diff --git a/.gitignore b/.gitignore
index 21cc758..fa645bd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -147,3 +147,9 @@ tramp
 Session.vim
 .netrwhist
 *~
+
+
+
+
+### Exclude ###
+!src/main/asm/chocopy/common 
diff --git a/.vscode/launch.json b/.vscode/launch.json
index 861fe91..53608f3 100644
--- a/.vscode/launch.json
+++ b/.vscode/launch.json
@@ -12,7 +12,8 @@
             "request": "launch",
             "classPaths": ["chocopy-ref.jar:target/assignment.jar"],
             "mainClass": "chocopy.ChocoPy",
-            "args": [ "--pass=rrs", "--test","--dir", "src/test/data/pa3/sample/list_set_element_oob_1.py"],
+            //"args": [ "--pass=rrs", "--test","--dir", "src/test/data/pa3/sample/list_set_element_oob_1.py"],
+            "args": [ "--pass=rrs", "--test","--dir", "test.py"],
             "sourcePaths": []
         }
     ]
diff --git a/conslist b/conslist
new file mode 100644
index 0000000..f4b83a2
--- /dev/null
+++ b/conslist
@@ -0,0 +1,27 @@
+
+        addi sp, sp, -8
+        sw ra, 4(sp)
+        sw fp, 0(sp)
+        addi fp, sp, 8
+        lw a1, 0(fp)
+        la a0, $.list$prototype
+        beqz a1, conslist_done
+        addi a1, a1, @listHeaderWords
+        jal alloc2
+        lw t0, 0(fp)
+        sw t0, @.__len__(a0)
+        slli t1, t0, 2
+        add t1, t1, fp
+        addi t2, a0, @.__elts__
+conslist_1:
+        lw t3, 0(t1)
+        sw t3, 0(t2)
+        addi t1, t1, -4
+        addi t2, t2, 4
+        addi t0, t0, -1
+        bnez t0, conslist_1
+conslist_done:
+        lw ra, -4(fp)
+        lw fp, -8(fp)
+        addi sp, sp, 8
+        jr ra
\ No newline at end of file
diff --git a/src/main/asm/chocopy/common/concat.s b/src/main/asm/chocopy/common/concat.s
new file mode 100644
index 0000000..f5bb346
--- /dev/null
+++ b/src/main/asm/chocopy/common/concat.s
@@ -0,0 +1,63 @@
+
+        addi sp, sp, -32
+        sw ra, 28(sp)
+        sw fp, 24(sp)
+        addi fp, sp, 32
+	sw s1, -12(fp)
+        sw s2, -16(fp)
+        sw s3, -20(fp)
+	sw s4, -24(fp)
+        sw s5, -28(fp)
+        lw t0, 4(fp)
+        lw t1, 0(fp)
+        beqz t0, concat_none
+        beqz t1, concat_none
+        lw t0, @.__len__(t0)
+        lw t1, @.__len__(t1)
+        add s5, t0, t1
+        addi a1, s5, @listHeaderWords
+        la a0, $.list$prototype
+        jal alloc2
+        sw s5, @.__len__(a0)
+	mv s5, a0
+        addi s3, s5, @.__elts__
+        lw s1, 4(fp)
+	lw s2, @.__len__(s1)
+        addi s1, s1, @.__elts__
+	lw s4, 12(fp)
+concat_1:
+        beqz s2, concat_2
+        lw a0, 0(s1)
+	jalr ra, s4, 0
+        sw a0, 0(s3)
+        addi s2, s2, -1
+        addi s1, s1, 4
+        addi s3, s3, 4
+        j concat_1
+concat_2:
+        lw s1, 0(fp)
+        lw s2, @.__len__(s1)
+        addi s1, s1, @.__elts__
+	lw s4, 8(fp)
+concat_3:
+        beqz s2, concat_4
+        lw a0, 0(s1)
+	jalr ra, s4, 0
+        sw a0, 0(s3)
+        addi s2, s2, -1
+        addi s1, s1, 4
+        addi s3, s3, 4
+        j concat_3
+concat_4:
+	mv a0, s5
+        lw s1, -12(fp)
+        lw s2, -16(fp)
+        lw s3, -20(fp)
+	lw s4, -24(fp)
+        lw s5, -28(fp)
+        lw ra, -4(fp)
+        lw fp, -8(fp)
+        addi sp, sp, 32
+        jr ra
+concat_none:
+        j error.None
\ No newline at end of file
diff --git a/src/main/asm/chocopy/common/conslist.s b/src/main/asm/chocopy/common/conslist.s
new file mode 100644
index 0000000..f4b83a2
--- /dev/null
+++ b/src/main/asm/chocopy/common/conslist.s
@@ -0,0 +1,27 @@
+
+        addi sp, sp, -8
+        sw ra, 4(sp)
+        sw fp, 0(sp)
+        addi fp, sp, 8
+        lw a1, 0(fp)
+        la a0, $.list$prototype
+        beqz a1, conslist_done
+        addi a1, a1, @listHeaderWords
+        jal alloc2
+        lw t0, 0(fp)
+        sw t0, @.__len__(a0)
+        slli t1, t0, 2
+        add t1, t1, fp
+        addi t2, a0, @.__elts__
+conslist_1:
+        lw t3, 0(t1)
+        sw t3, 0(t2)
+        addi t1, t1, -4
+        addi t2, t2, 4
+        addi t0, t0, -1
+        bnez t0, conslist_1
+conslist_done:
+        lw ra, -4(fp)
+        lw fp, -8(fp)
+        addi sp, sp, 8
+        jr ra
\ No newline at end of file
