check_default_param_type(
+                                                &v,
+                                                &type_annotation,
+                                                primitives_store,
+                                                unifier
+                                            ).map_err(|err| format!("{} at {}", err, x.location))?;
+                                            v
+                                        })
+                                    }
                                 })
                             })
                             .collect::<Result<Vec<_>, _>>()?
@@ -1282,7 +1307,20 @@ impl TopLevelComposer {
                         }
 
                         let mut result = Vec::new();
-                        for x in &args.args {
+                        
+                        let arg_with_default: Vec<(&ast::Located<ast::ArgData<()>>, Option<&ast::Expr>)> = args
+                            .args
+                            .iter()
+                            .rev()
+                            .zip(args
+                                .defaults
+                                .iter()
+                                .rev()
+                                .map(|x| -> Option<&ast::Expr> { Some(x) })
+                                .chain(std::iter::repeat(None))
+                            ).collect_vec();
+                        
+                        for (x, default) in arg_with_default.into_iter().rev() {
                             let name = x.node.arg;
                             if name != zelf {
                                 let type_ann = {
@@ -1327,8 +1365,20 @@ impl TopLevelComposer {
                                 let dummy_func_arg = FuncArg {
                                     name,
                                     ty: unifier.get_fresh_var().0,
-                                    // TODO: default value?
-                                    default_value: None,
+                                    default_value: match default {
+                                        None => None,
+                                        Some(default) => {
+                                            if name == "self".into() {
+                                                return Err(format!("`self` parameter cannot take default value at {}", x.location));
+                                            }
+                                            Some({
+                                                let v = Self::parse_parameter_default_value(default, class_resolver)?;
+                                                Self::check_default_param_type(&v, &type_ann, primitives, unifier)
+                                                    .map_err(|err| format!("{} at {}", err, x.location))?;
+                                                v
+                                            })
+                                        }
+                                    }
                                 };
                                 // push the dummy type and the type annotation
                                 // into the list for later unification
diff --git a/nac3core/src/toplevel/helper.rs b/nac3core/src/toplevel/helper.rs
index 35da97c9b..5c8b85e75 100644
--- a/nac3core/src/toplevel/helper.rs
+++ b/nac3core/src/toplevel/helper.rs
@@ -1,3 +1,8 @@
+use std::convert::TryInto;
+
+use nac3parser::ast::{Constant, Location};
+use crate::symbol_resolver::SymbolValue;
+
 use super::*;
 
