- Haskell-Cafe - Haskell.org

ANN: Groundhog-inspector, a tool for generating datatypes from database
by Boris Lykah 28 Dec '14

28 Dec '14

Hello everyone, I am pleased to announce groundhog-inspector. It analyzes database schema and creates corresponding datatypes and mapping configuration for Groundhog. It works with PostgreSQL, MySQL, and Sqlite. Composite keys, constraints, references across schemas, and other details of schema are reflected in the output. Groundhog-inspector can be used as a library and provides a standalone tool for simple scenarios. Here is an example of the standalone tool usage. JSON mapping in the output was manually converted to YAML for brevity. $ sqlite3 dbfile "CREATE TABLE mytable (id INTEGER PRIMARY KEY NOT NULL, str VARCHAR NOT NULL, ref INTEGER references mytable)" $ groundhog_inspector sqlite dbfile data Mytable = Mytable {mytableStr :: String, mytableRef :: (Maybe (AutoKey Mytable))} - entity: "Mytable" dbName: "mytable" constructors: - name: "Mytable" fields: - name: "mytableStr" dbName: "str" - name: "mytableRef" dbName: "ref" * [Hackage] (http://hackage.haskell.org/package/groundhog-inspector) * [GitHub] ( https://github.com/lykahb/groundhog/tree/master/groundhog-inspector/examples ) I would be happy to answer the questions. Enjoy! Regards, Boris Lykah

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ghc 7.10.1-rc1 ghc no longer supports single-file style package databases (dist/package.conf.inplace) use 'ghc-pkg init' to create the database with the correct format.
by Konstantine Rybnikov 27 Dec '14

27 Dec '14

Hi! I just did `sudo make install` on ghc 7.10.1-rc1, removed ~/.ghc and did `cabal update`. I'm now trying to upgrade to latest cabal by issuing `cabal install cabal-install`. I get the following: ``` ... on the commandline: Warning: -package-name is deprecated: Use -this-package-key instead ghc: ghc no longer supports single-file style package databases (dist/package.conf.inplace) use 'ghc-pkg init' to create the database with the correct format. Failed to install zlib-0.5.4.2 cabal: Error: some packages failed to install: HTTP-3001.0.4 depends on text-1.2.0.3 which failed to install. cabal-install-0.4.0 depends on zlib-0.5.4.2 which failed to install. mtl-2.2.1 failed during the building phase. The exception was: ExitFailure 1 network-2.6.0.2 failed during the building phase. The exception was: ExitFailure 1 parsec-3.1.7 depends on text-1.2.0.3 which failed to install. text-1.2.0.3 failed during the building phase. The exception was: ExitFailure 1 zlib-0.5.4.2 failed during the building phase. The exception was: ExitFailure 1 ``` Does anyone know a quick-fix? Thanks!

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compile ghc on Nexus 7 Android Tablet
by Cody Goodman 27 Dec '14

27 Dec '14

How would I go about this? I see a lot of stuff about compiling for android/arm, but not too much about putting ghc on an android arm tablet. Has anyone done this? I'm sure it's easier with ubuntu touch, but I'd like to try it using vanilla android. Thanks!

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Tutorials on Machines?
by gonzaw 27 Dec '14

27 Dec '14

Hi. I've been recently getting into the streaming libraries (pipes, conduit, etc), and noticed there was this talk about this "Machines" library which supposedly handles streaming too. However, I'm getting a little confused after reading its source. From what it seems, machines are a completely different beast than pipes or conduits, and I don't seem to find good guides on what exactly they are, other than a generic "a machine is a thingy that takes inputs and maybe produces some output or something". Pipes and conduits I see as constructions that only allow streaming. You put this construction in "between" a source of inputs and a consumer of outputs, and it streams from one to the other, possibly with side-effects, state, termination, etc. The thing is that the tutorials on them, and the examples that get used to show their power, make sense in this context, so you can easily grok them. But it's harder to grok Machines. I see the source and notice how you can model Moore machines, Mealy machines, Stacks, and other constructions, and all of this can be made into machines. But at the same time you can construct machines by yourself with Plans, using similar syntax used by pipes/conduit ("yield", "await"). So it confuses me, since I'm not sure what the connection between concepts like Mealy machines, and concepts like "yield"/"await" (which are also used in other streaming libraries), is. I'd like to know if there is a good tutorial on what all of these are, how they relate to each other, and allow you to easily understand all those constructions (moore/mealy machines, plans, processes, etc) and understand when you can use one or the other. Thanks. -- View this message in context: http://haskell.1045720.n5.nabble.com/Tutorials-on-Machines-tp5762883.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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FRP Tutorial
by Lucas Paul 27 Dec '14

27 Dec '14

I've been trying to get my feet wet with Functional Reactive Programming, and I'd like to play around with a library and some examples, particularly one that's already set up to work with a GUI framework like Gtk2Hs or wx. But it's been nightmarish trying to find something that works. - Grapefruit examples wouldn't compile because they were trying to import things I couldn't find in Hackage. (Codebreaker.hs, for instance) Examples using git-level stuff? - reactive-banana-wx wouldn't build because I have array-0.5 on the system level and cabal couldn't resolve dependencies. - threepenny-gui example Buttons.hs wouldn't compile (16:30: ‘jsStatic’ is not a (visible) constructor field name) Am I just having a run of bad luck, or is FRP really elusive right now for some reason? Should I just be learning some other GUI discipline if I want to write interfaces for my Haskell stuff? Sagely advice would be very much appreciated. - Lucas

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Generic "to tuple" function
by Michael Orlitzky 27 Dec '14

27 Dec '14

I have tons of code like this: from_tuple = uncurry MLBBoxScoreGameBreakdownXml to_tuple (MLBBoxScoreGameBreakdownXml a h) = (a,h) The first function, from_tuple, generalizes easily with `uncurryN` from Data.Tuple.Curry. But I'm wondering, is there any generic function that will take a simple data type and cram it into a tuple? So instead of writing, from_tuple = uncurryN MLBBoxScoreGameBreakdownTeamXml to_tuple (MLBBoxScoreGameBreakdownTeamXml w x y z) = (w,x,y,z) I could just do, from_tuple = uncurryN MLBBoxScoreGameBreakdownTeamXml to_tuple = toTupleGeneric because things get real ugly when there are ~20 fields in the data type.

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Computer Language Benchmarks Game: Mandelbrot
by Henk-Jan van Tuyl 27 Dec '14

27 Dec '14

L.S., The holidays a good time to do something about the Haskell entries for the Computer Language Benchmarks Game. I made the Mandelbrot entry[0] a bit smaller, see the attached file. I removed superfluous imports, type declarations and all bangs (except in the line "data T = T !Int !Int !Int !Double"). Both with and without bangs, there is a memory leak; in both cases, the run time is the same (tested on Windows 8.1, GHC 7.8.3). If no one knows any further improvements, I will submit my version to the Benchmarks Game. By the way, would it be a good idea to create a public (Darcs) repository for the Benchmarks Game entries? Regards, Henk-Jan van Tuyl [0] http://benchmarksgame.alioth.debian.org/u64q/program.php?test=mandelbrot&la… -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming

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Re: [Haskell-cafe] Handling Postgresql array types
by Riaan 27 Dec '14

27 Dec '14

Thank you very much. I have actually started to have a look at opaleye independently after the reddit discussion and I would like to experiment with it. I assume that I somehow have to declare my own queryRunnerColumn for the array. I am afraid that I did not understand the example so I was not able to generalise it. Date: Fri, 26 Dec 2014 11:02:12 +0000 From: Tom Ellis <tom-lists-haskell-cafe-2013(a)jaguarpaw.co.uk> To: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] Handling Postgresql array types Message-ID: <20141226110212.GJ31575@weber> Content-Type: text/plain; charset=us-ascii On Fri, Dec 26, 2014 at 10:52:46AM +0000, Tom Ellis wrote: > On Fri, Dec 26, 2014 at 02:36:07PM +1100, Riaan wrote: > > So went back to HDBC. But now my queries are starting to get fairly long > > and I have been looking at libraries like Persistent with Esqualeto, > > HaskellDB and Groundhog to make my queries a little more composable and > > type safe. > > Don't forget to look at Opaleye too :) It doesn't really have much support > for arrays at the moment, but if you let me know what you want to do I'm > happy to help you. > > > So to my question. Does anyone have experience with one of these libraries > > in dealing with postgresql arrays > > postgresql-simple has > > instance (FromField a, Typeable a) => FromField (PGArray a) > > Does that not do exactly what you want? import Database.PostgreSQL.Simple (query_, ConnectInfo(..), connect, Only) import Database.PostgreSQL.Simple.Types (PGArray) import Data.String (fromString) connectInfo :: ConnectInfo connectInfo = ConnectInfo { connectHost = "localhost" , connectPort = 25433 , connectUser = "tom" , connectPassword = "tom" , connectDatabase = "opaleye_test" } arrayQuery :: String arrayQuery = "select '{{1,2}, {3,4}}' :: integer[][]" main :: IO () main = do conn <- connect connectInfo results <- query_ conn (fromString arrayQuery) :: IO [Only (PGArray (PGArray Int))] print results -- Output -- -- ghci> main -- [Only {fromOnly = PGArray {fromPGArray = [PGArray {fromPGArray = [1,2]},PGArray {fromPGArray = [3,4]}]}}]

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ANN: hledger 0.24
by Simon Michael 25 Dec '14

25 Dec '14

Happy Christmas/Holidays/New Year all! I’m pleased to announce hledger and hledger-web 0.24. Highlights of this release include: CSV export, a non-floating point number representation, more powerful account aliases, speedups, and a streamlined web UI. Release notes: http://hledger.org/release-notes.html#hledger-0.24 Release contributors: Simon Michael, Julien Moutinho, Ryan Desfosses, Gergely Risko, Gwern. Installation: cabal install hledger[-web] or see http://hledger.org/download hledger (http://hledger.org) is a command-line tool, web app and haskell library for tracking and reporting on financial transactions, stored in a human-readable plain text format. It can also read CSV or timelog files, and export CSV. It provides useful reports and can also help you record new transactions interactively. Add-on commands include hledger-irr (for calculating internal rate of return) and hledger-interest (for generating interest transactions). hledger is inspired by and largely compatible with Ledger. I wish you a very merry, balanced and prosperous 2015. -Simon

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Building fresh cabal-install on raspberry-pi
by Konstantine Rybnikov 25 Dec '14

25 Dec '14

Hi! I just got raspberry pi and installed debian wheezy on it. It has ghc 7.4.1 with cabal 1.14.0. I tried to do cabal install cabal-install and got this: ``` In-place registering Cabal-1.20.0.3... Installing library in /home/pi/.cabal/lib/arm-linux-ghc-7.4.1/Cabal-1.20.0.3 Registering Cabal-1.20.0.3... Downloading cabal-install-1.20.0.4... Configuring cabal-install-1.20.0.4... cabal: At least the following dependencies are missing: random >=1 && <1.1 && ==1.1 cabal: Error: some packages failed to install: cabal-install-1.20.0.4 failed during the configure step. The exception was: ``` If I do `cabal list --installed | less` and search for random I see: ``` * random Synopsis: random number library Default available version: 1.1 Installed versions: 1.0.1.1, 1.1 License: BSD3 ``` Can anyone please help how do I resolve this and similar problems? Thanks!

