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Re: [Haskell-cafe] Fast JSON validation - reducing allocations
by Ben Gamari 02 Jul '17

02 Jul '17

David Turner <dave.c.turner(a)gmail.com> writes: > On 11 May 2017 at 19:40, Ben Gamari <ben(a)smart-cactus.org> wrote: > >> Ccing Luke Maurer under the assumption that he will appreciate seeing >> the fruits of his labor. >> >> >> David Turner <dct25-561bs(a)mythic-beasts.com> writes: >> >> > Dear Café, >> > >> (snip) >> > >> > There's a copy of the relevant code for option 4 at >> > https://github.com/DaveCTurner/json-validator. I've hacked around with >> it a >> > bit since producing the numbers above, so it's now apparently a bit >> slower >> > than Aeson but allocates less too (~65kB). >> > >> > Could anyone help, e.g. by pointing me at the bit in the Core that is >> > allocating within the main loop? >> > >> While turning this over in my head I realized that this is the sort of >> program which may be helped significantly by GHC 8.2's improved join >> point handling. Indeed the timings seem to support this hypothesis: >> >> GHC 8.0.2 >> >> benchmarking json-validator/Automaton/testEvent >> time 22.84 μs (22.76 μs .. 22.94 μs) >> 1.000 R² (1.000 R² .. 1.000 R²) >> mean 22.84 μs (22.76 μs .. 22.94 μs) >> std dev 297.4 ns (221.8 ns .. 378.8 ns) >> >> Alloc rate 4,015,256,078,038 bytes per MUT second >> >> GHC 8.2 >> >> benchmarking json-validator/Automaton/testEvent >> time 9.221 μs (9.141 μs .. 9.318 μs) >> 0.998 R² (0.996 R² .. 1.000 R²) >> mean 9.163 μs (9.084 μs .. 9.356 μs) >> std dev 399.8 ns (193.0 ns .. 745.4 ns) >> variance introduced by outliers: 54% (severely inflated) >> >> Alloc rate 123,141,635 bytes per MUT second >> >> >> Wow! I suspect your allocations have now vanished. >> > > > Ooo, that's more like it. > > Could you run again using the following to get Criterion's estimate of the > allocations-per-call? > > json-validator-exe --regress allocated:iters +RTS -T >benchmarking json-validator/Automaton/testEvent Here it is, GHC 8.0.2 benchmarking json-validator/Automaton/testEvent time 34.81 μs (33.48 μs .. 36.10 μs) 0.991 R² (0.988 R² .. 0.994 R²) mean 34.04 μs (33.28 μs .. 34.99 μs) std dev 2.828 μs (2.423 μs .. 3.247 μs) allocated: 1.000 R² (1.000 R² .. 1.000 R²) iters 65924.651 (65895.364 .. 65951.510) y -4175.284 (-46736.295 .. 39814.235) variance introduced by outliers: 78% (severely inflated) GHC 8.2 benchmarking json-validator/Automaton/testEvent time 9.021 μs (8.923 μs .. 9.162 μs) 0.998 R² (0.994 R² .. 1.000 R²) mean 8.970 μs (8.905 μs .. 9.232 μs) std dev 341.4 ns (94.90 ns .. 711.7 ns) allocated: 0.973 R² (0.956 R² .. 0.984 R²) iters 343.033 (332.692 .. 354.606) y -7326.339 (-57269.638 .. 47222.231) variance introduced by outliers: 47% (moderately inflated) Cheers, - Ben

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ANN: hledger 1.3
by Simon Michael 02 Jul '17

