fix bug

interpreter/code.c

@@ -364,14 +364,19 @@ void exec(Code* expr, int frame_ptr, int root_frame_ptr)
                 Thunk* thunk = get_dst(root_frame_ptr);
                 int newsize = slice->thunk_size;
 
-                if (thunk != NULL && thunk->desc->thunk_size < newsize) {
+                if (thunk == NULL)
+                {
+                    thunk = (Thunk*) alloc_heap(newsize);
+                    set_return(root_frame_ptr, thunk);
+                }
+                else if (thunk->desc->thunk_size < newsize) {
                     Thunk* target = thunk;
                     thunk = (Thunk*) alloc_heap(newsize);
                     target->desc = (Desc*) __FORWARD_PTR__;
                     target->_forward_ptr = thunk;
                     set_return(root_frame_ptr, thunk);
                 }
-
+                
                 thunk->desc = slice;
                 
                 assert(thunk->desc->arity == (*bt)->desc->arity + expr->nr_args);