任何方式在do / while / let块中打印出一个变量类型？ [英] Any way to print out a type of a variable in a do / while / let block?

问题描述

有没有办法在 ghci 中打印出嵌套变量的推断类型？考虑代码，

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

然后，查询 g ，例如：t f.g 会打印出 Int - > Int 。

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

推荐答案

您可以通过给出错误的类型注释并检查错误消息。

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...

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