many problems solved by complicated features in a purely object-oriented language are solved by a rich set of non-object features such as

Douglas Auclair's

Dylan, like other object-oriented programming languages (OOPLs), has classes, objects, functions and data. But what separates Dylan from most other well-known OOPLs is that it combines covariant and contravariant inheritance. "Balderdash!" you exclaim; what does this mean? Dylan allows you to associate functions with classes without damaging the preexisting class interface. This allows you to modify behavior of built-in classes, of your own classes, and classes that you do not have the source code. In other words, Dylan incorporates the Visitor(331) design pattern directly and naturally.

Behavior can be added to existing classes without subclassing or modifying the source code of those classes. Access to the source code is not even required. This is a direct result of the generic function object model.

Gregory Sullivan and Jonathan R. Bachrach

Dylan is the most ambitious attempt to date to add modern syntactic extension features to an infix language.

Ashley Yakeley

In Dylan, everything is an object, a direct instance of exactly one class.

Dylan has union types, limited types and singletons, all of which can be used as variable and constant types and specialising types in generic functions and methods.

Dylan has libraries for hiding implementations, and the ability to seal classes, generic functions and domains of generic functions to those libraries.

Jason Trenouth

Interactive programming languages like Dylan, Common Lisp and Smalltalk provide the kind of immediate feedback that emancipates developers and frees them to roam over the application space without being constrained by having to build custom test beds or utilize restricted scripting languages.