In the past year I have been passionately fighting what Simon Peyton Jones calls "the effects monster", although often it feels like I am fighting windmils instead. No useful programs can be written without effects, but effects turn bad when they are observable from within the program itself. Instead we should strive for encapsulating effects such that they become harmless first class pure values, but more on that in the future. In this first installment in a longer series on the perils of side-effects, we will look at one of the most beautiful examples of observable effects, namely closures and variable capture in imperative languages.
Nearly two years ago I posted Beyond LINQ: A Manifesto For Distributed Data-Intensive Programming on this forum. Now, within a period of a few weeks, both LINQ as well as a rather different realization of my original post-LINQ plans are shipping. I am particularly proud to announce that a community preview of Volta is available for immediate download from http://labs.live.com/volta/.
Volta is a collection of tools that enable programmers to develop asynchronous and distributed (including but not limited to AJAX) applications by successive refactoring of normal, sequential, programs written in standard .NET languages (this CTP requires Visual Studio 2008) and deploy the resulting applications on a wide variety of target platforms (this CTP supports Internet Explorer and FireFox). Or as I sometimes say when I am trying to sound like a marketing person â€œ Volta stretches the .NET platform to cover the Cloud.â€ Volta allows programmers to concentrate on the essential complexity involved in building AJAX application and have our tools take care of the gory details and accidental complexity.
When using Volta, programmers can specify their intent of running certain classes on the server by decorating the class declaration using a
Volta embraces the Lean Programming principle of delaying irreversible decisions until the last possible responsible moment. In particular we want to delay decisions about distribution as long as possible. To help developers make informed decisions about the distribution a program across tiers, the Rotunda profiler from MSR is fully integrated in the Volta toolchain. By automatically injection hooks for all interesting events, Rotunda creates trace information that can be inspected using the standard Service Trace Viewer tool.
When I speak about Volta or show a demo, the best compliment I can get is when people say this is â€œtrivialâ€ or â€œreally straightforwardâ€. The best tools are those that do their work unobtrusive hidden in the background. Anyway, with the holidays around the corner you may have some spare cycles to give Volta a spin and let us know what you think!
The day of the beast has passed without any noticeable effect; Bill Gates has announced his retirement and the Microsoft stock actually goes up. The coast finally seems safe for another post on the Lang .NET symposium!
Registration for this heavily debated event is now open. I believe that we have a very interesting set of non-Microsoft invited speakers including Gilad Bracha from Sun, William Cook from UT Austin, John Gough from QUT, Miguel de Icaza from Novel, and Shriram Krishnamurthi from Brown; Microsoft folks including Mike Barnett, Gary Flake, Jim Hugunin, Polita Paulus, Don Syme, and Paul Vick; and a fine line-up of submitted papers.
Hope to see you all in Redmond this August!
Gilad Is Right (Confessions From A Recovering Typoholic)
If you have not seen Gilad Bracha's talk on pluggable and optional type systems or read the corresponding paper, I really urge you to do so (or invite Gilad as the invited talk in your conference or workshop). The thesis of optional and pluggable type systems is that type-systems should be an optional layer on top of an otherwise dynamically typed system in such a way that (a) types cannot change the run-time behavior of the program, and (b) they cannot prevent an otherwise legal program form compiling or executing. In short what Gilad is saying is that you should not depend on static typing. However, we all know that static type-systems are very addictive, like the finest crack from the backstreets of the ghetto, and I will stop beating around the bush and confess "I am Erik, and I am a (recovering) typoholic".
To illustrate the tantalizing power of static typing, take the concept of axis members in Visual Basic 9. In our first design we keyed "late" binding over XML on the static type of the receiver. For example take the following element declaration
Dim Pu As XElement = <Atom AtomicWeight="244"> <Name>Plutonium</Name> <Symbol AtomicNumber="94">Pu</Symbol> <Radioactive>true</Radioactive> </Atom>
Since the static type of
Besides the child axis, we have special support for attribute axis, written using an
To solve our pain, we recently decided to also introduce special syntax for the child axis and write
I hope that you agree that we have masked out the seductive voices of the static typing sirens by providing a syntax that is more beautiful and a semantics that is much simpler than our previous one that relied heavily on static typing. Gilad is right!