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is gldrawingarea an instance of widgetclass
by briand＠aracnet.com 24 Dec '14

24 Dec '14

I get this : No instance for (Gtk.WidgetClass GtkGL.GLDrawingArea) arising from a use of `Gtk.boxPackStart' in code that was compiling at one point. This is how I'm importing import qualified Graphics.UI.Gtk.OpenGL as GtkGL then glCanvas <- GtkGL.glDrawingAreaNew glconfig and use it thusly: Gtk.boxPackStart hBox1 glCanvas Gtk.PackNatural 0 boxPackStart wants something WidgetClass, and GLDrawingArea seems to be an instance of widget class. The gtkglext hasn't been touched in quite a while. I'm wondering if it's become out of date with the latest gtk. ?? Thanks, Brian

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How best to deal with Monoid/Applicative changes in 7.10 in a backwards-compatable way
by Doug Burke 24 Dec '14

24 Dec '14

I'm trying out the ghc 7.10 RC and am seeing lots of warnings about Monoid and some symbols from Control.Applicative - e.g. The import of ‘Data.Monoid’ is redundant except perhaps to import instances from ‘Data.Monoid’ To import instances alone, use: import Data.Monoid() For now I'm wrapping the import with some CPP so that it will still compile with older ghc versions (and a probably-pointless attempt to be non-ghc-specific, since I have never tested my code with other compilers): #if (!defined(__GLASGOW_HASKELL__)) || (__GLASGOW_HASKELL__ < 710) import Control.Applicative (Applicative(pure), (<$>), (<*>)) import Data.Monoid (Monoid(..)) #else import Control.Applicative ((<$>)) #endif Is this the best way? Am I missing something really obvious? Thanks, Doug

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Re: [Haskell-cafe] HPC and Template Haskell (GHC 7.8.3, Yesod)
by David Turner 24 Dec '14

