- Haskell-Cafe - Haskell.org

Installing ghc + gtk2hs on linux
by Bulat Ziganshin 22 Oct '08

22 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 22 Oct '08

22 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 22 Oct '08

22 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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daemon process
by Rouan van Dalen 21 Oct '08

21 Oct '08

Hi Everyone. I have been learning Haskell the past few months and there are tons of things I still don't understand :) I would like to write a very very simple haskell daemon that disconnects itself from the terminal and sists in the background doing something. What is the easiest way to go about this. I have tried several things but can't seem to get the process disconnected from the terminal. Thanks in advance Rouan Send instant messages to your online friends http://uk.messenger.yahoo.com

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File handles and pipes
by Stephen Hicks 21 Oct '08

21 Oct '08

Hi, I'm trying to understand how to get pipes working in Haskell, in particular with the revamped System.Process (though I've tried similar experiments with System.Posix.IO and Control.Concurrent). Specifically I'm trying to concatenate the output of two system calls into the input of a third. The following code does not get the job done: > import Data.Maybe ( fromJust ) > import System.IO > import System.Process > sink :: String -> IO (Handle,ProcessHandle) > sink s = do let p = (shell s) { std_in = CreatePipe } > (mh, _, _, ph) <- createProcess p > return (fromJust mh,ph) > source :: String -> Handle -> IO () > source s h = do let p = (shell s) { std_out = UseHandle h, > close_fds = False } > (_, _, _, ph) <- createProcess p > waitForProcess ph > return () > main :: IO () > main = do (h,p) <- sink "sort" > source "df" h > source "df -h" h > waitForProcess p > return () When I run this, I see that the filehandle h is closed after the first df, so the output only has one of the two df's included in it. I tried also System.Posix.IO (createPipe, fdToHandle, dup) to make this work, but that gave a "read failed" error. Is there any way to get this done...? In general, given a handful of system calls (and/or read/write handles), is there a way to combine them all together? (I also tried using forkIO on my own function pipe :: [Handle] -> Handle -> IO (), which does what you'd expect given multiple read handles and a single write handle, but couldn't get any output from that at all...) Any help is appreciated, steve

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Re: [Haskell] Probably a trivial thing for people knowing Haskell
by Chris Eidhof 20 Oct '08

20 Oct '08

I think it might be more appropriate to move this discussion to haskell-cafe. On 19 okt 2008, at 17:24, Friedrich wrote: >> Learn to love types: one of the neat things about Haskell is that if >> you can write down the type of a function then you have usually done >> 90% of the work of writing the code for it. > Well I disagree. But that's another story. Well, it's definitely not true when you're starting out with Haskell. The thing is: once you start to think in types it does work like this. You just think: what do I need as my input and what's my output. That's what you write down as your type and you're almost done! It's very similar to test-driven development; the point with TDD is not so much about making sure your program is correct: the big win (for me) is that it helps you think about the design of your program. The same holds for types. > > >> Another is that in >> general, if you can't express the type of a function, it means you >> haven't thought through what you're trying to do. > > No that's not true. The use implies that. However I'm not advice > resistant and will see if I use types. But IMHO that's should be job > of the environment to figure out correctly and most of the time > Haskell does "guess" right. And I surely can ask for the types. I agree. However, sometimes, when things get really complex, you can't figure out a way to write down the code. That's when it can be handy to start out from the types and slowly work towards the definition. At first, you'll think that types are there to make your life harder. After a while, you'll start to love them and to be honest: I feel quite uncomfortable programming in an untyped language these days ;). -chris

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Haskell syntax inside QuasiQuote
by Reiner Pope 20 Oct '08

20 Oct '08

Hi, I have written a toy fixed-length-vector quasiquoter, so that you can write [$vec|1,2|] which has its type inferred as (Vec (S (S Z))) and you can write mkVec :: Double -> Vec (S (S (S Z))) mkVec x = [$vec|1,2,x|] However, these above examples essentially demonstrate the entire syntax it supports: number literals, and anti-quoted variables. I would like to extend my quasiquoter to support Haskell's full expression syntax, so that we can write, for example, mkVec2 x = [$vec| if x > 5 then sin x else cos x |] Is there a simple way to do this, i.e. using existing libraries? What I need is a Haskell expression parser which outputs values of type Language.Haskell.TH.Syntax.QExp, but I can't see one available in the TH libraries, or in the haskell-src(-exts) libraries. Thoughts? Cheers, Reiner

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Is there already an abstraction for this?
by Jeremy Shaw 20 Oct '08

20 Oct '08

Hello, I am trying to figure out if there is an existing abstraction I am missing here. I have an expression data-type: > data Expr > = Quotient Expr Expr > | Product Expr Expr > | Sum Expr Expr > | Difference Expr Expr > | Lit Double > | Var Char > deriving (Eq, Ord, Data, Typeable, Read, Show) > And I want to write a function that will take an expression and automatically apply the identity laws to simplify the expression. The basic identity laws are: a + 0 = a a * 1 = a I can implement these with some 'sugar' as: > identity (Sum (Lit 0) a) = a > identity (Sum a (Lit 0)) = a > identity (Difference a (Lit 0)) = a > identity (Product a (Lit 1)) = a > identity (Product (Lit 1) a) = a > identity (Quotient a (Lit 1)) = a > identity a = a This works fine when the identity only needs to be applied to the root of the expression tree: *Main> ppExpr $ identity (expr "1 + 0") 1 But for more complicated trees it does not fully apply the identity laws: *Main> ppExpr $ identity (expr "0 + (0 + 0) + (0 + 0)") ((0 + 0) + (0 + 0)) What we need to do is first apply the identity function to the children, and then apply them to the parent of the updated children. A first attempt would be to extend the identity function like this: > identity (Sum a b) = identity (Sum (identity a) (identity b)) However, that will not terminate because that same case will keep matching over and over. Another approach is to have two mutually recursive functions like: > identity' (Sum (Lit 0) a) = identityRec a > identity' (Sum a (Lit 0)) = identityRec a > identity' a = a > identityRec (Sum a b) = identity' (Sum (identity' a) (identity' b)) This prevents non-termination, but you have to be careful about calling identity' vs identityRec or you will either re-introduce non-termination, or you may not fully apply the identity laws. Another option to create a helper function like: > -- |Deep map of an expression. > eMap :: (Expr -> Expr) -> Expr -> Expr > eMap f (Sum a b) = f (Sum (eMap f a) (eMap f b)) > eMap f (Difference a b) = f (Difference (eMap f a) (eMap f b)) > eMap f (Product a b) = f (Product (eMap f a) (eMap f b)) > eMap f (Quotient a b) = f (Quotient (eMap f a) (eMap f b)) > eMap f (Var v) = f (Var v) > eMap f (Lit i) = f (Lit i) Now we can easily apply the identity law recursively like: > deepIdentity :: Expr -> Expr > deepIdentity = eMap identity *Main> ppExpr (deepIdentity (expr "0 + (0 + 0) + (0 + 0)")) 0 Sweet! But, having to write eMap out by hand like that somehow feels wrong -- as if I am missing some additional abstraction. In some respects eMap is like a Functor, but not quite. I expect there is a way to implement eMap using Data.Generics, which is perhaps better, but I still feel like that is missing something? Anyway, I just thought I would ask in case someone recognized this pattern and could point me in the right direction. I have attached a working example program you can play with. I would also be interested in alternative approaches besides the ones I outlined. thanks! j. >{-# LANGUAGE DeriveDataTypeable #-} > > import Control.Applicative (Applicative((<*>), pure), (*>), (<*)) > import Control.Monad (ap) > import Data.Generics (Typeable, Data) > import Data.List (isSuffixOf) > import Text.ParserCombinators.Parsec ((<|>)) > import qualified Text.ParserCombinators.Parsec as P > import qualified Text.ParserCombinators.Parsec.Expr as P > import Text.PrettyPrint.HughesPJ ((<+>)) > import qualified Text.PrettyPrint.HughesPJ as H > import Prelude hiding (sum, product) > > data Expr > = Quotient Expr Expr > | Product Expr Expr > | Sum Expr Expr > | Difference Expr Expr > | Lit Double > | Var Char > deriving (Eq, Ord, Data, Typeable, Read, Show) > > instance Applicative (P.GenParser token state) where > pure = return > (<*>) = ap > > parseExpr :: P.GenParser Char st Expr > parseExpr = P.buildExpressionParser optable (lit <|> var <|> parenExpr) > where > parenExpr = > (P.char '(' >> P.skipMany P.space) *> parseExpr <* (P.char ')' >> P.skipMany P.space) > optable = > [ [ P.Infix (P.char '/' >> P.skipMany P.space >> return Quotient) P.AssocLeft ] > , [ P.Infix (P.char '*' >> P.skipMany P.space >> return Product) P.AssocRight ] > , [ P.Infix (P.char '+' >> P.skipMany P.space >> return Sum) P.AssocRight ] > , [ P.Infix (P.char '-' >> P.skipMany P.space >> return Difference) P.AssocLeft ] > ] > lit = > do d <- P.try (P.many1 $ P.oneOf ('-' : '.' : ['0'..'9'])) > P.skipMany P.space > return (Lit (read d)) > var = > do sign <- (P.char '-' >> return (\x -> (Product (Lit (-1)) x))) <|> (return id) > v <- (P.upper <|> P.lower) > P.skipMany P.space > return (sign (Var v)) > > expr :: String -> Expr > expr str = either (error .show) id (P.parse parseExpr str str) > > ppExpr :: Expr -> H.Doc > ppExpr (Lit i) = H.text (let f s = if isSuffixOf ".0" s then init(init s) else s in f $ show i) > ppExpr (Var v) = H.char v > ppExpr (Quotient x y) = H.parens (ppExpr x <+> H.char '/' <+> ppExpr y) > ppExpr (Product x y) = H.parens (ppExpr x <+> H.char '*' <+> ppExpr y) > ppExpr (Sum x y) = H.parens (ppExpr x <+> H.char '+' <+> ppExpr y) > ppExpr (Difference x y) = H.parens (ppExpr x <+> H.char '-' <+> ppExpr y) > -- |Deep map of an expression. > eMap :: (Expr -> Expr) -> Expr -> Expr > eMap f (Sum a b) = f (Sum (eMap f a) (eMap f b)) > eMap f (Difference a b) = f (Difference (eMap f a) (eMap f b)) > eMap f (Product a b) = f (Product (eMap f a) (eMap f b)) > eMap f (Quotient a b) = f (Quotient (eMap f a) (eMap f b)) > eMap f (Var v) = f (Var v) > eMap f (Lit i) = f (Lit i) > identity (Sum (Lit 0) a) = a > identity (Sum a (Lit 0)) = a > identity (Difference a (Lit 0)) = a > identity (Product a (Lit 1)) = a > identity (Product (Lit 1) a) = a > identity (Quotient a (Lit 1)) = a > identity a = a > deepIdentity :: Expr -> Expr > deepIdentity = eMap identity > test :: IO () > test = > do print (ppExpr (deepIdentity (expr "1 + 2"))) > print (ppExpr (deepIdentity (expr "0 + (0 + 0) + (0 + 0)")))

