So what's a closure exactly ?

Should I follow the blogosphere more closely, I would have noticed that Neal Gafter had just been developing this idea in the context of closures for Java.

The precautionary principle

Designing language extensions is not just black art, we are trying to follow a certain number of principles. One of them could be called 'the precautionary principle", or as Guy Steele put it "planning for growth". In short, do not add features if they may hamper future developments. When in doubt, stay on the safe side. When facing a choice, if no argument stands out clearly in favor of one side or the other, devise restrictions in order to avoid making a choice rather than take the risk of having to carry the consequences of a wrong choice all over the language life time.

One specific example comes to mind : the design of "closures" for Java, which is currently a heavily debated topic. If you haven't been brainwashed by programming teachers, "closures" are a very natural thing: wrap some piece of code so that you can carry it away exactly like you would do for data. "Closures" are also the basic building block of lambda-calculus, widely recognized as the theoretical basis of computation, and available for decades in functional programming languages.

With "closures", you can define methods or functions that take as parameters not only data, such as integers or strings, but also things to do, in other words pieces of code that will be executed when you evaluate the parameter. If you're familiar to C, this is similar to a pointer to a function (often used as callbacks), with the difference that you do not have to provide a name, and that the type system makes sure that you're not breaking things. Outside the Java world, "closures" are commonplace in functional languages such as Caml and scripting languages such as JavaScript. "closures" have also recently been added to C#. As the story goes, "closures" where even on the feature list of the first version of the Java language, and were dropped because of time-to-market considerations.


The most widely publicized proposal for "closures for Java" today is named BGGA by its authors' initials, and I strongly feel that this proposal is breaking the precautionary principle mentioned above. Let us try to remove the quotes around the word "closure". Theoreticians and functional programming languages talk about "functions" and "functional languages". A closure in this context is an instance of a function that remembers part of the context where it has been defined, for instance the value of some local variables. In some sense, this object is "closed", hence the name:  it has its own copy of the context it needs, and can be carried away as a black box.

The problem is when you try to add functions to an imperative language such as Java. Variables in functional languages have one and only one value, while variables in imperative languages have values that can change in time; they refer to a memory location rather than to a mathematical value ("final" variables in Java are somewhat close to functional variables). Should a closure remember values or memory locations ? Said otherwise, if some value is changed within the closure, should the change be propagated to the original context ?

The BGGA answer is yes. I can see two reasons for this choice. One is about the list of features that a magazine would use for a comparative review : because most scripting languages today do that, if Java would appear as lacking a feature. The other reason is that closures in the BGGA proposal are in effect suggested as an answer for two really different things : macros (designing your own control structures) and functions (carrying away pieces of code). The meaning of what is a context, where should "return" return to, and so on, are totally different for macros and functions. Not surprisingly, macros and functions are compiled in very different ways.

My answer is no. This is not about some subjective notion of language aesthetics, this is about the precautionary principle. Closures are not only about writing more concise code. Intuition and theory tell us for instance that closures are the basic building blocks of parallel programming (google for "pi-calculus"). You want to be able to express distributed computation as closures that are dispatched among different processors or computers. But this is just plain impossible if closures are able to modify arbitrary locations in their originating context.

To put it shortly, the BGGA proposal for closures will go in the way of future language extension for parallel programming, which is the next "big thing" (most PCs sold today have 2 or 4 cores, and PCs with 100's of cores are not far away). The trade-off is between making a nice marketing announcement today and growing a language that will be able to handle multicore processing tomorrow.

One reason for this misunderstanding is the ambiguous meaning of the word "closure", hence the quotes. As you have guessed, I strongly recommend to drop this term and use instead "function" and "macro".


See also my first comment on this topic on Neil Gafter's blog and a few references about closures in general.

In the deep end.

Hello from Seattle ! Lauching our product so far away from home has been an experience with its share of panicking moments, such as when our presentation material got lost somewhere between two airports. It was finally delivered just before the exhibit started and we opened our booth on time.



During the first day we had representatives of most major players - we're talking world-class here - stopping at our booth. And many were enthusiastic about the product : « that's the way to go ! », they say. This has already translated into a dozen of qualified leads, articles in magazines with a world-wide audience, and a huge moral boost for the whole Ateji team.



Most french companies would first try to settle in their national market before attempting such a move. How strange. France would be about 2% of our market. Kick in other european countries and we may top 10%. Why building walls between yourself and your market? The fact that the product is developed in Paris is quite irrelevant. Even supporting clients on the other side of the globe is not much of an issue anymore using modern communication tools. I'd say it's more of a mental barrier.



Seattle is also the place where you find the most Starbucks cafés and the most venture capitalists per square kilometer (note for the locals: a kilometer is a kind of celsius mile). Before we had even recovered from jet-lag, our first seafood dinner ended with an introduction to an influential VC. That is just unthinkable in Paris.

The ever-expanding DSL syndrome

A DSL is a Domain Specific Language, a language designed for a particular application domain. You're likely to know already a few dozen DSLs : think of HTML, CSS and JavaFX (web), SQL (database), UML (modeling), COBOL and PL/1 (financial application), Fortran and Matlab (scientific applications), AutoCAD (3D design), Postscript (page design). Some more specialized DSLs are known only within their community : MLFi (finance), OPL, AMPL and GAMS (optimization), Lex and Yacc (parsing). Today there exist thousands of DSLs, and you could not imagine developing a software application without them. DSLs are important because they allow you to express quite directly the concepts you have in mind.

Most DSLs are subject to what I call the ever-expanding DSL syndrome : they come into existence as“small” languages specifically designed for expressing concepts specific to an application domain (they are often designed in-house by the domain experts, not by language specialists). But DSL users soon feel the need to express arbitrary expressions, to have access to more and more library functions, to access databases and web browsers, to handle programming-in-the-large via e.g. powerful type systems and modularization, to have better tools support, and so on.

