October 2008 - Haskell-Cafe

labels in HList
by roger peppe 22 Oct '08

22 Oct '08

hi, i'm trying to get labelled records working with the current version of HList. i've got code that looks like: >{-# language EmptyDataDecls #-} >module Tst where > import Data.HList > > data Foo; foo = proxy::Proxy Foo > data Bar; bar = proxy::Proxy Bar > rec1 = > foo .=. 1 .*. > bar .=. "hello" .*. > emptyRecord which gives me the error: Tst4.hs:8:2: No instance for (HEq (Proxy Foo) (Proxy Bar) HFalse) arising from a use of `.*.' at Tst4.hs:(8,2)-(10,12) Possible fix: add an instance declaration for (HEq (Proxy Foo) (Proxy Bar) HFalse) In the expression: foo .=. 1 .*. bar .=. "hello" .*. emptyRecord In the definition of `rec1': rec1 = foo .=. 1 .*. bar .=. "hello" .*. emptyRecord some discussion on #haskell suggesting importing Label4 and TypeEqGeneric1 but a) that's not possible because both are hidden inside the HList package and b) even when i get around that restriction, i still get a "No instance for (TypeCast HFalse HFalse)" error. thanks, rog.

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code generation
by z ghost 21 Oct '08

21 Oct '08

hello, im interested in using haskell to generate code and make little AI applications for fun.. is anyone already doing this sort of thing? it would be fun to collaborate with people on this. Here's some code as an example of the direction i'd like to go in. It builds up template haskell Exps and uses the Hint module to typecheck them. With some more work, it could be turned into a program that finds haskell programs (given a type as input).. http://www.sendspace.com/file/aj5r38 __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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cabal-install question
by Ken98 21 Oct '08

21 Oct '08

Hello, I recently started using cabal-install to install packages. However, ran into a problem today trying to install ftphs where the current HUnit dependency required base (==4). I'm using ghc-6.8.2 on ubuntu. To get around this, I looked through previous versions of HUnit and found that 1.2.0.0 was the last to have a successful build with ghc-6.8. So, I downloaded the tar.gz and did a runhaskell Setup.hs ... This worked and I was able to complete the ftphs install. So my question is, could I have used cabal install to specify the specific version of HUnit without having to do the manual download/configure/build/install? Thanks, Ken -- View this message in context: http://www.nabble.com/cabal-install-question-tp20098091p20098091.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Installing ghc + gtk2hs on linux
by Bulat Ziganshin 21 Oct '08

21 Oct '08

Hello haskell-cafe, i'm linux freshman what's the simplest way to install ghc + gtk2hs on Ubuntu x86 system? -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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FFI and GHCi
by Emil Axelsson 21 Oct '08

21 Oct '08

Hi, I'm making my first attempt at using some C code in my Haskell program. I need it because I have a large amount of small constant tables, and GHC takes ages to compile the if I use ordinary lists (and the object file gets huge). If there's any way of achieving this without going to C, I'd be interested to know. My question is about how to compile a library that contains C code. At the end of this message is a simple example of an 'increase' function. To compile, I run ghc Increase.hs --make -o increase increase.c and everything works as expected. But then when I want to load the example in GHCi, I need to give the object file at the command line ghci Increase increase.o or I get "unknown symbol `increase'" when I try to run main. It feels a bit awkward to have to list the object files every time I want to run GHCi. Is there any way of avoiding that? There must be, because if I install the files as a Cabal library, I can fire up GHCi without mentioning any object files. But I don't want to go through cabal every time I want test some part of my code. Thanks for any help, / Emil ---------------- increase.h: int increase(int x); increase.c: #include "increase.h" int increase(int x) { return x+1; } Increase.hs: {-# INCLUDE "increase.h" #-} {-# LANGUAGE ForeignFunctionInterface #-} import Foreign.C foreign import ccall "increase.h increase" inc :: CInt -> CInt main = print (inc 2, inc 20) ----------------

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Haddock on cygwin
by Tom Hawkins 21 Oct '08

21 Oct '08

I'm having the following issue with Haddock 2.0 and GHC 6.8.3 on cygwin: $ haddock -o doc --html -B /cygdrive/c/Program\ Files/Haskell/ghc-6.8.3/lib Test.hs $ haddock.exe: Can't find package.conf as \cygdrive\c\Program Files\Haskell\ghc-6.8.3\lib\driver\package.conf.inplace The windows install of GHC 6.8.3 does not have a "driver/package.conf.inplace" in ghc-6.8.3/lib. Any ideas? -Tom

