- Haskell-Cafe - Haskell.org

How to Hijack stdin,err,out, thread safely?
by Hiromi ISHII 30 Jun '15

30 Jun '15

Hi, I'm currently writing a web app to check the spec of input code usging QuickCheck. quickCheck* functions writes results to stderr & stdout, but I don't want them written to the app's original stdout/err. (I'm using SafeHaskell features to avoid malicious code executed, so don't worry about that :-)) So I want to execute I/O action hijacking stdout/err in a thread-safe manner. For example, I need function like below: censorHandles :: IO a -> IO (a, String, String) censorHandles = ... or withStd :: Handle -> Handle -> Handle -> IO a -> IO a withStd = ... -- Hiromi ISHII konn.jinro(a)gmail.com

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Munich Haskell Meeting, 2015-06-30 @ 19:30
by Christian Neukirchen 29 Jun '15

29 Jun '15

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Monday, June 30 at Cafe Puck at 19h30. For details see here: http://www.haskell-munich.de/dates If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-jun-2015/ **Please note that I cannot make it tomorrow, but I'll reserve the table for you.** Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

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Dealing with invertible functions
by Clinton Mead 29 Jun '15

29 Jun '15

I was trying to think of a way to deal with invertible functions, say if I want to set up a one-to-one mapping from A<->B without having to maintain two sets of functions (and worry about them getting out of sync). So I thought about making an "invertible" function. This is a function that knows it's own inverse, and you can compose them and get the inverses for free. Of course you need to set up the base functions manually, but then after that the composed functions don't have to be maintained separately both ways. Below I'm going to include some code, and I have a few questions: 1) Am I (badly) reinventing the wheel. 2) Is there otherwise something terrible with this approach. 3) I ended up wanting a function with signature "f a b -> a -> b". This feels strangly like applicative but not exactly. Am I reinventing the wheel here also or should I be doing this differently? Any advise appreciated, the ideone link is here: https://ideone.com/HlUHUd But I've also copied the code below: --- import Prelude hiding ((.)) import Control.Category ((.), (<<<), (>>>), Category) data InvertibleFunction a b = InvertibleFunction (a -> b) (b -> a) instance Category InvertibleFunction where (InvertibleFunction b_c c_b) . (InvertibleFunction a_b b_a) = InvertibleFunction (b_c . a_b) (b_a . c_b) inv (InvertibleFunction x y) = InvertibleFunction y x add :: (Num n) => n -> InvertibleFunction n n add x = InvertibleFunction (+x) (\y -> y - x) class KindaApplicative f where (<$>) :: f a b -> a -> b instance KindaApplicative InvertibleFunction where (InvertibleFunction f _) <$> x = f x main = print $ ((inv (add 2)) <$> 5)

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Promoting associated data types
by Kosyrev Serge 29 Jun '15

29 Jun '15

Good day! DataKinds doesn't allow promotion of type/data families. However, in the specific case of associated data families -- aren't they constrained more, and sufficiently so that the following, for example, could be made to work without stepping into dangerous territories: -- {-# LANGUAGE DataKinds #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE UnicodeSyntax #-} module M where class C a where data D a ∷ * data I instance C I where data D I class C1 a (b ∷ D I) where -- ..or, maybe, perhaps even the following: class C1 a (b ∷ D) where -- respectfully, Косырев Серёга

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Re: [Haskell-cafe] Tokenizing Haskell for future A.I.
by Stefan Reich 27 Jun '15

27 Jun '15

Oops. Subject should have read "Tokenizing" of course. :-) On 6/27/15, Stefan Reich <stefan.reich.maker.of.eye(a)googlemail.com> wrote: > Hi folks! > > I've been an avid Haskell user for a couple years. > > I am now making an A.I. system that will help programming in general. > It's based on a Java variation called JavaX (javax.tinybrain.de). > > However, any language can be processed. The most important step is > tokenization which is actually the bulk effort of the parsing process. > > Thus. Anyone in the mood for contributing a Haskell tokenizer? > > Instructions here: > http://tinybrain.blog.de/2015/06/27/a-standard-system-for-tokenization-2060… > > The benefit? One day, your Haskell coding (/refactoring) can be done > by A.I. (Or a part of it...) > > Cheers, > Stefan >

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Tokeninng Haskell for future A.I.
by Stefan Reich 27 Jun '15

27 Jun '15

Hi folks! I've been an avid Haskell user for a couple years. I am now making an A.I. system that will help programming in general. It's based on a Java variation called JavaX (javax.tinybrain.de). However, any language can be processed. The most important step is tokenization which is actually the bulk effort of the parsing process. Thus. Anyone in the mood for contributing a Haskell tokenizer? Instructions here: http://tinybrain.blog.de/2015/06/27/a-standard-system-for-tokenization-2060… The benefit? One day, your Haskell coding (/refactoring) can be done by A.I. (Or a part of it...) Cheers, Stefan

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Higher Kinded Void
by Anupam Jain 27 Jun '15

27 Jun '15

Hi all, I currently have some code for which I require a uninhabitable Functor. I currently just use - data VoidF a instance Functor VoidF where fmap = undefined Is there a reason something like this is not in the package void? Perhaps we could even have Void1 with kind * -> *, Void2 with kind * -> * -> * etc. I opened a github issue a few days ago but haven't received a response from ekmett yet - https://github.com/ekmett/void/issues/9 -- Anupam

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Generalizing a library
by Geraldus 26 Jun '15

26 Jun '15

Hi Cafe! I've written very first version of GHCJS port <https://github.com/geraldus/ghcjs-perch> of Perch <https://github.com/agocorona/haste-perch> library originally designed to work with Haste compiler. Most of work is already done, though some polishing is needed. In essence Haste and GHCJS versions are very similar, the major difference is how foreign functions are defined, and in fact Perch is built using just a few low-level primitives <https://github.com/geraldus/ghcjs-perch/blob/master/src/Internal/FFI.hs>. So, as these libraries are very similar I want to generalize Perch to make it independent of compiler somehow. My initial idea was to have a Perch library and several compiler specific back-ends which user should select depending on his toolchain, but my Haskell skills are still very poor to find a proper way to do this. Can someone point me in right direction or at least give some advices? Very appreciate any help!

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ANN: stack-0.1.1.0
by Emanuel Borsboom 26 Jun '15

26 Jun '15

New release of stack, a build tool. Changes: https://github.com/commercialhaskell/stack/releases/tag/v0.1.1.0 General information and download links: https://github.com/commercialhaskell/stack#readme This version includes a 'stack upgrade' command, which will make to much easier to upgrade to the NEXT version (but unfortunately you'll have to get this version the old way).

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Fwd: taking over urlencoded
by Francesco Gazzetta 25 Jun '15

25 Jun '15

The package urlencoded <https://hackage.haskell.org/package/urlencoded> wasn't updated since 2012 and needs a minor modification in the .cabal file. The author was contacted half an year ago, but he didn't respond, so -according to the instructions <https://wiki.haskell.org/Taking_over_a_package> on hackage- I state my intention to take over. Or, more simply, can an hackage admin just edit the cabal file?

