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voting sytem DSL
by Corentin Dupont 07 Jun '13

07 Jun '13

Hi haskellers! I am trying to make a DSL able to describe a voting system. That DSL should be able to describe many different voting procedures: unanimity or majority, open or secret ballot, one or two turns... It should also work for referendums (yes/no question) or elections (electing one or several people)... Are you aware of any such DSL? In Haskell I haven't see it, maybe in another language? Cheers, Corentin

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runghc dies silently when given large numbers of arguments
by Gareth Smith 07 Jun '13

07 Jun '13

Hi all, The other day, I wrote the following program in /tmp/test.hs --8<---------------cut here---------------start------------->8--- main = error "An Error message" --8<---------------cut here---------------end--------------->8--- Then I ran the following: ,---- | gds@lithium:/tmp$ runghc ./test.hs `seq 1 100000` | gds@lithium:/tmp$ ghc -o test test.hs | gds@lithium:/tmp$ ./test `seq 1 100000` | test: An Error message | gds@lithium:/tmp$ `---- Notice that when I use runghc, my main function doesn't appear to run at all. But when I run the compiled program, my main function does seem to run, and produce the error message I expected. It seems to me like runghc can't cope with that large a number of arguments or size of argument string, or similar. That seems entirely reasonable, but if so, then might it be a good idea to have an error message when we accidentally hit that limit? I'm using ghc 7.6.2 on Ubuntu 13.04. Thanks! Gareth.

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FRP memory leaks
by Łukasz Dąbek 07 Jun '13

07 Jun '13

Hello, Cafe! I've heard that one of the problems of FRP (Functional Reactive Programming) is that it's easy to create memory leaks. However I cannot find any natural examples of such leaks. Could anybody post some (pseudo)code demonstrating this phenomenon? Preferably something that arises when one is writing bigger applications in FRP style. Thanks in advance! -- Łukasz Dąbek

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PPDP'13: Last call for papers
by Tom Schrijvers 06 Jun '13

06 Jun '13

===================================================================== Last Call for Papers 15th International Symposium on Principles and Practice of Declarative Programming PPDP 2013 Special Issue of Science of Computer Programming (SCP) Madrid, Spain, September 16-18, 2013 (co-located with LOPSTR 2013) http://users.ugent.be/~tschrijv/PPDP2013/ ====================================================================== PPDP 2013 is a forum that brings together researchers from the declarative programming communities, including those working in the logic, constraint and functional programming paradigms, but also embracing a variety of other paradigms such as visual programming, executable specification languages, database languages, and knowledge representation languages. The goal is to stimulate research in the use of logical formalisms and methods for specifying, performing, and analysing computations, including mechanisms for mobility, modularity, concurrency, object-orientation, security, verification and static analysis. Papers related to the use of declarative paradigms and tools in industry and education are especially solicited. Topics of interest include, but are not limited to: * Functional programming * Logic programming * Answer-set programming * Functional-logic programming * Declarative visual languages * Constraint Handling Rules * Parallel implementation and concurrency * Monads, type classes and dependent type systems * Declarative domain-specific languages * Termination, resource analysis and the verification of declarative programs * Transformation and partial evaluation of declarative languages * Language extensions for security and tabulation * Probabilistic modelling in a declarative language and modelling reactivity * Memory management and the implementation of declarative systems * Practical experiences and industrial application This year the conference will be co-located with the 23nd International Symposium on Logic-Based Program Synthesis and Transformation (LOPSTR 2013) and held in cooperation with ACM SIGPLAN. The conference will be held in Madrid, Spain. Previous symposia were held at Leuven (Belgium), Odense (Denmark), Hagenberg (Austria), Coimbra (Portugal), Valencia (Spain), Wroclaw (Poland), Venice (Italy), Lisboa (Portugal), Verona (Italy), Uppsala (Sweden), Pittsburgh (USA), Florence (Italy), Montreal (Canada), and Paris (France). Papers must describe original work, be written and presented in English, and must not substantially overlap with papers that have been published or that are simultaneously submitted to a journal, conference, or workshop with refereed proceedings. Work that already appeared in unpublished or informally published workshop proceedings may be submitted (please contact the PC chair in case of questions). Proceedings will be published in the ACM International Conference Proceedings Series. After the symposium, a selection of the best papers will be invited to extend their submissions in the light of the feedback solicited at the symposium. The papers are expected to include at least 30% extra material over and above the PPDP version. Then, after another round of reviewing, these revised papers will be published in a special issue of SCP with a target publication date by Elsevier of 2014. Important Dates Abstract Submission: June 10, 2013 Paper submission: June 13, 2013 Notification: July 18, 2013 Camera-ready: August 4, 2013 Symposium: September 16-18, 2013 Invites for SCP: October 2, 2013 Submission of SCP: December 11, 2013 Notification from SCP: February 22, 2014 Camera-ready for SCP: March 14, 2014 Authors should submit an electronic copy of the paper (written in English) in PDF. Each submission must include on its first page the paper title; authors and their affiliations; abstract; and three to four keywords. The keywords will be used to assist us in selecting appropriate reviewers for the paper. Papers should consist of no more than 12 pages, formatted following the ACM SIG proceedings template (option 1). The 12 page limit must include references but excludes well-marked appendices not intended for publication. Referees are not required to read the appendices, and thus papers should be intelligible without them. Program Committee Sergio Antoy Portland State University, USA Manuel Carro IMDEA Software Institute, Spain Iliano Cervesato Carnegie Mellon University, Qatar Agostino Dovier Universita degli Studi di Udine, Italy Maria Garcia de la Banda Monash University, Australia Ralf Hinze University of Oxford, UK Yukiyoshi Kameyama University of Tsukuba, Japan Oleg Kiselyov USA Yanhong Annie Liu State University of New York at Stony Brook, USA Stefan Monnier Universite de Montreal, Canada Alan Mycroft University of Cambrige, UK Bruno C. d. S. Oliveira National University of Singapore, Singapore Alberto Pettorossi Universita di Roma Tor Vergata, Italy Enrico Pontelli New Mexico State University, USA Kristoffer Rose IBM Research, USA Sukyoung Ryu KAIST, South Korea Vitor Santos Costa University of Porto, Portugal Torsten Schaub University Potsdam, Germany Tom Schrijvers Ghent University, Belgium Martin Sulzmann Hochschule Karlsruhe, Germany Wouter Swierstra Universiteit Utrecht, The Netherlands Tarmo Uustalu Institute of Cybernetics, Estonia Janis Voigtlaender University of Bonn, Germany Meng Wang Chalmers University of Technology, Sweden Jan Wielemaker Universiteit van Amsterdam, The Netherlands Program Chair Tom Schrijvers Department of Applied Mathematics and Computer Science Ghent University 9000 Gent, Belgium General Chair Ricardo Pena Facultad de Informatica Universidad Complutense de Madrid 28040 Madrid, Spain -- prof. dr. ir. Tom Schrijvers Programming Languages Group Department of Applied Mathematics and Computer Science University of Ghent Krijgslaan 281 S9 9000 Gent Belgium Phone: +32 9 264 4805 http://users.ugent.be/~tschrijv/

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Typeable typeclass and type-level naturals
by TP 06 Jun '13

06 Jun '13

Hi all, I try to play with the "Typeable" typeclass, and I have some difficulties to make it work in this simple case where I use type-level naturals: --------------------- {-# LANGUAGE GADTs #-} {-# LANGUAGE DeriveDataTypeable #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE StandaloneDeriving #-} import Data.Typeable data Nat = Zero | Succ Nat deriving ( Show, Eq, Ord, Typeable ) data Box where Box :: (Typeable s, Show s, Eq s) => s -> Box deriving Typeable data Proxy a = P deriving Typeable deriving instance Show Box instance Eq Box where (Box s1) == (Box s2) = Just s1 == cast s2 main = do let one = undefined :: Main.Proxy ('Succ 'Zero) let foo = Box one print foo --------------------- I obtain: --------------------- No instance for (Typeable Nat 'Zero) arising from a use of ‛Box’ In the expression: Box one In an equation for ‛foo’: foo = Box one In the expression: do { let one = ...; let foo = Box one; print foo } --------------------- Note that it is necessary to use the HEAD version of GHC to obtain this message (I use version 7.7.20130525); with GHC 7.6.2, the message is different because recent improvements in Typeable are not present (1). What is the problem? I've tried different things without success. Tell me if the "beginners" diffusion list is more suitable than Haskell- Cafe. Thanks, TP (1): http://hauptwerk.blogspot.fr/2012/11/coming-soon-in-ghc-head-poly-kinded.ht…

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Why isn't hsc2hs functionality provided by ghc?
by silly8888 06 Jun '13

06 Jun '13

I was wondering today, why hasn't hsc2hs been merged with ghc so that it would be possible to add a {-# LANGUAGE ForeignFunctionInterface #-} at the top of a source file and then load it with ghci or compile it, without the intermediate step of calling hsc2hs? This would be exactly like the CPP extension. I don't have to call cpp manually. All I have to do is to add {-# LANGUAGE CPP #-} and then ghc will take care of the rest. This would also mean that there would be no need to have a separate file extension. Surely I must not be the first person to have that thought, so there must be a good reason why this hasn't happen yet, but what is it?

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Haskell Weekly News: Issue 269
by Daniel Santa Cruz 06 Jun '13

06 Jun '13

Welcome to issue 269 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of May 26 to June 1, 2013. Quotes of the Week * neutrino: i've been teaching people about functional programming etc (when I came in there was exactly 0 knowledge about this, after I joined that changed, but not sure in which direction) Top Reddit Stories * Haskell Platform 2013.2.0.0 is out Domain: haskell.org, Score: 103, Comments: 19 On Reddit: [1] http://goo.gl/Iabii Original: [2] http://goo.gl/DniAP * Elm & Prezi: I'm now working on Elm full-time! Domain: elm-lang.org, Score: 96, Comments: 18 On Reddit: [3] http://goo.gl/03Aab Original: [4] http://goo.gl/4o1Xh * ANN: Idris 0.9.8 released Domain: idris-lang.org, Score: 54, Comments: 58 On Reddit: [5] http://goo.gl/PGrXi Original: [6] http://goo.gl/birp8 * Type-Safe Runtime Code Generation with (Typed) Template Haskell Domain: gmainland.blogspot.co.uk, Score: 54, Comments: 17 On Reddit: [7] http://goo.gl/rMEFc Original: [8] http://goo.gl/MBOJn * Elm 0.8 released! Type annotations and aliases, better HTML/JS integration, and lots more Domain: elm-lang.org, Score: 50, Comments: 10 On Reddit: [9] http://goo.gl/B9AIa Original: [10] http://goo.gl/tM3Qq * Why did the Haskeller need to replace his keyboard regularly? Domain: self.haskell, Score: 48, Comments: 9 On Reddit: [11] http://goo.gl/FHiCn Original: [12] http://goo.gl/FHiCn * Towards a better Haskell package Domain: fvisser.nl, Score: 40, Comments: 26 On Reddit: [13] http://goo.gl/XNFGM Original: [14] http://goo.gl/jbW4Q * What does the Haskell runtime look like? Domain: self.haskell, Score: 37, Comments: 17 On Reddit: [15] http://goo.gl/n8bqD Original: [16] http://goo.gl/n8bqD * The AST Typing Problem Domain: blog.ezyang.com, Score: 33, Comments: 14 On Reddit: [17] http://goo.gl/nYMNg Original: [18] http://goo.gl/FYpD2 * [haskell.org Google Summer of Code 2013] Approved Projects Domain: haskell.org, Score: 28, Comments: 10 On Reddit: [19] http://goo.gl/hnSnz Original: [20] http://goo.gl/IUE0U Top StackOverflow Questions * What's the best way to exit a Haskell program? votes: 25, answers: 1 Read on SO: [21] http://goo.gl/3AQdw * Haskell Conduit: One processing conduit, 2 IO sources of the same type votes: 23, answers: 0 Read on SO: [22] http://goo.gl/12dwP * Why is length of “Níðhöggr” 9? votes: 22, answers: 2 Read on SO: [23] http://goo.gl/emGGm * What is a solid example of something that can be done with list comprehensions that is tricky with high order functions? votes: 11, answers: 5 Read on SO: [24] http://goo.gl/fJMcg * Fibonacci Seq. strange output forms (Haskell) votes: 10, answers: 2 Read on SO: [25] http://goo.gl/9OQYW * Gnuplot in Haskell: don't enter gnuplot terminal votes: 10, answers: 0 Read on SO: [26] http://goo.gl/Fwb66 * Haskell: YesNo type class. Why Integer? votes: 10, answers: 3 Read on SO: [27] http://goo.gl/jnLLH * Is it possible to use extended precision (80-bit) floating point arithmetic in GHC/Haskell? votes: 9, answers: 1 Read on SO: [28] http://goo.gl/HUUoL * Having trouble understanding list comprehensions votes: 9, answers: 2 Read on SO: [29] http://goo.gl/JkNL3 * What is the rule of the order of multiple type variables in haskell? votes: 9, answers: 1 Read on SO: [30] http://goo.gl/1whHM Until next time, +Daniel Santa Cruz References 1. http://www.haskell.org/platform/ 2. http://www.reddit.com/r/haskell/comments/1f6l2a/haskell_platform_2013200_is… 3. http://elm-lang.org/blog/announce/Elm-and-Prezi.elm 4. http://www.reddit.com/r/haskell/comments/1f9yd8/elm_prezi_im_now_working_on… 5. http://idris-lang.org/archives/272 6. http://www.reddit.com/r/haskell/comments/1f75ge/ann_idris_098_released/ 7. http://gmainland.blogspot.co.uk/2013/05/type-safe-runtime-code-generation-w… 8. http://www.reddit.com/r/haskell/comments/1feqhn/typesafe_runtime_code_gener… 9. http://elm-lang.org/blog/announce/version-0.8.elm 10. http://www.reddit.com/r/haskell/comments/1f77h0/elm_08_released_type_annota… 11. http://www.reddit.com/r/haskell/comments/1f6gjs/why_did_the_haskeller_need_… 12. http://www.reddit.com/r/haskell/comments/1f6gjs/why_did_the_haskeller_need_… 13. http://fvisser.nl/post/2013/may/28/towards-a-better-haskell-package.html 14. http://www.reddit.com/r/haskell/comments/1f70wi/towards_a_better_haskell_pa… 15. http://www.reddit.com/r/haskell/comments/1f48dc/what_does_the_haskell_runti… 16. http://www.reddit.com/r/haskell/comments/1f48dc/what_does_the_haskell_runti… 17. http://blog.ezyang.com/2013/05/the-ast-typing-problem/ 18. http://www.reddit.com/r/haskell/comments/1f91w3/the_ast_typing_problem/ 19. http://www.haskell.org/pipermail/haskell-cafe/2013-May/108458.html 20. http://www.reddit.com/r/haskell/comments/1f6ve7/haskellorg_google_summer_of… 21. http://stackoverflow.com/questions/16872898/whats-the-best-way-to-exit-a-ha… 22. http://stackoverflow.com/questions/16757060/haskell-conduit-one-processing-… 23. http://stackoverflow.com/questions/16779251/why-is-length-of-nidhoggr-9 24. http://stackoverflow.com/questions/16784162/what-is-a-solid-example-of-some… 25. http://stackoverflow.com/questions/16762009/fibonacci-seq-strange-output-fo… 26. http://stackoverflow.com/questions/16803070/gnuplot-in-haskell-dont-enter-g… 27. http://stackoverflow.com/questions/16824047/haskell-yesno-type-class-why-in… 28. http://stackoverflow.com/questions/16797802/is-it-possible-to-use-extended-… 29. http://stackoverflow.com/questions/16805135/having-trouble-understanding-li… 30. http://stackoverflow.com/questions/16860473/what-is-the-rule-of-the-order-o… 31. https://plus.google.com/105107667630152149014/about

