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  • Applying a function with multiple inputs using Map? (Haskell)

    - by Schroedinger
    G'day guys, Trying currently to finish up a bit of homework I'm working on, and having an issue where I'm trying to apply map across a function that accepts multiple inputs. so in the case I'm using processList f (x:xs) = map accelerateList f xs x xs processList is given a floating value (f) and a List that it sorts into another List Accelerate List takes a floating value (f) a List and a List Object through which it returns another List Object I know my Accelerate List code is correct, but I cannot for the life of me get the syntax for this code working: processList :: Float -> [Object] -> [Object] accelerate f [] = [] accelerate f [x] = [(accelerateForce f x x)] accelerate f (x:xs) = map accelerateList f xs x xs Any ideas? I've been scratching my head for about 3 hours now. I know it's something really simple.

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  • Does any method exist quickly to detect valid range versions of used library

    - by daneel-yaitskov
    I'm a beginner Haskell programmer. I have written some useful code for the last six month. And I want to release a library from it. The code will use system installation cabal as any Haskell library. A library is released with cabal has a meta data file where there is a logical predicate from the libraries and their versions. A developer usually uses one set libraries. It tediously care a set of the sets libraries. How to know either my library is compiled successfully or not for some subset libraries?

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  • How to protect against GHC7 compiled programs taking all memory?

    - by Petr Pudlák
    When playing with various algorithms in Haskell it often happens to me that I create a program with a memory leak, as it often happens with lazy evaluation. The program taking all the memory isn't really fun, I often have difficulty killing it if I realize it too late. When using GHC6 I simply had export GHCRTS='-M384m' in my .bashrc. But in GHC7 they added a security measure that unless a program is compiled with -rtsopts, it simply fails when it is given any RTS option either on a command line argument or in GHCRTS. Unfortunately, almost no Haskell programs are compiled with this flag, so setting this variable makes everything to fail (as I discovered in After upgrading to GHC7, all programs suddenly fail saying "Most RTS options are disabled. Link with -rtsopts to enable them."). Any ideas how to make any use of GHCRTS with GHC7, or another convenient way how to prevent my programs taking all memory?

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  • Type patterns in Haskell

    - by finnsson
    I'm trying to compile a simple example of generic classes / type patterns (see http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-classes.html) in Haskell but it won't compile. Any ideas about what's wrong with the code would be helpful. According to the documentation there should be a module Generics with the data types Unit, :*:, and :+: but ghc (6.12.1) complaints about Not in scope: data constructor 'Unit' etc. It seems like there's a package instant-generics with the data types :*:, :+: and U but when I import that module (instead of Generics) I get the error Illegal type pattern in the generic bindings {myPrint _ = ""} The complete source code is import Generics.Instant class MyPrint a where myPrint :: a -> String myPrint {| U |} _ = "" myPrint {| a :*: b |} (x :*: y) = "" (show x) ++ ":*:" ++ (show y) myPrint {| a :+: b |} _ = "" data Foo = Foo String instance MyPrint a => MyPrint a main = myPrint $ Foo "hi" and I compile it using ghc --make Foo.hs -fglasgow-exts -XGenerics -XUndecidableInstances P.S. The module Generics export no data types, only the functions: canDoGenerics mkGenericRhs mkTyConGenericBinds validGenericInstanceType validGenericMethodType

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  • Warning: newtype `CInt' is used in an FFI declaration,

    - by vivian
    When building gtk2hs-buildtools with ghc 7.4.2, I get the following warning: c2hs/toplevel/C2HSConfig.hs:110:1: Warning: newtype `CInt' is used in an FFI declaration, but its constructor is not in scope. This will become an error in GHC 7.6.1. When checking declaration: foreign import ccall safe "static bitfield_direction" bitfield_direction :: CInt I get similar warnings with FFI calls, even though I have import Foreign.C.Types(CInt). What is the correct way of getting rid of this warning?