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Re: [Haskell-cafe] Haskell users on Chile
by Ruben Astudillo 25 Jun '15

25 Jun '15

On 24/06/15 16:18, Anupam Jain wrote: > Sure I can do that. It would help if the group was already created though. > Do you want any help setting up a mailing list or something? I set-up a mailing list on google groups here: https://groups.google.com/forum/#!forum/haskellchile If you got problems or want to also be a maintainer send me a mail. Also I should set up a channel on freenode, but that one ought to be easy. #haskell-chile should do. For the time being we should reefer to people interested to the mailing list. -- Ruben Astudillo. pgp: 0x3C332311 , usala en lo posible :-) Crear un haiku, en diecisiete silabas, es complica...

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Haskell support in Apache Spark (I am preparing)
by Vasili I. Galchin 25 Jun '15

25 Jun '15

I am researching how to do. Hence, now is the time for everybody speak(!!) so I don't get blindsided, e.g. "I already did that" or "I am already working on that". Bad mojo. Vasili

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pqueue - repository and maintainer (taking over)
by lennart spitzner 24 Jun '15

24 Jun '15

Greetings, Regarding the pqueue package: 1) Does anyone have any (additional) contact details for the current maintainer/author, Louis Wasserman? 2) Is the package's repository available anywhere? The darcs link listed in the package 404s. 3) I would be willing to take over for basic maintenance if the current maintainer is unavailable. The pqueue package does not compile with ghc-7.10. Fixing requires just some quick changes (i have a working version locally). The last upload for the package is from 2012, but the author's github account lowasser shows some more recent activity. Yet I have not received a reply to my e-mail from six weeks ago. Lennart

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Reinventing the wheel with HList.
by Nicholls, Mark 24 Jun '15

24 Jun '15

My latest confusion.... I've got a typeclass (with associated types) monoid sort of thing.... I can get a Singleton family of Nat to be an instance of the typeclass. Lists are sort of Natural numbers...with a bit of extra functionality... So I should be able to take HList and make that a member of the same typeclass... I fail for 2 reasons...1...I have to wrestle with the kinds...in a way I find ununderstandbly irritating. And 2...because BOOM. "is a rigid type variable bound by" blab la. My Haskell in many ways is primitive...I seem to be messing with things beyond my ability....but that's the way to learn I suppose. > {-# LANGUAGE DataKinds #-} > {-# LANGUAGE ExplicitForAll #-} > {-# LANGUAGE FlexibleContexts #-} > {-# LANGUAGE FlexibleInstances #-} > {-# LANGUAGE GADTs #-} > {-# LANGUAGE MultiParamTypeClasses #-} > {-# LANGUAGE PolyKinds #-} > {-# LANGUAGE StandaloneDeriving #-} > {-# LANGUAGE TypeFamilies #-} > {-# LANGUAGE TypeOperators #-} > {-# LANGUAGE UndecidableInstances #-} > {-# LANGUAGE ScopedTypeVariables #-} > import Control.Effect > import Control.Effect.Helpers.List > import Control.Effect.WriteOnceWriter > import Prelude hiding ((>>=),(>>),return,fmap,fail) > --import GHC.TypeLits > import Data.Type.Equality > import Data.Type.Bool > --import Data.HList.HList > data Nat where > Z :: Nat > S :: Nat -> Nat > data family Sing (a :: k) > data SNat (a :: Nat) where > SZ :: SNat 'Z > SS :: SNat a -> SNat ('S a) > type family (n :: Nat) :+ (m :: Nat) :: Nat > type instance 'Z :+ m = m > type instance ('S n) :+ m = 'S (n :+ m) Define something like a monoid over the types... (note I have to wrestle with the kind signatures to get the instance of SNat to work, which is fine...but now closes doors to other instances) > class TMonoid (m :: k -> *) where > type O m :: k > zero :: m (O m) > type TPlus m (d :: k) (e :: k) :: k > add :: m a -> m b -> m (TPlus m a b) And this works quite nicely > instance TMonoid SNat where > type O SNat = 'Z > zero = SZ > type TPlus SNat a b = a :+ b > add SZ b = b > add (SS a) b = SS (add a b) Now.... (I have to declare different kind?....I can't get a single simple declaration of TMonoid?) > class TMonoid' (m :: [*] -> *) where > type O' m :: [*] > zero' :: m (O' m) > type TPlus' m (d :: [*]) (e :: [*]) :: [*] > add' :: m a -> m b -> m (TPlus' m a b) Steal the definition of HList > data family HList (l::[*]) :: * > data instance HList '[] = HNil > data instance HList (x ': xs) = x `HCons` HList xs And try to construct an analogous TMonoid of it... > instance TMonoid' HList where > type O' HList = '[] > zero' = HNil > type TPlus' HList a b = a :++ b > add' HNil b = b > add' (HCons x xs) ys = HCons x (add' xs ys) BOOM Couldn't match type 'a' with ''[]' 'a' is a rigid type variable bound by the type signature for add' :: HList a -> HList b -> HList (TPlus' HList a b) at broadcast2.lhs:90:5 Expected type: HList a Actual type: HList '[] Relevant bindings include add' :: HList a -> HList b -> HList (TPlus' HList a b) (bound at broadcast2.lhs:90:5) In the pattern: HNil In an equation for 'add'': add' HNil b = b In the instance declaration for 'TMonoid' HList' Hmmm....confused...why does add SZ b = b work, but the analogous add' HNil b = b fail CONFIDENTIALITY NOTICE This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited. While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data. Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us. MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

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ANNOUNCE: stack 0.1.0.0
by Emanuel Borsboom 23 Jun '15

23 Jun '15

Announcing stack, a new build tool, first stable release. More information at: https://www.fpcomplete.com/blog/2015/06/stack-0-1-release

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RebindableSyntax on individual do blocks
by Mark Roberts 22 Jun '15

22 Jun '15

I have a program that uses both monads and indexed monads, and I'd like to use do-notation for each in the same source file. Is there a way to rebind syntax for only the do blocks that make use of an indexed monad? Thanks, Mark

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Turning Monoids into Categories
by David Feuer 22 Jun '15

22 Jun '15

Is there a newtype defined in some normal sort of place for turning Monoids into Categories? I'm looking for something like this: newtype ConstConst m a b = ConstConst m instance Monoid m => Category (ConstConst m) where id = ConstConst mempty ConstConst x . ConstConst y = ConstConst (x <> y) Thanks, David Feuer

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Mild confusion around type family
by Nicholls, Mark 22 Jun '15

22 Jun '15

Below is a very simple almost canonical natural number model. I'm slightly confused by how type families work Wikipedia says.... "Type families are a feature of some type systems<https://en.wikipedia.org/wiki/Type_system> that allow PARTIAL functions between types to be defined by pattern matching<https://en.wikipedia.org/wiki/Pattern_matching>" So... > {-# LANGUAGE DataKinds #-} > {-# LANGUAGE ExplicitForAll #-} > {-# LANGUAGE FlexibleContexts #-} > {-# LANGUAGE FlexibleInstances #-} > {-# LANGUAGE GADTs #-} > {-# LANGUAGE MultiParamTypeClasses #-} > {-# LANGUAGE PolyKinds #-} > {-# LANGUAGE StandaloneDeriving #-} > {-# LANGUAGE TypeFamilies #-} > {-# LANGUAGE TypeOperators #-} > {-# LANGUAGE UndecidableInstances #-} > {-# LANGUAGE ScopedTypeVariables #-} lets do something simple > data Z > data S n > type family Sub a b > -- a - 0 == a > type instance Sub a Z = a > -- (a + 1) - (b + 1) == a - b > type instance Sub (S a) (S b) = Sub a b > oneMinusOne :: Z > oneMinusOne = undefined :: Sub (S Z) (S Z) I want this to be a type error!...but the above type family appears to not be partial...this IS defined...."Sub Z (S Z)" is a type! (I thought it wasn't) > oneMinusTwo :: Sub Z (S Z) > oneMinusTwo = undefined :: Sub (S Z) (S (S Z)) CONFIDENTIALITY NOTICE This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited. While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data. Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us. MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

