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ANN: hxt-css 0.1.0.0, a CSS selector engine for HXT
by Marios Titas 03 Oct '14

03 Oct '14

Hello everybody, I'd like to announce the first public release of hxt-css, a CSS selector engine for the Haskell XML Toolbox (HXT). Its main design goals are: * support as many CSS selectors as possible: it currently supports all CSS 3 selectors except the ones that do not make sense outside a web browser (e.g. such as :hover). For example, it supports weird things like div > span + p:not(:nth-of-type(3n-1)) * try to be 100% correct: in all tests I ran, the output of hxt-css was identical to that of firefox & chrome. * follow the conventions of other hxt packages: for example, error reporting is done the same way as hxt-xpath. Note, there is already a similar package in hackage called HandsomeSoup. - Marios

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u3502350@connect.hku.hk has indicated you're a friend. Accept?
by u3502350＠connect.hku.hk 03 Oct '14

03 Oct '14

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Need help with scrap-your-boilerplate
by Michael Sperber 02 Oct '14

02 Oct '14

I'm a casual Haskell user, and am trying to use scrap-your-boilerplate to write a transformation - and failing. The rub is that the base function is polymorphic, boiling down to this: data Foo a = Foo a bar :: Foo a -> Foo a bar x = x Now, I'm trying to use SYB like so: foo :: Typeable a => a -> a foo = mkT bar ... but I get: Could not deduce (Typeable a0) arising from a use of ‘mkT’ from the context (Typeable a) bound by the type signature for foo :: Typeable a => a -> a at foo.hs:... The type variable ‘a0’ is ambiguous Note: there are several potential instances: Is there any way I could make this work? Any help would be much appreciated! -- Regards, Mike

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Add linker flags to GHC 6.12.3 using extra-gcc-opts
by Shaun Jackman 02 Oct '14

02 Oct '14

Hi. I get the following error message when linking with GHC. ``` $ ghc -o hello-hs hello-hs.hs /projects/btl/linuxbrew/bin/ld: cannot find -lgmp collect2: ld returned 1 exit status ``` It's fixed by adding `-L/projects/btl/linuxbrew/lib` to the command line. ``` $ ghc -L/projects/btl/linuxbrew/lib -o hello-hs hello-hs.hs ``` I'd like to add the above `-L` option to the default linking arguments of GHC. I thought that I could do this by modifying the file `extra-gcc-opts`. I changed it from ` -fwrapv` to ` -fwrapv -L/projects/btl/linuxbrew/lib`, but it has no effect. I confirmed this by changing it to ` -fBROKEN`, and again no effect. The file location is `/projects/btl/linuxbrew/Cellar/ghc612/6.12.3/lib/ghc-6.12.3/extra-gcc-opts`. How do I change the default gcc link options of GHC 6.12.3? It would be difficult for me to upgrade to GHC 7.8.3 because the binary package does not run on CentOS 5.11. Yes, I know it's ancient. It's an HPC cluster, and I have no control over it. So, likewise, I'm not able to install `libgmp-devel` in `/usr`, which would also solve this issue. Thanks for your help. Cheers, Shaun http://sjackman.ca

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GHC 7.10 GHC-API Changes and proposed changes.
by Alan & Kim Zimmerman 02 Oct '14

02 Oct '14

There are a number of changes in GHC 7.10 that will make it easier for tool writers to use the GHC API. These include 1. More parser entrypoints, to explicitly parse fragments [Andrew Gibiansky] The following parsers are now provided parseModule, parseImport, parseStatement, parseDeclaration, parseExpression, parseTypeSignature, parseFullStmt, parseStmt, parseIdentifier, parseType, parseHeader 2. No more landmines in the AST [Alan Zimmerman] In the past it was difficult to work with the GHC AST as any generic traversals had to carefully tiptoe around an assortment of panic and undefined expressions. These have now been removed, allowing standard traversal libraries to be used. There is a third change currently being discussed, and I would like feedback on it's desirability. 3. Introduce an annotation structure to the ParsedSource to record the location of uncaptured keywords. At the moment the location of let / in / if / then / else / do etc is not captured in the AST. This makes it difficult to parse some source, transform the AST, and then output it again preserving the original layout. The current proposal, which can be seen at [1] and a proof of concept implementation at [2] returns a structure keyed to each AST element containing simply the specific SrcSpan's not already captured in the AST. This is the analogue of the Language.Haskell.Exts.Annotated.Syntax from haskell-src-exts, except a custom SrcSpanInfo structure is provided for each AST element constructor, and it is not embedded within the AST. [1] https://ghc.haskell.org/trac/ghc/wiki/GhcAstAnnotations [2] https://phabricator.haskell.org/D297 So, apart from HaRe, are there any other users who would be interested in using this? Regards Alan

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Haskell Weekly News: Issue 308
by Daniel Santa Cruz 02 Oct '14

02 Oct '14

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Reflection functional dependency as an associated type?
by Brandon Moore 01 Oct '14

01 Oct '14

I was trying to make a bridge like this class MonadStateTF m where type StateOf m :: *instance (MonadState s m) => MonadStateTF m where type StateOF m = s to allow writing constraints on state monads without a dangling type parameter type NumMonad m = (MonadStateTF m, Num (StateOf m)) Unfortunately, the declaration type StateOF m = s complains that "s" isn't mentioned on the left hand side rather than somehow making use of the fundep. Brandon

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Broken linkr in wiki for Ivo
by Evan Rowley 01 Oct '14

01 Oct '14

The theorem provers page has a link for Ivor at the bottom: http://www.haskell.org/haskellwiki/Libraries_and_tools/Theorem_provers This current link is dead: http://www.dcs.st-and.ac.uk/~eb/ivor.php This new link works: http://eb.host.cs.st-andrews.ac.uk/ivor.php -- -- - EJR

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A prototype concept for teaching type-class polymorphic functions
by Christopher Done 01 Oct '14

01 Oct '14

Hey there, For those teaching Haskell and making teaching tools, you might be interested in this mode of presentation of a function: http://chrisdone.com/fmap It's a little slow because the implementation is naive (it abuses my tryhaskell.org server), however the concept is: see what fmap really does by showing what you get when applying it to a variety of different types, including “strange” ones like Const and the function type. A given function has visually evident ways of applying to different data structures. The value changes and so does the type. Challenge: take this ball and run with it to illustrate return and >>= for a number of monads. Maybe, [], LogicT, Either, etc. Given that I've been using Haskell for 6 years and haven't yet written a monad tutorial, I don't want to break that clean sheet now. If that's too hard, there're plenty of simpler classes to experiment with. Some types require special handling to display in an intuitive way, like the ((->) r) example. But ignoring that, if you were sufficiently shrewd, you could automatically generate such an interactive page by taking a given typeclass, asking GHCi or the GHC API for all known instances of that type, which are Showable (or somehow representable) and then enumerating them in this kind of display. Others have suggested a "before and after" side-by-side look. So that's an option to consider. Technically you can get before/after with ‘id’ (a lesson in itself, the identity law!), but a two-column layout is an option. Ciao!

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Journal of Functional Programming - Call for PhD Abstracts
by Graham Hutton 01 Oct '14

01 Oct '14

============================================================ CALL FOR PHD ABSTRACTS Journal of Functional Programming Deadline: 31st October 2014 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. The first round of published abstracts can be downloaded from http://journals.cambridge.org/jfp/phd_abstracts. 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 31st October 2014. 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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