 impl TopLevelDef {
@@ -341,4 +346,121 @@ impl TopLevelComposer {
         }
         Ok(result)
     }
+
+    pub fn parse_parameter_default_value(default: &ast::Expr, resolver: &(dyn SymbolResolver + Send + Sync)) -> Result<SymbolValue, String> {
+        parse_parameter_default_value(default, resolver)
+    }
+
+    pub fn check_default_param_type(val: &SymbolValue, ty: &TypeAnnotation, primitive: &PrimitiveStore, unifier: &mut Unifier) -> Result<(), String> {
+        let res = match val {
+            SymbolValue::Bool(..) => {
+                if matches!(ty, TypeAnnotation::Primitive(t) if *t == primitive.bool) {
+                    None
+                } else {
+                    Some("bool".to_string())
+                }
+            }
+            SymbolValue::Double(..) => {
+                if matches!(ty, TypeAnnotation::Primitive(t) if *t == primitive.float) {
+                    None
+                } else {
+                    Some("float".to_string())
+                }
+            }
+            SymbolValue::I32(..) => {
+                if matches!(ty, TypeAnnotation::Primitive(t) if *t == primitive.int32) {
+                    None
+                } else {
+                    Some("int32".to_string())
+                }
+            }
+            SymbolValue::I64(..) => {
+                if matches!(ty, TypeAnnotation::Primitive(t) if *t == primitive.int64) {
+                    None
+                } else {
+                    Some("int64".to_string())
+                }
+            }
+            SymbolValue::Tuple(elts) => {
+                if let TypeAnnotation::Tuple(elts_ty) = ty {
+                    for (e, t) in elts.iter().zip(elts_ty.iter()) {
+                        Self::check_default_param_type(e, t, primitive, unifier)?
+                    }
+                    if elts.len() != elts_ty.len() {
+                        Some(format!("tuple of length {}", elts.len()))
+                    } else {
+                        None
+                    }
+                } else {
+                    Some("tuple".to_string())
+                }
+            }
+        };
+        if let Some(found) = res {
+            Err(format!(
+                "incompatible default parameter type, expect {}, found {}",
+                ty.stringify(unifier),
+                found
+            ))
+        } else {
+            Ok(())
+        }
+    }
+}
+
+pub fn parse_parameter_default_value(default: &ast::Expr, resolver: &(dyn SymbolResolver + Send + Sync)) -> Result<SymbolValue, String> {
+    fn handle_constant(val: &Constant, loc: &Location) -> Result<SymbolValue, String> {
+        match val {
+            Constant::Int(v) => {
+                if let Ok(v) = v.try_into() {
+                    Ok(SymbolValue::I32(v))
+                } else {
+                    Err(format!(
+                        "integer value out of range at {}",
+                        loc
+                    ))
+                }
+            }
+            Constant::Float(v) => Ok(SymbolValue::Double(*v)),
+            Constant::Bool(v) => Ok(SymbolValue::Bool(*v)),
+            Constant::Tuple(tuple) => Ok(SymbolValue::Tuple(
+                tuple.iter().map(|x| handle_constant(x, loc)).collect::<Result<Vec<_>, _>>()?
+            )),
+            _ => unimplemented!("this constant is not supported at {}", loc),
+        }
+    }
+    match &default.node {
+        ast::ExprKind::Constant { value, .. } => handle_constant(value, &default.location),
+        ast::ExprKind::Call { func, args, .. } if {
+            match &func.node {
+                ast::ExprKind::Name { id, .. } => *id == "int64".into(),
+                _ => false,
+            }
+        } => {
+            if args.len() == 1 {
+                match &args[0].node {
+                    ast::ExprKind::Constant { value: Constant::Int(v), .. } =>
+                        Ok(SymbolValue::I64(v.try_into().unwrap())),
+                    _ => Err(format!("only allow constant integer here at {}", default.location))
+                }
+            } else {
+                Err(format!("only allow constant integer here at {}", default.location))
+            }
+        }
+        ast::ExprKind::Tuple { elts, .. } => Ok(SymbolValue::Tuple(elts
+            .iter()
+            .map(|x| parse_parameter_default_value(x, resolver))
+            .collect::<Result<Vec<_>, _>>()?
+        )),
+        ast::ExprKind::Name { id, .. } => {
+            resolver.get_default_param_value(default).ok_or_else(
+                || format!(
+                    "`{}` cannot be used as a default parameter at {} (not primitive type or tuple / not defined?)",
+                    id,
+                    default.location
+                )
+            )
+        }
+        _ => unimplemented!("only constant default is supported now at {}", default.location),
+    }
 }
diff --git a/nac3core/src/toplevel/mod.rs b/nac3core/src/toplevel/mod.rs
index c96a7cac6..f6fc15b06 100644
--- a/nac3core/src/toplevel/mod.rs
+++ b/nac3core/src/toplevel/mod.rs
@@ -23,7 +23,7 @@ use inkwell::values::BasicValueEnum;
 pub struct DefinitionId(pub usize);
 
 pub mod composer;
-mod helper;
+pub mod helper;
 mod type_annotation;
 use composer::*;
 use type_annotation::*;
diff --git a/nac3core/src/toplevel/test.rs b/nac3core/src/toplevel/test.rs
index e2795474e..0f4fd83fb 100644
--- a/nac3core/src/toplevel/test.rs
+++ b/nac3core/src/toplevel/test.rs
@@ -35,6 +35,10 @@ impl ResolverInternal {
 struct Resolver(Arc<ResolverInternal>);
 
 impl SymbolResolver for Resolver {
+    fn get_default_param_value(&self, _: &nac3parser::ast::Expr) -> Option<crate::symbol_resolver::SymbolValue> {
+        unimplemented!()
+    }
+    
     fn get_symbol_type(
         &self,
         _: &mut Unifier,
diff --git a/nac3core/src/typecheck/type_inferencer/test.rs b/nac3core/src/typecheck/type_inferencer/test.rs
index d3aa09fa9..da51aa9db 100644
--- a/nac3core/src/typecheck/type_inferencer/test.rs
+++ b/nac3core/src/typecheck/type_inferencer/test.rs
@@ -19,6 +19,10 @@ struct Resolver {
 }
 
 impl SymbolResolver for Resolver {
+    fn get_default_param_value(&self, _: &nac3parser::ast::Expr) -> Option<crate::symbol_resolver::SymbolValue> {
+        unimplemented!()
+    }
+    
     fn get_symbol_type(
         &self,
         _: &mut Unifier,
diff --git a/nac3standalone/src/basic_symbol_resolver.rs b/nac3standalone/src/basic_symbol_resolver.rs
index 82c1ac312..9983d5079 100644
--- a/nac3standalone/src/basic_symbol_resolver.rs
+++ b/nac3standalone/src/basic_symbol_resolver.rs
@@ -2,7 +2,7 @@ use inkwell::values::BasicValueEnum;
 use nac3core::{
     codegen::CodeGenContext,
     location::Location,
-    symbol_resolver::SymbolResolver,
+    symbol_resolver::{SymbolResolver, SymbolValue},
     toplevel::{DefinitionId, TopLevelDef},
     typecheck::{
         type_inferencer::PrimitiveStore,
@@ -10,13 +10,14 @@ use nac3core::{
     },
 };
 use parking_lot::{Mutex, RwLock};
-use nac3parser::ast::StrRef;
+use nac3parser::ast::{self, StrRef};
 use std::{collections::HashMap, sync::Arc};
 
