Never Design a Language is the current post on Bertrand Meyer’s blog, and you’d expect Bertrand to be someone who knows what he’s talking about on this subject. Although, I don’t think it’s too unkind to point out that he didn’t take his own advice at least once.

Bertrand’s main point (and it’s a good one) is that the API is more important than the concrete syntax for invoking any operations. Perhaps I’d say “conceptual model” rather than API, but once an API has pre & post conditions & invariants then you’re pretty much talking about the same thing. But the API – indeed the concrete syntax – are also important: the real difficulties (perhaps the real reason why never to design a language) is that the devil is in the details of the feature interactions.

For example: Grace objects are self-sufficient (they’re not defined by a class or metaobjects). The object constructor expressions that create single objects support inheritance to abbreviate descriptions. Grace class declarations can be seen as creating a “factory” object that creates other objects (the class’s instances). So how should inheritance work between classes? If classes inherit, there is a clear (subtyping) relationship between their instances — but should the subclass’s factory likewise be a subtype of its superclass’s factory? Sounds good — but it turns out that requires a Family Polymorphic type system. Oops. Isn’t Grace supposed to be simple, easy to learn, easy to teach?

The real point of this post is to say that we’re not dead yet: in fact, below the surface, we’re making good progress: we have outlines of a module system for Grace, a solid design for pattern matching (we think), parser combinators, a specification of the concrete syntax (done in Grace via the parser combinators), and progress on prototype implementations. We’re working towards a consolidated spec that will include much of this and perhaps be worth some scrutiny – and once that is done, we’ll be able to blog about the motivation and design of each of these in detail.

But we’d like to get the spec out first. So, watch this space…