24 Dec '14

Ok, I can reproduce this with a bare Yesod scaffold (using the latest cabal-install) - see below. If I run cabal build a couple more times, it completes successfully, which is mighty strange! [linuxadmin@vm01 20:19:43 ~ ] $ yesod init Welcome to the Yesod scaffolder. I'm going to be creating a skeleton Yesod project for you. What do you want to call your project? We'll use this for the cabal name. Project name: linker-test Yesod uses Persistent for its (you guessed it) persistence layer. This tool will build in either SQLite or PostgreSQL or MongoDB support for you. We recommend starting with SQLite: it has no dependencies. s = sqlite p = postgresql pf = postgresql + Fay (experimental) mongo = mongodb mysql = MySQL simple = no database, no auth url = Let me specify URL containing a site (advanced) So, what'll it be? simple That's it! I'm creating your files now... --------------------------------------- ___ {-) |\ [m,].-"-. / [][__][__] $/\__/$/ [__][__][__][__]~~~~ | | [][__][__][__][__][] / | [__][__][__][__][__]| /| | [][__][__][__][__][]| || | ~~~~ ejm [__][__][__][__][__]__,__, \__/ --------------------------------------- The foundation for your web application has been built. There are a lot of resources to help you use Yesod. Start with the book: http://www.yesodweb.com/book Take part in the community: http://yesodweb.com/page/community It's highly recommended to follow the quick start guide for installing Yesod: http://www.yesodweb.com/page/quickstart If your system is already configured correctly, please run: cd linker-test && cabal install -j --enable-tests --max-backjumps=-1 --reorder-goals && yesod devel [linuxadmin@vm01 20:20:07 ~ ] $ cd linker-test [linuxadmin@vm01 20:20:11 ~/linker-test ] $ ~/cabal/cabal-install/.cabal-sandbox/bin/cabal configure --disable-tests --enable-coverage --disable-profiling Resolving dependencies... Configuring linker-test-0.0.0... [linuxadmin@vm01 20:20:25 ~/linker-test ] $ ~/cabal/cabal-install/.cabal-sandbox/bin/cabal build Building linker-test-0.0.0... Preprocessing library linker-test-0.0.0... [1 of 7] Compiling Settings.Development ( Settings/Development.hs, dist/build/Settings/Development.o ) [2 of 7] Compiling Settings ( Settings.hs, dist/build/Settings.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package array-0.5.0.0 ... linking ... done. Loading package stm-2.4.3 ... linking ... done. Loading package async-2.0.1.6 ... linking ... done. Loading package deepseq-1.3.0.2 ... linking ... done. Loading package bytestring-0.10.4.0 ... linking ... done. Loading package containers-0.5.5.1 ... linking ... done. Loading package text-1.1.1.3 ... linking ... done. Loading package hashable-1.2.2.0 ... linking ... done. Loading package scientific-0.3.3.2 ... linking ... done. Loading package attoparsec-0.12.1.2 ... linking ... done. Loading package base64-bytestring-1.0.0.1 ... linking ... done. Loading package blaze-builder-0.3.3.4 ... linking ... done. Loading package byteable-0.1.1 ... linking ... done. Loading package transformers-0.3.0.0 ... linking ... done. Loading package mtl-2.1.3.1 ... linking ... done. Loading package exceptions-0.6.1 ... linking ... done. Loading package base-unicode-symbols-0.2.2.4 ... linking ... done. Loading package transformers-base-0.4.3 ... linking ... done. Loading package monad-control-0.3.3.0 ... linking ... done. Loading package lifted-base-0.2.2.1 ... linking ... done. Loading package mmorph-1.0.4 ... linking ... done. Loading package resourcet-1.1.3 ... linking ... done. Loading package nats-0.2 ... linking ... done. Loading package unordered-containers-0.2.5.1 ... linking ... done. Loading package semigroups-0.15.4 ... linking ... done. Loading package void-0.6.1 ... linking ... done. Loading package conduit-1.2.3 ... linking ... done. Loading package filepath-1.3.0.2 ... linking ... done. Loading package old-locale-1.0.0.6 ... linking ... done. Loading package time-1.4.2 ... linking ... done. Loading package unix-2.7.0.1 ... linking ... done. Loading package directory-1.2.1.0 ... linking ... done. Loading package parsec-3.1.7 ... linking ... done. Loading package network-2.5.0.0 ... linking ... done. Loading package primitive-0.5.4.0 ... linking ... done. Loading package process-1.2.0.0 ... linking ... done. Loading package random-1.0.1.1 ... linking ... done. Loading package zlib-0.5.4.2 ... linking ... done. Loading package streaming-commons-0.1.6 ... linking ... done. Loading package conduit-extra-1.1.4.2 ... linking ... done. Loading package cryptohash-0.11.6 ... linking ... done. Loading package cryptohash-conduit-0.1.1 ... linking ... done. Loading package css-text-0.1.2.1 ... linking ... done. Loading package data-default-class-0.0.1 ... linking ... done. Loading package data-default-instances-base-0.0.1 ... linking ... done. Loading package data-default-instances-containers-0.0.1 ... linking ... done. Loading package dlist-0.7.1 ... linking ... done. Loading package data-default-instances-dlist-0.0.1 ... linking ... done. Loading package data-default-instances-old-locale-0.0.1 ... linking ... done. Loading package data-default-0.5.3 ... linking ... done. Loading package pretty-1.1.1.1 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package file-embed-0.0.7 ... linking ... done. Loading package utf8-string-0.3.8 ... linking ... done. Loading package language-javascript-0.5.13 ... linking ... done. Loading package hjsmin-0.1.4.7 ... linking ... done. Loading package case-insensitive-1.2.0.1 ... linking ... done. Loading package http-types-0.8.5 ... linking ... done. Loading package mime-types-0.1.0.4 ... linking ... done. Loading package old-time-1.1.0.2 ... linking ... done. Loading package system-filepath-0.4.12 ... linking ... done. Loading package system-fileio-0.3.15 ... linking ... done. Loading package unix-compat-0.4.1.3 ... linking ... done. Loading package vault-0.3.0.3 ... linking ... done. Loading package wai-3.0.2 ... linking ... done. Loading package blaze-markup-0.6.1.1 ... linking ... done. Loading package blaze-html-0.7.0.3 ... linking ... done. Loading package http-date-0.0.4 ... linking ... done. Loading package ansi-terminal-0.6.2.1 ... linking ... done. Loading package ansi-wl-pprint-0.6.7.1 ... linking ... done. Loading package transformers-compat-0.3.3.3 ... linking ... done. Loading package optparse-applicative-0.11.0.1 ... linking ... done. Loading package auto-update-0.1.2 ... linking ... done. Loading package fast-logger-2.2.3 ... linking ... done. Loading package stringsearch-0.3.6.5 ... linking ... done. Loading package byteorder-1.0.4 ... linking ... done. Loading package easy-file-0.2.0 ... linking ... done. Loading package binary-0.7.1.0 ... linking ... done. Loading package unix-time-0.3.4 ... linking ... done. Loading package wai-logger-2.2.3 ... linking ... done. Loading package word8-0.1.1 ... linking ... done. Loading package wai-extra-3.0.2.1 ... linking ... done. Loading package simple-sendfile-0.2.18 ... linking ... done. Loading package warp-3.0.2.3 ... linking ... done. Loading package wai-app-static-3.0.0.3 ... linking ... done. Loading package syb-0.4.2 ... linking ... done. Loading package vector-0.10.12.1 ... linking ... done. Loading package aeson-0.8.0.2 ... linking ... done. Loading package cereal-0.4.1.0 ... linking ... done. Loading package securemem-0.1.4 ... linking ... done. Loading package crypto-cipher-types-0.0.9 ... linking ... done. Loading package cipher-aes-0.2.9 ... linking ... done. Loading package crypto-random-0.0.8 ... linking ... done. Loading package cprng-aes-0.6.1 ... linking ... done. Loading package entropy-0.3.4.1 ... linking ... done. Loading package tagged-0.7.3 ... linking ... done. Loading package crypto-api-0.13.2 ... linking ... done. Loading package setenv-0.1.1.1 ... linking ... done. Loading package skein-1.0.9.1 ... linking ... done. Loading package clientsession-0.9.1.1 ... linking ... done. Loading package cookie-0.4.1.4 ... linking ... done. Loading package monad-loops-0.4.2.1 ... linking ... done. Loading package stm-chans-3.0.0.2 ... linking ... done. Loading package monad-logger-0.3.9 ... linking ... done. Loading package mwc-random-0.13.2.2 ... linking ... done. Loading package path-pieces-0.1.4 ... linking ... done. Loading package safe-0.3.8 ... linking ... done. Loading package shakespeare-2.0.2.1 ... linking ... done. Loading package yesod-core-1.4.4.5 ... linking ... done. Loading package yesod-static-1.4.0.3 ... linking ... done. Loading package yaml-0.8.10 ... linking ... done. Loading package publicsuffixlist-0.1 ... linking ... done. Loading package http-client-0.4.5 ... linking ... done. Loading package socks-0.5.4 ... linking ... done. Loading package hourglass-0.2.6 ... linking ... done. Loading package asn1-types-0.3.0 ... linking ... done. Loading package asn1-encoding-0.9.0 ... linking ... done. Loading package cipher-des-0.0.6 ... linking ... done. Loading package cipher-rc4-0.1.4 ... linking ... done. Loading package crypto-numbers-0.2.3 ... linking ... done. Loading package crypto-pubkey-types-0.4.2.3 ... linking ... done. Loading package crypto-pubkey-0.2.4 ... linking ... done. Loading package asn1-parse-0.9.0 ... linking ... done. Loading package pem-0.2.2 ... linking ... done. Loading package x509-1.5.0.1 ... linking ... done. Loading package x509-store-1.5.0 ... linking ... done. Loading package x509-validation-1.5.1 ... linking ... done. Loading package tls-1.2.13 ... linking ... done. Loading package x509-system-1.5.0 ... linking ... done. Loading package connection-0.2.3 ... linking ... done. Loading package http-client-tls-0.2.2 ... linking ... done. Loading package http-conduit-2.1.5 ... linking ... done. Loading package xml-types-0.3.4 ... linking ... done. Loading package xml-conduit-1.2.3 ... linking ... done. Loading package tagstream-conduit-0.5.5.3 ... linking ... done. Loading package authenticate-1.3.2.10 ... linking ... done. Loading package base16-bytestring-0.1.1.6 ... linking ... done. Loading package email-validate-2.0.1 ... linking ... done. Loading package mime-mail-0.4.6 ... linking ... done. Loading package resource-pool-0.2.3.1 ... linking ... done. Loading package silently-1.2.4.1 ... linking ... done. Loading package persistent-2.1.1 ... linking ... done. Loading package persistent-template-2.1 ... linking ... done. Loading package tagsoup-0.13.3 ... linking ... done. Loading package xss-sanitize-0.3.5.4 ... linking ... done. Loading package yesod-persistent-1.4.0.1 ... linking ... done. Loading package yesod-form-1.4.1.1 ... linking ... done. Loading package yesod-auth-1.4.1 ... linking ... done. Loading package yesod-1.4.1 ... linking ... done. [3 of 7] Compiling Settings.StaticFiles ( Settings/StaticFiles.hs, dist/build/Settings/StaticFiles.o ) [4 of 7] Compiling Foundation ( Foundation.hs, dist/build/Foundation.o ) [5 of 7] Compiling Import ( Import.hs, dist/build/Import.o ) [6 of 7] Compiling Handler.Home ( Handler/Home.hs, dist/build/Handler/Home.o ) [7 of 7] Compiling Application ( Application.hs, dist/build/Application.o ) /usr/bin/ld: dist/build/Foundation.dyn_o: relocation R_X86_64_PC32 against undefined symbol `_hpc_tickboxes_linkerzmtestzm0zi0zi0_Settings_hpc' can not be used when making a shared object; recompile with -fPIC /usr/bin/ld: final link failed: Bad value collect2: error: ld returned 1 exit status <no location info>: ghc: phase `Linker' failed (exitcode = 1) [linuxadmin@vm01 20:20:38 ~/linker-test ] $ On 19 December 2014 at 20:21, David Turner <dave.c.turner(a)gmail.com> wrote: > Ok, I can reproduce this with a bare Yesod scaffold: > > [linuxadmin@vm01 20:19:43 ~ ] > $ yesod init > Welcome to the Yesod scaffolder. > I'm going to be creating a skeleton Yesod project for you. > > What do you want to call your project? We'll use this for the cabal name. > > Project name: linker-test > Yesod uses Persistent for its (you guessed it) persistence layer. > This tool will build in either SQLite or PostgreSQL or MongoDB support for you. > We recommend starting with SQLite: it has no dependencies. > > s = sqlite > p = postgresql > pf = postgresql + Fay (experimental) > mongo = mongodb > mysql = MySQL > simple = no database, no auth > url = Let me specify URL containing a site (advanced) > > So, what'll it be? simple > That's it! I'm creating your files now... > > --------------------------------------- > > ___ > {-) |\ > [m,].-"-. / > [][__][__] $/\__/$/ > [__][__][__][__]~~~~ | | > [][__][__][__][__][] / | > [__][__][__][__][__]| /| | > [][__][__][__][__][]| || | ~~~~ > ejm [__][__][__][__][__]__,__, \__/ > > > --------------------------------------- > > The foundation for your web application has been built. > > > There are a lot of resources to help you use Yesod. > Start with the book: http://www.yesodweb.com/book > Take part in the community: http://yesodweb.com/page/community > > > It's highly recommended to follow the quick start guide for > installing Yesod: http://www.yesodweb.com/page/quickstart > > If your system is already configured correctly, please run: > > cd linker-test && cabal install -j --enable-tests > --max-backjumps=-1 --reorder-goals && yesod devel > [linuxadmin@vm01 20:20:07 ~ ] > $ cd linker-test > [linuxadmin@vm01 20:20:11 ~/linker-test ] > $ ~/cabal/cabal-install/.cabal-sandbox/bin/cabal configure > --disable-tests --enable-coverage --disable-profiling > Resolving dependencies... > Configuring linker-test-0.0.0... > [linuxadmin@vm01 20:20:25 ~/linker-test ] > $ ~/cabal/cabal-install/.cabal-sandbox/bin/cabal build > Building linker-test-0.0.0... > Preprocessing library linker-test-0.0.0... > [1 of 7] Compiling Settings.Development ( Settings/Development.hs, > dist/build/Settings/Development.o ) > [2 of 7] Compiling Settings ( Settings.hs, dist/build/Settings.o ) > Loading package ghc-prim ... linking ... done. > Loading package integer-gmp ... linking ... done. > Loading package base ... linking ... done. > Loading package array-0.5.0.0 ... linking ... done. > Loading package stm-2.4.3 ... linking ... done. > Loading package async-2.0.1.6 ... linking ... done. > Loading package deepseq-1.3.0.2 ... linking ... done. > Loading package bytestring-0.10.4.0 ... linking ... done. > Loading package containers-0.5.5.1 ... linking ... done. > Loading package text-1.1.1.3 ... linking ... done. > Loading package hashable-1.2.2.0 ... linking ... done. > Loading package scientific-0.3.3.2 ... linking ... done. > Loading package attoparsec-0.12.1.2 ... linking ... done. > Loading package base64-bytestring-1.0.0.1 ... linking ... done. > Loading package blaze-builder-0.3.3.4 ... linking ... done. > Loading package byteable-0.1.1 ... linking ... done. > Loading package transformers-0.3.0.0 ... linking ... done. > Loading package mtl-2.1.3.1 ... linking ... done. > Loading package exceptions-0.6.1 ... linking ... done. > Loading package base-unicode-symbols-0.2.2.4 ... linking ... done. > Loading package transformers-base-0.4.3 ... linking ... done. > Loading package monad-control-0.3.3.0 ... linking ... done. > Loading package lifted-base-0.2.2.1 ... linking ... done. > Loading package mmorph-1.0.4 ... linking ... done. > Loading package resourcet-1.1.3 ... linking ... done. > Loading package nats-0.2 ... linking ... 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cryptohash-0.11.6 ... linking ... done. > Loading package cryptohash-conduit-0.1.1 ... linking ... done. > Loading package css-text-0.1.2.1 ... linking ... done. > Loading package data-default-class-0.0.1 ... linking ... done. > Loading package data-default-instances-base-0.0.1 ... linking ... done. > Loading package data-default-instances-containers-0.0.1 ... linking ... done. > Loading package dlist-0.7.1 ... linking ... done. > Loading package data-default-instances-dlist-0.0.1 ... linking ... done. > Loading package data-default-instances-old-locale-0.0.1 ... linking ... done. > Loading package data-default-0.5.3 ... linking ... done. > Loading package pretty-1.1.1.1 ... linking ... done. > Loading package template-haskell ... linking ... done. > Loading package file-embed-0.0.7 ... linking ... done. > Loading package utf8-string-0.3.8 ... linking ... done. > Loading package language-javascript-0.5.13 ... linking ... done. > Loading package hjsmin-0.1.4.7 ... linking ... done. > 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crypto-cipher-types-0.0.9 ... linking ... done. > Loading package cipher-aes-0.2.9 ... linking ... done. > Loading package crypto-random-0.0.8 ... linking ... done. > Loading package cprng-aes-0.6.1 ... linking ... done. > Loading package entropy-0.3.4.1 ... linking ... done. > Loading package tagged-0.7.3 ... linking ... done. > Loading package crypto-api-0.13.2 ... linking ... done. > Loading package setenv-0.1.1.1 ... linking ... done. > Loading package skein-1.0.9.1 ... linking ... done. > Loading package clientsession-0.9.1.1 ... linking ... done. > Loading package cookie-0.4.1.4 ... linking ... done. > Loading package monad-loops-0.4.2.1 ... linking ... done. > Loading package stm-chans-3.0.0.2 ... linking ... done. > Loading package monad-logger-0.3.9 ... linking ... done. > Loading package mwc-random-0.13.2.2 ... linking ... done. > Loading package path-pieces-0.1.4 ... linking ... done. > Loading package safe-0.3.8 ... linking ... done. > Loading package shakespeare-2.0.2.1 ... linking ... done. > Loading package yesod-core-1.4.4.5 ... linking ... done. > Loading package yesod-static-1.4.0.3 ... linking ... done. > Loading package yaml-0.8.10 ... linking ... done. > Loading package publicsuffixlist-0.1 ... linking ... done. > Loading package http-client-0.4.5 ... linking ... done. > Loading package socks-0.5.4 ... linking ... done. > Loading package hourglass-0.2.6 ... linking ... done. > Loading package asn1-types-0.3.0 ... linking ... done. > Loading package asn1-encoding-0.9.0 ... linking ... done. > Loading package cipher-des-0.0.6 ... linking ... done. > Loading package cipher-rc4-0.1.4 ... linking ... done. > Loading package crypto-numbers-0.2.3 ... linking ... done. > Loading package crypto-pubkey-types-0.4.2.3 ... linking ... done. > Loading package crypto-pubkey-0.2.4 ... linking ... done. > Loading package asn1-parse-0.9.0 ... linking ... done. > Loading package pem-0.2.2 ... linking ... done. > Loading package x509-1.5.0.1 ... linking ... done. > Loading package x509-store-1.5.0 ... linking ... done. > Loading package x509-validation-1.5.1 ... linking ... done. > Loading package tls-1.2.13 ... linking ... done. > Loading package x509-system-1.5.0 ... linking ... done. > Loading package connection-0.2.3 ... linking ... done. > Loading package http-client-tls-0.2.2 ... linking ... done. > Loading package http-conduit-2.1.5 ... linking ... done. > Loading package xml-types-0.3.4 ... linking ... done. > Loading package xml-conduit-1.2.3 ... linking ... done. > Loading package tagstream-conduit-0.5.5.3 ... linking ... done. > Loading package authenticate-1.3.2.10 ... linking ... done. > Loading package base16-bytestring-0.1.1.6 ... linking ... done. > Loading package email-validate-2.0.1 ... linking ... done. > Loading package mime-mail-0.4.6 ... linking ... done. > Loading package resource-pool-0.2.3.1 ... linking ... done. > Loading package silently-1.2.4.1 ... linking ... done. > Loading package persistent-2.1.1 ... linking ... done. > Loading package persistent-template-2.1 ... linking ... done. > Loading package tagsoup-0.13.3 ... linking ... done. > Loading package xss-sanitize-0.3.5.4 ... linking ... done. > Loading package yesod-persistent-1.4.0.1 ... linking ... done. > Loading package yesod-form-1.4.1.1 ... linking ... done. > Loading package yesod-auth-1.4.1 ... linking ... done. > Loading package yesod-1.4.1 ... linking ... done. > [3 of 7] Compiling Settings.StaticFiles ( Settings/StaticFiles.hs, > dist/build/Settings/StaticFiles.o ) > [4 of 7] Compiling Foundation ( Foundation.hs, dist/build/Foundation.o ) > [5 of 7] Compiling Import ( Import.hs, dist/build/Import.o ) > [6 of 7] Compiling Handler.Home ( Handler/Home.hs, > dist/build/Handler/Home.o ) > [7 of 7] Compiling Application ( Application.hs, dist/build/Application.o ) > /usr/bin/ld: dist/build/Foundation.dyn_o: relocation R_X86_64_PC32 > against undefined symbol > `_hpc_tickboxes_linkerzmtestzm0zi0zi0_Settings_hpc' can not be used > when making a shared object; recompile with -fPIC > /usr/bin/ld: final link failed: Bad value > collect2: error: ld returned 1 exit status > > <no location info>: ghc: phase `Linker' failed (exitcode = 1) > [linuxadmin@vm01 20:20:38 ~/linker-test ] > $ > > On 19 December 2014 at 20:03, David Turner > <dct25-561bs(a)mythic-beasts.com> wrote: >> [Failed to copy haskell-cafe in to my first response:] >> >> I thought I had disabled profiling there, although it was enabled when >> I was using cabal which wrote the original command line so that might >> explain it. >> >> I will try a more recent cabal-install this evening. >> >> Thanks for the speedy response! >> >> [Time passes - second response:] >> >> I have tried cabal-install build from the latest revision (4aabb4f4b1) >> with the same result. From a clean checkout of my source: >> >> $ ~/cabal/cabal-install/.cabal-sandbox/bin/cabal configure >> --disable-tests --enable-coverage --disable-profiling >> $ ~/cabal/cabal-install/.cabal-sandbox/bin/cabal build -v >> >> Similar outcome. >> >> >> >> >> On 19 December 2014 at 18:53, Carter Schonwald >> <carter.schonwald(a)gmail.com> wrote: >>> i think the fix for this, or a related problem is merged into >>> cabal/cabal-install head, and will be in 1.22 >>> >>> does your problem go away if you dont enable profiled builds? (is so, its >>> likely the same problem) >>> >>> On Fri, Dec 19, 2014 at 1:32 PM, David Turner >>> <dct25-561bs(a)mythic-beasts.com> wrote: >>>> >>>> Hi, >>>> >>>> I'm having trouble making a HPC build of a Yesod application. It fails >>>> with: >>>> >>>> /usr/bin/ld: dist/build/StreamReading/Config.dyn_o: relocation >>>> R_X86_64_PC32 against undefined symbol >>>> `_hpc_tickboxes_tracszmenterprisezm0zi0zi0_Settings_hpc' can not be >>>> used when making a shared object; recompile with -fPIC >>>> >>>> I've narrowed it down to a call to ghc and posted the output in all >>>> its gory detail at http://lpaste.net/116872 if that's any help. >>>> >>>> Of note is that dist/build/Settings.dyn_o is unexpectedly missing from >>>> the list of parameters to the last call to gcc, and the missing symbol >>>> is defined in the same. There are, in fact, quite a number of missing >>>> .dyn_o files in that list. >>>> >>>> Slightly weirdly, when I run the same command line again, it seems to >>>> work. At least, there are no errors reported and the exit code is 0. >>>> >>>> Any ideas? >>>> >>>> Cheers, >>>> >>>> David >>>> _______________________________________________ >>>> Haskell-Cafe mailing list >>>> Haskell-Cafe(a)haskell.org >>>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >>>

