A typeclass is really nothing but a basic java/c# interface. The 4 things you do with an interface are: 1. Declare an interface 2. Describe the contract

A typeclass is really nothing but a basic java/c# interface. The 4 things you do with an interface are: 1. Declare an interface 2. Describe the contract of the interface 3. Declare that a datatype (or class) adheres to that interface 4. Provide an implementation of the the contract of the interface (fulfill the contract). A haskell Typeclass does exactly that. The keyword "class" is where you do #s 1 & 2. The keyword "instance" is where you do #'s 3 & 4. The only notable difference is: If an ISizable has int GetSize() method in haskell instead of the contract being int ISizable.GetSize(), it is static int GetSize(ISizable x). Or in Haskell: instance ISizable MyType where GetSize :: ISizable -> Int -- Note you don't actually type this line GetSize x = ...