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is 256M RAM insufficient for a 20 million element Int/Int map?
by Thomas Hartman 20 Oct '08

20 Oct '08

{-# LANGUAGE BangPatterns #-} import qualified Data.Map as M import Debug.Trace {- I'm trying to run a HAppS web site with a large amount of data: stress testing happstutorial.com. Well, 20 million records doesn't sound that large by today's standards, but anyway that's my goal for now. I have a standard Data.Map.Map as the base structure for one of my macid data tables (jobs), but I noticed something that is probably causing problems for me. Even a simple 20 million record with int/int key values causes an out of memory error for me in ghci, on a computer with 256M of ram. I'm wondering if there is a data structure that might be more suitable for large recordsets. Or do you just have to use a database, or some sort of file-based serialization, once your records are in the millions? Or is this some weird subtlety of lazy evalution, or some other haskell gotcha? -} size = 2 * 10^7 -- out of memory error t = (M.! size) . myFromList . map (\i->(i,i)) $ [1..size] -- Lists are no problem {- *Main> :! time ghc -e tL testMap.hs (20000000,20000000) 3.38user 0.09system 0:03.53elapsed 98%CPU (0avgtext+0avgdata 0maxresident)k -} tL = (!! (size-1)) . map (\i->(i,i)) $ [1..size] t2 = (M.fromList . map (\i->(i,i)) $ [1..10] ) M.\\ (M.fromList . map (\i->(i,i)) $ [6..15]) -- does this evaluate all of list l, or just whnf? myFromList (!l) = M.fromList l

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Re: [Haskell-cafe] is 256M RAM insufficient for a 20 millionelement Int/Int map?
by Max Bolingbroke 20 Oct '08

20 Oct '08

2008/10/20 Don Stewart <dons(a)galois.com>: > claus.reinke: >> Ideally, I'd just like to indicate the strictness in the types (hint to ghc >> hackers: 'Data.Map.Map Int !Int' and '[!a]' would really be useful!-), > In general, being able to specialise polymorphic structures so they look like unpacked > monomorphic ones would be awesome. > > (!Int, !Bool) -> (,) {-# UNPACK #-}!Int {-# UNPACK #-}!Bool I spent some time thinking about how one might actually go about implementing this in GHC today, and came to the conclusion that it interacts far too badly with separate compilation. In an ideal world, you know which specialisations to generate for the data structure when compiling it in the first place. You would then of course generate the appropriate specialisations for all subsequent polymorphic function definitions that use the speciliased type ((,), IntMap or whatever), so you don't lose the ability to apply your unpacked version to a function of type like (a, b) -> a - see http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.55.8984 that Claus pointed to. But we don't have that information yet at the point where we compile a data definition... The CLR has a similar problem but gets away with it because it has a JIT compiler that can see the original definitions of classes / methods and instantiate them at the necessary types at runtime (see http://research.microsoft.com/~akenn/generics/space2004generics.pdf) One possible approach for GHC would be to generate all possible specializations for a datatype + functions when compiling a module. This sounds bad, but actually you only need to cater for at most three unboxed field sizes: 1) 32 bit (Int#, Word#, Float#, Addr#) 2) 64 bit (Int64#, Word64#) 3) Usually 64 bit (Double#) Of course, if you have a type like (,,,) with 4 type arguments you still have to potentially generate 3^4 specialisations (and corresponding functions!) so this /can/ get bad quickly :-). This is also sort of a hack, in that it crucially relies on the fact that unboxed tuples don't really make sense as type arguments yet. This is because types like (# Int, Bool #) -> Int are rejected by the compiler - unboxed tuples can only occur on the right of function arrows. However, this is just a technical limitation, and were it to be lifted it might make sense to be able to instantiate data types at unboxed tuple types, blowing this scheme out of the water. You could also export the entire definition of functions+data structures you might need to specialise across module boundaries, and generate specialisations where they are needed, but this can lead to redundant code generation with diamond dependencies (see the Syme/Kennedy paper - though I don't think their problem with redundant type descriptors applies to Haskell, making it easier to apply) and would bloat .hi files. This might still be the best way to go about it, should someone choose to implement it,. A further alternative would be to just compile every function once, but pass something like a dictionary to every function to tell it how to handle its own arguments (how much stuff to pop off the stack etc). Clean ,but the huge runtime overhead of this approach kind of defeats the point of using unboxed types in the first place. A final alternative would be to somehow recompile a module with the desired instantiation if it turned out not to contain it. But this could potentially lead to greatly increased compile times... So, I can't really see a clean way to go about this without going the whole hog and turning GHC into a whole-program compiler :-) Cheers, Max

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Questions for Free!
by Creighton Hogg 20 Oct '08

20 Oct '08

Hello Haskellers, So I have a bit of a follow up question after reading Theorems For Free! this weekend. There's a throw away comment near the beginning about how you can recast the results into category theoretic form, but using lax natural transformations. Now I'm assuming this means a natural transformation but where the "naturality" square holds only up to isomorphism instead of equality, but is that correct? Also, why would you need such a condition? Cheers, Creighton

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Error building GHC 6.8.3: "version of ../../compiler/stage1/ghc-inplace could not be determined"
by Devin Mullins 20 Oct '08

