- Haskell-Cafe - Haskell.org

[ANN] SBV 5.4 is out
by Levent Erkok 10 Nov '15

10 Nov '15

I'm happy to announce a new release (v5.4) of SBV: SMT Based Verification. See: http://hackage.haskell.org/package/sbv New in this release is the 'sAssert' function, which allows boolean-assertions to be sprinkled in symbolic code, which can then be statically discharged (or shown violating assignments for) using the 'safe' function. See: http://hackage.haskell.org/package/sbv-5.4/docs/Data-SBV.html#g:39 A slightly larger example checks for lack-of-division-by-0 in a simple program: http://hackage.haskell.org/package/sbv-5.4/docs/Data-SBV-Examples-Misc-NoDi… Further documentation on SBV is available at: http://leventerkok.github.io/sbv/ Calls to sAssert calls are also preserved in the SBV->C compilation path. This feature is rather experimental and , and I'd love to hear if you give it a try and see any gotchas.. Happy proving. -Levent. PS. Thanks to Brett Letner for suggesting this functionality.

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Anybody using the "top-down" cabal-install solver?
by Bardur Arantsson 09 Nov '15

09 Nov '15

(Sorry if you get this twice, forgot to cross-post to -cafe initially.) Hi all, Just to get input from as many people as possible: I was pondering a plan for modularizing[2] the Cabal solver[1] and wanted to reach as many people as possible with my question: Is anybody is still using the top-down solver? Please respond to this list if you are, especially if you're doing so because there's no other way to get the modular solver to do what you want. (Obviously, I'm not promising to fix any problems you may have with the modular solver, but it would be valuable information since it could affect the decision of whether we have to keep the top-down solver around.) Regards, -- [1] https://github.com/haskell/cabal/pull/2768#issuecomment-154917165 [2] "Splitting it out into its own library" is perhaps a more accurate description, but somewhat unwieldly :).

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Where io-streams won't fit, comparing to conduit or pipes
by Daisuke Fujimura 09 Nov '15

09 Nov '15

Hello cafe, Now I'm preparing a presentatio for meetup for stream processing in functional programming(in Tokyo), and my part is something like "why stream processing library". While preparing material, I encountered the question that why io-streams is so simple comparing others, and the reason and downsides behind its simplicity. I'm guessing it's due to its resource handling strategy, but not so confident about it because I couldn't came up with a concrete example yet. Do you know any good example where io-streams won't fit? Let me know if you have. Thanks!

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How to get GHC to produce ADC instructions for long addition
by Clinton Mead 09 Nov '15

09 Nov '15

Here is some code that adds two 192 bit numbers, represented as three 64bit machine words (well, on my machine anyway), and returns the result and any carry: {-# LANGUAGE MagicHash #-} {-# LANGUAGE UnboxedTuples #-} import GHC.Prim( plusWord2#, Word#, or#) longAdd :: (# Word#, Word#, Word# #) -> (# Word#, Word#, Word# #) -> (# Word#, (# Word#, Word#, Word# #) #) longAdd (# xl, xm, xh #) (# yl, ym, yh #) = let plusWord2WithCarry x y c = let (# c1, r1 #) = plusWord2# x y (# c2, r2 #) = plusWord2# r1 c in (# plusWord# c1 c2, r2 #) (# cl, rl #) = plusWord2# xl yl (# cm, rm #) = plusWord2WithCarry xm ym cl (# ch, rh #) = plusWord2WithCarry xh yh cm in (# ch, (# rl, rm, rh #) #) (My code covers words other than size 3 btw) I'd like this to compile into something like: add x1 y1 adc x2 y2 adc x3 y3 Unfortunately, I think my problem is with the "plusWord2WithCarry". As there's no primitive operation in Haskell which adds two words and a carry. What seems to happen when I look at the generated assembly is the following: xor some_reg_1 some_reg_1 add x1 y1 adc $0 some_reg_1 xor some_reg_2 some_reg_2 adc x2 y2 adc $0 some_reg_2 xor some_reg_3 some_reg_3 adc some_reg_1 y2 adc $0 some_reg_3 add some_reg_2 some_reg_3 ... and so on Basically, instead of just using the carry flag in add of the next two higher words, it instead saves it to a register, adds the next higher order words without the carry, clears a register and then adds the carry to this register, adds the first mentioned carry, against clears a register and saves that carry, combines the two resulting carries and passes it to the next higher order addition. I know that sounds complex, and the code is a bit of a mess. Bizarrely, when I send it through the LLVM backend it ends up worse, generating a bunch of 32 bit shifts for reasons I can't understand. I was hoping the LLVM backend would be able to produce the "adc" instructions. Is there anything I could do to coax it into it. I know writing it in C (or inline assembly in C) is an option, but after you add the code to call and return such a small amount of work it seems hardly worth it. I'd like to keep it in GHC so it can be inlined where appropriate. Any ideas on how to entice GHC (either natively or via LLVM) to produce better code in this case?

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More death to partial functions: Should -fwarn-incomplete-uni-patterns be enabled with -Wall?
by Niklas Hambüchen 08 Nov '15

08 Nov '15

Hello everyone, to my dismay, a -Wall compiled program I deployed today crashed with Exception: Non-exhaustive patterns in lambda and I learned from http://dev.stephendiehl.com/hask/ that A more subtle case is when implicitly pattern matching with a single "uni-pattern" in a lambda expression. The following will fail when given a Nothing. boom = \(Just a) -> something GHC can warn about these cases with the -fwarn-incomplete-uni-patterns flag. And in fact: ghci -Wall > map (\Nothing -> "ok") [Just 'a'] ["*** Exception: <interactive>:2:6-21: Non-exhaustive patterns in lambda > :set -fwarn-incomplete-uni-patterns > map (\Nothing -> "ok") [Just 'a'] <interactive>:4:6: Warning: Pattern match(es) are non-exhaustive It really surprised me that -fwarn-incomplete-uni-patterns is not included in -Wall; I've felt really safe with my -Wall so far, especially about totality and similar things that will almost certainly lead to crashes. In an older mail from 2010 (https://mail.haskell.org/pipermail/glasgow-haskell-users/2010-September/019…) I saw Simon mention that it wasn't planned to warn about inexhaustive patterns like this. I feel like there has been a strong push towards more totality in the last years, and I would like to ask if enabling -fwarn-incomplete-uni-patterns in -Wall may be reconsidered for a coming next GHC version, or if there are still opponents to that. Niklas

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Pattern matching with OverloadedLists
by Vlatko Basic 06 Nov '15

06 Nov '15

Hello Cafe, wiki for OverloadedLists says that g [x,y,z] = ... is treated as g (toList-> [x,y,z]) = Shouldn't this work? Both 'f's should be treated the same. f :: Text -> Int f (toList -> ('9':_)) = 1 -- OK f ('1':_) = 2 -- Couldn't match expected type ‘Text’ with actual type ‘[Char]’ (OverloadedStrings is also on) Am I missing something? br, vlatko

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User guide for DeriveAnyClass
by Kostiantyn Rybnikov 06 Nov '15

06 Nov '15

Is there a topic for DeriveAnyClass extension in user guide? It is mentioned several times in different places, also I see link to it in from cabal haddocs [0] into its page inside "other type extensions" [1], but it leads nowhere. Thank you. [0]: https://www.haskell.org/cabal/release/cabal-latest/doc/API/Cabal/Language-H… [1]: https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/other-type-…

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How to install newest ghcjs-base
by Arie Peterson 05 Nov '15

05 Nov '15

5 days ago a change [1] was made to the ghcjs-base library. How can one obtain a ghcjs that incorporates such a recent version of ghcjs-base? I installed ghcjs from git master yesterday, and installed the boot libraries using "ghcjs-boot --dev". However, I still get "Module ‘JavaScript.Web.MessageEvent’ does not export ‘getData’", so apparently my ghcjs-base lags behind somehow. What determines the version of ghcjs-base that is installed? Regards, Arie [1] <https://github.com/ghcjs/ghcjs-base/commit/e827ded07053a3281c50ee52b3e3ebd3…>

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Yampa: upcoming changes; maintaining the projects we care about
by Ivan Perez 05 Nov '15

05 Nov '15

Dear all I am the current maintainer of the FRP implementation Yampa. (For context: I'm a PhD student at Nottingham, working with Henrik Nilsson.) Yampa contains legacy code that used to be useful to get things running quickly. In the interest of having minimal overhead and using existing robust solutions whenever possible, we'd like to remove some of that old auxiliary code. These changes will not affect the core of Yampa (SF definitions, arrow combinators, switches, etc.), but only auxiliary/miscelaneous stuff (vector spaces, deep strict evaluation type class, tupling/monad aux functions, etc.). We've been introducing these changes progressively over the last year, by first re-structuring the code base and marking some functions as deprecated. The time is coming for backwards incompatible changes, but I'd like to make sure that the projects you care about keep working as before. This may include (but is not limited to): * Code (which may not be on hackage, so it may be difficult for me to even know it exists). * Examples included in papers, slides, blog posts, etc. So, if you may be affected by these changes, please: - Watch the github project [1] and subscribe to yampa-users(a)cs.yale.edu, which is where details will be announced. It's a low traffic mailing list. - If you can deal with it yourself by upgrading your code, please do so. Otherwise, feel free to drop a line. - If your use case does not support easy upgrading (papers? talk videos?) please let me know. For starters, we may be able to concentrate all the potential compilation errors that your users might get in one place in the documentation. - If you are affected in a way that I'm not seeing, please let me know. All the best Ivan [1] http://github.com/ivanperez-keera/Yampa

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Looking for a new maintainer: Bindings-DSL, c2hsc
by John Wiegley 05 Nov '15

05 Nov '15

Hello, The Bindings-DSL libraries, and the c2hsc tool that parses C headers into .hsc files, both on Hackage, are looking for new maintainers. People are using these libraries to get real work done, and I no longer wish to be a stumbling block due to lack of time. If you're interested, please drop me a line. Anyone with experience at C parsing would be great, but those with a desire to learn it are good too. I'd be available to help with questions indefinitely, I just lack the time to stay on top of every bug. Thank you, John Wiegley

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Warnings suppression and examples
by Эдгар Жаворонков 05 Nov '15

05 Nov '15

Hello everyone! This may be a strange question, but nevertheless. I am interested in examples of warnings, thrown by GHC, that you, Haskell programmers, want to suppress. To be more precise, i am interested, what kind of warnings you would like to suppress in: 1. Functions 2. Imports 3. Typeclasses 4. Instances Thank you! P.S. I want to implement possibility of warning suppression with single pragma, that's why i am asking my question here --- С уважением, Жаворонков Эдгар Best regards, Edgar A. Zhavoronkov --- С уважением, Жаворонков Эдгар Best regards, Edgar A. Zhavoronkov

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Re: [Haskell-cafe] [Haskell] ANNOUNCE: polymap 0.1.0.1
by Roman Cheplyaka 04 Nov '15

