- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] ANN: leancheck-v0.7.4 with providers for Tasty, Hspec and test-framework
by Rudy Matela 08 Sep '18

08 Sep '18

Hello Haskell-Café, A new version of LeanCheck is out: v0.7.4. LeanCheck is a property testing library (like QuickCheck) that tests values enumeratively rather than at random (unlike QuickCheck). _Whats new?_ I have created providers to make it easy to incorporate LeanCheck properties in Tasty, Hspec and test-framework test suites. This is optional and provided in separate packages: LeanCheck can still be used alone. LeanCheck and its framework providers are available on Hackage. You can install them with: $ cabal install leancheck $ cabal install tasty-leancheck $ cabal install hspec-leancheck $ cabal install test-framework-leancheck Check out the README files for examples of use: * https://github.com/rudymatela/leancheck * https://github.com/rudymatela/tasty-leancheck * https://github.com/rudymatela/hspec-leancheck * https://github.com/rudymatela/test-framework-leancheck Here's a sneak peek of LeanCheck+Tasty: ## Test program import Test.Tasty import Test.Tasty.LeanCheck as LC import Data.List main :: IO () main = defaultMain tests tests :: TestTree tests = testGroup "Test properties checked by LeanCheck" [ LC.testProperty "sort == sort . reverse" $ \list -> sort (list :: [Int]) == sort (reverse list) , LC.testProperty "Fermat's little theorem" $ \x -> ((x :: Integer)^7 - x) `mod` 7 == 0 -- the following property do not hold , LC.testProperty "Fermat's last theorem" $ \x y z n -> (n :: Integer) >= 3 LC.==> x^n + y^n /= (z^n :: Integer) ] ## Output for the test program $ ./test Test properties checked by LeanCheck sort == sort . reverse: OK +++ OK, passed 200 tests. Fermat's little theorem: OK +++ OK, passed 200 tests. Fermat's last theorem: FAIL *** Failed! Falsifiable (after 71 tests): 0 0 0 3 1 out of 3 tests failed (0.00s) You can't see it here, but Tasty's output is highlighted in colours: "FAIL" appears in red so you can quickly see which properties failed. Best Regards, Rudy

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common class for Set (and Map, resp.) implementations with different constraints on the keys
by Johannes Waldmann 07 Sep '18

07 Sep '18

Dear Cafe, we have Data.Set, Data.IntSet, Data.HashSet, and they all have similar API, where the only difference is the constraint on the elements. (Same thing for maps.) Can we unify this as follows: {-# language ConstraintKinds, TypeFamilies #-} class SetC s where type Con s :: * -> Constraint singleton :: (Con s a) => a -> s a foldMap :: (Con s a, Monoid m) => (a -> m) -> s a -> m ... Then for Data.Set, we write instance SetC S.Set where type Con S.Set = Ord ; ... It seems to work, and it allows me to write polymorphic code, and switch implementations from the top. Full source: https://gitlab.imn.htwk-leipzig.de/waldmann/pure-matchbox/tree/master/src/D… Example use case (switch implementation): https://gitlab.imn.htwk-leipzig.de/waldmann/pure-matchbox/blob/master/src/M… Still, there are some clumsy corners in this code, perhaps you can help: * for instance SetC HashSet, there are two constraints. I want to write type Con HashSet = \ e -> (Hashable e, Eq, e) but this does not work (there is no "type lambda"?) * for maps, I want to write class (forall k . Foldable m k) => MapC m but this seems impossible now (This is would work with -XQuantifiedConstraints ?) * in some other code using the same idea (the class exports the constraint), I had an instance where the constraint was empty. Again, I cannot write type Con Foo = \ s -> () - J.W.

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Passing creation flags to CreateProcess on windows
by Yotam Ohad 07 Sep '18

07 Sep '18

Hello cafe, I'm working on a small debugger so I would like to use the winapi CreateProcess function with the appropriate flags for debugging. Unfortunately, it seems that in Haskell <http://hackage.haskell.org/package/process-1.6.4.0/docs/System-Process.html…>there is no way to pass the flags. I would like to not use LoadLibrary to get every function I need. Thanks Yotam

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Stack project, dependency with build flags
by John Z. 06 Sep '18

06 Sep '18

Hi everyone, I'll try with tl:dr; first: I have a project with a dependency that -on my system- needs a build flag, in order to correctly link against its native dependencies. What is a proper way to set up a project like this? A longer explanation: My project uses `ncurses` library and I'm running Arch. There seems to be some religious opinion going around about the layout of ncurses headers in /usr/include, and -naturally- Arch and `ncurses` disagree. Fortunately, author of `ncurses` included a build flag to allow (easy) build on systems which follow the 'wrong' layout. Thing is, I couldn't figure out how to add this configuration to the .cabal of my own project, so for now, I'm stuck with a Makefile that invokes `stack` commands with `--flag ncurses:force-narrow-library`. I looked in the manual and there doesn't seem to be a way to handle this aside the commandline argument. So this got me thinking - is there a different way projects like these are supposed to be organized? For example, am I supposed to check out `ncurses` as a submodule of my project, then replicate this build flag on my own project and 'pass it down' somehow? Any tips are highly appreciated; I'm really not proficient with organizing stack projects properly. Cheers! -- "That gum you like is going to come back in style."

