- Beginners - Haskell.org

How to check the help page of a function?
by Peng Yu 17 May '15

17 May '15

Hi, I can not find how to check the help page of a function. For example, I want to check the help page of "head". How should I do it? (":help" doesn't seem to help.) -- Regards, Peng

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ld: warning: directory not found for option '-L/private/tmp/ghc20150401-90656-rxy9sj/ghc-7.10.1/gmp-static'
by Peng Yu 17 May '15

17 May '15

Hi, I see the following error. Does anybody know what is wrong? Thanks. $ cat hello.hs main = putStrLn "Hello, World!" $ ghc -o hello hello.hs [1 of 1] Compiling Main ( hello.hs, hello.o ) Linking hello ... ld: warning: directory not found for option '-L/private/tmp/ghc20150401-90656-rxy9sj/ghc-7.10.1/gmp-static' -- Regards, Peng

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Parser
by Mike Houghton 17 May '15

17 May '15

Hi, I’me writing a simple parser and can test it in GHCI parseTest moveParser "(1,2)->(3,3)” and I get what I expect i.e. Move {from = Location 1 2, to = Location 3 3} I now have a text file (test.txt) with lots of (1,2)->(3,3) (3,6)->(3,9) etc etc and I really can’t see how I get the contents of the text file into the parser!! I have main = do handle <- openFile "test.txt" ReadMode contents <- hGetContents handle !! what goes here!!! - how do I invoke moveParser with contents ?? Thanks Mike