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Weird reachability issue with haskell.org my my Italian ISP (fastweb)
by Alfredo Di Napoli 23 Dec '14

23 Dec '14

Hello Cafè, let me start with the email I've sent to Rackspace, which will help you understand the context: Hi there! > I'm trying to understand how come I can't reach www.haskell.org from my ISP > here in Italy (fastweb). In order to troubleshoot the issue, I tried dig on > it, revealing it's hosted by you: > > dig haskell.org > > ; <<>> DiG 9.8.3-P1 <<>> haskell.org > ;; global options: +cmd > ;; Got answer: > ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 63629 > ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 > ;; QUESTION SECTION: > ;haskell.org.INA > ;; ANSWER SECTION: > haskell.org. 299 IN A 23.253.242.70 > ;; Query time: 139 msec > ;; SERVER: 8.8.8.8#53(8.8.8.8) > ;; WHEN: Tue Dec 23 18:33:00 2014 > ;; MSG SIZE rcvd: 45 > > Trying a whois reveals the subnet is the entire 23.253.0.0 one: > > Rackspace Cloud Servers RACKS-8-1387376775861482 (NET-23-253-80-0-1) > 23.253.80.0 - 23.253.95.255 > Rackspace Hosting RACKS-8-NET-15 (NET-23-253-0-0-1) 23.253.0.0 - > 23.253.255.25 > > If I try to ping the IP directly, it obviously doesn't work, so I have > tried contiguous IP addresses in the same subnet to see if the subnet > itself was reachable at all.. trying 23.253.89.73 indeed worked! It > resolved to > http://www.papamurphys.com/ > This means my ISP can reach that subnet, but doesn't explain why it can't > connect to 23.253.242.70. That's very weird indeed, as every other website is reachable, only haskell.org is not! How funny my fate is! I'm one of the few Haskellers in Italy and yet I cannot access the website.. perhaps is the consequence of "Avoid success at all costs"?? :) :) Jokes aside, do you guys know (I'm asking mainly to Austin here) if rackspace uses some weird setup for their website deployment or if haskell.org is hosted "the usual way" and listening on port 80? Thanks in advance for the 1% who is concerned, for all the other 99%, merry Xmas ;) Alfredo

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Allocating a new ByteString
by Tristan Seligmann 23 Dec '14

23 Dec '14

I'm calling a function by FFI that returns two strings by writing into output buffers that you provide. The code I currently have looks like this (minus some error handling): > import qualified Data.ByteString as S > import qualified Data.ByteString.Unsafe as SU > > import Foreign.C (CChar, CInt(..), CSize(..)) > import Foreign.ForeignPtr (mallocForeignPtrBytes, withForeignPtr) > import Foreign.Ptr (Ptr) > import System.IO.Unsafe (unsafePerformIO) > > seed_keypair :: S.ByteString -> (S.ByteString, S.ByteString) > seed_keypair seed | S.length seed /= signSeed = error "seed has incorrect length" > | otherwise = unsafePerformIO $ do > pk <- mallocForeignPtrBytes signPK > sk <- mallocForeignPtrBytes signSK > SU.unsafeUseAsCString seed $ \pseed -> > withForeignPtr pk $ \ppk -> > withForeignPtr sk $ \psk -> do > 0 <- c_sign_seed_keypair ppk psk pseed > bpk <- S.packCStringLen (ppk, signPK) > bsk <- S.packCStringLen (psk, signSK) > return (bpk, bsk) > > foreign import ccall "crypto_sign_seed_keypair" > c_sign_seed_keypair :: Ptr CChar -> Ptr CChar -> Ptr CChar -> IO CInt However, this needlessly makes a copy of the output buffers to create the final result. What I really want to do is just write the string directly into a buffer allocated and used by a new ByteString; is there some way to accomplish this? (Any other comments about what I'm doing would also be appreciated, this happens to be my first attempt at using FFI!) -- mithrandi, i Ainil en-Balandor, a faer Ambar

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Latest Template Haskell Breaks Package
by Dominic Steinitz 23 Dec '14

23 Dec '14

Hello Fellow Haskellers, I have become a maintainer for yarr (https://hackage.haskell.org/package/yarr) This no longer compiles with ghc-7.8.3 because it specifies base == 4.6. Relaxing this to base >=4.6 && <4.8 tells me I need a newer version of Template Haskell > rejecting: template-haskell-2.7.0.0, 2.6.0.0, 2.5.0.0, 2.4.0.1, 2.4.0.0, > 2.3.0.1, 2.3.0.0, 2.2.0.0 (conflict: yarr => template-haskell>=2.8 && <2.9) If I now relax the constraint for Template Haskell I get a compiler error as there has been a breaking change from Template Haskell 2.9 to 2.10. > Data/Yarr/Utils/FixedVector/VecTuple.hs:45:16: > Couldn't match expected type ‘TypeQ -> Q Dec’ > with actual type ‘Q Dec’ > The function ‘tySynInstD’ is applied to three arguments, > but its type ‘Name -> TySynEqnQ -> DecQ’ has only two And indeed looking at the changes in http://git.haskell.org/packages/template-haskell.git/commitdiff/ccd7891c536… I can see that the function in question has changed. > -tySynInstD :: Name -> [TypeQ] -> TypeQ -> DecQ > -tySynInstD tc tys rhs = > +tySynInstD :: Name -> [TySynEqnQ] -> DecQ > +tySynInstD tc eqns = Did I miss some announcement of this breaking change and the advice on what to do about it? If I did can someone please point me at the relevant document. If not then I feel sad and would be very grateful if someone could help me as I know very little about Template Haskell. Many thanks Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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ANNOUNCE: GHC version 7.8.4
by Austin Seipp 23 Dec '14

