在Common Lisp中，如何定义通用数据类型说明符（如整数列表）？ [英] In Common Lisp, how to define a generic data type specifier (like list of integers)?

问题描述

我想定义一个类型说明符，用于描述相同类型的事物的列表。所以我想要（整数列表）与（数组整数）（内置）相似）。我可以为特定类型创建它，例如：

I would like to define a type specifier that describes a list of things of the same type. So I would like to have (list-of integer) similar to (array integer) (which is built-in). I am able to create it for a specific type, like this:

(defun elements-are-integer (seq) 
  (every #'(lambda (x) (typep x 'integer)) seq))
(deftype list-of-integer ()
  '(and list (satisfies elements-are-integer)))

但是，这意味着我必须对每种可能的类型都要这样做。如何更改此代码，以便该类型将另一个类型用作参数，并动态构造 satisfies 谓词？问题是 satisfies 需要一个全局符号，而且我不知道如何在适当的上下文中定义谓词函数（我想我需要 gensym ，但是如何？）。另外，该解决方案应该可以起作用，以便可以在另一个包中创建类型。

However, this means I have to do this for every possible type. How can I change this code so that the type would take another type as an argument, and construct the satisfies predicate on the fly? The problem is that the satisfies requires a global symbol, and I don't know how to define the predicate function in proper context (I guess I need to gensym it somehow, but how?). Also, the solution should work so that the type could be created inside another package.

推荐答案

请尝试以下操作：

(defun elements-are-of-type (seq type)
  (every #'(lambda (x) (typep x type)) seq))

(deftype list-of-type (type)
  (let ((predicate (gensym)))
    (setf (symbol-function predicate)
      #'(lambda (seq) (elements-are-of-type seq type)) )
    `(and list (satisfies ,predicate)) ))

(typep '(1 2 3) '(list-of-type integer))
; -> T

(typep '(1 2 a) '(list-of-type integer))
; -> NIL

(typep '(a b c) '(list-of-type symbol))
; -> T

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