diff --git a/vm.c b/vm.c
index 0e9a1ac..b955cd2 100644
--- a/vm.c
+++ b/vm.c
@@ -11,9 +11,8 @@ struct virtualMachine *initVM() {
 
 void push(struct virtualMachine *vm, struct garbageObject *value) {
   if (vm->stackSize >= STACK_MAX) {
-    fprintf(stderr, "ERROR: push(): Refusing to overflow the stack!\n");
-    // FIXME: Must free memory before exiting
-    exit(-1);
+    fprintf(stderr, "ERROR: push(): refusing to overflow the stack!\n");
+    return;
   }
   vm->stack[vm->stackSize++] = value;
 }
@@ -21,9 +20,8 @@ void push(struct virtualMachine *vm, struct garbageObject *value) {
 struct garbageObject *pop(struct virtualMachine *vm) {
   if (vm->stackSize < 0) {
     fprintf(stderr,
-            "ERROR: pop(): Stack underflow - stack size cannot be negative!");
-    // FIXME: Must free memory before exiting
-    exit(-1);
+            "ERROR: pop(): Stack size cannot be negative!");
+    return NULL;
   }
 
   return vm->stack[--vm->stackSize];
@@ -33,5 +31,21 @@ struct garbageObject *initGarbage(struct virtualMachine *vm,
                                   enum garbageData type) {
   struct garbageObject *obj = malloc(sizeof(struct garbageObject));
   obj->type = type;
+  obj->mark = 0;
+  return obj;
+}
+
+void pushInt(struct virtualMachine *vm, int value) {
+  struct garbageObject *obj = initGarbage(vm, GARBAGE_INT);
+  obj->value = value;
+  push(vm, obj);
+}
+
+struct garbageObject *pushPair(struct virtualMachine *vm) {
+  struct garbageObject *obj = initGarbage(vm, GARBAGE_PAIR);
+  obj->tail = pop(vm);
+  obj->head = pop(vm);
+
+  push(vm, obj);
   return obj;
 }