04 Nov '15

(moving from haskell@ to haskell-cafe@) Hi David, As someone who is not familiar with the concept of polygonal maps, I find this package severely underdocumented. What is a polymap? Why would I want to use one? What is storage and how should I choose it? The example clears it up a bit, but it could also use more prose. And perhaps there could be a more motivated example (showing how polymap solves an actual problem). On 09/24/2015 09:53 PM, David Farrell wrote: > I'm excited to announce the first release of a package I've been working > on over the last week called polymap, a library providing type-safe > polygonal maps whose sides are defined by a kindlist of types zipped > with a storage type for each side. I've tried to match the interface > exposed by the containers package as closely as possible. For example: > > import Data.Set (Set) > import Data.PolyMap.Nat (first, second, third) > import qualified Data.PolyMap as PM > > mEmpty :: PM.PolyMap '[ '(String, Set), '(Int, Set) ] > mEmpty = PM.empty > > mOne :: PM.SimplePolyMap '[String, Int] Set > mOne = PM.singleton ("one", length "one") > > main = do > print mEmpty -- empty PolyMap > print mOne -- PolyMap with one Relation > print mTwo -- PolyMapwith two Relations > print (PM.member first "one" mTwo) -- True > print (PM.notMember first "asdf" mTwo) -- True > --print (PM.notMember second "asdf" mTwo) -- will not typecheck > --print (PM.notMember third "asdf" mTwo) -- will not typecheck > print (PM.lookup first "two" mTwo) -- second Relation of PolyMap > where mTwo = PM.insert ("two", length "two") mOne > > This is a short usage example of most of the functions currently written > for polymap. There's still a long way to go both in terms of exposed > functions and in terms of efficiency and such, but I felt it prudent to > make a public release of my work so far as I feel it's reached a stage > where it could be beneficial to others. Note that GHC 7.10 (base >=4.8, > GHC extensions) is required. > > Git Repository: > https://github.com/shockkolate/hs-polymap > > Issue Tracker: > https://github.com/shockkolate/hs-polymap > > Hackage: > https://hackage.haskell.org/package/polymap > > The code is licensed under the Unlicense license--that is to say, the > code is released into the public domain for the benefit of others. > > I'd love to hear any feedback/suggestions/improvements/anything you want > to say about polymap over the mailing list (which may be more suited to > the haskell-cafe mailing list; I don't know) or in #haskell on Freenode > (I'm usually in there as Shockk). > > N.B. Version 0.1.0.0 of the package will not build due to the use of a > function in containers that has been submitted as a pull request but > does not exist yet/at all. > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell >

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record field names vs. -fwarn-unused-binds
by Evan Laforge 04 Nov '15

04 Nov '15

[ ccing haskell-cafe since while it's a ghc flag, I'll bet most compilers have an equivalent ] I really like -fwarn-unused-binds because it frequently finds bugs where I forgot to call something or use some value. If I put an export list on, it can find dead functions I forgot to delete. However, there's one case where it frequently gives false positives, and that's unused record field names. The problem is that I sometimes use record field names as documentation, but the record itself is internal and small, so I'm comfortable using positional pattern matching to open it (and in fact that can be safer, since then warn-unused-binds will make sure I used all the fields). But GHC sees these as unused functions, so it warns about them. I can work around by putting underscores on field names I haven't used yet, but it's a hassle to go edit them when I want to use them. The warning can be useful if it indicates an unused field, but since fields can also be extracted via the positional syntax it's not reliable. The other use of the warning for dead code or functions you forgot to use doesn't apply to record accessors because they're trivial and compiler generated. So, would it be reasonable to exclude record field accessors from -fwarn-unused-binds? Or is there another way to work around it? I guess GHC doesn't have a "suppress warning" pragma like Java does, but even if we did it wouldn't be much better than changing the name, and more likely to get stale.

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Haskell positions in Moscow, Positive Technologies
by Kosyrev Serge 04 Nov '15

04 Nov '15

Good day! The Moscow office of Positive Technologies (http://ptsecurity.com) seeks Haskell developers with strong C background, as part of an effort to develop a next-generation (of course!) democratic security platform. Think widely available, easy-to-use, dramatically enhanced security. If this kind of thing feels motivating, please send your resume to career(a)ptsecurity.com and CC skosyrev(a)ptsecurity.com. Position: Senior Software Engineer Vague description: - bare-metal, kernel, userland development Required experience: - C programming - experience of applying GHC in FFI-heavy context - experience with kernel development (some of Linux, Windows, Darwin) - experience writing resource-efficient Haskell code - experience with parallelism - taming laziness - taming the GC (desirable) - experience with the Intel system platform (desirable) - some knowledge of GHC runtime internals (desirable) -- respectfully, Kosyrev Serge http://www.ptsecurity.com/ Habr: http://habr.ru/company/pt Twitter: @ptsecurity https://twitter.com/ptsecurity

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Haskell Engineer Needed for Machine Learning Group
by Charles Weitzer 04 Nov '15

04 Nov '15

Voleon Capital Management LP is a quantitative hedge fund located in Berkeley, California. We would like to hire a senior software engineer with strong functional programming experience as soon as possible. Voleon's founders previously worked together at one of the most successful quantitative hedge funds in the world. Our CEO has a PhD in Computer Science from Stanford and has been CEO and founder of a successful Internet infrastructure startup. Our Chief Investment Officer has a PhD in Statistics from Berkeley. Voleon's team includes PhD's from leading departments in statistics, computer science, and mathematics. We have made several unpublished advances in the field of machine learning and in other areas as well. Here is our formal job description: ********************************************************** * Senior Software Engineer * Technology-driven investment firm employing cutting-edge statistical machine learning techniques seeks an exceptionally capable software engineer. You will architect and implement new production trading systems, machine learning infrastructure, data integration pipelines, and large-scale storage systems. The firm researches and deploys systematic trading strategies designed to generate attractive returns without being dependent on the performance of the overall market. Join a team of under 30 people that includes a Berkeley statistics professor as well as over ten PhD's from Berkeley, Chicago, CMU, MIT, Princeton, Stanford, and UCLA, led by the founder and CEO of a successful Internet infrastructure technology firm. The firm's offices are walking distance from BART and the UC Berkeley campus in downtown Berkeley, California. We have a casual and collegial office environment, catered lunches, and competitive benefits packages. We seek candidates with a proven track record of writing correct, well-designed software, solving hard problems, and delivering complex projects on time. You should preferably have experience designing and implementing fault-tolerant distributed systems. Experience with building large-scale data infrastructure, stream processing systems, or latency-sensitive programs is a bonus. We are growing rapidly. Willingness to take initiative and a gritty determination to productize are essential. Required experience: - strong experience developing in a functional programming environment (Haskell, Erlang, others). - developing with C/C++/Python/Go in a Linux environment with a focus on performance, concurrency, and correctness. - working in TCP/IP networking, multi-threading, and server development. - working with common Internet protocols (IP, TCP/UDP, SSL/TLS, HTTP, SNMP, etc.). - architecting and designing highly available systems. - architecting and designing large-scale data management infrastructure. - working in large codebases and building modular, manageable code. Preferred experience.: - debugging and performance profiling, including the use of tools such as strace, valgrind, gdb, tcpdump, etc. - working with build and test automation tools. - working with well-defined change management processes. - diagnosing RDBMS performance problems, exploiting indexing, using EXPLAIN PLAN, optimizing at the code layer, etc. - working with messaging queues (RabbitMQ, Redis, etc.) as well as distributed caching systems. Interest in financial applications is essential, but experience in finance is not a primary factor in our hiring. Benefits and compensation are highly competitive. ********************************************************** The above job description is just a starting point in terms of possible duties and seniority. We can be very flexible for the right person. If you are interested please apply on our website: http://voleon.com/apply/. If you have any questions or if you know of anyone who might be interested, let us know the best way to get in touch and we can discuss details. Thank you, Charles Weitzer Senior Recruiter Voleon Capital Management LP Office: 510.704.9870 x 7012 Mobile: (510) 558-9182 www.Voleon.com<http://www.voleon.com/>

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Streaming a Conduit into a lazy list
by Jules Bean 04 Nov '15

04 Nov '15

Conduits seem like a popular and useful way to compose operations which consume and produce streams at various speeds. I hadn't used them before, so apologies for any obvious mistakes below. Conduits have lots of power in terms of how you can interleave monadic effects with the streaming; but I found that I had a stream with no effects at all and I wanted to convert it back into haskells more simplistic representation, lazy lists. This is probably a well-known trick, but I couldn't find how to do this from googling, so here is the solution I found in case it helps someone else: > {-# LANGUAGE DeriveDataTypeable, FlexibleContexts #-} > module Main where > > import Data.Conduit > import Control.Monad.Catch > import Control.Monad.Trans.Resource > import Control.Monad.Writer > import Control.Monad.Identity > import qualified Data.Conduit.List as CL > import Data.Typeable > > source123Error :: Monad m => Source m Int > source123Error = do > yield 1 > yield 2 > yield 3 > error "error" A source which produces some data and then hangs, to test lazy production. One solution which doesn't work is CL.consume (as its own docs say) - and instead this happens: *Main> :t runIdentity (source123Error $$ CL.consume) runIdentity (source123Error $$ CL.consume) :: [Int] *Main> runIdentity (source123Error $$ CL.consume) *** Exception: error But what we can do instead is push the data out via the Writer monad: > tellEverything :: MonadWriter [a] m => Sink a m () > tellEverything = awaitForever (\x -> tell [x]) *Main> :t source123Error $$ tellEverything source123Error $$ tellEverything :: MonadWriter [Int] m => m () *Main> snd $ runWriter (source123Error $$ tellEverything) [1,2,3*** Exception: error Success! A lazily produced list. If your output is of any size - and depending on the compositions pattern in your code - it may be much faster to use this version: > tellEveryEndo :: MonadWriter (Endo [a]) m => Sink a m () > tellEveryEndo = awaitForever (\x -> tell (Endo (x:))) *Main> ($[]) . appEndo . snd . runWriter $ (source123Error $$ tellOne) [1,2,3*** Exception: error I found a further case where the Conduit I was trying to run was pure but had a 'MonadThrow' constraint. You can use the same approach here, using the ExceptionT transformer to satisfy the MonadThrow constraint. > data MyError = MyError deriving (Show,Typeable) > instance Exception MyError > > source123Throw :: MonadThrow m => Source m Int > source123Throw = do > yield 1 > yield 2 > yield 3 > throwM MyError *Main Control.Monad.Except Control.Monad.Trans.Resource> snd . runWriter . runExceptionT $ (source123Error $$ tellEverything) [1,2,3*** Exception: error *Main Control.Monad.Except Control.Monad.Trans.Resource> snd . runWriter . runExceptionT $ (source123Throw $$ tellEverything) [1,2,3] An aside: I tried to measure the speed difference between the list-mappend and Endo-mappend approaches with the following code. count2N uses a binary-tree shaped recursion so it should be fairly bad for list-mappend with lots of long lists on the left. > count2N :: Monad m => Int -> Source m Int > count2N 0 = yield 0 > count2N n = count2N (n-1) >> count2N (n-1) > speedTest1 = print . length . snd . runWriter $ (count2N 24 $$ tellEverything) > speedTest2 = print . length . ($[]) . appEndo . snd . runWriter $ (count2N 24 $$ tellEveryEndo) With -O or -O2 I measure no speed difference between these, they both take a bit over 2 seconds. With no optimisation flag, speedTest2 is slower, 17 seconds vs 11 seconds. I'm quite surprised the Endo version isn't faster, it seems like something is rewriting those list appends? Cheers, Jules