23 Dec '14

============================================================== The (Interactive) Glasgow Haskell Compiler -- version 7.8.4 ============================================================== The GHC Team is pleased to announce a new patchlevel release of GHC, 7.8.4. This is an important bugfix release relative to 7.8.3 (with over 30 defects fixed), so we highly recommend upgrading from the previous 7.8 releases. The full release notes are here: https://downloads.haskell.org/~ghc/7.8.4/docs/html/users_guide/release-7-8-… How to get it ~~~~~~~~~~~~~ The easy way is to go to the web page, which should be self-explanatory: https://www.haskell.org/ghc/ We supply binary builds in the native package format for many platforms, and the source distribution is available from the same place. Packages will appear as they are built - if the package for your system isn't available yet, please try again later. Background ~~~~~~~~~~ Haskell is a standard lazy functional programming language. GHC is a state-of-the-art programming suite for Haskell. Included is an optimising compiler generating good code for a variety of platforms, together with an interactive system for convenient, quick development. The distribution includes space and time profiling facilities, a large collection of libraries, and support for various language extensions, including concurrency, exceptions, and foreign language interfaces (C, whatever). GHC is distributed under a BSD-style open source license. A wide variety of Haskell related resources (tutorials, libraries, specifications, documentation, compilers, interpreters, references, contact information, links to research groups) are available from the Haskell home page (see below). On-line GHC-related resources ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Relevant URLs on the World-Wide Web: GHC home page http://www.haskell.org/ghc/ GHC developers' home page http://ghc.haskell.org/trac/ghc/ Haskell home page http://www.haskell.org/ Supported Platforms ~~~~~~~~~~~~~~~~~~~ The list of platforms we support, and the people responsible for them, is here: http://ghc.haskell.org/trac/ghc/wiki/Platforms http://ghc.haskell.org/trac/ghc/wiki/CodeOwners Ports to other platforms are possible with varying degrees of difficulty. The Building Guide describes how to go about porting to a new platform: http://ghc.haskell.org/trac/ghc/wiki/Building Developers ~~~~~~~~~~ We welcome new contributors. Instructions on accessing our source code repository, and getting started with hacking on GHC, are available from the GHC's developer's site run by Trac: http://ghc.haskell.org/trac/ghc/ Mailing lists ~~~~~~~~~~~~~ We run mailing lists for GHC users and bug reports; to subscribe, use the web interfaces at http://www.haskell.org/mailman/listinfo/glasgow-haskell-users http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs There are several other haskell and ghc-related mailing lists on www.haskell.org; for the full list, see http://www.haskell.org/mailman/listinfo/ Some GHC developers hang out on #haskell on IRC, too: http://www.haskell.org/haskellwiki/IRC_channel Please report bugs using our bug tracking system. Instructions on reporting bugs can be found here: http://www.haskell.org/ghc/reportabug Hashes & Signatures ~~~~~~~~~~~~~~~~~ On https://downloads.haskell.org/~ghc/7.8.4/ you will find a signed copy of the SHA256 hashes for the tarballs, using my GPG key (keyid 0x3B58D86F). -- Regards, Austin Seipp, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/

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ANN: New FP meetup group in the Switzerland Romandie area
by Alois Cochard 23 Dec '14

23 Dec '14

Hey haskellers, I just wanted to let you know that I have created a new "Functional Romandie" meetup group: http://www.meetup.com/Functional-Romandie/ The aim is to gather as many as possible FP enthusiast in the area (not specific to given programming language). If you are interested please get in touch or join the meetup group! Cheers -- *Λ\ois* http://twitter.com/aloiscochard http://github.com/aloiscochard

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Cabal Config constraints vs. constraint
by Christopher Reichert 22 Dec '14

22 Dec '14

Hey everyone, I am trying to add a list of version constraints to my global cabal config (~/.cabal/config) using the `constraints` keyword. However, after adding the list to the end of the ~/.cabal/config file and running `cabal update`, I noticed this warning: $ cabal update Warning: /home/test/.cabal/config: Unrecognized field constraints on line 176 Downloading the latest package list from hackage.haskell.org I did find this issue annotated as a FIXME in the cabal source: https://github.com/haskell/cabal/blob/64761550bb617ee5d9449512bd3e500489cfd… It appears as though `constraints` are currently only supported in cabal.config (and maybe cabal.sandbox.config) Do individual constraints (e.g. `constraint:`) have the same effect as a list of constraints? Does the `constraint` setting work in both global (~/.cabal/config) and local cabal.config the exact same way (especially if I have a long list of them) Is there any reason I would use individual constraints over a list of constraints? My assumption is that they work the same way in both ~/.cabal/config && cabal.config. I'm considering patching the cabal source to support the `constraints` setting in the ~/.cabal/config file. Is there any reason this might have been passed up front? More discussion here: https://github.com/fpco/stackage-server/issues/67 Any help or advice would be greatly appreciated. Thanks, -Christopher -- Christopher Reichert irc: creichert gpg: C81D 18C8 862A 3618 1376 FFA5 6BFC A992 9955 929B

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Could someone help me to understand funB?
by Magicloud Magiclouds 22 Dec '14

22 Dec '14

Hi, Following code is to get a list of primes. Now it is hard for me to understand funB. I mean I can see what it does. But I cannot see the detailed process by every language part. import Control.Monad isPrime :: Integer -> Bool isPrime i = ap funA funB i funA :: Integer -> [Integer] -> Bool funA x xs = all (\x' -> (mod x x') /= 0) xs funB :: Integer -> [Integer] funB = flip takeWhile primes . ( . join (*)) . flip (<=) primes :: [Integer] primes = 2 : filter isPrime [3, 5 ..] main :: IO () main = print $ take 10 primes -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

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Template haskell: This pattern-binding binds no variables
by Michael Baikov 21 Dec '14

21 Dec '14

I'm trying to introduce a new local variable to some scope, in this example this scope is represented by print $( varE ohNoes) Everything works as expected, but I'm getting a warning message which I don't seem quite right to me. Am I doing anything wrong? ---- Blah.hs ---- {-# LANGUAGE TemplateHaskell #-} module Blah where import Language.Haskell.TH sample :: Q Exp sample = newName "ohNoes" >>= \ohNoes -> [| let $( varP ohNoes ) = "Teh warning!" in print $( varE ohNoes ) |] ---- Main.hs ---- {-# LANGUAGE TemplateHaskell #-} module Main where import Blah main :: IO () main = $( sample ) ---- output ---- Blah.hs:8:49: Warning: This pattern-binding binds no variables: $(varP ohNoes) = "Teh warning!" sample ======> let ohNoes_a2Al = "Teh warning!" in print ohNoes_a2Al

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ANN: deepseq-bounded, seqaid, leaky
by Andrew Seniuk 21 Dec '14

21 Dec '14

This trio of related packages explores strictness control in a variety of ways. deepseq-bounded provides classes and generic functions to artificially force evaluation, to extents controlled by static or dynamic configuration. seqaid puts that into practise, providing a GHC plugin to auto-instrument your package with a strictness harness, which is dynamically optimisable during runtime. This is supported directly in the GHC compilation pipeline, without requiring (or performing!) any edits to your sources. leaky is a minimal, prototypic executable that leaks space under current state-of-the-art compilation (GHC 7.8.3 -O2, at the present time). deepseq-bounded hackage: https://hackage.haskell.org/package/deepseq-bounded homepage: http://www.fremissant.net/deepseq-bounded seqaid hackage: https://hackage.haskell.org/package/seqaid homepage: http://www.fremissant.net/seqaid leaky hackage: https://hackage.haskell.org/package/leaky homepage: http://www.fremissant.net/leaky Reddit discussion for the three together: http://www.reddit.com/r/haskell/comments/2ps8f5/ann_deepseqbounded_seqaid_l… Easiest way to try them all, is to install seqaid and run the demo: cabal install seqaid seqaid demo This tests seqaid on a local copy of the leaky source package. It turned out to be routine to extend deepseq-bounded and seqaid to dynamically configurable parallelisation (paraid?). Many other wrappers could be explored, too! Maybe seqaid should be renamed to koolaid or something... It's a pretty complicated system, and just first release, so there's bound to be lots of problems. I've not set up a bug tracker, but will maintain a casual list of bugs and feature requests at http://www.fremissant.net/seqaid/trac and will set up a proper tracker if there's interest. Any isssues (or comments), I'm here, or on the reddit discussion (or email). Andrew Seniuk rasfar on #haskell

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Parametric kinds
by Gautier DI FOLCO 21 Dec '14

21 Dec '14

Hello all, I'm trying to port typeclasses to kind-level, here are my data types: -- newtype Fix f a = Fix (f (Fix f a)) -- data Mu f = In (f (Mu f)) data Fix (f :: k1 -> k0) (n :: k1) = Fx data Maybe a = Nothing | Just a If I try to create type families to represent Functors, I end up with this: -- type family MapFix (f :: (* -> k) -> * -> k) a :: * where -- type family MapFix f a where type family MapFix (f :: (k0 -> k1) -> k0 -> k1) (a :: k2) :: * where MapFix f (Fix a n) = Fix (f a) (MapFix f n) -- type family MapMaybe (f :: k -> k) (a :: Maybe k) :: Maybe k where -- type family MapMaybe f a where type family MapMaybe (f :: k0 -> k1) (a :: Maybe k0) :: Maybe k1 where MapMaybe f ('Just a) = 'Just (f a) MapMaybe f 'Nothing = 'Nothing But I can't defined a single open type family for these two data types. I think I lack of parametric kinds, for example: `*k p*` could let me fit `*Maybe k*`. Currently, in the way I see kinds, on `*k0 -> k1*` allow me to parameterize kinds, but `*Maybe k*` doesn't fit. I know that this is certainly unclear, don't hesitate to ask me for clarifications. I also know that my `*Fix*` sucks, any good idea on how to do it is welcome :) Also, if you have any links to have a deeper insight of Kinds it will save me from mental illness. Thanks in advance for your help, Regards.

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How to avoid keeping old data formats in your code?
by Corentin Dupont 21 Dec '14

21 Dec '14

Hi, I didn't had so much luck with this question. The question was: -> "How to avoid keeping old data formats in your code?" Indeed those old data formats are often needed for retro-compatibility with previous versions of your software. Say you have a data structure that is serialized in a file, and then you add a field in a later version. You are obliged to keep both versions of the data structure if you want to be able to read both versions of the file. Potentially, if you update very often your structure between releases, you are obliged to keep N versions of the data structure in your code. See the exemple at: http://acid-state.seize.it/safecopy On Sun, Nov 30, 2014 at 1:04 PM, Corentin Dupont <corentin.dupont(a)gmail.com> wrote: > Hi the list, > I have some question relative to data migration. > > Say you have a software in version A which save data in a file with format > FA. Later, you update your software to version B, with data format FB. > Now, if you want your version B of the software to be able to read data > saved by version A, you're obliged to include FA in version B, together > with some functions to translate from FA to FB. > > This is what I don't find elegant: you're obliged to keep old code (data > formats) in your software. > -> do you know of any way to avoid keeping old data formats (for > retro-compatiblilty) in your code? > > In practice I use acid-state with safecopy: > http://acid-state.seize.it/safecopy > In this example you can see the problem: the author is obliged to keep old > code (data structures) to maintain compatibility. Even worth, you might be > obliged to suffix your data structure with a version number: > > data MyType_V1 = MyType_V1 Intdata MyType_V2 = MyType_V2 Integer > > > Instead, I'm thinking of a process using GIT, or Cabal as a back-end. > The idea would be to have an additional program (or library) specialized > in the data migration of your main software. It would extract both version > A and B from the repo, and then would compile an application capable of > handling migrations from FA to FB. > > Does something like this exists (even outside of Haskell)? > > Cheers, > Corentin >

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[ANN]Haskell Rhythm game development tutorial
by Fumiaki Kinoshita 21 Dec '14

21 Dec '14

Hello, I've published a tutorial[0] to create a rhythm game. This tutorial focuses on the design of interactive, real-time application using lens, objective, Call package. Feel free to point out infelicities or offer suggestion. Cheers [0] http://fumieval.github.io/rhythm-game-tutorial/ -- Fumiaki Kinoshita

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<*> for Data.Sequence: mission accomplished
by David Feuer 20 Dec '14