20 Oct '08

Hi, I'm trying to build 6.8.3 on Linux PowerPC, based on an old binary of 6.4 (latest build for this arch that I found). stage1 seems to have built, but from there, building libraries almost immediately fails: > make -C libraries all > make[1]: Entering directory `/home/twifkak/arch/ghc/src/ghc-6.8.3/libraries' > rm -f -f stamp/configure.library.*.base base/unbuildable > ( cd base && setup/Setup configure \ > --enable-library-profiling --enable-split-objs \ > --prefix=/NONEXISTANT \ > --bindir=/NONEXISTANT \ > --libdir=/NONEXISTANT \ > --libsubdir='$pkgid' \ > --libexecdir=/NONEXISTANT \ > --datadir=/NONEXISTANT \ > --docdir=/NONEXISTANT \ > --htmldir=/NONEXISTANT \ > --interfacedir=/NONEXISTANT \ > --with-compiler=../../compiler/stage1/ghc-inplace \ > --with-hc-pkg=../../utils/ghc-pkg/ghc-pkg-inplace \ > --with-hsc2hs=../../utils/hsc2hs/hsc2hs-inplace \ > --with-ld=/usr/bin/ld \ > --haddock-options="--use-contents=../index.html \ > --use-index=../doc-index.html" \ > --configure-option='--prefix=/usr' --configure-option='CFLAGS=-mtune=powerpc -O2 -pipe -mpowerpc-gfxopt' \ > --configure-option=--with-cc=gcc ) \ > && touch stamp/configure.library.build-profiling-splitting.base || touch base/unbuildable > Configuring base-3.0.2.0... > Setup: ghc version >=6.2 is required but the version of ../../compiler/stage1/ghc-inplace could not be determined. > if ifBuildable/ifBuildable base; then \ > cd base && \ > cmp -s ../Makefile.local Makefile.local || cp ../Makefile.local .; \ > mv GNUmakefile GNUmakefile.tmp; \ > setup/Setup makefile -f GNUmakefile; \ > cmp -s GNUmakefile GNUmakefile.tmp && mv GNUmakefile.tmp GNUmakefile; \ > make -wr && \ > setup/Setup register --inplace; \ > fi > mv: cannot stat `GNUmakefile': No such file or directory > Setup: error reading dist/setup-config; run "setup configure" command? > > make[2]: Entering directory `/home/twifkak/arch/ghc/src/ghc-6.8.3/libraries/base' > make[2]: *** No targets specified and no makefile found. Stop. > make[2]: Leaving directory `/home/twifkak/arch/ghc/src/ghc-6.8.3/libraries/base' > make[1]: *** [make.library.base] Error 2 > make[1]: Leaving directory `/home/twifkak/arch/ghc/src/ghc-6.8.3/libraries' > make: *** [stage1] Error 2 (This particular transcript is from an unclean build, but the same error occurred on a freshly untarred ghc.) The subsequent errors seems to stem from the root one of being unable to configure: > [twifkak@ponyride base]$ setup/Setup configure -v3 > Configuring base-3.0.2.0... > Creating dist (and its parents) > /home/twifkak/usr/bin/ghc --numeric-version > Warning: cannot determine version of /home/twifkak/usr/bin/ghc : > "" > Setup: ghc version >=6.2 is required but the version of /home/twifkak/usr/bin/ghc could not be determined. > [twifkak@ponyride base]$ ghc --numeric-version > 6.4 > [twifkak@ponyride base]$ setup/Setup configure --with-compiler=../../compiler/stage1/ghc-inplace -v3 > Configuring base-3.0.2.0... > Creating dist (and its parents) > ../../compiler/stage1/ghc-inplace --numeric-version > Warning: cannot determine version of ../../compiler/stage1/ghc-inplace : > "" > Setup: ghc version >=6.2 is required but the version of ../../compiler/stage1/ghc-inplace could not be determined. > [twifkak@ponyride base]$ ../../compiler/stage1/ghc-inplace --numeric-version > 6.8.3 What's going wrong? How do I fix it? Is there a better mailing list to ask? Thanks, Devin

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Glut using freeglut and non starndard header / lib location?
by Marc Weber 20 Oct '08

20 Oct '08

Which is the way to install the glut library with non standard header / lib location? I've tried setting CFLAGS before running ./configure ./setup configure and adding the include directory this way include-dirs: include, /nix/store/rz4nfm5qcrjrk0jsr1lxnjwamgxmgip8-freeglut-2.4.0/include All results in checking for GL/glut.h... (cached) no checking GLUT/glut.h usability... no checking GLUT/glut.h presence... no checking for GLUT/glut.h... no configure: error: no GLUT header found, so this package cannot be built The configure script is meant to be run by cabal only? Marc

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Re: [Haskell] Probably a trivial thing for people knowing Haskell
by Paul Johnson 20 Oct '08

20 Oct '08

Friedrich wrote: > Paul Johnson <paul(a)cogito.org.uk> writes: > >> [...] Because file reading is lazy, >> each line is only read when it is to be processed, and then gets >> reaped by the garbage collector. So it all runs in constant memory. >> > Would you mind to elaborate a bit about it. What's so terrible to open > one file after the other, reading it line by line and close the file > thereafter. > Its not wrong, its just more work. Also from a structural point of view its better to separate the code that reads the files from the code that processes the text. The conventional way forces you to mix them. >> (By the way, putting in the top level type declarations helps a lot >> when you make a mistake.) >> > Well I have my problems with that. Probably it comes from using > Languages like Ruby and my special dislike of "typing things" comes > especially from Java, C++ (well C is not "innocent" in that regard > also. > > OK, its a matter of personal preference (although it really does help anyone else reading your code). However I find that if I leave out the top level definitions then type error messages at compile time are much harder to figure out, especially in a big program. So I find that the extra typing pays in the long run. :-/ Paul.

1 0

package question/problem
by Galchin, Vasili 20 Oct '08

20 Oct '08

Hello, I am trying to "cabal install" HSQL. I am using ghc 6.8.2. I get the following error about a non-visible/hidden package (old-time-1.0.0.0): vigalchin@ubuntu:~$ cabal install hsql Resolving dependencies... 'hsql-1.7' is cached. [1 of 1] Compiling Main ( Setup.lhs, dist/setup/Main.o ) Linking dist/setup/setup ... Configuring hsql-1.7... Warning: No 'build-type' specified. If you do not need a custom Setup.hs or ./configure script then use 'build-type: Simple'. Preprocessing library hsql-1.7... Building hsql-1.7... Database/HSQL.hsc:66:7: Could not find module `System.Time': it is a member of package old-time-1.0.0.0, which is hidden cabal: Error: some packages failed to install: hsql-1.7 failed during the building phase. The exception was: exit: ExitFailure 1 vigalchin@ubuntu:~$ I don't see (old-time-1.0.0.0) with parens around it so I am confused: vigalchin@ubuntu:~$ ghc-pkg list /usr/local/lib/ghc-6.8.2/package.conf: Cabal-1.2.3.0, GLUT-2.1.1.1, HUnit-1.2.0.0, OpenGL-2.2.1.1, QuickCheck-1.1.0.0, array-0.1.0.0, base-3.0.1.0, bytestring-0.9.0.1, cgi-3001.1.5.1, containers-0.1.0.1, directory-1.0.0.0, fgl-5.4.1.1, filepath-1.1.0.0, (ghc-6.8.2), haskell-src-1.0.1.1, haskell98-1.0.1.0, hpc-0.5.0.0, html-1.0.1.1, mtl-1.1.0.0, network-2.1.0.0, old-locale-1.0.0.0, old-time-1.0.0.0, packedstring-0.1.0.0, parallel-1.0.0.0, parsec-2.1.0.0, pretty-1.0.0.0, process-1.0.0.0, random-1.0.0.0, readline-1.0.1.0, regex-base-0.72.0.1, regex-compat-0.71.0.1, regex-posix-0.72.0.2, rts-1.0, stm-2.1.1.0, template-haskell-2.2.0.0, time-1.1.2.0, unix-2.3.0.0, xhtml-3000.0.2.1 /home/vigalchin/.ghc/i386-linux-6.8.2/package.conf: Cabal-1.4.0.1, GLFW-0.3, HDBC-1.1.5, HTTP-3001.0.4, MonadRandom-0.1.1, Stream-0.2.6, Takusen-0.8.3, X11-1.4.2, arrows-0.4, binary-0.4.2, category-extras-0.53.5, chp-1.1.0, dlist-0.4.1, event-list-0.0.7, ipc-0.0.3, midi-0.0.6, mtl-1.1.0.1, network-bytestring-0.1.1.2, non-negative-0.0.3, posix-realtime-0.0.0.1, posix-realtime-0.0.0.2, probability-0.2.1, quantum-arrow-0.0.4, unix-2.4.0.0, zlib-0.4.0.4 ?? What is the history of old-time package? Regards, Vasili

6 7

Detecting unused read handles? (was: File handles and pipes)
by Stephen Hicks 19 Oct '08

