我可以在body中间定义一个变量吗？

Question

当define不在程序的最外层时，define可以出现在body的中间吗？例如：

(define (f x)
  (display x)
  (define n 1)  ; <- Is this allowed?
  (+ n x))

或者内部 define 必须始终出现在 body 的开头？例如：

(define (f x)
  (define n 1)  ; <-
  (display x)
  (+ n x))

Answer 1

定义必须在函数体的开头。来自 R⁷RS 的第 5.3.2 节：

5.3.2. Internal definitions
Definitions can occur at the beginning of a <body> (that is, the body of a lambda, let, let*, letrec, letrec*, let-values, let*-values, let-syntax, letrec-syntax, parameterize, guard, or case-lambda). Note that such a body might not be apparent until after expansion of other syntax. Such definitions are known as internal definitions as opposed to the global definitions described above.

我可以在body中间定义一个变量吗？

Can I define a variable in the middle of a body?

scheme

language-lawyer