- Haskell-Cafe - Haskell.org

ANNOUNCE: Parsed 0.0.1
by Mike Izbicki 01 Apr '15

01 Apr '15

I'm pleased to announce the first release of the Parsed library (pronounced par-séd). Parsed is a reimplementation of Haskell's excellent Parsec library in the Unix shell. In particular, the Unix pipe operator | corresponds exactly to Haskell's Applicative bind *>. Here's a quick example to get a feel for the syntax. The following bash one liner creates a parser for matching balanced parenthesis: ``` parens() { choice "$1" "match '(' | parens \"$1\" | match ')'"; } ``` For more detailed examples and implementation notes, please see the Parsed paper accepted at SIGBOVIK2015: https://github.com/mikeizbicki/parsed/raw/master/sigbovik2015/paper.pdf You can download Parsed from its github page at: https://github.com/mikeizbicki/parsed

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Specify OS version
by Sergey Bushnyak 01 Apr '15

01 Apr '15

Hi Cafe! I have program written in Haskell and Swift that runs on Mac. This program uses some features that was introduced in last version of OS X “Yosemite” 10.10, but some of my users use previous version "Maverics " 10.9. Is there some technique that allows me to extend my cabal file and specify which *version* of os is currently in use and don't load some of modules? AFAIK, Cabal's `conditional` doesn't provide such mechanism, but something like ``` if os(osx) && ver(=10.10) if os(osx) && ver(<=10.9) ``` will be nice. Maybe there is other approach to this problem?I don't want to use `CPP` extension to handle this within code. Thanks -- Best regards, Sergey Bushnyak

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Speed up ghc -O2
by Kees Bleijenberg 01 Apr '15

01 Apr '15

My program reads a xls file and creates a haskell program that does exactly the same as what the xls does. Every cell in the xls is a function and contains 2 lines: the type declaration and 1 line the implementation. The type of a cell is XlsCell. data XlsCell = Reader ExternalCells XlsCellRes data XlsCellRes = XlsCellString String | XlsCellBool Bool | ..... type ExternalCells = Map String XlsCellRes -- search (or set) a value of a cell by its name. The externalCells are for the cells you can change at runtime. The generated program was first 30000 lines. When I compiled it with ghc 7.8.3. -O0 the program worked, but was terribly slow. With -O2 I got: out of memory. With a few trics the generated code is now split up in 2 files 5000 and 10000 lines. I've upgraded to ghc 7.8.4. If I do ghc -O2 the program takes more then 4 hours to compile. The -O2 compilation is essential. The resulting program is much (more then 10x) faster then without -O2. What can I do (changes in the generated code, changes to speed up ghc?) to make ghc faster with -O2? I tried ghc-make, but it doesn't make a big difference. Kees

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Journal of Functional Programming - Call for PhD Abstracts
by Graham Hutton 01 Apr '15

01 Apr '15

============================================================ CALL FOR PHD ABSTRACTS Journal of Functional Programming Deadline: 30th April 2015 http://tinyurl.com/jfp-phd-abstracts ============================================================ PREAMBLE: Many students complete PhDs in functional programming each year, but there is currently no common location in which to promote and advertise the resulting work. The Journal of Functional Programming would like to change that! As a service to the community, JFP recently launched a new feature, in the form of a regular publication of abstracts from PhD dissertations that were completed during the previous year. The abstracts are made freely available on the JFP website, i.e. not behind any paywall, and do not require any transfer for copyright, merely a license from the author. Please submit dissertation abstracts according to the instructions below. A dissertation is eligible if parts of it have or could have appeared in JFP, that is, if it is in the general area of functional programming. JFP will not have these abstracts reviewed. We welcome submissions from both the PhD student and PhD advisor/ supervisor although we encourage them to coordinate. ============================================================ SUBMISSION: Please submit the following information to Graham Hutton <graham.hutton(a)nottingham.ac.uk> by 30th April 2015. o Dissertation title: (including any subtitle) o Student: (full name) o Awarding institution: (full name and country) o Date of PhD award: (month and year; depending on the institution, this may be the date of the viva, corrections being approved, graduation ceremony, or otherwise) o Advisor/supervisor: (full names) o Dissertation URL: (please provide a permanently accessible link to the dissertation if you have one, such as to an institutional repository or other public archive; links to personal web pages should be considered a last resort) o Dissertation abstract: (plain text, maximum 1000 words; you may use \emph{...} for emphasis, but we prefer no other markup or formatting in the abstract, but do get in touch if this causes significant problems) Please do not submit a copy of the dissertation itself, as this is not required. JFP reserves the right to decline to publish abstracts that are not deemed appropriate. ============================================================ PHD ABSTRACT EDITOR: Graham Hutton School of Computer Science University of Nottingham Nottingham NG8 1BB United Kingdom ============================================================ This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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Enforcing data structures invariant in the type system
by Nicola Gigante 01 Apr '15

01 Apr '15

Hi all. I’m very interested in what can be done with Haskell’s type system regarding the enforcing of algorithms and data structures invariants. For example, I remember I saw a paper about an implementation of a red-black tree in Haskell where the types guaranteed the invariant about the alternation of rad and black nodes. I would like to learn those techniques, in particular the use of language features that enable this kind of things and then how to do them in practice. In the past tried hacking something with GADTs and Data Kinds but I've always got stuck with GHC errors that I could not understand, so I think I’m missing something. Where could I start from? Are there simple walk-through examples and/or fundational material? For example is it possible to write a sorting function that guarantees in the types that the output is sorted? I don’t need this specific example but you got the point. Thank you very much, Nicola

