SmallCheck生成满足不变量的数据

问题描述

我想用SmallCheck来测试我的代码。我设法生成了任意的int对列表，但这不是我的类型应该包含的。该列表表示一组范围，其中 [1,3]，[4,6）将被编码/存储为 [（1,3 ），（4,6）] 。

这些是我范围规格化形式的不变量：

  fst a< snd a 
 snd a< fst b其中a在列表中的b之前
  

我想与SmallCheck进行沟通，以便它不会产生我丢弃的大量值，因为它们不能满足我的不变量，但也许这是不可能的。

如何生成满足我的不变量的列表？

内置int类型的应用程序特定类型（Int，List）。这个建议不仅适用于SmallCheck，也适用于任何语言的任何软件。

  data Interval = Interval（Int， Int）
 data Domain = Domain [Interval] 
  

编写执行不变量的智能构造函数。

  interval :: Int  - > Int  - >间隔
间隔x y =间隔（min x y，max x y） - 如果您想要这个
 
域:: [间隔]  - > Domain 
 domain ints = Domain ...（可以将间隔排序，也许将它们合并）
  

I want to use SmallCheck to test my code. I managed to generate arbitrary lists of pairs of ints, but that's not what my type should contain. The list represents a set of ranges, where [1,3),[4,6) would be encoded/stored as [(1,3),(4,6)].

These are the invariants for the normalized form of my ranges:

fst a < snd a
snd a < fst b where a is before b in the list

I would like to communicate this to SmallCheck so that it doesn't generate loads of values that I throw away, because they aren't satisfying my invariants, but maybe that's not possible.

How can I generate lists satisfying my invariants?

解决方案

Favour application-specific types over built-int types (Int, List). This is advice not just for SmallCheck, but for any piece of software, in any language.

data Interval = Interval (Int,Int)
data Domain = Domain [Interval]

Write smart constructors that enforce your invariants.

interval :: Int -> Int -> Interval
interval x y = Interval (min x y, max x y) -- if you want this

domain :: [Interval] -> Domain
domain ints = Domain ... (something that sorts intervals, and perhaps merges them)

Then use these to create Serial instances.

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