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  • Why toInteger :: Int -> Integer is lazy?

    - by joppux
    I have the following code: {-# NOINLINE i2i #-} i2i :: Int -> Integer i2i x = toInteger x main = print $ i2i 2 Running GHC with -ddump-simpl flag gives: [Arity 1 NoCafRefs Str: DmdType U(L)] Main.i2i = GHC.Real.toInteger1 Seems that conversion from Int to Integer is lazy. Why is it so - is there a case when I can have (toInteger _|_ ::Int) /= _|_ ?

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  • Compiled Haskell libraries with FFI imports are invalid when imported into GHCI

    - by John Millikin
    I am using GHC 6.12.1, in Ubuntu 10.04 When I try to use the FFI syntax for static storage, only modules running in interpreted mode (ie GHCI) work properly. Compiled modules have invalid pointers, and do not work. I'd like to know whether anybody can reproduce the problem, whether this an error in my code or GHC, and (if the latter) whether it's a known issue. I'm using sys_siglist because it's present in a standard library on my system, but I don't believe the actual storage used matters (I discovered this while writing a binding to libidn). If it helps, sys_siglist is defined in <signal.h> as: extern __const char *__const sys_siglist[_NSIG]; I thought this type might be the problem, so I also tried wrapping it in a plain C procedure: #include<stdio.h> const char **test_ffi_import() { printf("C think sys_siglist = %X\n", sys_siglist); return sys_siglist; } However, importing that doesn't change the result, and the printf() call prints the same pointer value as show siglist_a. My suspicion is that it's something to do with static and dynamic library loading. Update: somebody in #haskell suggested this might be 64-bit specific; if anybody tries to reproduce it, can you mention your architecture and whether it worked in a comment? Code as follows: -- A.hs {-# LANGUAGE ForeignFunctionInterface #-} module A where import Foreign import Foreign.C foreign import ccall "&sys_siglist" siglist_a :: Ptr CString -- -- B.hs {-# LANGUAGE ForeignFunctionInterface #-} module B where import Foreign import Foreign.C foreign import ccall "&sys_siglist" siglist_b :: Ptr CString -- -- Main.hs {-# LANGUAGE ForeignFunctionInterface #-} module Main where import Foreign import Foreign.C import A import B foreign import ccall "&sys_siglist" siglist_main :: Ptr CString main = do putStrLn $ "siglist_a = " ++ show siglist_a putStrLn $ "siglist_b = " ++ show siglist_b putStrLn $ "siglist_main = " ++ show siglist_main peekSiglist "a " siglist_a peekSiglist "b " siglist_b peekSiglist "main" siglist_main peekSiglist name siglist = do ptr <- peekElemOff siglist 2 str <- maybePeek peekCString ptr putStrLn $ "siglist_" ++ name ++ "[2] = " ++ show str I would expect something like this output, where all pointer values identical and valid: $ runhaskell Main.hs siglist_a = 0x00007f53a948fe00 siglist_b = 0x00007f53a948fe00 siglist_main = 0x00007f53a948fe00 siglist_a [2] = Just "Interrupt" siglist_b [2] = Just "Interrupt" siglist_main[2] = Just "Interrupt" However, if I compile A.hs (with ghc -c A.hs), then the output changes to: $ runhaskell Main.hs siglist_a = 0x0000000040378918 siglist_b = 0x00007fe7c029ce00 siglist_main = 0x00007fe7c029ce00 siglist_a [2] = Nothing siglist_b [2] = Just "Interrupt" siglist_main[2] = Just "Interrupt"

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  • Why do compiled Haskell libraries see invalid static FFI storage?