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code generation
by Martin Hofmann 21 Oct '08

21 Oct '08

We try to learn functional programs from examples, but our system is not yet ported to Haskell, though we are working on it. However, we thought about using TH. Do you have any pointers to papers, etc. ? You'll find our project, system and papers here: http://www.cogsys.wiai.uni-bamberg.de/effalip/ Martin

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REMINDER: Haskell Communities and Activities Report
by Janis Voigtlaender 21 Oct '08

21 Oct '08

Dear Haskellers, The deadline for the November 2008 edition of the Haskell Communities and Activities Report is only ten days away. If you haven't already, please write an entry for your new project, or update your old entry. Please mail your entries to hcar(a)haskell.org in plain text or LaTeX format. More information can be found in the original Call for Contributions at: http://www.haskell.org/pipermail/haskell/2008-October/020651.html I look forward to receiving your contributions. Thanks a lot, Janis (current editor) -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de

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need help making sense of the relative indexing
by Daryoush Mehrtash 21 Oct '08

21 Oct '08

I am trying to make sense of the relative indexing example used in this "Charting Patterns on Price history" paper: http://serv1.ist.psu.edu:8080/viewdoc/download;jsessionid=CC3DEF7277760C535… In Section 3 it defines: type Indicator a = Bar → (Maybe a ) Indicator takes a bar b and returns an indicator value for that bar. .....bar is associated with five basic fields: high, low, open, close price, and transaction volume ...... It is very common while defining indicators to use past values of an indicator. To support this, we have a combina- tor (♯) which enables relative indexing into past data. Given a bar (time), while an indicator, say high , evaluates to the high price at the bar, high ♯ n yields the high price of n th previous bar. (♯) is defined as follows: (♯) :: Indicator a → Integer → Indicator a ind ♯ n = λ b . ind (b − n ) I can't figure out how (b-n) translates to n'th previous bar. Any ideas? daryoush

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external linking traumas
by Chris Dornan 21 Oct '08

21 Oct '08

Hi Folks, I am battling Database.HSQL to get it to work on GHC-6.8.3 running Cygwin/XP and I seem to have found a worthy opponent. I have got the following to work: import Database.HSQL import Database.HSQL.MySQL main :: IO () main = do c <- cnct tbs <- tables c putStr $ unlines $ "Tables:":[" "++tnm|tnm<-tbs] cnct :: IO Connection cnct = connect "host" "database" "user" "password" To work on *ghci* that is, but I can't get it to work with *ghc*. For ghci I use: ghci test.hs -llibmySQL with libmySQL.dll copied into the same directory. If I try the same with ghc: ghc test.hs -package hsql-1.7 -package hsql-mysql-1.7 -L. -llibmysql with libmysql.lib copied into the same directory I get: C:\Program Files\Haskell\hsql-mysql-1.7\ghc-6.8.3/libHShsql-mysql- 1.7.a(MySQL.o)(.text+0x748):fake: undefined reference to `mysql_init@4' C:\Program Files\Haskell\hsql-mysql-1.7\ghc-6.8.3/libHShsql-mysql- 1.7.a(MySQL.o)(.text+0x83f):fake: undefined reference to `mysql_real_connect@32' [...] C:\Program Files\Haskell\hsql-mysql-1.7\ghc-6.8.3/libHShsql-mysql- 1.7.a(MySQL.o)(.text+0x216c):fake: undefined reference to `mysql_stmt_affected_rows@4' collect2: ld returned 1 exit status If I try substituting -llibmySQL (to select the dll) I get the same results. GHC is clearly not resolving the links between Database.HSQL.MySQL and the native libmysql.lib/libmySQL.dll in the way that ghci does with the dll. I must be doing something silly. If someone can tell me I would be grateful. I would also like to know what I need to do to package this up inside CABAL; all my attempts so far have failed. It seems that there has been no maintainer for HSQL for some time, which is a shame, as folks seem to be repeatedly cracking their heads against these problems and re-solving them. I may be able to take on hsql and hsq-mysql myself, but not the other backends. Perhaps it is the prospect of maintaining them all may be stopping folks from stepping forward. (If it is being maintained and I am just making a hash of it then please accept my apologies.) Cheers, Chris

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