- Haskell-Cafe - Haskell.org

Prolog-style list syntax?
by Anthony Clayden 29 Jun '21

29 Jun '21

One of the annoying (to me) inconsistencies with Haskell syntax is that `[ ]` means 'here comes a list'; but for the most common way to write a list, you can't use `[ ]`: > elem x [] = False > elem x ( y: ys ) = ... Prolog syntax has lists, signalled by `[ ]`: [], [1], [2, 3], [4, 5, 6], [[7, 8], [9, 10, 11]] are all valid list literals. For cons it also uses `[ ]` syntax > elem x [y | ys ] = ... `[ x, y, z | zs ]` is also valid; pattern match or build a list with at least 3 elements, where `zs` is the tail -- 4th element onwards (if any). That structure is particularly ugly in Haskell syntax. Neither `|` inside `[ ]` in a pattern nor a comma-list with `|` inside `[ ]` is valid H98 syntax, nor valid in GHC extensions AFAICT. In an expression, `[ x | xs ]` could be taken as a list comprehension, which is I guess why Haskell didn't follow Prolog. I've come across another theorem-prover that follows Prolog style, except it uses `:` instead of `|` inside `[ ]`. Unfortunately ... > elem x [ y: ys ] = ... Is valid syntax, where `:` is cons, so this is a nested list. I'm thinking that's relatively uncommon, and means the same as `[ ( y: ys ) ]`. Would anyone be violently pro or anti changing the meaning of `:` appearing at top level in `[ ]` to mean cons-tail? AntC

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Help Improving Conduit Performance
by Matthew Leach 29 Jun '21

29 Jun '21

Hi there! I'm currently trying to write a program for the creation of IQ samples from various sound files; AM is my current focus. This seems like a really good application for the conduit library. I've so far got: --8<---------------cut here---------------start------------->8--- run :: AMOptions -> IO () run opts = do (info, Just (aSamps :: SV.Buffer Float)) <- SF.readFile $ inputFile opts putStr "Processing samples... " hFlush stdout runConduitRes $ yieldMany (SV.fromBuffer aSamps) .| modulateAM (modIndex opts) .| zeroStuff (upsample opts) .| mapC renderSample .| unsafeBuilderToByteString .| sinkFile (outputFile opts) --8<---------------cut here---------------end--------------->8--- However, this is *slow*. It takes over 40 seconds to run; I've previously implemented the above without using streaming and this code took approx 3 seconds to run with the same input. I compiled the code for profiling and it appears as though the main culprit is the function `injectLeftovers': --8<---------------cut here---------------start------------->8--- Mon Jun 28 22:55 2021 Time and Allocation Profiling Report (Final) ayeQ +RTS -p -RTS am -i /Users/matthew/40.flac -o /Users/matthew/out.cfile -u 15 -m 150 total time = 76.32 secs (76322 ticks @ 1000 us, 1 processor) total alloc = 445,275,685,456 bytes (excludes profiling overheads) COST CENTRE MODULE SRC %time %alloc injectLeftovers Data.Conduit.Internal.Pipe src/Data/Conduit/Internal/Pipe.hs:(410,1)-(418,38) 79.5 81.6 runPipe Data.Conduit.Internal.Pipe src/Data/Conduit/Internal/Pipe.hs:(395,1)-(399,33) 7.1 5.0 awaitForever Data.Conduit.Internal.Conduit src/Data/Conduit/Internal/Conduit.hs:(950,1)-(952,10) 5.3 3.7 run AM AM.hs:(62,1)-(77,88) 4.4 7.0 renderSample Render Render.hs:8:1-58 3.5 2.5 --8<---------------cut here---------------end--------------->8--- I'm at a bit of a loss as to where to start looking for why this particlar function is using so many resources, or which part of the pipeline is causing the issue. The custom pieces of code that I've got in the pipeline are: --8<---------------cut here---------------start------------->8--- modulateAM' :: Int -> Float -> IQ modulateAM' modIdx s = (base + amp) :+ 0.0 where x = fromIntegral modIdx / 200 amp = s * x base = 1 - x modulateAM :: Monad m => Int -> ConduitT Float IQ m () modulateAM = mapC . modulateAM' --8<---------------cut here---------------end--------------->8--- --8<---------------cut here---------------start------------->8--- zeroStuff :: Monad m => Int -> ConduitT IQ IQ m () zeroStuff factor = awaitForever (\v -> yield v >> replicateM_ (factor - 1) (yield zero)) where zero = 0 :+ 0 --8<---------------cut here---------------end--------------->8--- --8<---------------cut here---------------start------------->8--- renderSample :: IQ -> Builder renderSample (real :+ imag) = floatLE real <> floatLE imag --8<---------------cut here---------------end--------------->8--- Any help would be appreciated! Regards, -- Matt

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Re: [Haskell-cafe] Prolog-style list syntax?
by Johannes Waldmann 29 Jun '21

29 Jun '21

>> but it would be interesting if this worked: >> >> [x, y, z] ++ zs = list this works in Curry; a functional-logic PL, very roughly: Prolog semantics (in a sane way) with Haskell syntax and typing https://curry.pages.ps.informatik.uni-kiel.de/curry-lang.org/ - J.W.

