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ghci and TH cannot: unknown symbol `stat64`
by Michael Snoyman 13 Jul '12

13 Jul '12

Hi all, A quick search indicates that this problem has come up in the past, but I haven't seen any solutions yet. I'm working on the next Persistent release, and one of the changes is that the included sqlite3 C library has been updated (I believe that's the trigger here). I can compile programs against persistent-sqlite, but if there's TH code involved, or I try to runghc the file, I get an error message like: test.hs: /home/ubuntu/.cabal/lib/persistent-sqlite-1.0.0/ghc-7.4.1/HSpersistent-sqlite-1.0.0.o: unknown symbol `stat64' test.hs: test.hs: unable to load package `persistent-sqlite-1.0.0' I'm running GHC 7.4.1 on Ubuntu 12.04 64-bit. Does anyone have insight into what might be causing this? Thanks, Michael

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haskell.org is so fragile
by Takayuki Muranushi 13 Jul '12

13 Jul '12

Today I have observed that hackage.haskell.org/ timeout twice (in the noon and in the evening.) What is the problem? Is it that haskell users have increased so that haskell.org is overloaded? That's very good news. I am eager to donate some money if it requires server reinforcement. Sincerely, -- Takayuki MURANUSHI The Hakubi Center for Advanced Research, Kyoto University http://www.hakubi.kyoto-u.ac.jp/02_mem/h22/muranushi.html

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Monads with "The" contexts?
by oleg＠okmij.org 12 Jul '12

12 Jul '12

Tillmann Rendel has correctly noted that the source of the problem is the correlation among the random variables. Specifically, our measurement of Sun's mass and of Mars mass used the same rather than independently drawn samples of the Earth mass. Sharing (which supports what Functional-Logic programming calls ``call-time choice'') is indeed the solution. Sharing has very clear physical intuition: it corresponds to the collapse of the wave function. Incidentally, a better reference than our ICFP09 paper is the greatly expanded JFP paper http://okmij.org/ftp/Computation/monads.html#lazy-sharing-nondet You would also need a generalization of sharing -- memoization -- to build stochastic functions. The emphasis is on _function_: when applied to a value, the function may give an arbitrary sample from a distribution. However, when applied to the same value again, the function should return the same sample. The general memo combinator is implemented in Hansei and is used all the time. The following article talks about stochastic functions (and correlated variables): http://okmij.org/ftp/kakuritu/index.html#all-different and the following two articles show just two examples of using memo: http://okmij.org/ftp/kakuritu/index.html#noisy-or http://okmij.org/ftp/kakuritu/index.html#colored-balls The noisy-or example is quite close to your problem. It deals with the inference in causal graphs (DAG): finding out the distribution of conclusions from the distribution of causes (perhaps given measurements of some other conclusions). Since a cause may contribute to several conclusions, we have to mind sharing. Since the code works by back-propagation (so we don't have to sample causes that don't contribute to the conclusions of interest), we have to use memoization (actually, memoization of recursively defined functions).

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Another topic of ghc --make/ghci differences
by Andrey Yankin 12 Jul '12

12 Jul '12

1. I wrote this: -----8<----- test.hs --- module Main where import qualified Graphics.UI.GLFW as GLFW main = do True <- GLFW.initialize print =<< GLFW.openGLProfile print =<< GLFW.getGlfwVersion print =<< GLFW.getGlVersion print "Trying to open the window" result <- GLFW.openWindow GLFW.defaultDisplayOptions print result -----8<----- 2. Compiled like this: ghc --make -o test test.hs 3. Executed: ./test DefaultProfile Version {versionBranch = [2,7,2], versionTags = []} Version {versionBranch = [0,0,0], versionTags = []} "Trying to open the window" True 4. Window appeared. 2'. Executed in GHCI like this: ghci -fno-ghci-sandbox Prelude> :l test.hs Prelude> main 3'. Get (random numbers as GLVersion): Loading package GLFW-b-0.1.0.2 ... linking ... done. DefaultProfile Version {versionBranch = [2,7,2], versionTags = []} Version {versionBranch = *[34972080,-1323041296,-1334802519]*, versionTags = []} "Trying to open the window" False 4'. Window didn't appear. What should I do to get GLFW window in ghci too? What do I do wrong?

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Bad interface problem.
by Magicloud Magiclouds 12 Jul '12

12 Jul '12

Hi, This had never happened to me. And I have no idea what to do. $ cabal --upgrade-dependencies --enable-documentation --force-reinstalls --solver=topdown QuickCheck-2.5 Test/QuickCheck/All.hs:15:1: Bad interface file: /home/magicloud/.cabal/lib/template-haskell-2.6.0.0/ghc-7.4.2/Language/Haskell/TH.hi Something is amiss; requested module template-haskell-2.6.0.0:Language.Haskell.TH differs from name found in the interface file template-haskell:Language.Haskell.TH $ cabal --version cabal-install version 0.15.0 using version 1.15.0 of the Cabal library -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

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What's wrong with these foreign calls?
by Андрей Янкин 12 Jul '12

