Feedback on H:ACT

I haven't posted anything since I gave my talk to FringeDC last month. Here's how it went.

First, I want to thank Tom Moertel for his comment on limiting the amount of material to cover. I had outlined a lot of stuff that I wanted to cover, and it didn't really fit or flow very well. So I just started cutting stuff out. That actually worked very well.

It was an informal talk, and mostly extemporaneous. The talk took about 90 minutes, with a decent amount of time for questions and discussion throughout. The slides were about the first half, and hit the highlights:

• program at the highest layer of abstraction possible
• formal mathematical models for programming aren't scary
• you understand lambda calculus, even if you didn't know you understand it
• type inferencing is good
• explicit typing is better, and not odious
• monads are wonderful

The second half was a walk through of two Parsec parsers I wrote -- one to parse JSON in about a page of code (including a pretty printer), and a roman numeral parser. Both are trivial programs that do something more meaningful than the overused examples of fibonacci and factorial. There was some interesting discussion in this part of the talk.

At the end of it all, Conrad Barski presented his demo of a project he's working on to simplify tagging. It was pretty interesting demo of something that he whipped up in MzScheme.



About 20-25 people showed up for the talk, which is pretty impressive in DC. Many had some Haskell experience, dabbled in it, or were in the process of learning it. (I saw a few copies of various Haskell texts sitting around the room.)

The most embarrassing part of the meeting came during the end of my slides, when I was discussing one benefit of the type system. Programming using the standard types is useful, but doesn't let the type checker know what you're trying to do. The true benefit is defining domain specific types and letting the type checker determine whether your program is sane.

The example I used was the Mars Climate Orbiter, the mission that crashed into Mars because of a confusion between lbf and Newtons. Then I threw up some handwavy examples to show operations could be defined in terms of either Newtons or pounds of force, and let the compiler prevent this kind of mixup. The examples were handwavy because I wanted to refer people to the dimensional library, which automatically converts units of force, and prevents stupid things like adding feet to seconds and coming up with nonsense.

Why was this embarassing? Because I said that this was Bjorn Bringert's library, when actually it's Bjorn Buckwalter's library. And, unbeknownst to me, Bjorn Buckwalter was sitting right in front of me during the entire presentation. What does he use this library for? Making sure things like the Mars Climate Orbiter don't happen again on his watch. :-)

Overall, the talk went rather well. I got a lot of good feedback, and I think I covered just enough material.