Functional programming 也许是elisp中的monad

下面是我在elisp中实现Maybe monad的尝试。它是在第一个零上中断的函数组合。但是

值始终为
13
。我的错误在哪里

(defun .compose-maybe (&rest funcs)
  "Monad Maybe function composition with nil as Nothing."
  (lambda (arg)
    (if funcs
        (let ((value (funcall (apply #'.compose-maybe (cdr funcs)) arg)))
          (message "%s" value)
          (when value (funcall (car funcs) value))))
        arg))

(funcall (.compose-maybe (lambda (x) (* x 5)) (lambda (x) (+ 100 x))) 13)

您的
arg
不在
（如果funcs…
）的范围内，因此
.compose中的内部lambda可能总是返回
arg
，而不是仅当
funcs
为
nil
时返回

(defun .compose-maybe (&rest funcs)
  "Monad Maybe function composition with nil as Nothing."
  (lambda (arg)
    (if funcs
        (let ((value (funcall (apply #'.compose-maybe (cdr funcs)) arg)))
          (message "%s" value)
          (when value (funcall (car funcs) value)))
      arg)))