20 Dec '14

All right! It's taken a long time, but I finally managed to write a nice implementation of `<*>` for `Data.Sequence`! It looks nothing like my original concept, but it accomplishes my incremental performance goals while also being a little better than the current implementation when forcing the whole result. Anyone interested can see the code in the `ap` branch of treeowl/containers on GitHub. There are still some ugly special cases for sufficiently small arguments--any ideas for changing that would be most welcome. Many thanks to Joachim Breitner for helping implement an earlier approach, to Ross Paterson for coming up with a solution to a previous formulation of the problem (thus helping me understand that I had asked the wrong question), and to Carter Schonwald for putting up with my stream of consciousness rambling. On Sun, Nov 23, 2014 at 12:07 AM, David Feuer <david.feuer(a)gmail.com> wrote: > OK, sorry for the flood of posts, but I think I've found a way to make that > work. Specifically, I think I can write a three-Seq append that takes the > total size and uses it to be as lazy as possible in the second of the three > Seqs. I'm still working out the details, but I think it will work. It does > the (possibly avoidable) rebuilding, but I *think* it's at least > asymptotically optimal. Of course, if Ross Paterson can find something more > efficient, that'd be even better. > > On Sat, Nov 22, 2014 at 10:10 PM, David Feuer <david.feuer(a)gmail.com> wrote: >> >> OK, so I've thought about this some more. I think the essential *concept* >> I want is close to this, but it won't quite work this way: >> >> fs <*> xs = equalJoin $ fmap (<$> xs) fs >> >> equalJoin :: Int -> Seq (Seq a) -> Seq a >> equalJoin n s >> | length s <= 2*n = simpleJoin s >> | otherwise = simpleJoin pref >< >> equalJoin (2*n) mid >< >> simpleJoin suff >> where (pref, s') = splitAt n s >> (mid, suff) = splitAt (length s - 2*n) s' >> >> simpleJoin :: Seq (Seq a) -> Seq a >> simpleJoin s >> | null s = empty >> | length s == 1 = index s 0 >> | otherwise = simpleJoin front >< simpleJoin back >> where >> (front,back) = splitAt (length s `quot` 2) s >> >> I think the reason this doesn't work is that >< is too strict. I believe >> the only potential way around this is to dig into the FingerTree >> representation and build the thing top-down. I still don't understand how >> (if at all) this can be done. >> >> >> On Sat, Nov 22, 2014 at 12:57 PM, David Feuer <david.feuer(a)gmail.com> >> wrote: >>> >>> The ideal goal, which has taken me forever to identify and which may well >>> be unattainable, is to get O(log(min{i,mn-i})) access to each element of the >>> result, while maintaining O(mn) time to force it entirely. Each of these is >>> possible separately, of course. To get them both, if it's possible, we need >>> to give up on the list-like approach and start splitting Seqs instead of >>> lists. As we descend, we want to pass a single thunk to each element of each >>> Digit to give it just enough to do its thing. Representing the splits >>> efficiently and/or memoizing them could be a bit of a challenge. >>> >>> On Fri, Nov 21, 2014 at 02:00:16PM -0500, David Feuer wrote: >>> > To be precise, I *think* using the fromList approach for <*> makes us >>> > create O >>> > (n) thunks in order to extract the last element of the result. If we >>> > build the >>> > result inward, I *think* we can avoid this, getting the last element of >>> > the >>> > result in O(1) time and space. But my understanding of this data >>> > structure >>> > remains primitive. >>> >>> This modification of the previous should do that. >>> >>> mult :: Seq (a -> b) -> Seq a -> Seq b >>> mult sfs sxs = fromTwoLists (length sfs * length sxs) ys rev_ys >>> where >>> fs = toList sfs >>> rev_fs = toRevList sfs >>> xs = toList sxs >>> rev_xs = toRevList sxs >>> ys = [f x | f <- fs, x <- xs] >>> rev_ys = [f x | f <- rev_fs, x <- rev_xs] >>> >>> -- toRevList xs = toList (reverse xs) >>> toRevList :: Seq a -> [a] >>> toRevList = foldl (flip (:)) [] >>> >>> -- Build a tree lazy in the middle, from a list and its reverse. >>> -- >>> -- fromTwoLists (length xs) xs (reverse xs) = fromList xs >>> -- >>> -- Getting the kth element from either end involves forcing the lists >>> -- to length k. >>> fromTwoLists :: Int -> [a] -> [a] -> Seq a >>> fromTwoLists len_xs xs rev_xs = >>> Seq $ mkTree2 len_xs 1 (map Elem xs) (map Elem rev_xs) >>> >>> -- Construct a fingertree from the first n elements of xs. >>> -- The arguments must satisfy n <= length xs && rev_xs = reverse xs. >>> -- Each element of xs has the same size, provided as an argument. >>> mkTree2 :: Int -> Int -> [a] -> [a] -> FingerTree a >>> mkTree2 n size xs rev_xs >>> | n == 0 = Empty >>> | n == 1 = let [x1] = xs in Single x1 >>> | n < 6 = let >>> nl = n `div` 2 >>> l = Data.List.take nl xs >>> r = Data.List.take (n - nl) rev_xs >>> in Deep totalSize (mkDigit l) Empty (mkRevDigit r) >>> | otherwise = let >>> size' = 3*size >>> n' = (n-4) `div` 3 >>> digits = n - n'*3 >>> nl = digits `div` 2 >>> (l, xs') = Data.List.splitAt nl xs >>> (r, rev_xs') = Data.List.splitAt (digits - nl) rev_xs >>> nodes = mkNodes size' xs' >>> rev_nodes = mkRevNodes size' rev_xs' >>> in Deep totalSize (mkDigit l) (mkTree2 n' size' nodes rev_nodes) >>> (mkRevDigit r) >>> where >>> totalSize = n*size >>> >>> mkDigit :: [a] -> Digit a >>> mkDigit [x1] = One x1 >>> mkDigit [x1, x2] = Two x1 x2 >>> mkDigit [x1, x2, x3] = Three x1 x2 x3 >>> mkDigit [x1, x2, x3, x4] = Four x1 x2 x3 x4 >>> >>> -- length xs <= 4 => mkRevDigit xs = mkDigit (reverse xs) >>> mkRevDigit :: [a] -> Digit a >>> mkRevDigit [x1] = One x1 >>> mkRevDigit [x2, x1] = Two x1 x2 >>> mkRevDigit [x3, x2, x1] = Three x1 x2 x3 >>> mkRevDigit [x4, x3, x2, x1] = Four x1 x2 x3 x4 >>> >>> mkNodes :: Int -> [a] -> [Node a] >>> mkNodes size (x1:x2:x3:xs) = Node3 size x1 x2 x3:mkNodes size xs >>> >>> -- length xs `mod` 3 == 0 => >>> -- mkRevNodes size xs = reverse (mkNodes size (reverse xs)) >>> mkRevNodes :: Int -> [a] -> [Node a] >>> mkRevNodes size (x3:x2:x1:xs) = Node3 size x1 x2 x3:mkRevNodes size xs >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe(a)haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >

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LambdaConf 2015 - CFP
by John A. De Goes 20 Dec '14

20 Dec '14

Hi all, LambdaConf 2015 has officially opened its Call for Proposals. LambdaConf 2015 is being held in the beautiful foothills of the Rocky Mountains, in Boulder, Colorado (home to many companies using FP). The conference is devoted to helping people become better programmers through functional and declarative programming. We're looking for lightning talks, workshops, and presentations on the following themes: FP 101. Introductory material for the FP curious or those just getting their feet wet. Languages. New languages (functional / logic), functional ways to use existing languages, language extensions, etc. Theory. Type theory, category theory, abstract algebra, ongoing or new research, and anything useful or interesting to functional programmers or academics working in the field. Libraries. Cool libraries that demonstrate the power of functional programming in helping programmers get stuff done. Case Studies. Case studies showing how using a functional language or library proved to be game-changing in solving real world problems. We currently have talks or workshops lined up for Haskell, Purescript, Scala, and Rust. If you'd like to submit a proposal, just send a private email to me or visit the official website for more information. We are not yet open for registrations, but we are actively looking for a couple more volunteers, as well as sponsors. If you know someone who might be interested, please spread the word! Regards, John

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Random pattern generation with list comprehensions
by Mike Jones 20 Dec '14

20 Dec '14

I am looking for a way to generate random patterns for hardware validation. The goal is to separate patten generation from execution in hardware, and from pure code used to compute expected behavior from a model, detection of bad behavior, in the form of predicates, etc. The purpose of random patterns is to explore the behavior space in less time, as well as improve time to discovery by preventing long runs that focus in narrow areas for long periods. Patterns are to be infinite lists with the ability to specify run length for any run, which becomes a quality dial of sorts. I initially started with finite sequences expressed as list comprehensions, that generate tuples of ints, floats, structured data, and lists of attributes (bit combinations of hardware registers). I believe the list comprehension evaluates each generator (a | a <- ...) in a strict order, such that an infinite list will cause infinite evaluation of a single generator, such that other generators are not evaluated. Even if each generator is constrained (take n), results will not not be completely random. What I need is for each generator to supply one value each, and combine them into a tuple. I could probable express this in a monadic loop construct, as long as each generator is random and holds state, like the article I saw using the State Monad to generate random numbers. Or perhaps a State monad that holds multiple generators. Is there a better way to express the solution or a helpful module others use for this? Mike Sent from my iPad

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HPC and Template Haskell (GHC 7.8.3, Yesod)
by David Turner 19 Dec '14

19 Dec '14

Hi, I'm having trouble making a HPC build of a Yesod application. It fails with: /usr/bin/ld: dist/build/StreamReading/Config.dyn_o: relocation R_X86_64_PC32 against undefined symbol `_hpc_tickboxes_tracszmenterprisezm0zi0zi0_Settings_hpc' can not be used when making a shared object; recompile with -fPIC I've narrowed it down to a call to ghc and posted the output in all its gory detail at http://lpaste.net/116872 if that's any help. Of note is that dist/build/Settings.dyn_o is unexpectedly missing from the list of parameters to the last call to gcc, and the missing symbol is defined in the same. There are, in fact, quite a number of missing .dyn_o files in that list. Slightly weirdly, when I run the same command line again, it seems to work. At least, there are no errors reported and the exit code is 0. Any ideas? Cheers, David

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Hackage 2 archive.tar equivalent
by Alexander Solla 19 Dec '14

19 Dec '14

On the old hackage site (running Hackage 1.*), we used to be able to download a file called archive.tar, which contained the latest version of all of the Haskell packages. Is there any way to do this with Hackage 2? I understand that my case is definitely a corner case -- I don't have a regular net connection, so I'd really like to be able to download a snapshot of Hackage at regular, convenient intervals, and serve them up at home.

