- Haskell-Cafe - Haskell.org

LiberalTypeSynonyms: documentation issue
by Obscaenvs 02 Nov '13

02 Nov '13

In the docs for GHC 7.6.3, e.g. at [1], it is said that one can use LiberalTypeSynonyms as so: `type Discard a = forall b. Show b => a -> b -> (a, String)` This is, however, not possible without RankNTypes which is stated in a tutorial at FPComplete [2] and, of course, GHC 7.6.3 itself says so when trying to compile something with the above definition for Discard: ` Illegal polymorphic or qualified type: forall b. Show b => a -> b -> (a, String) Perhaps you intended to use -XRankNTypes or -XRank2Types In the type declaration for `Discard' ` Maybe the GHC User Guide should be updated to reflect this? /Fredrik References: [1] http://www.bugthunk.net/ghc/docs/7.6.3/html/users_guide_repl/data-type-exte… [2] https://www.fpcomplete.com/school/to-infinity-and-beyond/pick-of-the-week/g…

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beginners list for common lisp?
by Christopher Howard 02 Nov '13

02 Nov '13

Does anybody know if there is something like a Common Lisp version of the Haskell Beginner's mailing list? Haskell's great, of course, but I've also been picking up Lisp, and I'm looking for a Lisp list that is very newbie friendly.

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Re: [Haskell-cafe] Cabal sandboxes over cabal-dev (Rogan Creswick)
by Gregory Guthrie 02 Nov '13

02 Nov '13

"I *strongly* suggest everyone start transitioning from cabal-dev to cabal sandboxes." Is there any reason that this is not just the default install mode for Cabal? Anything that prevents the current cabal-swamp of broken dependencies is a great help. I have tried to use Haskell in some classes, but it is hard when students (and I) cannot install packages, and the only answer is the Microsoft-like; "delete everything and start over; reinstall". It certainly reduces their confidence that Haskell is a feasible working environment.

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ANNOUNCE: HList-0.3
by adam vogt 01 Nov '13

01 Nov '13

Greetings, We are pleased to announce HList-0.3. This is an update the well-known library for strongly typed heterogenous lists, records, type-indexed products (TIP) and co-products. Some of the highlights are: * works with lens. See examples/labelable.hs * modern features such as TypeFamilies, DataKinds (Symbol), ConstraintKinds, PolyKinds, QuasiQuotes * Data instances for HList and Record. One application is given in examples/cmdargs.hs * named and optional function parameters (using Keyword or perhaps RecordPuns) are part of the library proper * additional functions including: HTranspose, HZip, HFoldl, HScanr, HReplicate * improved type inference. To give an example: > let y = hMap (Fun' read :: Fun' Read String) x This is about the same as `let y = map read x', but each element of the HList `y' can have a different type. Only one of the two lengths needs to be specified. * more documentation and examples, which should make it easier to find your way around. Refer to the included ChangeLog or `darcs changes` for more details. This release requires ghc>=7.6. You can get the release from <http://hackage.haskell.org/package/HList> or use cabal-install: $ cabal update $ cabal install HList-0.3 For now it seems that hackage is rejecting the upload due to language extensions it doesn't know about, so in the meantime you can get it with: $ cabal install http://code.haskell.org/~aavogt/HList/HList-0.3.0.tar.gz With haddocks at <http://code.haskell.org/~aavogt/HList/docs/HList/>. -- Adam

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How do I lift Control.Monad.Reader.local?
by David Fox 01 Nov '13

01 Nov '13

I can write a stack push function in the reader monad like so: import Control.Monad.Reader push :: String -> Reader [String] a -> Reader [String] a push s action = local (s :) action How can I write a push that works inside a monad transformer? push' :: MonadTrans t => String -> t (Reader [String]) a -> t (Reader [String]) a push' s action = ???

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Internship opportunities at Galois
by Adam Foltzer 01 Nov '13