diff --git a/src/main/asm/chocopy/common/makebool.s b/src/main/asm/chocopy/common/makebool.s
new file mode 100644
index 0000000..898b587
--- /dev/null
+++ b/src/main/asm/chocopy/common/makebool.s
@@ -0,0 +1,5 @@
+
+	slli a0, a0, 4
+        la t0, @bool.False
+        add a0, a0, t0
+	jr ra
\ No newline at end of file
diff --git a/src/main/asm/chocopy/common/makeint.s b/src/main/asm/chocopy/common/makeint.s
new file mode 100644
index 0000000..7fd541d
--- /dev/null
+++ b/src/main/asm/chocopy/common/makeint.s
@@ -0,0 +1,11 @@
+
+    addi sp, sp, -8
+    sw ra, 4(sp)
+    sw a0, 0(sp)
+    la a0, $int$prototype
+    jal ra, alloc
+    lw t0, 0(sp)
+    sw t0, @.__int__(a0)
+    lw ra, 4(sp)
+    addi sp, sp, 8
+    jr ra
\ No newline at end of file
diff --git a/src/main/asm/chocopy/common/strcat.s b/src/main/asm/chocopy/common/strcat.s
new file mode 100644
index 0000000..c131574
--- /dev/null
+++ b/src/main/asm/chocopy/common/strcat.s
@@ -0,0 +1,57 @@
+
+        addi sp, sp, -12
+        sw ra, 8(sp)
+        sw fp, 4(sp)
+        addi fp, sp, 12
+        lw t0, 4(fp)
+        lw t1, 0(fp)
+        lw t0, @.__len__(t0)
+        beqz t0, strcat_4
+        lw t1, @.__len__(t1)
+        beqz t1, strcat_5
+        add t1, t0, t1
+        sw t1, -12(fp)
+        addi t1, t1, 4
+        srli t1, t1, 2
+        addi a1, t1, @listHeaderWords
+        la a0, $str$prototype
+        jal alloc2
+        lw t0, -12(fp)
+        sw t0, @.__len__(a0)
+        addi t2, a0, 16
+        lw t0, 4(fp)
+        lw t1, @.__len__(t0)
+        addi t0, t0, @.__str__
+strcat_1:
+        beqz t1, strcat_2
+        lbu t3, 0(t0)
+        sb t3, 0(t2)
+        addi t1, t1, -1
+        addi t0, t0, 1
+        addi t2, t2, 1
+        j strcat_1
+strcat_2:
+        lw t0, 0(fp)
+        lw t1, 12(t0)
+        addi t0, t0, 16
+strcat_3:
+        beqz t1, strcat_6
+        lbu t3, 0(t0)
+        sb t3, 0(t2)
+        addi t1, t1, -1
+        addi t0, t0, 1
+        addi t2, t2, 1
+        j strcat_3
+strcat_4:
+        lw a0, 0(fp)
+        j strcat_7
+strcat_5:
+        lw a0, 4(fp)
+        j strcat_7
+strcat_6:
+        sb zero, 0(t2)
+strcat_7:
+        lw ra, -4(fp)
+        lw fp, -8(fp)
+        addi sp, sp, 12
+        jr ra
\ No newline at end of file
diff --git a/src/main/asm/chocopy/common/streql.s b/src/main/asm/chocopy/common/streql.s
new file mode 100644
index 0000000..3dc5130
--- /dev/null
+++ b/src/main/asm/chocopy/common/streql.s
@@ -0,0 +1,27 @@
+
+        addi sp, sp, -8
+        sw ra, 4(sp)
+        sw fp, 0(sp)
+        addi fp, sp, 8
+        lw a1, 4(fp)
+        lw a2, 0(fp)
+        lw t0, @.__len__(a1)
+        lw t1, @.__len__(a2)
+        bne t0, t1, streql_no
+streql_1:
+        lbu t2, @.__str__(a1)
+        lbu t3, @.__str__(a2)
+        bne t2, t3, streql_no
+        addi a1, a1, 1
+        addi a2, a2, 1
+        addi t0, t0, -1
+        bgtz t0, streql_1
+        li a0, 1
+        j streql_end
+streql_no:
+        xor a0, a0, a0
+streql_end:
+        lw ra, -4(fp)
+        lw fp, -8(fp)
+        addi sp, sp, 8
+        jr ra
\ No newline at end of file
diff --git a/src/main/asm/chocopy/common/strneql.s b/src/main/asm/chocopy/common/strneql.s
new file mode 100644
index 0000000..76e316e
--- /dev/null
+++ b/src/main/asm/chocopy/common/strneql.s
@@ -0,0 +1,27 @@
+
+        addi sp, sp, -8
+        sw ra, 4(sp)
+        sw fp, 0(sp)
+        addi fp, sp, 8
+        lw a1, 4(fp)
+        lw a2, 0(fp)
+        lw t0, @.__len__(a1)
+        lw t1, @.__len__(a2)
+        bne t0, t1, strneql_yes
+strneql_1:
+        lbu t2, @.__str__(a1)
+        lbu t3, @.__str__(a2)
+        bne t2, t3, strneql_yes
+        addi a1, a1, 1
+        addi a2, a2, 1
+        addi t0, t0, -1
+        bgtz t0, strneql_1
+        xor a0, a0, a0
+        j strneql_end
+strneql_yes:
+        li a0, 1
+strneql_end:
+        lw ra, -4(fp)
+        lw fp, -8(fp)
+        addi sp, sp, 8
+        jr ra
\ No newline at end of file
diff --git a/src/main/java/chocopy/pa3/CodeGenImpl.java b/src/main/java/chocopy/pa3/CodeGenImpl.java
index 3225532..6e11970 100644
--- a/src/main/java/chocopy/pa3/CodeGenImpl.java
+++ b/src/main/java/chocopy/pa3/CodeGenImpl.java
@@ -1,5 +1,6 @@
 package chocopy.pa3;
 
