Edit detail for AxiomProgrammingDiscussion revision 1 of 4

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MetaClass versus Category

Axiom has a two-level type system consisting of categories and domains.

In Axom domains are
"classes":http://en.wikipedia.org/wiki/Class_(computer_science)
in the sense of
"object-oriented programming":http://en.wikipedia.org/wiki/Object-oriented_programming

The instances of domains are called objects. For example -1 is an object
of the domain Integer.

Each domain belongs to one or more categories. Categories specify the
external interface, i.e. what methods a domain exports plus optional
default implementations of some of these methods. For example the
domain Integer belongs to the category IntegerNumberSystem.

All types (domains and categories) in Axiom are "first-order", i.e.
they have some representation at run-time. They can be stored as
values of variables and they can be passed and returned as values of
functions. In other words Axiom domains are themselves objects.

So an Axiom category is actually a
"meta-class":http://en.wikipedia.org/wiki/Metaclass