Builtin function argument parsing

src/list.c

@@ -18,8 +18,9 @@ intptr_t list_length(LispVal *list) {
 
 bool list_length_eq(LispVal *list, intptr_t size) {
     assert(LISTP(list));
-    while (size-- && CONSP(list)) {
+    while (size && CONSP(list)) {
         list = XCDR(list);
+        --size;
     }
     return size == 0 && NILP(list);
 }