02 Jul '17

I'm pleased to announce hledger 1.3, released yesterday. Thank you release contributors: Mykola Orliuk, Christian G. Warden, Dmitry Astapov, Justin Le, Joe Horsnell, Nicolas Wavrant, afarrow, Carel Fellinger, flip111, David Reaver, Felix Yan, Nissar Chababy, and Jan Zerebecki. Notable user-visible changes in this release: terminology/UI improvements for the status field, selection/scrolling/movement improvements in hledger-ui, negative amounts shown in red, bugfixes. Full release notes are at http://hledger.org/release-notes#hledger-1.3 The next major release is scheduled for September 30. hledger (http://hledger.org) is a dependable, precise, cross-platform program for tracking money, time, or any other commodity, using double-entry accounting and a simple plain text file format. It is a haskell reimplementation of Ledger, provides command-line, curses and web interfaces, and aims to be a robust, practical tool for daily use. To get started, install the stack tool, eg by downloading from http://haskell-lang.org/get-started. Then install hledger (and optionally the alternate UIs): $ stack install hledger-lib-1.3 hledger-1.3 [hledger-ui-1.3] [hledger-web-1.3] [hledger-api-1.3] (cabal experts can use that instead. See http://hledger.org/download for more install options.) Ensure $HOME/.local/bin is in your $PATH, and try some commands: $ hledger # list commands $ hledger -h # quick help $ hledger --man # man page for the hledger CLI tool $ hledger info journal # info manual for the journal format etc. Our IRC channel is #hledger on Freenode, and you can find out more at http://hledger.org. If you have benefitted from hledger, please give back and make it stronger! Donate using one of the funding links on the home page, give feedback, report bugs, send pull requests, write about it, or help in some other way. Thanks for your support; I hope you enjoy hledger and that it helps you achieve your goals. -Simon

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install haddock only with cabal?
by Evan Laforge 01 Jul '17

01 Jul '17

It's pretty common to wind up with a package installed, but not its haddock. Pretty much any time you install the traditional way via runhaskell Setup.hs you can forget to run haddock, since it doesn't use ~/.cabal/config. And even if you do, it doesn't update the haddock html index. But it seems like cabal install wants to install all targets in the cabal file, which means it wants to reinstall, which is no good for e.g. 'stm'. In fact I can't tell any way to address individual targets (e.g. if I just want to install the executable), and haddock doesn't seem to be a proper target at all, and I can't find any documentation about it. I can run 'haddock' and manually copy dist/doc/html to ~/.cabal/share/doc/$arch/$package/, but shouldn't cabal be able to do that? Also, it looks like regenerateHaddockIndex is hardcoded into the postInstallActions, and there's no way to run it independently, so it seems if you missed documentation on some package, you have to reinstall everything from scratch to fix it. Is there a way to install just haddock without going through all that? And shouldn't cabal-install/bootstrap.sh make the haddock index? Otherwise, you're guaranteed to be missing links for a bunch of fundamental packages. Or maybe it could default to using its (undocumented?) --sandbox flag to install just the binary, and not the various libraries (which are also likely to be missing desired flags, like --enable-profiling, since ~/.cabal/config is not available yet).

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Nice clean code example?
by Han Joosten 01 Jul '17

01 Jul '17

I'd like to showoff some nice Haskell code to a CTO with no experience with FP. I promised to send him a small piece of Haskell so he could get an idea. The code should be easy to read, without obscure looking operators (so sorry, no lens, arrows stuff like that), optionally even do something interesting. Who has the nicest example laying around? (and yes, I need it by yesterday ;-) ) Thanks!

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Re: [Haskell-cafe] Nice clean code example?
by Chris Wong 01 Jul '17

01 Jul '17

How about Hackagebot? https://github.com/lfairy/hircine/blob/master/brigitte/Hackagebot.hs https://github.com/lfairy/hircine/blob/master/brigitte/Utils.hs It involves a lot of concurrency, networking, and data structure manipulation -- all areas Haskell excels in. It avoids using advanced features as well (except maybe pattern synonyms, but those aren't visible in the code that uses them) Here are some numbers: its sibling Cargobot boasts 3+ months continuous uptime, with memory usage never going beyond 12 MB. It has never crashed. I expect Hackagebot to have similar metrics. On Jul 1, 2017 06:34, "Han Joosten" <han.joosten.han(a)gmail.com> wrote: I'd like to showoff some nice Haskell code to a CTO with no experience with FP. I promised to send him a small piece of Haskell so he could get an idea. The code should be easy to read, without obscure looking operators (so sorry, no lens, arrows stuff like that), optionally even do something interesting. Who has the nicest example laying around? (and yes, I need it by yesterday ;-) ) Thanks! _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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Dynamically linking frameworks on macOS
by Ryan Trinkle 01 Jul '17

01 Jul '17

Hi everyone, I'm trying to ensure that beginner-level code that uses reflex-dom can be built by simply calling 'ghc myFile.hs', provided that all the necessary libraries are available in ghc-pkg. This works on linux, but on macOS, it's currently necessary for the user to add '-dynamic' to the command line. In particular, without -dynamic, the linker fails to find "_OBJC_CLASS_$_NSURL", which is a symbol in the Foundation system framework. Apple doesn't support (and strongly discourages) statically linked executables[1], so it's not terribly surprising that this doesn't work. Is there anything I can do to avoid the need for -dynamic here? Thanks, Ryan [1] https://developer.apple.com/library/content/qa/qa1118/_index.html

