Re: [Haskell-cafe] What's the problem with iota's type signature?

On Thu, May 28, 2009 at 10:33 AM, michael rice wrote:

Still exploring monads. I don't understand why the type signature for double is OK, but not the one for iota.

Michael

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--double :: (Int a) => a -> Maybe b --double x = Just (x + x)

Prelude> let double x = Just $ x + x Prelude> Just 2 >>= double Just 4 You can define double as double x = return $ x + x Prelude> let double x = return $ x + x Prelude> Just 2 >>= double Just 4

iota :: (Int a) => a -> [b] iota  n = [1..n]

--usage: [3,4,5] >>= iota --should produce [1,2,3,1,2,3,4,1,2,3,4,5]

I did. Prelude> let iota n = [1..n] Prelude> [3,4,5] >>= iota [1,2,3,1,2,3,4,1,2,3,4,5] lee