    - by John Millikin
    I am using GHC 6.12.1, in Ubuntu 10.04 When I try to use the FFI syntax for static storage, only modules running in interpreted mode (ie GHCI) work properly. Compiled modules have invalid pointers, and do not work. I'd like to know whether anybody can reproduce the problem, whether this an error in my code or GHC, and (if the latter) whether it's a known issue. Given the following three modules: -- A.hs {-# LANGUAGE ForeignFunctionInterface #-} module A where import Foreign import Foreign.C foreign import ccall "&sys_siglist" siglist_a :: Ptr CString -- -- B.hs {-# LANGUAGE ForeignFunctionInterface #-} module B where import Foreign import Foreign.C foreign import ccall "&sys_siglist" siglist_b :: Ptr CString -- -- Main.hs {-# LANGUAGE ForeignFunctionInterface #-} module Main where import Foreign import Foreign.C import A import B foreign import ccall "&sys_siglist" siglist_main :: Ptr CString main = do putStrLn $ "siglist_a = " ++ show siglist_a putStrLn $ "siglist_b = " ++ show siglist_b putStrLn $ "siglist_main = " ++ show siglist_main peekSiglist "a " siglist_a peekSiglist "b " siglist_b peekSiglist "main" siglist_main peekSiglist name siglist = do ptr <- peekElemOff siglist 2 str <- maybePeek peekCString ptr putStrLn $ "siglist_" ++ name ++ "[2] = " ++ show str I would expect something like this output, where all pointer values identical and valid: $ runhaskell Main.hs siglist_a = 0x00007f53a948fe00 siglist_b = 0x00007f53a948fe00 siglist_main = 0x00007f53a948fe00 siglist_a [2] = Just "Interrupt" siglist_b [2] = Just "Interrupt" siglist_main[2] = Just "Interrupt" However, if I compile A.hs (with ghc -c A.hs), then the output changes to: $ runhaskell Main.hs siglist_a = 0x0000000040378918 siglist_b = 0x00007fe7c029ce00 siglist_main = 0x00007fe7c029ce00 siglist_a [2] = Nothing siglist_b [2] = Just "Interrupt" siglist_main[2] = Just "Interrupt"

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  • in haskell, why do I need to specify type constraints, why can't the compiler figure them out?

    - by Steve
    Consider the function, add a b = a + b This works: *Main> add 1 2 3 However, if I add a type signature specifying that I want to add things of the same type: add :: a -> a -> a add a b = a + b I get an error: test.hs:3:10: Could not deduce (Num a) from the context () arising from a use of `+' at test.hs:3:10-14 Possible fix: add (Num a) to the context of the type signature for `add' In the expression: a + b In the definition of `add': add a b = a + b So GHC clearly can deduce that I need the Num type constraint, since it just told me: add :: Num a => a -> a -> a add a b = a + b Works. Why does GHC require me to add the type constraint? If I'm doing generic programming, why can't it just work for anything that knows how to use the + operator? In C++ template programming, you can do this easily: #include <string> #include <cstdio> using namespace std; template<typename T> T add(T a, T b) { return a + b; } int main() { printf("%d, %f, %s\n", add(1, 2), add(1.0, 3.4), add(string("foo"), string("bar")).c_str()); return 0; } The compiler figures out the types of the arguments to add and generates a version of the function for that type. There seems to be a fundamental difference in Haskell's approach, can you describe it, and discuss the trade-offs? It seems to me like it would be resolved if GHC simply filled in the type constraint for me, since it obviously decided it was needed. Still, why the type constraint at all? Why not just compile successfully as long as the function is only used in a valid context where the arguments are in Num? Thank you.

