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timestamp: Sat 06 Jun 2009 10:27:32 PM PDT
title: in which a brotherhood gathers
tags: "clojure"
id: 127
content: |
<p>This week I had the good fortune to be in San Francisco
for <a href=''>a
meeting of the Bay Area Clojure Meetup</a>. This meeting was a
special event since Clojure's creator, Rich Hickey, was in town
for the big JavaOne conference. We ended up packing out the room
with sixty people, which made it probably the largest gathering of
Clojure programmers ever.</p>
<p>The meeting began with a handful of so-called "lightning talks"
(of various lengths) on all sorts of topics. A few highlights were
Rathore's <a href=''>Swarmiji</a>
clustering library and George Jahad's talk
on <a href=''>decompiling
Clojure with jdb</a>, which showed tools to get a new perspective
on how your code gets compiled.</p>
<p>After these Rich gave a talk on the recent work he's been doing
on chunked sequences. Basically when a seq wraps a vector or
vector-like collection, rather than every first/rest invocation
breaking the vector down piece by piece, the seq can break a chunk
of the vector off to work on all at once and keep its own internal
counter that points to the current position in the chunk. The
motivation here was that while you generally can rely on the seq
abstraction to map over each element in a vector in a functional
manner, sometimes performance concerns force you to use a more
imperative-style loop instead. With the chunking in place, the map
approach is even faster than the less-idiomatic loop, so
there's one fewer reason to stray from the functional
approach. It's really encouraging to see that Rich is making this
a priority&mdash;he wants to make sure that you never get
penalized for doing things the elegant way.</p>
<p>After this Rich hosted a Q&amp;A session, from which two main
points stuck in my mind. He mentioned that before the 1.0 release,
he <a href=''>asked
what people thought would be a good set of short-term goals for
the project</a>, to which the response was overwhelmingly "move
off SVN to git". Since the project was still fresh of a jump from
SourceForge to Google Code, he was reluctant at first, but he
seems to have been convinced that the distributed approach is
what's best for the community. He promised us that the move will
happen. He's
currently <a href=''>experimenting
with GitHub</a> and making sure for himself that tool support is
good enough.</p>
<p>The other question of particular interest
was <a href=''>that
of tests</a>. Rich doesn't write tests for Clojure. The community
has contributed a test suite, but it's kept in a separate
repository and doesn't offer full coverage. Rich's opinion is that
tests are for finding bugs, and that he is able to avoid bugs by
reasoning out the problem up front, so it's not a wise use of his
time for him to write his own tests, though he does appreciate and
run the community-provided suite. This made me very nervous at
first, but the next day I read
<a href=''>Out
of the Tarpit</a> [PDF], a paper he recommended at the meeting.
The paper makes a strong case for informal reasoning being a
suitable substitute for test cases in codebases that exhibit
referential transparency. While I still prefer TDD for its help
in the design phase of coding, I'm much more ready to accept the
notion that thinking through the problem up front and verifying
it with manual tests is actually a feasible approach to getting
working code in functional languages, though of course in
situations where mutability is the norm it leads to disastrous
<p><b>Update</b>: <a href=''>Videos</a>
are up! (Unfortunately flash-only; sorry!)</p>
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