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ANNOUNCE: fgl-arbitrary
by Ivan Lazar Miljenovic 22 Jun '15

22 Jun '15

I've just released the first version of fgl-arbitrary [1], which provides Arbitrary instances for fgl graphs for use with QuickCheck. Also provided are some wrapper newtypes to produce specific types of graphs, and also the ability to generate just valid node and edge lists for use with other graph-like data structures. [1]: http://hackage.haskell.org/package/fgl-arbitrary -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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"SameConstraints?" type constraints
by Leza Morais Lutonda 22 Jun '15

22 Jun '15

Hi All, I have the following data type: data S e where SC :: d -> e -> S e And I want to declare a Show instance for it in the following way: instance Show e => Show (S e) where show (SC x y) = show x ++ show y But, of course it don't typechecks because: could not deduce `Show d` arising from a use of `show`. Is there a way to constraint the `d` type in the `SC` constructor definition to have the same constraints of the `e` type? Something like: SC :: SameConstraints d e => d -> e -> S e ??? Thanks! -- Leza Morais Lutonda, Lemol-C http://lemol.github.io 50 Aniversario de la Cujae. Inaugurada por Fidel el 2 de diciembre de 1964 http://cujae.edu.cu

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stack mailing list
by Michael Snoyman 22 Jun '15

22 Jun '15

We recently started a mailing list for discussions of stack[1], a new Haskell build tool (see initial release announcement[2]). This list is open for questions, requests, discussions, and internal development (though if that last becomes too chatty, we can always move it to a separate list). You can sign up for the mailing list at: https://groups.google.com/d/forum/haskell-stack [1] https://github.com/commercialhaskell/stack#readme [2] https://www.fpcomplete.com/blog/2015/06/announcing-first-public-beta-stack

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Do people use visitor pattern in Haskell...
by Nicholls, Mark 22 Jun '15

22 Jun '15

My initial guess would be no...its built into the language But.... I find myself tempted to use it (in order to match on a type that's the instance of a typeclass)...which makes me think I've missed something. So... > data Foo = Foo > data Bar = Bar Ooo...this looks like an OO design pattern...surely wrong? > class Wibble a where > visit :: (Foo -> b) -> (Bar -> b) -> a -> b > instance Wibble Foo where > visit f _ x = f x > instance Wibble Bar where > visit _ f x = f x I want a list of Wibbles.... hmmm... (Wibble a) => [a] is clearly wrong... I want [(Wibble a) =>a] so I package it up? > data WibblePackage where > WibblePackage :: (Wibble a) => a -> WibblePackage lets try this now...so pointless function across Wibbles in a list. > fizzBuzz :: [WibblePackage] -> Integer > fizzBuzz [] = 0 > fizzBuzz ((WibblePackage x) : xs) = (visit (\_ -> 1) (\_ -> 2) x) + (fizzBuzz xs) > help :: Integer > help = fizzBuzz [WibblePackage Foo,WibblePackage Bar] That works! OO nerds will get uptight about "closing" the Wibble typeclass....but I've managed to create a list of different types and have a mechanism for recovering the type. How would a Haskell nerd do this? (I have looked, but they look more complicated....maybe to my OO eye). CONFIDENTIALITY NOTICE This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited. While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data. Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us. MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

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"Universal" constraints?
by Michael Walker 21 Jun '15

21 Jun '15

Hi all, I was wondering about constraints in class declarations. Suppose we have something like this: class Monad m => Store m where type Var m :: * -> * new :: a -> m (Var m a) read :: Var m a -> m a write :: Var m a -> a -> m () Then some reasonable implementations would be IO and ST, using IORefs and STRefs, instance Store IO where type Var IO = IORef new = newIORef read = readIORef write = writeIORef instance Store (ST s) where type Var (ST s) = STRef s new = newSTRef read = readSTRef write = writeSTRef Now, both IORefs and STRefs have equality, which doesn't require equality of the contained type, instance Eq (IORef a) where ... instance Eq (STRef s a) where ... This corresponds to pointer equality and, because reading the values is a monadic action, is as good an Eq instance as we can get. Given this, it would be nice to be able to specify that all instances of our Store class have this property. Something like, class (Monad m, Eq (Var m a)) => Store m where ... But we can't write this! The `a` isn't in scope! What I really want to do is to be able to write class constraints like this, class (forall a. C (T a)) => D x where ... Or why not get really crazy: class (forall a. C a => D (T a)) => E x where ... Is there some extension or combination of extensions that would make this work without completely sacrificing type safety? FlexibleContexts allows it (the simpler form, at least) for function constraints, but not for class constraints. If not, has anyone thought about this sort of thing before? -- Michael Walker (http://www.barrucadu.co.uk)

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Troubles with HStringTemplate (compilation/runtime errors)
by Ilya Seleznev 21 Jun '15

21 Jun '15

Hello Haskellers, I hope I chose proper mailing list, if not I apologize. And thanks for reading this! I run into a problem with HStringTemplate ( http://hackage.haskell.org/package/HStringTemplate) that I have never seen before. Code, similar to {-# LANGUAGE OverloadedStrings, DeriveDataTypeable, NoImplicitPrelude #-} module Main where import Data.Data import qualified Data.Text as T import qualified Text.StringTemplate as Template renderTextTemplate :: (Template.ToSElem a) => T.Text -> a -> IO T.Text renderTextTemplate name input = do templatesGroup <- Template.directoryGroup "templates" case Template.getStringTemplate (T.unpack name) templatesGroup of Nothing -> return $ "Internal Error: template '" `mappend` name `mappend` "' can not be rendered" Just template -> return $ Template.render (Template.setAttribute "it" input (template:: Template.StringTemplate T.Text)) data Foo = Foo {value:: T.Text} deriving (Data, Typeable) main :: IO () main = do content <- renderTextTemplate "test" $ Foo {value = "oh hi there!"} putStrLn content with a simple template like this: Just a test $it.value$! started to cause complaints from GHC (7.8.2 and 7.8.4 on Linux x86_64): No instance for (Template.ToSElem Foo) Problem is - it didn't do that before. What even more confusing, older project[0] uses same approach, compiles (same machine, same compiler) and works just fine! I've exhausted all means to fix the problem that I could think off: - Adding 'instance Template.ToSElem Foo' allows code to compile but it doesn't work and prints message in console like this: Main.hs:30:10-29: No instance nor default method for class operation Text.StringTemplate.Classes.toSElem - Tried to use same version of HStringTemplate deps (syb was different) - All kinds of desperate messing around (exporting records from modules, changing field names...) - Updated ghc from 7.8.2 to 7.8.4 - Googled error messages to no avail. I hope almighty All would give me some ideas/directions because I have none left. [0] Function: https://github.com/itsuart/fdc_archivist/blob/master/src/HttpUtils.hs#L59 Data: https://github.com/itsuart/fdc_archivist/blob/master/src/ViewModels/HomeVie… Usage: https://github.com/itsuart/fdc_archivist/blob/master/src/HomeViewFeature.hs… -- With best regards, Ilya Seleznev