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[TFP 2015] 1st call for papers
by Peter Achten 19 Dec '14

19 Dec '14

----------------------------- C A L L F O R P A P E R S ----------------------------- ======== TFP 2015 =========== 16th Symposium on Trends in Functional Programming June 3-5, 2015 Inria Sophia Antipolis, France http://tfp2015.inria.fr/ The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below). Authors of draft papers will be invited to submit revised papers based on the feedback receive at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. The selected revised papers are expected to be published as a Springer Lecture Notes in Computer Science (LNCS) volume. TFP 2015 will be the main event of a pair of functional programming events. TFP 2015 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on June 2nd. The TFP symposium is the heir of the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in * Edinburgh (Scotland) in 2003; * Munich (Germany) in 2004; * Tallinn (Estonia) in 2005; * Nottingham (UK) in 2006; * New York (USA) in 2007; * Nijmegen (The Netherlands) in 2008; * Komarno (Slovakia) in 2009; * Oklahoma (USA) in 2010; * Madrid (Spain) in 2011; * St. Andrews (UK) in 2012; * Provo (Utah, USA) in 2013; * and in Soesterberg (The Netherlands) in 2014. For further general information about TFP please see the TFP homepage. (http://www.tifp.org/) == INVITED SPEAKERS == TFP is pleased to announce talks by the following two invited speakers: * Laurence Rideau is a researcher at INRIA and is interested in the semantics of programming languages , the formal methods, and the verification tools for programs and mathematical proofs. She participated in the beginnings of the Compcert project (certified compiler), and is part of the Component Mathematical team in the MSR-INRIA joint laboratory, who performed the formalization of the Feit-Thompson theorem successfully. Thirty years ago, computers barged in mathematics with the famous proof of the Four Color Theorem. Initially limited to simple calculation, their role is now expanding to the reasoning whose complexity is beyond the capabilities of most humans, as the proof of the classification of finite simple groups. We present our large collaborative adventure around the formalization of the Feit-Thompson theorem (http://en.wikipedia.org/wiki/Feit%E2%80%93Thompson_theorem) that is a first step to the classification of finite groups and that uses a palette of methods and techniques that range from formal logic to software (and mathematics) engineering. * Sam Aaron (?) == SCOPE == The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: leading-edge, previously unpublished research work Position Articles: on what new trends should or should not be Project Articles: descriptions of recently started new projects Evaluation Articles: what lessons can be drawn from a finished project Overview Articles: summarizing work with respect to a trendy subject Articles must be original and not simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Debugging and profiling for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2015 program chair, Manuel Serrano. == BEST PAPER AWARDS == To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. == SPONSORS == TFP is financially supported by ?????????????????? == PAPER SUBMISSIONS == Acceptance of articles for presentation at the symposium is based on a lightweight peer review process of extended abstracts (4 to 10 pages in length) or full papers (20 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate which authors are research students, and whether the main author(s) are students. A draft paper for which ALL authors are students will receive additional feedback by one of the PC members shortly after the symposium has taken place. We use EasyChair for the refereeing process. Papers must be submitted at: https://easychair.org/conferences/?conf=tfp2015 Papers must be written in English, and written using the LNCS style. For more information about formatting please consult the Springer LNCS web site: http://www.springer.com/computer/lncs?SGWID=0-164-6-793341-0 == IMPORTANT DATES == Submission of draft papers: March 17, 2015 Notification: March 24, 2015 Registration: April 7, 2015 TFP Symposium: June 3-5, 2015 Student papers feedback: June 9, 2015 Submission for formal review: July 1, 2015 Notification of acceptance: September 8, 2015 Camera ready paper: October 8, 2015 == PROGRAM COMMITTEE == Janis Voigtländer University of Bonn, DE Scott Owens University of Kent, UK Neil Sculthorpe Swansea University, UK Colin Runciman University of York, UK Manuel Serrano Inria (PC chair), FR Rinus Plasmeijer University of Nijmegen, NL Tomas Petricek University of Cambridge, UK Marco T. Morazan Seton Hall University, USA Wolfgang De Meuter Vrije Universiteit Brussel, BE Michel Mauny Ensta ParisTech, FR Sam Lindley The University of Edinburgh, UK Daan Leijen Microsoft, USA Jurriaan Hage Utrecht University, NL Andy Gill University of Kansas, USA Thomas Gazagnaire University of Cambrige, UK Lars-Ake Fredlund Universidad Politécnica de Madrid, ES Jean-Christophe Filliatre Université Paris Sud Orsay, FR Marc Feeley Université de Montréal, CA Olaf Chitil University of Kent, UK Edwin Brady University of St Andrews, UK

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GHC Heap Profiler time axis
by Anton Dessiatov 19 Dec '14

19 Dec '14

Hello, Haskell-Cafe! For the last 2 days I’m debugging something that looks like a space leak. My program is a rather long-running network service. When I first used heap profiler I was a bit confused with its output that showed that my program was running for only about 0.3-0.4 seconds when I launched it idling for about a minute. That was confusing enough for me to dig into GHC sources trying to figure out the reason behind this and I found that values of the sample times are taken from the mut_user_time function, which returns a time that process spent in user-mode code (outside the kernel) minus time spent on garbage collection. This introduces great amount of unpredictable non-linearity of the heap profile graph x axis, which I personally consider very counterintuitive. So my question is does anybody know why is it done this way? Wouldn’t it be better if x axis would just show a time elapsed since the process started? Kind regards, Anton.

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Re: [Haskell-cafe] cabal-install on openbsd
by Ramakrishnan Muthukrishnan 19 Dec '14

19 Dec '14

On Fri, Dec 19, 2014, at 03:47 PM, Gusoi Constantin - Codrut wrote: > I have the same problem on Ubunutu 14.04, what you need to do is to > use more RAM / SWAP. I have 1 GB of swap. I still get the error. The allocation error is for 1 MegaByte (1048576 bytes). That's what make me really surprised. May be it runs out of memory and fails when it cannot allocate one more megabyte of memory? Ramakrishnan

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cabal-install on openbsd
by Ramakrishnan Muthukrishnan 19 Dec '14

19 Dec '14

Hi, I have a new OpenBSD 5.6 installation on AMD64. The OpenBSD package collection has ghc 7.6.3 and Cabal-install 1.16.0.2. After installing them, I attempted to install a new version of cabal-install using the packaged cabal-install by doing `cabal install cabal-install'. But I get a "ghc: out of memory (requested 1048576 bytes)" error while it is compiling cabal-install 1.20.0.3. I have a ticket created against ghc but I wonder if it is a bug with ghc or cabal-install or OpenBSD or something else. Anyway.. the ticket is here [1]. I can help debug the problem on my OpenBSD box. Thanks Ramakrishnan [1] <https://ghc.haskell.org/trac/ghc/ticket/9904>

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Re: [Haskell-cafe] Typed TH
by oleg＠okmij.org 19 Dec '14

19 Dec '14

Typed meta-programming has a very rich history. For a good overview of various approaches and main problems, please see the Related work section of the following paper http://okmij.org/ftp/tagless-final/TaglessStaged/beyond-journal.pdf There is a special subsection on Typed TH. (The version of that paper with minor revisions will be uploaded in two-three months). The main problems are how to ensure hygiene in the presence of effects, and how to generate polymorphic bindings (let-bindings). Both problems have been essentially solved. (The solution to the second problem has been presented at small meetings so far). The paper explains the combinator library to generate TH code that is ensured to be well-typed, *by construction*. The library permits arbitrary monadic effects. There is no Q monad since it turns out not necessary.

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gracefully invoking `less` using System.Process (and ignoring ctrl-c)
by Guillaume Hoffmann 19 Dec '14

19 Dec '14

Hi, I'm looking at a bug that we should fix for the 2.10 release of darcs. I'd like to make the invocation of the pager (most of the time `less`) as identical to git as possible. Currently darcs has a workaround for the "resource vanished (broken pipe)" problem (that happens when you leave `less` before all of the text has been read by it). The workaround involves creating a temporary file and then passing it to less [1]. This works but it's slow (for big inputs) and ugly IMO. I have a fix proposal [2] that is made of two changes: * use System.Process.createProcess (just to update the code), and * in the "ortryrunning" function (that chains attempts at calling various pagers until one works), ignoring IOError's of the kind ResourceVanished (otherwise we would invoke every pager in the chain if we quit them before they read all their input) The problem is that pressing CTRL-C in `less` now kills everything (darcs+less). Is there a way to fix this? Note that the darcs executable runs inside of the function withSignalHandled [3], which defines its behaviour with respect to various signals. Guillaume [1] http://hub.darcs.net/darcs/darcs-reviewed/browse/src/Darcs/UI/External.hs#4… [2] http://hub.darcs.net/gh/darcs-screened_1/patch/20141210002305-5ef8f [3] http://hub.darcs.net/darcs/darcs-reviewed/browse/src/Darcs/Util/SignalHandl…

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Dockerfile for Yesod
by Jonathan Paugh 18 Dec '14

18 Dec '14

Greetings, all I'm brand new to Docker, and struggled to find resources specific to Yesod. So, once I managed to piece together a Dockerfile, I decided to share it. Hope it helps someone. The Dockerfile is pasted at the bottom. It can be used by dropping it in your Yesod application directory, and replacing "app" with the name of your app. If you're new to Docker like I was, cd to your Yesod app dir, and run $ docker build --tag app-image . $ docker run -d -p 3000:3000 app-image to get started. Your web app should now be available at http://localhost:3000 NB: The approot setting can make a profound and confusing difference if it is mis-configured. I recommend temporarily setting approot to "" so that it will use absolute (site-relative) urls instead of fully specified ones. Happy Holidays, Jon Dockerfile ----------- FROM haskell:7.8 RUN cabal update RUN apt-get update && apt-get install -y libpq5 libpq-dev ADD ./app.cabal /opt/app/app.cabal WORKDIR /opt/app RUN cabal sandbox init RUN cabal install --only-dependencies --max-backjumps=-1 --reorder-goals -j ADD . /opt/app RUN cabal build RUN dist/build/db-import/db-import ENV PATH /opt/app/.cabal-sandbox/bin:$PATH EXPOSE 3000 CMD ["/opt/app/dist/build/app/app", "production", "-p", "3000"]

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Missing `$` like operators in Haskell
by Clinton Mead 18 Dec '14

18 Dec '14

Below are the `$` like operators in Haskell (view in fixed width): --------------------------------------------------------------------- | Function first | Op | Function second | Op | ------------------------------------------------------------------------------- | Plain | (a -> b) -> a -> b | $ | a -> (a -> b) -> b | | | Functor | (a -> b) -> f a -> f b | <$> | f a -> (a -> b) -> f b | | | Applicat| f (a -> b) -> f a -> f b | <*> | f a -> f (a -> b) -> f b | <**> | | Monad | (a -> m b) -> m a -> m b | =<< | m a -> (a -> m b) -> m b | >>= | ------------------------------------------------------------------------------- The "function second" forms I couldn't find for "plain" and "functor". What are the most common operators to used in these places?