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Who's hiring, HS cafe edition Re: Haskell Engineer Needed for Machine Learning Group
by Carter Schonwald 03 Nov '15

03 Nov '15

My team at "megacorp " is hiring. Our main project right now is a domain specific sibling to Agda / idris that runs on top of strongly consistent replicated db that we're also in the process of iterating on. A colleague and I will be at Hac Phi this weekend, and we're also helping sponsor some of the catering costs. Talk to us if you're there! On Tuesday, November 3, 2015, Kim-Ee Yeoh <ky3(a)atamo.com> wrote: > > On Tue, Nov 3, 2015 at 6:24 PM, Adam Bergmark <adam(a)bergmark.nl > <javascript:_e(%7B%7D,'cvml','adam(a)bergmark.nl');>> wrote: > >> There are plenty of other places where people who don't want to work with >> haskell can look for employment. > > > You've lost me. Haskell-cafe is where people gather who want to work with > haskell. > > -- Kim-Ee >

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Re: [Haskell-cafe] process package with compilers besides GHC
by Malcolm Wallace 03 Nov '15

03 Nov '15

Clean-up is generally good. I have not maintained any Haskell compiler for about 5 years now, so I think it is safe to say you can go ahead. nhc98 did indeed build the 'process' package as part of its library set, but most recently at version 1.0.1.4. Regards, Malcolm On 2 Nov 2015, at 16:21, Michael Snoyman wrote: > Forwarding directly to you, in case you're not reading the mailing lists. > > ---------- Forwarded message ---------- > From: Michael Snoyman <michael(a)snoyman.com> > Date: Mon, Nov 2, 2015 at 8:10 AM > Subject: process package with compilers besides GHC > To: Haskell Cafe <haskell-cafe(a)haskell.org>, libraries <libraries(a)haskell.org> > > > I'm currently in the process* of a cleanup of the process package to reduce the usage of CPP conditionals in the code. Currently, as Simon PJ pointed out, it's quite difficult to follow the logic between Windows and POSIX platforms. During the cleanup, I've noticed that: > > 1. There's also quite a bit of complication around the __GLASGOW_HASKELL__ conditionals, intended to make the package compilable with other compilers > 2. There seems to be no way that - in its current state - the package could be compilable with a compiler besides GHC > > I wanted to reach out and see if anyone is currently using the process package on a compiler besides GHC, and if so, get information on whether recent releases also work, and get some kind of automated testing in place to prevent regressions. If there are no such users, I'm likely to remove the (presumably non-working) conditionals. > > * No pun intend >

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remove account
by Richard Torruellas III 03 Nov '15

03 Nov '15

Can you remove the account associated with this email address. I did not realize passwords were stored in plain text before sending (I missed the small print on the page) Thanks

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'Associative' order of calling
by Charles Durham 03 Nov '15

03 Nov '15

Is there a name for a fold that promises to call a function such that only an associative function will always return the same result. Or in other words, it has the property that it promises to call a function "associatively" on a set of data? Thanks! Charlie

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process package with compilers besides GHC
by Michael Snoyman 03 Nov '15

03 Nov '15

I'm currently in the process* of a cleanup of the process package to reduce the usage of CPP conditionals in the code. Currently, as Simon PJ pointed out, it's quite difficult to follow the logic between Windows and POSIX platforms. During the cleanup, I've noticed that: 1. There's also quite a bit of complication around the __GLASGOW_HASKELL__ conditionals, intended to make the package compilable with other compilers 2. There seems to be no way that - in its current state - the package could be compilable with a compiler besides GHC I wanted to reach out and see if anyone is currently using the process package on a compiler besides GHC, and if so, get information on whether recent releases also work, and get some kind of automated testing in place to prevent regressions. If there are no such users, I'm likely to remove the (presumably non-working) conditionals. * No pun intend

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ANN: dimensional-1.0 for statically checked physical dimensions
by Douglas McClean 02 Nov '15

02 Nov '15

Hello Haskellers, Björn Buckwalter and I are pleased to announce the release to Hackage of version 1.0 of the dimensional library, which statically tracks physical dimensions in Haskell code, as in the example below, preventing dimensional mistakes and requiring explicit documentation of units where raw values are exchanged with external systems. {-# LANGUAGE NoImplicitPrelude #-} module Example where import Numeric.Units.Dimensional.Prelude import Numeric.Units.Dimensional.NonSI -- a function that computes with dimensional values escapeVelocity :: (Floating a) => Mass a -> Length a -> Velocity a escapeVelocity m r = sqrt (two * g * m / r) where two = 2 *~ one g = 6.6720e-11 *~ (newton * meter ^ pos2 / kilo gram ^ pos2) >>> let re = 6372.792 *~ kilo meter >>> let me = 5.9742e24 *~ kilo gram >>> let ve = escapeVelocity me re >>> ve -- Show defaults to SI base units 11184.537332296259 m s^-1 >>> showIn (mile / hour) ve -- but we can show in other units "25019.09746845083 mi / h" >>> let vekph = ve /~ (kilo meter / hour) -- and extract raw values when needed 40264.33439626653 This version is a major upgrade, consolidating features from the classic dimensional package and the dimensional-tf package. It takes advantage of the DataKinds and ClosedTypeFamilies extensions in GHC 7.8 to offer even safer types with a nearly identical interface. Also included: - Units carry names which can be combined by multiplication, division, and (only where appropriate) application of metric prefixes. You can use expressions like: showIn (milli meter / second) timeTravelSpeed to get "39339.52 mm / s" - Exact conversion factors between units are available, even when those conversion factors involve multiples of pi, thanks to the exact-pi library - The dimensionally-polymorphic siUnit term represents the coherent SI base unit of any dimension, which can be convenient for wrapping and unwrapping quantities in some contexts. - Storable and Unbox instances for Quantity types are available thanks to the efforts of Alberto Valverde González. - The Numeric.Units.Dimensional.Dynamic module offers types for safely manipulating quantities and units whose dimensions are not known statically. Also available is a term-level representation for dimensions. - Several other missing instances have been provided, including Bounded, Data, and Typeable instances. - New commonly used US customary units have been added, including US fluid measures and the knot. We have several other development efforts underway, including a type-checker plugin inspired by Adam Gundry's work, and on which he has provided valuable advice, which we hope will lead to a clean library for dimensionally typed linear algebra. Comments and contributions are welcome at http://github.com/bjornbm/dimensional-dk. (The repository name is a carryover from the name we were using while developing this version.) One particularly welcome contribution would be assistance with developing a patch for GHC issue 10391 <https://ghc.haskell.org/trac/ghc/ticket/10391>. Cheers, Doug McClean

2 2

Why does disambiguation in RebindableSyntax sometimes requires type signatures?
by Jan Bracker 02 Nov '15

02 Nov '15

Hello, I am currently playing around with RebindableSyntax and having several bind/return/sequence functions in scope at the same time. I thought that it would be enough to just pick the right one to use in each do-block by using a "where" or a "let". Surprisingly, I get some type related issues I can only fix by adding in some type signatures, but I don't understand why these signatures are actually necessary. Here is my example program: {-# LANGUAGE RebindableSyntax #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE TypeOperators #-} import Prelude import qualified Prelude as P import qualified Control.Effect as E import Control.Effect.State ifThenElse :: Bool -> a -> a -> a ifThenElse True t e = t ifThenElse False t e = e main :: IO () main = do return () where return = P.return data Tree = Leaf Int | Branch Tree Tree process :: Tree -> State '[ "flatten" :-> Bool :! 'R ] (Either Tree [Int]) process (Leaf i) = do flatten <- get (Var :: (Var "flatten")) if flatten then return $ Right [i] else return $ Left $ Leaf i where --(>>=) :: (E.Inv State f g) => State f a -> (a -> State g b) -> State (E.Plus State f g) b (>>=) = (E.>>=) (>>) :: (E.Inv State f g) => State f a -> State g b -> State (E.Plus State f g) b (>>) = (E.>>) return = E.return fail = E.fail process (Branch tl tr) = do eitherL <- process tl eitherR <- process tr case (eitherL, eitherR) of (Left l, Left r) -> return $ Left $ Branch l r (Right l, Right r) -> return $ Right $ l ++ r where (>>=) :: (E.Inv State f g) => State f a -> (a -> State g b) -> State (E.Plus State f g) b (>>=) = (E.>>=) (>>) :: (E.Inv State f g) => State f a -> State g b -> State (E.Plus State f g) b (>>) = (E.>>) return = E.return fail = E.fail The program uses the "effect-monad" package in version 0.6.1. 1) The type signatures in the "where" following each do-block of the "process" function are required. If I remove the type signature of the sequence functions I get a type error of the following nature: examples/effect/Test.hs:33:16: Could not deduce (E.Inv m0 f0 g0) arising from a use of ‘E.>>’ Relevant bindings include (>>) :: m0 f0 a -> m0 g0 b -> m0 (E.Plus m0 f0 g0) b (bound at examples/effect/Test.hs:33:9) In the expression: (E.>>) In an equation for ‘>>’: (>>) = (E.>>) In an equation for ‘process’: process (Leaf i) = do { flatten <- get (Var :: Var "flatten"); if flatten then return $ Right [...] else return $ Left $ Leaf i } where (>>=) = (E.>>=) (>>) = (E.>>) return = E.return fail = E.fail examples/effect/Test.hs:33:16: No instance for (E.Effect m0) arising from a use of ‘E.>>’ In the expression: (E.>>) In an equation for ‘>>’: (>>) = (E.>>) In an equation for ‘process’: process (Leaf i) = do { flatten <- get (Var :: Var "flatten"); if flatten then return $ Right [...] else return $ Left $ Leaf i } where (>>=) = (E.>>=) (>>) = (E.>>) return = E.return fail = E.fail Which I interpret as the inability to infer the "E.Effect" and "E.Inv" constraints that are implied by the use of "E.>>". But why can't those constraints be inferred correctly? Shouldn't a definition like "(>>) = (E.>>)" just propagate the type signature and specialize it as needed? 2) If I remove the type signature for the bind operation, I get the following type error: examples/effect/Test.hs:38:3: Couldn't match type ‘'["flatten" :-> (Bool :! 'R)]’ with ‘'[]’ Expected type: State '["flatten" :-> (Bool :! 'R)] (Either Tree [Int]) -> (Either Tree [Int] -> State '[] (Either Tree [Int])) -> State '[] (Either Tree [Int]) Actual type: State '["flatten" :-> (Bool :! 'R)] (Either Tree [Int]) -> (Either Tree [Int] -> State '[] (Either Tree [Int])) -> State (E.Plus State '["flatten" :-> (Bool :! 'R)] '[]) (Either Tree [Int]) In a stmt of a 'do' block: eitherR <- process tr In the expression: do { eitherL <- process tl; eitherR <- process tr; case (eitherL, eitherR) of { (Left l, Left r) -> return $ Left $ Branch l r (Right l, Right r) -> return $ Right $ l ++ r } } In an equation for ‘process’: process (Branch tl tr) = do { eitherL <- process tl; eitherR <- process tr; case (eitherL, eitherR) of { (Left l, Left r) -> return $ Left $ Branch l r (Right l, Right r) -> return $ Right $ l ++ r } } where (>>=) = (E.>>=) (>>) :: (E.Inv State f g) => State f a -> State g b -> State (E.Plus State f g) b (>>) = (E.>>) return = E.return Which tells me that GHC is expecting the wrong type, but inferring the correct type. Again I don't see why this wrong type is expected and the right type is ignored. In either case, why does adding or removing the type signature for the local definitions make a difference at all? I suspect the issue has to do with the language extensions I enabled or the type-level computations that are done by the "effect-monad" package, but I cannot find a satisfying answer. Does anybody have a good explanation? I am working with GHC 7.10.2. Best, Jan

