您可以通过给出一个适当的错误类型注解并检查错误消息来诱导出这些信息。

*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...

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ghci调试器可以为你打印一个正确放置的断点（但你需要在一个模块中加载你的定义）：

{-# LANGUAGE ScopedTypeVariables #-} 

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

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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>

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