• Oct 24, 2012 · 6:30 PM

Speaker: Derek Wright.

A quick tour through the why rather than the how of monads. Trying to give an intuition about why these concepts matter in the first place.

From The Four Horsemen of the Catapocalypse (Failure, Dependence, Uncertainty and Destruction) through Kleisli arrows and ending up with monads and categorical programming. See why these abstract concepts should be part of every Haskell programmers toolkit.

Join us for the first talk of London Haskell 2.0, then participate in a discussion about the future meetings and shape the vision!

• ##### Alberto B.

Interesting talk, but difficult to follow if you are just a beginner Haskell programmer.

October 28, 2012

• ##### Tomasz K.

It was good, but I'm a bit disappointed with the theoretical background that was presented, we've heard about categories, arrows but there was no simple example of a monad in a category theory (or maybe I've missed that?), and I think that in case of monads building the intuition bottom up (theory and then code) rather than top down (well a monad is... so now I'll show some code... and voila we have a monad, or again was it only my impression?) would be better to understand the whole picture. I also know that it is not an easy task to explain it really smoothly, especially the theoretical part, so besides that I've also really liked the lecture :) I'm looking forward to see next talks! Cheers!

October 25, 2012

• ##### Derek W.

This approach deliberately avoids defining monads in terms of category theory (or at least using the normal category theory definition of monads) and uses a definition in terms of functions with specials ranges and the special composition. So the code should have been the examples. And you could use the same approach for other problems without understanding any category theory. The composition imposes an order that can be used by the code (f . g =/= g . f).

If any of it didn’t make sense then I really would recommend reading Chris’s blog post: http://cdsmith.wordpr...­ (he understands it and explains it better than I do) and then trying to work through the code and the proofs (at least as diagrams).

Anyway, glad you enjoyed it and see you next time!

October 25, 2012

• ##### Tomasz K.

You bet I'll be there next time! ;) Thanks for your answer.

October 26, 2012

• ##### Robert G.

Is the code going to be put online somewhere? It'd be great to get a chance to review and play with the examples given.

October 26, 2012

• ##### Andrea C.

Thanks for the great talk, that's really the right way to explain monads!

October 25, 2012

• ##### Ben F.

Brilliant talk Derek, I think the "beginner working through new material from first principals" approach worked really well!

October 25, 2012

• ##### Tim W.

It was great seeing so many people attend and I'm thoroughly looking forward to the next one!!!

October 24, 2012

• ##### Xabier B.

Interesting but quite hard to follow if you don't know haskell, it has triggered some curiosity, though.

October 24, 2012

• ##### Krzysztof

Is there really 40 people limit? I know a few people more who surely would like to attend.

October 13, 2012

• ##### Derek W.

We have moved to a bigger room at City University so now have 90 places!

October 18, 2012

• ##### Hok Shun P.

Good work!

October 19, 2012

• ##### Krzysztof

Great!

October 18, 2012

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