The LINQ project as embodied by C# 3.0 and Visual Basic 9 brings concepts from functional programming such as type-inference, lambda-expressions, and most importantly monad comprehensions into mainstream object-oriented programming. This is a definitively exciting for the programming language community, but realistically, it is just a tiny step towards democratizing building distributed data-intensive applications. To merely approach that goal there is still much work to do in (at least) the following areas:
As you can imagine, this is a lot of work and it will keep us language geeks off the streets for a long, long, time! And in case you are currently wandering the streets looking for a job as a compiler writer, virtual machine hacker, tool smith, etc. drop me an email. We have several job openings available.
On Wednesday October 19, 2005, Mads Torgersen, Amanda Silver, and yours truly will be presenting a BOF on LINQ in the Royal Palm Salon 1+2, 5:00 â€“ 7:30pm during OOPSLA 2005 in the Town & Country Resort & Convention Center in San Diego, CA.
With three language geeks (one from VB land, one ex-academic from the Java side, and one ex-academic from the Haskell side) presenting, this should be a fun night.
Slides The slides for the presentation are here.
The call for papers for FLOPS 2006 is now out.
FLOPS benefits from an eclectic mix of FP and LP papers,
We have two excellent invited speakers.
Submission deadline is 11 November 2005,
For those interested in the new VB9 language, there is an interview on DDJ with me and my partners in crime Paul Vick, Amanda Silver, together with our more pointy haired, but good, friends Alan Griver, Rob Copeland, Jay Roxe.
Over the last couple of months, both my existence and my judgments have been questioned several times on my favorite programming languages waterhole :-)
In the mean time, I was busily working with the SQL, XML, C# and the Visual Basic teams on language integrated query, or as it is now called project LINQ. In particular since early this year I am collaborating with Amanda Silver, Paul Vick, and Rob Copeland and Alan Griver on what has become my programming language of choice Visual Basic.
If you look closely at the new features introduced to C# and Visual Basic in the context of LINQ, you will recognize many familiar concepts that are regularly discussed on LTU ranging from monads, to meta-programming, lambda expressions, XML programming, to the relationship between static and dynamic typing.
The LINQ project consists of a base pattern of query operators (compare to the monad primitives) such as Select (map), SelectMany (concatMap), Where (filter), OrderBy (sort), and GroupBy (groupBy) on top of which Visual Basic and C# define query comprehensions (compare to monad comprehensions) that Â facilitate querying objects, relational data and XML. The C# syntax for query comprehensions is similar to FLWOR expressions, while the Visual Basic syntax stays close to SQL including aggregation.
In addition to the language extensions and base operators, LINQ provides two supplementary domain-specific APIs namely DLinq (compare to HaskellDB) for SQL relational data access, and XLinq (compare to HaXml) for XML hierarchical data access. Besides query comprehensions, Visual Basic provides deep XML integration with XML literals and XML late binding on top of XLinq (compare to Haskell Server Pages, XMl, Comega).
Both Visual Basic and C# have added several additional language extensions in support of LINQ, including local type inference (the type of local variable declarations are inferred from their initializers), lambda expressions (with type inference), local functions, anonymous types, object initializers, extension methods (static methods that can be called using instance method syntax), and meta-programming via expression trees (compare to type-based quote and quasi-quote).
Visual Basic adds some further enhancements to leverage the fact that it allows static typing where possible and dynamic typing where necessary in the form of relaxed delegates, improved nullable support, dynamic identifiers (makes writing meta-circular interpreters a breeze) and last but not least dynamic interfaces, or as I like to refer to them strong duck typing (compare to simplified qualified types/type classes).
LINQ general website: http://msdn.microsoft.com/netframework/future/linq/
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