- Haskell-Cafe - Haskell.org

Additional functionality using cabal configure flags
by Sumit Sahrawat, Maths & Computing, IIT (BHU) 13 Mar '15

13 Mar '15

Hi everybody, I am looking for the correct way to provide additional functionality using cabal configure flags. Even though the developer faq [1] says that it is not recommended, I don't see any downsides for an executable package. Is it 'not recommended' even for executable packages? If not, then how can I do it? [1]: https://wiki.haskell.org/Cabal/Developer-FAQ -- Regards Sumit Sahrawat

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Haskell Weekly News: Issue 320
by Semen Trygubenko / Семен Тригубен ко 13 Mar '15

13 Mar '15

New Releases The sbv package SBV can now generate proof goals that are discharged by ABC, using state-of-the-art SAT based techniques, has better support for IEEE-floats, and a reworked implementation of the connection to the Boolector solver. http://hackage.haskell.org/package/sbv-4.1 Talks Stop Treading Water: Learning to Learn A talk about the alternative to Feynman's algorithm (that can be taught), the total cost of using wrong solutions (integrated over your entire career), the dual of "How to be a Genius" (and how to become a Genius Consultant), and how to beat the exponential decay of human memory (using Spaced Repetition and Going Deeper When You Come Back strategies)! https://yow.eventer.com/yow-2014-1222/stop-treading-water-learning-to-learn… Discussion Solutions in search of problems and problems in search of solutions A comment by Edward Kmett. http://www.reddit.com/r/haskell/comments/2yfris/stop_treading_water_learnin… Once you've seen the beautiful, you don't want to go back to the ugly Discussion of which Haskell ways can benefit what other languages and how to stay employed and satisfied. http://www.reddit.com/r/haskell/comments/2y47rf/once_youve_seen_the_beautif… Learning Haskell — A Racket programmer's documentation of her foray into the land of Haskell (inspired by Learning Racket) Days 0 through 2 are documented so far. http://lexi-lambda.github.io/learning-haskell/ What imperative languages do Haskellers like? Haskell is at the top of the list, followed by C++. http://www.reddit.com/r/haskell/comments/2yqnst/what_imperative_languages_d… Quotes of the Week "Practically every modern human has at least half an hour of spare time a day. If you want to fill that with textbooks or Better Call Saul is up to you." (kqr) "Fritz Henglein's work on discrimination gives you linear time versions of almost everything." (edwardkmett) http://www.reddit.com/r/haskell/comments/2yfris/stop_treading_water_learnin… "I think learning C is just as enlightening as learning Haskell. It forces you to get intimate with your machine in ways other languages (including C++) actively discourage or even forbid." (TheManaKnight) "It seems that after trying haskell not only you can not write anything in other languages, but also you can not solve any problem without going to the deep of it and discover something that truly solves the problem in the deeper sense." (agocorona) http://www.reddit.com/r/haskell/comments/2y47rf/once_youve_seen_the_beautif… "How do I use lens confusing?" "You mean 'it's confusing'" "No, I mean Control.Lens.Traversal.confusing" (cocharles) http://hackage.haskell.org/package/lens-4.8/docs/Control-Lens-Traversal.htm…

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Re: [Haskell-cafe] Is there a name for this?
by Olaf Klinke 12 Mar '15

12 Mar '15

On 2015-03-09 11:26 AM, Ben Franksen wrote: >> Albert Y. C. Lai wrote: >>> Choose one: >>> >>> Foo' is a free Foo >>> >>> Foo' is a limit of the diagram of Foo >>> >>> Foo' is a terminal object of the [sub]category of Foo >> >> Interesting. Is the last variant how "free <whatever>" is usually defined? >> Or is it a coincidence that the two, well, coincide here? I remember I have >> seen other definitions that looked a lot less easy to understand. > > I have not checked, and too lazy to. > > The usual "free" is the less-easy-to-understand one: you need a > forgetful functor, then you need its left adjoint, and you call it your > free functor. Then the target objects hit by the free functor are the > free things. In general when talking about free things and adjunctions one must pay attention to what the functions are. The original definition of class Foo was coalgebraic: class Foo f where bar :: f -> Bool baz :: f -> Char -> Int meaning that the functions take an f and make something else rather than taking something and constructing an f (like e.g. the (:) of lists does). With the definition data Foo' = { bar' :: Bool, baz' :: Char -> Int} one can re-write class Foo f where barbaz :: f -> Foo’ Objects of our category Foo are instances of Foo, that are pairs <f,barbaz> where f is a Haskell type and barbaz is a function f -> Foo’. What are the morphisms? Well, we can consider Foo’ as a phantom type data F a = F Foo’ that is, a constant functor. Then instances of Foo are coalgebras for the functor F, and the right notion of function between coalgebras requires that some equations hold, namely: any h :: f -> f’ that wants to be a Foo-function must have barbaz . h = barbaz. Now we can see that Foo’ is indeed terminal: More precisely, the Foo-instance <Foo’,barbaz=id> is terminal. Indeed, if we have some h :: f -> Foo’ with id . h = barbaz then h must be barbaz, so there is precisely one Foo-function from the Foo-instance <f,barbaz> to <Foo’,id>. I can’t see how Foo’ would be the free Foo in this category, however. Things change if we let Foo-functions be arbitrary functions. Then the documentation of the free package tells us that the free Foo over type t is the instance <(Foo’,t),barbaz=fst>. Olaf

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Deriving Show for non-regular data types
by Mark Laws 12 Mar '15

12 Mar '15

Hi, As part of studying Okasaki's PFDS book, I wanted to add Show support for each of the data structures, and some have proven to be challenging, as some of the types are non-regular and automatic derivation of Show doesn't work. I've been able to add some code that introduces a supplementary type class that serves as a way to pass "proof" that the wrapping data type supports traversal for Show-ability, but the solution seems unsatisfactory. I would greatly appreciate any suggestions for improvements. I've attached the code; the relevant bits are in BankersDeque.hs, Example.hs, NestedShowable.hs, and SimpleCatenableDeque.hs. The same code is available here: https://gist.github.com/drvink/30fb2a2b257fc99af281 Thanks, Mark Laws -- |v\ /\ |\ |< |_ /\ \^| //

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Bad recursion? When can something be on both sides of an equation?
by Jeffrey Brown 12 Mar '15

12 Mar '15

Dear Haskellers, In another thread [1], I talked about computing what I've been lately calling the "total descendents" of a subset S of a graph: that is, the set of nodes t for which every maximal sequence of predecessors intersects S. I got it done, functionally [2]. But in the process I wrote something that hangs, and I can't figure out why. The problem arose in the following passage. (Glab stands for Graph Label, a synonym for Int.) totalDescendents :: S.Set Glab -> Graph -> S.Set Glab totalDescendents roots graph = b where (a,b,c,graph) = totalDescendentsCtrlr -- tricky (roots, S.empty, M.empty, graph) totalDescendentsCtrlr :: TotalDescendentsData -> TotalDescendentsData totalDescendentsCtrlr (a,b,c,gr) = if S.null a' -- fails, as does a == a' -- a == a' is one iteration slower but should have same effect then (a',b',c',gr') else totalDescendentsCtrlr (a',b',c',gr') where (a',b',c',gr') = visitUndetPrds $ visitTdSnvSucs (a,b,c,gr) Notice that in the equation marked "tricky", the object "graph" appears on both sides. I thought that was the problem, so I rewrote that line as the following: where (_,b,_,_) = totalDescendentsCtrlr and sure enough, the problem vanished. So I tried to distill that problem to something tiny, and came up with this: f (a) = a' where (a',b) = fBackend (a,b) -- tricky fBackend (a,b) = if a' < 1 then (a',b) else fBackend (a',b) where a' = a - 1 I see no substantive difference between the problem with the first body of code and the problem I expected f and fBackend to have -- but f and fBackend work fine! Any idea what might be happening? Thanks, Jeff [1] http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/115353 [2] https://github.com/JeffreyBenjaminBrown/digraphs-on-text/blob/master/TotalD…

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Layout rules for if then else
by Alan & Kim Zimmerman 12 Mar '15

12 Mar '15

I am working on ghc-exactprint, and need to flag points where layout must be preserved, and considering the `if` statement. My understanding of the layout rules for if then else is that the `then` has to start more to the right than the `if`. Using GHC 7.10 RC2, ghci cheerfully loads the following ``` f = if True then 1 else 2 ``` Is this valid? Have the rules been relaxed? Alan

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Monadic/sequential migration implementation for data in acid-state
by Sybils Leaf 12 Mar '15

12 Mar '15

Full description of my problem is on Stack Overflow: http://stackoverflow.com/questions/29011479/how-can-a-monadic-sequential-mi… Any comments or suggestions would be greatly appreciated!