01 Nov '13

Hello, Galois has some exciting opportunities for interns in software engineering and research for 2014. Most of our projects use Haskell to some extent, so this is a great chance to get experience applying functional programming to real-world problems. Please pass along this posting to anyone you think might be interested, even if they don't yet know Haskell! Thank you, Adam Foltzer --- # Galois Software Engineering/Research Intern # Galois is currently seeking software engineering and research interns for 2014 at all educational levels. We are committed to matching interns with exciting and engaging engineering work that fits their particular interests, creating lasting value for interns, Galois, and our community. A Galois internship is a chance to tackle cutting-edge, meaningful problems in a uniquely collaborative environment with world-leading researchers. Roles may include technology research and development, requirements gathering, implementation, testing, formal verification, and infrastructure development. Past interns have integrated formal methods tools into larger projects, built comprehensive validation suites, synthesized high-performance cryptographic algorithms, written autopilots for quad-copters, designed the syntax and semantics of scripting languages, and researched type system extensions for academic publication. We deeply believe in providing comprehensive support and mentorship to all of our employees, particularly interns. We provide our employees with a steward who regularly checks in to ensure that they feel welcome and safe in the Galois community while gaining real value from their experiences. ## About Galois ## Our mission is to create trustworthiness in critical systems. We're in the business of taking blue-sky ideas and turning them into real-world technology solutions. We've been developing real-world systems for over ten years using functional programming, language design, and formal methods. Galois values diversity. We believe that differing viewpoints and experiences are essential to the process of innovation. We look broadly, including outside of established communities, to deliver innovation. ## How to Prepare ## An internship is an opportunity for learning and growth as an engineer. To make the most of the opportunity, we ask that candidates have experience reading, writing, and maintaining code in a realistic project. Many university courses involve multi-week collaborative projects that provide this type of experience. Most of our projects use the Haskell programming language and the git version control system. These tools aren't often taught in computer science classes, but there are many free resources available that we recommend for learning: - [Learn You a Haskell for Great Good!] [1] by Miran Lipovača - [Real World Haskell] [2] by Bryan O'Sullivan, Don Stewart, and John Goerzen - [tryGit] [3] by Code School - [Pro Git] [4] by Scott Chacon [1]: http://learnyouahaskell.com/ [2]: http://book.realworldhaskell.org/ [3]: http://try.github.io [4]: http://git-scm.com/book ## Qualifications ## - The ability to be geographically located in Portland during the internship - Experience reading, writing, and maintaining code in a project as described above - Proficiency in software development practices such as design, documentation, testing, and the use of version control - Well-developed verbal and written communication skills; comfort in a collaborative team environment The following skills are not required, but may be relevant to a particular project. - Proficiency in Haskell or other programming languages with rich type systems (eg., OCaml, Standard ML, Scala) - Experience using C and assembly languages for low-level systems programming - Development experience in high assurance systems or security software - Specific experience in an area of Galois' expertise, such as: - Assured information sharing - Software modelling and formal verification - Cyber-physical systems and control systems - Operating systems, virtualization and secure platforms - Networking and mobile technology - Cyber defense systems - Scientific computing - Program analysis and software evaluation - Web security ## Logistics ## The length and start date of the internship are negotiable: starting any time from the new year through next fall is acceptable, but an intern must be at Galois for at least three continuous months. The internship is paid competitively, and interns are responsible for living arrangements (although we can certainly help you find arrangements). Galois is located in the heart of downtown Portland with multiple public transportation options available and world-class bicycle infrastructure. ## Application Details ## Send an email to careers(a)galois.com with the subject line "Internship 2014" with the following contents: - Email body: a brief plain-text note explaining your interests, experience, and other relevant details - Attachment: CV/Resume (PDF, plain text, or markdown only) **Applications must be received at least two months before the desired start date**. For example, we must receive your application by November 6, 2013, if you wish to start on January 6, 2014.

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Accessing own haddock files
by Corentin Dupont 01 Nov '13

01 Nov '13

Hi the list, I have an application that need to access its own haddock documentation (to display on a web site). What is the best way to do that? Unfortunatly Cabal doesn't seem to provide that. Cabal generates a file "<package name>_Path.hs" containing: *bindir = "/home/kau/.cabal/bin" libdir = "/home/kau/.cabal/lib/Nomyx-Language-0.4.0/ghc-7.6.3" datadir = "/home/kau/.cabal/share/Nomyx-Language-0.4.0"* But there is no: *docdir = "/home/kau/.cabal/share/doc/Nomyx-Language-0.4.0"* That would be handy in my situation :) Best, Corentin

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Cabal sandboxes over cabal-dev
by Graham Berks 01 Nov '13

01 Nov '13

Can someone point me in the direction of why you would use one over the other ?? Thanks Graham

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SYB: queries using IO Monad
by JP Moresmau 01 Nov '13

01 Nov '13

Hello cafe, I have code that works well using the syb package, and the ext1Q, extQ and gmapQ functions. This code that a Data and transforms it into something else. However I need to make a change, and this change involves calling a function in the IO monad (the function is from another library so I have no choice). However, the ext1Q, extQ and gmapQ functions have no monadic equivalent. There seems to be monadic transformation (from a to different a) but no monadic queries (from a to b). Do I have to rewrite these functions myself to work with monadic queries (it at all possible) or is there a better way? I've seen some functions that work with monads and MonadPlus, but I don't see anything that would work with IO. So far I've checked that the IO() function I'm calling does the job by using unsafePerformIO, but I know that's a sin and I'd like to find a better way! Thanks! JP -- JP Moresmau http://jpmoresmau.blogspot.com/

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cabal-install sandbox with happy and alex
by Badi' Abdul-Wahid 01 Nov '13

01 Nov '13

Hi I've run into difficulty building happy and alex using the sandbox feature of cabal-install 1.18.0.2. Installation of dependencies succeeds but both happy and alex fail with: setup: The program happy is required but it could not be found My workaround is to use the --only-dependencies flag, install the dependencies, and manually install the packages. This is on Mac OS X 10.8.4 with GHC 7.6.3. I've copied the steps demonstrating the problem on lpaste: http://lpaste.net/95027 Summary to reproduce: cabal sandbox init; cabal install happy alex Below is the script for my workaround. [0 :)] badi@olorin /tmp/sb ~> cat sandbox-install.sh #!/usr/bin/env bash packages="$@" cabal sandbox init cabal install --only-dependencies $packages for p in $packages; do cabal unpack $p pushd $p-* cabal sandbox --sandbox ../.cabal-sandbox init cabal configure cabal build runhaskell Setup.lhs install popd done -- Badi' Abdul-Wahid

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