[Haskell-cafe] Trouble with record syntax and classes
rossberg at ps.uni-sb.de
Tue Feb 27 10:32:31 EST 2007
<ajb at spamcop.net> wrote:
> 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.
I would add:
4. Define a namespace, also called "Foo", for a set of values (and
probably nested classes).
> 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".
4. You define a new namespace using "module".
Andreas Rossberg, rossberg at ps.uni-sb.de
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