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TH not compiling when writing the code directly does
by Michael Jones 12 Mar '15

12 Mar '15

I’m stuck getting a TH expansion to compile. When I take the generated code and compile it directly, it is fine. But when expanding and compiling, it fails. The problem seems related to instanceD, where I provide the type as: (appT (appT (conT devName') (varT $ mkName "Word8")) (varT $ mkName "BV”)) which expands to: IDENTIFICATION__MODEL_ID Word8 BV No matter what I put for the second type (BV), it generates the compile error. For example, Word8 or Word16 gives the same error. But if I take the resulting expression and just put it into the file and compile, it compiles fine. So something about expansion is causing the problem. Is there some more correct way to make the expression rather than nesting two appT? Any ideas? Note: the generation of the functions with (map (\f -> returnQ f) (concat funs)) is ugly in my opinion. I could not find the right way to express this. So all ideas welcome. Mike GEN DEC -------------- makeInstance :: String -> [String] -> Q [Dec] makeInstance devName regNames = do let devName' = mkName devName let regNames' = map mkName regNames let ctx = return [] :: Q [Pred] funs <- mapM (\regName -> [d| $(varP regName) = $(varE $ mkName "writeReadField") $(stringE $ nameBase regName)(get fi) (set fi) where fi = $(conE $ mkName "FieldInfo") 3 1 get info = $(varE $ mkName "getValue") info set info = $(varE $ mkName "setValue") info |]) regNames' instance_ <- instanceD ctx (appT (appT (conT devName') (varT $ mkName "Word8")) (varT $ mkName "BV")) (map (\f -> returnQ f) (concat funs)) return [instance_] COMPILE ERROR ------------------------- src/TestFields.hs:175:3: Illegal type variable name: ‘BV’ When splicing a TH declaration: instance IDENTIFICATION__MODEL_ID Word8 BV where id = writeReadField "id" (get_0 fi_1) (set_2 fi_1) where fi_1 = FieldInfo 3 1 get_0 info_3 = getValue info_3 set_2 info_4 = setValue info_4 ids = writeReadField "ids" (get_5 fi_6) (set_7 fi_6) where fi_6 = FieldInfo 3 1 get_5 info_8 = getValue info_8 set_7 info_9 = setValue info_9

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David Turner quote on lisp and FP
by Rustom Mody 12 Mar '15

12 Mar '15

There is this quote: *It needs to be said very firmly that LISP is not a functional language at all. My suspicion is that the success of Lisp set back the development of a properly functional style of programming by at least ten years.* David Turner found here and there on the net eg http://dis.4chan.org/read/prog/1376090701 Does anyone have/know the original reference? Thanks Rusi -- http://blog.languager.org

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Multiple compiles with cabal
by Ernesto Rodriguez 12 Mar '15

12 Mar '15

Dear Cafe, I have a program [1] which half of the code is meant to be compiled with GHCJS and the other half with GHC (Or any other Haskell compiler). Currently I do the compilation separately and simply include the compiled JS as a static resource for the regular project. Has anyone run into a similar scenario? Can Cabal handle this? Is there some way of having multiple compiles w/o requiring a shell script to initialize them? Thank you & Cheers N. [1] https://github.com/netogallo/Cryptographer (annoying bc Github now believes my project is like 99% JS since the GHCJS runtime is bundled as a static resource) -- Ernesto Rodriguez Masters Student Computer Science Utrecht University www.netowork.me github.com/netogallo

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Mathematical functions with multiple arguments
by Sumit Sahrawat, Maths & Computing, IIT (BHU) 12 Mar '15

12 Mar '15

Hi everybody, I have a function of type plot :: ([Double] -> Double) -- A function to plot -> [(Double, Double)] -- Range for all arguments -> IO () I want to enforce the fact that ranges for all arguments should be provided. Is there a way to make the type system enforce it? -- Regards Sumit Sahrawat

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Is there a name for this?
by Eric 11 Mar '15

11 Mar '15

Given a class Foo: > class Foo f where> bar :: f -> Bool> baz :: f -> Char -> Int does the record type Foo' > data Foo' = Foo' {> bar' :: Bool,> baz' :: Char -> Int> }> > instance Foo Foo' where> bar = bar'> baz = baz' where the fields of the record Foo' are just implementations of the functions of Foo have any special name? In some sense it's a canonical instance of Foo; we could trivially write a universal > toFoo' :: Foo f => f -> Foo' function. I ran across this pattern and wondered whether it was useful enough to have received a name. It vaguely resembles a typeclass dictionary or a vtable in an OOP language. --Eric

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missing rseq?
by Kees Bleijenberg 11 Mar '15

11 Mar '15

In the book Parallel and Concurrent Programming in Haskell http://chimera.labs.oreilly.com/books/1230000000929/ch02.html#sec_par-eval-s udoku2 a list of sudokus is solved in parallel. In version 2 (sudoku2.hs) the program splits the list of sudokus in 2 seperate lists and solves these lists in parallel. In version3 (sudoku3.hs) parMap is used. What I don't understand is why in sudoku2 the program has to wait until the parallel computations are finished with rseqs while in sudoku3.hs there is no rseq (not in the main program nor in parMap)? Why can't program sudoku3.hs terminate before all parallel calculations are finished as in Example 2-1. rpar/rpar? Kees

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Basic question about recursive data type...
by Nicholls, Mark 10 Mar '15

10 Mar '15

a long time since I did some Haskell and my brain has reverted to its OO dogma... > {-# LANGUAGE GADTs, TypeFamilies, TypeOperators, MultiParamTypeClasses, FlexibleInstances, UndecidableInstances, FlexibleContexts #-} consider > data Next input output where > End :: Next () () > Next :: (input -> output) -> Next input output this is a bit like curried function... I can construct > y :: Next Integer (Next String (Next () ())) > y = Next (\x -> > if (x == 1) then > Next (\y -> > if (y == "s") then > End > else > End) > else > Next (\y -> > if (y == "t") then > End > else > End)) which is a bit like "Integer->String->()" I can execute it... > exe :: Next input output -> input -> output > exe (Next f) i = f i > exe End () = () > p :: Next String (Next () ()) > p = exe y 1 ok.... but how do I constrain all the outputs to be of type Next? I don't want this to be valid > z :: Next Integer Integer > z = Next (\x -> x + 1) CONFIDENTIALITY NOTICE This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited. While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data. Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us. MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

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How to abstract away set representation
by martin 10 Mar '15

10 Mar '15

Hello all, I was trying to construct a data type "Profile" which allows some set-like behavior. I started with functions to count, add and filter profiles. type Count = Int data Prof a = P { pCount :: Count, pFilter :: (a -> Bool) -> Prof a, pAdd :: (Prof a) -> (Prof a) } | NoProfile When I tried to actually implement a Profile, the first two functions were easy: exProfile :: [Int] -> Prof Int exProfile xs = P { pCount = length xs, pFilter = \p -> exProfile [x | x<-xs, p x], } But I didn't know how to implement pAdd. I was tempted to write something like pAdd = exProfile (xs ++ ys) But I wouldn't know where to take the ys from. I also hesitate to declare a toList function (which would solve the problem) in Prof. I would only do this *because* it is handy in exProfile, not because it is an intrinsic feature of Prof. What would be a good way to work with set-like behavior without being tied to one particular implementation?

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[] == []
by Rustom Mody 10 Mar '15

10 Mar '15

My impression is that earlier [] == [] used to give a type error. Now it gives True. So 1. Which instance of == is being used? 2. Is there some option controlling this behavior?