+import java.net.Socket;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -30,74 +31,17 @@ import chocopy.common.codegen.RiscVBackend.Register;
  */
 public class CodeGenImpl extends CodeGenBase 
 {
+    /** Label for built-in routines. */
+    protected final Label makeintLabel = new Label("makeint");
+    protected final Label strneqlLablel = new Label("strneql");
+    protected final Label streqlLablel = new Label("streql");
+    protected final Label makeboolLablel = new Label("makebool");
+    protected final Label strcatLablel = new Label("strcat");
+    protected final Label concatLablel = new Label("concat");
+    protected final Label conslistLablel = new Label("conslist");
 
-    /** A code generator emitting instructions to BACKEND. */
-    public CodeGenImpl(RiscVBackend backend) 
-    {
-        super(backend);
-        
-    }
-    
-    /**
-     * Generates assembly code for PROGRAM.
-     *
-     * <p>This is the main driver that calls internal methods for emitting DATA section (globals,
-     * constants, prototypes, etc) as well as the the CODE section (predefined functions, built-in
-     * routines, and user-defined functions).
-     */
-    @Override
-    public void generate(Program program) {
-    		System.out.println("Inside generate");   
-        analyzeProgram(program);
-
-        backend.startData();
-
-        for (ClassInfo classInfo : this.classes) {
-            emitPrototype(classInfo);
-        }
-
-        for (ClassInfo classInfo : this.classes) {
-            emitDispatchTable(classInfo);
-        }
-
-        for (GlobalVarInfo global : this.globalVars) {
-            backend.emitGlobalLabel(global.getLabel());
-            emitConstant(
-                    global.getInitialValue(),
-                    global.getVarType(),
-                    String.format("Initial value of global var: %s", global.getVarName()));
-        }
-
-        backend.startCode();
-
-        Label mainLabel = new Label("main");
-        backend.emitGlobalLabel(mainLabel);
-        backend.emitLUI(A0, HEAP_SIZE_BYTES >> 12, "Initialize heap size (in multiples of 4KB)");
-        backend.emitADD(S11, S11, A0, "Save heap size");
-        backend.emitJAL(heapInitLabel, "Call heap.init routine");
-        backend.emitMV(GP, A0, "Initialize heap pointer");
-        backend.emitMV(S10, GP, "Set beginning of heap");
-        backend.emitADD(S11, S10, S11, "Set end of heap (= start of heap + heap size)");
-        backend.emitMV(RA, ZERO, "No normal return from main program.");
-        backend.emitMV(FP, ZERO, "No preceding frame.");
-
-        emitTopLevel(program.statements);
-
-        for (FuncInfo funcInfo : this.functions) {
-            funcInfo.emitBody();
-        }
-
-        emitStdFunc("alloc");
-        emitStdFunc("alloc2");
-        emitStdFunc("abort");
-        emitStdFunc("heap.init");
-        emitStdFunc("makeint");
-
-        emitCustomCode();
 
