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我使用模式与模式匹配警卫观察时,一个有趣的现象,所有的警告开启警告模式守卫并非详尽无遗,即使它是
{-# OPTIONS_GHC -Wall #-}
module Mood where
data Mood = Happy
| Indifferent
| Sad
deriving Show
flipMood :: Mood -> Mood
flipMood Happy = Sad
flipMood Indifferent = Indifferent
flipMood Sad = Happy
flipMood' :: Mood -> Mood
flipMood' mood
| Happy <- mood = Sad
| Indifferent <- mood = Indifferent
| Sad <- mood = Happy
即使flipMood
和flipMood'
是几乎做同样的事情,我收到以下错误信息:
Mood.hs:15:1: Warning:
Pattern match(es) are non-exhaustive
In an equation for ‘flipMood'’: Patterns not matched: _
Ok, modules loaded: Mood.
,因此需要添加一个包罗万象的情况下,像
| otherwise = mood
以满足穷举检查器。
核心似乎只是这两个功能表现同样的罚款:
flipMood =
\ ds_dTh ->
case ds_dTh of _ {
Happy -> Sad;
Indifferent -> Indifferent;
Sad -> Happy
}
flipMood' = flipMood
随着优化关闭我得到以下核心输出,这似乎解释这种现象:
flipMood' =
\ mood_axV ->
case mood_axV of wild_X9 {
__DEFAULT ->
case wild_X9 of _ {
Indifferent -> Indifferent;
Sad -> Happy
};
Happy -> Sad
}
为什么它是这样表现吗?我错过了什么吗?
亲切的问候, raichoo
我想这解释的东西:) – raichoo 2015-02-11 13:04:20