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raspberrypi and ghci
by Vasili I. Galchin 10 Mar '15

10 Mar '15

Hello, I have a B++ pi. I did a "apt-get install haskell-platform. No " ghci"!. So I did a google on this issue. Circa 2013 ghci seemed to be an issue with raspberrypi/arm. What is the current status of "ghci" on the pi/arm??. Vasili

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Fwd: Freelance and full-time Haskell development jobs in tech startups
by Vasili I. Galchin 10 Mar '15

10 Mar '15

Hello, Was this posted on this mail list? I am afraid of phishing. Vasili ---------- Forwarded message ---------- From: Vassili van der Mersch <vassvdm(a)sevendays.io> Date: Fri, Mar 6, 2015 at 10:21 AM Subject: Freelance and full-time Haskell development jobs in tech startups To: "biohaskell(a)biohaskell.org" <biohaskell(a)biohaskell.org> Hi BioHaskell, I'm a co-founder at Sevendays - it's a website where tech startups can find quality programmers and designers (amongst other jobs): https://www.sevendays.co <https://www.sevendays.co/?utm_source=Email_2&utm_medium=email&utm_campaign=…> We're looking for great programmers and designers who like to work at startups, either on freelance or permanent basis, on site or remotely. We're growing fast and we're constantly looking for talented developers - in particular, Haskell dev skills are highly demanded at the moment. We never take a cut - you'll keep 100% of your earnings. I'd be grateful if you could have a look and tell me what you think. Have a great day! Vassili ------------------------------------------------------------------------------- Co-founder at Sevendays - https://www.sevendays.co Customer support: info(a)sevendays.co Follow us on Twitter: https://twitter.com/sevendaysapp

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Leuven Haskell User Group meeting March 17 @ 19:00
by Tom Schrijvers 10 Mar '15

10 Mar '15

Dear all, Our next Leuven Haskell User Group meeting will take place on Tuesday, March 17 at 19h00. For details see here: https://groups.google.com/d/msg/leuven-haskell/q863tfr2Na4/Yp6AKMVzMcIJ Everyone is welcome! Tom -- prof. dr. ir. Tom Schrijvers Research Professor KU Leuven Department of Computer Science Celestijnenlaan 200A 3001 Leuven Belgium Phone: +32 16 327 830 http://people.cs.kuleuven.be/~tom.schrijvers/

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Re: [Haskell-cafe] ghc -O2 out of memory
by Kees Bleijenberg 10 Mar '15

10 Mar '15

Carter, Thank you. My assumption was that 7.8.3 is 32 bits and 7.8.4 is 64 bits. I got this idea from reading https://github.com/fpco/minghc#readme Kees Van: Carter Schonwald [mailto:carter.schonwald@gmail.com] Verzonden: dinsdag 10 maart 2015 3:10 Aan: Kees Bleijenberg CC: ghc-devs(a)haskell.org Onderwerp: Re: [Haskell-cafe] ghc -O2 out of memory there SHOULD be a 32bit 7.8.4 build available somewhere for windows, and if not , thats a real problem! I'm gonna shift this thread to ghc-devs, because that *should* get addressed @ghc-devs, how can we help this user get ahold of a 32bit windows 7.8.4 build? (eg, why do we not have one available yet?) -Carter On Mon, Mar 9, 2015 at 4:13 AM, Kees Bleijenberg <K.Bleijenberg(a)lijbrandt.nl> wrote: Thanks for your answer. I also use ghc to create 32 bits dll’s. 7.8.4 is 64 bits GHC and can’t create 32 bits dll’s (?). This means I have to install 7.8.3 and 7.8.4 on the same Windows machine. Is this possible? <snip>

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New Functional Programming Job Opportunities
by Functional Jobs 09 Mar '15

09 Mar '15

Here are some functional programming job opportunities that were posted recently: Hacker (Node.js, NOSQL, Data Science) at Mobitrans http://functionaljobs.com/jobs/8793-hacker-nodejs-nosql-data-science-at-mob… Full-Stack Senior Functional Web Engineer at Front Row Education http://functionaljobs.com/jobs/8792-full-stack-senior-functional-web-engine… Cheers, Sean Murphy FunctionalJobs.com

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Re: [Haskell-cafe] ghc -O2 out of memory
by Kees Bleijenberg 09 Mar '15

09 Mar '15

Thanks for your answer. I also use ghc to create 32 bits dll’s. 7.8.4 is 64 bits GHC and can’t create 32 bits dll’s (?). This means I have to install 7.8.3 and 7.8.4 on the same Windows machine. Is this possible? Kees Van: Carter Schonwald [mailto:carter.schonwald@gmail.com] Verzonden: zaterdag 7 maart 2015 20:02 Aan: Kees Bleijenberg Onderwerp: Re: [Haskell-cafe] ghc -O2 out of memory Upgrade to ghc 7.8.4, theres some known bugs in O2 optimization that resulted in excessive memory usage that are fixed in 7.8.4 You'll still have painful compilation times with a 30kloc module , but memory usage should be physically possible after the upgrade. On Mar 7, 2015 10:58 AM, "Kees Bleijenberg" <K.Bleijenberg(a)lijbrandt.nl> wrote: I’ve written a program that reads a Excel file, parses the contents and generates a haskell module. Every cell in the xls has it’s own function in the module. This worked fine. Now I have a bigger xls. The resulting module Xls.hs contains 30000 lines haskell code (without comment). I created a testprogram test.hs that calculates and prints one cell. I did ghc --make test.hs and everything works fine. The generated execuatable is very slow. I did ghc --make –O2 test.hs. The compilations takes 15 minutes and aborts with ‘ghc: out of memory’. I’am working on Win 7 64 bits , ghc version = 7.8.3. What can I do to fix this? I do need –O2. I found with smaller xls’s that optimization speeds up the executable dramatically. Before I start experimenting, does it help to split up the xls .hs in seperate files? I.e. the cells that refer to other cells and cells that don’t refer to other cells. Or will I still get ‘out of memory’ because the optimization is global? Kees _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe No virus found in this message. Checked by AVG - www.avg.com Version: 2015.0.5751 / Virus Database: 4299/9258 - Release Date: 03/09/15

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Building documentation only?
by Andrew Cowie 09 Mar '15

09 Mar '15

I've got a sandbox set up to build a local copy of Haddock documentation for various packages I'm using. Is there a way to get Cabal to just run Haddock and not actually build the packages in question? If the haddock program needs the compiled definitions then no, but I'm getting the impression it just runs over the raw sources. The config file I'm using at the moment is a very simple: $ cat cabal.config Documentation: True $ which is doing the trick to get Haddock run, I'm just wondering if there's ActualBuild: False equivalent? AfC

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ANNOUNCE: fgl 5.5.1.0
by Ivan Lazar Miljenovic 09 Mar '15

09 Mar '15

I'm pleased to announce that - after being pestered about it for the past few months ;-) - I've released a new version of the Functional Graph Library that should* now be compatible with GHC 7.10. fgl is now developed on GitHub: https://github.com/haskell/fgl * In that I can't test it on my own machines -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Haskell.org Committee Financial Statement 2014
by Gershom B 08 Mar '15

08 Mar '15

Dear Haskellers, The Haskell.org Committee [1] manages funds for haskell.org and oversees haskell.org infrastructure. The funds available to Haskell.org generally come from two sources: 1) Mentor payments from the Google Summer of Code program. 2) Since the end of 2013, occasional donations [2] from the Haskell community at large. Our funds are held by Software in the Public Interest, a 501(c)3 US non-profit, through which we also accept donations. In return for its services, SPI receives 5% of donations to Haskell.org. According to our charter, "Each year, the committee will post a statement of the haskell.org assets, and the transactions for that year.” We apologize for having been delinquent in this regard. Included in this message is a brief statement of Haskell.org assets over the period 31 December 2013 - 31 December 2014, as well as an approximate breakdown of expenses. The statements we receive from the SPI are not in the most usable format [3], and we hope to provide more accurate accounting in the future. Note that this statement does not reflect 2014 GSoC income, as that had not posted as of 31 December 2014. Thus the fact that we are in the black this year is entirely due to your generous donations. Thank you all so much! 1. Income and Expenses Total income over 2014: 5,187.00 Total expenses over 2014: 2,523.22 ---- Net income over 2014: 2,663.78 2. Expense breakdown Approximate monthly hosting fees (Hetzner): 160.00 Total approximate hosting fees: 1920.00 Other approximate expenses: 603.22 (Other expenses consist of A] payment processing fees for received funds and B] the 5% of donated funds transferred to the SPI). 3. Total Balance Balance as of 31 December 2013: 23,759.13 Balance as of 31 December 2014: 26,422.91 [1] https://wiki.haskell.org/Haskell.org_committee [2] https://wiki.haskell.org/Donate_to_Haskell.org [3] Those wishing to examine further for themselves can find the reports posted to the spi-general list: http://lists.spi-inc.org/pipermail/spi-general/ Best, Gershom Bazerman for the Haskell.org Committee

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CFP: TFPIE 2015
by Johan Jeuring 08 Mar '15

