检查缺点列表中是否存在缺点

Question

我正在构建一个程序和 lisp，需要检查缺点列表中是否存在缺点，但由于某种原因，它在 if 语句中保持 returning nil，这是我当前的代码正在使用它。

(defun countVertexTriangles (graph numOfVertices)
    (findTriangle graph numOfVertices)
)

(defun findTriangle(graph numOfVertices)
    (loop for (x y) in graph do
            (loop for z from 1 to numOfVertices do
                (write graph)
                (terpri)
                (write (cons z (cons y nil)))
                (terpri)
                (write (cons z (cons x nil)))
                (terpri)
                ; (if (AND (member (cons z (cons y nil)) graph) (member (cons z (cons x nil)) graph))
                ;     then (write (cons y z))
                ; )
            )
        (terpri)
    )
)

; (defun findEdge(graph edge)
;     (loop for x in graph do
;         (write x)
;         (write edge)
;         (if (eql x edge)
;             (write "A")
;             (write "B")
;         )
;     )
; )

(defun testFunct ()
    (setf g1 '((1 2)(2 3)(1 3)(2 4)(3 4)(4 5)(3 5)))
    (countVertexTriangles g1 5)
)

(testFunct)

为什么 member(cons z (cons y nil)) return nil 即使在第一次迭代中我们可以看到 (1 2) 存在于列表中？

编辑：

目前即使它是真的 return 也没有，为什么给出以下代码会出现这种情况？

(defun countVertexTriangles (graph numOfVertices)
    (findTriangle graph numOfVertices)
)

(defun findTriangle(graph numOfVertices)
    (loop for (x y) in graph do
            (loop for z from 1 to numOfVertices do
                ; (write graph)
                ; (terpri)
                ; (write (list z y ))
                ; (terpri)
                (write (findEdge graph (list z y)))
                (terpri)
                ; (if (AND (member (list z x) graph) (member (list z x ) graph))
                ;     then (write "TEST")
                ; )
            )
        (terpri)
    )
)

(defun findEdge(graph edge)
    (loop for x in graph do
        (if (equal x edge)
            (return-true)
            (return-false)
        )
    )
)

(defun return-true ()
   t)

(defun return-false ()
   nil)

(defun testFunct ()
    (setf g1 '((1 2)(2 3)(1 3)(2 4)(3 4)(4 5)(3 5)))
    (countVertexTriangles g1 5)
)

Answer 1

findEdge 没有 return 任何东西。调用 return-true 和 return-false 不会从 findEdge 调用 return。在找到匹配项之前，您也不应该 return。

(defun findEdge(graph edge)
    (loop for x in graph do
        (if (equal x edge)
            (return-from findEdge (return-true))
        )
    )
    (return-false)
)

这可以简化为：

(defun findEdge (graph edge) 
  (member edge findEdge :test #'equal))

检查缺点列表中是否存在缺点

Checking If Cons exist in list of Cons

lisp