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  • ghc6 install trouble: hGetContents: invalid argument (invalid UTF-8 byte sequence)

    - by olimay
    Having trouble installing ghc6. Here's what seems to be the relevant error that comes up when I try to (apt-get|aptitude) install ghc6: A package failed to install. Trying to recover: Setting up ghc6 (6.12.1-13ubuntu1) ... ghc-pkg: /home/opm/.ghc/i386-linux-6.12.1/package.conf.d/unix-compat-0.2-edefa7bced91ebe610d455bab466e200.conf: hGetContents: invalid argument (invalid UTF-8 byte sequence) (Here's the full output, if you're interested: http://paste.ubuntu.com/566475/ ) This still happens after apt-get clean and apt-get update. My searching around has not really helped me understand what's going on, except that it might be caused by a mismatch in locale. So, here's the output of locale too: LANG=en_US.utf8 LANGUAGE=en_US:en LC_CTYPE="en_US.utf8" LC_NUMERIC="en_US.utf8" LC_TIME="en_US.utf8" LC_COLLATE="en_US.utf8" LC_MONETARY="en_US.utf8" LC_MESSAGES="en_US.utf8" LC_PAPER="en_US.utf8" LC_NAME="en_US.utf8" LC_ADDRESS="en_US.utf8" LC_TELEPHONE="en_US.utf8" LC_MEASUREMENT="en_US.utf8" LC_IDENTIFICATION="en_US.utf8" LC_ALL= Any ideas? Additional background: this all seems very strange to me, because I used to have ghc6 installed correctly--I use XMonad as my main window manager most of the time. I tried to install haskell-platform (through apt), which failed and told me that there was something wrong with ghc6, and so I reinstalled ghc6 and began to get the above error message. (Originally posted here to SuperUser, until I remembered today that this SE site existed.)

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  • C compiler selection in cabal package

    - by ony
    Today I've tried C compiler (Clang) for C code I use in my haskell library and found that I can gain speed increase in comparsing with my system compiler (GCC 4.4.3) from 426.404 Gbit/s to 0.823 Tbit/s So I decided to add some flags to control the way that C source file is compiled (i.e. something like use-clang, use-intel etc.). Snippet of cabal package description file: C-Sources: c_lib/tiger.c Include-Dirs: c_lib Install-Includes: tiger.h if flag(debug) GHC-Options: -debug -Wall -fno-warn-orphans CPP-Options: -DDEBUG CC-Options: -DDEBUG -g else GHC-Options: -Wall -fno-warn-orphans Question is: which options in descritpion file need to be modified to change C compiler used to compile "c_lib/tiger.c"? I did found only CC-Options.

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  • ghc6 install trouble: hGetContents: invalid argument (invalid UTF-8 byte sequence)

    - by olimay
    Having trouble installing ghc6 on Ubuntu Maverick via apt. Here's what seems to be the relevant error that comes up when I try to (apt-get|aptitude) install ghc6: A package failed to install. Trying to recover: Setting up ghc6 (6.12.1-13ubuntu1) ... ghc-pkg: /home/opm/.ghc/i386-linux-6.12.1/package.conf.d/unix-compat-0.2-edefa7bced91ebe610d455bab466e200.conf: hGetContents: invalid argument (invalid UTF-8 byte sequence) (Here's the full output, if you're interested: http://paste.ubuntu.com/566475/ ) This still happens after apt-get clean and apt-get update. My searching around has not really helped me understand what's going on, except that it might be caused by a mismatch in locale. So, here's the output of locale too: LANG=en_US.utf8 LANGUAGE=en_US:en LC_CTYPE="en_US.utf8" LC_NUMERIC="en_US.utf8" LC_TIME="en_US.utf8" LC_COLLATE="en_US.utf8" LC_MONETARY="en_US.utf8" LC_MESSAGES="en_US.utf8" LC_PAPER="en_US.utf8" LC_NAME="en_US.utf8" LC_ADDRESS="en_US.utf8" LC_TELEPHONE="en_US.utf8" LC_MEASUREMENT="en_US.utf8" LC_IDENTIFICATION="en_US.utf8" LC_ALL= Any ideas? Additional background: this all seems very strange to me, because I used to have ghc6 installed correctly--I use XMonad as my main window manager most of the time. I tried to install haskell-platform (through apt), which failed and told me that there was something wrong with ghc6, and so I reinstalled ghc6 and began to get the above error message.