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How to debug stack build failure?
by David Banas 28 Jun '21

28 Jun '21

Anyone know how to start debugging this? $ stack build comonad > configure comonad > /home/david/.stack/programs/x86_64-linux/ghc-8.8.4/lib/ghc-8.8.4/bin/ghc: /lib64/libtinfo.so.5: no version information available (required by /home/david/.stack/programs/x86_64-linux/ghc-8.8.4/lib/ghc-8.8.4/bin/../haskeline-0.7.5.0/libHShaskeline-0.7.5.0-ghc8.8.4.so) comonad > /home/david/.stack/programs/x86_64-linux/ghc-8.8.4/lib/ghc-8.8.4/bin/ghc: /lib64/libtinfo.so.5: no version information available (required by /home/david/.stack/programs/x86_64-linux/ghc-8.8.4/lib/ghc-8.8.4/bin/../ghc-8.8.4/libHSghc-8.8.4-ghc8.8.4.so) comonad > /home/david/.stack/programs/x86_64-linux/ghc-8.8.4/lib/ghc-8.8.4/bin/ghc: /lib64/libtinfo.so.5: no version information available (required by /home/david/.stack/programs/x86_64-linux/ghc-8.8.4/lib/ghc-8.8.4/bin/../terminfo-0.4.1.4/libHSterminfo-0.4.1.4-ghc8.8.4.so) comonad > [1 of 2] Compiling Main ( /tmp/stack-038db506ab1301e1/comonad-5.0.6/Setup.lhs, /tmp/stack-038db506ab1301e1/comonad-5.0.6/.stack-work/dist/x86_64-linux/Cabal-3.0.1.0/setup/Main.o ) comonad > [2 of 2] Compiling StackSetupShim ( /home/david/.stack/setup-exe-src/setup-shim-mPHDZzAJ.hs, /tmp/stack-038db506ab1301e1/comonad-5.0.6/.stack-work/dist/x86_64-linux/Cabal-3.0.1.0/setup/StackSetupShim.o ) comonad > Linking /tmp/stack-038db506ab1301e1/comonad-5.0.6/.stack-work/dist/x86_64-linux/Cabal-3.0.1.0/setup/setup ... Progress 1/10 Did not find executable at specified path: /tmp/stack-038db506ab1301e1/comonad-5.0.6/.stack-work/dist/x86_64-linux/Cabal-3.0.1.0/setup/setup

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Munich Virtual Haskell Meeting, 2021-06-29 @ 19:30
by Leah Neukirchen 27 Jun '21

27 Jun '21

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Tuesday, June 29 on Jitsi at 19:30 CEST. **Due to bad weather for meetings outside this meeting will take place online!** For details see here: https://muenchen.haskell.bayern/dates.html A Jitsi link to join the room is provided on the page. Everybody is welcome, especially the Haskellers from Bavaria that do not usually come to our Munich meetings due to travel distance! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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How to eliminate Cabal warning message, re: internal library version number?
by David Banas 27 Jun '21

27 Jun '21

How do I eliminate these messages from my `cabal build` output? Warning: The package has an extraneous version range for a dependency on an internal library: {proj_name} >=0 && ==0.1.0.0. This version range includes the current package but isn't needed as the current package's library will always be used.

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How to fix linker error on MacOS
by David Banas 26 Jun '21

26 Jun '21

How do I fix this (from `cabal build`)? Undefined symbols for architecture x86_64: "___darwin_check_fd_set_overflow", referenced from: _awaitEvent in libHSrts.a(Select.o) System Info: ========= $ ghc --version The Glorious Glasgow Haskell Compilation System, version 8.10.5 $ cabal --version cabal-install version 3.4.0.0 compiled using version 3.4.0.0 of the Cabal library dbanas@Davids-MBP-2:~/Documents/Luminous/Projects/haskarch $ sw_vers ProductName: Mac OS X ProductVersion: 10.14.6 BuildVersion: 18G9216

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Why can't I seem to use environment variables in my cabal file?
by David Banas 26 Jun '21

26 Jun '21

I’m trying to make use of an environment variable in my cabal file: ${ENV_VAR}, but I don’t think its value is getting used correctly. Is this a known issue? Workaround?

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Cabal v misses changes to cxx-files: files?
by David Banas 25 Jun '21

25 Jun '21

Using Cabal v3.2.0.0 and with the following stanza in my *.cabal file: executable ex9 import: shared-properties main-is: src/ex/ex9.hs cxx-sources: src/ex/ex9.cpp {snip} if I edit the file: `src/ex/ex9.cpp`, and then execute: `cabal build`, I'm told: $ cabal build Up to date Is this a known issue? Is there a workaround? Thanks, -db

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ICFP 2021: Second Call for Students Volunteers
by Jaemin Hong 24 Jun '21

24 Jun '21

Please don't hesitate to share this information with your students, classmates or colleagues! ICFP'21 SECOND CALL FOR STUDENT VOLUNTEERS ========================================= ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. In order to smoothly run the conference, associated workshops, and tutorials, we need student volunteers to help out on the practical aspect of the organization. All the events associated with ICFP'21 will take place **virtually** from Sun 22 - Fri 27 August 2021. Even though the event will be virtual, we will more than ever need the help of student volunteers to make sure everything runs smoothly. In return, as an ICFP 2021 student volunteer, you will get more visibility and be able to interact closely with researchers, academics and practitioners from various disciplines and discuss with other students from around the world. While the exact structure of the conference is still being discussed, job assignments for student volunteers will probably include: 1- Assisting with technical sessions, workshops, tutorials, Q&A sessions, social activities, and panels. 2- Helping to get authors' videos prepped and ready for broadcast. 3- Managing channels on a virtual event platform. To be considered as a student volunteer for ICFP, please fill in the following application form. https://forms.gle/cEXE4GfXzm24f6mF6 <https://forms.gle/cEXE4GfXzm24f6mF6> The permanent link to this form can be found on the official conference website. https://icfp21.sigplan.org/track/icfp-2021-student-volunteers <https://icfp21.sigplan.org/track/icfp-2021-student-volunteers> There is one remaining round of a call with the following deadline: * deadline for second round: July 16th, 2021 AoE (notification: July 20th)

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