May 2011 - Haskell-Cafe

No fish, please
by Andrew Coppin 28 May '11

28 May '11

Both Hackage and Cabal seem to assume as a matter of course that I want to use Haddock to generate all my documentation. Suppose I decide to violate this assumption. Then what? 1. Is there some way I can include my own HTML documentation in the package tarball and have Hackage/Cabal use it? 2. Is there a way to tell Hackage/Cabal to use some tool besides Haddock?

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representing spreadsheets
by Eric Rasmussen 28 May '11

28 May '11

Hi everyone, I'm hoping someone can point me in the right direction for a project I'm working on. Essentially I would like to represent a grid of data (much like a spreadsheet) in pure code. In this sense, one would need functions to operate on the concepts of "rows" and "columns". A simple "cell" might be represented like this: data Cell = CellStr Text | CellInt Integer | CellDbl Double | CellEmpty The spreadsheet analogy isn't too literal as I'll be using this for data with a more regular structure. For instance, one grid might have 3 columns where every item in column one is a CellStr, every item in column two a CellStr, and every item in column 3 a CellDbl, but within a given grid there won't be surprise rows with extra columns or columns that contain some cell strings, some cell ints, etc. Representing cells in a matrix makes the most sense to me, in order to facilitate access by columns or rows or both, and I'd like to know if there's a particular matrix library that would work well with this idea. However, I'm certainly open to any other data structures that may be better suited to the task. Thanks! Eric

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Enterprise Haskell -- help
by Srinivasan Balram 27 May '11

27 May '11

folks: I was advised to post this request here. This is about needs of daily-grind enterprise development. Enterprise developers need 3 categories of books in Haskell urgently: (i) Haskell (CookBooks / Recipes) (ii) Haskell Enterprise Development i.e. how to connect commercial RDBMS and use Haskell along with SQL effectively (iii) Haskell Web/Network Development Books by Don Stewart & Miran Lipovaca are excellent for beginner/intermediaries. Erik Meijer's tutorial videos were very useful as well. But they are not enough. This may sound boring, but such books are badly needed "today". It's hard to convince clients/devs to start projects "without such resources". I am trying to push for Enterprise Haskell projects. Would appreciate pointers to resources for doing large scale Haskell development Thank you -ram

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Re: [Haskell-cafe] Policy for taking over a package on Hackage
by Mario Blažević 27 May '11

27 May '11

On 11-05-25 08:52 AM, Johan Tibell wrote: > On Wed, May 25, 2011 at 2:01 PM, Ivan Lazar Miljenovic > <ivan.miljenovic(a)gmail.com> wrote: >> With my wl-pprint-text package, Jason Dagit suggested to me on >> #haskell that it would make sense to make such a pretty-printer be >> class-based so that the same API could be used for String, ByteString, >> Text, etc. > I'm a bit skeptical of using type classes to abstract over Unicode > string types and byte sequence types. The only API shared by the two > kind of types is that of a sequence. Things like dot , spaces, etc. > don't make much sense on binary data. You must assume that the > ByteString contains text in some encoding to make sense of such > concepts. You don't necessarily need spaces and dot to abstract over bytestrings and Unicode string types. They both implement IsString and Monoid classes, as well as operations null, length, isPrefixOf, take, and drop. That's sufficient to implement a generic parser that works on any input type supporting these operations (see [1] for example), though there is some performance cost. I don't see why a pretty-printer should be any more difficult. [1] http://hackage.haskell.org/package/incremental-parser

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Parallel compilation and execution?
by michael rice 27 May '11

27 May '11

How do I compile and run this parallel program? Michael =========================== import Control.Parallel nfib :: Int -> Intnfib n | n <= 1 = 1 | otherwise = par n1 (seq n2 (n1 + n2 + 1)) where n1 = nfib (n-1) n2 = nfib (n-2) {-nfib :: Int -> Intnfib n | n <= 1 = 1 | otherwise = nfib (n-1) + nfib (n-2)-} main = do putStrLn $ show $ nfib 39 =========================== [michael@hostname ~]$ ghc --make -threaded nfib.hs[michael@hostname ~]$ ./nfib +RTS -N3nfib: the flag -N3 requires the program to be built with -threadednfib: nfib: Usage: <prog> <args> [+RTS <rtsopts> | -RTS <args>] ... --RTS <args>nfib: nfib: +RTS Indicates run time system options follownfib: -RTS Indicates program arguments follownfib: --RTS Indicates that ALL subsequent arguments will be given to thenfib: program (including any of these RTS flags)nfib: nfib: The following run time system options are available:nfib: nfib: -? Prints this message and exits; the program is not executednfib: --info Print information about the RTS used by this programnfib: nfib: -K<size> Sets the maximum stack size (default 8M) Egs: -K32k -K512knfib: -k<size> Sets the initial thread stack size (default 1k) Egs: -k4k -k2mnfib: nfib: -A<size> Sets the minimum allocation area size (default 512k) Egs: -A1m -A10knfib: -M<size> Sets the maximum heap size (default unlimited) Egs: -M256k -M1Gnfib: -H<size> Sets the minimum heap size (default 0M) Egs: -H24m -H1Gnfib: -m<n> Minimum % of heap which must be available (default 3%)nfib: -G<n> Number of generations (default: 2)nfib: -T<n> Number of steps in younger generations (default: 2)nfib: -c<n> Use in-place compaction instead of copying in the oldest generationnfib: when live data is at least <n>% of the maximum heap size set withnfib: -M (default: 30%)nfib: -c Use in-place compaction for all oldest generation collectionsnfib: (the default is to use copying)nfib: -w Use mark-region for the oldest generation (experimental)nfib: nfib: -t[<file>] One-line GC statistics (if <file> omitted, uses stderr)nfib: -s[<file>] Summary GC statistics (if <file> omitted, uses stderr)nfib: -S[<file>] Detailed GC statistics (if <file> omitted, uses stderr)nfib: nfib: nfib: -Z Don't squeeze out update frames on stack overflownfib: -B Sound the bell at the start of each garbage collectionnfib: nfib: -hT Heap residency profile (output file <program>.hp)nfib: -i<sec> Time between heap samples (seconds, default: 0.1)nfib: nfib: -C<secs> Context-switch interval in seconds.nfib: 0 or no argument means switch as often as possible.nfib: Default: 0.02 sec; resolution is set by -V below.nfib: -V<secs> Master tick interval in seconds (0 == disable timer).nfib: This sets the resolution for -C and the profile timer -i.nfib: Default: 0.02 sec.nfib: nfib: --install-signal-handlers=<yes|no>nfib: Install signal handlers (default: yes)nfib: nfib: RTS options may also be specified using the GHCRTS environment variable.nfib: nfib: Other RTS options may be available for programs compiled a different way.nfib: The GHC User's Guide has full details.nfib: [michael@hostname ~]$

