- Haskell-Cafe - Haskell.org

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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Building stack projects as docker images
by Daniel Rolls 04 Sep '18

04 Sep '18

I am building Haskell web services using docker. I do this utilising the stack tool within the official Haskell Docker image. Doing this has a number of advantages - It's predictable - I can control bringing in new versions of stack and ghc. - It's easy to share - no stack or Haskell installation is required to build the image - These services can interact with other services in a controlled environment using Docker compose. One downside is that I doing this naively means waiting for a modules to download every time docker build is run since the stack build command will start from scratch each time. I worked around this by adding two build steps. The first runs a hello world example with the stack.yml and package.yml from my project. The second build builds the intended code. This trick separated the downloading of dependent libraries from building the code and means day to day code changes are quick to build since the first stack build is cached as a docker image layer. Still though, making a small change to a stack yml file means a long wait re-downloading all dependent libraries. Firstly, is there a better way of doing this? I know stack supports building within docker but when I worked this way I still found projects depended on the system stack and would commonly fail due to stack bugs. Secondly, my two "stack build" calls where the first builds a hello world program feels a bit hacky. is there a better way to achieve this? Thanks, Dan

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Diagrams
by Roger Mason 04 Sep '18

04 Sep '18

Hello, Does anyone know the current status of the Diagrams package? I'm having some trouble and wonder if anyone can help, given the last release was in 2016. Thanks, Roger

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HDBC packages looking for maintainer
by Erik Hesselink 04 Sep '18

04 Sep '18

Hi all, I've been the maintainer for some of the HDBC packages for a while now. Sadly, I've mostly neglected them due to lack of time and usage. While the packages mostly work, there are occasional pull requests and updates for new compiler versions. Because of this I'm looking for someone who wants to take over HDBC and related packages [1]. If you use HDBC and would like to take over maintainership, please let me know and we can get things set up. Regards, Erik [1] https://github.com/hdbc

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