Head & Tail

新的head和tail函数定义如下。可以明显的看到在使用宏后，代码更清晰了。

lval* builtin_head(lval* a) {
  LASSERT(a, a->count == 1,
    "Function 'head' passed too many arguments!");
  LASSERT(a, a->cell[0]->type == LVAL_QEXPR,
    "Function 'head' passed incorrect type!");
  LASSERT(a, a->cell[0]->count != 0,
    "Function 'head' passed {}!");
  lval* v = lval_take(a, 0);
  while (v->count > 1) { lval_del(lval_pop(v, 1)); }
  return v;
}
lval* builtin_tail(lval* a) {
  LASSERT(a, a->count == 1,
    "Function 'tail' passed too many arguments!");
  LASSERT(a, a->cell[0]->type == LVAL_QEXPR,
    "Function 'tail' passed incorrect type!");
  LASSERT(a, a->cell[0]->count != 0,
    "Function 'tail' passed {}!");
  lval* v = lval_take(a, 0);
  lval_del(lval_pop(v, 0));
  return v;
}