3 3

Building glib
by C W Rose 15 May '15

15 May '15

I've been trying to build the glib package (pretty much any version) for a few days now, with no success. The sequence of results is: =================================================================== cwr@sixpence cabal $ cabal --verbose --global --package-db=/opt/cabal/package.conf.d install glib-0.12.5.4 '/opt/cabal/bin/alex' '--version' '/opt/cabal/bin/cpphs' '--version' '/usr/bin/gcc' '-dumpversion' '/opt/cabal/bin/haddock' '--version' '/opt/cabal/bin/happy' '--version' '/usr/bin/hpc' 'version' looking for tool hsc2hs near compiler in /usr/bin found hsc2hs in /usr/bin/hsc2hs '/usr/bin/hsc2hs' '--version' '/opt/cabal/bin/HsColour' '-version' '/usr/bin/ghc' '-c' '/tmp/6826.c' '-o' '/tmp/6826.o' '/usr/bin/ld' '-x' '-r' '/tmp/6826.o' '-o' '/tmp/6827.o' '/usr/bin/pkg-config' '--version' '/bin/tar' '--help' Reading available packages... Warning: The package list for 'hackage.haskell.org' is 52.1 days old. Run 'cabal update' to get the latest list of available packages. Choosing modular solver. Resolving dependencies... Ready to install glib-0.12.5.4 Waiting for install task to finish... Extracting /opt/cabal/packages/hackage.haskell.org/glib/0.12.5.4/glib-0.12.5.4.tar.gz to /tmp/glib-0.12.5.4-6826... Updating glib.cabal with the latest revision from the index. creating /tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist/setup creating /tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist creating /tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist/setup copy /tmp/glib-0.12.5.4-6826/glib-0.12.5.4/Setup.hs to /tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist/setup/setup.hs '/usr/bin/ghc' '--make' '-odir' '/tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist/setup' '-hidir' '/tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist/setup' '-i' '-i/tmp/glib-0.12.5.4-6826/glib-0.12.5.4' '-package-db' '/opt/cabal/package.conf.d' '-package-id' 'Cabal-1.22.1.1-98c5a01d59dd973fd7113dbb82e82560' '/tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist/setup/setup.hs' '-o' '/tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist/setup/setup' '-threaded' [1 of 2] Compiling SetupWrapper ( /tmp/glib-0.12.5.4-6826/glib-0.12.5.4/SetupWrapper.hs, /tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist/setup/SetupWrapper.o ) /tmp/glib-0.12.5.4-6826/glib-0.12.5.4/SetupWrapper.hs:118:28: Warning: In the use of `configCompiler' (imported from Distribution.Simple.Configure): Deprecated: "'configCompiler' is deprecated. Use 'configCompilerEx' instead." [2 of 2] Compiling Main ( /tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist/setup/setup.hs, /tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist/setup/Main.o ) Linking /tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist/setup/setup ... /tmp/glib-0.12.5.4-6826/glib-0.12.5.4/dist/setup/setup configure --verbose=2 --ghc --prefix=/opt/cabal --bindir=/opt/cabal/bin --libdir=/opt/cabal/lib --libsubdir=glib-0.12.5.4/ghc-7.6.3 --libexecdir=/opt/cabal/libexec --datadir=/opt/cabal/share --datasubdir=glib-0.12.5.4 --docdir=/opt/cabal/share/doc/glib-0.12.5.4 --htmldir=/opt/cabal/share/doc/glib-0.12.5.4/html --haddockdir=/opt/cabal/share/doc/glib-0.12.5.4/html --sysconfdir=/opt/cabal/etc --enable-library-profiling --enable-optimization=2 --global --package-db=/opt/cabal/package.conf.d --flags=closure_signals --dependency=utf8-string=utf8-string-0.3.8-51169ff3d90963aa54c0a13eee5c3a53 --dependency=containers=containers-0.5.0.0-e7e1a93d7945e93a00ce12660e9ff290 --dependency=base=base-4.6.0.1-220b875e77822b0e1bf50c8f35d37dff --disable-tests --exact-configuration --disable-benchmarks [1 of 2] Compiling Gtk2HsSetup ( Gtk2HsSetup.hs, dist/setup-wrapper/Gtk2HsSetup.o ) [2 of 2] Compiling Main ( SetupMain.hs, dist/setup-wrapper/Main.o ) Linking dist/setup-wrapper/setup ... unrecognized option `--sysconfdir=/opt/cabal/etc' unrecognized option `--dependency=utf8-string=utf8-string-0.3.8-51169ff3d90963aa54c0a13eee5c3a53' unrecognized option `--dependency=containers=containers-0.5.0.0-e7e1a93d7945e93a00ce12660e9ff290' unrecognized option `--dependency=base=base-4.6.0.1-220b875e77822b0e1bf50c8f35d37dff' unrecognized option `--exact-configuration' Failed to install glib-0.12.5.4 World file is already up to date. cabal: Error: some packages failed to install: glib-0.12.5.4 failed during the configure step. The exception was: ExitFailure 1 cwr@sixpence cabal $ =================================================================== Moving to the default version of glib, I then get: =================================================================== cwr@sixpence cabal $ cabal --verbose --global --package-db=/opt/cabal/package.conf.d install glib Reading available packages... Choosing modular solver. Resolving dependencies... Ready to install glib-0.13.1.0 Waiting for install task to finish... Extracting /opt/cabal/packages/hackage.haskell.org/glib/0.13.1.0/glib-0.13.1.0.tar.gz to /tmp/glib-0.13.1.0-3703... Updating glib.cabal with the