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如何定义这个无点?

let argmax m = (fst.(maximumBy (comparing snd)).(zip [0..])) m

按预期工作。最合乎逻辑的似乎只是放弃m这样的:

let argmax = (fst.(maximumBy (comparing snd)).(zip [0..]))

可以在 ghci 中定义,但是用它来调用它argmax [1,3,4,5,6,1]给了我

<interactive>:103:9:
    No instance for (Num ())
      arising from the literal `1'
    Possible fix: add an instance declaration for (Num ())
    In the expression: 1
    In the first argument of `argmax', namely `[1, 3, 4, 5, ....]'
    In the expression: argmax [1, 3, 4, 5, ....]

我认为这与类型有关:

:t (fst.(maximumBy (comparing snd)).(zip [0..]))
:: (Enum c, Num c, Ord a) => [a] -> c

对于点版本:

argmax :: (Enum c, Num c, Ord a) => [a] -> c

对于无积分版本:

argmax :: [()] -> Integer

这是 ghci 诡异还是我做错了什么?

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