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fyi GHC 7.2.1 release on the benchmarks game
by Isaac Gouy 12 Aug '11

12 Aug '11

1) Some of the GHC programs contributed to the benchmarks game have problems with recent GHC releases - meteor-contest #5 - Ambiguous occurrence `permutations' http://shootout.alioth.debian.org/u64q/program.php?test=meteor&lang=ghc&id=… - regex-dna #2 - Precedence parsing error http://shootout.alioth.debian.org/u64q/program.php?test=regexdna&lang=ghc&i… - reverse-complement #2 - parse error on input `->' http://shootout.alioth.debian.org/u64q/program.php?test=revcomp&lang=ghc&id… - reverse-complement #3 - Could not find module `Monad' http://shootout.alioth.debian.org/u64q/program.php?test=revcomp&lang=ghc&id… 2) I noticed `-fvia-C` has now gone away and there were half-a-dozen programs that had been written to use `-fvia-C` so how might that effect performance of those programs?

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Distributions link on Hackage
by Peter Simons 12 Aug '11

12 Aug '11

Hi, the home page of a package on Hackage links to various distributions to show which versions are available, i.e. Fedora, Debian, FreeBSD, etc. In NixOS, we have fairly up-to-date package set, and I would like to see that distribution included on Hackage. Now I wonder how to get that done? Can anyone advice on the procedure to add support for a distribution to Hackage? Take care, Peter

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Potential problem with AC-Vector-Fancy package
by Dave Tapley 12 Aug '11

12 Aug '11

Is anyone maintaining the AC-Vector-Fancy package? I haven't had a reply from the latest maintainer (Andrew Coppin) on Hackage, so I thought I'd open it up to cafe: I think I have found a problem with the union function: If you look here: http://hpaste.org/49889 You will see that line 4 gives a different result to lines 6, 8, 10; this shouldn't be the case because union is commutative.

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Building ? using kleene closure {not haskell specific}
by C K Kashyap 12 Aug '11

12 Aug '11

Hello gentle Haskell folks, I happened to read "Beautiful code"'s chapter 1 today and found Brian Kerninghan's regex implementation. In it he only shows the * meta character. I can easily understand how + can be built but am having trouble with building ? (zero or one). I'd really appreciate it if some one could help me understand it. Regards, Kashyap

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Help understanding Haskell runtime costs
by Thiago Negri 11 Aug '11

11 Aug '11

Hello all, I'm relatively new to Haskell and trying to solve some online judge's problems in it. One of the problems is to say if a given sentence is a tautogram or not. A tautogram is just a sentence with all the words starting with the same letter. My first try (solution is ok) was to do it as haskeller as possible, trying to overcome my imperative mind. But it did bad at performance (0.30 secs of runtime, 4.6 mb of memory): -- code start import Data.Char (toLower) main = getContents >>= mapM_ (putStrLn . toStr . isTautogram . words) . takeWhile (/= "*") . lines toStr :: Bool -> [Char] toStr True = "Y" toStr False = "N" isTautogram :: [[Char]] -> Bool isTautogram (x:[]) = True isTautogram (x:xs) = all ((== firstChar) . toLower . head) xs where firstChar = toLower . head $ x -- code end I tried to profile the code, but didn't find anything useful. My bet is that all this "words . lines" is consuming more memory than necessary, maybe saving space for the lines already processed. Then I tried a some-what tail-call function, consuming one line at each iteration: -- code start import Data.Char (toLower) main :: IO () main = getLine >>= mainLoop mainLoop :: [Char] -> IO () mainLoop s | (head s) == '*' = return () | otherwise = (putStrLn . toStr . isTautogram . words $ s) >> main toStr :: Bool -> [Char] toStr True = "Y" toStr False = "N" isTautogram :: [[Char]] -> Bool isTautogram (x:[]) = True isTautogram (x:xs) = all ((== firstChar) . toLower . head) xs where firstChar = toLower . head $ x -- code end Note that the only thing that changed between the two tries was the main-loop. The second version runs faster (got 0.11 secs) and with less memory (3.6 mb) Can someone explain to me what is really going on? Maybe pointing out how I can achieve these optimizations using profiling information... Thanks, Thiago.

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Trouble with readProcess
by Charles-Pierre Astolfi 11 Aug '11

11 Aug '11

Hi -cafe, I'm using readProcess and I don't know how to handle this issue: readProcess cmd [opt1,opt2] seems to execute the following: $ cmd "opt1" "opt2" That is usually fine, but I'm using an external program that doesn't understand the quotes, so I need to execute instead: $ cmd opt1 opt2 How should I do that? -- Cp

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ANNOUNCE: Chell: A quiet test runner (low-output alternative to test-framework)
by John Millikin 11 Aug '11

11 Aug '11

Homepage: https://john-millikin.com/software/chell/ Hackage: http://hackage.haskell.org/package/chell -------- This is just a quick package I whipped up out of frustration with test-framework scrolling an error message out of sight, for the millionth time. Chell has the same general purpose (aggregate your assertions + properties + whatever into a single executable), but only prints when a test fails or aborts. It also has a small built-in test library, similar to HUnit, so you don't need to depend on 2-3 separate libraries if you're just doing simple tests. Cool features thereof: * it reports the line number of failed assertions * you can use $expect instead of $assert, so even if it fails, the test keeps going (all the failures are printed at the end) * you can add "notes" to a test, which are saved in logs and reports. you can put in any sort of metadata you want (nice for figuring out why a test is failing) * assertions for text diffs, so if you're testing two big chunks of text for equality you don't have to copy+paste to see what's different.

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ANNOUNCE: Chell: A quiet test runner (low-output alternative to test-framework)
by Greg Weber 11 Aug '11

11 Aug '11

Hi John, I am wondering if you have seen the hspec package? [1] It seems to solve all the problems you are with chell, including that it silences Hunit output. We are using it for all the Yesod tests now. Thanks, Greg Weber [1]: http://hackage.haskell.org/packages/archive/hspec/0.6.1/doc/html/Test-Hspec…

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Re: [Haskell-cafe] [Haskell] ANNOUNCE: GHC version 7.2.1
by Henning Thielemann 11 Aug '11

11 Aug '11

On 09.08.2011 22:01, Ian Lynagh wrote: > > The GHC Team is pleased to announce a new major release of GHC, 7.2.1. > > The 7.2 branch is intended to be more of a "technology preview" than > normal GHC stable branches; in particular, it supports a significantly > improved version of DPH, as well as new features such as compiler > plugins and "safe Haskell". The design of these new features may evolve > as we get more experience with them. See the release notes for more > details of what's new and what's changed. These sound like a lot of exciting news. The release notes also mention a VECTORISE pragma, that is not mentioned in http://www.haskell.org/ghc/docs/7.2.1/html/users_guide/pragmas.html and not in the index. Is it about the planned GHC support for SSE/AltiVec vector units or is it about DPH?

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How to use cabal macros in .hsc files
by Bas van Dijk 11 Aug '11

11 Aug '11

Hello, Currently it's not possible to use cabal macros like MIN_VERSION_base(x,y,z) in .hsc files: http://hackage.haskell.org/trac/hackage/ticket/870 Is there a workaround to get the same effect? Regards, Bas

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