loops - Lisp 帮助 |错误 : Duplicate binding in LOOP : (result)

Question

(defmethod! expand-t-setclass (pcset &optional (n 12))
  :icon *PC_ICON*
  :doc "
Given any member of a t-setclass, lists every member of that t-setclass.
The optional parameter N can be used to set the number of equal steps per
octave to something other than the default of 12.

Will tolerate integers out of the mod-N range in PCSET."
  :initvals '((1 3 4) 12)
  :indoc '("pcset or list of them"
           "modulus of the pc space")
  (if (listp (first pcset))
    (expand-t-setclasses pcset)
    (let ((t-prime (t-primeform pcset n)))
      (loop with result = nil
            repeat n
            for x-pcset = pcset then (xpose x-pcset 1 n)
            unless (member x-pcset result) collect x-pcset into result
            finally return result))))


(defmethod! expand-t-setclasses (pcset &optional (n 12))
  (loop for item in pcset collect (expand-t-setclass item n)))

;-----

一般来说，我对 Lisp 不太熟悉，正在尝试找出导致此错误的错误:

错误:循环中的重复绑定(bind):(结果)

Answer 1

在引入变量 RESULT 的 LOOP 中有两种形式。

WITH result = nil

和

COLLECT ... INTO result

以上都创建了一个变量绑定(bind)。

我会将 COLLECT 替换为将项目推送到 RESULT 列表的表单。

(loop ...
      collect item into foo
      ...
      finally (return foo))

进入

(loop with foo = nil
      ...
      (push item foo)
      ...
      finally (return (reverse foo)))

你有另一个错误:

FINALLY RETURN result

LOOP 语法不支持。 FINALLY 期待复合形式。

替换为:

FINALLY (return result)

RETURN 是 Common Lisp 中定义的宏。