3 5

simple library for HTML form generation and processing
by Henning Thielemann 02 Nov '15

02 Nov '15

I posted the following already to web-devel(a)haskell.org but it seems to be relatively quiet there. ----- I like to get your advice about a simple library for web form generation and processing. So far I tried digestive-functors and reform. Both of them are advertised as being good in separating data from view. However, I am interested in one-off forms, that is, form data will always be rendered in one way. Thus I would like to save the efforts to combine data and view after they have been carefully separated. Formerly I have also used autolib-cgi: http://autolat.imn.htwk-leipzig.de/haddock/autolib-cgi-1.2/ It allowed me to generate the form and fetch and validate the data in one (monadic) go. The blaze-markup type MarkupM is a monad anyway, thus it seems to be straight-forward to use the monadic results for the data entered to the form. Is there a library that supports this style of web form handling?

1 0

testing for exceptions
by Roelof Wobben 02 Nov '15

02 Nov '15

Hello, I have made this exercise which can be found at the Craft of Functional Programming book. -- exercise 32 -- Suppose we have to raise 2 to the power n. If n is even, 2*m say, then -- 2n = 22*m = (2m)2 -- If n is odd, 2*m+l say, then -- 2n = 22*m+l = (2n)2*2 -- Give a recursive function to compute 2n which uses these insights. f2 :: Integer -> Integer f2 n | n < 0 = error "This will only run for positive numbers" | n == 0 = 1 | even n = f2 ( n `div` 2) ^ 2 | odd n = (f2 ( n `div` 2) ^ 2) * 2 Now I have to make Hunit tests for it, But is there a way I can test if the error message is shown when a negative number is being used ? Roelof

8 18

what do I have to do exactlry with this exercises
by Roelof Wobben 02 Nov '15

02 Nov '15

Hello, Im self studing Haskell with the Craft o ffunctional programmimg of Hutton. Now I see two exercises that I do not understand what is really the purpose here. The two exercises are : 4.21 Given a function f of type Integer -> Integer give a recursive definition of a function of type Integer -> Integer which on input n returns the maximum of the values f 0, f 1, ..., f n. You might find the max function defined in Section 3.4 useful. To test this function, add to your script a definition of some values of f thus: f 0 = 0 f 1 = 44 f 2 = 17 f _ = 0 and so on; then test your function at various values. 4.22 Given a function f of type Integer -> Integer give a recursive definition of a function of type Integer -> Bool which on input n returns True if one or more of the values f 0, f 1, ..., f n is zero and False otherwise.

3 10

Find a point inside (x,y,z) -> Bool
by martin 02 Nov '15

02 Nov '15

Hello all, I hope this is not a too silly question. It goes like this: Suppose I have a shape defined as (x,y,z) -> Bool how can I find a Point inside this shape? Obviously I could iterate through all possible x,y and z, but this appears very expensive. There may be no point at all at x=0. With brute force iteration I would have no clue that the False I am receiving with (0,1,1) is caused by x=0 and I may nedlessly try all combinations of y and z without ever receiving a True. Are there any alternative ways of finding points inside a shape?

11 16

Re: [Haskell-cafe] ANN: hledger-0.27, with more console power
by Simon Michael 01 Nov '15

01 Nov '15

Hi Johannes, quite right. I've added a few screenshots to the manual at http://hledger.org/manual#ui <http://hledger.org/manual#ui> . Some of them use the more realistic example data from the beancount project, thanks to Martin Blais. Best, -Simon > On Nov 1, 2015, at 10:16 AM, johannesjh(a)gmail.com wrote: > > Hi Simon! > > The availability of a text-based user interface for hledger sounds great. Could you please post some screenshots of what the UI looks like? > > thank you very much, > Johannes > > > > On Saturday, October 31, 2015 at 10:38:20 PM UTC+1, Simon Michael (sm) wrote: > I'm pleased to announce hledger 0.27! > > What is it ? > hledger is a cross-platform program for tracking money, time, or any > other commodity, using double-entry accounting and a simple, editable > file format. It can also read CSV or timelog files, and export CSV. > It provides command-line, curses and web interfaces, and aims to be a > reliable, practical tool for daily use. It is inspired by and largely > compatible with ledger(1). > > What's new ? > This release introduces hledger-ui, a new curses-style interface that > I'm quite pleased with (not yet available on Windows). Built on vty > and the new brick library, it lets you review account balances and > transactions with fewer keystrokes and less effort. Ledger users with > compatible journal files may also find this useful. > > hledger can now report current value based on market prices (hurrah); > wide characters are displayed properly; regular expression account > aliases are fast; and unix man pages are provided. You can see all > changes and bugfixes at http://hledger.org/release-notes#hledger-0.27 <http://hledger.org/release-notes#hledger-0.27> . > > Release contributors: > Simon Michael, > Carlos Lopez-Camey. > > How to get it ? > hledger can be installed with cabal or stack - see > http://hledger.org/download <http://hledger.org/download> for guidance. > If you'd like to contribute Windows or Mac binaries, please get in > touch. > > Happy Hallowe'en! > -Simon > > > -- > You received this message because you are subscribed to the Google Groups "hledger" group. > To unsubscribe from this group and stop receiving emails from it, send an email to hledger+unsubscribe(a)googlegroups.com <mailto:hledger+unsubscribe@googlegroups.com>. > For more options, visit https://groups.google.com/d/optout <https://groups.google.com/d/optout>.