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shakespeare >= 2.0.2 fails to install in OS X 10.6.8, Haskell-platform 2014.2.0.0; cabal-install 1.22.4.0
by Miguel A. Santos 20 Jun '15

20 Jun '15

(I already sent a comment on the Shakespeare site but couldn't get too far. So, if this isn't the right place for this issue, I'd appreciate you point me to the right one.) Hi, I can't install yesod. Doing a cabal install yesod-bin or cabal install yesod fails because it fails to build shakespeare. I tried with all versions of shapeare >= 2.0, as required by yesod-bin. Below are all outputs. My environment: OS X 10.6.8, Xcode 3.2 Haskell-platform 2014.2.0.0 ghc-7.8.3 cabal-install 1.22.4.0 using version 1.22.3.0 of the Cabal library. This corresponds to a fresh install of the HP, ghc, and cabal I didn't before trying to install yesod. The developer of Shakespeare suspects that be a bug of HP and suggested I try a clean install of GHC as explained in http://www.stackage.org/install#mac-os-x However, the bindist available there doesn't work with my OS 10.6.8 I have a large screen output from those trials that you can check on the Shakespeare github page corresponding to the thread I started there https://github.com/yesodweb/shakespeare/issues/156 If you prefer, I can paste it here as well. Thanks in advance. MA -- Public key ID: E8FE60D7 Public key server: see, e.g., hkp://keys.gnupg.net

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Re: [Haskell-cafe] [Haskell-beginners] Haskell -> JavaScript -> nodejs
by Sumit Sahrawat, Maths & Computing, IIT (BHU) 20 Jun '15

20 Jun '15

Better try on the cafe. cc-ing. On 20 June 2015 at 15:26, Martin Vlk <martin(a)vlkk.cz> wrote: > I made some progress - in order for Haskell modules to work with ghcjs > you need to use cabal with the --ghcjs flag to install them. > > Martin > > Martin Vlk: > > Hi, > > I can successfully compile a basic Hello World into JavaScript with > > ghcjs and run it with nodejs. > > But what I ultimately need to do is write a nodejs module in Haskell and > > compile down to JavaScript with ghcjs. I need to be able to require > > other nodejs modules as well. > > > > Could somebody point me in the right direction? E.g. what approach and > > libraries to use... > > > > I have tried a simple thing with jsaddle/lens, but when I try to compile > > with ghcjs it is not finding the imported modules, even though when > > compiling with ghc it does find them (they are installed using cabal). > > > > Many Thanks > > Martin > > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners > -- Regards Sumit Sahrawat

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Haskell and Spark(Hadoop)
by Vasili I. Galchin 20 Jun '15

20 Jun '15

> Hello, > > There was a posting from a Polish guy(Wojcieh .,,,, been trying to > contact him) on implementing a library/wrapper for Spark. Does anybody know > the status? > > Vasili >

1 0

Question about terminateProcess
by Niklas Hambüchen 20 Jun '15

20 Jun '15

Hi, http://hackage.haskell.org/package/process-1.2.0.0/docs/System-Process.html… says: " Note: on Windows, if the process was a shell command created by createProcess with shell, or created by runCommand or runInteractiveCommand, then terminateProcess will only terminate the shell, not the command itself. On Unix systems, both processes are in a process group and will be terminated together. " I don't see that happening, at least not in ghci. When I do import System.Process (_,_,_,p) <- createProcess $ (shell "sleep 10") -- wait a second or so terminateProcess p in ghci, then in `ps aux | grep "sleep 10"`, the sleep is still running; same when I'm using `(shell "sleep 10"){ create_group = True }` (`shell` defaults to `create_group = False`). What am I missing?

2 2

[ANN] wai-middleware-metrics package
by Sebastian 20 Jun '15

20 Jun '15

Hello everyone, I'm announcing the release of the wai-middleware-metrics package. http://hackage.haskell.org/package/wai-middleware-metrics https://github.com/Helkafen/wai-middleware-metrics Full example here with scotty: https://hackage.haskell.org/package/wai-middleware-metrics-0.2.1/docs/Netwo… It registers some ekg metrics in WAI web servers (scotty, servant, yesod...) using a middleware. Right now the metrics are: - wai.request_count - wai.server_error_count - wai.latency_distribution Time distributions will benefit from future developments <http://blog.johantibell.com/2014/05/ekg-04-released.html> in ekg and become more descriptive. Other metrics could be added. Ideas, contributions and comments are welcome! Cheers -- Sebastian de Bellefon

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OCL 2015: Second Call for Papers - Only Four Weeks Left
by Achim D. Brucker 19 Jun '15

