diff --git a/object.c b/object.c
index f5f34e2..f9021da 100644
--- a/object.c
+++ b/object.c
@@ -3,6 +3,8 @@
 #include <sysexits.h>
 #include <assert.h>
 
+#define USE_TAG  1
+
 #define USE_GC   1
 
 #if (USE_GC)
@@ -66,7 +68,7 @@ struct Undefined {
 
 struct Integer {
     type_t type;
-    int value;
+    int _value;
 };
 
 struct String {
@@ -120,9 +122,23 @@ union object {
 union object _null = {.Undefined = {Undefined}};
 oop null = &_null;
 
+int isInteger(oop obj)
+{
+#if (USE_TAG)
+    return (intptr_t)obj & 1;
+#else
+    return is(Integer, obj);
+#endif
+}
+
 type_t getType(oop ptr)
 {
     assert(ptr);
+#if (USE_TAG)
+    if (isInteger(ptr)) {
+        return Integer;
+    }
+#endif
     return ptr->type;
 }
 
@@ -157,12 +173,26 @@ void *memcheck(void *ptr)
 void print(oop ast);
 void println(oop ast);
 
+
+int getInteger(oop obj)
+{
+#if (USE_TAG)
+    return (intptr_t)obj >> 1;
+#else
+    return get(obj, Integer, _value);
+#endif
+}
+
 oop makeInteger(int value)
 {
+#if (USE_TAG)
+    return (oop) (((intptr_t)value << 1) | 1);
+#else
     oop newInt = memcheck(malloc(sizeof(union object)));
     newInt->type = Integer;
-    newInt->Integer.value = value;
+    newInt->Integer._value = value;
     return newInt;
+#endif
 }
 
 oop makeString(char *value)
@@ -205,8 +235,8 @@ bool map_hasIntegerKey(oop map, size_t index)
 {
     if (index >= get(map, Map, size)) return 0;
     oop key= get(map, Map, elements)[index].key;
-    if (!is(Integer, key)) return 0;
-    return index == get(key, Integer, value);
+    if (!isInteger(key)) return 0;
+    return index == getInteger(key);
 }
 
 int oopcmp(oop a, oop b)
@@ -215,7 +245,7 @@ int oopcmp(oop a, oop b)
     if (ta == tb) {
         switch (getType(a)) {
         case Integer:
-            return get(a, Integer, value) - get(b, Integer, value);
+            return getInteger(a) - getInteger(b);
         case String:
             return strcmp(get(a, String, value), get(b, String, value));
         default:
@@ -234,8 +264,8 @@ ssize_t map_search(oop map, oop key)
 
     ssize_t r = get(map, Map, size) - 1;
 
-    if (is(Integer, key)) {
-        ssize_t index = get(key, Integer, value);
+    if (isInteger(key)) {
+        ssize_t index = getInteger(key);
         if (index > r) {
             return -1 - (r + 1);
         }
@@ -367,7 +397,7 @@ void print(oop ast)
         printf("null");
         return;
     case Integer:
-        printf("%i", get(ast, Integer, value));
+        printf("%i", getInteger(ast));
         return;
     case String:
         printf("'%s'", get(ast, String, value));
diff --git a/parse.leg b/parse.leg
index 5491af5..ad53eae 100644
--- a/parse.leg
+++ b/parse.leg
@@ -480,14 +480,9 @@ SQUOTE  =    "'"                -
 %%
 ;
 
-int getInteger(oop obj)
-{
-    return get(obj, Integer, value);
-}
-
 int isFalse(oop obj)
 {
-    return obj == null || (is(Integer, obj) && (0 == get(obj, Integer, value)));
+    return obj == null || (isInteger(obj) && (0 == getInteger(obj)));
 }
 
 int isTrue(oop obj)
@@ -699,7 +694,7 @@ oop prim_exit(oop params)
     int status= 0;
     if (map_hasIntegerKey(params, 0)) {
     oop arg= get(params, Map, elements)[0].value;
-    if (is(Integer, arg)) status= get(arg, Integer, value);
+    if (isInteger(arg)) status= getInteger(arg);
     }
     exit(status);
 }
diff --git a/test1.txt b/test1.txt
index e83dac6..fd21f27 100644
--- a/test1.txt
+++ b/test1.txt
@@ -1,6 +1,22 @@
-var a = 20
-{
-    var a = 10
-    a
+fun sieve(n) {
+    var isPrime= {};
+    var i= 0;
+    while (i < n) {
+        isPrime[i]= 1;
+	i= i+1;
+    }
+    i= 2;
+    while (i < n) {
+        if (isPrime[i]) {
+	    print(i);
+	    var j= i+i;
+	    while (j < n) {
+	        isPrime[j]= 0;
+		j= j + i;
+	    }
+	}
+	i = i + 1;
+    }
 }
-a
\ No newline at end of file
+
+sieve(100);
\ No newline at end of file
diff --git a/test2.txt b/test2.txt
new file mode 100644
index 0000000..4beccaf
--- /dev/null
+++ b/test2.txt
@@ -0,0 +1,6 @@
+var a = 2
+fun f() {
+   var a = 10
+}
+a
+f()
\ No newline at end of file