G'day all.
Quoting Aaron McDaid
'class' in Haskell doesn't mean the same as 'class' in C++ or Java. I found it easier at first to thing of them as: A Haskell 'class' is more like a Java interface. Haskell types are more like what you might think of as 'class'es. Haskell 'instance' means Java 'implement' There is no word that means that same as 'instance' from Java/C++ terminology. I suppose we would call them 'values' or something. Somebody more knowledgeable can describe the etymology of the terms, but these 3 observations should help.
When you type "class Foo" in Java or C++, it does three things: 1. It declares a new type called "Foo". 2. It declares a _set_ of types (i.e. a "class"). 3. It declares that the type Foo (and all of its subtypes) is a member of the set of types Foo. In Haskell, these three operations are distinct. 1. You declare a new type using "data" or "newtype". 2. You declare a new set of types using "class". 3. You declare that a type is a member of a class using "instance". Cheers, Andrew Bromage