-        backend.startData();
-        emitConstants();
-    }
+    
 
     /** Operation on None. */
     private final Label errorNone = new Label("error.None");
@@ -106,12 +50,15 @@ public class CodeGenImpl extends CodeGenBase
     /** Index out of bounds. */
     private final Label errorOob = new Label("error.OOB");
     
-    /** Not implemented. */
+    /** Let's try to implement everything first.*/
     private final Label errorNI = new Label("error.NI");
     
-    
-    /** Label for built-in routine: makeint. */
-    protected final Label makeIntLabel = new Label("makeint");
+    /** A code generator emitting instructions to BACKEND. */
+    public CodeGenImpl(RiscVBackend backend) 
+    {
+        super(backend);
+        
+    }
     
     
     /**
@@ -339,36 +286,6 @@ public class CodeGenImpl extends CodeGenBase
             return A0;
         }
         
-        
-      
-      
-      @Override
-      public Register analyze(FuncDef node) {
-    	  		backend.emitLW(T6, FP, 0, "Inside FuncDef: " + node.name);
-      		// function
-    	  		return null;
-      }
-      
-      
-      
-      @Override
-      public Register analyze(GlobalDecl node) {
-    	  		backend.emitLW(T6, FP, 0, "Inside GlobalDecl: ");
-      		// function
-    	  		return null;
-      }
-      
-      
-      
-      @Override
-      public Register analyze(NonLocalDecl node) {
-    	  		backend.emitLW(T6, FP, 0, "Inside NonLocalDecl: ");
-      		// function
-    	  		return null;
-      }
-      
-      
-        
         public Register analyze(MethodCallExpr node) {
         		backend.emitLW(T6, FP, 0, "Inside MethodCallExpr: " + node.method.member.name);
             Register obj = node.method.object.dispatch(this);
@@ -411,6 +328,7 @@ public class CodeGenImpl extends CodeGenBase
         	    
         	    // All expressions should save their end result in A0
         	    expr.dispatch(this);
+                
             return A0;
         }
         
@@ -435,15 +353,6 @@ public class CodeGenImpl extends CodeGenBase
             return Register.A0;
         }
         
-        
-// FIXME: This is not correct. We need to use $int$prototype to create an integer literal, so commenting it
-//        @Override
-//        public Register analyze(IntegerLiteral node) 
-//        {
-//            backend.emitLI(Register.A0, node.value, "Load integer literal "+node.value);
-//            return Register.A0;
-//        }
-        
         @Override
         public Register analyze(BooleanLiteral node) 
         {
@@ -454,21 +363,32 @@ public class CodeGenImpl extends CodeGenBase
                 backend.emitLI(Register.A0, 0, "Load boolean literal: false ");
             return Register.A0;
         }
+
         
