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category theory - recap & part 2

Hello fellow friends of the functional!

Aside from the newcomers demand for usable stuff there is the not so occasional demand for *category theory* (yes really).

As we didn't finish with the first part - guess what - second part will be happening.

I will improve the slides from the first meetup with the input provided from lambdaheads at the first meetup.

Topic for the 2nd part is

• recap and remember everything done  in the first part.

• natural transformations, special objects (sum, product, initial, terminal)

• HASK and why it is not a category

Cheers and be excellent to each other

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  • Michael S.

    2 · February 10, 2016

    • martin 'ε/2' h.

      Hugs for example is mostly for learning purposes (nowadays) because it is said to have better error messages, but it is kinda ordered and most people use Ghc so the chance people can help you is way more likely.

      February 11, 2016

    • Michael S.

      To expand on Martin's answer a bit: yes, DataKinds [1], KindSignatures [2] and ScopedTypeVariables [3] are extensions to the Haskell2010 standard that are GHC-specific. They are however very well described by various research papers and are being used in production.

      There have been efforts to revive the Haskell Prime process lately, which originally aimed to produce new versions of the Haskell standard at regular intervals, incorporating research extensions that have worked out well in practice. For some reason that never happened. But maybe we'll get a Haskell2020 at some point... De facto, whatever GHC implements is "standard Haskell".

      [1] https://downloads.hask...­
      [2] https://downloads.hask...­
      [3] https://downloads.hask...­

      February 11, 2016

  • Christian H.

    Thank you for the interesting meetup. Although we repeated the content of last time, repetition helps me as well :)

    Also, the friendly reminder for fixing a slide: Please indent the second "simple" Functor example ("thus...").

    1 · February 10, 2016

  • martin 'ε/2' h.

    Hey - due to my current workload in my dayjob I will not be able to prepare part2 any further - therefore I suggest - let's do a recap of the first part we already had - aka. already forgot. and make part 2 for march.

    Any objections??

    Cheers Martin

    February 4, 2016

    • Michael S.

      Same here. Also, I could show a nice little dependently typed (kind of) solution to a small practical problem I recently had, if there's interest. It's just a little 5 min thing, but I thought it was kind of cool. It involves TypeLits and getting values out of types at runtime.

      February 10, 2016

    • martin 'ε/2' h.

      yeah sure - let us see what you've got!

      February 10, 2016

  • pivo

    Can't make it this time.

    I've been reading Spivak's Category Theory for the Sciences and like it so far. Through an abundance of examples and exercises it explores using category theory for modeling real-world concepts.

    February 9, 2016

  • Petra B.

    sorry, can't make it :(

    February 9, 2016

  • martin 'ε/2' h.

    Alternatively I could show what I managed to make of the coding dojo example we did last time

    1 · February 4, 2016

    • Christian H.

      Having written my comment below, I also learn from practical examples. I've seen a solution of that dojo in Haskell already - and apart from finally seeing a small, workable app in Haskell, I also hardly saw any of the raw theory learned so far. I knew what was happening in various backgrounds and it felt as if knowing how a combustion motor works while I'm actually wanting to drive a car...

      1 · February 5, 2016

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