- Haskell-Cafe - Haskell.org

bytestring, array and Safe Haskell
by Francesco Mazzoli 08 May '12

08 May '12

Why are http://hackage.haskell.org/packages/archive/bytestring/0.9.2.1/doc/html/Dat… and http://hackage.haskell.org/packages/archive/array/0.4.0.0/doc/html/Data-Arr… Safe-inferred? The first one uses inlinePerformIO, so it clearly shouldn't be marked as Safe. Maybe Safe Haskell doesn't check that function? The second is a bit messier since it uses unboxed types and primitive operations... But they clearly should be marked as Unsafe, and it surprises me that Safe Haskell is that relaxed when checking for safe functions. Francesco.

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Can Haskell outperform C++?
by Isaac Gouy 08 May '12

08 May '12

2012/5/8 Silvio Frischknecht >Also I challenge anyone to improve one of the haskell programs there. >It'd be cool if we could make haskell get a higher rank. I recently >managed to improve the Fasta algorithm, but not by much. Also I think >the benchmarks don't use llvm flag. It says somewhere that they don't >measure llvm because they don't have time. But I think they are >refering to clang. So maybe someone should tell them to turn on the >llvm flag since it makes a lot of haskell programs faster. Several GHC versions have come and gone since the Haskell benchmarks game programs were written, so perhaps it is time that a dozen new programs were written to replace those old programs - new programs that take advantage of GHC 7.4.1 and -llvm.

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ANN: hspec-1.1.0
by Simon Hengel 07 May '12

07 May '12

Hi, I'm glad to announce a new release of hspec[1]. Detailed release notes are at [2]. Introductory documentation is at [3]. Cheers, Simon [1] http://hackage.haskell.org/package/hspec-1.1.0 [2] https://github.com/hspec/hspec/blob/master/CHANGES.markdown [3] http://hspec.github.com/

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correction
by Serge D. Mechveliani 07 May '12

07 May '12

Correction to my last letter: Run on the second terminal > ./iface --> Run on the second terminal > ./a.out ------ Sergei mechvel(a)botik.ru

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Haskell-Type-Exts -- Typechecker as a Library
by Shayan Najd Javadipour 07 May '12

07 May '12

Hello Haskell Cafe! Recently, I got my proposal “Haskell-Type-Exts”--submitted to haskell community--accepted for Google SoC 2012! I have the luxury (thanks to Haskell.org GSoC committee) to develop a typechecker[1] for ASTs extracted by HSE[2] during this summer. HSE is one of the most widely used (if not the most popular) standalone parsers for Haskell 2010 plus a wide variety of extensions. HSE is written (and maintained) by Niklas Broberg and he is also mentoring this project. To be realistic, it is a rather challenging project and support of the community is vitally important to achieve the goals. I have a weblog accessible at http://cleantypecheck.wordpress.com/ dedicated to this topic. I plan to use it as the main media to communicate with people interested. Also, you can contact me directly through [shayan at chalmers d0t se]. If you see yourself as a potential user of the tool or by any reason you are interested , I'd highly appreciate if you would take a look at the following post and leave your comment/suggestions: http://cleantypecheck.wordpress.com/2012/05/03/inquiry/ Thanks! /Shayan [1] http://hackage.haskell.org/package/haskell-type-exts [2] http://hackage.haskell.org/package/haskell-src-exts

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MonadError vs Control.Exception
by Станислав Черничкин 06 May '12

06 May '12

Hi, guys, I'm interested in best practices in using of each approach. Personally I like MonadError because it is more explicit and Control.Exception-s becomes really ugly in complex scenarios. Here an example to illustrate my idea: http://hackage.haskell.org/packages/archive/network-conduit/0.4.0/doc/html/…. All network-conduit functions can raise IOException because of Socket-related stuff (and actually entire network-conduit is written to deal with IOException correctry) + Bind-port can raise ErrorCall (came from error "bindPort: addrs is empty"). User has to deal with both, but have no evidence on none of them from type signatures or documentation. Moreover, ErrorCall in this case can be caused by IOException (we try to bind only available address, we get IOException exception, we have no more address to try and raise ErrorCall), and I really don’t understand, why it should be treated in a different way. So, I hate exceptions, I blame it, I think exceptions is junk came from OO-world and horrible languages like C# or even more horrible like Java, and it should be wiped out from Haskell with fire. But it is only my humble opinion. Reality shows that Haskell provides extensive support for exceptions, it included in base libraries and everyone uses it, but MonadError is modest part of mtl, and don’t even have “bracket” and other useful functions. That is why I’m really interested in any your ideas and experience on using these approaches. Cheers, Stasik.

