diff --git a/assignments/PA3/cool.y b/assignments/PA3/cool.y
index f2a22a5..239ec7e 100644
--- a/assignments/PA3/cool.y
+++ b/assignments/PA3/cool.y
@@ -154,6 +154,7 @@
     /* all other binary operations are left-associative
      * assignment is right-associative,
      * three comparison operations do not associate.*/
+    %nonassoc LETEXPR
     %right ASSIGN
     %left NOT
     %nonassoc '<' LE '='
@@ -163,7 +164,6 @@
     %nonassoc '~'
     %nonassoc '@'
     %nonassoc '.'
-    %left LETEXPR
     
     
     %%
@@ -185,12 +185,14 @@
     
     /* If no parent is specified, the class inherits from the Object class. */
     class	: CLASS TYPEID '{' feature_list '}' ';'
-    { $$ = class_($2,idtable.add_string("Object"),$4,
-    stringtable.add_string(curr_filename)); }
+    { $$ = class_($2,idtable.add_string("Object"),$4,stringtable.add_string(curr_filename)); }
+    | CLASS TYPEID '{' '}' ';'
+    { $$ = class_($2,idtable.add_string("Object"),nil_Features(),stringtable.add_string(curr_filename)); }
     | CLASS TYPEID INHERITS TYPEID '{' feature_list '}' ';'
     { $$ = class_($2,$4,$6,stringtable.add_string(curr_filename)); }
     | CLASS TYPEID INHERITS TYPEID '{' '}' ';'
     { $$ = class_($2,$4,nil_Features(),stringtable.add_string(curr_filename)); }
+    | CLASS error '{' error '}' ';'
     ;
     
     /* Feature list may be empty, but no empty features in list. */
@@ -202,6 +204,11 @@
     
     feature : OBJECTID ':' TYPEID 
     /* Use no expr where optional expression omitted*/
+    /* The lineno for `no_expr` is somehow different from standard parser(std parser sets it to 0), 
+    * if you want to perfektly conform to that, the code below provides a workaround
+    * { auto _lineno = @$; SET_NODELOC(0); auto _no_expr = no_expr(); SET_NODELOC(_lineno); $$ = attr($1, $3, _no_expr); } 
+    * or you can modify cool-tree.h:754, manually override line_number to 0
+    */
     { $$ = attr($1, $3, no_expr()); }
     | OBJECTID ':' TYPEID ASSIGN expression
     { $$ = attr($1, $3, $5); }
@@ -269,37 +276,37 @@
     * there could be 2 interpretations: (let id1:T1 in expression).f() | let id1:T1 in (expression.f())
     * This should be specified to dis-ambiguite
     *
-    * The manual says, the expr extends as far as possible
+    * The manual says, the expr extends as far as possible, so we just set the lowest precedence
     */
     | LET nested_let
     { $$ = $2; }
     | CASE expression OF case_list ESAC
     { $$ = typcase($2, $4); }
     | NEW TYPEID
-    { $$ = new_($2); }
+    { SET_NODELOC(@2); $$ = new_($2); }
     | ISVOID expression
-    { $$ = isvoid($2); }
+    { SET_NODELOC(@2); $$ = isvoid($2); }
     /* the rules below need precedence specification */
     | expression '+' expression
-    { $$ = plus($1, $3); }
+    { SET_NODELOC(@3); $$ = plus($1, $3); }
     | expression '-' expression
-    { $$ = sub($1, $3); }
+    { SET_NODELOC(@3); $$ = sub($1, $3); }
     | expression '*' expression
-    { $$ = mul($1, $3); }
+    { SET_NODELOC(@3); $$ = mul($1, $3); }
     | expression '/' expression
-    { $$ = divide($1, $3); }
+    { SET_NODELOC(@3); $$ = divide($1, $3); }
     | '~' expression
-    { $$ = neg($2); }
+    { SET_NODELOC(@2); $$ = neg($2); }
     | expression '<' expression
-    { $$ = lt($1, $3); }
+    { SET_NODELOC(@3); $$ = lt($1, $3); }
     | expression LE expression
-    { $$ = leq($1, $3); }
+    { SET_NODELOC(@3); $$ = leq($1, $3); }
     | expression '=' expression
-    { $$ = eq($1, $3); }
+    { SET_NODELOC(@3); $$ = eq($1, $3); }
     | NOT expression
-    { $$ = comp($2); }
+    { SET_NODELOC(@2); $$ = comp($2); }
     | '(' expression ')'
-    { $$ = $2; }
+    { SET_NODELOC(@2); $$ = $2; }
     | OBJECTID
     { $$ = object($1); }
     | INT_CONST
diff --git a/assignments/PA3/myparser b/assignments/PA3/myparser
index 8bfe2aa..42cad06 100755
--- a/assignments/PA3/myparser
+++ b/assignments/PA3/myparser
@@ -1,2 +1,2 @@
-#!/bin/csh -f
+#!/bin/bash -f
 ./lexer $* | ./parser $*
diff --git a/include/PA3/cool-tree.h b/include/PA3/cool-tree.h
index d2312d2..0be1fa5 100644
--- a/include/PA3/cool-tree.h
+++ b/include/PA3/cool-tree.h
@@ -752,6 +752,7 @@ class no_expr_class : public Expression_class {
 protected:
 public:
    no_expr_class() {
+      line_number = 0;
    }
    Expression copy_Expression();
    void dump(ostream& stream, int n);