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Re: [Haskell-cafe] [haskell.org Google Summer of Code 2013] Approved Projects
by Dominic Steinitz 05 Jun '13

05 Jun '13

Hi Edward, Although the project I am interested in (as a user) has been accepted :-), I can't help feeling the selection process is a bit opaque. Is it documented somewhere and I just missed it? Apologies if I did. BTW I appreciate all the hard work that goes into the selection process. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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Different answers on different machines
by nadine.and.henry＠pobox.com 05 Jun '13

05 Jun '13

Dear HCafe-ers, Yesterday I decided to take a look at the most recent Euler problem, number 249, and give it a shot. I have a couple of computers at home, a Dell laptop and a desktop. I compiled this message with ghc -O2 --make ex429.lhs and ran it on each machine. On the Dell I get: time ./ex429 [650,16900,547924,27396200,746640991,773879749,683631060] [650,16900,547924,27396200,746640991,773879749,683631060] 136342232 ./ex429 8.66s user 0.02s system 99% cpu 8.695 total When I run this exact same file on the desktop, I get: time ./ex429 [650,16900,547924,27396200,746640991,773879749,683631060] [650,16900,547924,27396200,746640991,773879749,683631060] 98792821 ./ex429 6.50s user 0.03s system 99% cpu 6.537 total Which happens to be the right answer. But WHY is the output from the Dell different? Machine info is at the bottom of this message. >{-# LANGUAGE BangPatterns #-} >{-# LANGUAGE FlexibleContexts #-} >{-# OPTIONS -O2 -optc-O #-} >{- >Sum of squares of unitary divisors >Problem 429 >A unitary divisor d of a number n is a divisor of n that has the property gcd(d, n/d) = 1. >The unitary divisors of 4! = 24 are 1, 3, 8 and 24. >The sum of their squares is 12 + 32 + 82 + 242 = 650. > >Let S(n) represent the sum of the squares of the unitary divisors of n. Thus S(4!)=650. > >Find S(100 000 000!) modulo 1 000 000 009. > > >-} > > >import Control.Monad.ST >import Data.Array.ST >import Data.Array.IArray as I >import Data.Array.Unboxed as U >import Data.Word >import Data.Ord >import Data.List > >allfactors n = [ i | i <- [1..n] , n `mod` i == 0] > >factorial n = product [1..n] >ud0 n = > let > nf = factorial n > a = allfactors nf > b = filter (\x -> gcd x (nf `div` x) == 1) a > in b > >ud1 = sum . map (\x -> x*x) . ud0 >ansSlow n = ud1 n `mod` (fromIntegral modulus) > >largestExponentInFactorial n p = > let a = [ n `div` (p^i) | i <- [1..] ] > b = takeWhile (>0) a > in sum b > >modProduct :: [Int] -> Int >modProduct = foldl' (\a b -> times a b modulus) 1 > >pA n = primesA (fromIntegral n) > >primesN :: Int -> [Int] >primesN n = map fromIntegral $ primeS (pA n) > >times :: Int -> Int -> Int -> Int >times x y n = > let > x1 = fromIntegral x :: Integer > y1 = fromIntegral y :: Integer > n1 = fromIntegral n :: Integer > result = fromIntegral $! x1 * y1 `mod` n1 > in result > >fastPower :: Int -> Int -> Int -> Int >fastPower x 0 modulus = 1 >fastPower x 1 modulus = x `mod` modulus >fastPower x n modulus > | even n = fastPower (times x x modulus) (n `div` 2) modulus > | otherwise = (times x (fastPower x (n-1) modulus)) modulus > > >foldFun :: Int -> Int -> Int >foldFun n p = > let > a = largestExponentInFactorial n p > b = fastPower p a modulus > c = times b b modulus + 1 > in c > >ff :: Int -> [Int] -> Int >ff n = foldl' (\a p -> times a (foldFun n p) modulus) 1 > > >ans n = > let > ps = primeS $ primesA n > -- ps = takeWhile (<= n) primes > in ff n ps > >modulus = 1000000009 :: Int >main = do > print $ map ans [4..10] > print $ map ansSlow [4..10] > print $ ans 100000000 > > > >{- > >intended Usage: > >pA = primesA (10^9) >primes = primeS pA >isPrime = isPrimE pA > > > >-} > > > >sieve :: STUArray s Int Bool -> Int -> Int -> ST s (STUArray s Int Bool) >sieve !a !m !n > | n == m = return a > | otherwise = do > e <- readArray a (fromIntegral n) > if e > then let loop !j > | j <= m = writeArray a (fromIntegral j) False >> loop (j+n) > | otherwise = sieve a m (n+1) > in loop (n+n) > else sieve a m (n+1) > > >primesA :: Int -> UArray Int Bool >primesA sizeN = > runSTUArray (do a <- newArray (0,sizeN) True > :: ST s (STUArray s Int Bool) > writeArray a 0 False > writeArray a 1 False > sieve a sizeN 2) > > >primeS :: (IArray a1 Bool, Ix a) => a1 a Bool -> [a] >primeS primeArray = map fst $ filter (\x -> snd x) (assocs primeArray) > >isPrimE :: (IArray a e, Ix i) => a i e -> i -> e >isPrimE primeArray n = primeArray I.! n > AMD-64 Desktop uname -a Linux myth 3.2.0-4-amd64 #1 SMP Debian 3.2.41-2+deb7u2 x86_64 GNU/Linux ghc --version The Glorious Glasgow Haskell Compilation System, version 7.6.2 hwinfo --cpu 01: None 00.0: 10103 CPU [Created at cpu.304] Unique ID: rdCR.j8NaKXDZtZ6 Hardware Class: cpu Arch: X86-64 Vendor: "AuthenticAMD" Model: 21.1.2 "AMD FX(tm)-4100 Quad-Core Processor " Features: fpu,vme,de,pse,tsc,msr,pae,mce,cx8,apic,sep,mtrr,pge,mca,cmov,pat,pse36,clflush,mmx,fxsr,sse,sse2,ht,syscall,nx,mmxext,fxsr_opt,pdpe1gb,rdtscp,lm,constant_tsc,rep_good,nopl,nonstop_tsc,extd_apicid,aperfmperf,pni,pclmulqdq,monitor,ssse3,cx16,sse4_1,sse4_2, Clock: 1400 MHz BogoMips: 7248.25 Cache: 2048 kb Units/Processor: 4 Config Status: cfg=new, avail=yes, need=no, active=unknown 02: None 01.0: 10103 CPU [Created at cpu.304] Unique ID: wkFv.j8NaKXDZtZ6 Hardware Class: cpu Arch: X86-64 Vendor: "AuthenticAMD" Model: 21.1.2 "AMD FX(tm)-4100 Quad-Core Processor " Features: fpu,vme,de,pse,tsc,msr,pae,mce,cx8,apic,sep,mtrr,pge,mca,cmov,pat,pse36,clflush,mmx,fxsr,sse,sse2,ht,syscall,nx,mmxext,fxsr_opt,pdpe1gb,rdtscp,lm,constant_tsc,rep_good,nopl,nonstop_tsc,extd_apicid,aperfmperf,pni,pclmulqdq,monitor,ssse3,cx16,sse4_1,sse4_2, Clock: 3600 MHz BogoMips: 9201.22 Cache: 2048 kb Units/Processor: 4 Config Status: cfg=new, avail=yes, need=no, active=unknown 03: None 02.0: 10103 CPU [Created at cpu.304] Unique ID: +rIN.j8NaKXDZtZ6 Hardware Class: cpu Arch: X86-64 Vendor: "AuthenticAMD" Model: 21.1.2 "AMD FX(tm)-4100 Quad-Core Processor " Features: fpu,vme,de,pse,tsc,msr,pae,mce,cx8,apic,sep,mtrr,pge,mca,cmov,pat,pse36,clflush,mmx,fxsr,sse,sse2,ht,syscall,nx,mmxext,fxsr_opt,pdpe1gb,rdtscp,lm,constant_tsc,rep_good,nopl,nonstop_tsc,extd_apicid,aperfmperf,pni,pclmulqdq,monitor,ssse3,cx16,sse4_1,sse4_2, Clock: 1400 MHz BogoMips: 7253.01 Cache: 2048 kb Units/Processor: 4 Config Status: cfg=new, avail=yes, need=no, active=unknown 04: None 03.0: 10103 CPU [Created at cpu.304] Unique ID: 4zLr.j8NaKXDZtZ6 Hardware Class: cpu Arch: X86-64 Vendor: "AuthenticAMD" Model: 21.1.2 "AMD FX(tm)-4100 Quad-Core Processor " Features: fpu,vme,de,pse,tsc,msr,pae,mce,cx8,apic,sep,mtrr,pge,mca,cmov,pat,pse36,clflush,mmx,fxsr,sse,sse2,ht,syscall,nx,mmxext,fxsr_opt,pdpe1gb,rdtscp,lm,constant_tsc,rep_good,nopl,nonstop_tsc,extd_apicid,aperfmperf,pni,pclmulqdq,monitor,ssse3,cx16,sse4_1,sse4_2, Clock: 1400 MHz BogoMips: 6931.30 Cache: 2048 kb Units/Processor: 4 Config Status: cfg=new, avail=yes, need=no, active=unknown ------------------------------------------------------------------------ Dell Laptop uname -a Linux dell 3.2.0-4-amd64 #1 SMP Debian 3.2.41-2 x86_64 GNU/Linux ghc --version The Glorious Glasgow Haskell Compilation System, version 7.6.3 01: None 00.0: 10103 CPU [Created at cpu.304] Unique ID: rdCR.j8NaKXDZtZ6 Hardware Class: cpu Arch: Intel Vendor: "GenuineIntel" Model: 6.42.7 "Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz" Features: fpu,vme,de,pse,tsc,msr,pae,mce,cx8,apic,sep,mtrr,pge,mca,cmov,pat,pse36,clflush,dts,acpi,mmx,fxsr,sse,sse2,ss,ht,tm,pbe,syscall,nx,rdtscp,lm,constant_tsc,arch_perfmon,pebs,bts,nopl,xtopology,nonstop_tsc,aperfmperf,pni,pclmulqdq,dtes64,monitor,ds_cpl,vmx,e Clock: 800 MHz BogoMips: 3987.12 Cache: 6144 kb Units/Processor: 16 Config Status: cfg=new, avail=yes, need=no, active=unknown 02: None 01.0: 10103 CPU [Created at cpu.304] Unique ID: wkFv.j8NaKXDZtZ6 Hardware Class: cpu Arch: Intel Vendor: "GenuineIntel" Model: 6.42.7 "Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz" Features: fpu,vme,de,pse,tsc,msr,pae,mce,cx8,apic,sep,mtrr,pge,mca,cmov,pat,pse36,clflush,dts,acpi,mmx,fxsr,sse,sse2,ss,ht,tm,pbe,syscall,nx,rdtscp,lm,constant_tsc,arch_perfmon,pebs,bts,nopl,xtopology,nonstop_tsc,aperfmperf,pni,pclmulqdq,dtes64,monitor,ds_cpl,vmx,e Clock: 800 MHz BogoMips: 3986.91 Cache: 6144 kb Units/Processor: 16 Config Status: cfg=new, avail=yes, need=no, active=unknown 03: None 02.0: 10103 CPU [Created at cpu.304] Unique ID: +rIN.j8NaKXDZtZ6 Hardware Class: cpu Arch: Intel Vendor: "GenuineIntel" Model: 6.42.7 "Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz" Features: fpu,vme,de,pse,tsc,msr,pae,mce,cx8,apic,sep,mtrr,pge,mca,cmov,pat,pse36,clflush,dts,acpi,mmx,fxsr,sse,sse2,ss,ht,tm,pbe,syscall,nx,rdtscp,lm,constant_tsc,arch_perfmon,pebs,bts,nopl,xtopology,nonstop_tsc,aperfmperf,pni,pclmulqdq,dtes64,monitor,ds_cpl,vmx,e Clock: 800 MHz BogoMips: 3986.92 Cache: 6144 kb Units/Processor: 16 Config Status: cfg=new, avail=yes, need=no, active=unknown 04: None 03.0: 10103 CPU [Created at cpu.304] Unique ID: 4zLr.j8NaKXDZtZ6 Hardware Class: cpu Arch: Intel Vendor: "GenuineIntel" Model: 6.42.7 "Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz" Features: fpu,vme,de,pse,tsc,msr,pae,mce,cx8,apic,sep,mtrr,pge,mca,cmov,pat,pse36,clflush,dts,acpi,mmx,fxsr,sse,sse2,ss,ht,tm,pbe,syscall,nx,rdtscp,lm,constant_tsc,arch_perfmon,pebs,bts,nopl,xtopology,nonstop_tsc,aperfmperf,pni,pclmulqdq,dtes64,monitor,ds_cpl,vmx,e Clock: 800 MHz BogoMips: 3986.92 Cache: 6144 kb Units/Processor: 16 Config Status: cfg=new, avail=yes, need=no, active=unknown 05: None 04.0: 10103 CPU [Created at cpu.304] Unique ID: 94PJ.j8NaKXDZtZ6 Hardware Class: cpu Arch: Intel Vendor: "GenuineIntel" Model: 6.42.7 "Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz" Features: fpu,vme,de,pse,tsc,msr,pae,mce,cx8,apic,sep,mtrr,pge,mca,cmov,pat,pse36,clflush,dts,acpi,mmx,fxsr,sse,sse2,ss,ht,tm,pbe,syscall,nx,rdtscp,lm,constant_tsc,arch_perfmon,pebs,bts,nopl,xtopology,nonstop_tsc,aperfmperf,pni,pclmulqdq,dtes64,monitor,ds_cpl,vmx,e Clock: 800 MHz BogoMips: 3986.91 Cache: 6144 kb Units/Processor: 16 Config Status: cfg=new, avail=yes, need=no, active=unknown 06: None 05.0: 10103 CPU [Created at cpu.304] Unique ID: EBSn.j8NaKXDZtZ6 Hardware Class: cpu Arch: Intel Vendor: "GenuineIntel" Model: 6.42.7 "Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz" Features: fpu,vme,de,pse,tsc,msr,pae,mce,cx8,apic,sep,mtrr,pge,mca,cmov,pat,pse36,clflush,dts,acpi,mmx,fxsr,sse,sse2,ss,ht,tm,pbe,syscall,nx,rdtscp,lm,constant_tsc,arch_perfmon,pebs,bts,nopl,xtopology,nonstop_tsc,aperfmperf,pni,pclmulqdq,dtes64,monitor,ds_cpl,vmx,e Clock: 800 MHz BogoMips: 3986.92 Cache: 6144 kb Units/Processor: 16 Config Status: cfg=new, avail=yes, need=no, active=unknown 07: None 06.0: 10103 CPU [Created at cpu.304] Unique ID: JIVF.j8NaKXDZtZ6 Hardware Class: cpu Arch: Intel Vendor: "GenuineIntel" Model: 6.42.7 "Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz" Features: fpu,vme,de,pse,tsc,msr,pae,mce,cx8,apic,sep,mtrr,pge,mca,cmov,pat,pse36,clflush,dts,acpi,mmx,fxsr,sse,sse2,ss,ht,tm,pbe,syscall,nx,rdtscp,lm,constant_tsc,arch_perfmon,pebs,bts,nopl,xtopology,nonstop_tsc,aperfmperf,pni,pclmulqdq,dtes64,monitor,ds_cpl,vmx,e Clock: 800 MHz BogoMips: 3986.91 Cache: 6144 kb Units/Processor: 16 Config Status: cfg=new, avail=yes, need=no, active=unknown 08: None 07.0: 10103 CPU [Created at cpu.304] Unique ID: OPYj.j8NaKXDZtZ6 Hardware Class: cpu Arch: Intel Vendor: "GenuineIntel" Model: 6.42.7 "Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz" Features: fpu,vme,de,pse,tsc,msr,pae,mce,cx8,apic,sep,mtrr,pge,mca,cmov,pat,pse36,clflush,dts,acpi,mmx,fxsr,sse,sse2,ss,ht,tm,pbe,syscall,nx,rdtscp,lm,constant_tsc,arch_perfmon,pebs,bts,nopl,xtopology,nonstop_tsc,aperfmperf,pni,pclmulqdq,dtes64,monitor,ds_cpl,vmx,e Clock: 800 MHz BogoMips: 3986.91 Cache: 6144 kb Units/Processor: 16 Config Status: cfg=new, avail=yes, need=no, active=unknown -- Best wishes, Henry Laxen

