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ANN: hledger 1.4
by Simon Michael 01 Oct '17

01 Oct '17

Aloha! I'm pleased to announce hledger 1.4. Thank you release contributors: Nicholas Niro, Hans-Peter Deifel, Jakub Zárybnický, Felix Yan, Mark Hansen, Christian G. Warden, Nissar Chababy and Peter Simons. Also, if I haven't already mentioned it: this year hledger turns 10! Here's the first commit, from January 27 2007: https://github.com/simonmichael/hledger/commit/85864b41 We have come a way, but there is much yet to look forward to. Onward and upward! The next major release is scheduled for 2017/12/31. What is hledger ? ----------------- hledger (http://hledger.org) is an evolving, dependable, robust, cross-platform program for tracking money, time, or any other commodity, using double-entry accounting and a simple plain text file format. It is a haskell reimplementation of Ledger and the plain text accounting concept, providing command-line, curses and web interfaces. hledger aims to be a pleasant and practical tool for personal, business or institutional finance and time tracking. What's new ? ------------ The full release notes are at http://hledger.org/release-notes#hledger-1.4 . Some highlights: - Easy install script: we have a new installation method for the hledger tools, intended to dodge common pitfalls and just-work more often. Building on the stack team's install script, this bash script is cross platform, uses cabal or stack, installs stack and GHC if needed, and installs the latest release of all major hledger packages. See http://hledger.org/download for details. - More batteries included: most experimental addon commands formerly shipped in bin/ are now built in and work out of the box. - New commands: balancesheetequity (a balance sheet including equity), tags (list tags in use), import (detects new transactions in multiple input files and adds them to the main journal, particularly useful with CSV downloads). - Balance reports can be sorted by amount - makes those high expenses easy to spot. - CLI conveniences: @ARGSFILE is expanded to the set of args/flags in ARGSFILE. depth:2 or --depth=2 can be written as -2. - Help improvements: reorganized docs page, a more useful commands list, a smarter help command, --help and -h are the same again (by popular demand), Getting started --------------- See http://hledger.org/download for all install methods. To get the latest hledger release, you may need to build it yourself using stack or cabal. But don't worry, this is.. getting quite painless. The new hledger installer requires only bash and will install everything you need in one step: the hledger tools in $HOME/.local/bin/, and (if required) stack and GHC in $HOME/.stack/. Run it like so: $ curl -sSLO http://hledger.org/hledger-install.sh $ less hledger-install.sh # review script, for the security conscious $ bash hledger-install.sh # install the latest hledger tools Ensure $HOME/.local/bin is in your $PATH. Now try some commands: $ hledger -h # quick help $ hledger help # list built-in manuals $ hledger add # record some transactions $ hledger # list available commands Now perhaps work through the tutorial at http://hledger.org/step-by-step.html Or review the fine documents, presentations etc. at http://hledger.org and http://plaintextaccounting.org Or say hello and ask questions in the #hledger IRC channel on Freenode: http://irc.hledger.org If you have been finding hledger useful, I invite you to become a sponsor or contributor to make it stronger. Donate using one of the funding links on the home page, give feedback, report bugs, send pull requests, write about it, or help in some other way. Thanks for your support! I hope to meet you online. -Simon

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Mutable data structures and asynchronous exceptions
by Станислав Черничкин 30 Sep '17

30 Sep '17

It's quite hard to implement mutable data structures in presence of asynchronous exceptions. Since exception can arise at any point, it is not possible to guarantee atomicity of operation, hence mutable data structure may remain in incorrect state in case of interruption. One can certainly use maskAsyncExceptions# and friends to protect critical regions, but masking function are living in IO, mutable data structures on other hand trend to be state-polymorphic (to allow it usage in ST). This lead to conflicting requirements: - One should not care about asynchronous exceptions inside ST (it is not possible to catch exception in ST, hence not possible to use something in invalid state). More over, it is not even possible to do write “exception-safe” code, because masking functions not available. - One should provide accurate masking then using same data structures in IO. So I want do discuss several questions topics on this case. 1. Impact. Are async exceptions really common? Would not be easier to say: “ok, things can go bad if you combine async exceptions with mutable data structures, just don't do it”. 2. Documentation. Should library authors explicitly mention async exceptions safety? For example https://hackage.haskell.org/package/hashtables – is it async exceptions safe when used in IO? Or even worse https://hackage.haskell.org/package/ghc-prim-0.5.1.0/docs/GHC-Prim.html#v:r… - what will happened in case of async exception? This functions is sate-polimorphic, will it implicitly mask exceptions if used from IO? 3. Best practices. How should we deal with problem? Is creating separate versions of code for ST and IO is the only way? Probably it is possible to add “mask” to something like https://hackage.haskell.org/package/primitive-0.6.2.0/docs/Control-Monad-Pr… emit mask in IO instance and NOOP in ST version? Or maybe somebody know better patterns for async exeption safe code? -- Sincerely, Stanislav Chernichkin.

