Here is an article I wrote about constraints in OpenLaszlo and Garnet:
Constraints and Prototypes in Garnet and Laszlo
Oliver Steele (one of the architects of OpenLaszlo, and a great Lisp programmer) describes how OpenLaszlo supports "instance first development" and "rethinking MVC":
I've used OpenLaszlo a lot, and I will testify that the "instance first" technique that Oliver describes is great fun, works very well, and it's perfect for the kind of exploratory / productizing programming I like to do. (Like tacking against the wind, first exploring by creating instances, then refactoring into reusable building block classes, then exploring further with those...)
OpenLaszlo's declarative syntax, prototype based object system, xml data binding and constraints support that directly and make it easy.
OpenLaszlo's declarative syntax and compiler directly support instance first development (with a prototype based object system) and constraints (built on top of events and delegates -- the compiler parses the constraint expressions and automatically wires up dependences), in a way that is hard to express elegantly in less dynamic, reflective languages. (Of course it was straightforward for Garnet to do with Common Lisp macros!)