19 Oct '08

On Sun, Oct 19, 2008 at 1:44 AM, Brandon S. Allbery KF8NH <allbery(a)ece.cmu.edu> wrote: > On 2008 Oct 19, at 1:37, Stephen Hicks wrote: >> >> I'm trying to understand how to get pipes working in Haskell, in >> particular with the revamped System.Process (though I've tried similar >> experiments with System.Posix.IO and Control.Concurrent). >> Specifically I'm trying to concatenate the output of two system calls >> into the input of a third. The following code does not get the job >> done: > > Pipes are perhaps a bit misnamed: if you want to combine the output of two > pipes and funnel it into a third you can't simply "plumb them together", you > need to provide code which reads from the output pipes and writes into the > input pipe. If you don't care about order, forkIO a thread for each output > pipe which reads from the output pipe it's passed and writes to the input > pipe. If order is significant, use mapM/forM to run the output-to-input > code on each handle in turn. Thanks a lot - that seems to work very well, and even scales to large amounts of data nicely (and quickly, with Lazy ByteStrings). I've got one more question now. Suppose I want to do the same thing on the other side, with two processes *receiving* the data. Is there a way to tell whether the first process wants input, and if not, wait for the second process to do anything? That is, suppose I have something like > do (Just inh1, _, _, p1) <- createProcess (shell "echo 1") { std_in = CreatePipe } > -- wait for p1, possibly feeding it some input? > (Just inh2, _, _, p2) <- createProcess (shell "cat") { std_in = CreatePipe } Is there a way to figure out that the "echo 1" process never wanted any input, and therefore not give it any? I looked through all of System.IO and everything seemed to indicate that inh1 was open, even after the process ended. The only indication otherwise was that "hflush inh1" failed with "resource vanished". I guess what I'm asking is I want to "wait until the process p1 is waiting for input and/or terminates", and if it's the latter, move on to the next process in line, before actually doing any hPutStr into the read handles. Is that possible? Thanks, steve

2 1

external sort on hackage Re: [Haskell-cafe] External Sort and unsafeInterleaveIO
by Thomas Hartman 19 Oct '08

19 Oct '08

External sort is on hackage at http://hackage.haskell.org/cgi-bin/hackage-scripts/package/external-sort Ben, I forgot to correct your name, but I will fix it soon. Thomas. 2008/10/11 Ben <midfield(a)gmail.com>: > Fine with me, except my last name is "Lee" not "Midfield." Thanks for > doing this. > > Ben "Midfield" Lee > > On Sat, Oct 11, 2008 at 7:52 AM, Thomas Hartman <tphyahoo(a)gmail.com> wrote: >> I kinda-sorta half-cabalized it at >> >> darcs get http://darcsdump.dreamhosters.com/external-sort (untested >> via cabal install but mostly done) >> >> As soon as my project gets approved I'll put it up on hackage. >> >> If Ben wants it under his account at hackage of course I'll defer to him. >> >> Thomas. >> >> 2007/7/18 Donald Bruce Stewart <dons(a)cse.unsw.edu.au>: >>> midfield: >>>> hi -- >>>> >>>> thanks for the useful comments! i will definitely go through them >>>> carefully. unfortunately for this code (but fortunately for me) i >>>> defend my dissertation on monday so i'm a little distracted right >>>> now..... >>>> >>>> i'm more than happy to donate this code or whatever improvements >>>> happen to it. actually, hGetContentsWithCursor seems like a candidate >>>> for inclusion with Data.ByteStrings or Data.Binary or something -- it >>>> seems like it might find other uses. (i think you liked that bit of >>>> code because i ripped it off of you guys! it's very short hamming >>> >>> Can't fault that style ;) >>> >>>> distance from the original.) anyhow, all that will have to wait a >>>> couple weeks or so. also i've never cabalized anything so i may come >>>> begging for help. >>> >>> We have a tutorial for that, luckily: >>> >>> http://haskell.org/haskellwiki/How_to_write_a_Haskell_program >>> >>> And a tool to automate it, mkcabal, so should be fairly straightforward. >>> >>>> >>>> at some point i thought i saw how to do recursive external sort, to >>>> keep memory usage truly constant, but with my current lack of sleep i >>>> have lost that illusion. i'm also curious about the performance >>>> characteristics of this vs Prelude sort vs the version using the >>>> tournament mergesort apfelmus suggested. i need to find a computer >>>> with a lot more RAM than my weakling laptop. finally, it would be >>>> good to be able to have the blocksize controlled by Kb of RAM rather >>>> than # of elements, not sure how to get that information. >>>> >>>> ultimately this was part of my project to write lucene for haskell. i >>>> think with this out of the way, plus all the Data.Binary / ByteString >>>> goodness, it shouldn't take too long. keep writing good libraries for >>>> me! >>>> >>> >>> Great. Good to see things working. >>> >>> -- Don >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe(a)haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >> >

1 0

haskell & facebook
by Jason Dusek 19 Oct '08

19 Oct '08

Has anyone taken a stab at Haskell FaceBook bindings? -- _jsn

3 2

HDBC or HSQL
by George Moschovitis 19 Oct '08

19 Oct '08

Dear devs, I am a Haskell newbie and I would like to hear your suggestions regarding a Database conectivity library: HSQL or HDBC ? which one is better / more actively supported? thanks in advance, -g. -- http://phidz.com http://blog.gmosx.com http://cull.gr http://www.joy.gr http://nitroproject.org

15 25

Re: [Haskell-cafe] File handles and pipes
by Donn Cave 19 Oct '08

19 Oct '08

Quoth "Stephen Hicks" <sdh33(a)cornell.edu>: > In general, given a handful of system calls (and/or > read/write handles), is there a way to combine them all together? Well, sure - if I understand what you mean. Not "Handles", in the sense of a Haskell library construct, but UNIX pipes and processes are reasonably simple to work with in a general purpose programming language. I'm sorry to say the following isn't real code, since GHC doesn't run on the platform I'm using to write this mail, but I hope it will serve to demonstrate the principles using bare UNIX system calls, and that it doesn't contain any serious errors. forkProcess $ do -- pipe tail (pa0, pa1) <- createPipe -- Command exec'd in this fork reads from this pipe, -- so dup 0 (input) from pipe input fd. Both ends of -- pipe will be inherited by child forks. dupTo pa0 0 forkProcess $ do -- first pipe head -- Command exec'd in this fork writes to parent's pipe. dupTo pa1 1 -- Close parent's pipe so fds won't be inherited by -- next fork. closeFd pa0 closeFd pa1 forkProcess $ execFile "/bin/df" ... -- second pipe head execFile "/bin/df" ... -- Close own pipe write end, so child process exit(s) will cause EOF closeFd pa1 execFile "/usr/bin/sort" ... Key points: Input, output and error are file descriptors 0, 1 and 2, by definition (pronounced "unit 0", etc.) dupTo (UNIX system call dup2()) duplexes an I/O stream, so "dupTo p0 0" sets up a pipe for a standard UNIX command that reads from unit 0. Reads from the pipe's read fd will either return data or block, until exit of the *last* process with the pipe's write end open. Hence the importance of closing the write end of your own pipe, and not letting pipe fds "leak" into child processes. Donn Cave, donn(a)avvanta.com

1 0

Template Haskell and unsafePerformIO
by Achim Schneider 19 Oct '08

19 Oct '08

Shouldn't be there some kind of way to run IO code once at the beginning of template processing? Something like a pair of templateInit :: IO a and templateData :: a where the a of both functions is the same and the latter is automagically generated by TH. Right now, I have to either use unsafePerformIO or runIO and IORef's to load a file only once. Both solutions aren't necessarily pretty. -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.

1 0

Arch Haskell News: Oct 18 2008
by Don Stewart 19 Oct '08

19 Oct '08

= News about Haskell on Arch Linux = Arch Linux now has 639 Haskell packages in AUR. That’s an increase of 15 new Haskell packages in the last 7 days. Growth appears to be holding steady at just over 2 new packages a day on Hackage this month. Noteworthy * haskell-gnuplot-0.2: “2D and 3D plots using gnuplot” * alex-2.3: “Alex is a tool for generating lexical analysers in Haskell” * happy-1.18.1: “Happy is a parser generator for Haskell” * haskell-tfp-0.1: “Type-level programming library using type families” Full details on the site. http://archhaskell.wordpress.com/2008/10/18/arch-haskell-news-oct-18-2008/

1 0

Linux binary dist problems
by Leif Warner 19 Oct '08

19 Oct '08

I had the same problem with the 6.8.3 install on Dreamhost, "unable to determine current path" or something. Ended up using 6.8.2 install, and had to crack open the rpm of the old readline version they linked, put it in $HOME/lib, and set $LD_RUN_PATH to point to that. http://www.haskell.org/ghc/dist/6.8.2/ghc-6.8.2-i386-unknown-linux.tar.bz2 And there is actually an Eclipse plugin for Haskell: http://eclipsefp.sourceforge.net/ Not that I break it out for work. -Leif Warner

2 1

2008-10-13 Hackage status with GHC 6.10 release candidate
by Don Stewart 19 Oct '08