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Domain specific error diagnosis in Haskell, a proposal
by Alejandro Serrano Mena 30 Jun '17

30 Jun '17

Dear Haskellers, Some days ago Jurriaan Hage posted a video of our work on adding custom type error diagnosis to GHC. Here is a GHC proposal for incorporating this support in the mainline compiler: https://github.com/ghc-proposals/ghc-proposals/pull/59 Suggestions, criticisms and ideas are welcome. Alejandro

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Source code location in IO?
by Tom Ellis 30 Jun '17

30 Jun '17

Is it compatible with the semantics of Haskell to have a function sourceLocation :: IO String which when run returns the source file location at which it is used? For example, suppose Main.hs is module Main where main = do putStrLn =<< sourceLocation putStrLn "Hello" putStrLn =<< sourceLocation It would print the following when run Main.hs:4 Hello Main.hs:6 and module Main where main = do let s = sourceLocation putStrLn =<< s putStrLn "Hello" putStrLn =<< s It would print the following when run Main.hs:4 Hello Main.hs:4 If this is not compatible with the semantics of Haskell, why not? I agree that the two programs must have the same denotation, but is there anything that requires them to have the same output when run? Tom

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Problem with pipe/Is there a function that "lifts" functions to Producers?
by Cody Goodman 30 Jun '17

30 Jun '17

Hi all, I have a function from Text -> Text which I want to apply to each line using pipes-text and pipes-group. I'm pretty sure my pipe is not doing what I expect. I'm going back over the pipes tutorial now, but I think I could use some help figuring it out. I have the following (buildable github project: https://github.com/codygman/fixedWidthToDelimited) code: import Data.Monoid import Pipes import qualified Pipes.Text as Text import qualified Pipes.Text.IO as Text import System.IO import Lens.Family import qualified Pipes.Group as Group import qualified Data.Text as T appendAt :: Int -> T.Text -> T.Text -> (T.Text,T.Text) appendAt i appendBS bs = let (first, rest) = T.splitAt i bs in (first <> appendBS <> rest,rest) -- TODO figure out how to test a pipe (I'm sure pipes-text or any other libraries test their pipes) toDelimPipe :: Monad m => [Int] -> Pipe T.Text T.Text m r toDelimPipe offsets = do chunk <- await let text = (fixedWidthLine offsets) chunk if T.null text then (toDelimPipe offsets) else do yield text cat fixedWidthLine :: [Int] -> T.Text -> T.Text fixedWidthLine offsets bs = fst $ go offsets ("" :: T.Text,bs) where go :: [Int] -> (T.Text,T.Text) -> (T.Text,T.Text) go [] x = x go (x:xs) (acc,rest) = let (newAcc,newRest) = T.splitAt x rest in go xs (acc <> (fst $ appendAt x "|" newAcc),newRest) {- got: runEffect $ over Text.lines (Group.maps (>-> toDelimPipe [2,2,2] )) (Text.fromLazy (LT.replicate 2 "x" <> LT.replicate 2 "y" <> LT.replicate 2 "z")) >-> Text.stdout xx|||yyzz Expected: xx|yy|zz| When I use fixedWidthLine alone with the same offsets I get: λ> fixedWidthLine [2,2,2] (T.replicate 2 "x" <> T.replicate 2 "y" <> T.replicate 2 "z") "xx|yy|zz|" I think my pipe is wrong -}

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on the {lambda way}
by marty.alain 30 Jun '17

30 Jun '17

Dear Haskell-Café mailing list, Please excuse me if the Haskell-Café is not the appropriate place to post this question in but, following the advice of M. Simon Peyton Jones, I would like to know if one of you could tell me his opinion about such a work - http://lambdaway.free.fr/lambdaway/data/lambdatalk_20170615.pdf a PDF file directly printed from this wiki page - http://lambdaway.free.fr/lambdaway/?view=oxford introducing an “iconoclastic” approach detailed in long in this workshop - http://lambdaway.free.fr/ transforming a web markup syntax into a small functional programming language that an eleven years old child could understand: - http://lambdaway.free.fr/lambdaway/?view=teaching Best regards Alain Marty engineer architect

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