08 Mar '15

Trends in Functional Programming in Education (TFPIE 2015) Call for papers https://wiki.science.ru.nl/tfpie/TFPIE2015 The 4th International Workshop on Trends in Functional Programming in Education, TFPIE 2015, will be held on June 2, 2015 in Sophia-Antipolis in France. It is co-located with the Symposium on Trends in Functional Programming (TFP 2015) which takes place from June 3 - 5. *** Goal *** The goal of TFPIE is to gather researchers, teachers and professionals that use, or are interested in the use of, functional programming in education. TFPIE aims to be a venue where novel ideas, classroom-tested ideas and work-in-progress on the use of functional programming in education are discussed. The one-day workshop will foster a spirit of open discussion by having a review process for publication after the workshop. The program chair of TFPIE 2015 will screen submissions to ensure that all presentations are within scope and are of interest to participants. Potential presenters are invited to submit an extended abstract (4-6 pages) or a draft paper (up to 16 pages) in EPTCS style. The authors of accepted presentations will have their preprints and their slides made available on the workshop's website/wiki. Visitors to the TFPIE 2015 website/wiki will be able to add comments. This includes presenters who may respond to comments and questions as well as provide pointers to improvements and follow-up work. After the workshop, presenters will be invited to submit (a revised version of) their article for review. The PC will select the best articles for publication in the journal Electronic Proceedings in Theoretical Computer Science (EPTCS). Articles rejected for presentation and extended abstracts will not be formally reviewed by the PC. TFPIE workshops have previously been held in St Andrews, Scotland (2012), Provo Utah, USA (2013), and Soesterberg, The Netherlands (2014). *** Program Committee *** Peter Achten, Radboud University Nijmegen, The Netherlands Edwin Brady, University of St Andrews, UK Johan Jeuring, Utrecht University and Open University, The Netherlands (Chair) Shriram Krishnamurthi, Brown University, US Rita Loogen, Philipps-Universität Marburg, Germany Marco Morazan, Seton Hall University, US Norman Ramsey, Tufts University, US *** Submission Guidelines *** TFPIE 2015 welcomes submissions describing techniques used in the classroom, tools used in and/or developed for the classroom and any creative use of functional programming (FP) to aid education in or outside Computer Science. Topics of interest include, but are not limited to: - FP and beginning CS students - FP and Computational Thinking - FP and Artificial Intelligence - FP in Robotics - FP and Music - Advanced FP for undergraduates - Tools supporting learning FP - FP in graduate education - Engaging students in research using FP - FP in Programming Languages - FP in the high school curriculum - FP as a stepping stone to other CS topics - FP and Philosophy *** Best Lectures *** In addition to papers, we request “best lecture” presentations. What is your best lecture topic in an FP related course? Do you have a fun way to present FP concepts to novices or perhaps an especially interesting presentation of a difficult topic? In either case, please consider sharing it. Best lecture topics will be selected for presentation based on a short abstract describing the lecture and its interest to TFPIE attendees. *** Submission *** Papers and abstracts can be submitted via easychair at the following link: https://easychair.org/conferences/?conf=tfpie2015 It is expected at at least one author for each submitted paper will attend the workshop. *** Important Dates *** April 7, 2015: Early Registration for TFP closes April 27, 2015: Submission deadline for draft TFPIE papers and abstracts May 3 2015: Notification of acceptance for presentation ?? (Probably May 22 2015): Registration for TFPIE closes - as does late registration for TFP June 2, 2015: Presentations in Sophia-Antipolis, France July 7, 2015: Full papers for EPTCS proceedings due. September 1, 2015: Notification of acceptance for proceedings September 22, 2015: Camera ready copy due for EPTCS Submission of an abstract implies no obligation to submit a full version; abstracts with no corresponding full versions by the full paper deadline will be considered as withdrawn.

2 2

Difficulty making a TH template for a monadic expression
by Michael Jones 08 Mar '15

08 Mar '15

I’m at wits end as to how to express a monadic expression in TH. I’ll give here two ways to express a non TH version, and then a TH expression that does not quite work. It generates code that compiles, but it does not evaluate properly like the non TH version. Fundamentally, the problem is use of a recursive function using quasi quoting similar to what is in the standard Show example. Perhaps someone will have an idea on how to fix it. I have made several attempts and failed. Non TH Example A: Do notation ————————————— let r = BG.runBitGet flags (do let bits = [] v <- BG.getBit bits <- return $ if v then I1_7:bits else bits v <- BG.getBit bits <- return $ if v then I1_6:bits else bits v <- BG.getBit bits <- return $ if v then I1_5:bits else bits v <- BG.getBit bits <- return $ if v then I1_4:bits else bits v <- BG.getBit bits <- return $ if v then I1_3:bits else bits v <- BG.getBit bits <- return $ if v then I1_2:bits else bits v <- BG.getBit bits <- return $ if v then I1_1:bits else bits v <- BG.getBit bits <- return $ if v then I1_0:bits else bits return $! bits) Non TH Example B: Bind notation —————————————— let r = BG.runBitGet flags ( return [] >>= (\bits -> ifM BG.getBit (return $ I0_7:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_6:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_5:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_4:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_3:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_2:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_1:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_0:bits) (return $ bits))) A TH for Example B: ———————— let bitsP = varP $ mkName "bits" let bitsE = varE $ mkName "bits" let makeBits [] = [| "" |] makeBits (name:names) = [| (\bits -> ifM BG.getBit (return $ $(conE name) : $bitsE) (return $ $bitsE)) >>= $(makeBits names) |] parse <- [d| $(varP (mkName $ "parse" ++ nameBase name)) = do flags <- G.getByteString 1 let r = BG.runBitGet flags (return [] >>= $(makeBits bitNames)) case r of Left error -> fail error Right x -> return x |] This generates: parseTCA9535_INPUT_PORT_0_BITS = do {flags_0 <- Data.Binary.Strict.Get.getByteString 1; let r_1 = Data.Binary.Strict.BitGet.runBitGet flags_0 (GHC.Base.return [] GHC.Base.>>= ((\bits_2 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_7 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_3 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_6 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_4 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_5 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_5 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_4 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_6 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_3 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_7 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_2 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_8 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_1 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_9 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_0 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ""))))))))); Problems with TH ———————— The problem is the () that interferes with the order of evaluation, and the termination at the end ( “” ). I’m no so worried about the termination. I can put something harmless there. The parens are the main problem. Calling a quasi quoter recursively is the cause, as it nests the evaluation. I tried things like building the bits in a list, but that does not work because the BG.getBit has to run in the BitGit monad. I know I can write a simple evaluation that just returns a list of Bools and only TH for bit names, but in the final version the size of bit fields needs to be dynamic, so I need to dynamically generate code piece by piece. I would prefer to use quasi quoting rather than build the whole thing with data types so that it is more readable. If anyone knows of a module on hackage that does something similar, perhaps you can point me to that so I can study it. Thanks…Mike

2 6

ghc -O2 out of memory
by Kees Bleijenberg 08 Mar '15

08 Mar '15

I've written a program that reads a Excel file, parses the contents and generates a haskell module. Every cell in the xls has it's own function in the module. This worked fine. Now I have a bigger xls. The resulting module Xls.hs contains 30000 lines haskell code (without comment). I created a testprogram test.hs that calculates and prints one cell. I did ghc --make test.hs and everything works fine. The generated execuatable is very slow. I did ghc --make -O2 test.hs. The compilations takes 15 minutes and aborts with 'ghc: out of memory'. I'am working on Win 7 64 bits , ghc version = 7.8.3. What can I do to fix this? I do need -O2. I found with smaller xls's that optimization speeds up the executable dramatically. Before I start experimenting, does it help to split up the xls .hs in seperate files? I.e. the cells that refer to other cells and cells that don't refer to other cells. Or will I still get 'out of memory' because the optimization is global? Kees

5 5

[Announce] New release of SBV is out
by Levent Erkok 07 Mar '15

07 Mar '15

A new release of SBV is out (v4.1): http://hackage.haskell.org/package/sbv-4.1 The main change in this release is the connection to Berkeley's ABC <http://www.eecs.berkeley.edu/~alanmi/abc/> system, which is an industrial strength synthesis and verification system. SBV can now generate proof goals that are discharged by ABC, using state-of-the-art SAT based techniques. ABC is especially extremely well-tuned for dealing with problems in the bit-vector theory, and is heavily used in the hardware industry as a backend verification tool. Also included in this release is better support for IEEE-floats, and a reworked implementation of the connection to the Boolector <http://fmv.jku.at/boolector/> solver. Thanks to Adam Foltzer of Galois for contributing the connection to ABC, and Alan Mischenko from Berkeley to add the necessary infrastructure to ABC to allow for this bridge to be built. Full release notes: https://github.com/LeventErkok/sbv/blob/master/CHANGES.md SBV web page: http://leventerkok.github.io/sbv/ -Levent.

