我正在尝试在 clojure.core.logic 中实现与 membero 相反的东西，但它返回两个值而不是一个值。否则，它工作正常(当值在列表中时不返回任何内容，而在列表中时不返回任何内容)。

(defne nonmembero
  "A relation where l is a collection, such that l does not contain x"
  [x l]
  ([_ ()])
  ([_ [head]]
     (!= x head))
  ([_ [head . tail]]
     (!= x head)
     (nonmembero x tail)))

运行示例:

user> (run* [x] (nonmembero 1 [2 3 4 5]))
(_0 _0)
user> (run* [x] (nonmembero 1 [2 3 1 4 5]))
()

最佳答案

您不需要第二个模式，即 [_ [head]。这会在 core.logic 引擎的搜索空间中产生一个新分支，从而导致输出 2。最后一个模式即 [head . tail] 足以处理列表中只有一个元素的情况。现在您的解决方案变为:

(defne nonmembero
  "A relation where l is a collection, such that l does not contain x"
  [x l]
  ([_ ()])
  ([_ [head . tail]]
     (!= x head)
     (nonmembero x tail)))

https://stackoverflow.com/questions/16370327/