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How to write a pure String to String function in Haskell FFI to C++
by Ting Lei 05 Jun '13

05 Jun '13

Hi, I want to implement a function in C++ via Haskell FFI, which should have the (final) type of String -> String. Say, is it possible to re-implement the following function in C++ with the exact same signature? import Data.Char toUppers:: String -> String toUppers s = map toUpper senter code here In particular, I wanted to avoid having an IO in the return type because introducing the impurity (by that I mean the IO monad) for this simple task is logically unnecessary. All examples involing a C string I have seen so far involve returning an IO something or Ptr which cannot be converted back to a pure String. The reason I want to do this is that I have the impression that marshaling is not easy with FFI. Maybe if I can fix the simplest case above (other than primitive types such as int), then I can do whatever data parsing I want on the C++ side, which should be easy, practically. The cost of parsing is negligible compared to the computation that I want to do between the marshalling to/from strings. Thanks in advance.

6 7

Frankfurt Haskell User Group meets 19.6.13, topics: Netwire, Hackathon planning
by Peter Althainz 05 Jun '13

05 Jun '13

Dear All, all interested Haskellers are inivted to our Meetup on 19.6.13: http://www.meetup.com/Frankfurt-Haskell-User-Group/events/122879122/. Best regards Peter Althainz

1 0

code to HTML
by Corentin Dupont 03 Jun '13

03 Jun '13

Hello everybody, I'd like to transform a .hs file into a .html file. The objective is that the .html file, when rendered, looks exactly the same that the .hs, with the exeption that every function in the code is a link to its haddock documentation. Is that possible? The result would look like that: f xs = map<http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.ht…> head<http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.ht…>xs Thanks! Corentin

2 1

Announce: Leksah 0.13.2.2 (still a bit experimental)
by Hamish Mackenzie 03 Jun '13

03 Jun '13

Mostly just a refresh of the current development version binary installers, so people can use it with the latest Haskell Platform (which uses GHC 7.6.3). Unfortunately an official 0.14 release may still be a be a way off. I have been doing some work on getting Code Mirror working, but there are threading issues that will need to be resolved before it works (so best to leave the editor config set to GtkSourceView). I recommend you remove your ~/.leksah-0.13/prefs.lkshp file before installing as the format has changed slightly and it is not backwards compatibly. Hop on #leksah if you have any questions. OS X (Still no WebKit features) ------------------------------- Choose the version that matches your installed GHC http://leksah.org/packages/leksah-0.13.2.2-ghc-7.0.4.dmg http://leksah.org/packages/leksah-0.13.2.2-ghc-7.4.1.dmg http://leksah.org/packages/leksah-0.13.2.2-ghc-7.4.2.dmg http://leksah.org/packages/leksah-0.13.2.2-ghc-7.6.3.dmg Sorry, I am still having trouble building WebKitGTK+ on OSX. If you want a challenge... https://github.com/jralls/gtk-osx-build https://github.com/leksah/leksah/blob/master/osx/gtk.sh Alternatively we might have to build Leksah with -f-webkit to leave out the webkit stuff. Windows ------- Choose the version that matches your installed GHC http://leksah.org/packages/leksah-0.13.2.2-ghc-7.0.3.exe http://leksah.org/packages/leksah-0.13.2.2-ghc-7.0.4.exe http://leksah.org/packages/leksah-0.13.2.2-ghc-7.4.1.exe http://leksah.org/packages/leksah-0.13.2.2-ghc-7.4.2.exe http://leksah.org/packages/leksah-0.13.2.2-ghc-7.6.3.exe Linux ----- Follow the steps in the .travis.yml file... https://github.com/leksah/leksah/blob/master/.travis.yml Should go something like this... https://travis-ci.org/leksah/leksah

2 1

APLAS 2013 second call for papers
by Chung-chieh Shan 03 Jun '13

03 Jun '13

=============================================================== APLAS 2013 11th Asian Symposium on Programming Languages and Systems 9-11 December 2013 Melbourne, Australia (colocated with CPP 2013) CALL FOR PAPERS =============================================================== ========== BACKGROUND ========== APLAS aims to stimulate programming language research by providing a forum for the presentation of latest results and the exchange of ideas in programming languages and systems. APLAS is based in Asia, but is an international forum that serves the worldwide programming language community. APLAS is sponsored by the Asian Association for Foundation of Software (AAFS) founded by Asian researchers in cooperation with many researchers from Europe and the USA. Past APLAS symposiums were successfully held in Kyoto ('12), Kenting ('11), Shanghai ('10), Seoul ('09), Bangalore ('08), Singapore ('07), Sydney ('06), Tsukuba ('05), Taipei ('04) and Beijing ('03) after three informal workshops. Proceedings of the past symposiums were published in Springer's LNCS. ====== TOPICS ====== The symposium is devoted to foundational and practical issues in programming languages and systems. Papers are solicited on topics such as * semantics, logics, foundational theory; * design of languages, type systems and foundational calculi; * domain-specific languages; * compilers, interpreters, abstract machines; * program derivation, synthesis and transformation; * program analysis, verification, model-checking; * logic, constraint, probabilistic and quantum programming; * software security; * concurrency and parallelism; * tools and environments for programming and implementation. Topics are not limited to those discussed in previous symposiums. Papers identifying future directions of programming and those addressing the rapid changes of the underlying computing platforms are especially welcome. Demonstration of systems and tools in the scope of APLAS are welcome to the System and Tool presentations category. Authors concerned about the appropriateness of a topic are welcome to consult with program chair prior to submission. ========== SUBMISSION ========== We solicit submissions in two categories: *Regular research papers* describing original scientific research results, including tool development and case studies. Regular research papers should not exceed 16 pages in the Springer LNCS format, including bibliography and figures. They should clearly identify what has been accomplished and why it is significant. Submissions will be judged on the basis of significance, relevance, correctness, originality, and clarity. In case of lack of space, proofs, experimental results, or any information supporting the technical results of the paper could be provided as an appendix or a link to a web page, but reviewers are not obliged to read them. *System and Tool presentations* describing systems or tools that support theory, program construction, reasoning, or program execution in the scope of APLAS. System and Tool presentations are expected to be centered around a demonstration. The paper and the demonstration should identify the novelties of the tools and use motivating examples. System and Tool papers should not exceed 8 pages in the Springer LNCS format, including bibliography and figures. Submissions will be judged based on both the papers and the described systems or tools. It is highly desirable that the tools are available on the web. Papers should be submitted electronically via the submission web page: https://www.easychair.org/conferences/?conf=aplas2013 Acceptable formats are PostScript or PDF. Submitted papers must be unpublished and not submitted for publication elsewhere. Papers must be written in English. The proceedings will be published as a volume in Springer's LNCS series. Accepted papers must be presented at the conference. (While the general chair and the program chair cannot submit papers, other members of the program committee can.) ===== DATES ===== Abstract due: 10 June 2013 (Monday), 23:59 UTC Submission due: 14 June 2013 (Friday), 23:59 UTC Notification: 26 August 2013 (Monday) Final paper due: 19 September 2013 (Thursday) Conference: 9-11 December 2013 (Monday-Wednesday) ========== ORGANIZERS ========== General chair: Peter Schachte (University of Melbourne) Program chair: Chung-chieh Shan (Indiana University) Program committee: Filippo Bonchi (CNRS, ENS-Lyon, France) Yu-Fang Chen (Academia Sinica, Taiwan) Shigeru Chiba (The University of Tokyo, Japan) Jacques Garrigue (Nagoya University, Japan) Robert Glück (University of Copenhagen, Denmark) R. Govindarajan (Indian Institute of Science, India) Kazuhiro Inaba (Google, Inc., Japan) Jie-Hong Roland Jiang (National Taiwan University, Taiwan) Shin-ya Katsumata (Kyoto University, Japan) Gabriele Keller (University of New South Wales, Australia) Ana Milanova (Rensselaer Polytechnic Institute, USA) Keisuke Nakano (The University of Electro-Communications, Japan) Hakjoo Oh (Seoul National University, Korea) Bruno C. d. S. Oliveira (National University of Singapore, Singapore) Kaushik Rajan (Microsoft Research, India) Max Schäfer (Nanyang Technological University, Singapore) Ulrich Schöpp (Ludwig-Maximilians-Universität München, Germany) Paula Severi (University of Leicester, UK) Gang Tan (Lehigh University, USA) Hiroshi Unno (University of Tsukuba, Japan) Meng Wang (Chalmers University of Technology, Sweden) Jingling Xue (University of New South Wales, Australia) Mingsheng Ying (University of Technology, Sydney, Australia) Kenny Q. Zhu (Shanghai Jiao Tong University, China) ======= CONTACT ======= http://aplas2013.soic.indiana.edu/ aplas2013(a)easychair.org

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Re: [Haskell-cafe] Int is broken [Was: Different answers on different machines]
by Stephen Tetley 03 Jun '13

03 Jun '13

There was a quite long discussion here: http://conal.net/blog/posts/notions-of-purity-in-haskell On 2 June 2013 22:02, Tommy Thorn <tt1729(a)yahoo.com> wrote: ... > I wish this fatal flaw would be reconsidered for the next major revision. >

1 0

Two GHC-related GSoC Proposals
by Patrick Palka 02 Jun '13

02 Jun '13

Hi, I'm interested in participating in the GSoC by improving GHC with one of these two features: 1) Implement native support for compiling modules in parallel (see #910<http://hackage.haskell.org/trac/ghc/ticket/910>). This will involve making the compilation pipeline thread-safe, implementing the logic for building modules in parallel (with an emphasis on keeping compiler output deterministic), and lots of testing and benchmarking. Being able to seamlessly build modules in parallel will shorten the time it takes to recompile a project and will therefore improve the life of every GHC user. 2) Improve existing constant folding, strength reduction and peephole optimizations on arithmetic and logical expressions, and optionally implement a core-to-core pass for optimizing nested comparisons (relevant tickets include #2132 <http://hackage.haskell.org/trac/ghc/ticket/2132>, #5615 <http://hackage.haskell.org/trac/ghc/ticket/5615>,#4101<http://hackage.haskell.org/trac/ghc/ticket/4101>). GHC currently performs some of these simplifications (via its BuiltinRule framework), but there is a lot of room for improvement. For instance, the core for this snippet is essentially identical to the Haskell source: foo :: Int -> Int -> Int -> Int foo a b c = 10*((b+7+a+12+b+9)+4) + 5*(a+7+b+12+a+9) + 7 + b + c Yet the RHS is actually equivalent to 20*a + 26*b + c + 467 And: bar :: Int -> Int -> Int bar a b = a + b - a - b -- the RHS is should be optimized away to 0 Other optimizations include: multiplication and division by powers of two should be converted to shifts; multiple plusAddr calls with constant operands should be coalesced into a single plusAddr call; floating point functions should be constant folded, etc.. GHC should be able to perform all these algebraic simplifications. Of course, emphasis should be placed on the correctness of such transformations. A flag for performing unsafe optimizations like assuming floating point arithmetic is associative and distributive should be added. This proposal will benefit anybody writing or using numerically intensive code. I'm wondering what the community thinks of these projects. Which project is a better fit for GSoC, or are both a good fit? Is a mentor willing to supervise one of these projects? Thanks for your time. Patrick (A little about myself: I'm a Mathematics student in the US, and I've been programming in Haskell for about 3.5 years. Having a keen interest in Haskell and compilers, I began studying the GHC source about 1 year ago and I've since gotten a good understanding of its internals, contributing a few patches along the way.)

