Language Design: Complexity, Extensibility, and Intention
Posted by Dan Vanderboom on June 14, 2010
The object-oriented approach to software is great, and that greatness draws from the power of extensibility. That we can create our own types, our own abstractions, has opened up worlds of possibilities. System design is largely focused on this element of development: observing and repeating object-oriented patterns, analyzing their qualities, and adding to our mental toolbox the ones that serve us best. We also focus on collecting libraries and controls because they encapsulate the patterns we need.
This article explores computer languages as a human-machine interface, the purpose and efficacy of languages, complexity of syntactic structure, and the connection between human and computer languages. The Archetype project is an on-going effort to incorporate these ideas into language design. In the same way that some furniture is designed ergonomically, Archetype is an attempt to design a powerful programming language with an ergonomic focus; in other words, with the human element always in mind.
Programming Language as Human-Machine Interface
A programming language is the interface between the human mind and executable code. The point isn’t to turn human programmers into pure mathematical or machine thinkers, but to leverage the talent that people are born with to manipulate abstract symbols in language. There is an elite class of computer language experts who have trained themselves to think in terms of purely functional approaches, low-level assembly instructions, or regular, monotonous expression structures—and this is necessary for researchers pushing themselves to understand ever more—but for the every day developer, a more practical approach is required.
Archetype is a series of experiments to build the perfect bridge between the human mind and synthetic computation. As such, it is based as much as possible on a small core of extensible syntax and maintains a uniformity of expression within each facet of syntax that the human mind can easily keep separate. At the same time, it honors syntactic variety and is being designed to shift us closer to a balance where all of the elements, blocks, clauses and operation types in a language can be extended or modified equally. These represent the two most important design tenets of Archetype: the intuitive, natural connection to the human mind, and the maximization of its expressive power.
These forces often seem at odds with each other—at first glance seemingly impossible to resolve—and yet experience has shown that the languages we use are limited in ways we’re often surprised by, indicating that processes such as analogical extension are at work in our minds but not fully leveraged by those languages.
Syntactic Complexity & Extensibility
Most of a programming language’s syntax is highly static, and just a few areas (such as types, members, and sometimes operators) can be extended. Lisp is the most famous example of a highly extensible language with support for macros which allow the developer to manipulate code as if it were data, and to extend the language to encode data in the form of state machines. The highly regular, parenthesized syntax is very simple to parse and therefore to extend… so long as you don’t deviate from the parenthesized form. Therefore Lisp gets away with powerful extensibility at the cost of artificially limiting its structural syntax.
In Lisp we write (+ 4 5) to add two numbers, or (foo 1 2) to call a function with two parameters. Very uniform. In C we write 4 + 5 because the infix operator is what we grew up seeing in school, and we vary the syntax for calling the function foo(1, 2) to provide visual cues to the viewer’s brain that the function is qualitatively something different from a basic math operation, and that its name is somehow different from its parameters.
Think about syntax features as visual manifestations of the abstract logical concepts that provide the foundation for all algorithmic expression. A rich set of fundamental operations can be obscured by a monotony of syntax or confused by a poorly chosen syntactic style. Archetype involves a lot of research in finding the best features across many existing languages, and exploring the limits, benefits, problems, and other details of each feature and syntactic representation of it.
Syntactic complexity provides greater flexibility, and wider channels with which to convey intent. This is why people color code file folders and add graphic icons to public signage. More cues enable faster recognition. It’s possible to push complexity too far, of course, but we often underestimate what our minds are capable of when augmented by a system of external cues which is carefully designed and supported by good tools.
Imagine if your natural spoken language followed such simple and regular rules as Lisp: although everyone would learn to read and write easily, conversation would be monotonous. Extend this to semantics, for example with a constructed spoken language like Lojban which is logically pure and provably unambiguous, and it becomes obvious that our human minds aren’t well suited to communicating this way.
Now consider a language like C with its 15 levels of operator precedence which were designed to match programmers’ expectations (although the authors admitted to getting some of this “wrong”, which further proves the point). This language has given rise to very popular derivatives (C++, C#, Java) and are all easily learned, despite their syntactic complexity.
Natural languages and old world cities have grown with civilization organically, creating winding roads and wonderful linguistic variation. These complicated structures have been etched into our collective unconscious, stirring within us and giving rise to awareness, thought, and creativity. Although computers are excellent at processing regular, predictable patterns, it’s the complex interplay of external forces and inner voices that we’re most comfortable with.
Risk, Challenge & Opportunity
There are always trade-offs. By focusing almost all extensibility in one or two small parts of a language, semantic analysis and code improvement optimizations are easier to develop and faster to execute. Making other syntactical constructs extensible, if one isn’t careful, can create complexity that quickly spirals out of control, resulting in unverifiable, unpredictable and unsafe logic.
The way this is being managed in Archetype so far isn’t to allow any piece of the syntax tree to be modified, but rather to design regions of syntax with extensibility points built-in. Outputting C# code as an intermediary (for now) lays a lot of burden on the C# compiler to ensure safety. It’s also possible to mitigate more computationally expensive semantic analysis and code generation by taking advantage of both multicore and cloud-based processing. What helps keep things in check is that potential extensibility points are being considered in the context of specific code scenarios and desired outcomes, based on over 25 years of real-world experience, not a disconnected sense of language purity or design ideals.
Creating a language that caters to the irregular texture of thought, while supporting a system of extensions that are both useful and safe, is not a trivial undertaking, but at the same time holds the greatest potential. The more that computers can accommodate people instead of forcing people to make the effort to cater to machines, the better. At least to the extent that it enables us to specify our designs unambiguously, which is somewhat unnatural for the human mind and will always require some training.
So much of the code we write is driven by a set of rituals that, while they achieve their purpose, often beg to be abstracted further away. Even when good object models exist, they often require intricate or tedious participation to apply (see INotifyPropertyChanged). Having the ability to incorporate the most common and solid of those patterns into language syntax (or extensions which appear to modify the language) is the ultimate mechanism for abstraction, and goes furthest in minimizing development effort. By obviating the need to write convoluted yet routine boilerplate code, Archetype aims to filter out the noise and bring one’s intent more clearly into focus.
This entry was posted on June 14, 2010 at 8:22 pm and is filed under Archetype Language, Composability, Design Patterns, Language Extensions, Language Innovation, Linguistics, Metaprogramming, Object Oriented Design, Software Architecture. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.