19 Jun '15

(Apologies for duplicates) CALL FOR PAPERS 15th International Workshop on OCL and Textual Modeling Tools and Textual Model Transformations Co-located with ACM/IEEE 18th International Conference on Model Driven Engineering Languages and Systems (MODELS 2015) September 28th, 2015, Ottawa, Canada http://ocl2015.lri.fr Modeling started out with UML and its precursors as a graphical notation. Such visual representations enable direct intuitive capturing of reality, but some of their features are difficult to formalize and lack the level of precision required to create complete and unambiguous specifications. Limitations of the graphical notations encouraged the development of text-based modeling languages that either integrate with or replace graphical notations for modeling. Typical examples of such languages are OCL, textual MOF, Epsilon, and Alloy. Textual modeling languages have their roots in formal language paradigms like logic, programming and databases. The goal of this workshop is to create a forum where researchers and practitioners interested in building models using OCL or other kinds of textual languages can directly interact, report advances, share results, identify tools for language development, and discuss appropriate standards. In particular, the workshop will encourage discussions for achieving synergy from different modeling language concepts and modeling language use. The close interaction will enable researchers and practitioners to identify common interests and options for potential cooperation. Topics of interest include (but are not limited to) =================================================== - Mappings between textual modeling languages and other languages/formalisms - Algorithms, evaluation strategies and optimizations in the context of textual modeling languages for -- validation, verification, and testing, -- model transformation and code generation, -- meta-modeling and DSLs, and -- query and constraint specifications - Alternative graphical/textual notations for textual modeling languages - Evolution, transformation and simplification of textual modeling expressions - Libraries, templates and patterns for textual modeling languages - Tools that support textual modeling languages (e.g., verification of OCL formulae, runtime monitoring of invariants) - Complexity results for textual modeling languages - Quality models and benchmarks for comparing and evaluating textual modeling tools and algorithms - Successful applications of textual modeling languages - Case studies on industrial applications of textual modeling languages - Experience reports -- usage of textual modeling languages and tools in complex domains, -- usability of textual modeling languages and tools for end-users - Empirical studies about the benefits and drawbacks of textual modeling languages - Innovative textual modeling tools - Comparison, evaluation and integration of modeling languages - Correlation between modeling languages and modeling tasks This year, we particularly encourage submissions describing tools that support - in a very broad sense - textual modeling languages (if you have implemented OCL.js to run OCL in a web browser, this is the right workshop to present your work) as well as textual model transformations. Venue ===== The workshop will be organized as a part of MODELS 2015 Conference in Ottawa, Canada. It continues the series of OCL workshops held at UML/MODELS conferences: York (2000), Toronto (2001), San Francisco (2003), Lisbon (2004), Montego Bay (2005), Genova (2006), Nashville (2007), Toulouse (2008), Denver (2009), Oslo (2010), Zurich (2011, at the TOOLs conference), 2012 in Innsbruck, 2013 in Miami, and 2014 in Valencia, Spain. Similar to its predecessors, the workshop addresses both people from academia and industry. The aim is to provide a forum for addressing integration of OCL and other textual modeling languages, as well as tools for textual modeling, and for disseminating good practice and discussing the new requirements for textual modeling. Workshop Format =============== The workshop will include short (about 15 min) presentations, parallel sessions of working groups, and sum-up discussions. Submissions =========== Three types of papers will be considered: * short papers (between 6 and 8 pages) describing ideas, * tool papers (between 6 and 8 pages), and * full papers (between 12 and 16 pages) in LNCS format. Submissions should be uploaded to EasyChair (https://easychair.org/conferences/?conf=ocl20150) The program committee will review the submissions (minimum 2 reviews per paper, usually 3 reviews) and select papers according to their relevance and interest for discussions that will take place at the workshop. Accepted papers will be published online in a pre-conference edition of CEUR (http://www.ceur-ws.org) Important Dates =============== Submission of papers: July 17, 2015 Notification: August 21, 2015 Workshop date: September 28, 2015 Organizers ========== Achim D. Brucker, SAP SE, Germany Marina Egea, Indra Sistemas S.A., Spain Martin Gogolla, University of Bremen, Germany Frederic Tuong, Univ. Paris-Sud - IRT SystemX - LRI, France Programme Committee =================== Mira Balaban, Ben-Gurion University of the Negev, Israel Tricia Balfe, Nomos Software, Ireland Achim D. Brucker, SAP SE, Germany Fabian Buettner, Inria - Ecole des Mines de Nantes, France Jordi Cabot, Inria - Ecole des Mines de Nantes, France Dan Chiorean, Babes-Bolyai University, Romania Robert Clariso, Universitat Oberta de Catalunya, Spain Tony Clark, Middlesex University, UK Manuel Clavel, IMDEA Software Institute, Spain Carolina Dania, IMDEA Software Institute, Spain Birgit Demuth, Technische Universitat Dresden, Germany Marina Egea, Indra Sistemas S.A., Spain Geri Georg, Colorado State University, USA Martin Gogolla, University of Bremen, Germany Shahar Maoz, Tel Aviv University, Israel Istvan Rath, Budapest University of Technology and Economics, Hungary Bernhard Rumpe, RWTH Aachen, Germany Frederic Tuong, Univ. Paris-Sud - IRT SystemX - LRI, France Claas Wilke, Technische Universitat Dresden, Germany Edward Willink, Willink Transformations Ltd., UK Burkhart Wolff, Univ. Paris-Sud - LRI, France Steffen Zschaler, King's College, UK -- Dr. Achim D. Brucker, SAP SE, Vincenz-Priessnitz-Str. 1, D-76131 Karlsruhe Phone: +49 6227 7-52595, http://www.brucker.ch/

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Re: [Haskell-cafe] Haskell users on Chile
by Anupam Jain 19 Jun '15

19 Jun '15

Also, I am a part of the Startup Chile community. I would be happy to promote this group on their mailing list. On Friday, June 19, 2015, Ismael Figueroa <ismael.figueroa(a)ucv.cl> wrote: > Hi all, > > I definitely love the idea of having a chilean Haskell user group :-) > Even more so if it is in the V Region ;-) > > -- > Ismael > > On 18/06/15 18:14, Éric Tanter wrote: > >> I’m a CS professor at Universidad de Chile, doing research in PL, some >> of it in Haskell. I also use Haskell for part of my PL courses, so there >> might be some Haskellers that came out of these experiences. >> >> Also, Ismael Figueroa (in cc) graduated from his PhD under my >> supervision last year. His PhD thesis was entirely around Haskell >> (monadic embedding of aspects, compositional reasoning about >> interference), and we’ve done some other stuff on Haskell too (effect >> capabilities). Ismael is now professor at Universidad Católica de >> Valparaíso. >> >> -- Éric >> >> >> On Jun 18, 2015, at 2:44 PM, Roman Dzvinkovsky <romand.ne(a)gmail.com >>> <mailto:romand.ne@gmail.com>> wrote: >>> >>> Living in Viña del Mar, would love to participate. >>> >>> 2015-06-09 9:46 GMT-03:00 Anupam Jain <ajnsit(a)gmail.com >>> <mailto:ajnsit@gmail.com>>: >>> >>> Great idea! Though not a native Chilean, I lived in Chile (Santiago) >>> for the better part of a year in 2014-2015, where my favourite >>> activity was infiltrating JS meetups and evangelizing Haskell :) >>> >>> It would be great to have a dedicated Haskell community there. >>> >>> -- Anupam >>> >>> On Tue, Jun 9, 2015 at 5:44 PM, Ruben Astudillo >>> <ruben.astud(a)gmail.com <mailto:ruben.astud@gmail.com>> wrote: >>> > Hi all >>> > >>> > I would like to see how many haskellers are living on Chile with >>> hopes of >>> > forming a user group. If you are in here, you should reply this >>> thread and >>> > see >>> > how many of us there are. You can also contact me to my mail. >>> > >>> > -- >>> > Ruben Astudillo. pgp: 0x3C332311 , usala en lo posible :-) >>> > Crear un haiku, en diecisiete silabas, es complica... >>> > _______________________________________________ >>> > Haskell-Cafe mailing list >>> > Haskell-Cafe(a)haskell.org <mailto:Haskell-Cafe@haskell.org> >>> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe(a)haskell.org <mailto:Haskell-Cafe@haskell.org> >>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >>> >>> >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe(a)haskell.org <mailto:Haskell-Cafe@haskell.org> >>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >>> >> >> > -- > Ismael > -- Sent from my hyper-communicator

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Haskell users on Chile
by Ruben Astudillo 18 Jun '15

18 Jun '15

Hi all I would like to see how many haskellers are living on Chile with hopes of forming a user group. If you are in here, you should reply this thread and see how many of us there are. You can also contact me to my mail. -- Ruben Astudillo. pgp: 0x3C332311 , usala en lo posible :-) Crear un haiku, en diecisiete silabas, es complica...

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phantom types and record syntax
by Dimitri DeFigueiredo 18 Jun '15

18 Jun '15

Hi All, My apologies if this is not the right forum, but am not satisfied with my current understanding. I am surprised that this program compiles in GHC: ----- data UserSupplied = UserSupplied -- i.e. unsafe data Safe = Safe data Username a = Username { first :: String, last :: String} sanitize :: Username UserSupplied -> Username Safe sanitize name = name { first = "John" } main = putStrLn "Hi!" ----- My trouble is that it seems the record syntax is*implicitly* converting from one type to the other. It seems I would have to remove the phantom type by adding a tag to avoid this: ----- data Username a = Username { first :: String, last :: String, tag :: a } sanitize :: Username UserSupplied -> Username Safe sanitize name = name { first = "John" } -- FAIL as expected!! :-) ----- But this makes me unwilling to use phantom types for security as I would be worried of unwittingly making the conversion. Could somebody sprinkle some insight into why this is "converted automatically" for phantom types? Is there another way around this? Thanks! Dimitri

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Haskell and Spark
by Vasili I. Galchin 18 Jun '15

18 Jun '15

Hello, There was a posting from a Polish guy(Wojcieh .,,,, been trying to contact him) on implementing a library/wrapper for Spark. Does anybody know the status? Vasili