1 0

C2HS parse error on Windows ...
by aditya siram 07 Mar '15

07 Mar '15

Hi all, c2hs runs into the following error on all of my .chs files, but only on Windows: c:\\program files\\haskell platform\\2014.2.0.0\\mingw\\bin\\../lib/gcc/x86_64-w64-mingw32/4.6.3/../../../../x86_64-w64-mingw32/include/stddef.h:20: (column 11) [ERROR] >>> Syntax error ! The symbol `__attribute__' does not fit here. My c2hs version is: C->Haskell Compiler, version 0.23.1 Snowbounder, 31 Oct 2014 build platform is "x86_64-mingw32" <1, True, True, 1> This is the command being run: "c:\Users\deech\AppData\Roaming\cabal\bin\c2hs.exe" "--cpp=c:\Program Files\Haskell Platform\2014.2.0.0\mingw\bin\gcc.exe" "--cppopts=-E" "--cppopts=-D__GLASGOW_HASKELL__=708" "--cppopts=-Dmingw32_BUILD_OS=1" "--cppopts=-Dx86_64_BUILD_ARCH=1" "--cppopts=-Dmingw32_HOST_OS=1" "--cppopts=-Dx86_64_HOST_ARCH=1" "--cppopts=-I./c-src" "--cppopts=-I./" "--cppopts=-IC:/MinGW/include" "--cppopts=-IC:\Users\deech\Downloads\fltkhs-0.1.0.1/c-src" "--cppopts=-IC:\Users\deech\Downloads\fltkhs-0.1.0.1" "--include=dist\build" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib\process-1.2.0.0\include" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib\directory-1.2.1.0\include" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib\time-1.4.2\include" "--cppopts=-IC:\ProgramFiles\Haskell Platform\2014.2.0.0\lib\Win32-2.3.0.2\include" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib\bytestring-0.10.4.0\include" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib\base-4.7.0.1\include" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib\integer-gmp-0.5.1.0\include" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib/include" "--output-dir=dist\build" "--output=Graphics\UI\FLTK\LowLevel\HorValueSlider.hs" "src\Graphics\UI\FLTK\LowLevel\HorValueSlider.chs" A little Googling turned up this thread: http://haskell.1045720.n5.nabble.com/BUG-string-h-FC4-x86-64-td3196369.html which suggested I pass -D__attribute__(A)= to c2hs's opts. I tried it and it led to other errors. I didn't pursue any further because it's an old thread. I'm not sure what stddef.h is and I'm unfamiliar with Windows. Any help is appreciated. Thanks! -deech

2 3

Imperative graph algorithm, (tail?) recursion, and speed
by Jeffrey Brown 07 Mar '15

07 Mar '15

Suppose I have a general (not a tree) directed graph, and I would like to find all the "pure descendents" of a node N -- that is, all nodes M for which (1) N is an ancestor of M, and (2) every partial or maximal sequence of predecessors starting from M either consists entirely of descendents of N, or else includes N itself. I have an imperative algorithm (below) for doing that. I want to know how hard it would be to implement in Haskell. It's complex, but basically it sets up a few lists like "members of this list have had all their descendents processed", "members of this list have been processed but their descendents have not been", "members of this list have not been processed at all", etc. Then I iterate through the graph, moving nodes from one collection to the other until the "to be processed" list is empty. I would like a function Graph -> Graph that does that and does not need to rely on a monad. The only way I can think of involves a few mutually recursive functions, each of which passes not only the original graph of interest, but all the lists described in the previous paragraph, around to the others. I don't understand Haskell's evaluation strategy well enough to anticipate the result, but my vague sense is that a lot of copies of the same data would be floating around, ruining the speed of it. Python code for the algorithm: def descendedOnlyFrom(gset): "All Gnodes n for which every ancestry of n includes a Gnode in gset (which can be a set or a list)." # For efficiency improvement ideas and verbose comments, # see treeSearch/all.py/node.descendedOnlyFrom if 1: # variables # "pure" = "descended only from the calling Glist" pe = set(gset) # determined Pure, yet to Explore children of pf = set() # determined Pure, Finished exploring children of pb = set(gset) # determined Pure, Both kinds: pe | pf ud = set() # purity UnDetermined # descended from root, but might have parents outside of pb udp = {} # "Parents of the UnDetermined" # This is a dictionary, from gnodes to sets of gnodes. # The other four variables are sets. while pe: while pe: k = 1 i = pe.pop(); pf.add(i) for c in set(i._children()): if c in pb | ud: continue # If already handled, do not repeat. if set(c._parents()) <= pb: pe.add(c); pb.add(c) else: ud.add(c); udp[c] = set(c._parents()) - pb for i in ud: ipf = udp[i] & pb # (i)'s (p)arents newly (f)ound in pb if ipf: udp[i] -= ipf if udp[i]==set(): ud.remove(i); del( udp[i] ) pe.add(i); pb.add(i) break return pb

4 6

SPDX and hackage
by Mike Meyer 06 Mar '15

06 Mar '15

I stumbled across the SPDX (https://spdx.org/) Possibly the hackage license list should be expanded to incorporate this in some way? Or at least the OSI-approved entries?

2 1

Haskell on RedHat?
by Mario Blažević 06 Mar '15

06 Mar '15

What is the recommended route for installing a recent GHC on RedHat Enterprise Linux? All I could find on the official haskell.org Web pages is a GHC 7.8.4 repository for Fedora 21. Also, are there any potential difficulties with deploying a Haskell executable compiled on an Ubuntu system to RedHat EL, or vice versa? Thank you.

4 4

Beginner
by Sarthak Shetty 06 Mar '15

06 Mar '15

Hi everyone, this is Sarthak Shetty from India. I'm a CSE student who is somewhat comfortable with Java, C, Python and R. I would like to learn Haskell and start contributing right away. Can someone help me get started?

4 3

Lifting Writer to ListT
by Nicola Gigante 06 Mar '15

06 Mar '15

Hi all, Suppose I have this monad stack: type MyMonad = ListT (Writer W) Where ListT is done right (from the list-t package). What I want is a nondeterministic computation where each alternative logs to the same writer, and indeed the type of runWriter . toList is MyMonad a -> ([a], w) so I think I got it right. What I would like to do is to write an instance of MonadWriter for this monad, but I'm stuck with the implementation of listen. Just using lift won't work, and indeed I see that MonadWriter lifting instances for other monads (e.g MaybeT), are a bit convoluted. Could someone explain me a little bit what should I do (what listen should do in a ListT in the first place) Thank you :) Nicola

2 2

is it possible to implement Functor for ByteString and Text
by silvio 06 Mar '15

06 Mar '15

I have recently heard that some people want to burn bridges (introducing Foldable and Traversable to Prelude) and I've been wondering if it was possible somehow allow Text and Bytestring like containers to make use of those functions. Something along the lines of import qualified Data.ByteString as BS newtype ByteString' a = ByteString' BS.ByteString type ByteString = ByteString' Word8 instance (ByteString' a ~ ByteString' Word8) => Functor (ByteString') where fmap f (ByteString' bs) = ByteString' $ BS.map f bs Or if DataContexts worked as you would expect. newtype (Word8 ~ a) => ByteString' a = ByteString' BS.ByteString However I couldn't find a solution and I was just wondering if it is possible. P.S. Using GADTS it does actually work for Foldable, but only because it doesn't have to output any ByteStrings. It doesn't work for Functor for instance. data ByteString' a where ByteString' :: BS.ByteString -> ByteString' Word8 type ByteString = ByteString' Word8 instance Foldable ByteString' where foldr f ini (ByteString' bs) = BS.foldr f ini bs Silvio

7 9

Am I using Parsec correctly?
by Cody Goodman 06 Mar '15

06 Mar '15

-- trying to parse the text below using Parsec: -- ACT I. -- SCENE I. An open place. -- [An open place. Thunder and lightning. Enter three Witches.] -- FIRST WITCH. -- When shall we three meet again -- In thunder, lightning, or in rain? -- Here's the code I have import Text.Parsec import Control.Applicative import Data.Traversable (sequenceA) section s = sequenceA [string s, string " ", many1 letter] `endBy` char '.' act = section "ACT" scene = section "SCENE" main = do parseTest act "ACT I.\n" parseTest scene "SCENE I." -- this returns: -- λ> main -- [["ACT"," ","I"]] -- [["SCENE"," ","I"]] -- Am I using Parsec correctly so far? -- After this I want to match acts (many1 act) and scenes (many1 scene) and I believe I see how to do that, just wanting to make sure I'm on the right track.