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question about "singletons"
by TP 02 Jun '13

02 Jun '13

Hi all, Following a discussion on Haskell Cafe some time ago (1), Roman C. wrote: """ On the other hand, the type 'Succ 'Zero has kind 'Nat and doesn't have any inhabitants — only types of kind * do. """ Indeed, this is what seems to occur in the following example: ----------------------- {-# LANGUAGE DataKinds #-} data Nat = Zero | Succ Nat deriving ( Show, Eq, Ord ) main = do let one = undefined :: 'Succ 'Zero print one ----------------------- We obtain an error (ghc 7.6.2): ----------------------- Kind mis-match Expected kind `OpenKind', but `Succ Zero' has kind `Nat' In an expression type signature: Succ Zero In the expression: undefined :: Succ Zero In an equation for `one': one = undefined :: Succ Zero ----------------------- (note that the error is slightly different in the HEAD version of GHC (2)). Is it related to the sentence "As bottom is an inhabitant of every type (though with some caveats concerning types of unboxed kind), bottoms can be used wherever a value of that type would be. " found at address (3)? Here we have a non-* kind, such that bottom would not be an inhabitant of ('Succ 'Zero). Why is this so? This seems to be an assumed choice (4), but I would like to understand the reason for this design, which makes necessary to use singletons, as explained at (4). Now, if I use a singleton to make my example work, I obtain an error when trying to make the type (Sing a) an instance of Show: ----------------------- {-# LANGUAGE DataKinds #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE StandaloneDeriving #-} data Nat = Zero | Succ Nat deriving ( Show, Eq, Ord ) data Sing :: a -> * deriving instance Show (Sing a) main = do let one = undefined :: Sing ('Succ 'Zero) print one ----------------------- The error is simply: ----------------------- test_noinhabitant_corrected.hs: Void showsPrec ----------------------- Why? Thanks, TP References: ---------- (1): https://groups.google.com/forum/?fromgroups#!topic/haskell-cafe/AltmX5iCFi8 (2): ----------------------- Expected a type, but ‛Succ Zero’ has kind ‛Nat’ In an expression type signature: Succ Zero In the expression: undefined :: Succ Zero In an equation for ‛one’: one = undefined :: Succ Zero ----------------------- (3): http://www.haskell.org/haskellwiki/Bottom (4): http://hackage.haskell.org/trac/ghc/wiki/TypeNats/Basics """ Both numeric and symbol literal types are empty---they have no inhabitants. However, they may be used as parameters to other type constructors, which makes them useful. """ """ A singleton type is simply a type that has only one interesting inhabitant. """

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Re: [Haskell-cafe] question about "singletons"
by wren ng thornton 02 Jun '13

02 Jun '13

On 6/1/13 3:18 PM, TP wrote: > In other words, bottom can be an inhabitant of a concrete type, not a type > constructor, which I can understand. But a type of kind Nat is a concrete > type, so why bottom cannot be an inhabitant of this type? The technical term is "proper type". That is, types are used as a way of characterizing collections of values; but, all sorts of things can exist at the type level. For lack of a better name, we call everything at the type level a "type", in order to distinguish them from things at the value level or kind level, etc. But in order to be a *proper* type, a type-level expression must serve to characterize a collection of values. Types of kind * are proper types, because they serve to characterize collections of values. Types of other kinds are not proper, since they do not characterize collections of values. Thus, we can't say: undefined :: (->) nor: undefined :: Maybe because (->) and Maybe are not proper types. It doesn't make sense to say that some value (like undefined) belongs to the collection of values characterized by them, since there is no such collection to belong to! The same sort of thing holds for datakinds. Types of kind 'Nat are not proper, in exactly the same way that types of kind *->* or *->*->* are not proper. -- Live well, ~wren

1 0

ANN: hledger 0.21
by Simon Michael 02 Jun '13

02 Jun '13

I'm pleased to announce hledger and hledger-web 0.21! hledger is a command-line tool and haskell library for tracking financial transactions, which are stored in a human-readable plain text format. In addition to reporting, it can also help you record new transactions, or convert CSV data from your bank. Add-on packages include hledger-web (providing a web interface), hledger-irr and hledger-interest. hledger is inspired by and compatible with John Wiegley's Ledger. For more, see http://hledger.org . Install it: cabal update; cabal install hledger [hledger-web] For more installation help, see http://hledger.org/MANUAL.html#installing . Or, sponsor a ready-to-run binary for your platform: http://hledger.org/DOWNLOAD.html . Release notes (http://hledger.org/NEWS.html#hledger-0.21) **Bugs fixed:** - parsing: don't fail when a csv amount has trailing whitespace (fixes #113) - web: don't show prices in the accounts sidebar (fixes #114) - web: show one line per commodity in charts. Needs more polish, but fixes #109. - web: bump yesod-platform dependency to avoid a cabal install failure **Journal reading:** - balance assertions are now checked after reading a journal **web command:** - web: support/require yesod 1.2 - web: show zero-balance accounts in the sidebar (fixes #106) - web: use nicer select2 autocomplete widgets in the add form **Documentation and infrastructure:** - add basic cabal test suites for hledger-lib and hledger Release contributors: - Xinruo Sun enhanced the hledger-web add form - Clint Adams added cabal test suites - Jeff Richards did hledger-web cleanup - Peter Simons provided the build bot

1 0

Simplest way to learn FRP through use
by Christopher Howard 01 Jun '13

01 Jun '13

I want to learn FRP but am having trouble wading through all the theory about how FRP is implemented and how it /could/ be used for various applications. What is the simplest, easiest-to-learn module or system allowing you to quickly make something interesting (if not very impressive) in an FRP style? Say, a simple simulation of some physical phenomena outputting its state to the terminal; or an object moving on the screen; or some other toy application that I could create and play with. -- frigidcode.com

4 5

mapFst and mapSnd
by Dominique Devriese 01 Jun '13

01 Jun '13

Hi all, I often find myself needing the following definitions: mapPair :: (a -> b) -> (c -> d) -> (a,c) -> (b,d) mapPair f g (x,y) = (f x, g y) mapFst :: (a -> b) -> (a,c) -> (b,c) mapFst f = mapPair f id mapSnd :: (b -> c) -> (a,b) -> (a,c) mapSnd = mapPair id But they seem missing from the prelude and Hoogle or Hayoo only turn up versions of them in packages like scion or fgl. Has anyone else felt the need for these functions? Am I missing some generalisation of them perhaps? Regards, Dominique

12 13

lifted-base linking failure with GHC HEAD
by Mateusz Kowalczyk 01 Jun '13

01 Jun '13

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Greetings, I'm attempting to build lifted-base (as a dependency for ghc-mod) but cabal-install fails every time during the linking phase. I pasted the full log of `cabal install lifted-base --verbose' to hpaste at [1]. I'm attempting to build it with GHC HEAD. Now, I should note that I have different directories for each ghc version in my ~. So, for ghc 7.6.3 I would have ~/ghc-7.6.3 with appropriate bin, lib etc. in there. I thought that might have made `ld' confused but I just tried to `cabal install lifted-base' with 7.6.3 and it succeeded. Any ideas about what might be wrong? [1] - http://hpaste.org/89046 - -- Mateusz K. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (GNU/Linux) iQIcBAEBAgAGBQJRqTOjAAoJEM1mucMq2pqXt+QQALM9oWexq5NrWwOmcIj+m+08 DdNpj37KYx+M+3SUZYQ7RVyW7pf7ounsl/1OtGGndhGBeBpeamOMeZxaYvIZr7da IUjd3Vgnl0W44G+T9Wg64g+MIgyy75oLFPNnP0BGbcLzDk5wVgAl/xl+H193lLmu LbBJGAzAE+YHIx1mM+mNGsYgr80dhpGTs5jGdauAEdsnZFdFGj86sxBeFBeKVF78 md0PA1HDwJSVo2FyAAULWhgPDpwBrScjNjTU2etMpegMto1aDaV7rwvJeNeewv15 89o19tpWTvdwxtddOI6YlBKFTL0u80IBlCRQ+NWwu7PB35wR67MbOchXx4qGJSOt TxNelfW+C3h0BW7KLskQjqcEPUKD1hYB5lAnOH2VOaTSFEN9QN66GhC3BHLJCBiu UWZBRyUikAsjRvWL6eQI+vc8fnPSieNa5K2jdPe410uHojr7Eq28WCCXsejaQ3e+ TviDUWLmGfJk97Zmz2NPy4oGqwNYvOQqXKZ4GIpzD1/UHfNUw9wykPuDCapuvXPl OcSlSyjPk70jG32aLEalVZKPYZ1g15VSY6d6WYquZO0mGpwL15Gvc8V7SlZfNpvT 8maX5CQEeNXqfEbl2PwnkfoCwvW7x2p7uD+M2MHxOozkn5vtUonXqFCOVCftE/nL KsYrafRMuMzNRCn4kE/M =OCEQ -----END PGP SIGNATURE-----

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Performance difference between Linux and Windows?
by James Jones 31 May '13

31 May '13

I've been having a great deal of fun writing a program to solve this year's Code Jam "Fair and Square"problem in Haskell (and learning about Haskell in the process). Having gotten it to work, I've been optimizing it as best I can. I'm not quite in Captain Ahab mode, but before I let it go I would like to find out what's behind a difference I've seen compiling and running the program under Linux and under Windows 7. Profiling it under Linux (compiled with GHC 7.4.1), it had a total allocation of 165,375,112 bytes. I had an opportunity to compile and run on Windows 7, with GHC 7.4.2. I expected it to run faster, since the Windows computer had a 3.1 GHz i7 and my Linux computer has a 2.8 GHz AMD Propus, but what I didn't expect was that the total allocation on the Windows version was 88,438,372 bytes! Thinking it might be due to a compiler improvement, I upgraded my Linux computer to Ubuntu 13.04 so I could get a newer GHC, but it didn't make much difference: total allocation 163,248,688 bytes. So, I'm wondering: what is it about either the Windows implementation or GHC 7.4.2 in particular that would make a factor of two difference in memory allocation? Should anyone wish to compile the program, let me know the best way to make the source available and I will happily do so; I also use Twan van Laarhoven's semilattice search tree code available at http://twanvl.nl/blog/haskell/SemilatticeSearchTree. James Jones

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Job opening Ph D student in type error diagnosis for domain specific languages in Haskell
by Jurriaan Hage 31 May '13