 pub struct ResolverInternal {
     pub id_to_type: Mutex<HashMap<StrRef, Type>>,
     pub id_to_def: Mutex<HashMap<StrRef, DefinitionId>>,
     pub class_names: Mutex<HashMap<StrRef, Type>>,
+    pub module_globals: Mutex<HashMap<StrRef, SymbolValue>>,
 }
 
 impl ResolverInternal {
@@ -27,11 +28,24 @@ impl ResolverInternal {
     pub fn add_id_type(&self, id: StrRef, ty: Type) {
         self.id_to_type.lock().insert(id, ty);
     }
+
+    pub fn add_module_global(&self, id: StrRef, val: SymbolValue) {
+        self.module_globals.lock().insert(id, val);
+    }
 }
 
 pub struct Resolver(pub Arc<ResolverInternal>);
 
 impl SymbolResolver for Resolver {
+    fn get_default_param_value(&self, expr: &ast::Expr) -> Option<SymbolValue> {
+        match &expr.node {
+            ast::ExprKind::Name { id, .. } => {
+                self.0.module_globals.lock().get(id).cloned()
+            }
+            _ => unimplemented!("other type of expr not supported at {}", expr.location)
+        }
+    }
+
     fn get_symbol_type(
         &self,
         _: &mut Unifier,
diff --git a/nac3standalone/src/main.rs b/nac3standalone/src/main.rs
index 17b61b2bb..f6c4be68f 100644
--- a/nac3standalone/src/main.rs
+++ b/nac3standalone/src/main.rs
@@ -4,8 +4,8 @@ use inkwell::{
     OptimizationLevel,
 };
 use nac3core::typecheck::type_inferencer::PrimitiveStore;
-use nac3parser::parser;
-use std::env;
+use nac3parser::{ast::{Expr, ExprKind, StmtKind}, parser};
+use std::{borrow::Borrow, env};
 use std::fs;
 use std::{collections::HashMap, path::Path, sync::Arc, time::SystemTime};
 
@@ -15,7 +15,7 @@ use nac3core::{
         WorkerRegistry,
     },
     symbol_resolver::SymbolResolver,
-    toplevel::{composer::TopLevelComposer, TopLevelDef},
+    toplevel::{composer::TopLevelComposer, TopLevelDef, helper::parse_parameter_default_value},
     typecheck::typedef::FunSignature,
 };
 
@@ -48,6 +48,7 @@ fn main() {
         id_to_type: builtins_ty.into(),
         id_to_def: builtins_def.into(),
         class_names: Default::default(),
+        module_globals: Default::default(),
     }
     .into();
     let resolver =
@@ -66,6 +67,61 @@ fn main() {
     );
 
     for stmt in parser_result.into_iter() {
+        if let StmtKind::Assign { targets, value, .. } = &stmt.node {
+            fn handle_assignment_pattern(
+                targets: &[Expr],
+                value: &Expr,
+                resolver: &(dyn SymbolResolver + Send + Sync),
+                internal_resolver: &ResolverInternal,
+            ) -> Result<(), String> {
+                if targets.len() == 1 {
+                    match &targets[0].node {
+                        ExprKind::Name { id, .. } => {
+                            let val = parse_parameter_default_value(value.borrow(), resolver)?;
+                            internal_resolver.add_module_global(*id, val);
+                            Ok(())
+                        }
+                        ExprKind::List { elts, .. }
+                        | ExprKind::Tuple { elts, .. } => {
+                            handle_assignment_pattern(elts, value, resolver, internal_resolver)?;
+                            Ok(())
+                        }
+                        _ => unreachable!("cannot be assigned")
+                    }
+                } else {
+                    match &value.node {
+                        ExprKind::List { elts, .. }
+                        | ExprKind::Tuple { elts, .. } => {
+                            if elts.len() != targets.len() {
+                                Err(format!(
+                                    "number of elements to unpack does not match (expect {}, found {}) at {}",
+                                    targets.len(),
+                                    elts.len(),
+                                    value.location
+                                ))
+                            } else {
+                                for (tar, val) in targets.iter().zip(elts) {
+                                    handle_assignment_pattern(
+                                        std::slice::from_ref(tar),
+                                        val,
+                                        resolver,
+                                        internal_resolver
+                                    )?;
+                                }
+                                Ok(())
+                            }
+                        },
+                        _ => Err(format!("unpack of this expression is not supported at {}", value.location))
+                    }
+                }
+            }
+            if let Err(err) = handle_assignment_pattern(targets, value, resolver.as_ref(), internal_resolver.as_ref()) {
+                eprintln!("{}", err);
+                return;
+            }
+            continue;
+        }
+
         let (name, def_id, ty) = composer
             .register_top_level(stmt, Some(resolver.clone()), "__main__".into())
             .unwrap();