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how to Enumerate without lists?
by Johannes Waldmann 06 Sep '18

06 Sep '18

Dear Cafe (again), I was trying to write sum $ map (^ 2) $ [ 1 :: Int .. 10^8 ] in a list-free style getSum $ foldMap (Sum . (^ 2)) $ [ 1 :: Int .. 10^8 ] This avoids building an intermediate list (of squares) but it will allocate, since foldMap uses foldr (by default, and it's not overridden for lists) The conclusion would be: not to use lists at all. Which will be the point of my talk anyway. But here, we get a list from enumFromTo. Can we avoid that? Let's try: we just reify enumFromTo data Enumerator a = Enumerator {from :: a, to :: a} we have this for decades, it is called (a,a) in Data.Ix, and then instance Foldable Enumerator where ... Oh no, foldMap (and others) would need an Enum constraint! - J

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small example for space-efficiency via lazy evaluation?
by Johannes Waldmann 05 Sep '18

05 Sep '18

Dear Cafe, I wanted to demonstrate that main = print $ sum $ map (^ 2) $ [ 1 :: Int .. 10^8 ] without any optimisations, still runs in constant space because garbage is collected immediately. Except that it does not: ghc -O0 space.hs -rtsopts -ddump-simpl ./space +RTS -M80k -A10k gives me unoptimized Core as expected, but exhausts the heap. After some experimentation, I found that replacing Prelude.sum with Data.Foldable.foldl' (+) 0 achieves what I want. I think the reason is that instance Foldable [] implements sum by foldl (non-strict). Both versions will run without any allocation as soon as we compile with -O1 . So, my question is, what do you use as a (teaching) example for space-efficiency via lazy evaluation? Preferrably a one-liner, using only standard libraries, and such that the effect is not rendered moot by -O2. - J PS: It is magic that foldl and foldl' produce identical core here? $wgo_s5we (w_s5w8 :: GHC.Prim.Int#) (ww1_s5wc :: GHC.Prim.Int#) = case GHC.Prim.==# w_s5w8 ww_s5w5 of { __DEFAULT -> jump $wgo_s5we (GHC.Prim.+# w_s5w8 1#) (GHC.Prim.+# ww1_s5wc (GHC.Prim.*# w_s5w8 w_s5w8));

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Fwd: Setting RTS thread names useful?
by Michal J Gajda 05 Sep '18

05 Sep '18

It seems `GHC.Conc.labelThread` does not have corresponding `getThreadLabel`. It would be useful when redirecting all exceptions to `journald` etc. The problem might be, that this function is documented to function in debugging builds only :-(. Just like stack traces which need special options.

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Senior Haskell Developer opening at Mpowered
by Emil Axelsson 05 Sep '18

05 Sep '18

We are looking for a Haskeller to help us move our application forward using Haskell. We're a remote-only team based in South Africa and Sweden. Bonus if you've used some Nix or Ruby before! https://mpowered.co.za/jobs/ / Emil

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ANN: network 2.8.0.0
by evan＠evan-borden.com 05 Sep '18

05 Sep '18

Announcing the release of network 2.8.0.0 http://hackage.haskell.org/package/network-2.8.0.0 Version 2.8.0.0 * Breaking change: PortNumber originally contained Word32 in network byte order and used "deriving Ord". This results in strange behavior on the Ord instance. Now PortNumber holds Word32 in host byte order. [#347](https://github.com/haskell/network/pull/347) * Breaking change: stopping the export of the PortNum constructor in PortNumber. * Use bytestring == 0.10.* only. * Use base >= 4.7 && < 5. -- Evan Borden

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[Haskell, FP] Anduril Industries is Hiring
by Travis Whitaker 04 Sep '18

04 Sep '18

Anduril Industries (https://www.anduril.com/careers) is hiring. Come write Haskell, Nix, and a bit of C++ to solve problems in detection, tracking, hardware interfaces, sensor fusion, and computer vision. Here are just a few of the things we're hacking on in Haskell: - Nix workflow tools for cross-compilation, CI, deployment, and upgrades over heterogeneous, unreliable infrastructure. - Radar signal processing (with CUDA via *Accelerate*), target detection, and real-time visualization. - sUAS controls and mission planning. - Comprehensively tested (i.e. thoroughly QuickCheck'd/SmallCheck'd) implementations of industrial hardware interface protocols like CAN, CANopen, MAVLink, etc., as well as internally developed protocols. - High-reliability systems for performing health checks and over-the-air firmware upgrades of embedded systems deployed in remote environments. - A library of low-latency, high-throughput video processing components, used for performing image stabilization, object detection, and transcoding in real time on streaming video. - TUI debugging tools built with *brick*. We're looking for junior and senior devs who are able to relocate to our lab in Orange County, California, USA. If this sounds interesting, shoot me an email at travis(a)anduril.com Thanks for reading! Travis Whitaker

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