July 2016 - Haskell-Cafe

Is the #functional programming paradigm antithetical to efficient strings? #Haskell
by KC 14 Jul '16

14 Jul '16

Is the #functional programming paradigm antithetical to efficient strings? #Haskell -- -- Sent from an expensive device which will be obsolete in a few months! :D Casey

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Use GHC API in standalone executable?
by Mitchell Rosen 13 Jul '16

13 Jul '16

Hi, I'd like to compile an executable that internally uses the GHC API, but otherwise does not require users to have GHC installed on their machine. Is this possible? As far as I can tell, lots of functions in the GHC API read package databases per $GHC_PACKAGE_PATH and things of that nature. Thanks, Mitchell

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Can't log into to GHC trac
by Mitchell Rosen 13 Jul '16

13 Jul '16

Hi, embarrassingly I've forgotten my password (and username) to the GHC trac, and there's no automatic way to reset any of it: - When I try to register an account it says my email address is already in use - To reset my password I need to give both my username and password, but I don't know my username Who can I contact to help resolve the issue?

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ANN: tagsoup-megaparsec-0.1.0.0
by KwangYul Seo 13 Jul '16

13 Jul '16

Hello all, I'm pleased to announce the first release of tagsoup-megaparsec, a Tag token parser library. This library helps you build a megaparsec parser using TagSoup's Tags as tokens. https://hackage.haskell.org/package/tagsoup-megaparsec https://github.com/kseo/tagsoup-megaparsec Regards, Kwang Yul Seo

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Cannot install any packages after upgrading to GHC 8.0.1
by Magicloud Magiclouds 12 Jul '16

12 Jul '16

Hi, I update my GHC to 8.0.1 and failed to install any packages since then. If I use cabal, I got 'installed package info from too old version of Cabal (key field does not match id field)' for every package. If I use Setup.hs, I got 'Configuring Cabal-1.24.0.0... Setup.hs: ghc-pkg dump failed'. What should I do? Googling did not get me an answer.

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Re: [Haskell-cafe] Is the #functional programming paradigm antithetical to efficient strings? #Haskell
by Alex Belanger 11 Jul '16

11 Jul '16

That's not just about Haskell, it's C.S. in general. You're always going to make space and time tradeoffs. Funny how the same constraints appear in physics; I wonder if it is trying to tell us something... - nitrix On Jul 11, 2016 8:54 AM, "David Fox" <dsf(a)seereason.com> wrote: On Sun, Jul 10, 2016 at 11:44 AM, KC <kc1956(a)gmail.com> wrote: > Is the #functional programming paradigm antithetical to efficient strings? > #Haskell > I can certainly see how it might seem so. Our main string representation uses about 10 times more memory than seems necessary, and is relatively fast, though probably not compared to C. Recently I spent some time looking into how to reduce this memory overhead, and I modified the pretty library (https://github.com/ddssff/pretty/tree/textdetails) so it could use any type that was an instance of ListLike and StringLike ( https://github.com/JohnLato/listlike) Then I tried the UnitLargeDoc test with several different data types. This just concatenates a list of ten million "Hello" strings. Using String this happens in about 5 seconds. Using strict or lazy Text it immediately blew the stack. When I increased the stack size to over 1GB it took minutes to complete. When I used the Data.Text.Lazy.Builder type instead it took about 30 seconds to complete. Results with utf8 encoded ByteStrings were siimilar. When I mentioned some of this, I was told "different data structures for different purposes", which sort of makes sense, but honestly if Haskell is a language where you have to sit down and choose a representation every time you want to build some text, I get a bit discouraged. So is functional programming antithetical to efficient strings? In theory maybe not, but I would love to see some hard evidence. </rant> _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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ANN: enchant-0.1.0.0
by KwangYul Seo 11 Jul '16

11 Jul '16

Hello, I'm happy to announce the first release of enchant, binding for the Enchant library. https://hackage.haskell.org/package/enchant-0.1.0.0 https://github.com/kseo/enchant What is Enchant? (from http://www.abisource.com/projects/enchant/) On the surface, Enchant appears to be a generic spell checking library. You > can request dictionaries from it, ask if a word is correctly spelled, get > corrections for a misspelled word, etc... > > Beneath the surface, Enchant is a whole lot more - and less - than that. > You'll see that Enchant isn't really a spell checking library at all. > > "What's that?" you ask. Well, Enchant doesn't try to do any of the work > itself. It's lazy, and requires backends to do most of its dirty work. > Looking closer, you'll see the Enchant is more-or-less a fancy wrapper > around the dlopen() system call. Enchant steps in to provide uniformity and > conformity on top of these libraries, and implement certain features that > may be lacking in any individual provider library. Everything should "just > work" for any and every definition of "just working." Thanks, Kwang Yul Seo

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ANN: qtah-0.1.0
by Bryan Gardiner 11 Jul '16

11 Jul '16

Hello all, I'm happy to announce the first Hackage-ready release of Qtah, Qt bindings for Haskell. I announced Qtah earlier this year, but a lot of work was needed to get it to the point where you can just "cabal install" it. That work has now been done, so I invite you to install qtah-qt5 or qtah-examples[1] (currently just the Qt notepad example), and check out: http://khumba.net/projects/qtah https://gitlab.com/khumba/qtah As a small demonstration, I have a good portion of Goatee ported (board rendering clearly missing): http://khumba.net/tmp/20160710-goatee-qt.png However, there is still lots of the Qt API left to cover. Thanks to ezyang for help working with some Cabal internals. Cheers, Bryan [1] cabal install --enable-executable-dynamic qtah-examples

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Practical use of Stream's monad instance?
by Petr Pudlák 10 Jul '16

10 Jul '16

Hi, we've been debating the usefulness of Monad instances for Stream [2] or homogeneous tuples (fixed-length vectors). The Applicative implementation for them is simply zipping, very useful indeed. The "join" of their Monad instances takes the diagonal of a 2-dimensional plane (finite for tuples, infinite for Stream). (See also [1].) The question is, are such monad instances used in the wild? Are they actually useful or interesting for anything? [1] https://mail.haskell.org/pipermail/haskell-cafe/2009-April/thread.html#59079 [2] https://hackage.haskell.org/package/Stream-0.4.7.2/docs/Data-Stream.html Thanks Petr

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What's wrong in my Data.Generic.Zipper code?
by martin 10 Jul '16

10 Jul '16

Hello all, I do not understand why this simple piece of code returns Nothing instead of [1,2,3]. Can anybody help? {-# LANGUAGE BangPatterns,NoMonomorphismRestriction, DeriveDataTypeable #-} import Data.Typeable import Data.Data import Data.Generics.Zipper ex_list1 :: [Int] ex_list1 = [1,2,3] t1 = toZipper ex_list1 -- *Main> getHole t1 -- Nothing

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