March 2011 - Haskell-Cafe

Finalizer registered with System.Mem.Weak.addFinalizer is called surprisingly early
by balodja 10 Mar '11

10 Mar '11

Hello, I use addFinalizer from System.Mem.Weak for performing some actions on data just before that is reclaimed by GC. Registered in this way finalizer is called surprisingly early for me, much earlier the data is tend to be collected. I've attached source code of simple two-threaded program. Source code also can be found at [1]. It is pretty simple and should be readable enough. Program is intentioned to pass messages through transactional variable (TVar) for printing by worker thread. Messages consist of formatted to String Int values from 1 to 1000000. So the output should look like this: > 1 > 2 > ... > 1000000 But running the program gives something like that: > 1 > 2 > ... > 283 > finalizing > Test: thread blocked indefinitely in an STM transaction As far as I see, finalizer is called too early. If someone could point me out how to do the right thing, that would be helpful. Operaton system: Debian Squeeze Compiler: GHC 6.12.1 Compiling options: none, just "ghc --make Test.hs" Thanks, balodja [1] http://hpaste.org/44648

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Haskell Weekly News: Issue 172
by Daniel Santa Cruz 09 Mar '11

09 Mar '11

Welcome to issue 172 of the HWN, a newsletter covering developments in the [1]Haskell community. This release covers the week of February 27 to March 05, 2011. Announcements Jasper Van der Jeugt [2]announced the release of version 3 of Hakyll. He informs us that this is a complete re-write, and not backwards compatible. Horvath Zoltan [3]informed us about the 4th Central European Functional Programming School (CEFP 2011), which is to take place in Eotvos Lorand University, Budapest, Hungary, from June 14-24, 2011. "The invited lecturers are the most prominent researchers in the field in Europe, and they will present state-of-the-art functional programming techniques." Janis Voigtlander [4]issued a call for papers for the 20th International Workshop on Functional and (Constraint) Logic Programming (WFLP 2011) to be held in Odense, Denmark, on July 19, 2011. Michael Hanus [5]issued a call for papers for the 13th International ACM SIGPLAN Symposium on Principles and Practice of Declarative Programming (PPDP 2011) to be held in Odense, Denmark, on July 20-22, 2011. Trystan Spangler [6]released a new version (0.3.0) of hspec, with "improvements including fixing a base dependency problem, and better reporting of failed examples." Magnus Therming [7]released new versions of dataenc (0.14), and omnicodec (0.5). "It contains a large change to the API. The old, rather simplistic, lazy API has been removed. It has been replaced by an API based on incremental encoding/decoding. This should make the library easier to use together with left-fold enumerators..." Rogan Creswick [8]announced that cabal-dev 0.7.4.0 has been uploaded to hackage. "We strongly suggest that everyone upgrade to this release, since this release specifically addresses changes in Cabal-1.10 and newer, which the latest cabal-install new uses." Frederick Ross [9]announced a minor upgrade to haskell-pgm (0.1.2), with a minor upgrade to the library to make it work with GHC 7. Uwe Schmidt [10]announced an update to hxt to version 9.1. Eric Kow [11]announced that the date and venue for the sixth Darcs Hacking sprint has been confirmed for Paris, April 1-3, 2011. Ian Lynagh and the GHC Team [12]announced a new patchlevel release of GHC. "This release contains a number of bugfixes relative to 7.0.1, so we recommend upgrading." Denis Bueno [13]announced new releases of funsat (0.6.2) and bitset (1.1). Michal Konecny [14]announced version 0.3.2 of hmpfr, bindings to the MPFR arbitrary precision floating point arithmetic library. "The changes in this version are quite small but significant." Jonathan Daugherty [15]announced version 1.0 of the vty-ui terminal user interface library. "The vty-ui library is a complete interactive