BETA is an instructive example in the history of OO programming, but never really took off.
The language does contain a few worthwhile ideas. In languages like Java or C++, subclass methods can over-ride superclass methods, and optionally dispatch to the superclass. In BETA, the "inner" form of dispatch means that the superclass always controls the caller's interface, and optionally dispatches to the subclass. That's very attractive when the superclass doesn't necessarily trust subclass over-rides to maintain important invariants. BETA also goes a big step beyond the getX/setX methods that commonly export attributes. In BETA, the same syntax is used for assignment to variables as for methods calls. You can't tell the difference, by looking at the caller, whether you're looking at a reference to an attribute or to an accessor method. Although odd in other respects, that's one case where the assignment/call unification can solve some problems. Constructs for parallel programming a strength, but exception handling is a weakness and the <<SLOT>> interface definitions go beyond just weak. Scoping for programming in the large is mostly in the writers' imaginations.
The language uses peculiar syntax. The least of the problems is that the "left hand side" of an assignment is on the right, and that many syntactic markers rival C trigraphs for ugliness. The Danish authors generally use very good English, but often choose inexplicable terms (like "pattern") for familiar notions (like C++ "class"). As noted elsewhere, this is the only BETA book around, so there's really nothing to compare it to.
I'm not aware of any current use of BETA, so this book is of historical interest only. It's instructive as a bad example in choosing syntax for a programming language, but also as a good example for some of its creative semantics. I look forward to seeing some of those good ideas enter the main stream.
//wiredweird
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