diff --git a/assignments/PA4/bad_inherit.cl b/assignments/PA4/bad_inherit.cl
index a2ee04b..f6b6d46 100644
--- a/assignments/PA4/bad_inherit.cl
+++ b/assignments/PA4/bad_inherit.cl
@@ -90,4 +90,9 @@ class Err5 {
     hello(): NOEXIST { new Object };
     bye(): Bool { 10 };
     -- ala: Int <- 20;
+};
+
+class Err7 {
+    ala: Bool <- lal;
+    lal: NOEXIST <- 10;
 };
\ No newline at end of file
diff --git a/assignments/PA4/cool-tree.h b/assignments/PA4/cool-tree.h
index 679d727..8fad60d 100644
--- a/assignments/PA4/cool-tree.h
+++ b/assignments/PA4/cool-tree.h
@@ -80,7 +80,7 @@ class Expression_class : public tree_node {
 public:
    tree_node *copy()		 { return copy_Expression(); }
    virtual Expression copy_Expression() = 0;
-
+   virtual Symbol semant(Class_, ClassTable*) = 0;
 #ifdef Expression_EXTRAS
    Expression_EXTRAS
 #endif
diff --git a/assignments/PA4/cool-tree.handcode.h b/assignments/PA4/cool-tree.handcode.h
index 9f7abcf..2abc2e2 100644
--- a/assignments/PA4/cool-tree.handcode.h
+++ b/assignments/PA4/cool-tree.handcode.h
@@ -100,6 +100,7 @@ void dump_type(ostream&, int);               \
 Expression_class() { type = (Symbol) NULL; }
 
 #define Expression_SHARED_EXTRAS           \
-void dump_with_types(ostream&,int); 
+void dump_with_types(ostream&,int); 		\
+Symbol semant(Class_, ClassTable*);
 
 #endif
diff --git a/assignments/PA4/semant.cc b/assignments/PA4/semant.cc
index 53dd47a..c391a10 100644
--- a/assignments/PA4/semant.cc
+++ b/assignments/PA4/semant.cc
@@ -9,6 +9,7 @@
 #include <queue>
 #include <memory.h>
 #include "cool-tree.h"
+#include "cool-tree.handcode.h"
 #include "semant.h"
 #include "utilities.h"
 
@@ -546,26 +547,157 @@ void class__class::semant(ClassTable * classtable)
 
 void attr_class::semant(Class_ cur_class, ClassTable * classtable)
 {
-    if (typeid(*init) == typeid(no_expr_class)) {
-        /*
-        * Attr-No-Init: 
-        *   Check if Declared Type is defined, if so, do nothing because already
-        *   in AST; else, error report and set its type to Object
-        */
-        if (!classtable->class_exist(type_decl)) {
+    /*
+    * Attr-No-Init: 
+    *   Check if Declared Type is defined, if so, do nothing because already
+    *   in AST; else, error report and set its type to Object
+    */
+    if (!classtable->class_exist(type_decl)) {
+        classtable->semant_error(cur_class->get_filename(), this)
+            << "Class " << type_decl
+            << " of attribute " << name
+            << " is undefined.\n";
+        this->type_decl = Object;
+    }
+    /*
+    * Attr-Init:
+    *   Except checking existence of type_decl, type the init expression and 
+    *   check rhs's type conformance with type_decl
+    */
+    if (typeid(*init) != typeid(no_expr_class)) {
+        auto rhs_type = init->semant(cur_class, classtable);
+        if (!classtable->conform(rhs_type, type_decl)) {
             classtable->semant_error(cur_class->get_filename(), this)
-                << "Class " << type_decl
-                << " of attribute " << name
-                << " is undefined.\n";
+                << "Inferred type " << rhs_type
+                << "  of initialization of attribute " << name
+                << " does not conform to declared type " << type_decl
+                << " .\n";
             this->type_decl = Object;
         }
     }
-    else {
-        // Attr-Init
-    }
 }
 
 void method_class::semant(Class_ cur_class, ClassTable * classtable)
 {
 
-}
\ No newline at end of file
+}
+
+Symbol assign_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol static_dispatch_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol dispatch_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol cond_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol loop_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol typcase_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol block_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol let_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol plus_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol sub_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol mul_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol divide_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol neg_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol lt_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol eq_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol leq_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol comp_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol int_const_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol bool_const_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol string_const_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol new__class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol isvoid_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol no_expr_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}
+
+Symbol object_class::semant(Class_ cur_class, ClassTable* classtable)
+{
+    return Object;
+}