Haskell - how to cast types?

I am trying to do following:

10 ** length xs * x

but I get:

No instance for (Floating Int) ar开发者_JAVA技巧ising from a use of `**'

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You can use ^ to raise to an integral power. There's no need to convert to float here.

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Besides @sepp2k's answer, if you somehow really need to convert from an integer to some other types of Num, use fromIntegral.

-- # fromIntegral :: (Integral a, Num b) => a -> b

10 ** fromIntegral (length xs) * x