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Talks by Paul Chiusano and Ed Kmett

We have two great speakers this month! It should be entertaining for beginners and experts alike.

PS: Very sorry for the late announcement! I'll try my best not to announce this late again.

7:00-8:00: Paul Chiusano - How writing generic code in Haskell is a lot like bumper bowling!

This talk is an introduction to reasoning about type inhabitants in Haskell. I'll present a series of type signatures, starting from the very simple, and together we'll explore how parametricity (or lack thereof) in type signatures lets us constrain what function implementations are allowed to do. Time permitting, we'll also cover tricks for using rank n types to further craft meaningful type signatures, and discuss 'free theorems' as well. This will be an interactive talk, beginner friendly, with (hopefully) lots of audience participation!

8:00-9:00: Edward Kmett - Thrist Shopping for Monadic Binds on the Cheap

Ed will launch us headfirst into a brick wall, covering one of his new pet projects:


As always, we will be meeting at Akamai from 7-9pm.


Pizzas, salad and soda


If you can, please plan on arriving between 6:45pm and 7pm, but there will be someone in the lobby to greet stragglers.


If you'd like to stick around, a number of us tend to head down to the CBC or another pub afterwards to socialize. If you would like to give a talk or if you have any questions or concerns, please feel free to follow up here or email one of the organizers.

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  • Steven S.

    Sorry, I couldn't make it in person. Anyone mind Skyping me in on steshaw?

    July 16, 2014

    • Steven S.

      No worries. I'm watching the videos anyhow. Plus, I didn't actually post that comment until the talk had begun. I might have been in Brisbane, but I was also late :). I would be nice to be able to register as a remote attendee. Turns out that your start time for talks in Boston is 0900 in Brisbane :). It's not good to register for a meetup and "take" one of the reserved seats (when you're remote).

      July 20, 2014

    • Edward K.

      We don't have much in the way of a seat limit at the moment, so I wouldn't worry about it.

      I'll see what we can do going forward about better supporting remote attendees. If someone wanted to set up their laptop for google hangout or something I'd be more than open to it.

      1 · July 20, 2014

  • Edward K.

    We recorded the video from each talk separately.

    Video from my talk is already available here:

    We should be able to post Paul's video soon.

    1 · July 18, 2014

  • Edward K.

    The code I was talking about is available at

    1 · July 17, 2014

  • Paul C.

    Hi everyone, I posted a relatively standalone gist with notes re: my talk as well as links to some of the papers that were mentioned and an online free theorem generator:

    The free theorem scheme I gave for polymorphic functions of one type variable isn't the fully general case, which Ed and Dan pointed out. I don't totally follow Wadler's explanation in the original free theorems paper for how to generate free theorems for arbitrary polymorphic functions of multiple type variables (which may occur in positive and/or negative positions in the signature), so perhaps someone with a better understanding of this could offer a good explanation!

    July 17, 2014

  • Bryce A.

    Nice meetup. Paul showed in a very easy to understand way how types can be leveraged in Haskell to reason about the limits of what a function can do. While this may seem obvious after the fact, exposure to these alternative perspectives is illuminating.
    Ed's talk was so far above my head, I'm not sure I'm qualified to comment, even on the internet. I did learn that there is a whole other side of Haskell I'd not even heard of before; a universe apparently exposed by 10+ extensions. Seems like its time for me to head to the great bookstore in the cloud.

    2 · July 16, 2014

  • Edward K.

    Technically the code in question is mostly in the categories branch of free, not thrists, and is based on Oleg's "Reflection without Remorse" w/ Atze van der Ploeg:

    The thrists project on github was a place to hold the code while I figured out what I was going to do with it. ;)

    July 10, 2014

  • Ethan

    This looks really great! If anyone is on the fence about attending, please come! Both of these speakers write widely about cool stuff in Haskell, and the topics look really interesting.

    July 9, 2014

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