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managing local cabal package database
by Carl Eyeinsky 18 Dec '14

18 Dec '14

Dear Cafe readers, I'm wondering what do you guys use as the general method in developing projects using your own private projects? Cabal allows to specify a directory for local packages ('local-repo' in '.cabal/config') with specific structure. Are there any scripts that take a git repo, checkout its tags one by one and put them in some specified directory in the correct way? The crude structure I'm imagining is that I'd like to reuse general purpose stuff I have made myself before, and have it available similar to having it in Hackage. Why I don't want to put my things in the Hackage itself, is that the code often changes fast, and would be little help to others until some later date, when things have calmed down.. (Does this seem a reasonable procedure, or how do you do it?) Cheers, -- Carl Eyeinsky

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Why does Haskell PVP have two values for the major version? "A.B..." and a couple other questions
by Zach Moazeni 18 Dec '14

18 Dec '14

Hello, Forgive me if this is a frequently asked question, I've searched the web and can't find an answer. I originally sent this to the Beginners list and someone said this might get more responses here instead. What is the history that led up to the PVP <https://www.haskell.org/haskellwiki/Package_versioning_policy> specifying two values as the major version? I come from other tools that primarily use http://semver.org/ (or a variant) and I'm confused in what cases I should bump "A" but not "B" (or bump "B" but not "A")? A concrete example: If I make backwards incompatible changes to a package whose latest version is 1.0.x, should the next version be 2.0.x or 1.1.x? What sorts of things should I consider for choosing 2.0 over 1.1 and vice versa? Another question, by far most packages I have encountered either lead with a 0 or a 1 for "A". Does that have some bearing on the long term stability that package users should expect in the future? Finally, if "1.0.x.." is meant to convey a level of long term support, does "B" get rarely used? Since "C" version bumps to include backwards compatible additions, and "D"+ for backwards compatible bug fixes. (I know "D" isn't technically a PVP category, I'm just relating it to the patch version of semver). Thanks for your help! -Zach

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building hmatrix on OSX
by Erik Rantapaa 18 Dec '14

18 Dec '14

I'm trying to build hmatrix-0.16.1.1 on OSX 10.10.1, and I'm running into some undefined C functions and types in src/C/vector-aux.c: - struct random_data - random_r() - initstate_r() A specific error: src/C/vector-aux.c:738:24: error: variable has incomplete type 'struct random_data' struct random_data buffer; On a Linux system they seem to be defined in stdlib.h, but that doesn't seem to be the case on OSX. Is there a way to work around this? FWIW, I'm using GHC for OSX (https://ghcformacosx.github.io/) and I've installed `gsl` via `brew install gsl`.

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Ordered JSON objects?
by Tobias Dammers 18 Dec '14

18 Dec '14

I'm building a "thing" that is supposed to use JSON 'documents' as its building blocks, providing various (pluggable) storage backends and presentation frontends. Non-techie/semi-techie (frontend dev, web dev, etc.) compatibility is needed, which is why I want to keep the data model "simple" and dynamically typed. Anyway, one thing I'm running up against is that I am going to need ordered key/value collections, which I believe is something JSON does not support out-of-the-box: "objects" ({"foo":15, "bar":23}) are conceptually unordered key/value collections (and Aeson treats them as such, using hash maps as the intermediate storage format), so I lose ordering; OTOH, flat lists ([15, 23]) do not have keys, and lists of "pairs" (two-element lists) produce uglier syntax ([["foo",15], ["bar",23]]), but they are the "correct" solution. Ideally, someone is going to step up and tell me that both I and Aeson have misunderstood JSON, and objects are really supposed to be ordered after all, in which case I'd need an alternative to Aeson (or someone needs to patch it?). Or I could bite the bullet and go with [["foo",15], ["bar",23]]. Or I could ditch JSON as the canonical format and go with something custom, or, shudder, XML. Thoughts? Hints? Ideas? - Tobias (tdammers on freenode)

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how to handle FILE* with c2hs
by Johannes Waldmann 17 Dec '14

17 Dec '14

Hi. I could use an example of how to handle files (FILE *) with c2hs, but could not find any. I want to call some "void dump (..., FILE * f)" function. I want to use this for a handle that I obtained in Haskell land. Sure I can rewrite/add the C code so that it takes a filepath (string) and opens the file by itself, but should I? - J.W.

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PVP question
by Michael Snoyman 17 Dec '14

17 Dec '14

I'm a little bit uncertain of the PVP guidelines in a certain case[1], so I'd like to get some guidance/clarity. Suppose I have a library which provides the function: myFunction :: IO () myFunction = forever $ putStrLn "Still here" >> threadDelay 10^6 Later, I realize (or someone points out to me) that I've over-specified the type signature, and really myFunction should be: myFunction :: IO a In this case, does the PVP specify that we should have a minor or a major version bump? I'm not certain if this counts as a breaking change or not. [1] https://github.com/fpco/streaming-commons/pull/13

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Haskell Polishing [was: Missing `$` like operators in Haskell]
by Giacomo Tesio 16 Dec '14

16 Dec '14

2014-12-12 14:22 GMT+01:00 Johan Tibell <johan.tibell(a)gmail.com>: > > Everything doesn't have to have an operator! We use operators a bit too > much. It hurts readability of code when lines start looking like APL. > > Probably this has been discussed already (and I'd like to read previous material, btw, so please give me some reference), but as a long time programmer with experience in many different paradigms and languages I too feel Haskell a bit cumbersome from this point of view. I mean, the language in itself is the best I know, but libraries have different levels of quality and in general they miss organization: they often overlap in intent and interface, for example. Anyone tried to address this issue? And if so, how? I can see how backward compatibility prevents Haskell to be polished, but it's a pity. It's like an handbrake for it's evolution and adoption! Giacomo

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Request For Feedback: Emulating OO-style dispatch for binding ...
by aditya siram 16 Dec '14

16 Dec '14

I am writing a GUI binding but unfortunately could not find a OO-style dispatching scheme that I was happy with so I wrote my own ( https://gist.github.com/deech/6528a75e480378182052 ). The design goal is to: - provide a single function that will dispatch to a custom implementation based on the type of argument it is given - allow the user to extend and subclass the hierarchy and override functions in a way that doesn't involve recompiling the binding - use as few new extensions as possible - provide as familiar an API as possible, thereby allowing users to leverage existing documentation maintained by the C++ project. The look-and-feel of the API is on lines 128-140. It should just be a stand-alone file that can be loaded into GHCI. Thanks for your feedback! -deech

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Year-end deadline for Haskell.org donations
by Adam Foltzer 16 Dec '14

16 Dec '14

Dear Haskellers, HaskellWiki, Hackage, Hoogle, and all the other Haskell.org sites we depend on are hosted with funds donated by you, the Haskell community. As many of us are in tax jurisdictions where December 31st is a deadline for charitable giving, I’d like to remind you that donations to support these activities are tax-deductible. You can donate online right now at https://co.clickandpledge.com/advanced/default.aspx?wid=69561. Last year was the first time we were able to seek your help while offering tax relief, and you came through: we raised nearly $900 in the span of a few days! This year, with almost three weeks left before the end of the year, I'd love to see us double that. It has been quite a year for Haskell.org: we migrated of most of our infrastructure, including Hackage, to Rackspace in order to improve reliability. We implemented new proxying to improve speed and performance, and improved the documentation and standardization of our server administration practices. Many of these accomplishments and much else are detailed by Austin Seipp at the new Haskell.org infrastructure blog at https://blog.haskell.org/post/the_new_haskell_org/. Let's keep the momentum going in 2015! Thank you and best wishes for a happy new year, Adam Foltzer & The Haskell.org Committee

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No handles from createProcess
by Henk-Jan van Tuyl 15 Dec '14

15 Dec '14

L.S., I am experimenting with the createProcess function from the package "process"; this function does not return any handle, on both Ubuntu and Windows. I am doing something wrong, or is this a bug? (I am using GHC 7.8.3 on both platforms.) The program I am running: ---✂---------------------------------------------- import System.IO import System.Process f = do ( maybeStdinHandel , maybeStdoutHandel , maybeStderrHandel , processHandle ) <- createProcess (proc "cat" ["a.txt"]) case maybeStdinHandel of Just stdinHandel -> do putStrLn "stdin" _ -> putStrLn "No stdin handle" case maybeStdoutHandel of Just stdoutHandel -> do putStrLn "stdout" putStrLn =<< hGetContents stdoutHandel _ -> putStrLn "No stdout handle" case maybeStderrHandel of Just stderrHandel -> do putStrLn "stderr" putStrLn =<< hGetContents stderrHandel _ -> putStrLn "No stderr handle" main = f ---✂---------------------------------------------- The output: ---✂---------------------------------------------- $ ./ProcessTry No stdin handle No stdout handle No stderr handle asdf ---✂---------------------------------------------- (asdf is the contents of file a.txt) Regards, Henk-Jan van Tuyl -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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Converting non-primitive(?) recursive function to use scanl (or foldl maybe?)
by Cody Goodman 15 Dec '14

15 Dec '14

I've had some trouble wrapping my brain around how to use a scan to build this list: code below, but here's an lpaste link: http://lpaste.net/116494 {-# LANGUAGE OverloadedStrings #-} import Control.Monad import Data.Maybe import Text.Regex type RegexRes = Maybe (String, String, String, [String]) re = mkRegex "\$(\\w+)\$:([[:digit:]]+)" getParenNum :: String -> [String] getParenNum s = case matchRegexAll re s of Nothing -> [] Just (_,_,after,[word,num]) -> (word ++ num):getParenNum after getParenNumOnce' :: String -> String getParenNumOnce' s = case matchRegexAll re s of Nothing -> [] Just (_,_,after,[word,num]) -> (word ++ num) -- trying to accumulate the results of regexMatching repeatedly over a string f1 str = (\ (_, _, xs, acc) -> Just (xs, acc)) <=< (matchRegexAll re) $ str f2 str = fromMaybe "" $ (\ (_, _, after, [word,num]) -> Just after) <=< (matchRegexAll re) $ str -- f3 :: RegexRes -> RegexRes -- f3 :: RegexRes -> String f3 match = fromMaybe [] $ (\(_,_,after,[word,num]) -> Just (word ++ num)) =<< match f4 str = scanl (const f3) "" [(matchRegexAll re str)] f5 acc str = fromMaybe [] $ (\ (_, _, after, [word,num]) -> Just (acc ++ [word ++ num])) <=< (matchRegexAll re) $ str -- λ> scanl f5 [] ["(fish):1 sausage (cow):3 tree (boat):4"] -- [[],["fish1"]] str = "(fish):1 sausage (cow):3 tree (boat):4" -- λ> foldl (const . f3 . (matchRegexAll re)) "(fish):1 sausage (cow):3 tree (boat):4" ["(fish):1 sausage (cow):3 tree (boat):4"] -- "fish1" -- λ> -- want ["fish1","cow3","boat4"] -- λ> -- I feel like I should be using something in place of const that smartly chooses whether to pass String or... idk main = undefined

2 1

Typesafe API calls
by Fabian Bergmark 13 Dec '14

13 Dec '14

I just released a library on hackage (https://hackage.haskell.org/package/apis-0.0.0) The goal of the library is to provide typesafe API calls to a large amount of existing APIs. By typesafe I mean that, for each API the library provides two types, Input and Output, and a function :: Input -> IO Output. Internally the library knows how to serialize Input to make an HTTP request and how to deserialize the response into Output. Whats cool about this library is that it uses Template Haskell to generate the API interfaces. A combination of Open Data Tables, an internal YQL engine and JSON Schemas, all written in Haskell makes this possible. Right now only two APIs are included (Swedish weather data and Swedish public announcement), but more APIs are soon to follow. I have also implemented FFI exports of all types and functions so that, in combination with SWIG, this library can be used in almost any language. So far I have tried Java and Python with success. If anyone would like to try it and respond with feedback it would be greatly appreciated! If you want any specific API supported, I can try to import that right away Fabian Bergmark

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