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  • Weirdness with cabal, HTF, and HUnit assertions

    - by rampion
    So I'm trying to use HTF to run some HUnit-style assertions % cat tests/TestDemo.hs {-# OPTIONS_GHC -Wall -F -pgmF htfpp #-} module Main where import Test.Framework import Test.HUnit.Base ((@?=)) import System.Environment (getArgs) -- just run some tests main :: IO () main = getArgs >>= flip runTestWithArgs Main.allHTFTests -- all these tests should fail test_fail_int1 :: Assertion test_fail_int1 = (0::Int) @?= (1::Int) test_fail_bool1 :: Assertion test_fail_bool1 = True @?= False test_fail_string1 :: Assertion test_fail_string1 = "0" @?= "1" test_fail_int2 :: Assertion test_fail_int2 = [0::Int] @?= [1::Int] test_fail_string2 :: Assertion test_fail_string2 = "true" @?= "false" test_fail_bool2 :: Assertion test_fail_bool2 = [True] @?= [False] And when I use ghc --make, it seems to work correctly. % ghc --make tests/TestDemo.hs [1 of 1] Compiling Main ( tests/TestDemo.hs, tests/TestDemo.o ) Linking tests/TestDemo ... % tests/TestDemoA ... * Tests: 6 * Passed: 0 * Failures: 6 * Errors: 0 Failures: * Main:fail_int1 (tests/TestDemo.hs:9) * Main:fail_bool1 (tests/TestDemo.hs:12) * Main:fail_string1 (tests/TestDemo.hs:15) * Main:fail_int2 (tests/TestDemo.hs:19) * Main:fail_string2 (tests/TestDemo.hs:22) * Main:fail_bool2 (tests/TestDemo.hs:25) But when I use cabal to build it, not all the tests that should fail, fail. % cat Demo.cabal ... executable test-demo build-depends: base >= 4, HUnit, HTF main-is: TestDemo.hs hs-source-dirs: tests % cabal configure Resolving dependencies... Configuring Demo-0.0.0... % cabal build Preprocessing executables for Demo-0.0.0... Building Demo-0.0.0... [1 of 1] Compiling Main ( tests/TestDemo.hs, dist/build/test-demo/test-demo-tmp/Main.o ) Linking dist/build/test-demo/test-demo ... % dist/build/test-demo/test-demo ... * Tests: 6 * Passed: 3 * Failures: 3 * Errors: 0 Failures: * Main:fail_int2 (tests/TestDemo.hs:23) * Main:fail_string2 (tests/TestDemo.hs:26) * Main:fail_bool2 (tests/TestDemo.hs:29) What's going wrong and how can I fix it?

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  • Beginning Haskell: "not in scope" Unprecedented error

    - by user1071838
    So I just started learning Haskell, and this (http://learnyouahaskell.com) nifty book is giving a lot of help. So yesterday I wrote in a text file doubleMe x = x + x and saved it as double.hs. So after saving that I open up my command prompt, CD to the right folder, type in "ghci" to get haskell started, and then type in >doubleMe 5 10 and everything seems to work. Now today, I do the same thing and this happens (actual copy paste from command line) . . . C:\Users\myName\haskell>ghci GHCi, version 7.0.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Prelude> :l double.hs [1 of 1] Compiling Main ( double.hs, interpreted ) Ok, modules loaded: Main. *Main> doubleMe 5 <interactive>:1:1: Not in scope: `doubleMe' So basically, everything was working fine, but now haskell can't find the function I wrote in double.hs. Can anyone tell what is going on? I'm pretty lost and confused. This is just a guess but does it have to do with *Main at all? Thanks for the help.

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  • Inspirational software for end-users written in Haskell?

