完成编译指示不能防止出现不完整的模式警告 [英] COMPLETE pragma doesn't prevent incomplete-patterns warning

问题描述

我为一个类似列表的类制作了两种模式视图.

I made two pattern views for a list-like class.

infixr 5 :<
pattern (:<) :: Stream s => Token s -> s -> s
pattern b :< bs <- (uncons -> Just (b, bs))
  where b :< bs = cons b bs

pattern Nil :: Stream s => s
pattern Nil <- (uncons -> Nothing)
  where Nil = empty

uncons 签名: uncons :: ::(Stream s)=>s->也许(令牌，s).

假设我也有使用这些模式的函数，

Suppose I also have function that uses these patterns like that:

foo (b:<bs) = …
foo Nil = …

在这种情况下，模式匹配非常详尽，我想指定它.

It's obvious in this case that pattern matches are exhaustive, and I would like to specify that.

所以我尝试使用完整的杂注表示: {-#COMPLETE Nil，(:<)::流#-} .

So I tried using a COMPLETE pragma like that: {-# COMPLETE Nil, (:<) :: Stream #-}.

那是行不通的，警告没有发到任何地方.为什么不呢?可以做我想做的事吗?

That didn't work, warning didn't go anywhere. Why didn't it? Is it possible to do what I want?

推荐答案

COMPLETE 编译指示只能附加到类型，而不能附加在类型类上.当前尚无法指定适用于给定类的所有类型的完整模式集.

COMPLETE pragmas can only be attached to types, not type classes. There is currently no way to specify a complete set of patterns that works for all types of a given class.

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