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Strange Type Error
by jean-christophe mincke 27 May '11

27 May '11

Hello, Could anyone help me understand what is wrong with the definition of f2 in the code below? class C a b where convert :: a -> b convertToInt :: (C a Int) => a -> Int convertToInt x = convert x f1 x = convertToInt x f2 = \x -> convertToInt x f3 :: (C a Int) => a -> Int f3 = \x -> convertToInt x Thank you Regards J-C

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Email spam from my account on May 26, 2011
by Gregory Propf 27 May '11

27 May '11

I just discovered that some evil spammer has somehow gotten my contacts list and used it to send out a bunch of spam. This is just to notify you that if you get an email from me on May 26, 2011 (other than this one or one like it - the problem was more extensive than I first thought) it wasn't from me. Please don't add me to your spam filters. I've changed my password and hopefully that's the end of it. At this point I don't know how they did it though. - Greg

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(no subject)
by Gregory Propf 27 May '11

27 May '11

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Policy for taking over a package on Hackage
by Ivan Lazar Miljenovic 26 May '11

26 May '11

With my wl-pprint-text package, Jason Dagit suggested to me on #haskell that it would make sense to make such a pretty-printer be class-based so that the same API could be used for String, ByteString, Text, etc. I was thinking of doing so, and in such a case it would probably make the most amount of sense to actually then migrate the package back to the wl-pprint package instead of defining yet another package (and corresponding namespace), especially as I recalled from when I first started hacking on wl-pprint-text at the beginning of the year that the last (and only) upload had been in 2007 by Stefan O'Rear. As such, I was going to email Stefan and asked if he minded if I took over maintaining wl-pprint. However, when I went to the package page to get his email address, I saw that Otakar Smrz had released a new version about a month ago, and that the only change in the package that I could find was that OverlappingInstances was added to the .cabal file (which I thought wouldn't make a difference anyway). Now, for all I know, Otakar had already asked Stefan for permission to take over the package (I've CC'd both of them just in case). But even if he didn't, we don't officially have any policies set in place - especially ones that are enforced by requiring registering a package and specifying a maintainer - to indicate that such a thing shouldn't be done. Furthermore, if packages aren't announced then there's no way for people to know that there _is_ a new maintainer. This situation also arose last year [1], and was resolved by someone volunteering to take over a package. However, no formal policy was set in place (despite one being proposed). As such, I'd like to propose the following policy based upon the one Ben Millwood proposed last time on how to take over maintainership of a package that hasn't been updated for a while: 1. Email the current listed maintainer and wait a specified period of time (e.g. 2 weeks). 2. Email haskell-cafe, explicitly CC'ing maintainers of reverse dependencies (at least those that are themselves still active) and request permission to take over. This way, people who know the maintainer might point out that they are indeed still around, etc. 3. If no-one objects within another two weeks, announce that you have taken over maintainership with a new email (in case people are ignoring the previous thread). 4. Upload a point release of the previous package (assuming it follows the PVP) with yourself as the new maintainer (just to get it out there). Alternatively, if you already have a new version ready to go then upload that. Of course, having a policy like this is useless if there is no way to enforce it. Is it possible at the very least to have Hackage note when a new version of a package is uploaded with a new maintainer and require it to be approved by someone before it iis officially available? I think this would be the bare minimum (as opposed to requiring explicit logins on a per-package basis or some kind of signing) required for this kind of scheme to be effective. [1]: http://www.haskell.org/pipermail/haskell-cafe/2010-August/081353.html and http://www.haskell.org/pipermail/haskell-cafe/2010-August/082319.html -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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Function application layout
by Jonas Almström Duregård 26 May '11

26 May '11

Hi, Would it be possible to allow this in Haskell (where <applied to> is some new operator or keyword): f <applied to> {x a;y b;z c} As an equivalent to: f (x a) (y b) (z c) Of course my intention is that the new keyword should initiate layout syntax so we can write this: f <applied to> x a y b z c In addition to the case where you have a big function application, this is useful for defining trees: Branch <applied to> Branch <applied to> Leaf Leaf Leaf Has something like this been suggested before? Are there any disadvantages other than a new keyword and some potential confusion for readers? Any suggestions for a good keyword? I suppose some variant of $ makes sense, a textual keyword like "with" would be nice but probably break a lot of code. Regards, Jonas

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