diff --git a/nac3core/src/toplevel/helper.rs b/nac3core/src/toplevel/helper.rs
index d7ce477f..2dcb3590 100644
--- a/nac3core/src/toplevel/helper.rs
+++ b/nac3core/src/toplevel/helper.rs
@@ -399,7 +399,7 @@ pub fn parse_parameter_default_value(default: &ast::Expr, resolver: &(dyn Symbol
         ast::ExprKind::Name { id, .. } => {
             resolver.get_default_param_value(default).ok_or_else(
                 || format!(
-                    "this module global `{}` cannot be used as a default parameter at {} (should be primitive type or tuple)",
+                    "`{}` cannot be used as a default parameter at {} (not primitive type or tuple / not defined?)",
                     id,
                     default.location
                 )
diff --git a/nac3standalone/src/basic_symbol_resolver.rs b/nac3standalone/src/basic_symbol_resolver.rs
index 31b3713b..9983d507 100644
--- a/nac3standalone/src/basic_symbol_resolver.rs
+++ b/nac3standalone/src/basic_symbol_resolver.rs
@@ -3,7 +3,7 @@ use nac3core::{
     codegen::CodeGenContext,
     location::Location,
     symbol_resolver::{SymbolResolver, SymbolValue},
-    toplevel::{DefinitionId, TopLevelDef, helper::parse_parameter_default_value},
+    toplevel::{DefinitionId, TopLevelDef},
     typecheck::{
         type_inferencer::PrimitiveStore,
         typedef::{Type, Unifier},
@@ -17,7 +17,7 @@ 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, ast::Expr>>,
+    pub module_globals: Mutex<HashMap<StrRef, SymbolValue>>,
 }
 
 impl ResolverInternal {
@@ -29,8 +29,8 @@ impl ResolverInternal {
         self.id_to_type.lock().insert(id, ty);
     }
 
-    pub fn add_module_global(&self, id: StrRef, expr: &ast::Expr) {
-        self.module_globals.lock().insert(id, expr.clone());
+    pub fn add_module_global(&self, id: StrRef, val: SymbolValue) {
+        self.module_globals.lock().insert(id, val);
     }
 }
 
@@ -40,10 +40,7 @@ impl SymbolResolver for Resolver {
     fn get_default_param_value(&self, expr: &ast::Expr) -> Option<SymbolValue> {
         match &expr.node {
             ast::ExprKind::Name { id, .. } => {
-                let expr = self.0.module_globals.lock().get(id).cloned();
-                expr.map(|x| {
-                    parse_parameter_default_value(&x, self).unwrap()
-                })
+                self.0.module_globals.lock().get(id).cloned()
             }
             _ => unimplemented!("other type of expr not supported at {}", expr.location)
         }
diff --git a/nac3standalone/src/main.rs b/nac3standalone/src/main.rs
index 33fc0e6f..71e29335 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::{ast::{ExprKind, StmtKind}, 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,
 };
 
@@ -67,14 +67,57 @@ fn main() {
     );
 
     for stmt in parser_result.into_iter() {
-        // handle module globals
         if let StmtKind::Assign { targets, value, .. } = &stmt.node {
-            if targets.len() == 1 {
-                if let ExprKind::Name { id, .. } = &targets[0].node {
-                    internal_resolver.add_module_global(*id, value);
+            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))
+                    }
                 }
-            } else {
-                unimplemented!("only single assign supported now")
+            }
+            if let Err(err) = handle_assignment_pattern(targets, value, resolver.as_ref(), internal_resolver.as_ref()) {
+                eprintln!("{}", err);
+                return;
             }
             continue;
         }