19 Oct '08

Hey all. The GHC 6.10 RCs are out, and we're preparing the release of GHC proper. To help manage the transistion to GHC 6.10 it is now possible to actually build all the 3rd party Haskell packages, and publish their results wrt. the release candidate. For the first time ever, we're able to have all the 3rd party code tested and ready to go *prior* to the release of the new compiler and base libraries. Using GHC 6.10 RC from today, Cabal 1.6 and cabal-install 1.16, of 682 libraries and apps tried in total, 1 UnpackFailed 2 DownloadFailed 2 InstallFailed 16 ConfigureFailed 68 DependencyFailed 122 BuildFailed 469 InstallOk Since yesterday, * dependency failures have reduced by 5 * build failures have reduced by 10 * total successfully installed packages are **up by 14** These new packages now all build ok with the GHC 6.10 release candidate, Graphalyze-0.4 alsa-midi calc glome-hs harpy heap hmp3 ircbouncer mohws panda pandoc roguestar-engine type-level typeof unicode-prelude urlcheck Good work everyone! Some packages are still not ready though, if you maintain one of the following packages, and are able to fix it before GHC 6.10 is released, your users will be happy. The most common issues for these differences are, * Changes to Arrow class definition * Changes to types of Map and Set functions * Cabal changes * Changes to ghc-api * Changes to when 'forall' is parsed (add Rank2Types) * GHC.Prim was moved, * Changes to -fvia-C and headers * GADT changes, * pragma warnings tightened * Integer constructors have moved * New warnings and used -Werror The following packages are still producing different results than with ghc 6.8.2. Package maintainers are invited to look at them. I've marked the easy ones. ArrayRef-0.1.2 Easy: duplicate type signatures CLASE-2008.9.23.2 Hard: GADT changes EdisonCore-1.2.1.2 Easy: Monadic Map HPDF-1.4 Easy: Monadic Map HaLeX-1.1 Easy: Name clash with permutations Hashell-0.15 ? : GHC API Hipmunk-0.2 Easy: Monadic Map MemoTrie-0.0 Easy: 'forall' parsing NewBinary-0.1.1 Easy: Integer constructors moved PArrows-0.1 Easy: GHC.Prim moved (use GHC.Exts) TypeCompose-0.5 Easy: Arrow class changes YamlReference-0.9.2 Hard. Unknown Yampa-0.9.2.2 Arrow class changes arrows-0.4 Arrow class changes bytestring-show-0.2 Easy: Integer constructors moved cabal-setup-1.2.1 Hard: Cabal changes chp-1.1.0 Easy: Arrow class changes cmath-0.3 Hard: -fvia-C changes fixpoint-0.1 Easy: Uses -Werror unnecessarily hasim-0.1 Hard: GADT changes hask-home-2007.12.6 Easy: Cabal changes hetris-0.2 Easy: header macros/-fvia-C hexpat-0.2 Easy: 'forall' parsing in RULES hinstaller-2008.2.16 Easy: Cabal changes hint-0.2.4.1 Hard? GHC API hslackbuilder-0.0.1 Easy: Cabal changes hxt-8.1.0 Easy: Arrow class change iException-0.0.1 ? Exception changes libGenI-0.16.1 Easy: Monadic Map changes mage-1.1.0 Hard: -fvia-C changes numeric-prelude-0.0.4 Easy: Lanuage pragma plugins-1.3 Easy: Cabal changes quantum-arrow-0.0.4 Easy: Arrow class changes regex-tdfa-0.94 Easy: Map changes streamproc-1.1 Easy: Arrow class changes stringtable-atom-0.0.4 Easy: Monadic Map typalyze-0.1.1 ? GHC API xmonad-utils-0.1 ? GHC API yhccore-0.9 ? Pragma parsing Build reports for everything, produced today, are here, http://galois.com/~dons/tmp/build-logs-2008-10-13/ How to address these, as library maintainers, is addressed here, http://haskell.org/haskellwiki/Upgrading_packages If you'd like to try your own build of all of hackage, grab a package list (such as this one), http://www.galois.com/~dons/tmp/pkgs-6.10 Install a GHC 6.10 release candidate, upgrade to Cabal 1.6 (on hackage), and cabal-install 0.6 (on hackage), and then simply, cabal install -v -O0 $(cat pkgs-6.10) --build-reports This will construct a clever plan to install all the packages in the right order, and write logs to ~/.cabal/logs and a full structured build report into ~/.cabal/packages/hackage.*/build-report.log I'll start mailing maintainers personally tomorrow. -- Don

4 5

Re: [Haskell-cafe] ANNOUNCE: Glob 0.1, globbing library
by Krzysztof Skrzętnicki 19 Oct '08

19 Oct '08

On Sat, Oct 18, 2008 at 19:28, Matti Niemenmaa <matti.niemenmaa%2Bnews(a)iki.fi> wrote: > Gah, I fail at posting to mailing lists. For posterity, the message I sent to > Krzysztof: > > Krzysztof Skrzętnicki wrote: >> On Fri, Oct 17, 2008 at 22:02, Matti Niemenmaa <matti.niemenmaa%2Bnews(a)iki.fi> >> wrote: >>> Web page at: http://iki.fi/matti.niemenmaa/glob/index.html Hackage: >>> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Glob >> >> I tried out your package, but it doesn't seem to work correctly on Windows. I >> checked the code and it has directory separator hard coded, which seem to be >> the source of problems. > > Interesting, given that I've only tested it on Windows. ;-) Can you give an > example which doesn't work? > Ouch... I feel like I deserve an entry on http://failblog.org/ Somehow I assumed that globDir has type [Pattern] -> FilePath -> IO [FilePath] where in reality it has type [Pattern] -> FilePath -> IO ([[FilePath]], [FilePath]) When I saw lots of files that didn't match my query I thought there is a bug... I'll certainly doublecheck any bug reports before submitting. Sorry for the noise. All best Christopher Skrzętnicki

1 0

ANNOUNCE: Glob 0.1, globbing library
by Matti Niemenmaa 19 Oct '08

19 Oct '08

Greetings to all, I hereby announce the release of Glob 0.1, a small library for glob-matching purposes based on a subset of zsh's syntax. Web page at: http://iki.fi/matti.niemenmaa/glob/index.html Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Glob Simple example: match (compile "foo*baz") "foobarbaz" == True. It can also group the contents of a directory given a list of patterns to match: globDir [compile "foo*baz"] "<a directory containing foobarbaz and joe>" gives (["dir/foobarbaz"],["dir/joe"]). Comments, complaints, feature requests, bug reports are all welcome. It should work on both GHC 6.8 and 6.10, but I've only tested the latter.