2 1

Re: [Haskell-cafe] Hackage and Free Software
by Duncan Coutts 05 Mar '15

05 Mar '15

All, Hackage has of course always been for open source Haskell software (and has always rejected "AllRightsReserved" packages). Prompted by this recent discussion, Gershom, SPJ, and the hackage admins have come up with a few changes to make our current implicit open source policy a bit more explicit: * The hackage homepage will say "Hackage is the Haskell community's central package archive of open source software." * The signup and upload pages will have a new blurb on open source licenses. See below. * We will accept a patch along the lines of https://mail.haskell.org/pipermail/cabal-devel/2015-March/010019.html to continue to reject "AllRightsReserved" on hackage (though we may move the check from cabal into hackage). * And on a somewhat related topic: we will finish the discussion on hackage trustee guidelines (mostly about editing package metadata) and post them. https://github.com/haskell/hackage-server/commit/66a7acd125d486e55bb6674358… Here's the new blurb: Open source licenses The code and other material you upload and distribute via this site must be under an open source license. This is a service operated for the benefit of the community and that is our policy. It is also so that we can operate the service in compliance with copyright laws. The hackage operators do not want to be in the business of making judgements on what is and is not a valid open source license, but we retain the right to remove packages that are not under licenses that are open source in spirit, or that conflict with our ability to operate this service. (If you want advice, see the ones Cabal recommends.) The hackage operators do not need and are not asking for any rights beyond those granted by the open source license you choose to use. All normal open source licenses grant enough rights to be able to operate this service. In particular, we expect as a consequence of the license that: 1. we have the right to distribute what you have uploaded to other people 2. we have the right to distribute certain derivatives and format conversions, including but not limited to: * documentation derived from the package * alternative presentations and formats of code (e.g. html markup) * excerpts and presentation of package metadata * modified versions of package metadata Please make sure that you comply with the license of all code and other material that you upload. For example, check that your tarball includes the license files of any 3rd party code that you include. We hope this will be uncontroversial as it is just the status quo. Note that the hackage admins are not getting involved in a license debate, and we are not asking for any grant of rights (implicitly or explicitly) when you upload stuff. The open source license you use grants all the rights we need to be able to run the site. Duncan On Sat, 2015-02-28 at 19:27 +0200, fr33domlover wrote: > Hello haskellers! > > I would like to make a proposal regarding the license of software in Hackage. > > > > One of the major parts of the Haskell community infrastructure in the package > database server Hackage. As far as I know - please correct me if I'm wrong - > Hackage makes no restriction on the license of packages upload to it. But as a > community working in cooperation to make good software, the Haskell community > has embraced licenses like (L)GPL, MIT and BSD, which are free software > licenses. > > Actually the all-rights-reserved tag in Hackage [1] has only two packages > tagged by it - the dummy no-op project HNop, and another package whose COPYING > file contains a broken link and whose README says "BSD style license". > > > > Software freedom is an ethical basis for collaboration on making software > that's truly good and loayl to its users, and providing them control and > freedom to access and use their computing resources. > > It seems to me that the Haskell community is already enbracing this ethical > basis, but Hackage doesn't provide any guarantees and it means that you'd have > to check each package to be sure. By having that all-rights-reserved tag it > also in a way welcomes software that doesn't go by these rules - however it > seems that no packages do that even in the presence of the possibility. > > > > > I'd like to make a suggestion: have Hackage accept only packages released under > free software licenses. This is probably true for most/all packages there, but > making it official will both send a strong message to and from the community, > and provide people with the security and peace of mind, knowing their software > is free as in freedom. > > It is also possible that companies use Haskell to create proprietary software > using permissive-licensed libraries and tools from Hackage. I hope this isn't > true, but even if it is, this software isn't offered by Hackage and I hope its > existence doesn't affect the community's use of Hackage and free software. > > > > Would you consider to embrace free software officially, including in Hackage? > > > > Thanks for reading, > waiting to hear from the community and from haskell.org maintainers, > fr33domlover > > > > [1] http://hackage.haskell.org/packages/tag/all-rights-reserved > > --- > fr33domlover <http://www.rel4tion.org/people/fr33domlover> > GPG key ID: 63E5E57D (size: 4096) > GPG key fingerprint: 6FEE C222 7323 EF85 A49D 5487 5252 C5C8 63E5 E57D > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

1 0

GHCi timing statistics
by David Rush 05 Mar '15

05 Mar '15

Hi all - Is it my imagination, or are the statistics printed by GHCi when :set +s has been enabled entirely spurious when SMP parallelism is turned on? I'm trying to determine if I am actually getting any improvement, and - both by the wall clock and by the reported statistics I don't seem to be; however, the reported statistics don't seem to line up very well with the wall clock time. An additional oddity that I've noted is that my algorithm's reference implementation - which simply can't run in parallel due to a foolishly introduced data dependency - still seems to kick 16 CPUs well into the 90%+ utilization range when I have +RTS -N. This code has no parallelism primitives in it whatsoever. I realize that I'm not being terribly rigorous in my description here, but that is partly because I am not sure how to report on this yet. I think my next step is going to be to build a standalone executable to check using the Unix time command. For reference I am running Haskell platform from Debian Jessie on a 16- core amd64 system with 29GiB or RAM available. This would appear to be GHC 7.6.3 :( - d

3 2

Design of protocol implementation?
by Magnus Therning 05 Mar '15

05 Mar '15

By now I've written a couple of implementations of (reply / response) protocols in Haskell. They all basically follow the same pattern: 1. One message type with a constructor for each, e.g. data Message = PingMsg | ... 2. One reply type with a constructor for each, e.g. data Reply = PingReply | ... 3. Any message or reply containing data has a constructor taking an argument of a type for that data, e.g. data Message = ... | SendDataMsg SendDataD | ... data SendDataD = SendDataD ByteString 4. The raw data is received from somewhere and passed through a parser written using attoparsec. 5. The messages are rendered into ByteString using ByteString.Builder. So, in essence something like this: +------+ +----------+ +-------+ +------------+ +------+ | read | --> | parse | --> | stuff | --> | render | --> | send | | raw | | into | +-------+ | to | | raw | +------+ | Messages | | ByteString | +------+ +----------+ +------------+ I'm curious to hear about other ways to handle protocols. Are there any papers written on implementing protocols using FP in particular? The protocols I've faced are rather simple things, what about more complicated ones, e.g. multi-layered protocols (ala IP - TCP)? /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus In order to understand recursion you must first understand recursion.

4 3

(no subject)
by S J Rajath Krishna 05 Mar '15

05 Mar '15

I would like to create an account with the following user name User name : "raxerz" (Without the quotes) Thanks,S J Rajath Krishna

3 6

ghci and dynamically linking to Objective-C objects on Mac OS X
by Sean Seefried 05 Mar '15

05 Mar '15

Hi all, I fear I might be unaware of something I should be. Say I have a file objc_util.m with the following contents: #include <Foundation/Foundation.h> void ns_log(const char *s) { NSString *str = [NSString stringWithUTF8String:s]; NSLog(@"%@", str); } I also have a file Main.hs with contents: {-# LANGUAGE ForeignFunctionInterface #-} module Main where import Foreign.C.Types import Foreign.C.String foreign import ccall "ns_log" cNSLog :: CString -> IO () nsLog s = withCString s cNSLog I compile objc_util.m with: gcc -c objc_util.m And then I try to open it up in GHCi. ghci objc_util.o Main.hs -framework Foundation I add the flag '-frame Foundation' in the hopes that symbols in objc_util.o will get resolved dynamically. However I get: GHCi, version 7.8.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading object (static) objc_util.o ... ghc: panic! (the 'impossible' happened) (GHC version 7.8.3 for x86_64-apple-darwin): Loading temp shared object failed: dlopen(/var/folders/pv/pfxcyy117v31vt6lsshtgr_w0000gn/T/ghc33546_0/ghc33546_1.dylib, 9): Symbol not found: _OBJC_CLASS_$_NSString Referenced from: /var/folders/pv/pfxcyy1 17v31vt6lsshtgr_w0000gn/T/ghc33546_0/ghc33546_1.dylib Expected in: flat namespace in /var/folders/pv/pfxcyy117v31vt6lsshtgr_w0000gn/T/ghc33546_0/ghc33546_1.dylib Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug However, I have found a work around to this. If I do this: ln -s /System/Library/Frameworks/Foundation.framework/Foundation Foundation.o and then run ghci Foundation.o objc_util.o Main.hs I get this: GHCi, version 7.8.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading object (static) Foundation.o ... done Loading object (static) objc_util.o ... done final link ... done Everything has worked! And I can happily run 'nsLog' from GHCi and have it appear in the 'Console' app. However, it doesn't seem like I should have to do this. Where am I going wrong? Sean

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[TFPIE 2015] 2nd call for papers
by Peter Achten 05 Mar '15