user interface development toolkit for terminal applications." Jason Dusek [16]announced his now bash-0.0.0, which has "types and functions for generation of Bash scripts, with safe escaping and composition of large subsets of Bash statements and expressions." Quotes of the Week * lpsmith: I didn't take the time to figure out what should be done in finite cases. * <companion_cube> edwardk, you mean it's 2 phD/nick in average ? :) <edwardk> clearly this is why SPJ stays away, he doesn't want to dilute that metric. * edwardk: Haskell 98 is a laudable goal. * douglas-adams: I love deadlines, I especially like the swooshing sound they make as they fly past * kmc: the way to convert imperative code to functional is to think about what your code actually means, and then throw out most of the irrelevant details that imperative programming has forced on you * MonadsSuck: man, I hate it when an adjoint pair of functors get together and compose. So damn annoying * bwright: I don't get it everyone keeps telling me java is a safe language but it melted the plastic on my eeepc900 * danka: you could be a monadic vampire. I hear they bleed semicolons. Top Reddit Stories * ANNOUNCE: GHC version 7.0.2: From (haskell.org) scored 46 with comments. Read on [17]reddit or the [18]original post. * Greenfield Haskell: From (self.haskell), scored 36 with 188 comments. Read on [19]reddit or the [20]original post. * Patches for monad comprehensions are in and will be in the upcoming GHC 7.2 release: From (hackage.haskell.org) scored 34 with 15 comments. Read on [21]reddit or the [22]original post. * GHC 7.0.2 released!: From (haskell.org) scored 32 with 10 comments. Read on [23]reddit or the [24]original post. * Haskell on Android: From (self.haskell), scored 31 with 22 comments. Read on [25]reddit or the [26]original post. * Do you think Haskell will ever catch on?: From (self.haskell), scored 26 with 63 comments. Read on [27]reddit or the [28]original post. * hakyll 3.0 released (static site generator): From (jaspervdj.be), scored 25 with 1 comments. Read on [29]reddit or the [30]original post. * New release of cabal-dev: sandboxed, reproducible build environments for Haskell: From (haskell.org) scored 24 with 9 comments. Read on [31]reddit or the [32]original post. * News on Well-Typed, the Parallel GHC Project, and Eric Kow joins the team.: From (well-typed.com) scored 22 with 3 comments. Read on [33]reddit or the [34]original post. * Build Yourself a Bluetooth Controlled Six-Legged Robot : A Neighborhood of Infinity: From (blog.sigfpe.com) scored 21 with comments. Read on [35]reddit or the [36]original post. Top StackOverflow Answers * [37]Goto in Haskell: Can anyone explain this seemingly insane effect of continuation monad usage? votes: 14 Here's a somewhat informal answer, but hopefully useful. getCC' returns a continuation to the current point of execution; you can think of it as saving a stack frame. The continuation returned by getCC' has not only ContT's state at the point of the call, but also the state of any monad above ContT on the stack. When you restore that state by calling the ... * [38]How do Haskell compilers decide whether to allocate on the heap or the stack? votes: 13 When you call a function like this f 42 (g x y) then the runtime behaviour is something like the following: p1 = malloc(2 * sizeof(Word)) p1[0] = &Tag_for_Int p1[1] = 42 p2 = malloc(3 * sizeof(Word)) p2[0] = &Code_for_g_x_y p2[1] = x p2[2] = y f(p1, p2) That is, arguments are usually passed as pointers to objects on the heap like in Java, but ... * [39]Quick question about Arrow operators votes: 11 (***) :: (Arrow a) => a b c -> a b' c' -> a (b, b') (c, c') So specialize a to -> and we get: (***) :: (Arrow a) => (b -> c) -> (b' -> c') -> (b, b') -> (c, c') And that's great, except we want to, for whatever reason, take the first two arguments as a single pair instead. But that's easy, we just uncurry. Prelude ... * [40]QuickCheck: defining Arbitrary instance in terms of other Arbitraries votes: 9 I'd do