    - by Lenny222
    I think great technology ist invisible. Besides the usual suspects (GHC, Xmonad, proprietary trading software) what great examples are there for end-user software written in Haskell? I think good examples are FreeArc, Hledger and "Nikki And The Robots". Do you have more examples (full blown GUI apps, small CLI tools, etc)? Edit: For example i am fascinated by Wings3D, because while written in Erlang, users can not tell that. It just works. Among Haskell's weak spots are cross-platform GUIs. There are not many GUI apps written in Haskkel in general and most of them are no easy to use, install or even compile. What are good examples to learn from how to make hard things look easy?

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  • Languages with C/C++ output [closed]

    - by Vag
    Which languages have compilers able to emit plain standard C/C++ code? For a start: Haxe // uses Boehm GC Haskell (JHC) Haskell (old GHC) // -fvia-c, removed recently (emitted code is super ugly) Clay ATS Cython RPython (Shed Skin) // experimental RPython (PyPy) Python (Nuitka) // although author claims there are no speedups Common Lisp (ECL) COBOL (OpenCobol) Scheme (Chicken) APL // So far I've not found working implementation available for free download Ur/Web // GCC-specific output, and intended to be used only for web developments (included for completeness only) I'd like to build comprehensive up-to-date list but found only these ones so far. I've tested only Haxe and it works pretty well and quite fast. What about other ones? What is your expirience? How much ugly is generated code? Update. Any language chains (e.g. X - Scheme - C) will be perfectly OK as answer if its use is practical enough and suited for production use.

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  • Performance of looping over an Unboxed array in Haskell

    - by Joey Adams
    First of all, it's great. However, I came across a situation where my benchmarks turned up weird results. I am new to Haskell, and this is first time I've gotten my hands dirty with mutable arrays and Monads. The code below is based on this example. I wrote a generic monadic for function that takes numbers and a step function rather than a range (like forM_ does). I compared using my generic for function (Loop A) against embedding an equivalent recursive function (Loop B). Having Loop A is noticeably faster than having Loop B. Weirder, having both Loop A and B together is faster than having Loop B by itself (but slightly slower than Loop A by itself). Some possible explanations I can think of for the discrepancies. Note that these are just guesses: Something I haven't learned yet about how Haskell extracts results from monadic functions. Loop B faults the array in a less cache efficient manner than Loop A. Why? I made a dumb mistake; Loop A and Loop B are actually different. Note that in all 3 cases of having either or both Loop A and Loop B, the program produces the same output. Here is the code. I tested it with ghc -O2 for.hs using GHC version 6.10.4 . import Control.Monad import Control.Monad.ST import Data.Array.IArray import Data.Array.MArray import Data.Array.ST import Data.Array.Unboxed for :: (Num a, Ord a, Monad m) => a -> a -> (a -> a) -> (a -> m b) -> m () for start end step f = loop start where loop i | i <= end = do f i loop (step i) | otherwise = return () primesToNA :: Int -> UArray Int Bool primesToNA n = runSTUArray $ do a <- newArray (2,n) True :: ST s (STUArray s Int Bool) let sr = floor . (sqrt::Double->Double) . fromIntegral $ n+1 -- Loop A for 4 n (+ 2) $ \j -> writeArray a j False -- Loop B let f i | i <= n = do writeArray a i False f (i+2) | otherwise = return () in f 4 forM_ [3,5..sr] $ \i -> do si <- readArray a i when si $ forM_ [i*i,i*i+i+i..n] $ \j -> writeArray a j False return a primesTo :: Int -> [Int] primesTo n = [i | (i,p) <- assocs . primesToNA $ n, p] main = print $ primesTo 30000000

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  • Installing EclipseFP on Mac OS X