1 0

Month in Haskell Mode October 2015
by Gracjan Polak 01 Nov '15

01 Nov '15

Welcome Haskell Mode users, Haskell Mode progress report for October 2015. It is also available online <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-October-…> and on reddit <https://www.reddit.com/r/haskell/comments/3r26px/month_in_haskell_mode_octo…> . For previous issue see September 2015 <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-Septembe…> . <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-October-…>What is Haskell Mode? Haskell Mode is an umbrella project for multiple Emacs tools for efficient Haskell development. Haskell Mode is an open source project developed by a group of volunteers. For more information see https://github.com/haskell/haskell-mode. <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-October-…>Important developments Functionality provided by haskell-indentation received a lot of fixes and contributions lifting it to a complete new level of quality. haskell-indentation is now a default indentation mode enabled when haskell-mode itself is enabled. ATTENTION TUTORIAL WRITERS: The following line is NO LONGER NEEDED: (add-hook 'haskell-mode-hook 'haskell-indentation-mode) PLEASE REMOVE IT FROM ALL THE TUTORIALS OUT THERE. Thanks. Note that for backward compatibility all other indentation modes know how to properly handle new defaults. We have also improved our development process by defining Complete functionality <https://github.com/haskell/haskell-mode/wiki/Complete-functionality> as a concept. <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-October-…>Cooperation with related projects As noted last time Haskell Mode wanted to reach out to other projects in editor space. This has not happened because even better events unfolded. Things of note: haskell-ide-(backend) <https://github.com/haskell/haskell-ide> project got started by Alan Zimmerman. The goal is to bring in all the backend tools that editors need to properly handle advanced Haskell editing. ghc-mod <https://github.com/kazu-yamamoto/ghc-mod> does not need to be introduced. We are thinking how to better split work between haskell-mode and ghc-mod. HaRe <https://github.com/RefactoringTools/HaRe> is a Haskell refactorer. It can rename all the one letter variables to something more descriptive! It can also do other things. And it has somewhat working Emacs integration. <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-October-…>Heads up tutorial writers! There are plenty tutorials out there how to setup haskell-mode. Thanks for writing those! Note that some of them are quite outdated at this point in time and a bit confusing due to the improvements in haskell-mode. Can I ask tutorial writers to contribute directly to haskell mode documentation so that Haskell Mode Manual can be kept up to date with haskell-mode developments? Please contribute documentation back to the project. External tutorials get out of hand pretty fast. Thanks <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-October-…>Heads up! Cruft removal! haskell-mode is about to loose some weight so that it can be better carried by Haskell Mode Community. On the list to be removed are: - Remove haskell-bot.el <https://github.com/haskell/haskell-mode/pull/960> - Remove scc functions <https://github.com/haskell/haskell-mode/pull/961> - Remove horizontal whitespace based smart indentation mode haskell-simple-indent <https://github.com/haskell/haskell-mode/pull/958> - Remove Unicode input method <https://github.com/haskell/haskell-mode/pull/939> - Remove haskell-checkers.el <https://github.com/haskell/haskell-mode/pull/959> If you use one of the above yourself, feel strongly that it should be supported by the community and volunteer to write some unit tests and documentation, please speak up! The changes above will be merged no earlier than December 2015 so there is time to chime in. <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-October-…>Current project focus Current project focus is to lower entry barrier for newcomers by defining bite-sized tasks. Get 50 'well-defined-tasks' done as by the metric: https://github.com/haskell/haskell-mode/issues?q=is%3Aissue+label%3Awell-de… A 'well-defined-task' is a category of tasks that have the field cleared for them, questions already sorted out and detailed information how to get them done. So you can just sit, search for 'well-defined-task' label and enjoy the coding! The point is to lower the entry barrier for new users, new issue reporters and advanced programmers but Emacs lisp beginners to contribute to the project. Current status: 13 well-defined-tasks closed <https://github.com/haskell/haskell-mode/issues?q=is%3Aissue+label%3Awell-de…> plus 13 more open <https://github.com/haskell/haskell-mode/issues?q=is%3Aissue+label%3Awell-de…> . If only you can help with reaching our targets please do so! <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-October-…>Issues closed in October - Disable Indentation #90 <https://github.com/haskell/haskell-mode/issues/90> - Unicode symbols inside ghci prompt hang inferior-haskell-mode #176 <https://github.com/haskell/haskell-mode/issues/176> - Multi-line -ferror-spans syntax not supported #192 <https://github.com/haskell/haskell-mode/issues/192> - [Discussion] Add end-to-end guide for configuring haskell-mode in a place where users will see it #197 <https://github.com/haskell/haskell-mode/issues/197> - Sorting imported functions from a module alphabetically #206 <https://github.com/haskell/haskell-mode/issues/206> - After the newline have to hit twice to start cycling #276 <https://github.com/haskell/haskell-mode/issues/276> - indent-according-to-mode opens the help buffer for haskell-mode-hook #290 <https://github.com/haskell/haskell-mode/issues/290> - Can't get type info unless file compiles #294 <https://github.com/haskell/haskell-mode/issues/294> - Parsing broken on quasi quotes #323 <https://github.com/haskell/haskell-mode/issues/323> - getLine behaves not correctly in Interactive-Haskell-mode. #333 <https://github.com/haskell/haskell-mode/issues/333> - Overly aggressive indenting after recent Emacs update #377 <https://github.com/haskell/haskell-mode/issues/377> - haskell-indentation-mode parse error on indenting import declaration #397 <https://github.com/haskell/haskell-mode/issues/397> - Pick one indentation mode as preferred in the documentation/customize. #414 <https://github.com/haskell/haskell-mode/issues/414> - haskell-indendation and guards #481 <https://github.com/haskell/haskell-mode/issues/481> - Running indent-according-to-mode moves the cursor way to the right #488 <https://github.com/haskell/haskell-mode/issues/488> - haskell-session-change-target should list available targets #534 <https://github.com/haskell/haskell-mode/issues/534> - Haskell-mode crashing and buffer erased (not sure exactly where problem is) #594 <https://github.com/haskell/haskell-mode/issues/594> - haskell-indentation breaks with UnicodeSyntax #715 <https://github.com/haskell/haskell-mode/issues/715> - Handle Template Haskell / DataKinds names in haskell-indentation #760 <https://github.com/haskell/haskell-mode/issues/760> - No indentation suggested for case clauses #786 <https://github.com/haskell/haskell-mode/issues/786> - Pull in ghc-mod's ghc-make-indent-shallower/deeper into haskell-mode #826 <https://github.com/haskell/haskell-mode/issues/826> - Clean up example init.el on wiki #843 <https://github.com/haskell/haskell-mode/issues/843> - Indentation mode needs to be able to recover from parser errors #861 <https://github.com/haskell/haskell-mode/issues/861> - haskell-simple-indent-mode non-responsive #867 <https://github.com/haskell/haskell-mode/issues/867> - Get hit by 'Invalid Token := )' #875 <https://github.com/haskell/haskell-mode/issues/875> - Invalid Token :| #878 <https://github.com/haskell/haskell-mode/issues/878> - Parse error: Illegal token: where #883 <https://github.com/haskell/haskell-mode/issues/883> - parse-error "Expecting then" "Expecting else" DoAndIfThenElse in indentation #884 <https://github.com/haskell/haskell-mode/issues/884> - Illegal tokens and QuasiQuotes #894 <https://github.com/haskell/haskell-mode/issues/894> - Haskell Interactive Shell Stuck in Insert Mode (spacemacs) #895 <https://github.com/haskell/haskell-mode/issues/895> - Syntax highlighting: no difference between data constructor and type ? #898 <https://github.com/haskell/haskell-mode/issues/898> - Let the enter create a new line despite the indentation errors #905 <https://github.com/haskell/haskell-mode/issues/905> - Parse Error inside QuasiQuotes #907 <https://github.com/haskell/haskell-mode/issues/907> - "Expecting else" error message #917 <https://github.com/haskell/haskell-mode/issues/917> - Support commas in first indentation column #918 <https://github.com/haskell/haskell-mode/issues/918> - haskell-process changes the directory which causes loaded modules to be unloaded #923 <https://github.com/haskell/haskell-mode/issues/923> - Syntax highlighting only #924 <https://github.com/haskell/haskell-mode/issues/924> - haskell-process.el binds C-c c but should not #926 <https://github.com/haskell/haskell-mode/issues/926> - Simple indent vs haskell-indentation when using autofill on comments #932 <https://github.com/haskell/haskell-mode/issues/932> - How to use REPL with stack? #953 <https://github.com/haskell/haskell-mode/issues/953> - Wiki documentation out of sync ? #968 <https://github.com/haskell/haskell-mode/issues/968> ### Pull requests merged in October - Support where keyword after any expression #897 <https://github.com/haskell/haskell-mode/pull/897> - Support names starting with quotes #903 <https://github.com/haskell/haskell-mode/pull/903> - Fix switching to the presentation buffer #904 <https://github.com/haskell/haskell-mode/pull/904> - Implement QuasiQuotes syntax in indentation #909 <https://github.com/haskell/haskell-mode/pull/909> - Add build notification to #haskell-emacs #912 <https://github.com/haskell/haskell-mode/pull/912> - Mobile friendly README.md #913 <https://github.com/haskell/haskell-mode/pull/913> - Add failing tests for indentation #916 <https://github.com/haskell/haskell-mode/pull/916> - Toplevel indentation bugfixes for data, newtype, instance #919 <https://github.com/haskell/haskell-mode/pull/919> - Document failing indentation #920 <https://github.com/haskell/haskell-mode/pull/920> - Navigate to top level declaration in indenatation #921 <https://github.com/haskell/haskell-mode/pull/921> - Make haskell indentation the default indentation mode #922 <https://github.com/haskell/haskell-mode/pull/922> - Don't change directory when using stack-ghci. #925 <https://github.com/haskell/haskell-mode/pull/925> - Add rather baroque indentation test which cause parse failure #927 <https://github.com/haskell/haskell-mode/pull/927> - Yet another parser failure #928 <https://github.com/haskell/haskell-mode/pull/928> - Reloading: haskell-process-file-loadish needs the current buffer as an argument #929 <https://github.com/haskell/haskell-mode/pull/929> - Fix nested layout 1 #930 <https://github.com/haskell/haskell-mode/pull/930> - Filter only sections bearing targets - fixes #534 #931 <https://github.com/haskell/haskell-mode/pull/931> - Honour curly braces in target sections #933 <https://github.com/haskell/haskell-mode/pull/933> - Add failing tests for multiline string literals #934 <https://github.com/haskell/haskell-mode/pull/934> - Mark some indentation tests as passing #936 <https://github.com/haskell/haskell-mode/pull/936> - Remove useless debugging functions #937 <https://github.com/haskell/haskell-mode/pull/937> - Write tests properly, mark them as passing #944 <https://github.com/haskell/haskell-mode/pull/944> - Remove auto-fill code from indentation #945 <https://github.com/haskell/haskell-mode/pull/945> - Improve can grab prefix for completions #946 <https://github.com/haskell/haskell-mode/pull/946> - Remove dynamic indentation showing #947 <https://github.com/haskell/haskell-mode/pull/947> - Indentation of guards with commas is working properly #948 <https://github.com/haskell/haskell-mode/pull/948> - Fix indent for do inside a list #956 <https://github.com/haskell/haskell-mode/pull/956> - Recognize top level constructs in indentation #965 <https://github.com/haskell/haskell-mode/pull/965> - Remove indentation safety hack #966 <https://github.com/haskell/haskell-mode/pull/966> - Change 'w.r.t' to 'with regards to' for clarity #967 <https://github.com/haskell/haskell-mode/pull/967> <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-October-…>Contributors active in October Alexey Khudyakov, Chris Done, Gracjan Polak, Gregor Riegler, Kabelo Moiloa, Marlo Major, vlatkoB <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-October-…> Contributing Haskell Mode needs volunteers like any other open source project. For more information see: https://github.com/haskell/haskell-mode/wiki Also drop by our IRC channel: #haskell-emacs at irc.freenode.net. Thanks!

1 0

Re: [Haskell-cafe] testing for exceptions
by Darren Grant 01 Nov '15

01 Nov '15

Great points. I often run into situations where sketching out non-terminating endpoints leads to a precise domain, but after peer review it becomes clear that a much simpler program would result from compromising with a less precise domain that eliminates these points altogether. Eliminating branching on constructors in Haskell is a common aspect of this refinement, it's true. Cheers, Darren On Nov 1, 2015 03:18, <joachifm(a)fastmail.fm> wrote: The ability to express non-termination is a feature, not a bug. If the program truly cannot produce a useful result for some input, it should crash, the earlier the better. Wrapping the return value ONLY to make a non-total program *appear* total is kind of ugly (and commits you to a potentially inappropriate/nonsensical model for the problem at hand). It is cleaner to either constrain the input to values you're prepared to deal with or crash when the implicit invariant is violated. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

1 0

ANN: hledger-0.27, with more console power
by Simon Michael 31 Oct '15

31 Oct '15

I'm pleased to announce hledger 0.27! What is it ? hledger is a cross-platform program for tracking money, time, or any other commodity, using double-entry accounting and a simple, editable file format. It can also read CSV or timelog files, and export CSV. It provides command-line, curses and web interfaces, and aims to be a reliable, practical tool for daily use. It is inspired by and largely compatible with ledger(1). What's new ? This release introduces hledger-ui, a new curses-style interface that I'm quite pleased with (not yet available on Windows). Built on vty and the new brick library, it lets you review account balances and transactions with fewer keystrokes and less effort. Ledger users with compatible journal files may also find this useful. hledger can now report current value based on market prices (hurrah); wide characters are displayed properly; regular expression account aliases are fast; and unix man pages are provided. You can see all changes and bugfixes at http://hledger.org/release-notes#hledger-0.27 . Release contributors: Simon Michael, Carlos Lopez-Camey. How to get it ? hledger can be installed with cabal or stack - see http://hledger.org/download for guidance. If you'd like to contribute Windows or Mac binaries, please get in touch. Happy Hallowe'en! -Simon

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Re: [Haskell-cafe] Determining the length of a Foldable Applicative.
by David Banas 31 Oct '15

