为什么这两个函数得到不同的结果？

Question

在源文件中：

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addV1 x y = (if x > y then y else x) + 5\naddV2 = \\x -> \\y -> (if x > y then y else x) + 5\n

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在 ghci 中：

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ghci> :l h.hs\nghci> addV1 4.5 10\n\n<interactive>:1083:1: warning: [-Wtype-defaults]\n    \xe2\x80\xa2 Defaulting the following constraints to type \xe2\x80\x98Double\xe2\x80\x99\n        (Show a0) arising from a use of \xe2\x80\x98print\xe2\x80\x99 at <interactive>:1083:1-12\n        (Ord a0) arising from a use of \xe2\x80\x98it\xe2\x80\x99 at <interactive>:1083:1-12\n        (Fractional a0)\n          arising from a use of \xe2\x80\x98it\xe2\x80\x99 at <interactive>:1083:1-12\n    \xe2\x80\xa2 In a stmt of an interactive GHCi command: print it\n9.5\nghci> addV2 4.5 10\n\n<interactive>:1084:7: error:\n    \xe2\x80\xa2 No instance for (Fractional Integer)\n        arising from the literal \xe2\x80\x984.5\xe2\x80\x99\n    \xe2\x80\xa2 In the first argument of \xe2\x80\x98addV2\xe2\x80\x99, namely \xe2\x80\x984.5\xe2\x80\x99\n      In the expression: addV2 4.5 10\n      In an equation for \xe2\x80\x98it\xe2\x80\x99: it = addV2 4.5 10\n

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当我加载源文件时，我确实收到以下警告：

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h.hs:10:1: warning: [-Wmissing-signatures]\n    Top-level binding with no type signature:\n      addV1 :: (Num a, Ord a) => a -> a -> a\n   |\n10 | addV1 x y = (if x > y then y else x) + 5\n   | ^^^^^\n\nh.hs:11:1: warning: [-Wmissing-signatures]\n    Top-level binding with no type signature:\n      addV2 :: Integer -> Integer -> Integer\n   |\n11 | addV2 = \\x -> \\y -> (if x > y then y else x) + 5\n   | ^^^^^\n\nh.hs:11:46: warning: [-Wtype-defaults]\n    \xe2\x80\xa2 Defaulting the following constraints to type \xe2\x80\x98Integer\xe2\x80\x99\n        (Num a0) arising from a use of \xe2\x80\x98+\xe2\x80\x99 at h.hs:11:46\n        (Ord a0) arising from a use of \xe2\x80\x98>\xe2\x80\x99 at h.hs:11:27\n    \xe2\x80\xa2 In the expression: (if x > y then y else x) + 5\n      In the expression: \\ y -> (if x > y then y else x) + 5\n      In the expression: \\ x -> \\ y -> (if x > y then y else x) + 5\n   |\n11 | addV2 = \\x -> \\y -> (if x > y then y else x) + 5\n   |                                              ^\nOk, one module loaded.\n

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非常感谢！

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编辑：\n似乎当从源文件加载这些函数时，haskell 决定第二个函数应默认为 Integer。但是当我在 ghci 命令行定义这两个函数时，它们都具有相同的类型：

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ghci> addV1 x y = (if x > y then y else x) + 5\n\n<interactive>:1093:1: warning: [-Wname-shadowing]\n    This binding for \xe2\x80\x98addV1\xe2\x80\x99 shadows the existing binding\n      defined at h.hs:2:1\nghci> :t addV1\naddV1 :: (Num a, Ord a) => a -> a -> a\nghci> addV2 = \\x -> \\y -> (if x > y then y else x) + 5\n\n<interactive>:1095:1: warning: [-Wname-shadowing]\n    This binding for \xe2\x80\x98addV2\xe2\x80\x99 shadows the existing binding\n      defined at h.hs:3:1\nghci> :t addV2\naddV2 :: (Num a, Ord a) => a -> a -> a\n

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编辑：\n当我将类型签名添加到源文件时，两个函数都执行良好：

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addV2 :: (Num a, Ord a) => a -> a -> a\naddV2 = \\x -> \\y -> (if x > y then y else x) + 5\n

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我刚刚开始使用 haskell。我想我在这里学到的教训是，始终提供显式类型声明很重要，这正是我计划做的事情（只是做书上的练习）。

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