BA Haskell User Group meeting on October 18, 2012 (Thu)

[Ivan Tarasov]

Hello, fellow Haskell enthusiasts,

This month we have quite a treat, with Edward Kmett making a talk about Lenses and Traversals. This is a very important topic, and our last month's guest Russell O'Connor strongly urged everybody to come and listen to this talk. There is suggested reading for the talk: "The Essence of the Iterator Patttern" paper by Jeremy Gibbons and Bruno C. d. S. Oliveira, please take a look at it if you have a chance.

Our venue this time is Google office in San Francisco SoMa:

345 Spear Str, San Francisco

Contact phone (mine): 650-762-6644.
Host: Satnam Singh, sat...@raintown.org, cell: 408 656 4590. Please contact Satnam if you have questions about the venue or need help with the venue.

Please arrive a little bit earlier, so that we could start at 7pm. Also if you arrive around 6:30pm, you can get some dinner at

We may try to set up the video feed through Google Hangout (hangout link, also available through our calendar), however please don't rely on it and try to visit the meeting in person if possible. If you are going to be joining the hangout, please mute your microphone before you join.

Some people will be going from the South Bay and East Bay to the meeting and back, so there's a possibility of carpooling. Also, it's very easy to get to the venue from the 4th & King Caltrain Station: check Google Maps for directions, it's also not a very long walk from Caltrain. Please send me a message if you need help figuring out transportation. If you are driving and can take some people with you, please send a message to the baha...@googlegroups.com mailing list.

Please retweet/post to reddit/forward this email to those who may be interested in attending. If you plan to attend and you're not yet subscribed, please subscribe to BAHaskell Google Group to follow all the discussions related to this meeting (if you have troubles with the captcha while joining, please send me a direct email).

Cheers,
Ivan

[Myles C. Maxfield]

+1 for hangout :-)

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[Ian Zimmerman]

Ivan> Hello, fellow Haskell enthusiasts, This month we have quite a
Ivan> treat, with Edward Kmett making a talk about Lenses and
Ivan> Traversals.

Ivan> Our venue this time is Google office in San Francisco SoMa:

Ivan> 345 Spear Str, San Francisco

I "Suggested" it on Meetup. Not sure what needs to be done to make it
final.

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Ian Zimmerman
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[Shachaf Ben-Kiki]

On Wed, Oct 10, 2012 at 9:51 AM, Ivan Tarasov <ivan.t...@gmail.com> wrote:
>

Several people have asked me if the talk will be recorded. Is there
any possibility of that?

Shachaf

[Edward A Kmett]

I can bring my ipad, but a better recording device would be welcome.

Sent from my iPhone

[Byron Hale]

I'll be coming from Sonoma County.  Perhaps I can bring a regular video camera.

Byron

[Ivan Tarasov]

Here's what Edward has to say about his talk (I wanted to include that into the announcement, but it did not quite work out):

I plan to give an introduction to the lens library. My current plan is for the talk to be broken into two parts, so if there is some kind of refreshment or food break, there should be a pretty good point in the middle to insert it.

First, I want to give a fairly general introduction to the concept of a Lens, and some of the easier refinements of the idea used by the lens library, such a Traversal, Fold, Getter, Setter. It would be helpful for the audience to have passing familiarity with Applicative, Foldable and Traversable from base, and maybe a rough understanding of Rank2Types, but pretty much everything else that I need I'll be introducing, including the concept of a lens and the lens laws.

Second, I'll show how deep the rabbit hole goes, by showing off some of the more interesting bits of the library, such as the generalization of Neil Mitchell's uniplate to work with arbitrary Traversals (simultaneously gaining generality, ease of use, and speed) and some nice examples of how we can use the type-safe Traversal-based Zippers from lens as well. This part will admittedly be a lot of material presented in a fairly short time.

If I had to hazard a guess based on how long the talk took at Boston Haskell, it may run about an hour and a half, with the first segment being somewhere between a half hour and 45 minutes.

TL;DR I plan to give a crash course on lenses and traversals covering how they work in practice and how you can use them to clean up code along with some non-obvious applications.

Cheers,
Ivan

On Wed, Oct 10, 2012 at 9:51 AM, Ivan Tarasov <ivan.t...@gmail.com> wrote:

[Jonathan Fischoff]

Here is some additional background material.

Edward's old lens talks

http://www.youtube.com/watch?v=efv0SQNde5Q

Also there is "Applicative Programming with Effects" which introduced the Traversable class.

http://www.soi.city.ac.uk/~ross/papers/Applicative.pdf

Best,

Jonathan

[Arthur Chan]

Thanks, Jonathan!

Arthur :: LittleBrick

[Edward Kmett]

Another useful reference is Jeremy Gibbons' "The Essence of the Iterator Pattern":

http://www.cs.ox.ac.uk/jeremy.gibbons/publications/iterator.pdf

I will be making good use of the laws from that paper.

-Edward