31 Oct '15

Thanks to all, whom responded to this! With your help, I found my way to this, which seems to work correctly: app_len :: (Foldable f) => f a -> Int app_len = foldl' (flip ((+) . const 1)) 0 -db On Oct 30, 2015, at 2:47 PM, David Kraeutmann <kane(a)kane.cx> wrote: > Your types don't match here, but you have the right idea. > > 'sum' won't be enough. Take a look at the definition of sum: > >> sum :: (Foldable t, Num a) => t a -> a >> sum = getSum . foldMap Sum > > That won't work, since that requires '(Num a)'. > > We just want to count 1 up whenever we map an element. > Try doing something with const and Data.Monoid.Sum. > > > On 10/30/2015 9:03 PM, David Banas wrote: >> Hi all, >> >> I thought I had a simple way to determine the “length" (i.e. - number of elements in) of a Foldable Applicative container: >> >> import Prelude hiding (sum) >> import Data.Foldable (Foldable(..), sum) >> import Control.Applicative >> >> -- Calculate the "length" (i.e. - number of elements in) an Applicative container. >> app_len :: (Applicative f, Foldable f) => f a -> Int >> app_len = sum $ pure 1 >> >> but I didn’t: >> >> app_len_test.hs:9:11: >> Could not deduce (Foldable t0) arising from a use of ‘sum’ >> from the context (Applicative f, Foldable f) >> bound by the type signature for >> app_len :: (Applicative f, Foldable f) => f a -> Int >> at app_len_test.hs:8:12-52 >> The type variable ‘t0’ is ambiguous >> Note: there are several potential instances: >> instance Foldable ((,) a) -- Defined in ‘Data.Foldable’ >> instance GHC.Arr.Ix i => Foldable (GHC.Arr.Array i) >> -- Defined in ‘Data.Foldable’ >> instance Foldable (Const m) -- Defined in ‘Data.Foldable’ >> ...plus four others >> In the expression: sum >> In the expression: sum $ pure 1 >> In an equation for ‘app_len’: app_len = sum $ pure 1 >> >> app_len_test.hs:9:17: >> Could not deduce (Applicative t0) arising from a use of ‘pure’ >> from the context (Applicative f, Foldable f) >> bound by the type signature for >> app_len :: (Applicative f, Foldable f) => f a -> Int >> at app_len_test.hs:8:12-52 >> The type variable ‘t0’ is ambiguous >> Note: there are several potential instances: >> instance Data.Monoid.Monoid a => Applicative ((,) a) >> -- Defined in ‘Control.Applicative’ >> instance Applicative ((->) a) -- Defined in ‘Control.Applicative’ >> instance Control.Arrow.Arrow a => >> Applicative (Control.Arrow.ArrowMonad a) >> -- Defined in ‘Control.Applicative’ >> ...plus 14 others >> In the second argument of ‘($)’, namely ‘pure 1’ >> In the expression: sum $ pure 1 >> In an equation for ‘app_len’: app_len = sum $ pure 1 >> >> Can anyone help me understand what I’m missing? >> >> Thanks, and have a great weekend, >> -db >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >> >

1 0

Determining the length of a Foldable Applicative.
by David Banas 30 Oct '15

30 Oct '15

Hi all, I thought I had a simple way to determine the “length" (i.e. - number of elements in) of a Foldable Applicative container: import Prelude hiding (sum) import Data.Foldable (Foldable(..), sum) import Control.Applicative -- Calculate the "length" (i.e. - number of elements in) an Applicative container. app_len :: (Applicative f, Foldable f) => f a -> Int app_len = sum $ pure 1 but I didn’t: app_len_test.hs:9:11: Could not deduce (Foldable t0) arising from a use of ‘sum’ from the context (Applicative f, Foldable f) bound by the type signature for app_len :: (Applicative f, Foldable f) => f a -> Int at app_len_test.hs:8:12-52 The type variable ‘t0’ is ambiguous Note: there are several potential instances: instance Foldable ((,) a) -- Defined in ‘Data.Foldable’ instance GHC.Arr.Ix i => Foldable (GHC.Arr.Array i) -- Defined in ‘Data.Foldable’ instance Foldable (Const m) -- Defined in ‘Data.Foldable’ ...plus four others In the expression: sum In the expression: sum $ pure 1 In an equation for ‘app_len’: app_len = sum $ pure 1 app_len_test.hs:9:17: Could not deduce (Applicative t0) arising from a use of ‘pure’ from the context (Applicative f, Foldable f) bound by the type signature for app_len :: (Applicative f, Foldable f) => f a -> Int at app_len_test.hs:8:12-52 The type variable ‘t0’ is ambiguous Note: there are several potential instances: instance Data.Monoid.Monoid a => Applicative ((,) a) -- Defined in ‘Control.Applicative’ instance Applicative ((->) a) -- Defined in ‘Control.Applicative’ instance Control.Arrow.Arrow a => Applicative (Control.Arrow.ArrowMonad a) -- Defined in ‘Control.Applicative’ ...plus 14 others In the second argument of ‘($)’, namely ‘pure 1’ In the expression: sum $ pure 1 In an equation for ‘app_len’: app_len = sum $ pure 1 Can anyone help me understand what I’m missing? Thanks, and have a great weekend, -db

4 3

MonadFix wiki confusion
by Samuel Rødal 30 Oct '15

30 Oct '15

Hello, the MonadFix wiki at https://wiki.haskell.org/MonadFix has a statement that I feel is a bit misleading. In section "2.2 Lazy algorithm interleaved with effects", it claims that making the BTree data structure strict doesn't cause endless recursion. Well, that's true, but that's just because rep_x_sum returns a tuple containing the BTree and the summed values of the current subtree, and the tuple is lazily constructed - postponing the construction of the tree value. So highlighting the fact that the function still works when the BTree structure is made strict is kind of a red herring. Maybe the confusion could be avoided by removing the part about making BTree strict, or adding a note about the tuple still ensuring lazy construction? -- Samuel

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Re: [Haskell-cafe] Find a point inside (x,y,z) -> Bool
by Olaf Klinke 30 Oct '15

30 Oct '15

Martin, this may be impractical performance-wise, but Haskell offers magic data structures for searching. Have a look at Martin Escardo's blog post [1] on infinite search in finite time. There is a package on Hackage [2] implementing it. The `shapes` you get are compact, non-empty subsets of types. If you have a shape shape :: Data.Searchable.Set a then Data.Searchable.search (const True) shape will return some element of your shape. As far as I know nobody has ever used this data structure for solid geometry. You'd need to combine it with some implementation of exact reals [*] to have geometry in a product of closed intervals. A downside is that general intersections don't exist, since the shapes must be non-empty. But since images of searchable sets are searchable, you could define complicated shapes by starting with a simple one and distort it with a function. If your type of space is discrete, then the search function might resort to brute force enumeration if the shape was defined that way. -- Olaf [1] http://math.andrej.com/2008/11/21/a-haskell-monad-for-infinite-search-in-fi… [2] http://hackage.haskell.org/package/infinite-search [*] As far as I am aware there is no appropriate package on Hackage, but Haskell implementations exist in several theses.

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Re: [Haskell-cafe] haskell-ide repository name
by Alan & Kim Zimmerman 30 Oct '15

30 Oct '15

This post generated some discussion on the mailing list(s) [1],[2] and on reddit [3]. The straw poll [4] garnered (as of time of writing this mail) 138 votes, broken down as ghc-ide-engine 56 votes 41% ghc-ide-service 43 votes 31% haskides 19 votes 14% ghc-ide-daemon 16 votes 12% something else 4 votes 3% So it seems -ide-engine is the favourite In a bait-and-switch operation, I think it makes sense to keep the current "haskell-ide" prefix, and so rename it to haskell-ide-engine This has the advantages of a) The prefix is the same, so continuity is slightly better b) It does not mentally shut out any tooling constructed using other compilers/techniques, such as haskell-src-exts If anyone feels strongly that this is wrong, please let me know. Regards Alan [1] https://mail.haskell.org/pipermail/haskell-cafe/2015-October/121965.html [2] https://groups.google.com/forum/#!topic/haskell-ide/hI3MzXbwqTo [3] https://www.reddit.com/r/haskell/comments/3qh19i/rename_haskellide_project/ [4] http://strawpoll.me/5842105/r On Mon, Oct 26, 2015 at 11:06 PM, Alan & Kim Zimmerman <alan.zimm(a)gmail.com> wrote: > At the moment the repository/project is called haskell-ide > > This leads to the impression that it is an IDE. > > It is actually a backend/server to provide services for an IDE > > We are considering changing the name. > > The options are > > haskides / ghc-ide-daemon / ghc-ide-service / ghc-ide-engine > > Please cast your vote at http://strawpoll.me/5842105 > > Thanks > Alan >

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New release Csound-expression 4.9 is out
by Anton Kholomiov 30 Oct '15

30 Oct '15

*The 4.9.0 is out! New features:* csound-expression - Functions for creation of FM-synthesizers. We can create the whole graph of FM-units (with feedback). Check out the module Csound.Air.Fm - Support for Monosynth patches. See atMono in the module Csound.Air.Patch see the function atMono and atMonoSharp. - Easy to use Binaural panning. See the module Csound.Air.Pan It’s like: headPan :: (Sig, Sig) -> Sig -> Sig2headPan (azimuth, elevation) asig = (aleft, aright) the compiler can supply the right extra files by reading the header of .csd - Construction of patches for sound fonts (sfPatch, sfPatchHall). - Table of tables. We can create a table that contains tables. - Harmonic oscillators for subtractive synth: buz and gbuz (the functions are adapted from the Csound ones) - Reverbs for patches. It’s very easy to add a reverb to your patch (withSmallHall patch, withLargeHall patch, etc) - Some bug-fixes csound-catalog - Many mono-synth were added. You can use them with function atMono in place of atMidi. The mono versions of patches have suffix m. Like hammonOrganm or nightPadm. We can use it like this: > dac $ atMono nightPadm - SHARC instruments. SHARC db contains a FFT-samples for sustain notes. It includes many orchestra instruments. There are many new patches that use natural sounding timbres taken from the SHARC library. Check out functions soloSharc, padSharc, dreamSharc. We can use it like this: > dac $ atMidi $ padSharc shCello csound-sampler - Handy function withBpm allows to query current bpm with in the scope of expression. - Sampler mappers were generalized. - Char trigering functions are synchronized with bpm. Cheers! Anton

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2nd CfP: Haskell in Leipzig (Germany) 2015
by Johannes Waldmann 29 Oct '15

29 Oct '15

HaL-10 Haskell in Leipzig (December 4/5) http://nfa.imn.htwk-leipzig.de/HAL2015/ We are proud to present Joachim Breitner (nomeata) as our invited speaker. The submission deadline (November 2) is approaching! See you - Johannes Waldmann (PC chair)

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Re: [Haskell-cafe] GHC can't find DLL dependencies on Windows
by Ryan Scott 29 Oct '15

29 Oct '15

Never mind, I figured it out. Previously, I had been placing C:\msys64\mingw64\bin at the end of my user PATH. It turns out that my PATH was in fact on the DLL search path, but for some reason, an earlier directory on my PATH was causing problems. I can't exactly pinpoint what was causing the problem, but after moving C:\msys64\mingw64\bin to the start of my system PATH, I can run Haskell executables in PowerShell/cmd.exe without a problem. Ryan S.