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Reinventing the wheel? Does any existing package provide an applicatively lifted (>>) ?
by Viktor Dukhovni 28 Sep '17

28 Sep '17

When generating a report file from a database I found it much more efficient (significantly shorter runtime) to represent each row by an I/O action that prints the row, rather than to construct a Row object that to print and throw away. But the naive way to construct the I/O action can be tedious to maintain once the column count gets appreciably high: newtype Foo = Foo { _foo :: IO () } instance FromRow Foo where fromRow = Foo <$> (rowPrinter <$> field <*> field <*> field <*> ... <*> field) where rowPrinter :: Type1 -> Type2 -> Type3 -> ... -> TypeN -> IO () rowPrinter p1 p2 p3 ... pN = do printP1 printP2 printP3 ... printPN So I decided to applicatively decompose the rowPrinter function (with the actual name of "andthen" to be determined later) as: rowPrinter = (printP1 <$> field) `andthen` (printP2 <$> field) `andthen` (printP3 <$> field) `andthen` ... (printPN <$> field) which avoids the need to package the column printers explicitly into a single function, and may be somewhat more efficient a well. What was not immediately obvious to me was whether there's an "off the shelf" implementation of "andthen" I could just reuse. The necessary operator satisfies: andthen (f (m a)) (f (m b)) = f (ma >> mb) or, equivalently: a `andthen` b = (>>) <$> a <*> b for which http://pointree.io dutifully gives me: andthen = (<*>) . ((>>) <$>) Its type signature is: Prelude> :set prompt "l> " l> :m + Control.Applicative l> :m + Control.Monad l> :t ((<*>) . ((>>) <$>)) ((<*>) . ((>>) <$>)) :: (Monad m, Applicative f) => f (m a) -> f (m b) -> f (m b) l> It seems to me that this would have been done before, and the operator would already be present in some package, but I'm having trouble finding it. (Due to the hidden constructors of FromRow defining a Semigroup does not work out here, so I can't use (<>), which also inconveniently conflicts with Monoid (<>)). So my question is whether the operator in question is already available, under some name in some package, or else suggested names for it if new. -- Viktor.

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[ANN] brittany-0.8.0.3
by lennart spitzner 28 Sep '17

28 Sep '17

- Support for ghc-8.2.1 - Fix quadratic performance bug full changelog at https://hackage.haskell.org/package/brittany-0.8.0.3/changelog -- lennart

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[hs-bibutils] intention to take over package
by Václav Haisman 28 Sep '17

28 Sep '17

Hi. I would like to take over the hs-bibutils Hackage package. It has not been updated since 2014, the listed maintainer is not responsive to emails, and listed home page is 404 page. -- VH

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Re: [Haskell-cafe] EduHaskell
by erwig 25 Sep '17

25 Sep '17

Thanks for all the useful hints and suggestions! Maybe I should have explained the constraints (and where they come from) in more detail. First, the course is NOT an introduction to programming, but an introduction to computer science more generally and thus also discusses several topics not typically addressed by a programming course. Second, computing concepts are introduced with the help of stories, and programming will only take place in the second half of the course (more details about the approach can be found at web.engr.oregonstate.edu/~erwig/SBT) Thus the goal of minimizing the need for explaining advanced type system features. Also, we have already created Haskell code, so that's why Elm, although a really nice language, is currently not an option because of its different syntax. Code.world is also a cool system, but we do currently require a REPL. I definitely will take another look a Helium. Again, thanks for all the responses so far! I'm still wondering which, if any, of the existing alternative preludes would potentially be a good substitute for educational purposes. -- Martin

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(no subject)
by Vladyslav Nikolayevich 25 Sep '17

25 Sep '17

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deploy wxHaskell app on Windows
by Olaf Klinke 25 Sep '17

25 Sep '17

Dear Cafe, I need help deploying a wxHaskell application on Windows. (The gui(a)haskell.org list seems to be dormant, as is wxhaskell-users on sourceforge.) I am explicitly CC-ing some people who recently posted about wxHaskell on this list. TL;DR: How to deploy a wxHaskell application on several Windows machines? Option (a): Automate the installation of DLLs and tweaking of PATH Option (b): Build static libs of wxWidgets to be linked into a static binary. I don't know how to do either. I developed a GUI application based on wxWidgets. I love the wx package, since wxWidgets provides all the high-level dialogs I need, like file and date pickers. The necessary installations on my Linux development machine went like a charm. Next I tried a Windows 10 machine. I installed stack, which installed a ghc.exe in %HOME%/AppData/Local/Programs/.../bin/ and cabal and stack binaries in %HOME%/AppData/Roaming/local/bin/. I downloaded a wx-config.exe binary and placed it in the latter directory and added that to the PATH. I downloaded wxInstall-Achelanne-64.0.1 and after adding the above path to ghc.exe to it's Install.bat, the Installation completed. Install.bat suggested to add two directories to the PATH, which I did. I set WXWIN to wxInstall-Achelanne-64.0.1/wxWidgets and WXCFG to gcc_dll/mswu With this, wx-config outputs some flags if requested. Next, I added %WXWIN%/include to extra-include-dirs and %WXWIN%/lib/gcc_dll to extra-lib-dirs in my stack.yaml. I also added %WXWIN%/DLLs to the extra-lib-dirs in the .cabal file. %WXWIN%/include/wx/platform.h mentions wx/setup.h which is not there. Remedy: Copy %WXWIN%/include/wx/msw/setup.h to %WXWIN%/include/wx/setup.h I believe I did set SHARED=0 in the wxWidgets config but there are no .lib, only .dll files in %WXWIN%, so I can not use ghc -optl-static. Hence the binaries produced by stack need to be told the place of the DLLs via the PATH environment variable. This is something I'd like to avoid on all the machines. Any suggestions welcome. Olaf

