问题
Is there a simple function to round a Double or Float to a specified number of digits? I've searched here and on Hoogle (for (Fractional a) => Int -> a -> a), but haven't found anything.
回答1:
Not sure whether any standard function exists, but you can do it this way:
(fromInteger $ round $ f * (10^n)) / (10.0^^n)
回答2:
It depends on what you are going to do with the rounded number.
If you want to use it in calculations, you should use Data.Decimal from Decimal library.
If you want just to format the number nicely, you should use Text.Printf from the standard library (base package).
回答3:
λ: ((/100) $ fromIntegral $ round (0.006 * 100)) == 0.006
λ: False
λ: ((/100) $ fromIntegral $ round (0.06 * 100)) == 0.06
λ: True
来源：https://stackoverflow.com/questions/12450501/round-number-to-specified-number-of-digits