31 May '13

Dear Haskellers, Apologies in case you have received multiple copies. best, Jur =============================================================================== VACANCY : 1x Phd Student in domain specific type error diagnosis for Haskell =============================================================================== The activities of the Software Systems division at Utrecht University include research on programming methodologies, compiler construction, and program analysis, validation, and verification. For information about the research group of Software Technology, see: http://www.cs.uu.nl/wiki/Center Financed by the Netherlands Organisation for Scientific Research (NWO), we currently have a job opening for: * 1x PhD researcher (Ph D student) Software Technology Domain-specific languages (DSLs) have the potential both to reduce the effort of programming, and to result in programs that are easier to understand and maintain. For various good reasons, researchers have proposed to embed DSLs (then called EDSLs) into a general purpose host language. An important disadvantage of such an embedding is that it is very hard to make type error diagnosis domain-aware, because inconsistencies are by default explained in terms of the host language. We are currently looking for a highly motivated Ph D student to investigate this problem in the context of the functional language Haskell. The basic approach is to scale the concept of specialized type rules as developed by (Heeren, Hage and Swierstra, ICFP '03, see link below) for Haskell '98 to modern day Haskell with all of its type system extensions. The work is both technically challenging, i.e., how do you ensure that modifications to the type diagnositic process do not inadvertently change the type system, and practically immediately useful: making domain-specific type error diagnosis a reality for a full sized language such as Haskell is likely to have a pervasive influence on the field of domain-specific languages, and the language Haskell. The ICFP '03 paper can be found at http://www.cs.uu.nl/people/jur/scriptingthetypeinferencer.pdf A project paper that describes the context and aims of the current project can be found here: http://www.cs.uu.nl/people/jur/tfp2013_submission_2.pdf At first, the work will be prototyped in our own Utrecht Haskell Compiler. If succesfull, the work will also make its way into the GHC. We expect the candidate to communicate the results academically, to present the work at scientific conferences, to supervise Master students, and to assist in teaching courses at Bachelor or Master level. --------------------------------- What we are looking for --------------------------------- The candidate should have an MSc in Computer Science, be highly motivated, speak and write English very well, and be proficient in producing scientific reports. Knowledge of and experience with at least one of the following two areas is essential: * functional programming, and Haskell in particular * type system concepts Furthermore, we expect the candidate to be able to reason formally. Experience in compiler construction is expected to be useful in this project. --------------------------------- What we offer --------------------------------- You are offered a full-time position for 4 years. The gross salary is in the range between € 2083,- and maximum € 2664,- per month. The salary is supplemented with a holiday bonus of 8% and an end-of-year bonus of 8,3% per year. In addition we offer: a pension scheme, a partially paid parental leave, flexible employment conditions. Conditions are based on the Collective Labour Agreement Dutch Universities. We aim to start November 1, 2013 at the latest, but preferably sooner. --------------------------------- In order to apply --------------------------------- To apply please attach a letter of motivation, a curriculum vitae, and (email) addresses of two referees. Make sure to also include a transcript of the courses you have followed (at bachelor and master level), with the grades you obtained, and to include a sample of your scientific writing, e.g., the pdf of your master thesis. It is possible to apply for this position if you are close to obtaining your Master's. In that case include a letter of your supervisor with an estimate of your progress, and do not forget to include at least a sample of your technical writing skills. Application closes on the 20th of June 2013. For application, visit http://www.cs.uu.nl/vacatures/en/583630.html and follow the link to the official job application page at the bottom. --------------- Contact person --------------- For further information you can direct your inquiries to: Dr. Jurriaan Hage Phone: (+31) 30 253 3283 e-mail: J.Hage(a)uu.nl. website: http://www.cs.uu.nl/wiki/Hage/WebHome

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Call for Papers IFL 2013
by publicityifl＠gmail.com 31 May '13

31 May '13

=============================================================================== VACANCY : 1x Phd Student in domain specific type error diagnosis for Haskell =============================================================================== The activities of the Software Systems division at Utrecht University include research on programming methodologies, compiler construction, and program analysis, validation, and verification. For information about the research group of Software Technology, see: http://www.cs.uu.nl/wiki/Center Financed by the Netherlands Organisation for Scientific Research (NWO), we currently have a job opening for: * 1x PhD researcher (Ph D student) Software Technology Domain-specific languages (DSLs) have the potential both to reduce the effort of programming, and to result in programs that are easier to understand and maintain. For various good reasons, researchers have proposed to embed DSLs (then called EDSLs) into a general purpose host language. An important disadvantage of such an embedding is that it is very hard to make type error diagnosis domain-aware, because inconsistencies are by default explained in terms of the host language. We are currently looking for a highly motivated Ph D student to investigate this problem in the context of the functional language Haskell. The basic approach is to scale the concept of specialized type rules as developed by (Heeren, Hage and Swierstra, ICFP '03, see link below) for Haskell '98 to modern day Haskell with all of its type system extensions. The work is both technically challenging, i.e., how do you ensure that modifications to the type diagnositic process do not inadvertently change the type system, and practically immediately useful: making domain-specific type error diagnosis a reality for a full sized language such as Haskell is likely to have a pervasive influence on the field of domain-specific languages, and the language Haskell. The ICFP '03 paper can be found at http://www.cs.uu.nl/people/jur/scriptingthetypeinferencer.pdf A project paper that describes the context and aims of the current project can be found here: http://www.cs.uu.nl/people/jur/tfp2013_submission_2.pdf At first, the work will be prototyped in our own Utrecht Haskell Compiler. If succesfull, the work will also make its way into the GHC. We expect the candidate to communicate the results academically, to present the work at scientific conferences, to supervise Master students, and to assist in teaching courses at Bachelor or Master level. --------------------------------- What we are looking for --------------------------------- The candidate should have an MSc in Computer Science, be highly motivated, speak and write English very well, and be proficient in producing scientific reports. Knowledge of and experience with at least one of the following two areas is essential: * functional programming, and Haskell in particular * type system concepts Furthermore, we expect the candidate to be able to reason formally. Experience in compiler construction is expected to be useful in this project. --------------------------------- What we offer --------------------------------- You are offered a full-time position for 4 years. The gross salary is in the range between Û 2083,- and maximum Û 2664,- per month. The salary is supplemented with a holiday bonus of 8% and an end-of-year bonus of 8,3% per year. In addition we offer: a pension scheme, a partially paid parental leave, flexible employment conditions. Conditions are based on the Collective Labour Agreement Dutch Universities. We aim to start November 1, 2013 at the latest, but preferably sooner. --------------------------------- In order to apply --------------------------------- To apply please attach a letter of motivation, a curriculum vitae, and (email) addresses of two referees. Make sure to also include a transcript of the courses you have followed (at bachelor and master level), with the grades you obtained, and to include a sample of your scientific writing, e.g., the pdf of your master thesis. It is possible to apply for this position if you are close to obtaining your Master's. In that case include a letter of your supervisor with an estimate of your progress, and do not forget to include at least a sample of your technical writing skills. Application closes on the 20th of June 2013. For application, visit http://www.cs.uu.nl/vacatures/en/583630.html and follow the link to the official job application page at the bottom. --------------- Contact person --------------- For further information you can direct your inquiries to: Dr. Jurriaan Hage Phone: (+31) 30 253 3283 e-mail: J.Hage(a)uu.nl. website: http://www.cs.uu.nl/wiki/Hage/WebHome

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Projects using Shake
by Frerich Raabe 31 May '13

31 May '13

Hi, I'm considering to convert one of my projects to Shake; everything I've seen so far seemed really interesting! However, before I start, I'd like to see how other people structure their Shake-based build systems. I tried to find some open source projects which showcase how Shake is used, but unfortunately I didn't find anything yet. Is anybody aware of open source projects which I could look at, or is there maybe a conventional file extension for… what do you call them, "Shakefiles"? other than .hs which I could google for? -- Frerich Raabe - raabe(a)froglogic.com www.froglogic.com - Multi-Platform GUI Testing

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Haskell Weekly News: Issue 268
by Daniel Santa Cruz 31 May '13

31 May '13

Welcome to issue 268 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of May 12 to 25, 2013. Quotes of the Week * tikhonjelvis: the lesson is that the fix function exists to "fix" any type problems you may encounter * shachaf: The trouble with peano arithmetic is that it stops at 88. * Peaker: Python's dynamic nature adds slowness and unsafety, but doesn't actually make things more expressive * sj4nz: Programming in weakly-typed languages forever after will feel like working with punch cards. Send in your program to the nodejs interpreter and hope for a result to come back. * xplat: if you want to carry your machete all the time and not make people nervous, you need to constantly blaze trails * otters: heh, F# is just the unboxed version of F * quchen: This was the first time in months that I thought imperatively. Conclusion: 1. it complicated things, 2. it was refreshing * cmccann: I still kind of expect that the next standard will be haskell2017 or something, and all it will do is a minor change to lexical syntax of comments that fixes nothing but nevertheless breaks 20% of hackage. * cmccann: [on reimplementing cryptography in pure Haskell] writing in Haskell lets you use type safety to ensure that all the security holes you create are subtle instead of obvious. Top Reddit Stories * Haskell in Production [slides] Domain: mth.io, Score: 60, Comments: 114 On Reddit: [1] http://goo.gl/ldnv0 Original: [2] http://goo.gl/tMjTd * B-trees with GADTs Domain: matthew.brecknell.net, Score: 56, Comments: 6 On Reddit: [3] http://goo.gl/Sjf9U Original: [4] http://goo.gl/sQnYW * Yearly revisions to the Haskell language: who killed Haskell Prime? Domain: self.haskell, Score: 54, Comments: 19 On Reddit: [5] http://goo.gl/5GWKg Original: [6] http://goo.gl/5GWKg * Elm paper accepted at PLDI: Asynchronous FRP for GUIs! Domain: people.seas.harvard.edu, Score: 51, Comments: 4 On Reddit: [7] http://goo.gl/iYiyh Original: [8] http://goo.gl/98jft * The complete correctness of sorting [Agda] Domain: twanvl.nl, Score: 49, Comments: 5 On Reddit: [9] http://goo.gl/PLH6m Original: [10] http://goo.gl/RQGZn * Anatomy of an MVar operation Domain: blog.ezyang.com, Score: 47, Comments: 7 On Reddit: [11] http://goo.gl/7miao Original: [12] http://goo.gl/3ZHSI * Typing Haskell in Haskell Domain: web.cecs.pdx.edu, Score: 44, Comments: 34 On Reddit: [13] http://goo.gl/q1ghy Original: [14] http://goo.gl/M5csQ * STM in Haskell is better because of types Domain: joeyh.name, Score: 44, Comments: 8 On Reddit: [15] http://goo.gl/wj9Ab Original: [16] http://goo.gl/fmLM1 * Typed Template Haskell ready for testing in GHC Domain: haskell.org, Score: 44, Comments: 13 On Reddit: [17] http://goo.gl/he61y Original: [18] http://goo.gl/YJIZB * A detailed look at GHC's STM implementation from a non-GHC hacker Domain: fryguybob.github.io, Score: 38, Comments: 11 On Reddit: [19] http://goo.gl/pTp2c Original: [20] http://goo.gl/4oe3Y * New Haskell Communities and Activity Report (May 2013) is out Domain: haskell.org, Score: 37, Comments: 2 On Reddit: [21] http://goo.gl/P2kz1 Original: [22] http://goo.gl/YoIE4 * Three examples of problems with Lazy I/O Domain: newartisans.com, Score: 36, Comments: 31 On Reddit: [23] http://goo.gl/reKqZ Original: [24] http://goo.gl/ZagPt * Understanding the Yoneda Lemma Domain: fpcomplete.com, Score: 35, Comments: 48 On Reddit: [25] http://goo.gl/RUZ4h Original: [26] http://goo.gl/xbAJj * Simon Peyton Jones to keynote Haskell eXchange 2013! Domain: skillsmatter.com, Score: 35, Comments: 2 On Reddit: [27] http://goo.gl/DlfRt Original: [28] http://goo.gl/5lpwh * Greg Hale's "Functional programming elevator pitch" Domain: fpcomplete.com, Score: 34, Comments: 8 On Reddit: [29] http://goo.gl/gbhX3 Original: [30] http://goo.gl/QrrxP * FP Complete is looking for a Technical Sales Engineer and Support Specialist Domain: fpcomplete.com, Score: 32, Comments: 1 On Reddit: [31] http://goo.gl/nYNci Original: [32] http://goo.gl/VGCoa * A Typed Markup Language Based On Haskell Domain: blog.functorial.com, Score: 31, Comments: 9 On Reddit: [33] http://goo.gl/eLLjV Original: [34] http://goo.gl/wFxcv * Announcing: Snap Framework v0.12 Domain: snapframework.com, Score: 28, Comments: 2 On Reddit: [35] http://goo.gl/5wYLk Original: [36] http://goo.gl/KibyP * John Wiegley's "Understanding Continuations", on School of Haskell Domain: fpcomplete.com, Score: 27, Comments: 17 On Reddit: [37] http://goo.gl/ZT7d6 Original: [38] http://goo.gl/YitVR Top StackOverflow Questions * Why are if expressions frowned upon in Haskell? votes: 20, answers: 6 Read on SO: [39] http://goo.gl/NejhX * Haskell: `Map (a,b) c` versus `Map a (Map b c)`? votes: 19, answers: 3 Read on SO: [40] http://goo.gl/8f1hf * Why recursive `let` make space effcient? votes: 18, answers: 3 Read on SO: [41] http://goo.gl/QTLYQ * Should do-notation be avoided in Haskell? [duplicate] votes: 16, answers: 7 Read on SO: [42] http://goo.gl/MGiFr * Correspondence between type classes and grammar levels in the Chomsky hierarchy votes: 15, answers: 1 Read on SO: [43] http://goo.gl/LRJy2 * Calling Haskell from C# votes: 14, answers: 2 Read on SO: [44] http://goo.gl/n9QB1 * How do exceptions work in Haskell (part two)? votes: 13, answers: 1 Read on SO: [45] http://goo.gl/U2GDR * Can a monad be a comonad? votes: 11, answers: 5 Read on SO: [46] http://goo.gl/ESrc2 * Dynamic Programming Memoization in Haskell votes: 11, answers: 1 Read on SO: [47] http://goo.gl/Gp7c8 * Employing arrows to fold a list of tuples votes: 11, answers: 1 Read on SO: [48] http://goo.gl/shRWV Until next time, +Daniel Santa Cruz References 1. http://mth.io/talks/haskell-in-production/ 2. http://www.reddit.com/r/haskell/comments/1etssw/haskell_in_production_slide… 3. http://matthew.brecknell.net/post/btree-gadt/ 4. http://www.reddit.com/r/haskell/comments/1efuog/btrees_with_gadts/ 5. http://www.reddit.com/r/haskell/comments/1esmhj/yearly_revisions_to_the_has… 6. http://www.reddit.com/r/haskell/comments/1esmhj/yearly_revisions_to_the_has… 7. http://people.seas.harvard.edu/~chong/pubs/pldi13-elm.pdf 8. http://www.reddit.com/r/haskell/comments/1eie6m/elm_paper_accepted_at_pldi_… 9. http://twanvl.nl/blog/agda/sorting 10. http://www.reddit.com/r/haskell/comments/1exv2t/the_complete_correctness_of… 11. http://blog.ezyang.com/2013/05/anatomy-of-an-mvar-operation/ 12. http://www.reddit.com/r/haskell/comments/1eostu/anatomy_of_an_mvar_operatio… 13. http://web.cecs.pdx.edu/~mpj/thih/TypingHaskellInHaskell.html 14. http://www.reddit.com/r/haskell/comments/1e6s68/typing_haskell_in_haskell/ 15. http://joeyh.name/blog/entry/the_newinwheezy_game:_STM/ 16. http://www.reddit.com/r/haskell/comments/1e8ow9/stm_in_haskell_is_better_be… 17. http://www.haskell.org/pipermail/ghc-devs/2013-May/001255.html 18. http://www.reddit.com/r/haskell/comments/1egfra/typed_template_haskell_read… 19. http://fryguybob.github.io/STM-Commentary/ 20. http://www.reddit.com/r/haskell/comments/1ejgjo/a_detailed_look_at_ghcs_stm… 21. http://haskell.org/communities/05-2013/html/report.html 22. http://www.reddit.com/r/haskell/comments/1e601k/new_haskell_communities_and… 23. http://newartisans.com/2013/05/three-examples-of-problems-with-lazy-io 24. http://www.reddit.com/r/haskell/comments/1e8k3k/three_examples_of_problems_… 25. https://www.fpcomplete.com/user/bartosz/understanding-yoneda 26. http://www.reddit.com/r/haskell/comments/1eelao/understanding_the_yoneda_le… 27. http://skillsmatter.com/event/scala/haskell-exchange/te-7391 28. http://www.reddit.com/r/haskell/comments/1ewq54/simon_peyton_jones_to_keyno… 29. https://www.fpcomplete.com/user/imalsogreg/functional-programming-elevator-… 30. http://www.reddit.com/r/haskell/comments/1ewvhm/greg_hales_functional_progr… 31. https://www.fpcomplete.com/page/product_specialist 32. http://www.reddit.com/r/haskell/comments/1ezeng/fp_complete_is_looking_for_… 33. http://blog.functorial.com/posts/2013-05-18-Typed-Markup-Language.html 34. http://www.reddit.com/r/haskell/comments/1elhj2/a_typed_markup_language_bas… 35. http://snapframework.com/blog/2013/05/15/snap-0.12-released 36. http://www.reddit.com/r/haskell/comments/1ef3kt/announcing_snap_framework_v… 37. https://www.fpcomplete.com/user/jwiegley/understanding-continuations 38. http://www.reddit.com/r/haskell/comments/1e977w/john_wiegleys_understanding… 39. http://stackoverflow.com/questions/16572446/why-are-if-expressions-frowned-… 40. http://stackoverflow.com/questions/16613032/haskell-map-a-b-c-versus-map-a-… 41. http://stackoverflow.com/questions/16632143/why-recursive-let-make-space-ef… 42. http://stackoverflow.com/questions/16726659/should-do-notation-be-avoided-i… 43. http://stackoverflow.com/questions/16607637/correspondence-between-type-cla… 44. http://stackoverflow.com/questions/16615641/calling-haskell-from-c-sharp 45. http://stackoverflow.com/questions/16678165/how-do-exceptions-work-in-haske… 46. http://stackoverflow.com/questions/16551734/can-a-monad-be-a-comonad 47. http://stackoverflow.com/questions/16585741/dynamic-programming-memoization… 48. http://stackoverflow.com/questions/16676758/employing-arrows-to-fold-a-list… 49. https://plus.google.com/105107667630152149014/about