05 Mar '15

Trends in Functional Programming in Education (TFPIE 2015) 2nd Call for papers https://wiki.science.ru.nl/tfpie/TFPIE2015 The 4th International Workshop on Trends in Functional Programming in Education, TFPIE 2015, will be held on June 2, 2015 in Sophia-Antipolis in France. It is co-located with the Symposium on Trends in Functional Programming (TFP 2015) which takes place from June 3 - 5. *** Goal *** The goal of TFPIE is to gather researchers, teachers and professionals that use, or are interested in the use of, functional programming in education. TFPIE aims to be a venue where novel ideas, classroom-tested ideas and work-in-progress on the use of functional programming in education are discussed. The one-day workshop will foster a spirit of open discussion by having a review process for publication after the workshop. The program chair of TFPIE 2015 will screen submissions to ensure that all presentations are within scope and are of interest to participants. Potential presenters are invited to submit an extended abstract (4-6 pages) or a draft paper (up to 16 pages) in EPTCS style. The authors of accepted presentations will have their preprints and their slides made available on the workshop's website/wiki. Visitors to the TFPIE 2015 website/wiki will be able to add comments. This includes presenters who may respond to comments and questions as well as provide pointers to improvements and follow-up work. After the workshop, presenters will be invited to submit (a revised version of) their article for review. The PC will select the best articles for publication in the journal Electronic Proceedings in Theoretical Computer Science (EPTCS). Articles rejected for presentation and extended abstracts will not be formally reviewed by the PC. TFPIE workshops have previously been held in St Andrews, Scotland (2012), Provo Utah, USA (2013), and Soesterberg, The Netherlands (2014). *** Program Committee *** Peter Achten, Radboud University Nijmegen, The Netherlands Edwin Brady, University of St Andrews, UK Johan Jeuring, Utrecht University and Open University, The Netherlands (Chair) Shriram Krishnamurthi, Brown University, US Rita Loogen, Philipps-Universität Marburg, Germany Marco Morazan, Seton Hall University, US Norman Ramsey, Tufts University, US *** Submission Guidelines *** TFPIE 2015 welcomes submissions describing techniques used in the classroom, tools used in and/or developed for the classroom and any creative use of functional programming (FP) to aid education in or outside Computer Science. Topics of interest include, but are not limited to: - FP and beginning CS students - FP and Computational Thinking - FP and Artificial Intelligence - FP in Robotics - FP and Music - Advanced FP for undergraduates - Tools supporting learning FP - FP in graduate education - Engaging students in research using FP - FP in Programming Languages - FP in the high school curriculum - FP as a stepping stone to other CS topics - FP and Philosophy *** Best Lectures *** In addition to papers, we request “best lecture” presentations. What is your best lecture topic in an FP related course? Do you have a fun way to present FP concepts to novices or perhaps an especially interesting presentation of a difficult topic? In either case, please consider sharing it. Best lecture topics will be selected for presentation based on a short abstract describing the lecture and its interest to TFPIE attendees. *** Submission *** Papers and abstracts can be submitted via easychair at the following link: https://easychair.org/conferences/?conf=tfpie2015 It is expected at at least one author for each submitted paper will attend the workshop. *** Important Dates *** April 7, 2015: Early Registration for TFP closes April 27, 2015: Submission deadline for draft TFPIE papers and abstracts May 3 2015: Notification of acceptance for presentation ?? (Probably May 22 2015): Registration for TFPIE closes - as does late registration for TFP June 2, 2015: Presentations in Sophia-Antipolis, France July 7, 2015: Full papers for EPTCS proceedings due. September 1, 2015: Notification of acceptance for proceedings September 22, 2015: Camera ready copy due for EPTCS Submission of an abstract implies no obligation to submit a full version; abstracts with no corresponding full versions by the full paper deadline will be considered as withdrawn.

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Haskell Weekly News
by Kim-Ee Yeoh 04 Mar '15

04 Mar '15

*Top picks:* Jasper Van der Jeugt <http://jaspervdj.be/posts/2015-02-24-lru-cache.html> shows how you can write an intuitive, obviously correct LRU cache perfectly polymorphic in both the key and value types of the cache lookup function. (Reddit discussion.) <http://www.reddit.com/r/haskell/comments/2wz4tj/writing_an_lru_cache_in_has…> Core is broken! Well, no, ticket 9858 <https://ghc.haskell.org/trac/ghc/ticket/9858> reported previously is still open, and it's about translating an exotic species of Haskell into Core. But Javran Cheng <https://ghc.haskell.org/trac/ghc/ticket/10121> found out that the documented specification of Core's operational semantics is incomplete. Neil Mitchell <http://neilmitchell.blogspot.com/2015/02/making-withsocketsdo-unnecessary.h…> removes the error-prone wart of withSocketsDo <http://hackage.haskell.org/package/network-2.6.0.2/docs/Network.html#v:with…> in Windows network programming. Moving in for the kill is the triple combo of evaluate, NOINLINE, and unsafePerformIO. (Reddit discussion.) <http://www.reddit.com/r/haskell/comments/2x7js6/making_withsocketsdo_unnece…> Can you write a sorting algorithm? Can you write a fancy sorting algorithm? Can you write a sorting algorithm so fancy it hides a subtle bug? Can you write a sorting algorithm so fancy that it hides a bug so subtle <https://github.com/timjb/haskell-timsort/commit/d9c3e1e454c7d338320f8c2aa12…> that it evades even QuickCheck because the smallest testcase is 2^49 big? But the good news is that QuickCheck doesn't see any regression in the bugfix. (Hacker News discussion.) <https://news.ycombinator.com/item?id=9100107#up_9112425> The consequence of misspelling pragmas <https://ghc.haskell.org/trac/ghc/ticket/10106>, Or: when stumped on a compile error, turn on -Werror to see if you aren't missing something obvious. *Quote of the week:*garry__cairns <https://twitter.com/garry__cairns/status/571087073739976704>: The trouble with learning #haskell is the more I expose myself to it the more I dislike what I have to work with to pay the bills. *Repo of the week: *Kalium <https://github.com/int-index/kalium>: Turn Pascal <https://int-index.github.io/kalium/examples.html> into Haskell -- Kim-Ee

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Haskell 2015: 2nd Call for Papers
by Ben Lippmeier 04 Mar '15