12 Jul '12

Hi all! I want to use GLFW-b ( http://hackage.haskell.org/packages/archive/GLFW-b/0.1.0.2/doc/html/Graphic…) and I wrote this: initWindow = do True <- GLFW.initialize print =<< GLFW.openGLProfile print =<< GLFW.getGlfwVersion print =<< *GLFW.getGlVersion* print "Trying to open the window" result <- GLFW.openWindow GLFW.defaultDisplayOptions print result And got this: DefaultProfile Version {versionBranch = [2,7,2], versionTags = []} Version {versionBranch = [*-1867951663,39789305,39789305*], versionTags = []} "Trying to open the window" False Why do I always get random numbers as GLVersion? How can I detect incompatibility preventing me from opening a window? Thanks in advance

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Hackage is down?
by Edward Amsden 12 Jul '12

12 Jul '12

http://www.downforeveryoneorjustme.com/hackage.haskell.org -- Edward Amsden Student Computer Science Rochester Institute of Technology www.edwardamsden.com

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Monad with limited backtracking
by Darryn Reid 12 Jul '12

12 Jul '12

Kind Sirs/Madams, Thanks in advance for your patience; the solution will no doubt be obvious to those with greater experience than me. I have formulated a monad to provide limited backtracking for implementing a rewrite system. The success case works fine, but my intention is that on failure the result should contain the list of input symbols consumed up to the failure, and it is this part that I would like some advice about. Code follows: ------------------------------------------------------------------------------- import Control.Monad import Debug.Trace newtype Rewrite a b = Rewrite { run :: Input a -> Result a b } data Input a = Input [a] data Result a b = Fail [a] | Ok b [a] deriving (Eq, Show) instance (Show a) => Monad (Rewrite a) where return y = Rewrite $ \(Input xs) -> Ok y xs p >>= f = Rewrite $ \inp -> case run p inp of Fail xs -> trace ("1.xs=" ++ show xs) $ Fail xs Ok y xs -> case run (f y) (Input xs) of Fail xs' -> trace ("2.xs=" ++ show xs) $ Fail xs okay -> okay instance (Show a) => MonadPlus (Rewrite a) where mzero = Rewrite $ \inp -> Fail [] p `mplus` q = Rewrite $ \inp -> case run p inp of Fail _ -> run q inp okay -> okay (>>=?) ::(Show a) => Rewrite a b -> (b -> Bool) -> Rewrite a b p >>=? f = p >>= \y -> guard (f y) >> return y next :: Rewrite a a next = Rewrite $ \(Input xs) -> case xs of [] -> Fail [] (x:xs') -> Ok x xs' exactly :: (Show a, Eq a) => [a] -> Rewrite a [a] exactly = mapM $ \i -> next >>=? (==i) ------------------------------------------------------------------------------- For example, using ghci: *Main> run (exactly [1,2]) (Input [1,2,3,4]) Ok [1,2] [3,4] which is what I intend. However, while the thing correctly reports failure, I cannot get it to return the list of symbols up to the point of failure: *Main> run (exactly [1,2,3]) (Input [1,2,7,4]) 1.xs=[] 2.xs=[4] 1.xs=[4] 1.xs=[4] 2.xs=[7,4] 1.xs=[7,4] 2.xs=[2,7,4] Fail [2,7,4] *I would like Fail [1,2] here instead* I thank you in advance for any guidance you might offer. Dr Darryn J Reid.

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Solutions for multi-platform compilation?
by Ivan Perez 12 Jul '12

12 Jul '12

Hi, I work developing multi-platform applications in Haskell. This poses the following problem: I cannot compile binaries for windows from linux (AFAIK). I "solved" this problem with the following sledgehammer: I installed windows in a VM, I installed GHC, I installed all the C/C++ headers & binaries of the libraries that I use (Gtk, OpenGL, SDL, OpenCV, etc.) their Haskell counterparts, and I created several scripts that connect to the VM using SSH, push the changes to the repo, cabal clean & cabal install all my packages in sequence without me having to even login into the windows machine. I did this because I was unable to get GHC to run properly in Wine at that time (over 2 years ago). This solution is still unsatisfactory because: 1) It's slow, even though Windows itself works fine (well, as well as windows can work, but it runs at a decent spped, I can play games and all). 2) When I update a library with lots of dependencies, or GHC itself, I have to rebuild almost everything. This is particularly painful with big packages like Gtk, for instance. Because I have to tell cabal where headers and libraries are located, updating a package is almost never an automatic process. I haven't always been able to make GHC "just pick them up" properly with pkg-config. 3) When I make a change in a library with lots of dependencies, recompiling all the packages can take several hours. I don't think it's a problem with my machine: I'm giving a fair amount of resources to windows, and I use a 3Ghz quadcore with 8GB of RAM. Another relevant fact is: I use this for commercial purposes. I have customers, each requiring a completely different program, they do not have infinite budgets and, if there's a problem in the compilation process and something requires my attention and manual intervention too often, my salary per hour can easily drop to a ridiculous amount. If I'm going to redo this, I'd rather just redo it once. Any suggestions? How do you solve this kind of problem in your work environment? Cheers, Ivan

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Control defaulting in ghci
by Roman Cheplyaka 12 Jul '12

12 Jul '12

Is there a way to control defaulting in ghci? (Like the "default" declaration in source files does.) ghci 7.4.1 doesn't accept "default" declarations. I tried loading a module with a "default" declaration, but that also didn't affect the ghci session. It would be ironic if this is possible in source files but not in ghci, since defaulting is much more useful in an interactive session than in modules. -- Roman I. Cheplyaka :: http://ro-che.info/

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