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Learn you
by Kazu Yamamoto 06 May '12

06 May '12

Hello cafe, Translating "Learn You a Haskell for Great Good" into Japanese was finished and will be published on 22 May. I guess it's worth watching its cover page: http://www.amazon.co.jp/%E3%81%99%E3%81%94%E3%81%84Haskell%E3%81%9F%E3%81%A… There are two translators: Tanaka is the author of "peggy" and Muranushi is the author of "Monadius". Regards, --Kazu

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Issues with installing packages
by Graham Berks 06 May '12

06 May '12

New to haskell and having issues resolving packages, have the following output below and can't seem to resolve it. Text seems to have diff hash dependancies when I try and instal a diff version of 0.11.2.0 etc Any ideas on what todo ?? Thanks $ ghc-pkg check There are problems in package scion-browser-0.2.8: dependency "text-0.11.2.0-2b6cea8526e93af24bb0154400fd64a6" doesn't exist There are problems in package persistent-template-0.9.0.1: dependency "text-0.11.2.0-2b6cea8526e93af24bb0154400fd64a6" doesn't exist There are problems in package persistent-sqlite-0.9.0.1: dependency "text-0.11.2.0-2b6cea8526e93af24bb0154400fd64a6" doesn't exist There are problems in package persistent-0.9.0.3: dependency "text-0.11.2.0-2b6cea8526e93af24bb0154400fd64a6" doesn't exist There are problems in package aeson-0.6.0.2: dependency "text-0.11.2.0-2b6cea8526e93af24bb0154400fd64a6" doesn't exist There are problems in package path-pieces-0.1.1: dependency "text-0.11.2.0-2b6cea8526e93af24bb0154400fd64a6" doesn't exist There are problems in package hashable-1.1.2.3: dependency "text-0.11.2.0-2b6cea8526e93af24bb0154400fd64a6" doesn't exist There are problems in package conduit-0.4.1.1: dependency "text-0.11.2.0-2b6cea8526e93af24bb0154400fd64a6" doesn't exist There are problems in package blaze-html-0.4.3.4: dependency "text-0.11.2.0-2b6cea8526e93af24bb0154400fd64a6" doesn't exist There are problems in package blaze-builder-0.3.1.0: dependency "text-0.11.2.0-2b6cea8526e93af24bb0154400fd64a6" doesn't exist There are problems in package attoparsec-0.10.1.1: dependency "text-0.11.2.0-2b6cea8526e93af24bb0154400fd64a6" doesn't exist There are problems in package buildwrapper-0.5.2: dependency "aeson-0.6.0.2-f5264d3642c44cd43d87b542486e49c9" doesn't exist dependency "attoparsec-0.10.1.1-d3ad0453e3127b6c51ccb14a5cb6f38d" doesn't exist dependency "unordered-containers-0.2.1.0-9b5d4d7fe2d79561a684ee5184ea5fd0" doesn't exist There are problems in package hoogle-4.2.11: dependency "blaze-builder-0.3.1.0-adf48413bb3bfeef99ef5e18de097dbd" doesn't exist dependency "conduit-0.4.1.1-6c1a48d4c94e05132c53b85e7ca48cd9" doesn't exist dependency "parsec-3.1.1-d3c0b4413115a5e82a1a5cf9b0b35fee" doesn't exist There are problems in package warp-1.2.0.1: dependency "blaze-builder-0.3.1.0-adf48413bb3bfeef99ef5e18de097dbd" doesn't exist dependency "conduit-0.4.1.1-6c1a48d4c94e05132c53b85e7ca48cd9" doesn't exist There are problems in package wai-1.2.0.1: dependency "blaze-builder-0.3.1.0-adf48413bb3bfeef99ef5e18de097dbd" doesn't exist dependency "conduit-0.4.1.1-6c1a48d4c94e05132c53b85e7ca48cd9" doesn't exist There are problems in package network-conduit-0.4.0: dependency "conduit-0.4.1.1-6c1a48d4c94e05132c53b85e7ca48cd9" doesn't exist There are problems in package blaze-builder-conduit-0.4.0.1: dependency "blaze-builder-0.3.1.0-adf48413bb3bfeef99ef5e18de097dbd" doesn't exist dependency "conduit-0.4.1.1-6c1a48d4c94e05132c53b85e7ca48cd9" doesn't exist There are problems in package network-2.3.0.5: dependency "parsec-3.1.1-d3c0b4413115a5e82a1a5cf9b0b35fee" doesn't exist There are problems in package http-types-0.6.10: dependency "blaze-builder-0.3.1.0-adf48413bb3bfeef99ef5e18de097dbd" doesn't exist There are problems in package case-insensitive-0.4.0.1: dependency "hashable-1.1.2.3-037c817e51d5d10d89306e9472e2e0bd" doesn't exist There are problems in package test-framework-th-0.2.2: dependency "test-framework-0.6-7d2482720de09487769f301ebc001970" doesn't exist There are problems in package test-framework-quickcheck2-0.2.12.1: dependency "test-framework-0.6-7d2482720de09487769f301ebc001970" doesn't exist There are problems in package test-framework-quickcheck-0.2.8: dependency "test-framework-0.6-7d2482720de09487769f301ebc001970" doesn't exist There are problems in package test-framework-hunit-0.2.7: dependency "test-framework-0.6-7d2482720de09487769f301ebc001970" doesn't exist The following packages are broken, either because they have a problem listed above, or because they depend on a broken package. scion-browser-0.2.8 persistent-template-0.9.0.1 persistent-sqlite-0.9.0.1 persistent-0.9.0.3 aeson-0.6.0.2 path-pieces-0.1.1 hashable-1.1.2.3 conduit-0.4.1.1 blaze-html-0.4.3.4 blaze-builder-0.3.1.0 attoparsec-0.10.1.1 buildwrapper-0.5.2 hoogle-4.2.11 warp-1.2.0.1 wai-1.2.0.1 network-conduit-0.4.0 blaze-builder-conduit-0.4.0.1 network-2.3.0.5 http-types-0.6.10 case-insensitive-0.4.0.1 test-framework-th-0.2.2 test-framework-quickcheck2-0.2.12.1 test-framework-quickcheck-0.2.8 test-framework-hunit-0.2.7 unordered-containers-0.2.1.0 pool-conduit-0.1.0.1 resource-pool-0.2.1.0 simple-sendfile-0.2.3 cgi-3001.1.7.4 haskell-platform-2011.4.0.0 HTTP-4000.1.2