04 Mar '15

===================================================================== ACM SIGPLAN CALL FOR SUBMISSIONS Haskell Symposium 2015 Vancouver, Canada, 3-4 September 2015, directly after ICFP http://www.haskell.org/haskell-symposium/2015 ===================================================================== ** The Haskell Symposium has an early track this year ** ** See the Submission Timetable for details. ** The ACM SIGPLAN Haskell Symposium 2015 will be co-located with the International Conference on Functional Programming (ICFP 2015) in Vancouver, Canada. The Haskell Symposium aims to present original research on Haskell, discuss practical experience and future development of the language, and to promote other forms of denotative programming. Topics of interest include: * Language Design, with a focus on possible extensions and modifications of Haskell as well as critical discussions of the status quo; * Theory, such as formal semantics of the present language or future extensions, type systems, effects, metatheory, and foundations for program analysis and transformation; * Implementations, including program analysis and transformation, static and dynamic compilation for sequential, parallel, and distributed architectures, memory management, as well as foreign function and component interfaces; * Libraries, that demonstrate new ideas or techniques for functional programming in Haskell; * Tools, such as profilers, tracers, debuggers, preprocessors, and testing tools; * Applications, to scientific and symbolic computing, databases, multimedia, telecommunication, the web, and so forth; * Functional Pearls, being elegant and instructive programming examples; * Experience Reports, to document general practice and experience in education, industry, or other contexts. Papers in the latter three categories need not necessarily report original academic research results. For example, they may instead report reusable programming idioms, elegant ways to approach a problem, or practical experience that will be useful to other users, implementors, or researchers. The key criterion for such a paper is that it makes a contribution from which other Haskellers can benefit. It is not enough simply to describe a standard solution to a standard programming problem, or report on experience where you used Haskell in the standard way and achieved the result you were expecting. More advice is available via the Haskell wiki: (http://wiki.haskell.org/HaskellSymposium/ExperienceReports) Regular papers should explain their research contributions in both general and technical terms, identifying what has been accomplished, explaining why it is significant, and relating it to previous work, and to other languages where appropriate. In addition, we solicit proposals for: * System Demonstrations, based on running software rather than novel research results. These proposals should summarize the system capabilities that would be demonstrated. The proposals will be judged on whether the ensuing session is likely to be important and interesting to the Haskell community at large, whether on grounds academic or industrial, theoretical or practical, technical, social or artistic. Please contact the program chair with any questions about the relevance of a proposal. Travel Support: =============== Student attendees with accepted papers can apply for a SIGPLAN PAC grant to help cover travel expenses. PAC also offers other support, such as for child-care expenses during the meeting or for travel costs for companions of SIGPLAN members with physical disabilities, as well as for travel from locations outside of North America and Europe. For details on the PAC program, see its web page (http://pac.sigplan.org) Proceedings: ============ Accepted papers will be included in the ACM Digital Library. Authors must grant ACM publication rights upon acceptance (http://authors.acm.org/main.html) Authors are encouraged to publish auxiliary material with their paper (source code, test data, etc.); they retain copyright of auxiliary material. Accepted proposals for system demonstrations will be posted on the symposium website, but not formally published in the proceedings. All accepted papers and proposals will be posted on the conference website one week before the meeting. Publication date: The official publication date of accepted papers is the date the proceedings are made available in the ACM Digital Library. This date may be up to two weeks prior to the first day of the conference. The official publication date affects the deadline for any patent filings related to published work. Submission Details: =================== Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines (http://www.acm.org/sigs/sigplan/authorInformation.htm) The text should be in a 9-point font in two columns. The length is restricted to 12 pages, except for "Experience Report" papers, which are restricted to 6 pages. Papers need not fill the page limit -- for example, a Functional Pearl may be much shorter than 12 pages. Each paper submission must adhere to SIGPLAN's republication policy, as explained on the web. Demo proposals are limited to 2-page abstracts, in the same ACM format as papers. "Functional Pearls", "Experience Reports", and "Demo Proposals" should be marked as such with those words in the title at time of submission. The paper submission deadline and length limitations are firm. There will be no extensions, and papers violating the length limitations will be summarily rejected. A link to the paper submission system will appear on the Haskell Symposium web site closer to the submission deadline. Submission Timetable: ===================== Early Track Regular Track System Demos ---------------- ------------------- --------------- 13th March Paper Submission 1st May Notification 19th May Abstract Submission 22nd May Paper Submission 5th June Resubmission Demo Submission 26th June Notification Notification Notification 19th July Final papers due Final papers due Deadlines stated are valid anywhere on earth. In this iteration of the Haskell Symposium we are trialling a two-track submission process, so that some papers can gain early feedback. Papers can be submitted to the early track on 13th March. On 1st May, strong papers are accepted outright, and the others will be given their reviews and invited to resubmit. On 5th June early track papers may be resubmitted, and are sent back to the same reviewers. The Haskell Symposium regular track operates as in previous years. Papers accepted via the early and regular tracks are considered of equal value and will not be distinguished in the proceedings. Although all papers may be submitted to the early track, authors of functional pearls and experience reports are particularly encouraged to use this mechanism. The success of these papers depends heavily on the way they are presented, and submitting early will give the program committee a chance to provide feedback and help draw out the key ideas. Program Committee: =================== Mathieu Boespflug - Tweag I/O Edwin Brady - University of St Andrews Atze Dijkstra - Utrecht University Tom DuBuisson - Galois Torsten Grust - University of Tuebingen Patrik Jansson - Chalmers University of Technology Patricia Johann - Appalachian State University Oleg Kiselyov - Tohoku University Edward Kmett - McGraw Hill Financial Neelakantan Krishnaswami - University of Birmingham Ben Lippmeier (chair) - Vertigo Technology Hai (Paul) Liu - Intel Labs Garrett Morris - University of Edinburgh Dominic Orchard - Imperial College London Matt Roberts - Macquarie University Tim Sheard - Portland State University Joel Svensson - Indiana University Edsko de Vries - Well Typed =====================================================================

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ANN: ZuriHac 2015: registration is open
by Alexander Bernauer 04 Mar '15

04 Mar '15

Hi everybody, it is my pleasure to announce that the registration for ZuriHac 2015 <https://wiki.haskell.org/ZuriHac2015> is open now. If you want to participate in this year's Haskell Hackathon in Zurich, please fill out this form <http://goo.gl/forms/L24NgFRvCw>. Make sure to wait for a confirmation email afterwards before booking. The event can only host around 90 participants. We will confirm registrations at a first come first served basis. Please spread the word. Hope to see you soon! Alex

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Re: [Haskell-cafe] [Haskell] Constraint Satisfaction Problem
by Henning Thielemann 04 Mar '15

04 Mar '15

On Wed, 4 Mar 2015, K Sai Anirudh wrote: > Hello, > > I tried to solve simple constraint satisfaction problem. This is my code " http://pastebin.com/VAaRYSEA " . > This gives solution for present list of domains, but when I change the domain of 'd' in the list 'ld' then I > get error. I think the error is in line 52. I indexed the first value, but I tried filtering the results > where all the variables are assigned and I get error. I think this fits better to Haskell Cafe <haskell-cafe(a)haskell.org> where I send this reply, too.

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Help needed
by S J Rajath Krishna 03 Mar '15

03 Mar '15

I am a newbie to contributing to open source.I need help or the procedure for the following. 1.Replying to a thread2.Creating an account with the forum that will help me get started off for GSOC 2015. I apologize if this is not the right forum to be posting this, please direct me to the right forum. Thanks,S J Rajath Krishna

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Re: [Haskell-cafe] Hackage and Free Software
by Mike Meyer 03 Mar '15

03 Mar '15

On Sat, Feb 28, 2015 at 11:27 AM, fr33domlover <fr33domlover(a)riseup.net> wrote: > Hello haskellers! > I'd like to make a suggestion: have Hackage accept only packages released under > free software licenses. Anything that excludes software that we could use, or otherwise discourages people from making software available to the community, is a bad idea. A restriction to OSF-approved licenses would exclude anything released under a Creative Commons license, since the OSF doesn't list those, which makes sense as they aren't "software licences" per se. And your restriction of "released under a license" would exclude public domain software - at least in countries that recognize such a thing. Yes, these are nits, but these are nits that could cause someone to decide not to put software that is otherwise perfectly acceptable on Hackage. > Actually the all-rights-reserved tag in Hackage [1] has only two packages > tagged by it - the dummy no-op project HNop, and another package whose COPYING > file contains a broken link and whose README says "BSD style license". This is a general problem on any site that offers downloads with a license type tag. What happens if the selected license tag and the included license have different rights? My suspicion is that if it went to court, you could justify using it under either license, meaning that such things are effectively dual licensed. We might make add a statement making that explicit. In particular, an "all-rights-reserved" tag implies that you may have to ask someone's permission to even download the package from Hackage, so it doesn't make a lot of sense. Given that - with the dual license interpretation - it effectively isn't used, removing it might make sense. Or renaming it to "other not listed" may be more appropriate. <mike

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Re: [Haskell-cafe] Hackage and Free Software
by Mike Meyer 03 Mar '15

03 Mar '15

On Mon, Mar 2, 2015 at 3:36 PM, fr33domlover <fr33domlover(a)riseup.net> wrote: > On 2015-02-28 > Mike Meyer <mwm(a)mired.org> wrote: > > > > > There are open source projects that are systematically excising GPL'ed > > software because of the problems it shares with ShareAlike licenses. > Should > > we disallow the GPL because some people have problems with it? > > > > Making Hackage better to help users sort out which licenses they are > > willing to accept in their project - which I personally would like to do > on > > a project-by-project basis! - is a solution to these problems. > Restricting > > the licenses that are acceptable on Hackage to meet some arbitrary set of > > criteria is a knee-jerk. > The restrictions aren't arbitrary at all. They're based on ethics. On > Software > freedom. > Until you've got an objective set of ethics - or a definition of "software freedom" - that everyone accepts, that's just a long-winded way of saying "arbitrary". Here's a suggestion: We can talk about this forever, because there seem to > be > no official guidelines to really discuss. Why don't we put clear > guidelines at > hackage.haskell.org ? If these guidelines would be "proprietary software > allowed", then there's a point to discuss. But if the guideline requires > certain tagging - currently all the license tags except > all-rights-reserved are > free software licenses - maybe the problem is already solved. > Not quite. "OtherLicense" is an accepted license tag, and I take it to mean I can use any license I want. If you're going to place a restriction on the license types beyond "use one of our tags" (and if you disallow the otherLicense tag, then I'd say that's an arbitrary restriction), then you should either define the terms in it, or choose terms that are well defined. "free software" is so ill defined that gnu.org has to explain what they mean by "free software" (https://www.gnu.org/philosophy/free-sw.html) They even point out that there are open source software licenses that don't meet their definition of free ( https://www.gnu.org/philosophy/open-source-misses-the-point.html) Their definition of proprietary as "not free" makes software licensed under such licenses proprietary, though that's certainly not common usage. So just saying "only free software licenses" or "no proprietary software" would make matters worse, not better, because those terms have multiple meanings in common use. And that makes them not only arbitrary, but vague.

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