- Haskell-Cafe - Haskell.org

Database.CouchDB broken?
by Moritz Ulrich 31 Jul '10

31 Jul '10

Hello, I'm currently learning Haskell and I want to write a small tool to collect some data in a CouchDB-Database Sadly, the Database.CouchDB module from hackage (and from git) seems broken. It looks like a bug deep in the JSON handling of the lib. Some examples can be found in this gist: http://gist.github.com/475323 ('test' is a database with two simple documents, the doc with the id '8e9112011580882422393f6291000f7d' exists) I filed an issue, but the maintainer hasn't responded in 5 days. Is there anything I missed? Thanks in advance! -- Moritz Ulrich Programmer, Student, Almost normal Guy http://www.google.com/profiles/ulrich.moritz

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Definition of List type?
by michael rice 31 Jul '10

31 Jul '10

From: Data.Maybe Description The Maybe type, and associated operations. From: Data.List Description Operations on lists. One description has the type and associated operations, the other only has the operations. Where can I find the type definition for List, and why isn't it in Data.List? Michael

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Problem with haskell types
by Anupam Jain 30 Jul '10

30 Jul '10

Hi, I am having trouble getting a small program to compile. The helpful folks at #haskell created a version of the program that does compile - http://hpaste.org/fastcgi/hpaste.fcgi/view?id=28406#a28408 but it is not very clear to them (and to me) why the original program wouldn't type compile in the first place. Here's the program that refuses to compile - module Delme () wheredata DecisionState = A | B | C | Dd_test :: Eq b => b -> b -> DecisionState -> DecisionState -> ()d_test test testVal trueState falseState = if (test == testVal) then d trueState else d falseStated :: DecisionState -> ()d A = d_test True True B Cd B = d_test 1 2 C Dd C = d_test True False A Bd D = () I get an error like - Delme.hs:13:0: Contexts differ in length (Use -XRelaxedPolyRec to allow this) When matching the contexts of the signatures for d_test :: forall b. (Eq b) => b -> b -> DecisionState -> DecisionState -> () d :: DecisionState -> () The signature contexts in a mutually recursive group should all be identical When generalising the type(s) for d_test, d Putting in the extension does get the program to type check but the original program should have type compiled in the first place. The ironic thing we discovered is that if we remove the type declaration for 'd', the program type checks, and GHC then derives the exact same type which we removed! Can some of the smarter people in the room please shed more light on this? -- Anupam

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couchDB
by Andrew U. Frank 30 Jul '10

30 Jul '10

a few weeks ago a question was posed on this list for examples how to use couchDB. i post the 'hello world' for couchDB using the haskell interface - perhaps it helps other to start! a more extensive and complicate example is found at www.maztravel.com/haskell/mySqlToCouchDB.html I created with Futon a db names "first" (i had no luck with names containing a - or a _ , but have not investigated further). the runcouchDB' affects the couchDB at localhost. andrew ps: if there is a better place to document examples? a wiki on haskell.org would be nice and should be available for any project in hackage. ---- {-# LANGUAGE DeriveDataTypeable #-} module Main ( ) where import Database.CouchDB import Data.Data (Typeable) import Text.JSON s1 = JSString $ toJSString "Peter" m1 = makeObj [("FirstName", s1), ("FamilytName", JSString . toJSString $ "Miller")] mydb1 = db "first" -- convert db name to checked couchdb -- problem with "-" or "_" in db names in haskell?? main = do putStrLn "start couchdb tests" (doc, rev) <- runCouchDB' $ newDoc mydb1 m1 -- works return ()

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[Yi Editor]Cabal Problem
by Alessandro Stamatto 30 Jul '10

30 Jul '10

Installing Yi Editor i get the following error: ------------------------------ ----------------------------------------------- Missing dependencies on foreign libraries: * Missing C libraries: gobject-2.0, glib-2.0, intl, iconv ----------------------------------------------------------------------------- Im on windows, using Cabal in Cygwin. How should i install those missing libs?

