替换=>代替 - >在函数类型签名中 [英] Replacing => in place of -> in function type signature

问题描述

我刚才注意到，如果不是 - > ，我在类型签名定义中写入 => 的函数，它不会导致编译时错误。示例代码：

  mysum :: Num a => [a] => a  -  Notice =>在列表[a] 
 mysum [] = 0 
之后[mysum xs] = x + mysum xs 
  

为什么会发生这种情况？有没有办法避免这种情况？

使用的编译器：GHC 7.6.2

更新：在 ideone 中成功编译。

解决方案

这是GHC 7.6.2中的一个错误。你应该在最近的编译器中尝试它，如果它仍然没有提供错误，那么你应该提交一个错误报告。

其实，我认为这个bug已经在GHC 7.8中已知和修复。

I just observed that if instead of ->, I write => in the type signature definition of a function, it doesn't result in an compile time error. Example code:

mysum :: Num a => [a] => a -- Notice => after the list [a]
mysum [] = 0
mysum (x:xs) = x + mysum xs

Why does this happen ? And is there a way to avoid this ?

Compiler Used: GHC 7.6.2

Update: Successful compilation in ideone.

解决方案

This is a bug in GHC 7.6.2. You should try it in the most recent compiler and if it still doesn't give an error there, then you should file a bug report.

Actually, I think this bug is already known and fixed in GHC 7.8.

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