it like this: instance Arbitrary C where arbitrary = do a <- arbitrary b <- arbitrary return (C a b) Although sclv's idea of using liftM2 from Control.Monad is probably better: instance Arbitrary C where arbitrary = liftM2 C arbitrary arbitrary Top StackOverflow Questions * Running a Haskell program on the Android OS (votes: 21, answers: 1) [41]read * Goto in Haskell: Can anyone explain this seemingly insane effect of continuation monad usage? (votes: 18, answers: 2) [42]read * Proving equality of streams (votes: 15, answers: 1) [43]read * Rotate the first argument to a function to become nth (votes: 12, answers: 7) [44]read * How do Haskell compilers decide whether to allocate on the heap or the stack? (votes: 9, answers: 2) [45]read About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. I'm in dire need of finding good "quotes of the week". If you happen to come across any, please don't hesitate to send it along. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.hakyll/128 3. http://article.gmane.org/gmane.comp.lang.haskell.general/18527 4. http://article.gmane.org/gmane.comp.lang.haskell.general/18528 5. http://article.gmane.org/gmane.comp.lang.haskell.general/18530 6. http://article.gmane.org/gmane.comp.lang.haskell.general/18533 7. http://article.gmane.org/gmane.comp.lang.haskell.libraries/15426 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/86897 9. http://article.gmane.org/gmane.comp.lang.haskell.general/18542 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/86922 11. http://article.gmane.org/gmane.comp.version-control.darcs.user/25916 12. http://article.gmane.org/gmane.comp.lang.haskell.general/18535 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/86937 14. http://article.gmane.org/gmane.comp.lang.haskell.cafe/86882 15. http://article.gmane.org/gmane.comp.lang.haskell.general/18540 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/86975 17. http://www.reddit.com/r/haskell/comments/fwk78/announce_ghc_version_702/ 18. http://www.haskell.org/pipermail/haskell/2011-March/022610.html 19. http://www.reddit.com/r/haskell/comments/fvabx/greenfield_haskell/ 20. file://localhost/r/haskell/comments/fvabx/greenfield_haskell/ 21. http://www.reddit.com/r/haskell/comments/fxjcl/patches_for_monad_comprehens… 22. http://hackage.haskell.org/trac/ghc/ticket/4370#comment:48 23. http://www.reddit.com/r/haskell/comments/fwkdh/ghc_702_released/ 24. http://www.haskell.org/ghc/download_ghc_7_0_2 25. http://www.reddit.com/r/haskell/comments/ful84/haskell_on_android/ 26. http://www.reddit.com/r/haskell/comments/ful84/haskell_on_android/ 27. http://www.reddit.com/r/haskell/comments/ftxc7/do_you_think_haskell_will_ev… 28. http://www.reddit.com/r/haskell/comments/ftxc7/do_you_think_haskell_will_ev… 29. http://www.reddit.com/r/haskell/comments/fusve/hakyll_30_released_static_si… 30. http://jaspervdj.be/hakyll/tutorial.html 31. http://www.reddit.com/r/haskell/comments/fx47b/new_release_of_cabaldev_sand… 32. http://www.haskell.org/pipermail/haskell-cafe/2011-March/089831.html 33. http://www.reddit.com/r/haskell/comments/fw311/news_on_welltyped_the_parall… 34. http://www.well-typed.com/blog/51 35. http://www.reddit.com/r/haskell/comments/ftxzx/build_yourself_a_bluetooth_c… 36. http://blog.sigfpe.com/2011/02/build-yourself-bluetooth-controlled-six.html 37. http://stackoverflow.com/questions/5193876/goto-in-haskell-can-anyone-expla… 38. http://stackoverflow.com/questions/5132350/how-do-haskell-compilers-decide-… 39. http://stackoverflow.com/questions/5200462/quick-question-about-arrow-opera… 40. http://stackoverflow.com/questions/5134259/quickcheck-defining-arbitrary-in… 41. http://stackoverflow.com/questions/5151858/running-a-haskell-program-on-the… 42. http://stackoverflow.com/questions/5193876/goto-in-haskell-can-anyone-expla… 43. http://stackoverflow.com/questions/5179821/proving-equality-of-streams 44. http://stackoverflow.com/questions/5188212/rotate-the-first-argument-to-a-f… 45. http://stackoverflow.com/questions/5132350/how-do-haskell-compilers-decide-…

