February 2015 - Haskell-Cafe

Testing polymorphic properties with QuickCheck
by Stuart Hungerford 18 Feb '15

18 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 18 Feb '15

18 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 18 Feb '15

18 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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quickcheck for compiler testing
by Maurizio Vitale 17 Feb '15

17 Feb '15

I'm starting to work on my first real haskell program (I've only RWH exercises under my belt) and wondering whether people use quickcheck at all for compiler testing. I've seen uses of quickcheck for testing parsers, but I'm interested in generating well-formed programs (e.g. random programs with all declarations in reasonable random places). This could be used to test passes other than parsing (or even parsing, for languages that needs to distinguish identifiers, like the 'typedef' problem in C/C++). The only thing I can think of, is to use quickcheck for randomly generating statements, go over them and figure out free variables (incl. functions) and generate declarations in random places for them. But I'm not sure how this would play with test size reduction and doesn't look like a nice solution anyhow. Any idea or pointers to examples? or should I give up on quickcheck for this and just do direct testing? Thanks, Maurizio

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Haskell Weekly News
by Kim-Ee Yeoh 17 Feb '15

17 Feb '15

Welcome. Here are this week's picks: - Scott Turner <http://ghc.haskell.org/trac/ghc/ticket/8539#comment:25> proffered a solution in getting exponentiation of complex numbers right, which includes an at-a-glance table to see if everything's sane. - GHC is unsound! <https://mail.haskell.org/pipermail/ghc-devs/2015-January/008189.html> It has a type safety leak. Iavor Diatchki <https://mail.haskell.org/pipermail/ghc-devs/2015-February/008269.html> is hard at work plugging the hole. - Richard Eisenberg <https://mail.haskell.org/pipermail/ghc-devs/2015-February/008271.html> discovered that Debug.Trace.traceStack does a better job debugging GHC than pprTrace. - The curtain is pulled back on the new face of www.haskell.org. Chris Done designed it, Gershom Bazerman announced it, and unsung heroes migrated it and kept it running under the flash crowd onslaught. The raves include: - This is far more welcoming and user-friendly, especially to those who might be curious about Haskell. [link] <https://news.ycombinator.com/item?id=9052129#up_9052355> - The website redesign is great from a new programmer's perspective. I just started learning Haskell a week ago, and I wish this was the first thing I saw. Looks wonderful. Cheers! [link] <http://www.reddit.com/r/haskell/comments/2vy1lw/new_haskell_homepage_is_liv…> - This new, awesome site is using the framework Yesod, which is kinda like the Rails of the Haskell world, only it can do rad stuff like prevent XSS and 404s at *compile *time. Yes, you read that right. [link] <https://news.ycombinator.com/item?id=9052129#up_9052279> - Repo of the week: Samuel Gélineau's hawk <https://github.com/gelisam/hawk>, a haskell command-line text-processor similar to unix awk. Quotes of the week: - "I have made several forays into the impredicative swamp, and barely made it back to the shore alive." - Simon Peyton Jones - "Web programming is like a mature RPG: everything's extremely complicated and everyone's overpowered." - Max Goldstein Tweets: - In Buenos Aires, Marcote Torres tweets <https://twitter.com/marcote_torres/status/565644584060198914> about the first ever Haskell meetup. - And "In Soviet Russia, #haskell learns a you" as @aberls <https://twitter.com/aberls/status/565669752853778432> reminds us. Got a letter to the editor? Hit reply. -- Kim-Ee

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Re: [Haskell-cafe] Refactor unqualified imports to qualified ones automatically?
by Jeffrey Brown 17 Feb '15

17 Feb '15

Thank you, Henning. I found a description [1] of what the -ddump-minimal-imports flag you suggest does ("Dump a minimal set of imports"), and I don't know what that means. I tried running it anyway, but I can't get the code to compile via GHC (or make, or cabal install, though it seems to want to be built via at least one of those). It was abandoned long ago, and I'm not convinced its network of dependencies is something I can disentangle. [1] https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/flag-refere… On Sun, Feb 15, 2015 at 1:20 PM, Henning Thielemann < lemming(a)henning-thielemann.de> wrote: > > Maybe the GHC flag > > -ddump-minimal-imports > > helps? >

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HaskBoard?
by Mike Meyer 16 Feb '15

16 Feb '15

I asked about running GHCI on something like the Arduino due, and was told that there wasn't enough CPU on it for that. How about getting it running on something like a PyBoard? http://www.adafruit.com/products/2390

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New Functional Programming Job Opportunities
by Functional Jobs 16 Feb '15

16 Feb '15

Here are some functional programming job opportunities that were posted recently: Senior Developer (Big Data Tech Stack) at Recruit IT Group Ltd http://functionaljobs.com/jobs/8783-senior-developer-big-data-tech-stack-at… Senior Development Engineer at Lookingglass Cyber Solutions http://functionaljobs.com/jobs/8782-senior-development-engineer-at-lookingg… Cheers, Sean Murphy FunctionalJobs.com

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