1 0

RFC: "Native -XCPP" Proposal
by Herbert Valerio Riedel 18 Jun '15

18 Jun '15

Hello *, As you may be aware, GHC's `{-# LANGUAGE CPP #-}` language extension currently relies on the system's C-compiler bundled `cpp` program to provide a "traditional mode" c-preprocessor. This has caused several problems in the past, since parsing Haskell code with a preprocessor mode designed for use with C's tokenizer has caused already quite some problems[1] in the past. I'd like to see GHC 7.12 adopt an implemntation of `-XCPP` that does not rely on the shaky system-`cpp` foundation. To this end I've created a wiki page https://ghc.haskell.org/trac/ghc/wiki/Proposal/NativeCpp to describe the actual problems in more detail, and a couple of possible ways forward. Ideally, we'd simply integrate `cpphs` into GHC (i.e. "plan 2"). However, due to `cpp`s non-BSD3 license this should be discussed and debated since affects the overall-license of the GHC code-base, which may or may not be a problem to GHC's user-base (and that's what I hope this discussion will help to find out). So please go ahead and read the Wiki page... and then speak your mind! Thanks, HVR [1]: ...does anybody remember the issues Haskell packages (& GHC) encountered when Apple switched to the Clang tool-chain, thereby causing code using `-XCPP` to suddenly break due to subtly different `cpp`-semantics?

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Canberra Functional Programming Group
by Ivan Lazar Miljenovic 18 Jun '15

18 Jun '15

In case you live in Canberra, Australia and were unaware of this already, Alex Mason (aka Axman6) is helping to arrange/organise a new functional programming group. The first meeting for it is next week on 24 June (including free pizza!). For more information please see http://www.meetup.com/CanFPG/ -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Haskell Weekly News
by Kim-Ee Yeoh 18 Jun '15

18 Jun '15

*Top Picks:* - Andrew Gibiansky <http://www.reddit.com/r/haskell/comments/37uqqk/ihaskell_online_help_choose…> announces the Mathematica-inspired REPL 2.0 IHaskell as a web-app you can play with right now <http://try.jupyter.org/>. Bouquets include: "This is an awesome step up from the tryhaskell window." Also, "I love IHaskell. I've already started preferring it to ghci since it's so much easier to use." More /r/haskell love here <https://www.reddit.com/r/haskell/comments/376aqh/ihaskell_on_tryjupyterorg/> . - Mihai Maruseac and Alejandro Serrano Mena publish the 28th Haskell Communities and Activities Report <https://www.haskell.org/communities/05-2015/html/report.html>. Top comment on HN <https://news.ycombinator.com/item?id=9627260>: "Haskell is backed by a truly amazing community. Haskell will continue to inspire people to build better, safer software. I hope that the values of tolerance, respect and benevolence that most of the Haskell community is supporting will also contribute to make tech a more friendly and equal place for everyone." - Bicycling in circles just to find parking in Utrecht? Bas van Dijk launches a city-wide monitoring system that guides you to a space that's free, dry, and safe <https://bicycledutch.wordpress.com/2015/06/09/bicycle-parking-guidance-syst…>. Written in Haskell 'natch, even the front-end leverages GHCJS. Devops'ed in NixOS. He tips off his fellow redditors <http://www.reddit.com/r/haskell/comments/3959r0/haskellbased_bicycle_parkin…> about using blaze-react to wrap Facebook's React library. HN-worthy <https://news.ycombinator.com/item?id=9690683>. - Announcing on haskell-cafe <http://haskell.1045720.n5.nabble.com/A-Dockerfile-to-provision-a-build-envi…> and /r/haskell <http://www.reddit.com/r/haskell/comments/387uct/building_an_android_game_wr…>, Sean Seefried open sources a Docker script that instantly gets you a Haskell build environment for Android game development <https://github.com/sseefried/docker-epidemic-build-env>. No more fiddling with cross-compiles. He even gives you an open source game <https://github.com/sseefried/open-epidemic-game> all mobile-ready. Thanks, Sean! - Vincent Hanquez releases cryptonite <http://hackage.haskell.org/package/cryptonite>, a single package that consolidates 10-20 other crypto packages. Why? Because maintaining multiple packages is a pain involving fiddling with dependency version bounds and changelog/cabal/version metadata. Benefit for the user? Easier discovery of crypto widgets now that they are all in one haddock, as opposed to hidden in a package whose name eludes you. Kibbitz on /r/haskell <http://www.reddit.com/r/haskell/comments/389tpg/announcing_cryptonite/>. - Joe Nelson <https://news.ycombinator.com/item?id=9642665#up_9643923>discovered Haskell two years ago <http://www.wagonhq.com/blog/first-two-weeks-haskell-wagon> and calls it "moon language." Now he works full-time at Wagon, an all-Haskell start-up offering "a modern data collaboration tool." He's proud of his team that "excels at debugging gnarly issues, including a memory leak caused by a useful yet tricky language feature called lazy evaluation." But what's the buzz that HN <https://news.ycombinator.com/item?id=9703500> and /r/haskell <http://www.reddit.com/r/haskell/comments/39izi6/my_first_two_weeks_of_haske…> latch on? Answer: The pros and cons of effectful point-free refactoring. - Fredrik Olsen migrates from Ruby on Rails (RoR) to Haskell <https://medium.com/@folsen/haskell-in-production-bdellium-1df48de40e19> at fintech start-up Bdellium. Unlike RoR where he "always had a much harder time" with an existing codebase, he testifies that "Haskell let me quickly browse the code, read the types and almost instantly understand the structure and layout of the program." Hiring for RoR nets him "a few hundred applications" where only "10–20% I’d say are people that I’d actually be interested in hiring." Hiring for Haskell gets "50 responses to the Reddit post, all of them were people that I could have hired. Many of the applicants were even grossly over-qualified and were willing to take the job just because it would let them work in Haskell." Ben Ford of Fynder.io corroborates Fredrik in the top comment on /r/haskell <http://www.reddit.com/r/haskell/comments/38nooh/haskell_in_production_bdell…> . Phil Wadler reblogs <http://wadler.blogspot.com/2015/06/haskell-in-production-bdellium.html> the story and zooms in on how Fredrik gained 3.7x parallelism from 4 cores by merely tweaking a single line of code. Control.Parallel.Strategies <http://hackage.haskell.org/package/parallel-3.2.0.6/docs/Control-Parallel-S…> ftw! - Arnaud Bailly <https://news.ycombinator.com/item?id=9642665#up_9643923> shares on HN that he had "no issue finding talent" for Haskell jobs in Singapore. "150 qualified applicants (i.e. passed the test, which was to design an inventory management system in Haskell) for ~10 positions, all foreign; the majority came from the US, Germany and Scandinavia." - If type errors can be deferred, why not also "name not found"? Tom Ellis asks <http://haskell.1045720.n5.nabble.com/fdefer-more-errors-tp5809991.html>. He thinks it would make Haskell "gentler for newcomers." For veterans: even more stub-driven-dev opportunities. Coincidentally, Dan Burton spitballed the same on /r/haskell <http://www.reddit.com/r/haskell/comments/37km7e/fdeferscopeerrors_anyone/>. This idea has a history stretching back at least 3 years: see trac ticket #5910 <https://ghc.haskell.org/trac/ghc/ticket/5910#comment:19>. - David Luposchainsky proposes to move the fail method out of the Monad type class <https://github.com/quchen/articles/blob/master/monad_fail.md>. With the deeply thought out blueprint he provides, /r/haskell reports <http://www.reddit.com/r/haskell/comments/397k1a/monadfail_proposal_mfp_movi…> that the community's already working on it. Discussion on libraries list <http://haskell.1045720.n5.nabble.com/MonadFail-proposal-MFP-Moving-fail-out…> . - Anthony Cowley proposes a shorter syntax for imports on haskell-cafe <http://haskell.1045720.n5.nabble.com/Proposal-Shorter-Import-Syntax-td58104…> and trac <https://ghc.haskell.org/trac/ghc/ticket/10478>. He withdraws his proposal five days later because the "disdainful mockery" and "strongly worded rebuttals" have him overwhelmed on what is only a "nights and weekends project." Reddit discussion here <https://www.reddit.com/r/haskell/comments/38vsef/proposal_shorter_import_sy…> . - Henk-Jan van Tuyl <http://haskell.1045720.n5.nabble.com/a-files-not-found-td5810165.html> runs smack into a library .a-extension File Not Found problem when installing data-default-instances-old-locale on 7.10. Culprit? Windows! And its %&@#! 255-character filepath limit. He is not alone <https://github.com/haskell/cabal/issues/2502>. Why is 7.8 ok? Because package names in the filepath used to be abbreviated. Workaround? Instead of cabal install X, download it first: cabal get X, then cabal install ./X. Thanks to Matej Borovec and Michal Antkiewicz for sorting it out. - FP Complete announces Stack <https://www.fpcomplete.com/blog/2015/06/announcing-first-public-beta-stack>, a replacement for cabal-install <https://hackage.haskell.org/package/cabal-install> the command-line tool (not Cabal the library infrastructure). Stack leverages Stackage <https://www.stackage.org/> Long-Term Support (LTS) releases for a speedy escape from cabal hell. Warmly received on /r/haskell <http://www.reddit.com/r/haskell/comments/3957e1/announcing_first_public_bet…>. Dan Burton blogs on how Stack eases development by removing the need to remember a sequence of cabal commands <http://www.reddit.com/r/haskell/comments/3a6p9h/how_stack_lowers_the_barrie…>. HN-worthy <https://news.ycombinator.com/item?id=9687274> and a troll that Haskell's "an esoteric language that no one uses" provokes many a valiant, evidence-backed defense <https://news.ycombinator.com/item?id=9687274#up_9688248>. - Redditor beerdude26 nudges folks on /r/haskell <http://www.reddit.com/r/haskell/comments/37y1yi/my_approach_to_centralizing…> to continue cultivating the haskell wiki <https://wiki.haskell.org/Haskell>. He sets an example by splicing in the common newtype workaround <https://wiki.haskell.org/Orphan_instance#Common_workaround> into the entry on orphan instances. - In HN news <https://news.ycombinator.com/item?id=9662705>: Cloud Haskell <http://haskell-distributed.github.io/> -- Erlang-style concurrent and distributed programming. Top comment notes that whereas the web site suggests that activity stopped in 2014, CH actually thrives on Github <https://github.com/haskell-distributed>. - In HN news <https://news.ycombinator.com/item?id=9696086>: Haskell wiki entry on Frag <https://wiki.haskell.org/Frag>, a 2005 undergrad project by Mun Hon Cheong who recreated a Quake3-like First-Person Shooter (FPS) game using Yampa FRP. Although a decade old, Cody Goodman <https://news.ycombinator.com/item?id=9696086#up_9696700> reports that he's gotten it to compile. - In HN news <http://news.ycombinator.com/item?id=9704851>: APL lives! A functional programmer investigates APL <http://theburningmonk.com/2015/06/fear-and-loathing-with-apl/>, discovers that it "looks every bit as mind-bending and unbelievable as scenes from Johnny Depp’s *Fear and Loathing in L**as Vegas*", and summarizes the syntax for the benefit of all. *Quotes of the Week:* - A typeclass with only one instance is nonsensical, and often a symptom of trying to use typeclasses as OO classes. -- Brandon Allbery <http://haskell.1045720.n5.nabble.com/Disambiguating-a-Num-RealFrac-instance…> - That Haskell shows the developer things about themselves even they didn't know is enough to make it worth learning. It's mind-bending and ideology-exposing. -- Redditor on /r/haskell <http://www.reddit.com/r/haskell/comments/39ci9j/coming_from_php_working_in_…> - Haskell's great for writing an ugly solution and fixing it later because refactoring is so cheap. No need to get it right the first time. -- Gabriel Gonzalez on Twitter <https://twitter.com/GabrielG439/status/606831084655902720> -- Kim-Ee nights and weekends project