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Fail to install SDL with Cabal
by Eitan Goldshtrom 30 Jul '10

30 Jul '10

I'm trying to install SDL through Cabal -- I don't know another way to install it. However, I'm getting this: setup.exe: The package has a './configure' script. This requires a Unix compatibility toolchain such as MinGW+MSYS or Cygwin. cabal: Error: some packages failed to install: SDL-0.5.10 failed during the configure step. The exception was: exit: ExitFailure 1 I have MinGW and MSYS, so I don't understand why I'm having this problem. Do I need to set something special up so that Cabal can access their tools? -Eitan

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ANN: weighted-regexp-0.1.0.0
by Sebastian Fischer 30 Jul '10

30 Jul '10

Hello, this year's ICFP features A Play on Regular Expressions where two Haskell programmers and an automata theory guru develop an efficient purely functional algorithm for matching regular expressions. A Haskell library based on their ideas is now available from Hackage. For more information (and a link to the play) visit: http://sebfisch.github.com/haskell-regexp/ Cheers, Sebastian -- Underestimating the novelty of the future is a time-honored tradition. (D.G.)

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data.binary get reading beyond end of input bytestring?
by Conrad Parker 29 Jul '10

29 Jul '10

Hi, I am reading data from a file as strict bytestrings and processing them in an iteratee. As the parsing code uses Data.Binary, the strict bytestrings are then converted to lazy bytestrings (using fromWrap which Gregory Collins posted here in January: -- | wrapped bytestring -> lazy bytestring fromWrap :: I.WrappedByteString Word8 -> L.ByteString fromWrap = L.fromChunks . (:[]) . I.unWrap ). The parsing is then done with the library function Data.Binary.Get.runGetState: -- | Run the Get monad applies a 'get'-based parser on the input -- ByteString. Additional to the result of get it returns the number of -- consumed bytes and the rest of the input. runGetState :: Get a -> L.ByteString -> Int64 -> (a, L.ByteString, Int64) The issue I am seeing is that runGetState consumes more bytes than the length of the input bytestring, while reporting an apparently successful get (ie. it does not call error/fail). I was able to work around this by checking if the bytes consumed > input length, and if so to ignore the result of get and simply prepend the input bytestring to the next chunk in the continuation. However I am curious as to why this apparent lack of bounds checking happens. My guess is that Get does not check the length of the input bytestring, perhaps to avoid forcing lazy bytestring inputs; does that make sense? Would a better long-term solution be to use a strict-bytestring binary parser (like cereal)? So far I've avoided that as there is not yet a corresponding ieee754 parser. Conrad.

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Announce snm-0.0.2: The Simple Nice-Looking Manual Generator
by Johnny Morrice 29 Jul '10

29 Jul '10

Hi list, Recently, I've been working on a compiler/programming language project.[2] I became rather unstuck when I started spending more time documenting the semantics instead of actually getting to work on the implementation. Hence this program! snm allows you to write clean, web-friendly reports, user guides and manuals without having to edit fickle html. snm allows you to structure your document in a modular fashion. snm document sections are written in yaml and are easy to write and understand. snm is a generator of small, valid xhtml files. Read the snm user guide here: http://www.killersmurf.com/static/snm_help.html snm uses Yaml and generates XHTML, so it's a little like John MacFarlane's yst[1], but yst is for making websites, while snm is exclusively for creating structured reports. It still has a lot of problems, not to mention no support for images, or multiple pages, but I'm finding it usable (enough to document itself!) so I thought it best to share :) Sorry if I have left typos, it's very late Have fun, Johnny [1] John MacFarlane's yst: http://hackage.haskell.org/package/yst [2] Yon aforementioned programming language project, in case anyone fancies a peep. Demoted to reference #2, on account of it not yet compiling code :) http://github.com/elginer/Obelisk

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Search for documentation as data fails with Haskell Platform on Windows 7
by John D. Ramsdell 29 Jul '10

29 Jul '10

I contributed the CPSA package to Hackage, and tried using it on a PC running Windows 7. The package installs six executables and documentation as PDF and XHTML into the package's data directory. Haskell Platform with Cabal installs the package without a problem. It was actually quite smooth and simple. So far so good. The trouble came when I tried to locate the documentation. The XHTML document is called cpsauser.html, but the search command on Windows 7 cannot find the document. Is there some way to tell it to try harder? How are users supposed to know how to locate program documentation when using Windows 7? I'm not much of a Windows user, so let me apologize in advance if this is a silly question, and search is, in fact, easy. John

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