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Doing the course "Functional Systems in Haskell"
by Damian Nadales 31 Dec '16

31 Dec '16

Hi, I want to follow the material in this course: http://www.scs.stanford.edu/16wi-cs240h/ Is anybody interested in studying the course material and completing the exercises? Has anybody tried to complete earlier versions of the course? Cheers, Damian.

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hackagebot future ?
by Simon Michael 30 Dec '16

30 Dec '16

Hello all, hackagebot is the bot I've been maintaining for a few years which announces new hackage uploads in the #haskell IRC channel. I've tried to keep it "a well-behaved, non-annoying bot". It's configured to announce up to 5 uploads at a time, with at least a 5 minute interval between announcements. As our community grows, upload activity increases, and more megaprojects with many uploads appear, I've seen more complaints about the noise, and noticed channel ops muting it temporarily. A few weeks ago this happened, and also a possible problem with the correctness of the announcements or the feed was reported. I didn't have time to investigate, so I left it offline, inviting feedback if anyone missed it. Since then I've heard nothing. So, even though I personally like seeing the uploads, and the conversations and connections that sometimes result, I'm inclined to let hackagebot rest indefinitely. Or, would a new maintainer like to take it on ? If you have feelings about it one way or the other, please reply on-list. Thanks! -Simon

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many haskell's mails are detected as spam on gmail
by Takenobu Tani 29 Dec '16

29 Dec '16

Hi, I'm using gmail. Recently, many haskell's mails are detected as spam on gmail. (ghc-devs, haskell-cafe, ghc-commit, ...) Does anyone know why? Do you know the workaround? Regards, Takenobu

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References on GADT's
by Damian Nadales 29 Dec '16

29 Dec '16

Hi, I'm climbing up the standardized ladder of functional programming: https://news.ycombinator.com/item?id=13067741 The next topic on my list is to gain some understanding and practice on GADT's (competent section of the ladder). Do you have any resources that you would recommend? Are there any books that cover the topic? Thanks in advance, Damian.

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Multi groupby with foldl' and Map.insertWithKey
by Olaf Klinke 29 Dec '16

29 Dec '16

I'd say the cleanest way to go is to split your Info data structure into an intermediate key and a value part like so: type Key = String data Value = Value {count :: !Int, healthTopics :: ![String]} keyvalue :: Info -> (Key,Value) keyvalue (Info _ h k) = (k,Value 1 [h]) and give Value a Monoid instance: instance Monoid Value where mempty = Value 0 [] mappend (Value c s) (Value c' s') = Value (c+c') (s++s') (Or you could use (Sum Int) instead of Int and have type Value = (Sum Int,[String]). Then the Monoid instance is derived for you.) Now you can transform a list of Infos into a Map using a generic function: makeMap :: [Info] -> M.Map Key Value makeMap = M.fromListWith mappend . map keyvalue Semantically, it's pretty identical to ALeX Kazik's suggestion of using foldl' and alter. Internally, fromListWith uses a strict fold, so strictness should be the same as using foldl'. Olaf

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[NL-FP 2017] 2nd CFP: Dutch Functional Programming Day 2017
by J. Stutterheim 29 Dec '16

29 Dec '16

Second Call for Participation: Dear Friends of Functional Programming, There is still room for more participants for the FP day. Please register until December 31st so we can make arrangements for lunch and dinner. The next Dutch FP Day will be held on Friday, January 6 2017 at the Radboud University in Nijmegen. You are invited to some or all of: participate, give a presentation, join the dinner. For further information, please see the website. https://wiki.clean.cs.ru.nl/NL-FP_dag_2017 Feel free to forward this invitation to colleagues and students who might be interested. Best Regards on behalf of Markus Klinik

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Multi groupby with foldl' and Map.insertWithKey
by Cody Goodman 28 Dec '16