2 1

Haskell Weekly News: Issue 89 - October 18, 2008
by Brent Yorgey 18 Oct '08

18 Oct '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20081018 Issue 89 - October 18, 2008 --------------------------------------------------------------------------- Welcome to issue 89 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements New Haskell tutorial. Miran Lipovaca (BONUS) has written a new and most excellent Haskell tutorial, [2]"Learn You a Haskell For Great Good!". Glob 0.1, globbing library. Matti Niemenmaa [3]announced the release of [4]Glob 0.1, a [5]small library for glob-matching purposes based on a subset of zsh's syntax. hledger 0.1, command-line accounting tool. Simon Michael [6]announced the [7]first release of [8]hledger, a command-line accounting tool similar to John Wiegley's c++ ledger. hledger generates simple ledger-compatible transaction and account balance reports from a plain text ledger file. [ANN] Haskell Cheatsheet v1.0. Justin Bailey [9]announced a [10]"cheat sheet" for Haskell, a PDF that tries to summarize Haskell 98's syntax, keywords and other language elements. Salsa: A .NET Bridge for Haskell. Andrew Appleyard [11]announced the [12]first release of [13]Salsa, an experimental Haskell library that allows Haskell programs to access .NET libraries. Salsa operates by loading the .NET runtime into your Haskell process and using the FFI (and run-time code generation) to marshall calls between the .NET and Haskell runtimes. It includes a code generator and a type-level library (which uses type families) to provide type-safe access to .NET libraries in Haskell with C#-style method overload resolution and implicit conversions. maccatcher-1.0.0. Jason Dusek [14]announced the [15]maccatcher package, which obtains a MAC address on *NIX and Windows. Call for Contributions - Haskell Communities and Activities Report, November 2008 edition. Janis Voigtlaender sent out [16]call for contributions to the 15th edition of the [17]Haskell Communities & Activities Report. The submission deadline is 31 October 2008. If you are working on any project that is in some way related to Haskell, please write a short entry and submit it. Even if the project is very small or unfinished or you think it is not important enough -- please reconsider and submit an entry anyway! Data.IVar 0.1. Luke Palmer [18]announced the release of the [19]Data.IVar module, which provides write-once variables that can be blocked on in parallel. Unlike other implementations, Data.IVar does not use thread racing, since empirical tests have shown that the GHC scheduler is not quite good enough to handle thread-racing efficiently. A wiki page for managing the 6.10 handover. Don Stewart [20]announced a [21]wiki page to help with the transition to GHC 6.10. It collects the 7 or so known issues that break code with GHC 6.10. Please feel free to clean up, and especially add techniques for handling each change. GHC 6.10.1 RC 1. Ian Lynagh [22]announced [23]GHC 6.10.0.20081007, the first release candidate for GHC 6.10.1. There is also a [24]status page for GHC 6.10.1. Graphalyze-0.4 and SourceGraph-0.2. Ivan Lazar Miljenovic [25]announced the release of version 0.4 of the [26]Graphalyze library and version 0.2 of the [27]SourceGraph programme. SourceGraph is a programme designed to help you analyse the static complexity of your Haskell code when represented as a graph. These releases fix the bugs reported by Gwern Branwen, Magnus Therning, and Christopher Hinson. ListZipper-1.1.0.0. Ryan Ingram [28]announced the release of a simple list zipper library to Hackage, [29]ListZipper-1.1.0.0. darcs 2.1.0. Eric Kow [30]announced the release of [31]darcs 2.1.0. This version provides over 20 bug fixes and 7 new features since darcs 2.0.2. Most notably, the darcs-2 repository format is now the default, there is better HTTP support, and a longstanding 'pending patch' regression has been fixed. Yi 0.5.0.1. Jean-Phillipe Bernardy [32]announced the [33]0.5 release of Yi, a text editor written and extensible in Haskell. The long-term goal of the Yi project is to provide the editor of choice for Haskell programmers. Discussion OT: Haskell desktop wallpaper?. Magnus Therning [34]asked for Haskell-themed desktop wallpapers, and the community responded with quite a few nice images. Abusing quickcheck to check existential properties. Norman Ramsey [35]asked about using QuickCheck to check existential properties; suggestions involved SmallCheck and skolemization. Repair to floating point enumerations?. Malcolm Wallace began a [36]discussion on the merits of changing the (admittedly wonky) H98 [37]semantics for the Enum instances of Float and Double in Haskell Prime. A general question about the use of classes in defining interfaces. S. Doaitse Swierstra [38]asked about the feasibility of including top-level functions implemented using Applicative combinators as class methods with default implementations, to allow for the possibility of giving them more efficient implementations in specific instances. Proposal #2659: Add sortOn and friends to Data.List. Twan van Laarhoven [39]proposed adding sortOn (:: Ord b => (a -> b) -> [40]-> [a) and related functions to Data.List. Blog noise [41]Haskell news from the [42]blogosphere. * Andy Gill: [43]Pretty Printing Code with Markup. writes about a [44]new version of the HughesPJ pretty printing library which allows for pretty-printing with markup. * "FP Lunch": [45]Is purity inefficient?. Are idiomatic pure functional programs less efficient than idiomatic impure ones? * Eric Kow (kowey): [46]darcs weekly news #8. * Conal Elliott: [47]Composing memo tries. * Conal Elliott: [48]Elegant memoization with functional memo tries. * >>> Paolo Capriotti: [49]Monads for Markov chains. * Real-World Haskell: [50]Production status update: we're in QC1. * Joachim Breitner: [51]Infinite loops in Haskell. * Luke Palmer: [52]FRP Rant. * Luke Palmer: [53]data-memocombinators. * Bryan O'Sullivan: [54]Using Bloom filters for large scale gene sequence analysis in Haskell. Bryan and Ketil Malde's paper was accepted to PADL 09! * Arnar Birgisson: [55]Generating legal subsets of a dependency graph. * Creighton Hogg: [56]A silly example and a brief history. * >>> Robert Ottaway: [57]Sorting using Haskell. * Dan Piponi (sigfpe): [58]Untangling with Continued Fractions: part 5. * Holumbus: [59]Source Links Are Back!. * London Haskell Users Group: [60]Getting things going again. * >>> Justin Bailey: [61]The Haskell Cheatsheet. * >>> Nathan Sanders: [62]Type-directed programming. * >>> Micah Cowan: [63]Adventures in Haskell, Part 2: Kewlness. * Manuel M T Chakravarty: [64]GpuGen: Bringing the Power of GPUs to Haskell.. * >>> Binu Raghavan: [65]Haskell.... Binu is trying to learn Haskell. * Bjoern Edstroem: [66]Let's build an MP3-decoder!. Quotes of the Week * mckinna: you don't need to produce elements of an *arbitrary* whatever-it-is when you can produce elements of the *initial* whatever-it-is * tristes_tigres: thinks that programming languages can be divided into two broad classes: functional and dysfunctional * luqui: Down with the IO bourgeoisie! Long live the purely functional proletariat * ystael: it seems like every time i switch channels over to #haskell someone is talking about launching missiles. one might be inclined to draw freudian conclusions. About the Haskell Weekly News New editions are posted to [67]the Haskell mailing list as well as to [68]the Haskell Sequence and [69]Planet Haskell. [70]RSS is also available, and headlines appear on [71]haskell.org. To help create new editions of this newsletter, please see the information on [72]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [73]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://learnyouahaskell.com/ 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46583 4. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Glob 5. http://iki.fi/matti.niemenmaa/glob/index.html 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46461 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hledger 8. http://joyful.com/Ledger#hledger 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46122 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/CheatSheet 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46076 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Salsa 13. http://haskell.org/haskellwiki/Salsa 14. http://article.gmane.org/gmane.comp.lang.haskell.cafe/46072 15. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/maccatcher 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45967 17. http://www.haskell.org/communities/ 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45953 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/data-ivar 20. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/15442 21. http://haskell.org/haskellwiki/Upgrading_packages#Typical_breakages_with_GH… 22. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/15376 23. http://www.haskell.org/ghc/dist/stable/dist/6.10.1-rc-1/rc.html 24. http://hackage.haskell.org/trac/ghc/wiki/GHC-6.10.1 25. http://article.gmane.org/gmane.comp.lang.haskell.general/16473 26. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Graphalyze 27. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SourceGraph 28. http://article.gmane.org/gmane.comp.lang.haskell.general/16468 29. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ListZipper 30. http://article.gmane.org/gmane.comp.lang.haskell.general/16465 31. http://darcs.net/darcs-2.1.0.tar.gz 32. http://www.haskell.org//pipermail/haskell/2008-October/020648.html 33. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/yi 34. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/45961 35. http://thread.gmane.org/gmane.comp.lang.haskell.general/16477 36. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2678 37. http://haskell.org/onlinereport/basic.html#sect6.3.4 38. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/10206 39. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/10184 40. file://localhost/home/brent/haskell/hwn/a] 41. http://planet.haskell.org/ 42. http://haskell.org/haskellwiki/Blog_articles 43. http://blog.unsafeperformio.com/?p=31 44. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/marked%2Dpretty 45. http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=113 46. http://koweycode.blogspot.com/2008/10/darcs-weekly-news-8.html 47. http://feeds.feedburner.com/~r/conal/~3/422189172/ 48. http://feeds.feedburner.com/~r/conal/~3/422171822/ 49. http://pcapriotti.wordpress.com/2008/10/16/monads-for-markov-chains/ 50. http://www.realworldhaskell.org/blog/2008/10/15/production-status-update-we… 51. https://www.joachim-breitner.de/blog/archives/308-Infinite-loops-in-Haskell… 52. http://luqui.org/blog/archives/2008/10/15/frp-rant/ 53. http://luqui.org/blog/archives/2008/10/14/data-memocombinators/ 54. http://www.serpentine.com/blog/2008/09/28/using-bloom-filters-for-large-sca… 55. http://www.hvergi.net/2008/10/generating-legal-subsets-of-a-dependency-grap… 56. http://abstractabsurd.blogspot.com/2008/10/silly-example-and-brief-history.… 57. http://tech-nickel.blogspot.com/2008/10/sorting-using-haskell.html 58. http://sigfpe.blogspot.com/2008/10/untangling-with-continued-fractions.html 59. http://holumbus.fh-wedel.de/blog/?p=15 60. http://www.londonhug.net/2008/10/11/getting-things-going-again/ 61. http://blog.codeslower.com/2008/10/The-Haskell-Cheatsheet 62. http://sandersn.com/blog/index.php?title=type_directed_programming 63. http://micah.cowan.name/2008/10/10/computers/software-development/adventure… 64. http://justtesting.org/post/53418059 65. http://variably-volatile.blogspot.com/2008/10/haskell.html 66. http://blog.bjrn.se/2008/10/lets-build-mp3-decoder.html 67. http://www.haskell.org/mailman/listinfo/haskell 68. http://sequence.complete.org/ 69. http://planet.haskell.org/ 70. http://sequence.complete.org/node/feed 71. http://haskell.org/ 72. http://haskell.org/haskellwiki/HWN 73. http://code.haskell.org/~byorgey/code/hwn/

1 0

Implementing pi-calculus using STM
by Edsko de Vries 18 Oct '08

18 Oct '08

Hi, (Note: assumes knowledge of pi-calculus.) I am playing with writing a simple interpreter for the pi-calculus using STM. The implementation of most of the operators of the pi- calculus is straightforward, but I am unsure on how to implement the replication operator. The interpretation of !P should be the interpretation of the infinite number of parallel processes P | P | P ... . I am implementing parallel processes using the fork operation, but spawning an infinite amount of processes -- even if the (infinite) majority of them all immediately lock -- seems like a bad idea. So I would prefer to spawn one P, and as soon as the thread that interprets P makes any progress at all, spawn another, and so on. I'm not too sure however how to achieve this. Any ideas? Edsko