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Re: [Haskell-cafe] using a win32 dll (Happy too soon)
by Brandon Allbery 31 May '13

31 May '13

On Thu, May 30, 2013 at 3:15 AM, Kees Bleijenberg < k.bleijenberg(a)lijbrandt.nl> wrote: > argument. The dll is in the PATH. I don't understand why it needs the -L > argument. I'll figure this out later. If I use -lglasPng.dll (additional > .dll) it doesn't work either. > Unix has standard places to install and search for libraries; Windows doesn't, and almost every library that doesn't come with your build system will need at least one -L option to tell the linker where to find it. As I mentioned in my first message, it looks for multiple file names with -l: first it tries a .dll, then it tries a .lib (static library or import library for older DLLs). It does this mechanically; if you also include the .dll suffix, then it looks for library.dll.dll and library.dll.lib, which is almost certainly wrong. -- brandon s allbery kf8nh sine nomine associates allbery.b(a)gmail.com ballbery(a)sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

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Re: [Haskell-cafe] [haskell.org Google Summer of Code 2013] Approved Projects
by Stephen Tetley 31 May '13

31 May '13

Similarly (to some degree), in the ML world John Reppy had a very nice system that employed user customization via combinators rather than inference to generate application/library specific FFIs, see: http://people.cs.uchicago.edu/~jhr/papers/2006/gpce-fig.pdf On 29 May 2013 18:57, Jason Dagit <dagitj(a)gmail.com> wrote: > Are you folks aware of the work on this topic by Tristan Ravitch? > https://github.com/travitch/foreign-inference > > Jason > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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ANN stm-chans 2.1 / 3.0
by wren ng thornton 30 May '13

30 May '13

-------------------------------------------- -- stm-chans 2.1 / 3.0 -------------------------------------------- The stm-chans package offers a collection of channel types, similar to Control.Concurrent.STM.{TChan,TQueue} but with additional features. -------------------------------------------- -- Changes (since 2.0.0) -------------------------------------------- By popular demand, the functions newBroadcastTMChan{,IO} have been added. However, these rely on newBroadcastTChan{,IO} which are only available in stm >= 2.4 and do not appear to be replicable using the public API of stm < 2.4. Thus, the minimum version of stm is now 2.4, which obviates all the compatibility modules. Version 2.1.0 adds the new functions and issues deprecation warnings about using the compatibility modules. This version is just to help people transition. If you can use this version without warnings (i.e., you don't use the Compat modules directly) then you should be able to use version 3.0 as well. Version 3.0 removes the compatibility modules. -------------------------------------------- -- Long description -------------------------------------------- In particular stm-chans offers the following data types: * Control.Concurrent.STM.TBChan: Bounded FIFO channels. When the channel is full, writers will block/retry. This ensures that the writers do not get too far ahead of the readers, which helps to make sure that memory and cpu resources are used responsibly. * Control.Concurrent.STM.TMChan: Closeable FIFO channels. * Control.Concurrent.STM.TMQueue: Closeable FIFO queues. Like TChan (Maybe a) but with a monotonicity guarantee that once Nothing is returned all future reads will be Nothing as well. * Control.Concurrent.STM.TBMChan: Bounded Closeable FIFO channels. * Control.Concurrent.STM.TBMQueue: Bounded Closeable FIFO queues. Combines the capabilities of TBChan and TMChan. -------------------------------------------- -- Links -------------------------------------------- Homepage: http://code.haskell.org/~wren/ Hackage: http://hackage.haskell.org/package/stm-chans Darcs: http://community.haskell.org/~wren/stm-chans Haddock (Darcs version): http://community.haskell.org/~wren/stm-chans/dist/doc/html/stm-chans -- Live well, ~wren

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Re: [Haskell-cafe] using a win32 dll (Happy too soon)
by Brandon Allbery 30 May '13

30 May '13

On Thu, May 30, 2013 at 11:46 AM, Kees Bleijenberg < k.bleijenberg(a)lijbrandt.nl> wrote: > Brandon, thanks again for your explanation > Are you sure about the non existing search order for dynamic loaded dll’s? > I.e. > http://msdn.microsoft.com/en-us/library/windows/desktop/ms682586(v=vs.85).a… there is a search order, starting with the current directory (I think). > There is a search order. What I said is that there are no standard locations to install things. That is, every library package stows stuff in its own directory structure and no compiler can possibly know all the places it needs to look to find every library off in its own directory. > I don’t understand why the linker needs to see the dll anyway. Because it's better to catch "that symbol doesn't exist" at build time instead of throwing an ugly error at runtime, among other things. > possible in Delphi. Is Haskell dynamic loading more limited? > There are ways to do that kind of dynamic linking; this is not one of them. C and C++ don't automatically dynload the way you're thinking either, because you should test for the DLL you're distributing (you are distributing it, right, not forcing the end user on a wild goose chase to find their own copy of the DLL, hoping it's the right/compatible version, and figure out where to put it so your program will run?) being the right one *when you build the program*, not defer that test until it is run. If you think about it, this is very similar to doing your type checking at compile time instead of runtime. If you want lazy type checking, why are you using Haskell? If you want lazy library checking, why are you using a compiler? -- brandon s allbery kf8nh sine nomine associates allbery.b(a)gmail.com ballbery(a)sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

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Re: [Haskell-cafe] Problem with compilation on MAC OS X
by Simon Thompson 30 May '13

30 May '13

Thanks - unfortunately it breaks cabal-install too! S. On 30 May 2013, at 13:28, Artyom Kazak <artyom.kazak(a)gmail.com> wrote: > Apparently, Agda has been broken by the recent decision to remove 'catch', which had already been deprecated for some time, from Prelude. You can fix the source yourself, or wait for a new release. > > On May 30, 2013 3:04 PM, "Simon Thompson" <s.j.thompson(a)kent.ac.uk> wrote: > Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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Problem with compilation on MAC OS X
by Simon Thompson 30 May '13

30 May '13

New machine, latest version of the Haskell Platform for 64 bit Mac OS X. In trying to build a new version of cabal-install and also of Agda I get variants of the same error dist/build/autogen/Paths_Agda.hs:21:13: Not in scope: `catch' any thoughts on what I am doing wrong? I have XCode command line tools installed. Thanks! Simon T. Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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Re: [Haskell-cafe] using a win32 dll (Happy too soon)
by Brandon Allbery 30 May '13

30 May '13

On Wed, May 29, 2013 at 9:40 AM, Kees Bleijenberg < k.bleijenberg(a)lijbrandt.nl> wrote: > If I compile with ghc --make testGlasPng.hs –lglasPng I get: ….\ld.exe: > cannot find –lglasPng. Collect 2: ld returned 1 exit status. > > ** > > Ld can’t find lglasPng (with the l in front, does it trim the l?). Why? > Okay I try > It's reproducing the thing passed to it, rather than outputting both the dll and implib versions that it actually looks for. Same happens on unixlikes where it's looking for a .so/.dylib/whatever or a .a. **** > > ghc --make testGlasPng.hs –L<path to glasPng.dll> I get: > Not quite right; -L identifies a *directory* to search, then you must specify the actual filename afterward. > **** > > testGlasPng.o: fake: (.text + 0x82) :undefined reference to > ‘getPngVersion@0’. I think it has found the > This just means it can't find the symbol; it does not mean it necessarily found the DLL. > I run ghc on a 64 bits computer. The dll is 32 bits. Is that the problem? > That can certainly be a problem, yes, and is likely why it wasn't found with the first one. But it's not so much what kind of machine you are on, as what kind of ghc you are using: a 64-bit ghc cannot link 32-bit libraries, and vice versa. But a 32-bit ghc and toolchain will work fine on a 64-bit system, aside from not linking 64-bit DLLs. -- brandon s allbery kf8nh sine nomine associates allbery.b(a)gmail.com ballbery(a)sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

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ANN: yi-0.6.7
by Dmitry Ivanov 30 May '13

30 May '13

Hello Cafe After about a year we've released a new version of Yi, text editor written and extensible in Haskell. Please have a look, hopefully you can find something interesting for you, whether you are emacs, vim or $(your-favorite-editor) fan. Changelog is available at https://github.com/yi-editor/yi/blob/master/CHANGELOG We currently lack active maintainers for Pango and Cocoa frontends, Emacs emulation and some smaller modules. Contributors in these areas are especially welcome. Also we have almost no user-level documentation compared to other editors, so if someone new to yi would set it up to his liking and share the experience on wiki or his blog or somewhere else, that would also be a very nice contribution. Places to dicuss using and developing yi: mailing list: https://groups.google.com/group/yi-devel issue tracker: https://github.com/yi-editor/yi/issues IRC channel: #yi@freenode (it's very slow compared to #haskell, please don't quit after 10 mins) Regards, Dmitry

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ANN: hsbencher-1.1, with Fusion Table upload
by Ryan Newton 30 May '13

30 May '13

I'm pleased to announce a new benchmarking framework, HSBencher. It's an early prototype, but it's flexible, extensible and uploads benchmark data to Google Fusion Tables. Right now the fusion table upload depends on a pre-release version of "handa-gdata" (0.6.2), which you can get at one of these locations: https://code.google.com/p/hgdata/ https://github.com/rrnewton/hgdata_mirror (It should be released soon.) Here's a blog post explaining HSBencher's usage: http://parfunk.blogspot.com/2013/05/towards-cloud-based-crowd-sourced.html Hackage: http://hackage.haskell.org/package/hsbencher Github (see README) https://github.com/rrnewton/hsbencher

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ANN: prelude-safeenum
by wren ng thornton 30 May '13

30 May '13

-------------------------------------------- -- prelude-safeenum 0.1.0 -------------------------------------------- The prelude-safeenum package offers a safe alternative to the Prelude's Enum class in order to render it safe. While we're at it, we also generalize the notion of enumeration to support types which can only be enumerated in one direction. -------------------------------------------- -- Description -------------------------------------------- The prelude-safeenum package offers an alternative to the notion of enumeration provided by the Prelude. For now it is just a package, but the eventual goal is to be incorporated into haskell prime. Some salient characteristics of the new type-class hierarchy are: * Removes partial functions: The Haskell Language Report defines pred, succ, fromEnum, and toEnum to be partial functions when the type is Bounded[1], but this is unacceptable. The new classes remove this problem by correcting the type signatures for these functions. * Generalizes the notion of enumeration: Rather than requiring that the type is linearly enumerable, we distinguish between forward enumeration (which allows for multiple predecessors) and backward enumeration (which allows for multiple successors). * Adds new functions: enumDownFrom, enumDownFromTo One of the big problems with the partiality of pred is that there is no safe way to enumerate downwards since in the border case (enumFromThen x (pred x)) will throw an error rather than evaluating to [x] as desired. These new functions remove this problem. * Removes the requirement that the enumeration order coincides with the Ord ordering (if one exists). Though, of course, it's advisable to keep them in sync if possible, for your sanity. * Ensures that the notion of enumeration is well-defined: This much-needed rigor clarifies the meaning of enumeration. In addition, it rules out instances for Float and Double which are highly problematic and often confuse newcomers to Haskell. Unfortunately, this rigor does render the instance for Ratio problematic. However, Ratio instances /can/ be provided so long as the base type is enumerable (and Integral, naturally); but they must be done in an obscure order that does not coincide with Ord. * The obscure order required for well-defined enumeration of Ratio is provided. [1] <http://www.haskell.org/onlinereport/haskell2010/haskellch6.html#x13-1310006…> -------------------------------------------- -- Links -------------------------------------------- Homepage: http://code.haskell.org/~wren/ Hackage: http://hackage.haskell.org/package/prelude-safeenum Darcs: http://community.haskell.org/~wren/prelude-safeenum Haddock (Darcs version): http://community.haskell.org/~wren/prelude-safeenum/dist/doc/html/prelude-s… -- Live well, ~wren

