在函数式编程中，不完整的模式匹配是否被认为是一种不好的做法 [英] In Functional Programming, is it considered a bad practice to have incomplete pattern matchings

问题描述

在 Haskell 或 F# 等函数式语言中使用非穷举模式是否通常被认为是一种不好的做法，这意味着指定的情况未涵盖所有可能的输入情况?

Is it generally considered a bad practice to use non-exhaustive pattern machings in functional languages like Haskell or F#, which means that the cases specified don't cover all possible input cases?

特别是，我应该允许代码因 MatchFailureException 等而失败，还是应该始终涵盖所有情况并在必要时明确抛出错误?

In particular, should I allow code to fail with a MatchFailureException etc. or should I always cover all cases and explicitly throw an error if necessary?

示例:

let head (x::xs) = x

或

let head list = 
    match list with
    | x::xs -> x
    |    _  -> failwith "Applying head to an empty list"

F#(与 Haskell 不同)对第一个代码给出警告，因为 []-case 没有被覆盖，但是为了简洁，我可以在不破坏函数样式约定的情况下忽略它吗?毕竟，MatchFailure 确实很好地说明了问题......

F# (unlike Haskell) gives a warning for the first code, since the []-case is not covered, but can I ignore it without breaking functional style conventions for the sake of succinctness? A MatchFailure does state the problem quite well after all ...

推荐答案

如果您使用构造函数 [] 而不是包罗万象的 _ 完成模式匹配，编译器将有机会告诉您再次查看该函数，并在有人向列表中添加第三个构造函数的那一天发出警告.

If you complete your pattern-matchings with a constructor [] and not the catch-all _, the compiler will have a chance to tell you to look again at the function with a warning the day someone adds a third constructor to lists.

我和我的同事在一个大型 OCaml 项目(200,000 多行)上工作，强迫自己避免部分模式匹配警告(即使这意味着编写 | ... -> assert false 不时)并避免所谓的脆弱的模式匹配"(以这样一种方式编写的模式匹配可能不会检测到构造函数的添加).我们认为可维护性是有益的.

My colleagues and I, working on a large OCaml project (200,000+ lines), force ourselves to avoid partial pattern-matching warnings (even if that means writing | ... -> assert false from time to time) and to avoid so-called "fragile pattern-matchings" (pattern matchings written in such a way that the addition of a constructor may not be detected) too. We consider that the maintainability benefits.

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