28 Dec '16

My goal is to take data like this: [ Info 0 "Alcohol" "TX" , Info 1 "Alcohol" "TX" , Info 2 "Pregnancy" "MA" ] and build a Map like this: [("MA",[("Pregnancy",1)]),("TX",[("Alcohol",2)])] Here is my failed attempt: {-# LANGUAGE ScopedTypeVariables, BangPatterns #-} import qualified Data.Map as M import Data.List (foldl') import Data.Maybe import Debug.Trace data Info = Info { i :: !Int, healthTopic :: !String, state :: !String } deriving Show m :: M.Map String (M.Map String Integer) m = M.fromList [("MA", M.fromList[("Pregnancy",1)]),("TX", M.fromList[("Alcohol",2)])] constantValsPerState = foldl' (\accum currentRow -> do M.insert (state currentRow) "xxx" accum ) M.empty [ Info 0 "Alcohol" "TX" , Info 1 "Alcohol" "TX" , Info 2 "Pregnancy" "MA" ] -- λ> constantValsPerState -- fromList [("MA","xxx"),("TX","xxx")] -- how can I get something like: -- λ> numTopicsPerState -- fromList [("MA", fromList[("Pregnancy",1)]),("TX", fromList[("Alcohol",2)])] -- so we need to give the modified stae of the new map isntead of M.empty -- λ> m -- fromList [("MA",fromList [("Pregnancy",1)]),("TX",fromList [("Alcohol",2)])] -- λ> M.insertWith (\new old -> new) "MA" M.empty m -- fromList [("MA",fromList []),("TX",fromList [("Alcohol",2)])] numTopicsPerState = foldl' (\(accum :: M.Map String (M.Map String Integer)) currentRow -> do M.insertWithKey (\k new old -> M.insert (healthTopic currentRow) ((fromMaybe 0 $ M.lookup (healthTopic currentRow) old) + 1) new ) (state currentRow) (fromMaybe (M.empty) (M.lookup (state currentRow) accum)) accum ) M.empty [ Info 0 "Alcohol" "TX" , Info 1 "Alcohol" "TX" , Info 2 "Pregnancy" "MA" ] -- WRONG OUTPUT -- λ> numTopicsPerState -- fromList [("MA",fromList []),("TX",fromList [("Alcohol",1)])] -- TODO -- turn -- fromList [("Alcohol",fromList []),("MA",fromList [("Pregnancy",1)]),("TX",fromList [("Alcohol",2)])] -- into -- fromList [("MA",fromList [("Pregnancy",1)]),("TX",fromList [("Alcohol",3)])]

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Call for new Stackage Curator
by Michael Snoyman 27 Dec '16

27 Dec '16

I'm copying the text from my blog post today[1]. On behalf of the Stackage curators, I'm putting out a call for a volunteer to join the team. The Stackage curators are responsible for the day-to-day management of the Stackage project: merging PRs, managing builds, reporting bounds issues and build or test failures, and every once in a while making a judgement call on when to bump to newer package versions. The curator team currently consists of Adam Bergmark, Dan Burton, Jens Petersen, and me. The processes we follow are documented in the curator guide[2]. We each rotate shifts, taking one week at a time on duty. Overall, the workload is light and straightforward: usually less than 30 minutes a day. We're putting out this call for a new volunteer since we've been running as a four-person show for a while now, and want to make sure we're getting our processes well documented enough for newcomers to easily come up to speed on the process. While we are currently asking for just one new addition to the team, if there are multiple enthusiastic candidates, we will definitely consider expanding the team further. Joining the curator team is a great way to both contribute to the Haskell ecosystem, and to become more familiar with how things work. You'll also get an opportunity to interact (albeit in brief discussions) with many package maintainers in the Haskell community. If you're interested in applying, please send a message to the Stackage mailing list[3] or, if you prefer applying privately, send me an email and I'll pass the message along to the rest of the team. [1] http://www.snoyman.com/blog/2016/12/call-for-new-stackage-curator [2] https://github.com/fpco/stackage/blob/master/CURATORS.md [3] https://groups.google.com/d/forum/stackage

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happy parser generator - stack space overflow error
by Mageshkumar Kuppusamy 26 Dec '16

26 Dec '16

Hello folks, I am generating a parser for SystemVerilog language using happy parser generator. I have the *.y file which i run using happy as below happy -gca ParSysverilog.y and i get the below error. Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize -RTS' to increase it. to increase the stack size and to get more info on the error, i learned that i need to use something like below. happy -RTS -K16384 -sstderr +RTS -gca ParSysverilog.y but i got an error message happy: Most RTS options are disabled. Link with -rtsopts to enable them. does this mean that, i need to recompile happy source code using the "-rtsopts" to use the +RTS...-RTS options ? any recommendations from your experience ? Thank you in advance Magesh

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Re: [Haskell-cafe] happy parser generator - stack space overflow error
by Tobias Dammers 25 Dec '16

25 Dec '16

In my experience, using one of the excellent parser-combinator libraries out there (megaparsec, attoparsec, trifecta) is usually less painful and perfectly adequate. On Dec 25, 2016 7:49 AM, "Mageshkumar Kuppusamy" <magesh.kuppusamy(a)gmail.com> wrote: Hello folks, I am generating a parser for SystemVerilog language using happy parser generator. I have the *.y file which i run using happy as below happy -gca ParSysverilog.y and i get the below error. Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize -RTS' to increase it. to increase the stack size and to get more info on the error, i learned that i need to use something like below. happy -RTS -K16384 -sstderr +RTS -gca ParSysverilog.y but i got an error message happy: Most RTS options are disabled. Link with -rtsopts to enable them. does this mean that, i need to recompile happy source code using the "-rtsopts" to use the +RTS...-RTS options ? any recommendations from your experience ? Thank you in advance Magesh _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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