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Ghent FPG meeting on 26 June, 2013
by Jasper Van der Jeugt 30 May '13

30 May '13

Hello, The "Functional Programming Group Ghent" (GhentFPG) [1] is a friendly group for all people interested in functional programming, with a tendency towards Haskell. It is organised as part of Zeus WPI [2]. We are pleased to announce that we will hold a next meeting on Wednesday, 26th of June, starting at 19h00! There will be three talks. The main presentation, by Adam Bergmark from Silk [3] is about Fay [4]: Fay is a proper subset of Haskell that compiles to JavaScript. There is a compiler with the same name written in Haskell. Web browsers only speak JavaScript but more and more people find that they want to compile to JavaScript instead. Why do we want to compile Haskell to JavaScript, and what advantages does Fay have compared to other compilers? What are the challenges in compiling Haskell and supporting a language ecosystem, and how do we do it? What can Fay currently do, and what is planned for the future? This will be a broad overview about Fay for prospective users, followed by an in-depth look at interesting parts of the compiler internals. Additionally, there will be two short talks by two students who did an Msc. Thesis about functional programming languages: "Genetic Algorithms in Haskell" by Matthias Delbar "Automatic Detection of Recursion Patterns" by Jasper Van der Jeugt The meeting will take place in the Jozef Plateauzaal at the following address, Faculteit Ingenieurswetenschappen Universiteit Gent Plateaustraat 22 9000 Gent As mentioned above, we aim to start at 19:00. After the meeting we can go for drinks in a nearby pub (this latter part is, of course, completely optional) We hope to see you all there! Regards, On behalf of the GhentFPG organising committee. [1]: http://groups.google.com/group/ghent-fpg [2]: http://zeus.ugent.be/ [3]: http://www.silkapp.com/ [4]: http://www.fay-lang.org/

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[haskell.org Google Summer of Code 2013] Approved Projects
by Edward Kmett 29 May '13

29 May '13

We've worked our way through the project approval process for another year. This year we accepted 9 projects for haskell.org in general and are hosting 2 additional projects for darcs as an umbrella organization. haskell.org: * Parallelise 'cabal build' by Mikhail Glushenkov, mentored by Johan Tibell * Extending GHC to support building modules in parallel by Patrick Palka, mentored by Thomas Schilling * Communicating with mobile devices by Marcos Pividori, mentored by Michael Snoyman * Improve Haddock Markup and Capabilities by Fūzetsu, mentored by Simon Hengel * Haskell Qt Binding Generator by Zhengliang Feng, mentored by Carter Schonwald with help from Ian-Woo Kim * Improve the feedback of the cabal-install dependency solver by Martin Ruderer, mentored by Andres Löh * Interactive-diagrams and a paste site with the ability for dynamic rendering of diagrams by Dan Frumin, mentored by Luite Stegeman * Overloaded record fields for GHC by Adam Gundry, mentored by Simon Peyton-Jones * Port Charts to use Diagrams by Jan Bracker, mentored by Tim Docker darcs: * Better record command for darcs by José Neder, mentored by Gillaume Hoffmann * Enhancing Darcsden by BSRK Aditya, mentored by Ganesh Sittampalam Students have from now through Jun 16th to get up to speed and get to know their mentors. And while the summer of code officially starts on Jun 17th, keep in mind that the mid-term evaluations aren't that much farther behind, starting July 29th, so you'll want to hit the ground running. If you put in a project proposal and it wasn't accepted and/or you would like feedback, please feel free to email me or contact me on the #haskell-gsoc channel on irc.freenode.net. We received more proposals than slots this year, and so we were forced to make a few hard decisions. Shachaf Ben-Kiki is helping out as this year's backup administrator and he should also be able to help out with administrivia or questions as well. I'd like to thank everyone for participating in the selection process and I think we can look forward to another excellent summer of code! Edward Kmett haskell.org Google Summer of Code Administrator

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Re: [Haskell-cafe] using a win32 dll (Happy too soon)
by Robert Jakob 29 May '13

29 May '13

> If I compile with ghc --make testGlasPng.hs -lglasPng I > get: ..\ld.exe: cannot find -lglasPng. Collect 2: ld returned 1 exit > status. > > Ld can't find lglasPng (with the l in front, does it trim the l?). > Why? Okay I try > > ghc --make testGlasPng.hs -L<path to glasPng.dll> I get: > > testGlasPng.o: fake: (.text + 0x82) :undefined reference to > 'getPngVersion@0'. I think it has found the dll, but it complains the > function is not in the dll. But TDump and Dll export viewer say > getPngVersion is in the dll. I think you should use both -L and -l. ghc --make testGlasPng.hs -L/path/to/folder/where/glasPng/is -lglasPng -L should point to the folder, NOT the dll itself. Hope this helps. R.

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using a win32 dll (Happy too soon)
by Kees Bleijenberg 29 May '13

29 May '13

Unfortunatly the proposed solutions didn't work after all (It worked once, I think, but.) Here again the problem: glasPng.dll is a Delphi dll with the function getPngVersion in it. Calling convention is stdCall. I want to use this dll. The code: {-# LANGUAGE ForeignFunctionInterface #-} module Main( main ) where import Control.Monad import Foreign.C import Foreign.Marshal.Alloc import Foreign.Marshal.Array import System.Win32.Types foreign import stdcall "getPngVersion" getPngDllVersion :: IO CString main :: IO () main = do s <- getPngDllVersion putStrLn (show s) glasPng.dll is in the Windows path (I've checked it). If I compile with ghc --make testGlasPng.hs -lglasPng I get: ..\ld.exe: cannot find -lglasPng. Collect 2: ld returned 1 exit status. Ld can't find lglasPng (with the l in front, does it trim the l?). Why? Okay I try ghc --make testGlasPng.hs -L<path to glasPng.dll> I get: testGlasPng.o: fake: (.text + 0x82) :undefined reference to 'getPngVersion@0'. I think it has found the dll, but it complains the function is not in the dll. But TDump and Dll export viewer say getPngVersion is in the dll. I run ghc on a 64 bits computer. The dll is 32 bits. Is that the problem? What can I do? Kees

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Re: [Haskell-cafe] using a win32 dll
by Kees Bleijenberg 29 May '13

29 May '13

Thank you Krzystof! This did the trick. Now I also have a better understanding what is going on. Great. Kees Van: Krzysztof Skrzętnicki [mailto:gtener@gmail.com] Verzonden: woensdag 29 mei 2013 11:58 Aan: Kees Bleijenberg Onderwerp: Re: [Haskell-cafe] using a win32 dll Oh, I didn't mean kernel32. And -L provides search path not the actual library. The idea was to use -l<yourLibrary.dll> , so it would be -lpngDLL.dll, provided it is in library search path. If not use -Ldirectory-with-dll -lpngDLL.dll On Wed, May 29, 2013 at 11:49 AM, Kees Bleijenberg <k.bleijenberg(a)lijbrandt.nl> wrote: I’ve tried to compile it with –l kernel32, but nothing changed. I’ve also tried -LpngDll.dll but that didn’t work either. Kees My first guess would be missing -l parameter. The examples you have linked read: ghc --make compname.hs -lkernel32 Best regards, Krzysztof Skrzętnicki On Wed, May 29, 2013 at 9:13 AM, Kees Bleijenberg <k.bleijenberg(a)lijbrandt.nl> wrote: I made a Delphi dll (32 bits windows). This dll exports a function named getPngVersion. This is a function with no arguments that returns a pointer to a array of chars. If I examine the dll with a tools like tdump, I can see the function getPngVersion on index 1. Now I want to use this dll in Haskell: {-# LANGUAGE ForeignFunctionInterface #-} module Main( main ) where import Control.Monad import Foreign.C import Foreign.Marshal.Alloc import Foreign.Marshal.Array import System.Win32.Types foreign import stdcall "glasPng getPngVersion" getPngDllVersion :: IO CString main :: IO () main = do s <- getPngDllVersion putStrLn (show s) Compiling this with ghc --make glasPng.hs gives: GlasPng.o: fake: (.text +0x82): undefined reference to ‘getPngVersion@0’ collect2 : Id returned 1 exit status I wonder what went wrong. In the foreign import line I use “glasPng…. “ to tell ghc, it has to searh in glasPng.dll (changing glasPng to glasPng.dll doesn’t help). I’ve changed the name of the function in the dll to getPngVersion@0 but no luck. I’ve read and tested the last example at http://stackoverflow.com/questions/1027246/haskell-foreign-import-stdcall-o… (win32_getComputername, this works!). I wonder how haskell knows which dll to use in this example?) Probably I’am doing something wrong with the way I tell ghc which dll to link or…. Any ideas? Kees _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Install wx on Windows XP
by Eric Wong 29 May '13

29 May '13

Hi Haskellers, I'm trying to install wxHaskell on Windows XP. I have already installed Haskell Platform 2012.04.0.0, MinGW and wxWidgets. When I try to install wx, I got the following error when cabal is installing wxcore: $ cabal install wx Resolving dependencies... [1 of 1] Compiling Main ( C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\wxcore- 0.90.0.3-896\wxcore-0.90.0.3\Setup.hs, C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\wxcore -0.90.0.3-896\wxcore-0.90.0.3\dist\setup\Main.o ) Linking C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\wxcore-0.90.0.3-896\wxcore-0.90.0.3\d ist\setup\setup.exe ... Configuring wxcore-0.90.0.3... Generating class type definitions from .h files generating: src/haskell/Graphics/UI/WXCore/WxcClassTypes.hs reading class definitions: parsing: C:\Documents/include/wxc.h wxdirect: C:\Documents/include/wxc.h: openFile: does not exist (No such file or directory) Generating class info definitions generating: src/haskell/Graphics/UI/WXCore/WxcClassInfo.hs reading class definitions: parsing: C:\Documents/include/wxc.h wxdirect: C:\Documents/include/wxc.h: openFile: does not exist (No such file or directory) Generating class method definitions from .h files parsing: Data\cabal\wxc-0.90.0.4\ghc-7.4.2\include/wxc.h wxdirect: Data\cabal\wxc-0.90.0.4\ghc-7.4.2\include/wxc.h: openFile: does not ex ist (No such file or directory) Building wxcore-0.90.0.3... Preprocessing library wxcore-0.90.0.3... src\haskell\Graphics\UI\WXCore\WxcClassTypes.hs:1:1: File name does not match module name: Saw: `Main' Expected: `Graphics.UI.WXCore.WxcClassTypes' cabal.exe: Error: some packages failed to install: wx-0.90.0.1 depends on wxcore-0.90.0.3 which failed to install. wxcore-0.90.0.3 failed during the building phase. The exception was: ExitFailure 1 It looks like it's confused by the spaces in the path and can't find the wxc.h file. I tried to configure cabal to install all user packages into a simpler directory. But cabal always install to the C:\Documents and Settings\Administrator\Application Data\cabal directory no matter how I change the config file there. Anyone knows how to fix this problem or change cabal directory on Windows? Thanks. p.s. I'm using the user Administrator.

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Re: [Haskell-cafe] using a win32 dll
by Robert Jakob 29 May '13

29 May '13

On Wed, 29 May 2013 09:13:09 +0200 "Kees Bleijenberg" <k.bleijenberg(a)lijbrandt.nl> wrote: > I made a Delphi dll (32 bits windows). This dll exports a function > named getPngVersion. This is a function with no arguments that > returns a pointer to a array of chars. Did you annotate the exported function with stdcall? The calling conventions of Delphi are different to that of C. I had problems with that sometimes (not with Haskell, but with C) R.

