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Comment by ff_ | Hacker News Reader

I don't know about OCaml, but Haskell has typeclasses (which look like "polymorphic interfaces"?) so you can define functions generically and put a typeclass constraint to make them work on a certain class of types. E.g. your avg function would be of type:

avg :: Num a => a -> a -> a

Where your "a" is a number (that is, a type that implements the Num typeclass)

This would work out of the box on floats, ints, etc

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The signature is not really helpful. Can you show me how do you implement the actual function?

If you have operators that are typed like + and +. how can you make this work with Num?

Also the + operator is typed with Num; from a Haskell repl:

  λ> :t (+)
  (+) :: Num a => a -> a -> a

In case of average we need /:

  λ> :t (/)
  (/) :: Fractional a => a -> a -> a

So our type is going to be constrained by Fractional instead of Num). So an implementation could be (from here [1]):

  import Data.List
  average :: (Real a, Fractional b) => [a] -> b
  average xs = realToFrac (sum xs) / genericLength xs

[1]: https://stackoverflow.com/questions/2376981

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