As a result, DSL users are always waiting for a new feature, while DSL developers try to catch on by expanding the language and/or adding tool support, getting engaged in a never-ending spiral, in effect developing a general purpose language with a full-blown programming environment. This resulting language is obviously incompatible with anything existing, and is quite often plagued with quality problems and poor tooling support.

As an example, let us look at the new features advertised for existing modeling languages. The following excerpts are taken from the respective manufacturer's web sites : you will note that all the features mentioned here are unrelated to the domain of modeling, and are already present in mainstream general-purpose languages.

• AIMMS :
  
  
  
  • Web services
    
  
  
• AMPL :
  
  
  
  • Character strings
    
  • Database access
    
  • Looping and testing (writing "scripts")
    
  • Reporting and display
    
  
  
• GAMS :
  
  
  
  • Conditional statements
    
  
  
• OPL :
  
  
  
  • Connection with spreadsheets and relational databases
    
  • Scripting
    
  • Interactive development environment
    
  • External function calls
    

On the contrary, Ateji believes in designing DSLs that are "large" languages, namely DSLs designed as extensions of mainstream generalist languages. Rather than starting with a few domain-specific concepts and progressively adding additional features, we start with a full-featured general-purpose language and add domain-specific concepts.

The difference is striking : you will never complain again that your DSL doesn't allow you to add 1+1 (think CSS), since it already has all the features of a large programming language. Additional benefits are integration at the language level (DSL code and application code work on the same objects) and availability of state-of-the-art development environment and tools.

DSLs as extensions of mainstream languages also have a very fast learning curve. If you know the mainstream language, you'll only have to learn a few additional concepts. If you're a domain expert, you'll find a familiar language expressing the concepts of your domain. In both cases, you won't need to learn yet another different way of writing 1+1.

Preparing for Seattle

Ateji will be holding a booth at the Informs conference in Seattle, Nov. 4th to 8th. This is our first booth abroad, we'll be introducing our OptimJ language to the operational research community.

When you discover all the work this implies, developing software looks easy in retrospect. Of course, we first made sure the product works fine by running a large-scale beta-test program. Software developpers can still handle this.

But then you need to prepare brochures (how many ?), brush up your english (can you ripit plize ?), prepare your speech for the plenary session (sorry everybody, I promise, my demo used to work until 5min ago), make reservations for chairs and tables (apparently cheaper to buy and throw away than rent for 4 days), understand the union regulations (it is strictly forbidden to carry yourself your own luggage between the entrance door and the booth, but the 10,000kms before reaching the entrance door are ok), think about the booth décor, print posters, try to find an insurance company for civil liability (french companies simply don't want to ensure an event abroad -- I'm still looking, in case you know someone who can help), set up appointments with the press, and most important, research what kind of french sweets would be most successful in attracting prospective customers around our booth (provided the customs don't consider them as potentially lethal).

I used to work as a researcher, and even published a few involved theorems. A breeze. I managed the transition to becoming an engineer and now an entrepreneur. Cool. But setting up a booth in a conference is about to knock me down.

Well, I'll sleep in the plane. See you in Seattle !

Code generators

I have often been asked "After all, what you provide is a code generator ?". Well, yes and no.

Yes, because every compiler is a code generator. Whether you generate assembly code, virtual machine instructions or source code doesn't make much a difference, as far as execution of the program is concerned.

No, because the words "code generator" convey the idea that the "true" source code is the generated code, not the one you wrote. If you have ever played with a code generator, you have certainly noticed how little support there is for your original source code. You have probably felt the need to patch the generated code, and you have probably complained about the lack of tool support (think about debugging) at the original source level.

At Ateji we're indeed generating source code, for one specific reason : generating source code enables the reuse of all legacy software engineering tools and techniques available in the Java ecosystem. It would actually have been easier to directy generate byte code for the JVM. But you never actually see the generated code : our languages extend Java or other mainstream general-purpose languages, so you won't ever need to patch the generated code. Our languages are integrated at the IDE level, so that you always work directly with the original source code that you wrote.

This is why we never use the word "code generator" when referring to our products : the generated source code does indeed exist, but is only an engineering artefact.

What's in a name

Choosing Ateji®  ("ah-teh-gee") as a company name came quite naturally : it relates to my personal experience (I used to live in Japan, and even spent some time teaching japanese language), and it reflects quite well the goal we are trying to achieve.

An ateji is a japanese technique for associating ideographics characters with words (http://en.wikipedia.org/wiki/Ateji). A computer scientist would say associating syntax with semantics.

When the japanese began importing chinese characters, they had basically two choices : import the chinese reading (more precisely a japanized version of the chinese pronunciation) together with the characters, or use the chinese characters to denote the existing japanese words with their existing pronunciation. Both versions are still common today.

But the two languages do not always agree on what is a word. 'Otona' is the original japanese word for adult, written with the two chinese characters 'Big' + 'Person' : there is no way to cut 'otona' in two pieces in order to account for the two characters. This is the typical example of an ateji. Another example of an ateji is a kind of rebus, where unrelated characters are used on purpose to introduce some additional nuance. 'Kurabu', written with the kanjis 'Ku' (together), 'Ra' (fun) and 'Bu' (group), is a word created at the end of the 19th century to convey the meaning of 'club' while preserving a sound close to the original english pronunciation.

As you see, bringing together sound (syntax) and meaning (semantics) can be quite tricky, but also can provide deep insight when they are cleverly designed. This is precisely what we are trying to do at Ateji® : design languages where you can express what you need to express, bringing the important semantic concepts at the language level, while making sure syntax doesn't go in the way.