diff --git a/ExampleCodes/3-Structure.fig b/ExampleCodes/3-Structure.fig
new file mode 100644
index 0000000..cc929b9
--- /dev/null
+++ b/ExampleCodes/3-Structure.fig
@@ -0,0 +1,30 @@
+import std.io;
+
+struct Point
+{
+    x: Int; // type specifiers are optional
+    y: Int; // type specifiers are optional
+
+    // x and y are private fields, can only reached by internal context
+
+    public func toString() -> String
+    {
+        return "(" + (x as String) + "," + (y as String) + ")";
+    } 
+    // public func toString() {} is ok
+}
+
+// make points
+
+var p1 := new Point{1, 2};
+io.println(p1.toString()); // (1,2)
+
+var p2 := new Point{x: 2, y: 3};
+io.println(p2.toString()); // (2,3)
+
+var x := 114;
+var y := 514;
+
+var p3 := new Point{y, x}; // shorthand mode, can be unordered, auto match field and variable!
+//                 = Point{x: x, y: y}
+io.println(p3.toString()); // (114,514)
\ No newline at end of file
diff --git a/ExampleCodes/4-Interface.fig b/ExampleCodes/4-Interface.fig
new file mode 100644
index 0000000..4cfc9dc
--- /dev/null
+++ b/ExampleCodes/4-Interface.fig
@@ -0,0 +1,2 @@
+import std.io;
+
diff --git a/src/Ast/Statements/InterfaceDefSt.hpp b/src/Ast/Statements/InterfaceDefSt.hpp
index e0fb141..67ef077 100644
--- a/src/Ast/Statements/InterfaceDefSt.hpp
+++ b/src/Ast/Statements/InterfaceDefSt.hpp
@@ -35,10 +35,22 @@ namespace Fig::Ast
         }
     };
 
+    /*
+        interface IO : Writable + Readable
+        {
+        }
+
+        interface XX
+        {
+        }
+    
+    */
+
     class InterfaceDefAst final : public StatementAst
     {
     public:
         FString name;
+        std::vector<Expression> bundles;
         std::vector<InterfaceMethod> methods;
         std::vector<FString> parents; // Feature, NOT NOW
         bool isPublic;
@@ -48,8 +60,8 @@ namespace Fig::Ast
             type = AstType::InterfaceDefSt;
         }
 
-        InterfaceDefAst(FString _name, std::vector<InterfaceMethod> _methods, bool _isPublic) :
-            name(std::move(_name)), methods(std::move(_methods)), isPublic(_isPublic)
+        InterfaceDefAst(FString _name, std::vector<Expression> _bundles, std::vector<InterfaceMethod> _methods, bool _isPublic) :
+            name(std::move(_name)), bundles(std::move(_bundles)), methods(std::move(_methods)), isPublic(_isPublic)
         {
             type = AstType::InterfaceDefSt;
         }
diff --git a/src/Evaluator/Core/EvalInitExpr.cpp b/src/Evaluator/Core/EvalInitExpr.cpp
index f6acc51..03936df 100644
--- a/src/Evaluator/Core/EvalInitExpr.cpp
+++ b/src/Evaluator/Core/EvalInitExpr.cpp
@@ -183,9 +183,9 @@ namespace Fig
                         // we've checked argument count before, so here
                         // must be a default value
 
-                        // evaluate default value in definition context
+                        // evaluate default value in definition context!
                         ObjectPtr defaultVal = check_unwrap(eval(field.defaultValue,
-                                                                 ctx)); // it can't be null here
+                                                                 defContext)); // it can't be null here
 
                         // type check
                         if (!isTypeMatch(expectedType, defaultVal, ctx))
@@ -345,13 +345,12 @@ namespace Fig
                 }
             }
         }
-        ContextPtr stDefCtx = structT.defContext;
 
         // load struct method
-        for (auto &[id, fn] : stDefCtx->getFunctions())
+        for (auto &[id, fn] : defContext->getFunctions())
         {
             const FString &funcName = fn.name;
-            const auto &funcSlot = stDefCtx->get(funcName);
+            const auto &funcSlot = defContext->get(funcName);
             
             instanceCtx->def(funcName,
                              ValueType::Function,
diff --git a/src/Evaluator/Core/EvalStatement.cpp b/src/Evaluator/Core/EvalStatement.cpp
index e2399e0..2d2b763 100644
--- a/src/Evaluator/Core/EvalStatement.cpp
+++ b/src/Evaluator/Core/EvalStatement.cpp
@@ -1,3 +1,4 @@
+#include "Ast/Statements/InterfaceDefSt.hpp"
 #include <Evaluator/Core/ExprResult.hpp>
 #include <Ast/AccessModifier.hpp>
 #include <Ast/Expressions/FunctionCall.hpp>
@@ -14,6 +15,7 @@
 