1 0

More instances for Identity?
by Niklas Hambüchen 17 Jun '15

17 Jun '15

Hi, I just noticed that Data.Functor.Identity [1] lacks many useful instances like Eq, Ord, Show ... etc. Is there a reason for this? Otherwise, shouldn't we make a proposal for it? In my opinion, if the seven-tuple has an instance, then Identity deserves it as well. Niklas [1]: https://downloads.haskell.org/~ghc/7.8.3/docs/html/libraries/transformers-0…

1 1

About my commitment to my passions, Haskell and the world
by Jesus Gonzalez 17 Jun '15

17 Jun '15

Hi everybody, I have a very important announcement. I’ve decided to dedicate the next big part of my life to improve the world through Haskell. And you can help! (I’m not asking for money…) I plan to go to live at a “poor” village where my grandparents live. Poor because it is very hard to get a higher education. My grandfather founded some time ago some schools nearby the village, but if people wanted to have a bright future, they had to leave the village. My father moved to the nearest capital city. The story repeated. My father and my mother (together with other people) founded a school at the city where I was born. I left this city to get an even higher education at one of the best universities of my continent. At college, I got the opportunity to study a year as an exchange student at one of the best CS universities in the world. Knowing that probably I would never be able to study at such a good university again, I took the hardest subjects I could. The first semester, I took 2 undergrad courses an 2 grad courses (Program Transformations, Software Design, etc…) This first semester was hard, but at the end I got ok grades, so I thought that maybe I could give a little bit more. For the next semester, I tried to encode the knowledge I acquired as clearly as I could. Very quickly, I got more interested in how to model this knowledge more than the knowledge itself. When I failed with Java, I turned to Haskell and so it begun. I did enjoy my time also. I got to see the inauguration of the Gates Computer Science Building, I found the time to play the piano and learned how to drive the bike without hands very well. When I returned, my parents kindly forced me to finish colleague. When I graduated, I got a scholarship for grad school (that I took, but I left 3 months later) and a job making iOS and Android apps. I couldn’t use Haskell but I did work some months with F#. Now that I’ve seen the world, the good, the bad and the ugly things, Now that I’ve tasted the impoverishing money and repented, Now I’m ready, I flipped the arrows. The hardest thing so far has been to finish my NDA… I’m still on it… It looks like the story will repeat once more. I want to retreat my self and found a next generation school where my grandparents live. I believe that we need to create high performant Haskellers and that we owe to teach children as young and fast as they can happily take it. I would appreciate encouragement, tutorials for all ages and levels of math encoded in Haskell, advice, anything good. I’m already burning bridges! I’ll keep reporting.

