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build troubles with ghc binary
by briand＠aracnet.com 19 Feb '15

19 Feb '15

(i hope this is not a repost - sent it to haskell-cafe-bounces the first time) new thread because i have the details i should have provided in the first place. development system is centos 6.6 but i suspect something's broken because... i built and installed gmp-4.3.2 only to find that it's being build as a 32-bit library and will only build as 32-bits. which is really weird, because 64-bit system: 2.6.32-504.3.3.el6.x86_64 #1 SMP Wed Dec 17 01:55:02 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux however- no problem- i'll simply download the 32-bit version of the ghc binary, which was built on centos no less, and install that instead of the 64-bit version. so i do that, point configure at my gmp thusly ./configure --prefix=/home/denheyer/local --with-gmp-includes=/home/denheyer/local/include --with-gmp-libraries=/home/denheyer/local/lib and get this checking for path to top of build tree... utils/ghc-pwd/dist-install/build/tmp/ghc-pwd: error while loading shared libraries: libgmp.so.3: cannot open shared object file: No such file or directory configure: error: cannot determine current directory ok- i haven't seen it do that before, but it's probably because i'm pointing it away from it's internal libgmp. that's fine, i'll set LD_LIBRARY_PATH. I do that and make install starts to work. yay! and then i get THIS ghc-cabal: Bad interface file: dist-install/build/GHC/CString.hi magic number mismatch: old/corrupt interface file? (wanted 33214052, got 129742) somebody really hates me. so originally i had downloaded the xz file, and even though i figure it's pretty much impossible that the archive was actually corrupted, i decide to download the bzip version just in case. yeah- not surprisingly, the build still breaks. any ideas ?? Thanks, Brian

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FLTK bindings near completion. Need community assistance ...
by aditya siram 19 Feb '15

19 Feb '15

Hi all, I've been working on bindings [1] to the FLTK GUI toolkit [2] and I've come to the point where it's mostly complete but I could use some help from the community before I put it up on Hackage. My hope is to eventually fill the need in the Haskell ecosystem for a native GUI library that: - runs on all platforms - is easily installable - is small and fast - has a minimum of dependencies. Currently this library uses only base, stm, bytestring and c2hs. - is conservative with extensions. Currently the most recent extension required is GADTs. If any of this sounds good to you, I could use some help with: - testing the build on Linux and OSX. This should be as simple as installing FLTK, cloning the repo [1] and running `cabal build`. Better instructions are in included README. - getting it to build on Windows. I unfortunately don't have access to a Windows machine. - getting it to build on older GHC's. I used 7.8.3 because that is what I have, but it should work back to the first version of GHC that introduced GADTs. Unfortunately the included `Setup.hs` is non-trivial and I been having trouble getting it work with versions of Cabal older than 1.20 due to breaking API changes across versions. - building a single library. Currently the C/C++ wrappers and Haskell bindings are two separate statically linked libraries. They are copied to the same location so applications built with this package don't have to know that, but it would be ideal if it was all-in-one. - building a shared library on Mac OSX. Any other feedback you have is totally welcome. Thanks! -deech [1] https://github.com/deech/fltkhs [2] http://www.fltk.org/index.php

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Let's teach GHC idiom brackets!
by Oliver Charles 19 Feb '15

19 Feb '15

Hi friends, Last night I was having a good natter with Chris Done, and the topic of idiom brackets came up. Specifically, Chris' hindent and structured-haskell-mode tools have both recently become aware of the quasiquoter in applicative-quoters <http://hackage.haskell.org/package/applicative-quoters> - allowing one to write ordinary Haskell code but have it formatted/edited as if it wasn't even inside a quasiquoter. However, it's a shame that Chris has to now be aware of this specific quasiquoter just to get his tools to work properly. Furthermore, it's a shame that *everyone* has to do the same whenever they want to manipulate Haskell code. That said, idiom brackets - at least to me - appears to be a very desirable syntax extension. A recent desire for this came to me while working with reactive-banana. As almost everything "interesting" is even an Event or a Behavior, there tends to be a lot of assembling programs with applicative syntax. Another obvious example is when using parser combinators. Therefore, I'd like to propose that we teach GHC about this desugaring, properly. Now, how we do that, and in fact, what I'm even proposing... that's all up for discussion! I spoke briefly with David Christiansen and a few others in the Idris IRC channel last night about their particular variation of idiom brackets, and it seems people are generally happy with that. Copying that almost verbatim is probably the first proposal I'd put forward. This is the first time I've proposed an extension to GHC, so I'll need some guidance to make this happen - both in terms of guiding the discussion through to a proposal, but ultimately implementing it. Perhaps the proposal will be ready for ZuriHac, and some GHC devs could help me work on it there. Anyway, that's enough rambling from me. I would love to hear your thoughts - do you think idiom brackets are a good idea? Do you have a particular tricky case that you think they need to support? I'm all ears. -- Ollie

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Very large data structures in the heap
by Dr. Olaf Klinke 19 Feb '15

19 Feb '15

I have a function that builds a (cyclic) data structure for searching text. The resulting object can be serialized and re-built. Real-world problems would, however, result in a tree with about 10^9 nodes. I take it that standard data type declarations are not very memory-efficient, so my (fully evaluated) search tree would not fit into memory as a heap object. Its serialised form should be of tractable size, e.g. by storing an array of labels and the tree structure as a bit array of parentheses. I'd like to separate serialization (IO) from traversal of the stucture (pure), but how can one avoid the entire heap object from being built? Can lazyness be exploited? Olaf

