Re: [Haskell-cafe] Re: Newbie question

So, the function type "(Num a)=>Integer->a" means that return value of this function can be cast to any particular instance of class Num. Ok. I have a my own class "class A a" and want to write function like this "f:: (A a)=>Integer->a". Can I do it? 2008/1/21, Jon Fairbairn :

"Alexander Seliverstov" writes:

...

How does caller choose which particular instance of Num they want?

They specify the type... or just pass the result to something that specifies the type. Try it in ghci:

Prelude> let f:: Integral i => Integer -> i; f = fromIntegral Prelude> let g :: Int -> Int; g = id Prelude> :t g (f 5) g (f 5) :: Int Prelude> let h :: Integer -> Integer; h = id Prelude> :t h (f 5) h (f 5) :: Integer Prelude>

...

What the difference between haskell class and interface in object-oriented languge such Java or C#?

Really they are completely different animals that look a lot alike because they serve similar purposes -- convergent evolution!

-- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk

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