    - by Dom Kennedy
    I am trying to install EclipseFP. I'm running OS X Mavericks. I've tried following both the official installation instructions and the advice in this answer on SU, but I'm still having the same problem. I can get the plugin itself installed painlessly using Help -> Install New Software..., Bbut when I restart and switch to the Haskell perspective, things start to go wrong. The installation instructions tells me that I should receive a prompt to install BuildWrapper and Scion Browser. I do not receive this prompt. Furthermore, if I create a new Haskell project, my code has no syntax highlighting, and the Hoogle search feature does not appear to do anything. It's clear that the plugin is not set up correctly yet. I've tried running cabal update in Terminal, but this does not change anything. After several attempts going round in circles with this on Eclipse Juno, I uninstalled Eclispe and the Haskell Platform and performed a clean install of Eclipse Luna and the latest Haskell Platform. However, the problems are persisting. I've tried going into Preferences to see if I could sort any of this out manually. I should initially point out that my GHC installation seems to be correctly references under Preferences -> Haskell Implementations Under Haskell -> Helper executables, there are areas for configuring the options of both BuildWrapper and Scion Browser. At present, both are blank. I tried clicking the Install from Hackage... button beside each of them with no success; I receive an error message saying Expected executable <workspace>/.metadata/.plugins/net.sf.eclipsefp.haskell.ui/sandbox/.cabal-sandbox/bin/buildwrapper not found!` (replace buildwrapper for scion-browser and the message is the same) The Eclipse console displays the following exception after doing the above with BuildWrapper: src/Language/Haskell/BuildWrapper/GHCStorage.hs:313:32: Not in scope: data constructor ‘MatchGroup’ cabal.real: Error: some packages failed to install: buildwrapper-0.7.4 failed during the building phase. The exception was: ExitFailure 1 and after doing it for Scion-Browser: zip-archive-0.2.3.4 (reinstall) changes: text-1.1.0.0 -> 0.11.3.1 pandoc-1.12.3.3 (latest: 1.13) -http-conduit (new version) Graphalyze-0.14.1.0 (reinstall) changes: pandoc-1.12.4.2 -> 1.12.3.3, text-1.1.0.0 -> 0.11.3.1 cabal.real: The following packages are likely to be broken by the reinstalls: pandoc-1.12.4.2 unordered-containers-0.2.4.0 aeson-0.7.0.4 scientific-0.2.0.2 case-insensitive-1.1.0.3 HTTP-4000.2.10 Use --force-reinstalls if you want to install anyway. After receiving similar results as the above on previous attempts, I've tried using force-reinstalls and ended up at more dead ends. I am at a loss as to what is wrong and how to solve this. I should point out that my GHC installation appears to be correctly configured under Preferences -> Haskell -> Haskell Implementations. Apologies if any of this information is irrelevant, I'm just not really sure what is important and what isn't at this point. Any help anyone could provide me with would be greatly appreciated.

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  • Why am I not getting an sRGB default framebuffer?

    - by Aaron Rotenberg
    I'm trying to make my OpenGL Haskell program gamma correct by making appropriate use of sRGB framebuffers and textures, but I'm running into issues making the default framebuffer sRGB. Consider the following Haskell program, compiled for 32-bit Windows using GHC and linked against 32-bit freeglut: import Foreign.Marshal.Alloc(alloca) import Foreign.Ptr(Ptr) import Foreign.Storable(Storable, peek) import Graphics.Rendering.OpenGL.Raw import qualified Graphics.UI.GLUT as GLUT import Graphics.UI.GLUT(($=)) main :: IO () main = do (_progName, _args) <- GLUT.getArgsAndInitialize GLUT.initialDisplayMode $= [GLUT.SRGBMode] _window <- GLUT.createWindow "sRGB Test" -- To prove that I actually have freeglut working correctly. -- This will fail at runtime under classic GLUT. GLUT.closeCallback $= Just (return ()) glEnable gl_FRAMEBUFFER_SRGB colorEncoding <- allocaOut $ glGetFramebufferAttachmentParameteriv gl_FRAMEBUFFER gl_FRONT_LEFT gl_FRAMEBUFFER_ATTACHMENT_COLOR_ENCODING print colorEncoding allocaOut :: Storable a => (Ptr a -> IO b) -> IO a allocaOut f = alloca $ \ptr -> do f ptr peek ptr On my desktop (Windows 8 64-bit with a GeForce GTX 760 graphics card) this program outputs 9729, a.k.a. gl_LINEAR, indicating that the default framebuffer is using linear color space, even though I explicitly requested an sRGB window. This is reflected in the rendering results of the actual program I'm trying to write - everything looks washed out because my linear color values aren't being converted to sRGB before being written to the framebuffer. On the other hand, on my laptop (Windows 7 64-bit with an Intel graphics chip), the program prints 0 (huh?) and I get an sRGB default framebuffer by default whether I request one or not! And on both machines, if I manually create a non-default framebuffer bound to an sRGB texture, the program correctly prints 35904, a.k.a. gl_SRGB. Why am I getting different results on different hardware? Am I doing something wrong? How can I get an sRGB framebuffer consistently on all hardware and target OSes?