2 1

mysql server on Linux
by Galchin, Vasili 18 Oct '08

18 Oct '08

Hello, I want to use the mysql server (mysqld) on Linux. What Haskell packages must I install in order to write a Haskell mysql package?? Thank you, Vasili

2 1

Fwd: [Haskell-beginners] HaXml.SAX successfully parses a malformed XML document
by David Frey 18 Oct '08

18 Oct '08

I asked this question on the haskell-beginners list, but I didn't get a response, so I am forwarding it on to the cafe list. David --- Original Message --- Date: 10/16/2008 From: "David Frey" <dpfrey(a)shaw.ca> Subject: [Haskell-beginners] HaXml.SAX successfully parses a malformed XML document It seems that saxParse from Text.XML.HaXml.SAX will successfully parse a malformed XML document. Notice that the SubElem opening and closing tag are not matched in the XML document below. --- input.xml --- <RootNode> <ElemOne> <SubElem attr="foo">element data</SubElemBroken> <NoDataElem/> <ElemOne> </RootNode> --- end input.xml --- The Haskell code below runs without error. It prints out the type of elements found during the parse. --- Haskell Code --- module Main where import qualified Text.XML.HaXml.SAX as SAX import Data.Maybe main = let inputFilename = "input.xml" in do content <- readFile inputFilename let (elements, error) = SAX.saxParse inputFilename content if isNothing error then mapM_ putStrLn (summarizeElements elements) else putStrLn $ "ERROR:" ++ (fromJust error) summarizeElements :: [SAX.SaxElement] -> [String] summarizeElements elements = map summarizeElement elements summarizeElement :: SAX.SaxElement -> String summarizeElement element = case element of (SAX.SaxDocTypeDecl d) -> "DocType" (SAX.SaxProcessingInstruction p) -> "Processing Instruction" (SAX.SaxComment s) -> "Comment" (SAX.SaxElementOpen name attrs) -> "Element Open" (SAX.SaxElementClose name) -> "Element Close" (SAX.SaxElementTag name attrs) -> "No Content Element" (SAX.SaxCharData charData) -> "Character Data" (SAX.SaxReference reference) -> "Reference" --- End Haskell Code --- The Python code below throws an exception when parsing the same input document. --- Python Code --- from xml.sax import make_parser from xml.sax.handler import ContentHandler def main(): c = ContentHandler() p = make_parser() p.setContentHandler(c) p.parse(open('input.xml')) if __name__ == '__main__': main() -- End Python Code --- Is this a bug in the HaXml SAX parser? Thanks, David _______________________________________________ Beginners mailing list Beginners(a)haskell.org http://www.haskell.org/mailman/listinfo/beginners

1 0

How to deal with pointers to pointers in the FFI
by Jefferson Heard 18 Oct '08

18 Oct '08

I have the following functions in C: OGRErr OGR_G_CreateFromWkb (unsigned char *, OGRSpatialReferenceH, OGRGeometryH *, int) OGRErr OGR_G_CreateFromWkt (char **, OGRSpatialReferenceH, OGRGeometryH *) void OGR_G_DestroyGeometry (OGRGeometryH) OGRGeometryH OGR_G_CreateGeometry (OGRwkbGeometryType) The normal sequence of calls is OGRGeometryH handle = OGR_G_CreateGeometry(SOME_TYPE); // do stuff OGR_G_DestroyGeometry(handle); OR OGR_G_CreateFromWkb(blob, ref, &handle, 0); // do stuff OGR_G_DestroyGeometry(handle); As you can see, in one case, I have to pass in a pointer to the returned handle, and not just the handle. How can I accomplish this feat using a single type? I had data OGRGeometryH type Geometry = Ptr OGRGeometryH but then can I declare that a function returns a Ptr (Geometry) ? -- I try to take things like a crow; war and chaos don't always ruin a picnic, they just mean you have to be careful what you swallow. -- Jessica Edwards

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Troubles getting isA of ArrowIf from HXT 8.10 to work as expected
by Corey O'Connor 18 Oct '08

18 Oct '08

I'm attempting to use ifA to conditionalize generated XHTML. ifA (arr test_status >>> arr (/= "Running")) (mkelem "a" [attr "href" (arr test_log_URL >>> mkText)] [txt "log"]) (mkelem "a" [attr "href" (arr test_log_URL >>> mkText)] [txt "no log"]) The arrow type at the point of the ifA is (I think) "XmlArrow a => a XmlTree TestRun" where TestRun is defined as: data TestRun = TestRun { test_log_URL :: String, test_status :: String } The issue I'm seeing is that regardless of the predicate arrow the result is always the same: The XmlTree for the True branch is always generated. In other words, I get the same behavior using this code: ifA (arr (const False)) (mkelem "a" [attr "href" (arr test_log_URL >>> mkText)] [txt "log"]) (mkelem "a" [attr "href" (arr test_log_URL >>> mkText)] [txt "no log"]) Which, I thought, the "arr (const False)" would force the ifA to always descend the False path. This is my first attempt at using HXT and Arrows (Which is otherwise going great!) so I figure I'm missing something. Any ideas? Cheers, Corey O'Connor

1 0

Temlpate Haskell: [d| ... |]
by Achim Schneider 18 Oct '08

18 Oct '08

> [d| ... |], where the "..." is a list of top-level declarations; the > quotation has type Q [Dec]. (http://www.haskell.org/ghc/docs/latest/html/users_guide/template-haskell.ht…) Can someone elaborate on what a list means here? Neither declarations = [d| foo = "bar" bar = "foo" |] nor declarations = [d| [ foo = "bar" , bar = "foo" ] |] work. I'm trying to automatically generate a bunch of functions out of an xml file. -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.

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Re: What I wish someone had told
by John Lato 18 Oct '08

18 Oct '08

Richard O'Keefe wrote: > On 17 Oct 2008, at 9:53 am, Daryoush Mehrtash wrote: > >> So does this mean that the reason for complexity of generics is the >> Java inheritance? > > No. The reason for the complexity of generics in Java is that > they weren't designed into the language in the first place. > It took several attempts and quite a lot of work to come up with > a version of generics that was 100% interoperable with earlier > JVMs *and* still worth having. > > You could have something very like Java generics but without > the strangeness if you designed it into the language from the > beginning, as Betrand Meyer did with Eiffel. Of course, what > _he_ didn't design in from the beginning was lambdas, now > present as "agents". Eiffel has its own kinds of strangeness. > Or C# generics, which are built into the IL (in .Net 2.0 and above). In many ways, C# is a very nice language, and having generics fully supported in reflection is pretty cool. I do have some words to say about various ASP.Net libraries, however...

1 0

howto mix <- within do?
by Larry Evans 18 Oct '08

18 Oct '08

The attached code produces error: <-- cut here -- runghc -dcore-lint do_with_assignment.proto.hs do_with_assignment.proto.hs:30:2: Couldn't match expected type `[]' against inferred type `IO' Expected type: [t] Inferred type: IO () In the expression: putStr "v0=" In a 'do' expression: putStr "v0=" >-- cut here-- However, similar code here: http://www.nabble.com/List-as-input-p19987726.html apparently does work. Is there some compiler option I need to use? The compiler is ghc: ghc --version The Glorious Glasgow Haskell Compilation System, version 6.8.2

4 6

Invalid declaration names in TH that typecheck
by Sean Leather 18 Oct '08

18 Oct '08

[I posted this on the Template Haskell list, but nobody seemed interested. Thus, I'm re-posting it here for higher coverage.] Apparently, I can create a function declaration (FunD) with a name containing an invalid sequence of characters. It passes typechecking and compiles. It even shows up in GHCi! The function name is "ep:#:", and the ":#:" is derived from an infix type constructor. In GHCi (6.8.3), I type "ep", hit <Tab> to get the list of completions, and, sure enough, there it is! When I try to use it, GHCi interprets it as two distinct symbols, "ep" and ":#:", as it should. Template Haskell's claim to fame is that it allows you to do "type-safe compile-time meta-programming," and while this issue is perhaps considered lexical rather than type-level, I'm wondering if there should be some additional error checking (somewhere) to account for this. I admit though, that I wouldn't know how to do this easily within the bounds of the TH API. The Name type is common to functions, infix operators, and everything else. That which is valid for one is not necessarily so for the other. Regards, Sean