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Data.EnumMap ?
by Johannes Waldmann 01 Apr '15

01 Apr '15

Dear Cafe, in containers, we have Data.IntMap/IntSet . Because of the underlying implementation (patricia trees), keys/elements indeed have to be Int (we need their bits). This is a conflict with type-safety: I try to avoid Int, and use some newtype T = T Int instead. E.g., I want to distinguish several different indices for the same structure, like row and column numbers in (sparse) matrices, or vertices in bipartite graphs. So, I made these trivial wrappers EnumMap and EnumSet: https://github.com/jwaldmann/satchmo-solver/tree/master/src/Data Is this reasonable (do from/toEnum really have zero cost)? Would this be a useful addition to containers? - J.W.

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Hackage trustee proposal: Curating the Hackage package collection
by Adam Bergmark 01 Apr '15

01 Apr '15

Dear Haskell Community, For some time Hackage has contained a user group called "Trustees", http://hackage.haskell.org/packages/trustees/ . Description: The role of trustees is to help to curate the whole package collection. Trustees have a limited ability to edit package information, for the entire package database (as opposed to package maintainers who have full control over individual packages). Trustees can edit .cabal files, edit other package metadata and upload documentation but they cannot upload new package versions." In short, making sure that packages keep building and filling the gap between unreachable maintainers and package take-overs. Up until now we have been very careful with changes since we haven't had a defined process. Spurred by SPJ and others we have been working on a proposal for how we should operate. You can find the proposal here: https://gist.github.com/bergmark/76cafefb300546e9b90e We would now like your feedback! Some specific things from the proposal that we'd like your opinion on: * Section 1: No opt-out for restricting bounds * Section 2: Opt-out rather than opt-in procedure for loosening version constraints * Section 2: Do you care whether you are notified before or after a version constraint is loosened? * Section 3: The time frame for publishing simple source changes * Section 3: What exactly should constitute a "simple source change" We also have a github repository where YOU can file issues about broken packages, you can start doing this right now! https://github.com/haskell-infra/hackage-trustees/ Please share this with as many people as possible. We are looking forward to hear your thoughts! Sincerely, Adam Bergmark

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Opt-in upper-bounds notification service?
by Joachim Breitner 01 Apr '15

01 Apr '15

Hi, I don’t always have a complete oversight of what our ecosystem provides... do we already have a way to (opt-in) get a mail when a dependency of one of my packages was uploaded in a version that is beyond the upper-bound specified by my packages? Currently I get pinged by Michael Snoyberg when that happens, e.g. in https://github.com/fpco/stackage/issues/514, but that’s always a short while after the problem, and I’d like to fix this before anyone manually notices. If someone would hack up such as service, I’d be happy to use it. Greetings, Joachim -- Joachim “nomeata” Breitner mail(a)joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata(a)joachim-breitner.de • GPG-Key: 0xF0FBF51F Debian Developer: nomeata(a)debian.org

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Template haskell and the dependencies of the generated executable
by Aldo Davide 01 Apr '15

01 Apr '15

When I use template haskell to generate some code at compile time and splice it in my program, the generated executable still depends on template haskell (in case of -dynamic), or the Template haskell library is included in my executable (in the case of -static). Isn't that unnecessary? For example. Suppose that I use the almost trivial raw-strings-qq package to implement a hello world program: {-# LANGUAGE QuasiQuotes #-} import Text.RawString.QQ (r) main = putStrLn [r|Bonjour tout le monde|] Then the r quasi quoter runs at compile time and generates a string literal. So basically, the program that gets compiled is the following: main = putStrLn "Bonjour tout le monde" Despite that template haskell is only used at compile time, the generated executable (compiled with the -dynamic flags) depends on the following libraries: libHSarray-0.5.0.0-ghc7.8.4.so libHScontainers-0.5.5.1-ghc7.8.4.so libHSdeepseq-1.3.0.2-ghc7.8.4.so libHSpretty-1.1.1.1-ghc7.8.4.so libHSraw-strings-qq-1.0.2-ghc7.8.4.so libHStemplate-haskell-2.9.0.0-ghc7.8.4.so in addition to the ones that the non template haskell version of the program depends. Shouldn't ghc avoid that?

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Looking for Haskell contract work
by Alexander Berntsen 31 Mar '15

31 Mar '15

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Hallo Haskell friends, My company[0] uses Haskell for most of our work. Speaking of work, we are currently looking for some more of it. If anyone has some work (FSVO "work" that includes hacking, advising, teaching, etc.), please contact me off-list. Thanks! [0] plaimi: <https://secure.pe.plaimi.net>. - -- Alexander alexander(a)plaimi.net https://secure.plaimi.net/~alexander -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iF4EAREIAAYFAlUaphUACgkQRtClrXBQc7UySwD/digSIVDgS25tRW4zUtfoO/E3 /vWOMwMRnn9nfFcirrAA/0fFsl8WogNG/J2AP188517xcV4zLV1up7YtUsbEWRnh =JbNc -----END PGP SIGNATURE-----

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