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  • How to use GD binding in Haskell?

    - by milosz
    I've installed the GD package (http://hackage.haskell.org/package/gd-3000.4.0) using cabal. When I try to compile the program which uses GD I receive an error: [mp262554@students:~/jpp/haskell]$ ghc gd.hs compilation IS NOT required gd.o: In function `sV8_info': (.text+0x1bf): undefined reference to `gdzm3000zi4zi0_GraphicsziGD_saveJpegFile_closure' gd.o: In function `sUY_info': (.text+0x3be): undefined reference to `gdzm3000zi4zi0_GraphicsziGD_drawLine_closure' gd.o: In function `sUI_info': (.text+0x51a): undefined reference to `gdzm3000zi4zi0_GraphicsziGD_newImage_closure' gd.o: In function `sUI_info': (.text+0x6a5): undefined reference to `__stginit_gdzm3000zi4zi0_GraphicsziGD_' gd.o: In function `sVc_srt': (.data+0x34): undefined reference to `gdzm3000zi4zi0_GraphicsziGD_drawLine_closure' gd.o: In function `sVc_srt': (.data+0x38): undefined reference to `gdzm3000zi4zi0_GraphicsziGD_saveJpegFile_closure' gd.o: In function `sUI_srt': (.data+0x4c): undefined reference to `gdzm3000zi4zi0_GraphicsziGD_newImage_closure' collect2: ld returned 1 exit status

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  • How to define a function in ghci across multiple lines

    - by Peter McGrattan
    I'm trying to define any simple function that spans multiple lines in ghci, take the following as an example: let abs n | n >= 0 = n | otherwise = -n So far I've tried pressing Enter after the first line: Prelude> let abs n | n >= 0 = n Prelude> | otherwise = -n <interactive>:1:0: parse error on input `|' I've also attempted to use the :{ and :} commands but I don't get far: Prelude> :{ unknown command ':{' use :? for help. I'm using GHC Interactive version 6.6 for Haskell 98 on Linux, what am I missing?

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  • How to view output .mp files from Functional MetaPost

    - by Jared Updike
    I'm interested in using Functional MetaPost on Mac OS X: http://cryp.to/funcmp/ I'm looking for a tutorial like: http://haskell.org/haskellwiki/Haskell_in_5_steps but for a trivial FuncMP example, i.e. using GHC, I can compile something simple such as: import FMP myPicture = text "blah" main = generate "foo" 1 myPicture but I can't figure out how to view this foo.1.mp output. (It gives a runtime error about not finding 'virmp'; my MetaPost binary is 'mpost'; I can't figure out how to override this Parameter or what my .FunMP file is or should be doing...) I can run mpost on that but the output (foo.1.1) is what, PostScript? EPS? How do I use this? (I imagine I just need a simple LaTeX file with an EPS figure in it or something...) Preferably, I'd like to generate output (.ps or .pdf that I can view) so I an actually get somewhere with Functional MetaPost, learning it, playing with it, not banging my head against paths and binaries and shell commands.

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