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Re: [Haskell-cafe] EduHaskell
by Johannes Waldmann 24 Sep '17

24 Sep '17

Dear Martin, I use Haskell for teaching as well (not for beginners) [1]. I do use ghci in lab classes. For the problems you mention, I have these sort-of work-arounds: > Errors resulting from overloading numerical literals, arithmetical operators? avoid built-in (Prelude) numbers and the Num class. stuff that's been generalized from list to Foldable (e.g., length)? avoid built-in (Prelude) lists [2] > Errors due to undefined type class instances > (specifically, Eq and Show) I think these classes are somewhat easy to motivate - at least Eq is (we need "==" to notate and test properties of programs, not every type has decidable equality (functions have not), so we need to mark the types that do) For Show, it's not that nice (ghci uses "show" but implicitly - then why do we need to write the Show instance explicitly) Still, adding "deriving (Eq, Show)" after each data declaration is not too much of a burden. I agree it is a distraction. > Errors in the context of parametric polymorphism Well, it's an important concept to teach, so it is natural that it takes some time and work. (slightly tangential - I think it would already help if it would be easier to declare types of identifiers - to remove unwanted polymorphism. E.g., "\ (x::Bool) (y::Bool) -> x || y" currently requires a language pragma (!) whose name mentions type variables (!!) ) - Johannes. [1] https://www.imn.htwk-leipzig.de/~waldmann/talk/17/wflp [2] https://www.imn.htwk-leipzig.de/~waldmann/etc/untutorial/list-or-not-list/

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3rd International Workshop on Real World Domain Specific Languages (RWDSL'18)
by Rob Stewart 22 Sep '17

22 Sep '17

CALL FOR PAPERS ================================= 3rd International Workshop on Real World Domain Specific Languages https://sites.google.com/site/realworlddsl In conjunction with The International Symposium on Code Generation and Optimisation 2018. http://cgo.org/cgo2018/ Vienna, Austria, 24 February, 2018 ==================================== As the use of computers proliferates, the complexity and variety of systems continues to grow. As a result, it is becoming increasingly inflexible to "hard wire" behaviours into software. Software developers can enable more control over their software configurations by exploiting Domain Specific Languages (DSLs). Such DSLs provide a systematic way to structure the underlying computational components: to coin a phrase, a DSL is a library with syntax. There is an enormous variety of DSLs for a very wide range of domains. Most DSLs are highly idiosyncratic, reflecting both the specific natures of their application domains and their designers' own preferences. This workshop will bring together constructors of DSLs for "real world" domains; that is, DSLs intended primarily to aid in building software to solve real world problems rather than to explore the more theoretical aspects of language design and implementation. We are looking for submissions that present the motivation, design, implementation, use and evaluation of such DSLs. ================================= Key Dates: ---------------- Paper submission deadline : 15th December2017 Author notification: 26th January 2018 Final manuscript due: 9th February 2018 Workshop: 24th February 2018 ---------------- Submission Instructions: The EasyChair submission page for this workshop is: https://easychair.org/conferences/?conf=rwdsl18 We anticipate that accepted submissions will be published in the ACM Digital Library within its International Conference Proceedings Series, as were RWSDL'16 and RWDSL'17. Submissions should be 8-10 pages in ACM double-column format. Authors should follow the information for formatting ACM SIGPLAN conference papers, which can be found at http://www.acm.org/publications/proceedings-template. Full submission details are on the workshop web page. ================================= Program Chairs Rob Stewart, Heriot-Watt University, UK Greg Michaelson, Heriot-Watt University, UK PC Members Riyadh Baghdadi, MIT, USA Allin Cottrell, Wake Forest University, USA Nina Dethlefs, University of Hull, UK And Gill, X - The Moonshot Factory, USA Kevin Hammond, University of St Andrews, UK Patrick Maier, University of Glasgow, UK Mathijs Schuts, Phillips Healthcare, Netherlands Simon Thompson, University of Kent, UK Phil Trinder, University of Glasgow, UK Contact Please email inquiries concerning the workshop to: R.Stewart(a)hw.ac.uk

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