Clojure 1.0 and git

I’m chipping away at my Mashup project tasks, namely an OAuth library for Twitter and other providers of protected resources. But I wanted to pass on a concrete contribution, so here are some tips about taking advantage of Clojure’s availability through git, and how to put your clojure-contrib library in sync with the big Clojure 1.0 release.

Date management for the mashup project

I’m posting the code I’ve written for date management in the mashup project. It’s just a sketch, really. There’s plenty of work to do to fill it out. But I wanted to post what I’ve got now.

A bit of Clojure at RubyNation 2009

Just a quick post to mention how Clojure was mentioned at the RubyNation conference in Reston last weekend.

I gave a lightning talk on day 2. Slides are posted. I only had 6 minutes, so I kept it brief. I don’t think I convinced a lot of the audience members to try it out. Afterwards, though, I got to talk to Aaron Bedra of Relevance, who was a technical editor for Stu’s book. He reports Clojure is actually in use on commercial projects. He’s a swell fellow.

Russ Olsen gave an impromptu talk at the end of the day about Clojure, Scala, Erlang, and Reia. Two things struck me about his approach to new languages. First, he gives a lot of important to “curb appeal”, or how nice the code looks. The parentheses bother him about Clojure and other lisps, same old story. The second thing, though, is the importance given to metaprogramming, which Ruby has brought into the forefront of a lot of developers’ minds. As Russ pointed out, any Lisp makes metaprogramming easy. So that may be a selling point for Clojure among Rubyists.

Coding Meeting May 16th 1pm at HacDC

We’re meeting face-to-face again on Saturday, May 16th at 1pm, at HacDC’s meeting space in DC. We’ll be meeting to hack some code on our mashup project. Check out the group’s google group for discussion and code produced so far.

Capstone project: stepping back for a moment

We have a capstone project, a reworking in Clojure of some of the mashup features of Yahoo Pipes. At our last meeting, Luke VanderHart presented a framework for building and connecting components. I’m going to recap the framework as well as a few philosophical decisions we hammered out. But I’m also going to invite you to take a look at the code with me, with an eye towards 1) understanding each bit and 2) replaying the development of the framework by starting with simple building blocks. Luke and I both agree that the current framework, although awesome, has leapfrogged the kind of discussion and collaboration we want to foster in the study group. So I’m going to try an experiment with coding in public. On this blog, and soon on github, we’re going to build the framework again, together, feature by feature, always embracing the principle of the simplest thing that could possibly work. We’ll build up the might of Luke’s framework, but in a way that we get there together. And we’ll probably make it better from all being involved.

Unofficial Clojure 1.0 release candidate

Clojure 1.0 is on the way, and as a result a lot of activity is occurring in the Subversion repository.  Revision 1357 of the Clojure source was proclaimed the likely release candidate, although a few minor changes have been checked in since.  Likewise, clojure-contrib revision 723 is the likely release candidate corresponding to 1.0. It should be interesting to watch what unfolds in the source until the actual release.

It’s not too late to contribute, and no contribution is too small.

-m

Meeting recap, Pipes/Tubes/Clinks, and next meeting info

At our latest meeting, we discussed macros and adopted a capstone project, an open-source Clojure implementation of some of the functions of Yahoo Pipes.

Macros

Regarding macros, we touched on the chain of events when a Clojure program is evaluated: evaluation runs from top to bottom, and each S-expression is macro-expanded (if possible) and then evaluated. If an expression expands into something that itself contains a macro, the the new macro expression will be expanded before it is evaluated. This allows a macro to use a previously defined function in the determination of its expansion.

“Macros” in Lisp are very different from “macros” in other languages, as they allow the programmer to use all the power of Lisp to determine the macro’s expansion. Macros are not first-class members of the Clojure language, however. You cannot use them as you use functions–you can not use them with map or apply, for example–because macroexpansion happens before an expression can be used in this way.