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Haskell Platform web page is out of date
by Paul Johnson 09 Mar '11

09 Mar '11

The Haskell Platform web page at http://hackage.haskell.org/platform// seems to need updating. (Incidentally, that double slash at the end doesn't look right). * The "next release" is promised in Jan 2011. * The "Release Timetable" schedules the next release for 5 March 2011. I just worry that this is one of the first things someone investigating Haskell sees, and it creates a bad first impression. Paul.

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Haskell Platform 2011.2
by tsuraan 09 Mar '11

09 Mar '11

The wiki page for Haskell Platform is still listing March 5 (today) as the planned release date. Is this still the plan, or should the page be updated?

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Overlaping Parsec rules
by Hauschild, Klaus (EXT) 09 Mar '11

09 Mar '11

Hi, to solve this ICFP task http://www.cs.cornell.edu/icfp/task.htm I'm currnetly working on the parser. With the hint from Thu (reading Phillip Wadlers monadic parser paper) and consulting http://en.wikibooks.org/wiki/Write_Yourself_a_Scheme_in_48_Hours/Parsing I produce a first working version of the parser. After this great moment I completed the token definition and near all parsing rules. For the complete code have a look at http://code.google.com/p/hgmltracer/source/browse/#svn%2Ftrunk%2FhGmlTracer data GmlToken = -- structures FunctionToken TokenSequence | ArrayToken TokenSequence | -- control operators ApplyToken | IfToken | -- number operators AddiToken | AddfToken | ACosToken | ASinToken | ClampfToken | CosToken | DiviToken | DivfToken | EqiToken | EqfToken | FloorToken | FracToken | LessiToken | LessfToken | ModiToken | MuliToken | MulfToken | NegiToken | NegfToken | ToRealToken | SinToken | SqrtToken | SubiToken | SubfToken | -- points GetXToken | GetYToken | GetZToken | PointToken | -- arrays GetToken | LengthToken | -- environment IdentifierToken String | BinderToken String | -- types BoolToken Bool | IntToken Int | RealToken Double | StringToken String deriving Show And parseGml :: String -> [GmlToken] parseGml input = case parse parseList "gml" input of Left err -> error ("Parse error: " ++ (show err)) Right gml -> gml parseList = sepBy parseGml' spaces parseGml' = -- structures -- parseFunction -- <|> parseArray -- control operators parseControlOperators -- number operators <|> parseNumberOperators -- points <|> parsePointOperators -- arrays <|> parseArrayOperators -- types <|> parseBool <|> parseInteger <|> parseString -- environment <|> parseIdentifier <|> parseBinder parseArray = parseSequence '[' ']' parseFunction = parseSequence '{' '}' parseSequence start end = do char start array <- parseList char end return $ ArrayToken array parseControlOperators = parseApply <|> parseIf parseApply = do string "apply" return $ ApplyToken parseIf = do string "if" return $ IfToken parseNumberOperators = do string "addi" return $ AddiToken <|> do string "addf" return $ AddfToken <|> do string "acos" return $ ACosToken <|> do string "asind" return $ ASinToken <|> do string "clampf" return $ ClampfToken <|> do string "cos" return $ CosToken <|> do string "divi" return $ DiviToken <|> do string "divf" return $ DivfToken <|> do string "eqi" return $ EqiToken <|> do string "eqf" return $ EqfToken <|> do string "floor" return $ FloorToken <|> do string "frac" return $ FracToken <|> do string "lessi" return $ LessiToken <|> do string "lessf" return $ LessfToken <|> do string "modi" return $ ModiToken <|> do string "muli" return $ MuliToken <|> do string "mulf" return $ MulfToken <|> do string "negi" return $ NegiToken <|> do string "negf" return $ NegfToken <|> do string "real" return $ ToRealToken <|> do string "sin" return $ SinToken <|> do string "Sqrt" return $ SqrtToken <|> do string "subi" return $ SubiToken <|> do string "subf" return $ SubfToken parsePointOperators = do string "getx" return $ GetXToken <|> do string "gety" return $ GetYToken <|> do string "getz" return $ GetZToken <|> do string "point" return $ PointToken parseArrayOperators = do string "get" return $ GetToken <|> do string "length" return $ LengthToken parseInteger = liftM (IntToken . read) $ many1 digit parseBool = do string "true" return $ BoolToken True <|> do string "false" return $ BoolToken False parseString = do char '"' string <- many (noneOf "\"") char '"' return $ StringToken string parseIdentifier = do identifier <- many (noneOf " ") return $ IdentifierToken identifier parseBinder = do char '/' binder <- many (noneOf " ") return $ BinderToken binder parseComment = do char '%' many (noneOf "") newline return $ () spaces = skipMany1 space After gluing all this together in my mind all worked well. But it doesn't. The test file for parsing looks like: { /self /n n 2 lessi { 1 } { n 1 subi self self apply n muli } if } /fact 12 fact fact apply * I think there is a problem with overlaping rules. There is a parser rule consuming "negi" and resulting in the NegiToken. A single "n" is a valid identifier. For the example file my parser says: unexpected " ", expecting "negi" * I think the same problem is present for "parseInteger" and "parseReal" (currently no in code but looks like "parseReal = do a <- many1 digit \n char '.' \n b <- many1 digit \n return $ RealToken (read (a ++ "." ++ b)" * Something with "parseFunction" is going really wrong. * All parsig rules are designed with the condition that each "construct" is separated by whitespaces. For this before parsing the input will be preprocessed: insert spaces, removing whitespaces and so on. Now in the parsed result appears (IdentifierToken ""). I think my version is not the best way to parse a identifer: parseIdentifier = do identifier <- many (noneOf " ") return $ IdentifierToken identifier Please help me. Klaus