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[Hiring] Infrastructure Engineer @ Elastic (makers of Elasticsearch) Location: Anywhere
by Joe Hillenbrand 16 Jun '15

16 Jun '15

Although not strictly a Haskell developer position. Haskel experience/interest is a huge plus. https://www.elastic.co/about/careers/engineering/infrastructure-engineer?id… (Note: the id param is required or else you'll get a 404)

1 1

Type constraint with RankNTypes gradually slows down function?
by Ben Gunton 16 Jun '15

16 Jun '15

When I write a function with the type constraint "embedded" in the function's type declaration, instead of at the beginning, the function takes longer each time it is run. The simplest example I could write is this: http://lpaste.net/134563. "run1" is near instantaneous the first time, but gets marginally slower after each iteration... after thousands of iterations it takes about a millisecond to run (and keeps getting worse). "run2" is always near instantaneous. What is happening in "run1" that makes it slow down? PS: The example is fairly contrived, I know "run1"'s type declaration wouldn't be used in practice. Thanks for any guidance! {-# LANGUAGE RankNTypes #-} {-# LANGUAGE FlexibleContexts #-} module Main where import Control.Monad.State.Strict import qualified Data.Time.Clock as Clock import Control.Exception run1 :: (Int -> (Num Int => State Int Bool)) -> Int -> IO () run1 f state = do t1 <- Clock.getCurrentTime evaluate $ runState (f 1) state t2 <- Clock.getCurrentTime print $ Clock.diffUTCTime t2 t1 run1 f state run2 :: Num s => (Int -> State s Bool) -> s -> IO () run2 f state = do t1 <- Clock.getCurrentTime evaluate $ runState (f 1) state t2 <- Clock.getCurrentTime print $ Clock.diffUTCTime t2 t1 run2 f state main :: IO () main = run1 (const $ return False) 1 --main = run2 (const $ return False) 1

3 2

Space leak with replicateM
by Ken Takusagawa II 16 Jun '15

16 Jun '15

In the following program, the function "test1" results in huge memory usage, but substituting "test2", which does essentially the same thing, does not. GHC 7.10.1, AMD64. Is there a different implementation of replicateM that avoids the space leak? module Main where { import Control.Monad; numbers :: [Int]; numbers=[1..200]; -- has a space leak test1 :: [[Int]]; test1 = replicateM 4 numbers; -- no space leak test2 :: [[Int]]; test2 = do { x1 <- numbers; x2 <- numbers; x3 <- numbers; x4 <- numbers; return [x1,x2,x3,x4]; }; main :: IO(); main = print $ length $ test1; } Thanks, --ken

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Question about constraining functions to particular ADT constructors
by Román González 16 Jun '15

16 Jun '15

Hello there, I've been thinking on different approaches to constraint particular functions to a particular constructor of an ADT in order to reduce representation of invalid states. Say for example I've this types: data Address = Address { ... } newtype Email = Email String data Package = Package { ... } data EmailMsg = EmailMsg { ... } data User = RealUser Address | VirtualUser Email And I would like to implement two functions: deliverPackage :: User -> Package -> IO Bool sendEmail :: User -> EmailMsg -> IO () I would like to constraint both deliverPackage and sendEmail to receive only the semantically correct constructor of User. I know of an approach I could use, that is wrapping each constructor in it's own newtype, and create some smart constructor that way, that approach works, but I find it rather verbose. Is there any other well known approach to deal with this scenarios?

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Link to BayHac presentation and code files.
by David Banas 16 Jun '15

16 Jun '15

Hi all, Great to have seen you all again at BayHac! I couldn’t find any reference to a central repository for presentation/code upload. So, here’s my stuff (“Cracking the Vigenere Cipher in Haskell”): https://github.com/capn-freako/BayHac_2015 Many thanks to Graham Hutton for permission to post his code, along with my own. Cheers, -db

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returning a polymorphic function
by Paolino 15 Jun '15

15 Jun '15

Hello list, I'm trying to accomplish something along this line {-# LANGUAGE ScopedTypeVariables #-} f :: IO (a -> a) f = return id main = do (g :: a -> a) <- f print $ g 1 print $ g "ciao" Is it possible or I have to call f more than once to get different g's Thanks paolino

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PhD student or postdoc position announcement
by Thiemann, Rene 15 Jun '15

15 Jun '15

2-year postdoc or 3-year PhD-student position at the University of Innsbruck ============================================================================ The Computational Logic research group at the University of Innsbruck has one open position funded by the FWF (Austrian science fund) via the START project „Certifying Termination and Complexity Proofs of Programs“. The project aims at increasing the reliability in current complexity and termination provers by independently checking the generated proofs. To this end, several analysis techniques will be formalized in the theorem prover Isabelle/HOL, with a focus on term rewriting and Haskell. For this project, we are looking for an enthusiastic young researcher with a background in computational logic. Knowledge of automated termination analysis, complexity analysis, or theorem proving would be an asset. Candidates with a strong theoretical background in related areas are also encouraged to apply. The PhD-student candidate must have a Master's or equivalent degree. Knowledge of German is not essential. The salary is determined by the FWF-funding scheme (3.546,00 EUR monthly gross salary for postdocs, and 2.024,90 EUR for PhD-students, cf. http://www.fwf.ac.at/en/research-funding/personnel-costs/) Applications (including a CV, a publication list (only for postdocs), and a letter of recommendation) may be emailed to the project leader René Thiemann (rene.thiemann at uibk.ac.at) no later than July 6, 2015. We plan to make decisions on these position until July 10. The preferred starting date is summer or autumn 2015. Informal inquiries are also welcome via email. The city of Innsbruck is superbly located in the beautiful surroundings of the Tyrolean Alps. The combination of the Alpine environment and urban life in this historic town provides a high quality of living. Further information is available from the following links: START Project: http://cl-informatik.uibk.ac.at/research/projects/certifying-termination-an… Institute of Computer Science: http://informatik.uibk.ac.at/ University of Innsbruck: http://www.uibk.ac.at/ City of Innsbruck: http://www.innsbruck.at/

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Data.Hashable instance generation?
by Matti Nykänen 15 Jun '15

15 Jun '15

Hello, A practical question about getting hashing to work. Having used Data.Map before, I wanted to try Data.HashMap.Lazy instead: ---- {-# LANGUAGE DeriveGeneric #-} import Data.HashMap.Lazy as HM import GHC.Generics (Generic) import Data.Hashable data Colour = Red | Green | Blue deriving Generic instance Hashable Colour foo = HM.insert Red ---- The data and its instance definition are directly from the web page <https://hackage.haskell.org/package/hashable-1.2.1.0/docs/Data-Hashable.html>. However, I det the following error: ---- GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main ( htest.hs, interpreted ) htest.hs:13:8: No instance for (hashable-1.1.2.5:Data.Hashable.Hashable Colour) arising from a use of `insert' Possible fix: add an instance declaration for (hashable-1.1.2.5:Data.Hashable.Hashable Colour) In the expression: insert Red In an equation for `foo': foo = insert Red Failed, modules loaded: none. ---- I do not know what is wrong or how I could fix it. Note that my Haskell had originally the older hashable-1.0.0 package, but I cabal-installed this hashable-1.1.2.5 because surfing the net suggested that it would be much better. Could it be the case that the instance goes somehow in the wrong class? -- Matti Nykänen

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Haskell dev role in Strats at Standard Chartered London
by Don Stewart 15 Jun '15

15 Jun '15

I'm hiring another Haskell dev to join the Strats team in London. Details here: https://donsbot.wordpress.com/2015/06/15/haskell-dev-role-in-strats-at-stan…

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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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