2 1

List as input
by leledumbo 17 Oct '08

17 Oct '08

module Main where import Data.List -- quicksort of any list qsort [] = [] qsort (x:xs) = qsort(filter(<x) xs) ++ [x] ++ qsort(filter(>=x) xs) -- optimized quicksort, uses middle element as pivot qsortOpt [] = [] qsortOpt x = qsortOpt less ++ [pivot] ++ qsortOpt greater where pivot = x !! ((length x) `div` 2) less = filter (<pivot) (delete pivot x) greater = filter (>=pivot) (delete pivot x) main = do putStr "Enter a list: " l <- readLn print (qsortOpt l) -- end of code Why do I get ERROR "qsort.hs":17 - Unresolved top-level overloading *** Binding : main *** Outstanding context : (Read b, Show b, Ord b) ? -- View this message in context: http://www.nabble.com/List-as-input-tp19987726p19987726.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

10 16

Terminal-like Application Design
by Jeff Wheeler 17 Oct '08

17 Oct '08

Hi, I'm a slight Haskell newbie, but I'm trying to write a terminal-like application that accepts simple commands with optional arguments, and can then execute them. Most of these commands will need IO, as later I will want to communicate over USB for most of them. I was hoping, though, that I could get some comments on the initial architecture I've been playing with [1]. I suspect I should be using some sort of monad to represent the commands, but I don't fully understand monads, and am not sure how it would apply in this context. Should I be using a monad here, and if so, how? Thanks in advance, Jeff Wheeler [1] http://media.nokrev.com/junk/cli/

6 5

[fun] HaskellDB Talk trailer
by Ahn, Ki Yung 17 Oct '08

17 Oct '08

There is an impressive HaskellDB Talk trailer on the web. http://www.vimeo.com/1983774 Cheers to the HaskellDB developers :-)

3 2

Arch Haskell News: Oct 4 2008
by Don Stewart 17 Oct '08

17 Oct '08

A weekly update about Haskell on Arch Linux. Highlights, * Arch now has 609 Haskell packages in AUR. That’s a record increase of 19 new packages in the last 7 days. Noteworthy, * mp3decoder-0.0.1: “MP3 decoder for teaching.” * yi-0.4.6.2: “The Haskell-Scriptable Editor” * haskell-haskore-0.0.5.1: “The Haskore Computer Music System” Full update list, http://archhaskell.wordpress.com/2008/10/04/arch-haskell-news-oct-4-2008/ -- Don

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What I wish someone had told me...
by John Lato 17 Oct '08

17 Oct '08

I was just thinking about what I wish someone had told me when I started working with Haskell (not that long ago). It would have saved me a great deal of trouble. The Difference Between Interfaces and Type Classes. Many "Introduction to Haskell for the OOper" style tutorials claim that type classes are like Interfaces (for languages with that feature). I now think that, although this is technically true, it's fundamentally misleading. Here's a simple example demonstrating my line of thought: In C# (and presumably Java), this sort of function is common: public IList GetListOfData() In Haskell, a similar function may be GetListOfData :: (Foldable a, Indexable a) => IO a In C#, it doesn't matter what the actual type returned by GetListOfData is, as long is it supports the IList interface. It's not uncommon for GetListOfData to make a choice between several different implementations, depending on the nature of the data to be returned. The following code is perfectly reasonable in C# : // List and MyList are different classes if (something) { return new List(); } else { return new MyList(); } The equivalent won't compile in Haskell, because the actual return type does matter, and *is determined by the calling code*. Our fictional GetListOfData can't return a List or a Mylist depending on some conditional, in fact it can't explicitly return either one at all, because the actual type of the result, as determined by the caller, could be either one, or something else entirely (ignoring the IO bit for the time being). So I've come to the conclusion that stating type classes are like interfaces is misleading to newcomers to Haskell, because it leads people to think they should use type classes for the same sorts of problems OO-languages solve with interfaces. In turn this means new programmers are encouraged to use OO-style architecture in programs, reassured that they're in a "functional" idiom because they're using the "functionally-approved" feature of type classes. I think that if I had understood this earlier, I would have embraced functional idioms more quickly. Incidentally, I'm still horrible at designing functional APIs and modules, but at least now I know it, and I'm no longer trying to force OO interfaces into Haskell. So I've made progress.

21 47

Haskell newbie indentation query.
by Ramaswamy, Vivek 17 Oct '08

17 Oct '08

Hello All~ I have just started with Haskell, and I must confess; I am in love with it. However one area that I am really confused about is indentation. Lets take a look at if-else if- else block. The way I understand it: {------} if something then do something 1 something2 else if nothing then do something3 something4 else do different {-------} The code above gives out an error. I have been programming in python and the above appears fine. But it does not work. What works is: if something then do something1 something2 else if then do something3 something4 else do different I find the above scheme extremely confusing. I tried going to: http://en.wikibooks.org/wiki/Programming:Haskell_indentation after reading I am even more confused. Can somebody please explain how the Haskell indentation works? The else-if and else seem to be aligning up with "then". They should be aligning with "If" in my opinion. Thanks in advance. Regards -Vivek Ramaswamy-

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Re: [Haskell-cafe] What is this function? (RESOLVED)
by John Ky 17 Oct '08

17 Oct '08

Hi Luke, Thankyou so much. I need the sequence function. What I was after was this: class Scramblable a where scramble :: a -> [a] instance Scramblable [MyType] where scramble values = sequence (map scramble values) instance Scramblable MyType where scramble myType = {- blah blah -} I was basically after exhaustively generating lots ASTs given a template AST with lots of leaf values changed. Thanks, -John On Thu, Oct 16, 2008 at 8:39 PM, Luke Palmer <lrpalmer(a)gmail.com> wrote: > 2008/10/16 John Ky <newhoggy(a)gmail.com>: > > Hi, > > > > I've written this function here: > > > > scramble [] = [] > > scramble [x] = [[z] | z <- scramble x] > > scramble (x:xs) = > > [(y:z)|y <- scramble x, z <- scramble xs] > > > > and (I think) it roughly does what I want it to: > > > > *Main> scramble ([]::[Int]) > > [] > > *Main> scramble ([1]::[Int]) > > [[1],[2]] > > So, um, this is nonsense. You've given it only 1, and yet it outputs > a 2, yet there is no mention of addition or the literal 2 anywhere in > your function. > > This function looks a lot like the more sensible: > > scramble' n xs = sequence (replicate n xs) > > >>> scramble' 0 [1,2,3] > [[]] > >>> scramble' 1 [1,2,3] > [[1],[2],[3]] > >>> scramble' 2 [1,2,3] > [[1,1],[1,2],[1,3],[2,1],[2,2],[2,3],[3,1],[3,2],[3,3]] > > Where your examples all had [1,2] as the argument. > > Luke >

1 0

About do notation.
by Magicloud 17 Oct '08

17 Oct '08

Hi, As some articles say, do notation is expand to (>>) and (>>=) when being compiled. So I want to know the details. Like: main = do a <- getArgs b <- getLine myFunc1 (head a) b myFunc2 b (head a) I cannot figure out what is the (>>) and (>>=) way of this. Thanks.

6 5

Re: Where did House/hOp go?
by Kenny Graunke 17 Oct '08

17 Oct '08

Hello! On Thu, Oct 16, 2008, Donnie Jones <donnie at darthik.com> wrote: [snip] > The site is working for me even now. > Unfortunately, the site hasn't really been updated much over the past > couple of years and when I e-mailed some people on the Programatica > project about the status of House & Osker I never got anything back. > The biggest obstacle you may find when trying to set up House & hOp is > that hOp is based upon a modified version of a very old GHC and from > the last time I looked at it the GHC runtime has changed enough that > making a new hOp will be non-trivial. Indeed! House 0.8, as listed on the official programatica page, is based on GHC 6.2...not so fun to work with these days. I've spent the last year or so working on House as part of my research, and have updated it to GHC 6.8.2 (with a lot of help). You can get a copy of my unofficial "House 0.8.91" sources here: http://web.cecs.pdx.edu/~kennyg/house/ It's still a bit of a challenge to build. Notably, you'll need a 32-bit Linux system - it doesn't build on 64-bit linux nor Mac OS X (yet). If you just want a floppy image, you may as well stick with House 0.8 from http://programatica.cs.pdx.edu/House/ ... it's basically the same. --Kenny

2 1

Re: Haskell-Cafe Digest, Vol 46, Issue 118
by Alberto G. Corona 17 Oct '08

17 Oct '08

>Personally, I'm loving the whole concept of this puppy: > GHC.Prim.*reallyUnsafePtrEquality# >I have absolutely no idea what it does, but it must be something really >unsafe! ;-)i I really need reallyUnsafePtrEquality# !!!!! . I need it in inside GHC.Exts if GHC.Prim is being removed. Please!.. I´m involved in a project for storage and retrieval of heavily autoreferenced data structures. This functionality is absolutely needed for that!!.

1 0