         @Override
         public Register analyze(AssignStmt node) 
         {
-        		backend.emitLW(T6, FP, 0, "Inside AssignStmt: ");
+            backend.emitLW(T6, FP, 0, "Inside AssignStmt: ");
             Type t = node.value.getInferredType();
-            if(t.isSpecialType() || t.isListType())
+            // if(t.isSpecialType() || t.isListType())
             {
-                node.value.dispatch(this);
+                Register reg = node.value.dispatch(this);
+                if (reg == null)
+                    reg = A0;
                 if (sym.getParent() == null) 
                 {
                     for(Expr target: node.targets)
                     {
-                        GlobalVarInfo gvi=(GlobalVarInfo)sym.get(((Identifier)target).name);
-                        backend.emitSW(Register.A0, gvi.getLabel(), Register.T0, "Assign global: "+gvi.getVarName()+"(using tmp register)");
+                        if(target instanceof Identifier)
+                        {
+                            GlobalVarInfo gvi=(GlobalVarInfo)sym.get(((Identifier)target).name);
+                            backend.emitSW(reg, gvi.getLabel(), Register.T0, "Assign global: "+gvi.getVarName()+"(using tmp register)");
+                        }
+                        else
+                        {
+                            Register ret = target.dispatch(this);
+                            backend.emitSW(T1, ret, 0, "Set list element"); 
+                        }
                     }
                 }
                 else
@@ -477,13 +397,9 @@ public class CodeGenImpl extends CodeGenBase
                     {
                         StackVarInfo svi = (StackVarInfo) sym.get(((Identifier)target).name);
                         int loc = offsetMap.get(svi);
-                        backend.emitSW(Register.A0, Register.FP, -loc*4, "Load local variable: "+svi.getVarName());
+                        backend.emitSW(reg, Register.FP, -loc*4, "Load local variable: "+svi.getVarName());
                     }
                 }
-            }
-            else
-            {//TODO: Object Assignment
-
             }
             return Register.A0;
         }
@@ -506,7 +422,7 @@ public class CodeGenImpl extends CodeGenBase
             backend.emitLocalLabel(elseBlock, "Else part of if expression");
             node.elseExpr.dispatch(this);
             backend.emitLocalLabel(ln, "End of if expression");
-            return null;
+            return A0;
         }
         
         @Override
@@ -601,9 +517,9 @@ public class CodeGenImpl extends CodeGenBase
             }
             else if(node.left.getInferredType().equals(Type.STR_TYPE) && node.right.getInferredType().equals(Type.STR_TYPE))
             {
-
+                
             }
-            return null;
+            return A0;
         }
         
         @Override
@@ -695,7 +611,7 @@ public class CodeGenImpl extends CodeGenBase
         public Register analyze(IntegerLiteral node) {
         		backend.emitLW(T6, FP, 0, "Inside IntegerLiteral: " + node.value);
         		backend.emitLI(A0, node.value, "Load integer literal " + node.value);
-        		backend.emitJAL(makeIntLabel, "Box integer");
+        		backend.emitJAL(makeintLabel, "Box integer");
 //    			System.out.println("+++ Inside IntegerLiteral");
 //    			backend.emitLA(A0, new Label("$int$prototype"), "Load prototype");
 //    			backend.emitJAL(new Label("ra, alloc"), "");
@@ -723,12 +639,34 @@ public class CodeGenImpl extends CodeGenBase
             
          }
          
-         @Override
-         public Register analyze(IndexExpr node) 
-         {
-            //System.out.println(node);
-            return defaultAction(node);
-         }
+            @Override
+            public Register analyze(IndexExpr node) 
+            {
+                incSp(1);
+                Register listObj = node.list.dispatch(this);
+                backend.emitSW(listObj, FP, -sp_off * wordSize, String.format("Push on stack slot %d", sp_off));
+                Register index = node.index.dispatch(this);
+                Register vacantReg = (index != A0) ? A0 : A1;
+
+                if (node.list.getInferredType().isListType()) {
+                    backend.emitLW(vacantReg, FP, -sp_off * wordSize, String.format("Pop stack slot %d", sp_off));
+
+                    this.d(vacantReg);
+                    return this.a(vacantReg, index, A0, false);
+                }else{
+                    this.a(0, vacantReg);
+                    Register a = a(index);
+                    Label ch = generateLocalLabel();
+                    backend.emitLW(a, vacantReg, getAttrOffset(strClass, "__len__"), "Load attribute: __len__");
+                    backend.emitBLTU(index, a, ch, "Ensure 0 <= idx < len");
+                    backend.emitJ(f, "Go to error handler");
+                    backend.emitLocalLabel(ch, "Index within bounds");
+                    this.c(index);
+                    Register a2 = this.a(false);
+                    this.a(1);
+                    return a2;
+                }
+            }
   
         public Register analyze(MemberExpr node) 
         {
@@ -764,10 +702,19 @@ public class CodeGenImpl extends CodeGenBase
      * to out-of-bounds error and abort");
      */
     protected void emitCustomCode() {
+        
+        emitStdFunc("concat");
+        emitStdFunc("conslist");
+        emitStdFunc("strcat");
+        emitStdFunc("streql");
+        emitStdFunc("strneql");
+        emitStdFunc("makeint");
+        emitStdFunc("makebool");
+
         emitErrorFunc(errorNone, "Operation on None");
         emitErrorFunc(errorDiv, "Division by zero");
         emitErrorFunc(errorOob, "Index out of bounds");
-        emitErrorFunc(errorNI, "Not Implemented");
+        // emitErrorFunc(errorNI, "Not Implemented.");
     }
 
     /** Emit an error routine labeled ERRLABEL that aborts with message MSG. */