[英]Define struct with one field in scheme
I am working on a homework assignment for a class. 我正在上课的作业。 The problem statement says to use the data definition:
问题说明说使用数据定义:
(define-struct diff-exp exprs)
(define-struct mult-exp exprs)
;; An Expr is one of
;; -- Number
;; -- (make-diff-exp (cons Expr LOExpr))
;; -- (make-mult-exp (cons Expr LOExpr))
;; Interpretation: a diff-exp represents a difference,
;; and a mult-exp represents a multiplication.
;; A List of Exprs (LOExpr) is one of
;; -- empty
;; -- (cons Expr LOExpr)
However, when I have just that in the source, Dr. Scheme (Intermediate Student Language) says: 但是,当我在源头中只有那个内容时,Scheme博士(中级学生语言)说:
define-struct: expected a sequence of field names after the structure type name in `define-struct', but found something else
Is there something I am missing here or did my teacher give me an invalid data definition? 我在这里缺少什么吗?还是老师给了我一个无效的数据定义?
Like Anon suggested in the comment above, define-struct
takes a list of fields; 就像上面评论中建议的Anon一样,
define-struct
接受一个字段列表; if you need only one, then use a list of one element. 如果只需要一个,则使用一个元素的列表。 Example code:
示例代码:
(define-struct diff-exp (exprs))
(let ((myexpr (make-diff-exp (list foo bar))))
(diff-exp-exprs myexpr))
You can rifle through the many sundry features of define-struct
in the PLT Scheme documentation . 您可以浏览PLT Scheme文档中的
define-struct
的许多杂项功能。
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