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Stripe-Haskell Updates !
by David Johnson 29 Oct '15

29 Oct '15

*stripe-haskell 2.0* has been released on hackage. *The 2.0 release will entail the following:* - All types will now live in their own repository 'stripe-core' (for better use w/ ghcjs projects). - 'stripe-http-streams' is a specific http client backend for 'stripe-haskell' - Other backends (wreq, conduit, etc.) can be added. As always, pull requests welcome. - 'stripe-haskell' is now a virtual package that wraps 'stripe-http-streams' and 'stripe-core'. - We have a 'gitter' chat for our repo, to promote collaboration. - We now have a multi-ghc travis build that uses stack. - Jeremy Shaw has implemented a novel approach to the optional parameters problem using typeclasses. The docs will contain more information. - For existing stripe-haskell users version 2.0 is a breaking change, but it features a nicer interface due to Jeremy Shaw's changes. *Other notes:* - Existing 1.4 users will not be neglected. We can continue to submit patches up to 2.0. *Future goals:* - Migrate to servant-client ASAP. - Continue to beg Stripe for a machine readable specification that will relieve us from having to perform manual updates on subsequent API changes, and furthermore will allow us to fully take advantage of this wonderful service. Please respond here if you have questions, or visit our gitter at https://gitter.im/dmjio/stripe.

1 0

installing GSL packages on Windows
by Sean Matthews 28 Oct '15

28 Oct '15

I'm currently trying to install the gsl packages (in particular hmatrix-gsl) for a Windows 7/32 system. I've been using a fairly stripped down version of the GHC for a while, but now that I'm trying to install packages like this, I'm running into problems. Anyway, I have installed pkg-config, etc. and I believe I've got the various bits of gsl installed. However cabal is still failing at attaching this to the appropriate haskell modules, at what looks to be very near the end, and suggstions for what I can try to get things to finish would be welcome. Below is the output as generated by cabal (this is the result of several iterations and systematic googling, but google seems to have run out on me). All suggestions, advice, etc. very welcome, Sean Matthews > cabal install hmatrix-gsl --extra-include-dirs="C:\Users\sematthews\My Software\gsl-1.15-dev-win32\include" --extra-lib-dirs="C:\Users\sematthews\My Software\gsl-1.15-dev-win32\lib" > cabal install hmatrix-gsl --extra-include-dirs="C:\Users\sematthews\My Software\gsl-1.15-dev-win32\include" --extra-lib-dirs="C:\Users\sematthews\My Software\gsl-1.15-dev-win32\lib" > Resolving dependencies... > Configuring hmatrix-gsl-0.17.0.0... > Building hmatrix-gsl-0.17.0.0... > Failed to install hmatrix-gsl-0.17.0.0 > Build log ( C:\Users\sematthews\AppData\Roaming\cabal\logs\hmatrix-gsl-0.17.0.0.log ): > Building hmatrix-gsl-0.17.0.0... > Preprocessing library hmatrix-gsl-0.17.0.0... > [ 1 of 17] Compiling Graphics.Plot ( src\Graphics\Plot.hs, dist\build\Graphics\Plot.o ) > [ 2 of 17] Compiling Numeric.GSL.Internal ( src\Numeric\GSL\Internal.hs, dist\build\Numeric\GSL\Internal.o ) > [ 3 of 17] Compiling Numeric.GSL.Integration ( src\Numeric\GSL\Integration.hs, dist\build\Numeric\GSL\Integration.o ) > [ 4 of 17] Compiling Numeric.GSL.Fourier ( src\Numeric\GSL\Fourier.hs, dist\build\Numeric\GSL\Fourier.o ) > [ 5 of 17] Compiling Numeric.GSL.Polynomials ( src\Numeric\GSL\Polynomials.hs, dist\build\Numeric\GSL\Polynomials.o ) > [ 6 of 17] Compiling Numeric.GSL.Minimization ( src\Numeric\GSL\Minimization.hs, dist\build\Numeric\GSL\Minimization.o ) > [ 7 of 17] Compiling Numeric.GSL.Root ( src\Numeric\GSL\Root.hs, dist\build\Numeric\GSL\Root.o ) > [ 8 of 17] Compiling Numeric.GSL.Fitting ( src\Numeric\GSL\Fitting.hs, dist\build\Numeric\GSL\Fitting.o ) > [ 9 of 17] Compiling Numeric.GSL.ODE ( src\Numeric\GSL\ODE.hs, dist\build\Numeric\GSL\ODE.o ) > [10 of 17] Compiling Numeric.GSL.Interpolation ( src\Numeric\GSL\Interpolation.hs, dist\build\Numeric\GSL\Interpolation.o ) > [11 of 17] Compiling Numeric.GSL.LinearAlgebra ( src\Numeric\GSL\LinearAlgebra.hs, dist\build\Numeric\GSL\LinearAlgebra.o ) > [12 of 17] Compiling Numeric.GSL.SimulatedAnnealing ( src\Numeric\GSL\SimulatedAnnealing.hs, dist\build\Numeric\GSL\SimulatedAnnealing.o ) > [13 of 17] Compiling Numeric.GSL.Vector ( src\Numeric\GSL\Vector.hs, dist\build\Numeric\GSL\Vector.o ) > [14 of 17] Compiling Numeric.GSL.IO ( src\Numeric\GSL\IO.hs, dist\build\Numeric\GSL\IO.o ) > [15 of 17] Compiling Numeric.GSL.Random ( src\Numeric\GSL\Random.hs, dist\build\Numeric\GSL\Random.o ) > [16 of 17] Compiling Numeric.GSL.Differentiation ( src\Numeric\GSL\Differentiation.hs, dist\build\Numeric\GSL\Differentiation.o ) > [17 of 17] Compiling Numeric.GSL ( src\Numeric\GSL.hs, dist\build\Numeric\GSL.o ) > In-place registering hmatrix-gsl-0.17.0.0... > setup-Simple-Cabal-1.22.4.0-i386-windows-ghc-7.10.2.exe: > 'C:\Users\sematthews\My Software\Haskell\bin\ghc-pkg.exe' exited with an > error: > hmatrix-gsl-0.17.0.0: Warning: haddock-interfaces: > C:\Users\SEMATT~1\AppData\Local\Temp\cabal-tmp-8196\hmatrix-gsl-0.17.0.0\dist\doc\html\hmatrix-gsl\hmatrix-gsl.haddock > doesn't exist or isn't a file > hmatrix-gsl-0.17.0.0: Warning: haddock-html: > C:\Users\SEMATT~1\AppData\Local\Temp\cabal-tmp-8196\hmatrix-gsl-0.17.0.0\dist\doc\html\hmatrix-gsl > doesn't exist or isn't a directory > hmatrix-gsl-0.17.0.0: library-dirs: /usr/local/lib is a relative path which > makes no sense (as there is nothing for it to be relative to). You can make > paths relative to the package database itself by using ${pkgroot}. (use > --force to override) > hmatrix-gsl-0.17.0.0: include-dirs: /usr/local/include is a relative path > which makes no sense (as there is nothing for it to be relative to). You can > make paths relative to the package database itself by using ${pkgroot}. (use > --force to override) > cabal: Error: some packages failed to install: > hmatrix-gsl-0.17.0.0 failed during the building phase. The exception was: > ExitFailure 1 -- Sean Matthews seanmatthews1(a)gmail.com / +49 1515 800 1901

1 0

No warn on type in expression?
by amindfv＠gmail.com 28 Oct '15

28 Oct '15

An expression like: x = 5 :: Int Fails with -Wall -Werror, with "Top-level binding with no type signature". I propose we don't warn on bindings whose entire expressions are typed. This cuts in half the line noise for trivial variable values. Tom

3 2

GHC can't find DLL dependencies on Windows
by Ryan Scott 28 Oct '15

28 Oct '15

I recently decided to try out a simple diagrams-cairo project on Windows 8 (x86_64) to discover that GHC (7.10.2, to be specific) acts rather bizarrely when dealing with external DLL dependencies. To start, I downloaded MSYS2 [1], installed the libraries needed for cairo and pango to work [2], installed diagrams-cairo [3], and tried running a simple diagrams program: module Main (main) where import Diagrams.Prelude import Diagrams.Backend.Cairo.CmdLine main :: IO () main = mainWith (circle 1 :: Diagram B) like so from MSYS2: runghc Cairo.hs -o circle.svg -w 400 And it worked. Hooray! Now, I normally use cmd.exe/PowerShell for most of my Windows command-line tasks, so later I tried invoking the above command on PowerShell, only to be greeted with an error message: $ runghc.exe .\Cairo.hs -o circle.svg -w 400 Cairo.hs: warning: _tzset from msvcrt is linked instead of __imp__tzset Cairo.hs: libcairo-2: The specified procedure could not be found. Cairo.hs: <command line>: can't load .so/.DLL for: libcairo-2.dll (addDLL: could not load DLL) PowerShell, alas, couldn't find libcairo-2.dll when MSYS2 had no trouble whatsoever. I realized that MSYS2 stores all of its MinGW-related DLL files in a special location (C:\msys64\mingw64\bin). This can be observed by running cygcheck on the executable: $ C:\msys64\usr\bin\cygcheck.exe .\Cairo.exe C:\Users\ryanscot\Documents\Hacking\Haskell\Cairo.exe cygcheck: track_down: could not find libcairo-2.dll cygcheck: track_down: could not find libglib-2.0-0.dll cygcheck: track_down: could not find libgobject-2.0-0.dll cygcheck: track_down: could not find libpango-1.0-0.dll cygcheck: track_down: could not find libpangocairo-1.0-0.dll ... After reading about DLL search paths in Windows [4], I got the impression that I could add C:\msys64\mingw64\bin to my PATH, and then executables would look for DLLs there. Adding C:\msys64\mingw64\bin to my PATH seemed to make cygcheck happy: $ C:\msys64\usr\bin\cygcheck.exe .\Cairo.exe C:\Users\ryanscot\Documents\Hacking\Haskell\Cairo.exe C:\msys64\mingw64\bin\libcairo-2.dll ... But invoking runghc Cairo.exe on PowerShell still fails with the same error message! For the life of me, I can't figure out what kind of sorcery MSYS2 is doing to make C:\msys64\mingw64\bin visible to the DLL search path from GHC. The only way I can trick PowerShell into seeing libcairo-2.dll is to (1) Copy libcairo-2.dll directly to C:\Windows\System32, or (2) Invoke SetDllDirectory("C:\msys64\mingw64\bin") [5] from a PowerShell startup script Neither of these options are very satisfying, since (1) has massive security implications, and (2) only works when you have one external DLL directory (if you called SetDllDirectory again with a different directory, it overrides the first one). I know there are folks out there who have managed to get diagrams working on Windows, so can someone let me know if I'm doing something wrong? Ryan S. ----- [1] http://msys2.github.io/ [2] pacman -S mingw-w64-x86_64-cairo mingw-w64-x86_64-pango 1.38.1-1 [3] cabal install diagrams-cairo [4] https://msdn.microsoft.com/en-us/library/ms682586.aspx#search_order_for_des… [5] https://msdn.microsoft.com/en-us/library/windows/desktop/ms686203%28v=vs.85…