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operations on lists with continuations
by Evan Laforge 08 Mar '11

08 Mar '11

I have a few functions for operating on lists that take continuations: -- | Like takeWhile but with a continuation, so you can chain takes without -- copying. takeWhileThen :: (a -> Bool) -> ([a] -> [a]) -> [a] -> [a] takeWhileThen _ _ [] = [] takeWhileThen f cont (x:xs) | f x = x : takeWhileThen f cont xs | otherwise = cont (x:xs) But of course this isn't enough, then I start wanting a takeThen. And then a filterThen. That makes me think plain explicit recursion would be clearer, but the problem I have with that is that it has an imperative feel. What I mean by that is that the result is a product of the changing state of the recursing function, and it's non-composable. E.g. filterUntil start end msgs = go where go [] = [] go (m:ms) | msg_start m >= start = takeWhile ((<end) . msg_start) (m : ms) | condition m = m : go ms | otherwise = go ms Whereas with filterThen I can write: filterUntil start end = filterThen condition ((>=start) . msg_start) . takeWhile ((<end) . msg_start) This looks much more functional to me, and can be composed: filterUntilPlus1 start end = filterThen condition ((>=start) . msg_start) $ takeWhileThen ((<end) . msg_start) $ take 1 So my question is, am I about to discover this already exists in the Prelude, or is unnecessary because of something I'm overlooking? I imagine it must be a special case of some kind of generalization, right? Surely someone has thought of this and taken it much further than I have. I suppose this starts to look like maybe a CPS version of a parser... but it seems lighter-weight for simple tasks.

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cabal install / upgrade (was: Re: some problem with Cabal)
by Evan Laforge 08 Mar '11

08 Mar '11

> Generally, it shouldn't (and doesn't), but here some packages have to be > reinstalled because they have to be built against different dependencies. > > I'd prefer cabal install to refuse here (overridable with a --force flag) > because reinstalling boot libs (containers, filepath, directory, process, > time) tends to be a bad idea. Seconded! I've had my setup screwed up because some package wanted to recompile base against a tiny version bump on the random package for whatever reason. The presence of two bases with the same version, one in the ghc dir and one in /usr/local/lib proceded to screw up all kinds of things. It took a long time to figure out because I wasn't expecting two copies of base with the same version, and it somehow managed to overwrite the package file in package.conf.d so the original metadata was gone. Eventually I gave up and reinstalled ghc. And all I did was accidentally run cabal upgrade somepackage when I wanted to install a newer version of somepackage. By the time I realized it was apparently still aliased to cabal break-everything and hit ^C it was too late. And it's not like I haven't been warned away from cabal upgrade either... but it made me think, if the command is so dangerous, should it have a scarier name?

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Tagless interpreter, expression problem and zipper
by Roel van Dijk 08 Mar '11

