How does Haskell handle overloading polymorphism?

Question

I have a question about Haskell polymorphism.

As I\'ve learned, there are two types of polymorphism:

1. Parametric: where you do not spe

Answer 1

Basically overriding is quite different in Haskell, although you can do something similiar.

I. Use Classes as selected answer.

class YesNo a where  
    yesno :: a -> Bool  

You have to implement it using instance, and then you can use it like this:

> yesno $ length []  
False  
> yesno "haha"  
True  
> yesno ""  
False  
> yesno $ Just 0  
True  
> yesno True  
True  
ghci> yesno EmptyTree  
False  
> yesno []  
False  
> yesno [0,0,0]  
True  

http://learnyouahaskell.com/making-our-own-types-and-typeclasses

II. Use pattern matching of type constructor, such as:

data Shape = Circle Float Float Float | Rectangle Float Float Float Float 
surface :: Shape -> Float  
surface (Circle _ _ r) = pi * r ^ 2  
surface (Rectangle x1 y1 x2 y2) = (abs $ x2 - x1) * (abs $ y2 - y1)

and then you can use them like this:

> surface $ Circle 10 20 10  
314.15927  
> surface $ Rectangle 0 0 100 100  
10000.0

http://learnyouahaskell.com/making-our-own-types-and-typeclasses

III. Have the "oveloaded" function in sepatate module, but you will need to prefix the import name or qualified imports name

http://learnyouahaskell.com/modules