Seeing stars

We also talked about “star” functions and macros. The macroexpansion of an expression that uses ‘and‘ includes something called let*:

(macroexpand '(and 1 2 3))
->(let* [and__2863 1]
(if and__2863 (clojure.core/and 2 3) and__2863))

We concluded that you really aren’t supposed to see let*. You only do in this case because macroexpand completely expands the expression it is given, and it turns out that let is a macro whose definition includes the mysterious let*. In fact, a lot of Clojure’s core macros use “star” constructs that appear to be special forms. Some digging at the REPL confirmed that they are not symbols. Likely the “star” forms are transformed by the Clojure parser directly into Java. If you have some special knowledge about this, please post a comment or join our discussion group. We’d like to know more.

Capstone project

Luke presented the case for a project that implemented some of the Yahoo Pipes application. By general acclamation we adopted this project as our capstone. We’ve decided to spend the next two weeks hacking on the basic problems of the project ourselves, keeping in touch through the group mailing list. David set up a github repo for us, with a wiki for collaboration. There you can find the summary of our initial work on defining the project, thanks to Keith. Serge dug up Yahoo’s Pipes documentation.

We’re calling this Tubes right now (as in “teh tubes”), but a final decision on the name (I’m not saying I don’t like Tubes) is one of many tasks we’re deferring. Right now we just want to get things moving. Personally, I expect Paul to have it all done by this afternoon.

Multimethods on Sunday, April 19th, 1pm

Our next meeting will be at least partly devoted to the final topic in Stu’s book: multimethods. Read chapter 8 of Programming Clojure and bring any questions or comments you’d like to discuss. Please notice two things about the next meeting date: 1) it is in two weeks, not three; and 2) it is on a Sunday. The location is still HacDC’s meeting space at St. Stephens, and the time is still 1pm. We hope to see you there.

Project Proposal: Clojure Pipes

This Saturday, April 4, at our face-to-face meeting at HacDC, member Luke VanderHart will informally present a case for a Yahoo Pipes-like content aggregator as a possible capstone project. Interested?

Read up on Pipes.

Read Luke’s initial comments.

Of course, we’ll also discuss macros, including the material in Chapter 7 of Programming Clojure.

We hope to see you there: 1PM at HacDC.

March 14 meeting recap, next meeting April 4

We had another successful meeting at HacDC’s workshop on Saturday. We covered functional programming, walking through the concepts in the chapter from Programming Clojure and then putting them to work in translating a decision tree modeling program from Python to Clojure: watch for a separate announcement on how we will continue to work on that. We had an especially good time unraveling this bit of code…

(def head-fibo (lazy-cat [0 1] (map + head-fibo
                                      (rest head-fibo))))

…and understanding what’s less than optimal about it: that it keeps a reference to the head of a lazy sequence, and thus (nth head-fibo x) fails for large values of x.

Next, we’ll tackle macros on April 4th, at 1PM, at HacDC’s workshop. The reading is Chapter 7 of Programming Clojure. We’ll be looking at simple implementations of defmacro and reviewing different uses for macros. We may also tackle a bit of Paul’s proposed templating language, putting what we’ve learned to use. Hope to see you there!

Meeting Recap, Next Meeting, and Group Projects

The Study Group met on February 21st at 1PM at HacDC’s workshop to continue our discussion of concurrency.

We worked through Stuart Halloway’s snake program, taking note of the way he organized his program by separating the functions that dealt only with immutable data from the ones that dealt with changes in state. We noted his use of “update-” at the beginning of his names for the state-aware functions, and we agreed this was a pretty good convention for functions that were going to update the state of some refs, agents, or atoms. We also paid a fair amount of attention to his consistent use of destructuring as well as the syntax for the alter function. Finally, we looked at Halloway’s atom-snake, which actually stores the state of the entire snake game in an atom and updates it with swap!, and in so doing creates a transaction-free version of the game. This precipitated a discussion of Software Transactional Memory, which allows copies of complex objects, such as the state of a snake game, to be made without duplicating data from original to copy.

Our next meeting is March 14th, at 1PM, at HacDC’s workshop in St. Stephen’s Church in Washington DC. Homework: chapters 5 and 7 (on Functional Programming and Macros) from Stuart Halloway’s Programming Clojure. We hope to see you there.

We’re also starting to consider our capstone project. Watch the Google group for discussions about the project.