Wednesday, June 29, 2011

PL nerds: learn cryptography instead

I've never studied cryptography. So when the paper Tahoe – The Least-Authority Filesystem fell in my lap, I was perplexed.

Using just two primitives, secret-key and public-key cryptography, they build an amazing solution to information storage. (Try to understand the two main diagrams in the paper. It's not hard, and it's amazing.)

Before encountering Tahoe-LAFS, cryptography was just a way to keep stuff secret to me. But cryptography also provides us with tools to design programs that wouldn't be possible otherwise.

Monday, June 27, 2011

State of Code interview

Zef Hemel has interviewed me for his weblog, State of Code: Lisp: The Programmable Programming Language. I don't feel qualified to be the "Lisp guy", but as you know, I never leave out an opportunity to blather about PLs.

Zef (@zef) is an academic developing mobl, a language for mobile apps, and is now working for a web-based IDE company, so the State of Code is a place to watch.

Wednesday, June 22, 2011

John Shutt's blog

John Shutt now has a blog: Structural insight.

John is pushing the envelope of Lisp with his Kernel programming language, a "dialect of Lisp in which everything is a first-class object". And when he says everything, he means it.

Not content with just first-class functions and continuations, John also wants first-class environments and first-class macros. Some fun LtU discussions in which John participated come to mind:

Thursday, June 16, 2011

David Barbour's soft realtime model

David Barbour is to me one of the most important thinkers on distributed programming languages and systems.

He frequently posts on LtU and on Ward's wiki.

(And he now has a blog!)

In this LtU post he describes a very interesting soft realtime programming model, reminiscent of Croquet/TeaTime:

I'm also using vat semantics inspired from E for my Reactive Demand Programming model, with great success.

I'm using a temporal vat model, which has a lot of nice properties. In my model:

  • Each vat has a logical time (getTime).
  • Vats may schedule events for future times (atTime, atTPlus).
  • Multiple events can be scheduled within an instant (eventually).
  • Vats are loosely synchronized. Each vat sets a 'maximum drift' from the lead vat.
  • No vat advances past a shared clock time (typically, wall-clock). This allows for soft real-time programming.

This model is designed for scalable, soft real-time programming. The constraints on vat progress give me an implicit real-time scheduler (albeit, without hard guarantees), while allowing a little drift between threads (e.g. 10 milliseconds) can achieve me an acceptable level of parallelism on a multi-core machine.

Further, timing between vats can be deterministic if we introduce explicit delays based on the maximum drift (i.e. send a message of the form 'doSomething `atTime` T' where T is the sum of getTime and getMaxDrift.

Previously: Why are objects so unintuitive

Sunday, June 12, 2011

Everything in JavaScript, JavaScript in Everything

We can now run Linux, LLVM bitcode, and a lot of other languages in JavaScript.

And we can run JavaScript in everything - browsers, servers, toasters, Lisp.

Like IP in networking, JavaScript is becoming the waist in the hourglass.

I don't know what it means yet, but it sure is exciting.

Friday, June 10, 2011

No No No No

// Note: The following is all standard-conforming C++, this is not a hypothetical language extension.
 assert( top( o-------o
|L \
| L \
| o-------o
| ! !
! ! !
o | !
L | !
L| !
o-------o ) == ( o-------o
| !
! !
o-------o ) );

Multi-Dimensional Analog Literals

Tuesday, June 7, 2011


In any language design, the total time spent discussing
a feature in this list is proportional to two raised to
the power of its position.

0. Semantics
1. Syntax
2. Lexical syntax
3. Lexical syntax of comments

(That is, twice as much time is spent discussing syntax
than semantics, twice as much time is spent discussing
lexical syntax than syntax, and twice as much time is
spent discussing syntax of comments than lexical syntax.)
(source, via Debasish Ghosh)