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Re: [Haskell-cafe] using a win32 dll
by Krzysztof Skrzętnicki 29 May '13

29 May '13

My first guess would be missing -l parameter. The examples you have linked read: ghc --make compname.hs -lkernel32 Best regards, Krzysztof Skrzętnicki On Wed, May 29, 2013 at 9:13 AM, Kees Bleijenberg < k.bleijenberg(a)lijbrandt.nl> wrote: > I made a Delphi dll (32 bits windows). This dll exports a function named > getPngVersion. This is a function with no arguments that returns a pointer > to a array of chars.**** > > If I examine the dll with a tools like tdump, I can see the function > getPngVersion on index 1.**** > > Now I want to use this dll in Haskell:**** > > ** ** > > {-# LANGUAGE ForeignFunctionInterface #-}**** > > module Main(**** > > main**** > > )**** > > ** ** > > where**** > > import Control.Monad**** > > import Foreign.C**** > > import Foreign.Marshal.Alloc**** > > import Foreign.Marshal.Array**** > > import System.Win32.Types**** > > ** ** > > foreign import stdcall "glasPng getPngVersion" getPngDllVersion :: IO > CString**** > > ** ** > > main :: IO ()**** > > main = do **** > > s <- getPngDllVersion**** > > putStrLn (show s)**** > > ** ** > > Compiling this with ghc --make glasPng.hs gives:**** > > GlasPng.o: fake: (.text +0x82): undefined reference to ‘getPngVersion@0’ > collect2 : Id returned 1 exit status **** > > ** ** > > I wonder what went wrong. In the foreign import line I use “glasPng…. “ to > tell ghc, it has to searh in glasPng.dll (changing glasPng to glasPng.dll > doesn’t help). I’ve changed the name of the function in the dll to > getPngVersion@0 but no luck. I’ve read and tested the last example at > http://stackoverflow.com/questions/1027246/haskell-foreign-import-stdcall-o… > (win32_getComputername, this works!). I wonder how haskell knows which > dll to use in this example?)**** > > Probably I’am doing something wrong with the way I tell ghc which dll to > link or….**** > > ** ** > > Any ideas?**** > > ** ** > > Kees**** > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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using a win32 dll
by Kees Bleijenberg 29 May '13

29 May '13

I made a Delphi dll (32 bits windows). This dll exports a function named getPngVersion. This is a function with no arguments that returns a pointer to a array of chars. If I examine the dll with a tools like tdump, I can see the function getPngVersion on index 1. Now I want to use this dll in Haskell: {-# LANGUAGE ForeignFunctionInterface #-} module Main( main ) where import Control.Monad import Foreign.C import Foreign.Marshal.Alloc import Foreign.Marshal.Array import System.Win32.Types foreign import stdcall "glasPng getPngVersion" getPngDllVersion :: IO CString main :: IO () main = do s <- getPngDllVersion putStrLn (show s) Compiling this with ghc --make glasPng.hs gives: GlasPng.o: fake: (.text +0x82): undefined reference to 'getPngVersion@0' collect2 : Id returned 1 exit status I wonder what went wrong. In the foreign import line I use "glasPng.. " to tell ghc, it has to searh in glasPng.dll (changing glasPng to glasPng.dll doesn't help). I've changed the name of the function in the dll to getPngVersion@0 but no luck. I've read and tested the last example at http://stackoverflow.com/questions/1027246/haskell-foreign-import-stdcall-on -dll-function (win32_getComputername, this works!). I wonder how haskell knows which dll to use in this example?) Probably I'am doing something wrong with the way I tell ghc which dll to link or.. Any ideas? Kees

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Lista dos aprovados em concurso Rodrigues Alves
by Edson 29 May '13

29 May '13

Lista dos aprovados em concurso Rodrigues Alves: Novo São Joaquim: ANA ANGELICA PEREIRA ALVES, LETICIA BAIRLE, FRANCISCO ANDERSON VALE DO NASCIMENTO, PAULO DE SIQUEIRA SILVA, JOÃO CARLOS MOREIRA DE CARVALHO, DAMIANA PEREIRA DE OLIVERIA, MARIA DO SOCORRO DE ALBURQUERQUE ARRUDA BARBOSA, JAIME CUSTODIO DA SILVA FILHO. SEBASTIANA MÁRCIA GOMES DE MELO, ÉRICA FRANCISCA BATISTA DE MELO, MAYRES RAQUEL DA SILVA PINHEIRO, JUCIMARA VICENTE DOS SANTOS, WEULLER TEIXEIRA DE MAGALHAES. Governador Nunes Freire. Rodrigues Alves, ADISSON SOUZA TAVARES, JULIO CESAR DA SILVA MOURA FILHO, ERIDAN FERREIRA LEITE, MICHAEL LIMA SILVA, JOÃO CARLOS MOREIRA DE CARVALHO, CARLOS EDNAELTON DE MELO FERREIRA, MANOEL MARQUES DA CUNHA FILHO, IEDA BENTO BARROSO. ROBERTO FERREIRA LOPES FILHO, DOMINGOS SAVIO VIDAL DE LIMA FILHO, MARIANA ISABEL E SILVA, JOSE ALDER BRAGA JUNIOR, THAYS RAQUEL DA SILVA. Brás Pires. Morpará e ANNA JESSYCA ANDRADE LACERDA, LUCAS DE PAULA OLIVEIRA, GEORGE FACUNDO RICARDO, RAFAEL WESLEY MENESES MAIA, JOÃO CARLOS MOREIRA DE CARVALHO, DEBORAH LIMA BRAGA, MARIA MARIANA RIBEIRO VIEIRA, JOÃO VICTOR RODRIGUES DE C. MEDEIROS. TATIANA RODRIGUES DE CASTRO MELO, CAIO URBANO CAMURCA, MAIARA FRANKLIN DE AZEVEDO, IAGO TELES GARCIA, RITA PAULA SEVERO PATU. Hidrolândia.

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Re: [Haskell-cafe] Hackage Update Brigade
by wren ng thornton 29 May '13

29 May '13

On 5/27/13 5:29 PM, Alexander Solla wrote: > As per recent discussions, I'm making a list of volunteers who are willing > to pick up some slack in Hackage package maintenance, so that we can submit > an amendment to the Haskell Prime Committee's ticket 113 ( > http://hackage.haskell.org/trac/haskell-prime/ticket/113) I'd much prefer sticking with the names (<*>), (<*), (*>), and deprecating `ap` and (>>). There's no good name for (<*) since we already have (<<) = flip (>>) which means something different entirely. Plus "`ap`" is longer than "<*>" and loses the suggestive relationship between the operator names. Not to mention the fact that these name changes would cause immense breakage for all users of Applicative, rather than relatively minor breakage for those who define Monad instances. -- Live well, ~wren

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Hackage Update Brigade
by Alexander Solla 29 May '13

29 May '13

As per recent discussions, I'm making a list of volunteers who are willing to pick up some slack in Hackage package maintenance, so that we can submit an amendment to the Haskell Prime Committee's ticket 113 ( http://hackage.haskell.org/trac/haskell-prime/ticket/113) I think that showing that people are willing to pick up missing package maintainer's slack will alleviate the concern of breaking lots of code by refactoring the monad/applicative/functor hierarchy. Code will be broken, but publicly available packages can be fixed by the community during a "staging" period. To that end, I have made a Google Form to collect some volunteer information. If you are interested in helping, please visit: https://docs.google.com/forms/d/1o4B8CEE_42u9f-sgmu2t5iSEvm0cq6-um6g_fHJt6G…

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Design of extremely usable programming language libraries
by Andrey Chudnov 29 May '13

29 May '13

Dear Cafe, I'm exploring the design space of programming language libraries with enhanced usability and I'd your help and comments. I'll start with a few short questions, but offer a detailed discussion of the motivations and the problems I'm facing below. So, if you have interest in the subject or feel you can offer some insight, please, do read on. * Does any generic traversal/transformation (uniplate-style) library support GADTs? * What is the best choice, performance- and memory-wise, for a parser combinator library with support for arbitrary look-ahead? Parsec is considered slow by some [1], but is it only in comparison with attoparsec (which, unfortunately, doesn't support arbitrary look-ahead)? Is there any parser library that performs better than Parsec while still supporting arbitrary look-ahead. * Any multi-mode pretty printer libraries? By multi-mode I mean writing code once and being able to generate, say, both "pretty" and "minified" text representations of a program by changing just one parameter. Also, what's the most efficient pretty-printing library nowadays? Blaze? I've been using Haskell for quite a while now, primarily, for programming-language applications: program analysis, transformation and compilation. I'm sure many would agree that PL work is where Haskell shines. In the recent years new language features and libraries --namely, GADTs, Template Haskell, quasi-quotation and generic programming--- have appeared that could make working with languages even easier than before. That's why it's sad to see that none of the PL libraries seem to make good use of these features (however, I might be starting to understand why). So, I'm currently exploring the design space for a library that uses these advanced Haskell features for delivering better usability, and I'm having problems with implementing some of them. I welcome comments on both the motivations, overall design and the more technical aspects. I've omitted a few details because it's a long e-mail as is. If something is not clear or doesn't make sense, please, let me know. I'll start by listing the features that an "ideal" PL library should have, and that I've come to cherish as both a heavy user and a developer of such. The basic features (pretty much every library has them) include a parser (text->AST (abstract syntax tree)) and a pretty-printer (AST->text), as well as a Haskell representation of the AST that is somewhat easy to use. Pretty much every library has that --- although some might debate the ease of use of the AST representations. However, there are other features that, in my opinion, are essential to a PL library. The features are motivated by three requirements: static safety (as few run-time errors as possible), minimal code duplication (DRY) and ease of use and inspection of the code. 1) the pretty-printer should be multi-mode. One should be able to write code once and be able to generate different textual representations of the AST: - the "pretty" which is nice to the eye with white spaces, indentations etc. - minified, with minimum white space (while still being valid) - debuggable which inserts comments based on AST annotations - source-map generation - being able to generate colored LaTeX/HTML code would be nice, but non-essential 2) ASTs should be statically safe: you should only be able construct values that represent valid programs, or get a typechecker/compiler error otherwise. Languages that have syntactic productions that can appear in one context but not in another need GADTs with type witnesses to achieve that. In fact, such languages are often used to motivate GADTs in the first place [2]. And while the problem in [2] could have been solved by splitting the Expr datatype into two (IntExpr and BoolExpr), in some languages this can't be done (or produces awkward syntax trees). 3) a quasi-quoter with support for anti-quotation and quoted patterns. This also saves a lot of typing *and* makes your code less error-prone and easier to read. What is better (to both write and read)? > [js|#x# = (function (a, b) {return {t1: a + b, t2: a*b};})(#x#, #y#);|] or > ExprStmt def $ AssignExpr def x (CallExpr def (FuncExpr def Nothing > [Id def "a", Id def "b"] $ ReturnStmt def $ ObjectLit [(PropId def $ > Id def "t1", InfixExpr def OpAdd (VarRef def $ Id def "a") (VarRef def $ > Id def "b")), PropId def $ > Id def "t2", InfixExpr def OpMul (VarRef def $ Id def "a") (VarRef def $ > Id def "b")])) [x, y] The caveat here is that, to help ensure correctness, the quasi-quoter and the parser should share code as much code as possible. Ideally, there should be just one parser that has a switch for recognizing normal and quasi-quoted programs. However, that would require adding additional constructors representing anti-quotations to our AST. And with that the user might be able to generate invalid AST's and cause a run-time error. The solution to the last problem is to statically constrain all the values that are passed to, say, the pretty-printer so that they are guaranteed to be free of anti-quotes (see an example definition below). However, that, again, requires GADTs (e.g. have all the AST datatypes have an extra type parameter). > data EType = Complete | HasHoles > type family Quoted a b :: * > canHaveHolesT :: a -> b -> Quoted a b > canHaveHolesT _ _ = undefined > type instance Quoted HasHoles Complete = HasHoles > type instance Quoted Complete HasHoles = HasHoles > type instance Quoted HasHoles HasHoles = HasHoles > type instance Quoted Complete Complete = HasHoles > data Expr t where > EInt :: Int -> Expr Complete > EAdd :: Expr t1 -> Expr c2 -> Expr (Holes t1 t2) > ... > EQuote :: String -> Expr HasHoles And then we could have a normal parser return a value 'Expr Complete' and a quasi-quotation parser retunr a value 'Expr HasHoles'. Similarly, the pretty printer function could have type 'Expr Complete -> Doc'. 4) We should be able to annotate ASTs with arbitrary values, and change the types of those values as we go. The most user friendly way, IMO, is to have the AST datatypes be polymorphic and have that type parameter as an extra field in every constructor. E.g., > data Expr t a where > EInt :: a -> Int -> Expr Complete a > EAdd :: a -> Expr t1 a -> Expr c2 a -> Expr (Holes t1 t2) a > ... > EQuote :: a -> String -> Expr HasHoles a Then we can use the functions in Traverseable to change types of annotations, and inspect the values by pattern-matching on constructors. 5) support for generic operations on syntax trees. Uniplate, which has been designed to work with ASTs, and is awesome for that purpose because it saves a lot of time. I use transform(Bi) and universe(Bi) all the time and it saves *a lot* of typing. Pretty much all my analysis/transformation code uses those four small-but-powerful function calls -- and, dare I say, it's quite elegant. Other useful, but not crucial features include: 1) diffs for ASTs (in the spirit of the 'gdiff' library, which, alas, doesn't work with polymorphic datatypes) 2) QuickCheck arbitrary instances for ASTs. No technical difficulty there, but writing instances that generate interesting programs and don't run out of memory is quite hard :) I wish 'Agata' was still supported, or there was some library that helps writing Arbitrary instances for ASTs. If you think there's another feature in mind that is missing from the list, please, let me know. The (perceived) challenges in implementing the functionality outlined above are as follows: 1) No multi-mode pretty-printing library. I think that the mutli-mode functionality could be implemented on top of an existing library by definining new combinators, but it would be nice to have a library that supports them out of the box. The particular features that I'm missing are: - "non-essential space/(soft-)line break" combinators that are interpreted as spaces/line-breaks in the "pretty" mode and as empty docs in the "minified" mode. - "comment" combinator which inserts the text in a comment only if the "debug" mode is on - being able to record the positions of AST nodes in the resulting text (for generating source maps). Not sure what would be a convenient interface for that. Note: I know that mainland-pretty has position information, but I don't think it's helpful for generating source maps. 2) The biggest problem is that there are two good reasons to use GADTs when specifying AST datatypes. However, uniplate doesn't work with GADTs and, as far as I know, no currently supported generic programming library does (to be precise, I need support for families of mutually recursive polymorphic GADTs). Am I missing some library, or is my understanding correct? If it's the latter, is there any fundamental limitation that prevents creating such a library? Maybe there are other (but still elegant) ways to satisfy my requirements without using GADTs? 3) 'gdiff' doesn't support polymorphic datatypes. Is there any other library that does? [1] http://www.serpentine.com/blog/2010/03/03/whats-in-a-parsing-library-1/ [2] http://en.wikibooks.org/wiki/Haskell/GADT PS: My attempts so far are in https://github.com/achudnov/language-nextgen/blob/master/Language/Nextgen/S… Regards, Andrey Chudnov

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