08 Mar '11

Hello everyone, I am stuck rewriting some code in the tagless style. My problem can be thought of as an interpreter for a very simple language: > data Exp = Lit Integer > | Add Exp Exp > | Mul Exp Exp > deriving (Show) But some complexity is added by the fact that my interpreter also needs to know the context in which literals appear in an expression. So given the example > t1 :: Exp > t1 = (Lit 3 `Add` Lit 4) `Mul` Lit 2 I want to have access to the fact that the literal 3 appears on the left side of an addition. Therefore I created a type: > data Ctx = Empty > | AddL Exp Ctx > | AddR Exp Ctx > | MulL Exp Ctx > | MulR Exp Ctx > deriving (Show) This is almost a zipper over the Exp type. I left out a context for literals themselves because it wasn't necessary. Now I can create a simple evaluation function: > eval :: (a -> a -> a) > -> (a -> a -> a) > -> (Integer -> Ctx -> a) > -> Exp > -> a > eval add mul lit = go Empty > where > go ctx (Lit n) = lit n ctx > go ctx (Add x y) = let x' = go (AddL y ctx) x > y' = go (AddR x ctx) y > in x' `add` y' > go ctx (Mul x y) = let x' = go (MulL y ctx) x > y' = go (MulR x ctx) y > in x' `mul` y' This function can evaluate an expression to any type 'a', but it needs some additional functions to accomplish that: add, mul and lit. Notice how the 'lit' function has access to a literal's context. To interpret an Exp as an Integer I use: > evalInt :: Exp -> Integer > evalInt = eval (+) (*) const Or as a String: > evalStr1 :: Exp -> String > evalStr1 = eval addStr mulStr (const . show) > addStr x y = "(" ++ x ++ " + " ++ y ++ ")" > mulStr x y = "(" ++ x ++ " * " ++ y ++ ")" Or a silly example which uses the context: > evalStr2 :: Exp -> String > evalStr2 = eval addStr mulStr lit > where > lit _ (AddL (Lit 4) (MulL _ _)) = "Foo!" > lit n _ = show n The silly example replaces a literal with "Foo!" if it appears on the left side of an addition with 4, and the whole addition is the left side of a multiplication, like in (x + 4) * ?. All of this works. But I want to be able to add additional constructors to the Exp language without changing existing code. This looks like the expression problem. Ignoring the zipper-like context I came up with the following: First define the language: > class Lit a where lit :: Integer -> a > class Add a where add :: a -> a -> a > class Mul a where mul :: a -> a -> a Integer interpreter: > instance Lit Integer where lit = fromInteger > instance Add Integer where add = (+) > instance Mul Integer where mul = (*) String interpreter, using a newtype so I don't need TypeSynonymInstances: > newtype Str = Str {unS :: String} > instance Show Str where show = show . unS > instance Lit Str where lit = Str . show > instance Add Str where add x y = Str $ addStr (unS x) (unS y) > instance Mul Str where mul x y = Str $ mulStr (unS x) (unS y) Same example expression, now polymorphic: > t1 :: (Lit a, Add a, Mul a) => a > t1 = (lit 3 `add` lit 4) `mul` lit 2 This expression can now be interpreted in multiple ways: > t1 :: Integer >> 14 > t1 :: Str >> "((3 + 4) * 2)" This solves the expression problem. I can add new structures to my language in other modules without having to change existing code. The necessary parts are mentioned in the type constraint (Lit a, Add a, Mul a). But I lost the power of the context! How do I get it back? Attached are the two approaches, WithTags.hs and Tagless.hs (but without context). Any help would be greatly appreciated!

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some problem with Cabal
by Qi Qi 08 Mar '11

08 Mar '11

Hi, When I tried the haskell platform 2011.2 source, from here http://code.galois.com/darcs/haskell-platform/download-website/linux.html . Configuration passed successfully. But when making, it gives the following error: scripts/build.sh ************************************************** Scanning system for any installed Haskell Platform components... Found:None. New packages to install: None! All done. ************************************************** Building "/usr/local/bin/ghc" "--make" "Setup" "-o" "Setup" "-package" "Cabal-1.10.1.0" <command line>: cannot satisfy -package Cabal-1.10.1.0: Cabal-1.10.1.0-64e8f05722ea5bbdf07df2e5a3491105 is unusable due to missing or recursive dependencies: directory-1.1.0.0-85d1d0f9d96dffdacf64f3cc6fba6f2f process-1.0.1.5-4cab1bf0666275ac101dd48c7565b64c (use -v for more information) Error: Compiling the Setup script failed make: *** [build.stamp] Error 2 I think this is the same problem as I got during installing some other packages via cabal such as hmatrix, ghc-mod, happy and etc. Does anyone have any idea about how to solve it? Thanks! -- Qi Qi

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have anyone tried GHC 7.0.2
by Qi Qi 08 Mar '11

08 Mar '11

Hi, After I installed GHC 7.0.2 and cabal-install 0.10.0 using Cabal library 1.10.1, I found that some package failed to install. For example like Happy, I got the following error: cabal install happy Resolving dependencies... <command line>: cannot satisfy -package Cabal-1.10.1.0: Cabal-1.10.1.0-64e8f05722ea5bbdf07df2e5a3491105 is unusable due to missing or recursive dependencies: directory-1.1.0.0-85d1d0f9d96dffdacf64f3cc6fba6f2f process-1.0.1.5-4cab1bf0666275ac101dd48c7565b64c (use -v for more information) cabal: Error: some packages failed to install: happy-1.18.6 failed during the configure step. The exception was: ExitFailure 1 Besides happy package, some other packages like ghc-mod, hmatrix also failed to install. Does anyone else have the same issue after installed ghc 7.0.2? By the way, does anyone hear anything about Haskell-platform 2011.2 ? Thanks! -- Qi Qi

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