 #include <Utils/utils.hpp>
 #include <unordered_map>
+#include <unordered_set>
 
 namespace Fig
 {
@@ -165,6 +167,7 @@ namespace Fig
                 auto ifd = std::static_pointer_cast<Ast::InterfaceDefAst>(stmt);
 
                 const FString &interfaceName = ifd->name;
+                const std::vector<Ast::Expression> &bundle_exprs = ifd->bundles;
 
                 if (ctx->containsInThisScope(interfaceName))
                 {
@@ -173,11 +176,54 @@ namespace Fig
                         std::format("Interface `{}` already declared in this scope", interfaceName.toBasicString()),
                         ifd);
                 }
+
+                std::vector<Ast::InterfaceMethod> bundle_methods;
+                std::unordered_map<FString, FString> cache_methods;
+                //   K: interface method name    V: method owner (interface)
+                for (const auto &exp : bundle_exprs)
+                {
+                    ObjectPtr itf_val = check_unwrap_stres(eval(exp, ctx));
+                    if (!itf_val->is<InterfaceType>())
+                    {
+                        throw EvaluatorError(
+                            u8"TypeError",
+                            std::format(
+                                "Cannot bundle type '{}' that is not interface",
+                                prettyType(itf_val).toBasicString()
+                            ),
+                            exp
+                        );
+                    }
+                    const InterfaceType &itfType = itf_val->as<InterfaceType>();
+                    for (const auto &method : itfType.methods)
+                    {
+                        if (cache_methods.contains(method.name))
+                        {
+                            throw EvaluatorError(
+                                u8"DuplicateInterfaceMethodError",
+                                std::format(
+                                    "Interface `{}` has duplicate method '{}' with '{}.{}'",
+                                    itfType.type.toString().toBasicString(),
+                                    method.name.toBasicString(),
+                                    cache_methods[method.name].toBasicString(),
+                                    method.name.toBasicString()
+                                ),
+                                ifd
+                            );
+                        }
+                        cache_methods[method.name] = itfType.type.toString();
+                        bundle_methods.push_back(method);
+                    }
+                }
+
+                std::vector<Ast::InterfaceMethod> methods(ifd->methods);
+                methods.insert(methods.end(), bundle_methods.begin(), bundle_methods.end());
+
                 TypeInfo type(interfaceName, true); // register interface
                 ctx->def(interfaceName,
                          type,
                          (ifd->isPublic ? AccessModifier::PublicConst : AccessModifier::Const),
-                         std::make_shared<Object>(InterfaceType(type, ifd->methods)));
+                         std::make_shared<Object>(InterfaceType(type, methods)));
                 return StatementResult::normal();
             }
 
diff --git a/src/Parser/parser.cpp b/src/Parser/parser.cpp
index a750b21..e556a01 100644
--- a/src/Parser/parser.cpp
+++ b/src/Parser/parser.cpp
@@ -386,6 +386,29 @@ namespace Fig
         // entry: current is interface name
         FString interfaceName = currentToken().getValue();
         next();                       // consume name
+
+        std::vector<Ast::Expression> bundles;
+
+        if (isThis(TokenType::Colon))
+        {
+            next(); // consume `:`
+            // parse bundle interfaces
+        
+            if (isThis(TokenType::LeftBrace))
+            {
+                throwAddressableError<SyntaxError>(u8"expect interfaces to bundle");
+            }
+            while (true)
+            {
+                if (isThis(TokenType::LeftBrace)) { break; }
+                bundles.push_back(parseExpression(0, TokenType::Plus, TokenType::LeftBrace));
+                if (isThis(TokenType::Plus))
+                {
+                    next(); // consume `+`
+                }
+            }
+        }
+
         expect(TokenType::LeftBrace); // `{
         next();                       // consume `{`
 
@@ -427,7 +450,7 @@ namespace Fig
                 throwAddressableError<SyntaxError>(FString(u8"Invalid syntax"), currentAAI.line, currentAAI.column);
             }
         }
-        return makeAst<Ast::InterfaceDefAst>(interfaceName, methods, isPublic);
+        return makeAst<Ast::InterfaceDefAst>(interfaceName, bundles, methods, isPublic);
     }
 
     Ast::Implement Parser::__parseImplement()