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unsafePerformIO usage
by Serge D. Mechveliani 06 May '12

06 May '12

People, can anybody explain what incorrect may happen with the following program which uses exchange through two Unix pipes and unsafePerformIO ? The pipes are created by the Unix commands mkfifo toA; mkfifo fromA gcc iface.c compiles the C program to a.out. ghc --make Main compiles the Haskell program by GHC to ./Main Run on the second terminal > ./iface Run on the first terminal > ./Main It prints the result to the screen. In Main.hs, the function iface :: String -> String is defined via hPutStr, hGetLine, hFlush, unsafePerformIO. It outputs str :: String to the pipe toA; the process iface (programmed in C) waits for delay and returns the respond string through the pipe fromA; iface inputs this respond string. So far, I put the respond string to be the same string, I think, this is not essential, but another map can be considered. Assume that the parallel computation is not allowed. In the below `main', I tried f ss where ss = [iface $ shows i "\n" | i <- [1 .. 4]], f [s1, s2, s3, s4] = [s3++s1, s3++s2, s1++s2], and it works correct. The question is: what a simple definition is possible for f which will evaluate incorrect? Is this true that unsafePerformIO is _safe_ for all f in this context? The `delay' constant can be edited in fifo.c. See both sources below. Please, copy the respond to mechvel(a)botik.ru Thanks, ------ Sergei mechvel(a)botik.ru ------------------------------------------------------------------------ import System.IO (IOMode(..), IO(..), Handle, openFile, hPutStr, hGetLine, hFlush) import System.IO.Unsafe (unsafePerformIO) dir = showString "/home/mechvel/haxiom/unsafeTest/" -- openFile :: FilePath -> IOMode -> IO Handle -- hPutStr :: Handle -> String -> IO () -- hGetLine :: Handle -> IO String toA_IO = openFile (dir "toA") WriteMode :: IO Handle fromA_IO = openFile (dir "fromA") ReadMode toA = unsafePerformIO toA_IO fromA = unsafePerformIO fromA_IO initIO :: IO (Handle, Handle) initIO = do to <- toA_IO from <- fromA_IO return (to, from) ifaceIO :: (Handle, Handle) -> String -> IO String ifaceIO (h1, h2) str = do hPutStr h1 str hFlush h1 str' <- hGetLine h2 return str' iface :: String -> String iface str = unsafePerformIO $ ifaceIO (toA, fromA) str main = putStr $ shows [s3++s1, s3++s2, s1++s2] "\n" where ss@[s1, s2, s3, s4] = [iface $ shows i "\n" | i <- [1 .. 4]] -- The C program fifo.c --------------------------------------------- #include <stdio.h> #include <string.h> #define BOUND 64 static char str[BOUND]; main() { int l, i; long j; FILE *toA, *fromA; toA = fopen("/home/mechvel/haxiom/unsafeTest/toA", "r"); if (toA == NULL) {perror("fopen(toA, r) failed: "); return;}; fromA = fopen("/home/mechvel/haxiom/unsafeTest/fromA", "w"); if (fromA == NULL) {perror("fopen(fromA, w) failed: "); return;}; for (;;) { if (fgets(str, BOUND, toA) == NULL) { perror("fgets(str, bound, toA) failed: "); return; }; j = 20000000; // delay. edit it while (j > 0) {j = j-1;}; fputs(str, fromA); fflush(fromA); }; return; }

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library conflicts and how to resolve them
by Graham Berks 06 May '12

06 May '12

Attempting $ cabal install persistent Resolving dependencies... In order, the following would be installed: aeson-0.6.0.2 (reinstall) changes: mtl-2.1.1 -> 2.0.1.0 persistent-0.9.0.3 (new package) cabal: The following packages are likely to be broken by the reinstalls: buildwrapper-0.5.2 Use --force-reinstalls if you want to install anyway. Any ideas what is going on ? I believe aeson-0.6.0.2 is already installed. And as far as I can tell the build of aeson-0.6.0.2 doesn't require that specific version of mtl. Am I missing something ? Is there a way to force ghc to ignore this ?? Thanks

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