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Haskell in Vietnam?
by Tom Schrijvers 15 Jun '15

15 Jun '15

Dear all, I would like to get in touch with people learning, teaching or using Haskell in Vietnam. Can anyone on this list help me? Thanks, Tom -- prof. dr. ir. Tom Schrijvers Research Professor KU Leuven Department of Computer Science Celestijnenlaan 200A 3001 Leuven Belgium Phone: +32 16 327 830 http://people.cs.kuleuven.be/~tom.schrijvers/

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Recognizing projects schemes
by Ruben Astudillo 14 Jun '15

14 Jun '15

I recently came across the following blog-post: http://blog.cleancoder.com/uncle-bob/2015/04/15/DoesOrganizationMatter.html It speaks a bit of simplicity, efficiency and stuff that isn't important. What is important at least to me was the concept of project scheme, summarized on the following phrase: ``And so this gets to the crux of the question that you were really asking. You were asking whether the time required to learn the organization scheme of the system is worth the bother. Learning that organization scheme is hard. Becoming proficient at reading and changing the code within that scheme take time, effort, and practice. And that can feel like a waste when you compare it to how simple life was when you only had 100 lines of code.'' And that is something I totally struggle at approaching new projects. The only reason I could understand XMonad for example is because they gave a general overview (thanks) of it on the Developing module. I feel I got a problem of methodology. What approaches are you guys using to understanding new projects schemes on a efficient manner? How long it usually takes you?. Any advices? Thanks in advance. -- Ruben Astudillo. pgp: 0x3C332311 , usala en lo posible :-) Crear un haiku, en diecisiete silabas, es complica...

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ANN: TestExplode 0.1.0.0: testscript generator for all target languages
by Hans-Juergen Guth 13 Jun '15

13 Jun '15

My new Haskell program/library is released! What it does: ------------- Instead of writing one test-script after another, you define the structure of test-sets. Advantages: ----------- More test-scripts with less code, better overview, easier review of the testcases, easier change and addition of testcases. Details: -------- TestExplode generates testcases out of program snippets. The snippets are treated as text, with variables, that are subsituted (thanks the package perl6-interpolated-strings). The text-snippets are annotated and can form a directed acyclic graph. Each path and each variable substitution is a testcase. Subgraphs can be defined and used in many testcases. The graph can be printed with graphviz. The expected results of the testcase can partially defined by changing the state of the testcase by each testsnippet. So you can define a state-machine in haskell and the annotations to the text-snippets give the input to the state-machine, dependant of the test-input and which path through the graph is chosen. The program/library is designed with users in mind, who have little or no knowledge of haskell at the beginning. It's my first bigger haskell program, so it is probably relativ simple haskell code in the library and in the user interface. Examples can be found in the documentation. Further info: ------------- A "Getting Started": https://hackage.haskell.org/package/TestExplode-0.1.0.0/readme The Library which generates the testcases https://hackage.haskell.org/package/TestExplode-0.1.0.0/docs/TestExplode-Te… The Library which makes FGL-Graphs for the module grahpviz out of my own definition of directed acyclic graphs https://hackage.haskell.org/package/TestExplode-0.1.0.0/docs/TestExplode-Di… I would be happy about comments!

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To "instance C D", GHCI responds that C "is applied to too many type arguments".
by Jeffrey Brown 13 Jun '15

13 Jun '15

jeff@jeffLenovUbu:~$ ghci -XNullaryTypeClasses GHCi, version 7.8.4: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude> class C Prelude> data D = DConstructor Prelude> instance C D <interactive>:4:10: ‘C’ is applied to too many type arguments In the instance declaration for ‘C D’ Prelude>

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Lazy patterns
by Jon Schneider 13 Jun '15

13 Jun '15

Good day, I am trying to understand the lazy patterns as explained at https://www.haskell.org/tutorial/patterns.html If I type in the example without putting a ~ round the pattern sure enough I do not get an answer as the text says. What I completely fail to understand is why there is no CPU usage, increasing memory usage, stack overflow or other runtime error before I use ^C to stop it. What is going on under the hood ? Jon

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Replacing cpp?
by Mike Meyer 12 Jun '15

12 Jun '15

I know the subject of cpp not working well with Haskell comes up every so often, usually with the conclusion that we need a preprocessor that understands Haskell code. If someone is working on that, this should probably be ignored. Maybe gpp could be used instead of having to write one from scratch? it allows you to define the syntax it uses for macros - both user and "meta". Possibly it's flexible enough to do what's needed?

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Proposal: Shorter Import Syntax
by Anthony Cowley 12 Jun '15

12 Jun '15

Hi Everyone, I didn't think this would see any resistance as it doesn't break anything, but this is the internet, so, if you haven't already, take a look at this GHC feature request <https://ghc.haskell.org/trac/ghc/ticket/10478> The idea is that rather than writing, import Data.Map (Map) import qualified Data.Map as M you could instead write, import Data.Map (Map) as M The Map identifier would imported unqualified, while M would be introduced as an alias for the qualified import of Data.Map. Note that, currently, following a parenthesized group with the "as" keyword is a parse error. So allowing this syntax would not affect any currently working programs. I've mentioned this proposal before and gotten good response, so I finally wrote it up last night after people on IRC responded positively to it. As well as IRC and trac, I put the link up on Twitter to get it in front of a large audience, and here's what we have after a bit over 12 hours (not counting the handful of supporters in IRC): +20 -2 You can see the tweet at <https://twitter.com/a_cowley/status/605909841148702720> I'll try to summarize the two negative votes: 1) This isn't that big a burden, and we should instead focus on controlled export of class instances; and 2) We should instead focus on exporting name spaces, and that the ordering of parentheses and the "as" keyword is too close to the existing "import Foo as F(foo)" syntax. Since there are these negative votes, I think it best if as many people as possible at least see the proposal so the GHC developers can get a better sense for the overall response. Anthony

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GHC.Generics: how to derive a Generic instance for an existential type?
by Andreas Abel 12 Jun '15

12 Jun '15

I wonder whether GHC.Generics supports existential types yet... {-# LANGUAGE DeriveGeneric #-} {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE StandaloneDeriving #-} import GHC.Generics data U = forall a. (Generic a) => U a -- deriving (Generic) -- Can't make a derived instance of ‘Generic U’: -- Constructor ‘U’ has existentials or constraints in its type -- Possible fix: use a standalone deriving declaration instead -- deriving instance Generic U -- Can't make a derived instance of ‘Generic U’: -- U must be a vanilla data constructor -- In the stand-alone deriving instance for ‘Generic U’ data D1Ser data C1_0Ser instance Generic U where type Rep U = D D1Ser (C1 C1_0Ser (S1 NoSelector (Rep a))) -- Not in scope: type variable ‘a’ -- How to bring the existential type `a' into scope? -- Andreas Abel <>< Du bist der geliebte Mensch. Department of Computer Science and Engineering Chalmers and Gothenburg University, Sweden andreas.abel(a)gu.se http://www2.tcs.ifi.lmu.de/~abel/

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Lecturer position in Programming Languages / Security at Kent
by Simon Thompson 12 Jun '15

12 Jun '15

We’re looking for excellent PL/security people to recruit as faculty to join us in the School of Computing at Kent. Do apply if you’re interested, or mail me if you want to find out more. Simon Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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TH to generate imports?
by Corentin Dupont 11 Jun '15

11 Jun '15

Hi guys, I wanted to know if it's possible to use TH on an "import" statement. What I want to do is to generate the names of the packages I need to import. For example: import $(genImport "MyPackage") genImport :: String -> Q TH.Exp genImport s = ... Is that possible? Thanks! Corentin

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