{ "last_list_entry":
  { "vars": ["list"]
  , "expression":
    {"type": "[]", "index": -1, "list": {"type": "var", "name": "list"}}
  }
, "first_list_entry":
  { "vars": ["list"]
  , "imports": {"last": "last_list_entry"}
  , "expression":
    {"type": "[]", "index": 0, "list": {"type": "var", "name": "list"}}
  }
}