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ghc and libgmp compiled separately
by briand＠aracnet.com 19 Feb '15

19 Feb '15

i downloaded the centos65 binary of ghc only to find there was some sort of problem with libgmp on the system i am using. No problem i think, I'll just go grab the latest 4.x gmp compile it and use the --with-gmp flags to point ghc to my compiled version. didn't work. Don't have access to the machine from home, so i can't relay the precise error message (forgot to email it to myself), but it seems that the --with-gmp flags should have solved my problem (gmp compiled cleanly without any problems and put all the files in the right place). any obvious trickery involved when attempting something like this ? Thanks, Brian

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Testing polymorphic properties with QuickCheck
by Stuart Hungerford 19 Feb '15

19 Feb '15

Hi, I'd like to use QuickCheck to test polymorphic properties and I'm wondering if there's any community consenus on how to do this while avoiding creating large amounts of boilerplate test code. As an example, suppose I have this simple simplistic Monoid typeclass: class Monoid a where zero :: a (|+|) :: a -> a -> a And suppose I make these types Monoid instances: instance Monoid Integer where zero = 0 (|+|) = (+) instance Monoid Rational where zero = 0 (|+|) = (+) instance (Monoid a, Monoid b) => Monoid (a, b) where zero = (zero, zero) (|+|) (x, y) (u, v) = (x |+| u, y |+| v) Using QuickCheck and the Tasty test framework I'd like to test the Monoid laws across the relevant types (I'm only showing one part of one law here) as QuickCheck properties: prop_left_add_id :: (Eq a, Monoid a) => a -> Bool prop_left_add_id x = zero |+| x == x monoid_suite :: TestTree monoid_suite = testGroup "monoid" [ testProperty "left additive identity (Integer)" (prop_left_add_id :: Integer -> Bool), testProperty "left additive identity (Rational)" (prop_left_add_id :: Rational -> Bool), testProperty "left additive identity ((Integer, Integer))" (prop_left_add_id :: (Integer, Integer) -> Bool), -- ...] And this is where I start creating a lot of essentially boilerplate code. I'm wondering if there's any consensus on the way to go about this kind of testing? Researching this issue I've found ways of combining various GHC extensions and the type system to (I think) write the properties more at the type level. There are QuickCheck and Tasty modules that aim to find all properties in a module and test them, but polymorphic properties are automatically defaulted to Integer arguments. I'm also tempted by Template Haskell to write what's essentially code generation templates. Is there a better way to go about this? Thanks, Stu

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Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 138, Issue 30
by Stuart Hungerford 19 Feb '15

19 Feb '15

On Thu, Feb 19, 2015 at 12:13 PM, <haskell-cafe-request(a)haskell.org> wrote: > From: Tom Ellis <tom-lists-haskell-cafe-2013(a)jaguarpaw.co.uk> > To: haskell-cafe(a)haskell.org > Subject: Re: [Haskell-cafe] Testing polymorphic properties with > QuickCheck > I'm not quite sure what you're asking specifically, but maybe this will > help: > > {-# LANGUAGE ScopedTypeVariables #-} > > monoid_suite :: forall m. (Eq m, Monoid m) => String -> Proxy m -> TestTree > monoid_suite typename _ = testGroup "monoid" [ > testProperty ("left additive identity (" ++ typename ++ ")") > (prop_left_add_id :: m -> Bool), > > ... <other general monoid properties here> > ] > > monoid_suite_integer :: TestTree > monoid_suite_integer = monoid_suite "Integer" (Proxy :: Integer) Please excuse my ignorance as a relatively new Haskell user but is there anything special about that "Proxy m" type? Thanks, Stu

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How to force James Cook (author of dependent-map) evaluation?
by Alexey Uimanov 19 Feb '15

19 Feb '15

Hello people. There is a pull request https://github.com/mokus0/dependent-map/pull/2 which I need to be on hackage. I have sent a email to mokus(a)deepbondi.net but nothing happened. Does anyone can contact with James and tell him about my problem?

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Re: [Haskell-cafe] quickcheck for compiler testing
by Doug McIlroy 18 Feb '15

18 Feb '15

>> I'm ... wondering whether people use quickcheck at all for >> compiler testing. > it's worth giving a try, but keep in mind that you might still > need to use unit tests If your compiler is for a widely used language, you might consider a hybrid approach due to Bill McKeeman: generate random code and check it by automated crowd-sourcing. The crowd is a jury of other compilers, not necessarily even for the same hardware. The check is to compare compilability, compile time, run time and run results against those of the jury. McKeeman used a generative grammar whose productions were adjustably weighted to influence the characteristics of the generated code. Over the course of several months of overnight runs torturing a production C compiler, he turned up something like one anomaly per day, excluding jury errors and extra reports from a common root cause. (One amusing find was that the compiler took Omega(INT_MAX) time to evaluate the constant expression 1<<INT_MAX.) Doug

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cryptography in haskell
by Julian Ospald 18 Feb '15

18 Feb '15

Hi, I've been wondering about the state of cryptography in haskell. Not so much in the sense of "what libraries are out there?", but rather about the question what crpyto and IT security people think about ideas like rewriting something as OpenSSL in haskell. I know it can be technically done, but are there any remarks in this area that are important for practical security? For example, some people think that it can be dangerous to implement something like this in high-level languages (e.g. java which was vulnerable to timing attacks). Of course I think haskell can do a lot for us to make things safer: * type safety * referential transparency * explicit knowledge about side-effects and which kind ... But that doesn't tell me if it introduces new pitfalls/attack-vectors for practical cryptography implementations. -- Regards, Julian Ospald

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