1 0

best practice for lifting of IO and could lifting be automated?
by Oleg 28 Oct '15

28 Oct '15

Dimitri DeFigueiredo wrote: > Imagine I need to read a .CSV file which may or may not contain column > titles on its first line. I'm not interested in the column titles, I > just want the rest of the file. I am provided a library function to read > the contents of the file (using a "callback"). The library author > provided this function in the IO monad. > withCSV :: FilePath -> (Handle -> IO r) -> IO r > withCSV path action = do > putStrLn "opening file" > h <- openFile path ReadWriteMode > r <- action h > hClose h > putStrLn "file closed" > return r > The problem arises because I also want to use the ReaderT monad > transformer. My environment information will tell me > whether or not to disregard the first (i.e. column title) line. For this particular example, the answer is easy: If you have the IO monads, you have the Reader monad, and the State/Writer as well. This is just an IORef. > getFileContents :: IO String > getFileContents = do > ref <- newIORef False > withCSV "data.csv" (myReadFile ref) > where > myReadFile :: IORef Bool -> Handle -> IO String > myReadFile ref handle = do > header <- readIORef ref -- ask --- OOOPPSss!!! FAIL! Can't ask. > case header of > False -> return "" > True -> hGetLine handle -- skip first line > text <- hGetContents handle > return text Using just IO, you can get State, Reader, Writer, and Exception (and in a modular way!) As to you general question, I will and do advocating abandoning monad transformers altogether. The paper on extensible effects demonstrated a new solution to the MonadCatchIO problem that solved the long-standing issue of discarding state upon exception. See Sec 6 of http://okmij.org/ftp/Haskell/extensible/more.pdf

6 9

haskell-ide repository name
by Alan & Kim Zimmerman 28 Oct '15

28 Oct '15

At the moment the repository/project is called haskell-ide This leads to the impression that it is an IDE. It is actually a backend/server to provide services for an IDE We are considering changing the name. The options are haskides / ghc-ide-daemon / ghc-ide-service / ghc-ide-engine Please cast your vote at http://strawpoll.me/5842105 Thanks Alan

5 4

asked for a mentor for some math exercises
by Roelof Wobben 28 Oct '15

28 Oct '15

Hello, I try to learn Haskell by the Craft of Functional programming book. But on Chapter 4 Designing there are a lot of very math questions which I do not understand. Is there someone who wants to be a volunteerbasis a mentor for me for this sort of problems. Regards, Roelof

1 0

Cabal depend on local package with foreign dependencies
by Richard Lewis 27 Oct '15

27 Oct '15

Hi there, I have two libraries that I'm working on, packageA and packageB. packageA was written some time ago and depends on a foreign C library, libfoo, which I also wrote and which is installed in a non-standard location. packageB depends on packageA and is new and under active development. I have the following things, then: - libfoo is installed in ~/.local/lib, with includes in ~/.local/include/foo - packageA is in ~/src/packageA - packageB is in ~/src/packageB packageA has a .cabal file which includes: library build-depends: base, ... exposed-modules: A include-dirs: /home/richard/.local/include extra-lib-dirs: /home/richard/.local/lib executable testA ... extra-lib-dirs: /home/richard/.local/lib extra-libraries: foo I've created a cabal sandbox in packageA and I can successfully build it. Now, packageB makes use of packageA. It has a .cabal file which looks like this: library build-depends: base, packageA, ... exposed-modules: B executable testB ... extra-lib-dirs: /home/richard/.local/lib extra-libraries: foo Again, I've created a cabal sandbox in packageB. In order to be able to use packageA (which is not installed anywhere) I believe I have to do: $ cabal add-source ~/src/packageA Next, when I try and configure, it says: cabal: At least the following dependencies are missing: packageA -any That's fine, I assume, because I can now just `cabal install --only-dependencies` to get packageA built into packageB's sandbox. But when I try and do this, I get: $ cabal install --only-dependencies Resolving dependencies... Configuring packageA-0.1... Building packageA-0.1... Preprocessing library packageA-0.1... In-place registering packageA-0.1... Preprocessing executable 'testA' for packageA-0.1... Foo.hsc:10:33: fatal error: foo/foo.h: No such file or directory compilation terminated. So a target of packageA which compiles fine when doing cabal build directly from packageA now fails to compile when I attempt to build it from packageB by installing packageB's dependencies. I'm not sure how to proceed. It feels like maybe I have to tell cabal--when running it from packageB--where the include files are for packageA, because packageA needs to get compiled (which involves linking against libfoo and using libfoo's includes). I know that packageA *does* compile (because I've done that already), but it won't compile inside packageB's sandbox. Any suggestions? Richard

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Let, Equations, and Monad
by PATRICK BROWNE 27 Oct '15

27 Oct '15

{- From Learn Haskell Fast and Hard : 4.3.1. Maybe is a monad http://yannesposito.com/Scratch/en/blog/Haskell-the-Hard-Way/#maybe-monad Concerning the code below I have the following questions: 1) Are eligibleLet and eligibleEquational operationally equivalent (i.e. perform the same operations) and/or semantically equivalent(i.e. Church-Rosser)? 2) Apart from the return type of Maybe instead of Bool how does eligibleMonad differ from eligibleLet? Regards, Pat -} deposit value account = account + value withdraw value account = account - value -- You are eligible for a bonus only if your sequence of transactions stays out of the red. eligibleLet :: (Num a,Ord a) => a -> Bool eligibleLet account = let account1 = deposit 100 account in if (account1 < 0) then False else let account2 = withdraw 200 account1 in if (account2 < 0) then False else let account3 = deposit 100 account2 in if (account3 < 0) then False else let account4 = withdraw 300 account3 in if (account4 < 0) then False else let account5 = deposit 1000 account4 in if (account5 < 0) then False else True eligibleEquational :: (Num a,Ord a) => a -> Bool eligibleEquational account = let account1 = deposit 100 account in if (account1 < 0) then False else let account2 = withdraw 200 account1 in if (account2 < 0) then False else let account3 = deposit 100 account2 in if (account3 < 0) then False else let account4 = withdraw 300 account3 in if (account4 < 0) then False else let account5 = deposit 1000 account4 in if (account5 < 0) then False else True -- Monadic version depositM :: (Num a) => a -> a -> Maybe a depositM value account = Just (account + value) withdrawM :: (Num a,Ord a) => a -> a -> Maybe a withdrawM value account = if (account < value) then Nothing else Just (account - value) eligibleMonad :: (Num a, Ord a) => a -> Maybe Bool eligibleMonad account = do account1 <- depositM 100 account account2 <- withdrawM 200 account1 account3 <- depositM 100 account2 account4 <- withdrawM 300 account3 account5 <- depositM 1000 account4 Just True main = do print $ eligibleLet 300 -- True print $ eligibleLet 299 -- Falsen print $ eligibleEquational 300 -- True print $ eligibleEquational 299 -- False print $ eligibleMonad 300 -- Just True print $ eligibleMonad 299 -- Nothing -- This email originated from DIT. If you received this email in error, please delete it from your system. Please note that if you are not the named addressee, disclosing, copying, distributing or taking any action based on the contents of this email or attachments is prohibited. www.dit.ie Is ó ITBÁC a tháinig an ríomhphost seo. Má fuair tú an ríomhphost seo trí earráid, scrios de do chóras é le do thoil. Tabhair ar aird, mura tú an seolaí ainmnithe, go bhfuil dianchosc ar aon nochtadh, aon chóipeáil, aon dáileadh nó ar aon ghníomh a dhéanfar bunaithe ar an ábhar atá sa ríomhphost nó sna hiatáin seo. www.dit.ie Tá ITBÁC ag aistriú go Gráinseach Ghormáin – DIT is on the move to Grangegorman <http://www.dit.ie/grangegorman>

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SQL select for HDBC.ODBC MSSQL driver
by Anakreontas 27 Oct '15

27 Oct '15

Hello. I obtain a connection and try to execute a query on MSSQL server with HDBC c <- connectODBC "Driver={SQL Server};Server=.;Database=Pure_Local;Trusted_Connection=yes;" stm <- quickQuery c "select count(*) as cnt from X__FD" [] HDBC obtains the connection but the SQL query raises an exception with the following message: SqlError {seState = "[\"25000\"]", seNativeError = -1, seErrorMsg = "disconnect: [\"0: [Microsoft][ODBC SQL Server Driver]Invalid transaction state\"]"} No matter which statement I tried, I always get the "Invalid transaction state" message.

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Haskell Report Infelicity?
by Dominic Steinitz 27 Oct '15

27 Oct '15

I have probably misunderstood but is the following expected? floor, round, truncate and ceiling give similar results (all methods of the RealFrac class). properFraction :: (Integral b, RealFrac a) => a -> (b, a) *Girsanov> properFraction (-1 / 0) (-17976931348623159077293051907890247336179769789423065727343008115773267 5805500963132708477322407536021120113879871393357658789768814416622492847 4306394741243777678934248654852763022196012460941194530829520850057688381 5068234246288147391311054082723716335051068458629823994724593847971630483 5356329624224137216,0.0) *Girsanov> properFraction (1 / 0) (179769313486231590772930519078902473361797697894230657273430081157732675 8055009631327084773224075360211201138798713933576587897688144166224928474 3063947412437776789342486548527630221960124609411945308295208500576883815 0682342462881473913110540827237163350510684586298239947245938479716304835 356329624224137216,0.0) *Girsanov> properFraction (0 / 0) (-26965397022934738615939577861835371004269654684134598591014512173659901 3708251444699062715983611304031680170819807090036488184653221624933739271 1459592111865666518401372982279144533294018691411791796244281275086532572 2602351369432221086966581124085574502576602687944735992086890771957445725 3034494436336205824,0.0) The Haskell Report "6.4.6 Coercions and Component Extraction" is silent on what to expect with NaN, Infinity and -Infinity so I think it should be amended. Alternatively, one could expect implementations to throw a runtime error? In ghc, the problem is here https://phabricator.haskell.org/D160a /* This is expected to replace uses of __decodeDouble_2Int() in the long run */ StgInt __decodeDouble_Int64 (StgInt64 *const mantissa, const StgDouble dbl) { if (dbl) { int exp = 0; *mantissa = (StgInt64)scalbn(frexp(dbl, &exp), DBL_MANT_DIG); return exp-DBL_MANT_DIG; } else { *mantissa = 0; return 0; } } I believe frexp [1] and scalbn [2] both pass through NaN, Infinity and -Infinity and I think type coercion in C is undefined for these values. Furthermore exp is undefined for these values [1]. 1. http://en.cppreference.com/w/cpp/numeric/math/frexp 2. http://en.cppreference.com/w/cpp/numeric/math/scalbn Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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