有什么方法可以在 do / where / let 块中打印出变量的类型吗？

发布于 2024-11-25 07:31:27 字数 190 浏览 1 评论 0原文

有没有办法打印出 ghci 中嵌套变量的推断类型？考虑一下代码，

let f = g where
    g (x :: Int) = x

那么，最好查询 g 的类型，例如 :t fg 会打印出 Int ->整数。

原文

Is there any way to print out the inferred type of a nested variable in ghci? Consider the code,

let f = g where
    g (x :: Int) = x

then, it'd be nice to query the type of g, e.g. :t f.g would print out Int -> Int.

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

锦欢 2024-12-02 07:31:27

您可以通过给出适当的错误类型注释并检查错误消息来诱骗此信息。

*Main> let f = g where g::a; g (x::Int) = x

<interactive>:1:23:
    Couldn't match type `a1' with `Int -> Int'
      `a1' is a rigid type variable bound by...

You can coax this information out by giving an appropriately wrong type annotation and checking the error message.

*Main> let f = g where g::a; g (x::Int) = x

<interactive>:1:23:
    Couldn't match type `a1' with `Int -> Int'
      `a1' is a rigid type variable bound by...

回复收藏 0 原文

空宴 2024-12-02 07:31:27

ghci 调试器可以使用正确放置的断点为您打印它（但您需要在模块中加载定义）：

{-# LANGUAGE ScopedTypeVariables #-} 

f a = g a where
    g (x :: Int) = x

然后在 ghci 中：

Prelude> :l tmp2.hs
[1 of 1] Compiling Main             ( tmp2.hs, interpreted )
Ok, modules loaded: Main.
*Main> :b 3 9
Breakpoint 0 activated at tmp2.hs:3:7-9
*Main> f undefined
Stopped at tmp2.hs:3:7-9
_result :: Int = _
a :: Int = _
g :: Int -> Int = _
[tmp2.hs:3:7-9] *Main>

ghci debugger can print it for you with a properly placed breakpoint (but you'll need to load your definition within a module):

{-# LANGUAGE ScopedTypeVariables #-} 

f a = g a where
    g (x :: Int) = x

Then in ghci:

Prelude> :l tmp2.hs
[1 of 1] Compiling Main             ( tmp2.hs, interpreted )
Ok, modules loaded: Main.
*Main> :b 3 9
Breakpoint 0 activated at tmp2.hs:3:7-9
*Main> f undefined
Stopped at tmp2.hs:3:7-9
_result :: Int = _
a :: Int = _
g :: Int -> Int = _
[tmp2.hs:3:7-9] *Main>

回复收藏 0 原文

~没有更多了~