我已经开始学习合同,并且有这样的程序:
(define/contract (foldr-map f a xs)
foldr-map/c
(define (it a xs ys)
(if (null? xs)
(cons ys a)
(let* [(p (it a (cdr xs) ys))
(fc (f (car xs) (cdr p)))]
(cons (cons (car fc) (car p)) (cdr fc)))))
(it a xs null))
(foldr-map (lambda (x a) (cons a (+ a x))) 0 `(1 2 3))
而且我将flodr-map/c
合同定义为:
(define foldr-map/c
(parametric->/c [x a] (->
(-> x a (cons/c a number?))
a
(listof x)
(cons/c (listof a) a))))
但是我看到这样的错误:
foldr-map: broke its own contract
promised: a
produced: 3
in: the 2nd argument of
the 1st argument of
(parametric->/c
(x a)
(->
(-> x a (cons/c a number?))
a
(listof x)
(cons/c (listof a) a)))
contract from: (function foldr-map)
blaming: (function foldr-map)
(assuming the contract is correct)
我知道程序可以正常运行,因此合同一定是错误的。该过程使用参数f
,它是一个函数。
合同具有两个参数:
x
是列表xs
]的元素>a
是累加器当我将合同更改为:
(define foldr-map/c (parametric->/c [x a] (-> (-> x number? (cons/c number? number?)) a (listof x) (cons/c (listof a) a))))
我收到这样的错误:
foldr-map: broke its own contract promised: number? produced: #<a> in: the 2nd argument of the 1st argument of (parametric->/c (x a) (-> (-> x number? (cons/c number? number?)) a (listof x) (cons/c (listof a) a))) contract from: (function foldr-map) blaming: (function foldr-map) (assuming the contract is correct)
所以这时我迷路了。
我已经开始学习合同,并且我有这样的程序:(定义/合同(folder-map fa xs)foldr-map / c(定义(it xs ys)(if(null?xs)(cons ys a) (让* [[p((cdr ...
我找到了解决方案: