July 2010 - Haskell-Cafe

new Cabal user question -- installing to Haskell Platform on Windows network drive?
by Peter Schmitz 02 Aug '10

02 Aug '10

I have recently installed the Haskell Platform (for the first time) to a MS Windows network drive; e.g.: H:\aaa\bbb\Haskell Platform\2010.1.0.0\ I did so without admin privs. It has ghc-6.12.1 I need to not install to C:. I would like to install and use Gtk2Hs and Glade on the Platform also. I have used Gtk2Hs and Glade in Haskell (with just ghc, not the Platform), but I have never used Cabal or the Haskell Platform. I see at http://www.haskell.org/gtk2hs/ that Gtk2Hs now comes in a Cabal package ("Gtk2Hs 0.11.0 released"). The info there says you can just install "the Gtk+ libraries", and then do: cabal install gtk2hs-buildtools cabal install gtk I interpret "the Gtk+ libraries" to mean "gtk: the base GUI library" package listed at http://www.haskell.org/gtk2hs/download/ (is that correct?). That is a link to http://hackage.haskell.org/package/gtk which has "gtk-0.11.0.tar.gz (Cabal source package)", which I downloaded and unpacked to a temp directory which now contains "gtk-0.11.0". I've reviewed the Cabal documentation (that came with the Platform) and I'm having a little trouble determining exactly what to do next -- the exact commands to use for my non-C: / network drive installation. (I have not used Cabal before.) I would prefer to do this without admin privs, if possible. ** If anyone could help me out here with a step-by-step, I would appreciate it. Hopefully the procedure for glade will then be similar. Thanks (very much) in advance. -- Peter Schmitz

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Microsoft's Singularity Project and Haskell
by Vasili I. Galchin 02 Aug '10

02 Aug '10

Hello, In the latest ACM CACM is a paper on Singularity. Here also is an overview: http://lambda-the-ultimate.org/node/1081. I haven't finished the CACM paper yet but I only mention of languages like C# and F#. Singularity is predicated around providing a safe environment. IMO Haskell is even better than their languages. My $.02. Regards, Vasili

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ANNOUNCE: Takusen 0.8.6
by Jason Dagit 02 Aug '10

02 Aug '10

Hello, The Takusen team would like to announce the latest release of Takusen, 0.8.6. This is primarily a bug fix and test suite enhancement release. The most notable new feature is limited support for string encodings with ODBC. The full list of changes is included at the at the end of this announcement. = Interested in Takusen development? = Takusen is looking for a new long term maintainer. I have agreed to fill the role of maintainer for now, but we are seeking an enthusiastic individual with spare time and a desire to lead Takusen development. = How to get it = This release is available on hackage: cabal update && cabal install Takusen The source code is available on code.haskell.org: darcs get http://code.haskell.org/takusen = New features = - Alistair Bayley: * Database/PostgreSQL/PGFunctions.lhs: show instance for UUID prints Word64s in hex. * Database/PostgreSQL/Enumerator.lhs: add UUID and marshaling functions. * Database/PostgreSQL/PGFunctions.lhs: add UUID and marshalling functions. * Database/ODBC/OdbcFunctions.hsc: add support for different String encodings. New functions to marshal to/from various encodings (Latin1, UTF8, UTF16), and bind/get functions changed to use these. - Daniel Corson * binary data with postgres = Bug fixes = - Alistair Bayley: * Database/ODBC/OdbcFunctions.hsc: fix bug in mkBindBufferForStorable for Nothing (null) case: pass -1 (sqlNullData) as value size. * Database/ODBC/OdbcFunctions.hsc: use sqlNullData in bindParamString Nothing case, rather than -1. A bit more descriptive. * Database/ODBC/Enumerator.lhs: store bind buffers in stmt object, so we retain reference to them for lifetime of statement. Destroy with statement (well, lose the reference). Should fix bind errors found by Jason Dagit. * Database/ODBC/Enumerator.lhs: Oracle only supports two transaction isolation levels (like Postgres). String output bind parameters have max size 8000 (we use 7999 because module OdbcFunctions adds one to the size). * Database/ODBC/OdbcFunctions.hsc: string parameters have different SQL data types when binding columns (SQL_CHAR) and parameters (SQL_VARCHAR). Oracle only supports two transaction isolation levels. * Database/PostgreSQL/PGFunctions.lhs: fix byteaUnesc and add byteaEsc. = Refactoring = - Jason Dagit: * update urls in cabal file - Alistair Bayley: * Takusen.cabal: fixed QuickCheck version spec. * Takusen.cabal: bump version to 0.8.6. * Database/ODBC/OdbcFunctions.hsc: makeUtcTimeBuffer: pass struct size as both buffer size and data size in call to mkBindBuffer. * Database/ODBC/OdbcFunctions.hsc: mkBindBufferForStorable calls mkBindBuffer (reduces duplicated code). * Database/ODBC/Enumerator.lhs: add instance for EnvInquiry to change session char encoding. * Database/ODBC/Enumerator.lhs: add comments to beginTransaction. * Database/Util.lhs: print "printArrayContents", to match function name. * Database/PostgreSQL/Enumerator.lhs: expose byteaEsc and byteaUnesc. = New tests and changes to tests = - Alistair Bayley: * Database/ODBC/Test/OdbcFunctions.lhs: added testBindDouble to test Nothing (null) case for Storable types. * Database/ODBC/Test/OdbcFunctions.lhs: split transaction isolation level tests so there is one test per level. String marshaling tests use 0x10FF40 as max unicode codepoint, because that keeps Oracle happy. Max size for String parameter buffer is 7999 (SQL Server restriction). Don't bury errors raised by tests; print, but continue. Fix fixture cleanup bug in testBindOutput (dropped wrong procedure). * Database/ODBC/Test/Enumerator.lhs: suffix xxx to bindOutput test expected value. * Database/PostgreSQL/Test/PGFunctions.lhs: tests for UUID. * Database/PostgreSQL/Test/Enumerator.lhs: round-trip test for UUID. * Database/PostgreSQL/Test/PGFunctions.lhs: test select of UUID value. * Database/ODBC/Test/OdbcFunctions.lhs: set client charset to UTF8 when postgresql. * Database/Test/Enumerator.lhs: add order-bys to tests with unions. * Database/PostgreSQL/Test/PGFunctions.lhs: add order-by to union test. * Database/ODBC/Test/Enumerator.lhs: set char encoding to UTF8. inquire InfoDbmsName already returns lowercase. * Takusen.cabal: add random to build-depends for tests. * Database/Test/Enumerator.lhs: make test fixtures more friendly to MS Access. * Database/ODBC/Test/OdbcFunctions.lhs: tests modified for MS Access (date tests), plus use new char-encoding aware functions. * Database/ODBC/Test/Enumerator.lhs: change boundary dates test to not use union. Union seems to make MS Access choke. * Database/PostgreSQL/Test/PGFunctions.lhs: add tests for bytea, including QuickCheck roundtrip. * Database/PostgreSQL/Test/Enumerator.lhs: add bytea bind and select test.

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Laziness question
by michael rice 02 Aug '10

02 Aug '10

From: http://en.wikibooks.org/wiki/Haskell/Laziness Given two functions of one parameter, f and g, we say f is stricter than g if f x evaluates x to a deeper level than g x Exercises 1. Which is the stricter function? f x = length [head x] g x = length (tail x) Prelude> let f x = length [head x] Prelude> let g x = length (tail x) Prelude> f undefined 1 Prelude> g undefined *** Exception: Prelude.undefined Prelude> So, g is stricter than f? Wouldn't both functions need to evaluate x to the same level, *thunk* : *thunk* to insure listhood? f x = length [head *thunk* : *thunk*] g x = length (tail *thunk* : *thunk*) Michael

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Chart package segfaults when rendering to window
by briand＠aracnet.com 01 Aug '10

01 Aug '10

Seems to be ok rendering to png files. I was wondering if anybody has been using Chart and may have seen the same thing. I'm running ghc 6.12.1 and the latest and greatest gtk2hs :-) Thanks, Brian p.s. the amplitude modulation

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Anyone here from New Zealand?
by Tim Matthews 01 Aug '10

01 Aug '10

Any of the haskellers here from NZ? Are you using haskell in production, internally within your company or just outside of work in your own time? In Aus they've got hackathons<http://www.haskell.org/haskellwiki/AusHac2010>and user groups <http://www.haskell.org/haskellwiki/User_groups#Australia>. Anything even remotely similar here in New Zealand? Thanks Tim Matthews

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Problem loading hxt
by David Place 01 Aug '10

01 Aug '10

Hello: I am trying to load hxt into my Haskell Platform 2010.2.0.0 on OSX. I get the following bizarre comment: David-Places-Mac-Mini:dev2 davidplace$ cabal install hxt Resolving dependencies... cabal: dependencies conflict: ghc-6.12.3 requires directory ==1.0.1.1 however directory-1.0.1.1 was excluded because ghc-6.12.3 requires directory ==1.0.1.2 I see that I have the older directory in my global package list and the newer one in my local list. Help? Thanks. David-Places-Mac-Mini:dev2 davidplace$ ghc-pkg list /Library/Frameworks/GHC.framework/Versions/612/usr/lib/ghc-6.12.3/package.conf.d Cabal-1.8.0.6 GLUT-2.1.2.1 HTTP-4000.0.9 HUnit-1.2.2.1 OpenGL-2.2.3.0 QuickCheck-2.1.1.1 array-0.3.0.1 base-3.0.3.2 base-4.2.0.2 bin-package-db-0.0.0.0 bytestring-0.9.1.7 cgi-3001.1.7.3 containers-0.3.0.0 deepseq-1.1.0.0 directory-1.0.1.1 dph-base-0.4.0 dph-par-0.4.0 dph-prim-interface-0.4.0 dph-prim-par-0.4.0 dph-prim-seq-0.4.0 dph-seq-0.4.0 extensible-exceptions-0.1.1.1 ffi-1.0 fgl-5.4.2.3 filepath-1.1.0.4 ghc-6.12.3 ghc-binary-0.5.0.2 ghc-prim-0.2.0.0 haskell-src-1.0.1.3 haskell98-1.0.1.1 hpc-0.5.0.5 html-1.0.1.2 integer-gmp-0.2.0.1 mtl-1.1.0.2 network-2.2.1.7 old-locale-1.0.0.2 old-time-1.0.0.5 parallel-2.2.0.1 parsec-2.1.0.1 pretty-1.0.1.1 process-1.0.1.3 random-1.0.0.2 regex-base-0.93.2 regex-compat-0.93.1 regex-posix-0.94.2 rts-1.0 stm-2.1.2.1 syb-0.1.0.2 template-haskell-2.4.0.1 time-1.1.4 unix-2.4.0.2 xhtml-3000.2.0.1 zlib-0.5.2.0 /Users/davidplace/.ghc/i386-darwin-6.12.3/package.conf.d Cabal-1.8.0.6 binary-0.5.0.2 directory-1.0.1.2 fingertree-0.0.1.0 haskell98-1.0.1.1 process-1.0.1.3 random-1.0.0.2 time-1.2.0.3 uu-parsinglib-2.4.2 uu-parsinglib-2.4.4 uu-parsinglib-2.4.5 uu-parsinglib-2.5.0 uulib-0.9.12

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dear traversable
by Ben 31 Jul '10

31 Jul '10

dear traversable geniuses -- i am looking for "better" implementations of unzipMap :: M.Map a (b, c) -> (M.Map a b, M.Map a c) unzipMap m = (M.map fst m, M.map snd m) unliftMap :: (Ord a) => M.Map a (b -> c) -> M.Map a b -> M.Map a c unliftMap mf ma = M.mapWithKey (\k v -> mf M.! k $ v) ma the first is obviously inefficient as it traverses the map twice. the second just seems like it is some kind of fmap. any ideas? ben

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Type Families: deleting from HList.
by Serguey Zefirov 31 Jul '10

31 Jul '10

Is it possible to delete an element from heterogenous list using type families alone? I can do it using multiparameter type classes: class Del a list result instance Del a (a,list) list instance Del a list list' => Del a (a',list) list' instance Del a () () I tried to express the same using type families: type family Del a list type instance Del a () = () type instance Del a (a,list) = list type instance Del a (a',list) = (a',Del a list) to no avail. I got "conflicting family instance declarations" error. I tried to express that with associated type synonyms that contains both multiparameter type classes and type families: class HDel a list where type Del a list instance HDel a () where type Del a () = () instance HDel a (a,list) where type Del a (a,list) = list instance HDel a list => HDel a (a',list) where type Del a (a',list) = (a',Del a list) And I once again got "conflicting family instance declaration". It looks like right now there is no way to express type equality or inequality with type families, even when they are combined with multiparameter type classes. What is the right way to express something like that? Only MPTC?

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Constructor question
by michael rice 31 Jul '10

31 Jul '10

From: Data.Complex data (RealFloat a) => Complex a = !a :+ !a What's the purpose of the exclamation marks? Michael

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