latest revision from the index. creating /tmp/glib-0.13.1.0-3703/glib-0.13.1.0/dist/setup creating /tmp/glib-0.13.1.0-3703/glib-0.13.1.0/dist creating /tmp/glib-0.13.1.0-3703/glib-0.13.1.0/dist/setup Failed to install glib-0.13.1.0 World file is already up to date. cabal: Error: some packages failed to install: glib-0.13.1.0 failed during the configure step. The exception was: user error (The package 'glib' requires Cabal library version -any && >=1.18 but no suitable version is installed.) cwr@sixpence cabal $ cabal --version cabal-install version 1.18.0.2 using version 1.18.1.2 of the Cabal library cwr@sixpence cabal $ =================================================================== And moving to the default version of cabal, I get: =================================================================== cwr@sixpence cabal $ cabal --verbose --global --package-db=/opt/cabal/package.conf.d install glib '/opt/cabal/bin/alex' '--version' '/opt/cabal/bin/cpphs' '--version' '/usr/bin/gcc' '-dumpversion' '/opt/cabal/bin/haddock' '--version' '/opt/cabal/bin/happy' '--version' '/usr/bin/hpc' 'version' looking for tool hsc2hs near compiler in /usr/bin found hsc2hs in /usr/bin/hsc2hs '/usr/bin/hsc2hs' '--version' '/opt/cabal/bin/HsColour' '-version' '/usr/bin/ghc' '-c' '/tmp/4186.c' '-o' '/tmp/4186.o' '/usr/bin/ld' '-x' '-r' '/tmp/4186.o' '-o' '/tmp/4187.o' '/usr/bin/pkg-config' '--version' '/bin/tar' '--help' Reading available packages... Warning: The package list for 'hackage.haskell.org' is 51.4 days old. Run 'cabal update' to get the latest list of available packages. Choosing modular solver. Resolving dependencies... Ready to install glib-0.13.1.0 Waiting for install task to finish... Extracting /opt/cabal/packages/hackage.haskell.org/glib/0.13.1.0/glib-0.13.1.0.tar.gz to /tmp/glib-0.13.1.0-4186... Updating glib.cabal with the latest revision from the index. creating /tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist/setup creating /tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist creating /tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist/setup copy /tmp/glib-0.13.1.0-4186/glib-0.13.1.0/Setup.hs to /tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist/setup/setup.hs '/usr/bin/ghc' '--make' '-odir' '/tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist/setup' '-hidir' '/tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist/setup' '-i' '-i/tmp/glib-0.13.1.0-4186/glib-0.13.1.0' '-package-db' '/opt/cabal/package.conf.d' '-package-id' 'Cabal-1.22.1.1-98c5a01d59dd973fd7113dbb82e82560' '/tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist/setup/setup.hs' '-o' '/tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist/setup/setup' '-threaded' [1 of 2] Compiling SetupWrapper ( /tmp/glib-0.13.1.0-4186/glib-0.13.1.0/SetupWrapper.hs, /tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist/setup/SetupWrapper.o ) [2 of 2] Compiling Main ( /tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist/setup/setup.hs, /tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist/setup/Main.o ) Linking /tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist/setup/setup ... /tmp/glib-0.13.1.0-4186/glib-0.13.1.0/dist/setup/setup configure --verbose=2 --ghc --prefix=/opt/cabal --bindir=/opt/cabal/bin --libdir=/opt/cabal/lib --libsubdir=glib-0.13.1.0/ghc-7.6.3 --libexecdir=/opt/cabal/libexec --datadir=/opt/cabal/share --datasubdir=glib-0.13.1.0 --docdir=/opt/cabal/share/doc/glib-0.13.1.0 --htmldir=/opt/cabal/share/doc/glib-0.13.1.0/html --haddockdir=/opt/cabal/share/doc/glib-0.13.1.0/html --sysconfdir=/opt/cabal/etc --enable-library-profiling --enable-optimization=2 --global --package-db=/opt/cabal/package.conf.d --flags=closure_signals --dependency=utf8-string=utf8-string-0.3.8-51169ff3d90963aa54c0a13eee5c3a53 --dependency=text=text-1.1.1.3-3a54592a9f7d64cef4851163d5553453 --dependency=containers=containers-0.5.0.0-e7e1a93d7945e93a00ce12660e9ff290 --dependency=bytestring=bytestring-0.10.0.2-14ba8002009bf89cdad6038c30eda3fd --dependency=base=base-4.6.0.1-220b875e77822b0e1bf50c8f35d37dff --disable-tests --exact-configuration --disable-benchmarks [1 of 2] Compiling Gtk2HsSetup ( Gtk2HsSetup.hs, dist/setup-wrapper/Gtk2HsSetup.o ) Gtk2HsSetup.hs:167:16: Not in scope: `LBI.getComponentLocalBuildInfo' Failed to install glib-0.13.1.0 Updating world file... cabal: Error: some packages failed to install: glib-0.13.1.0 failed during the configure step. The exception was: ExitFailure 1 cwr@sixpence cabal $ =================================================================== Does anyone have any idea how to fix any or all of these errors? Thanks - Will

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Haskell data generics
by Eduardo 15 May '15

15 May '15

Hello everyone, Here is what I am trying to do: using Data and Typeable generate a representation of any datatype. After looking at some examples this was my attempt: http://lpaste.net/132669. But I can't seem to understand how extQ should work. For instance https://github.com/faylang/fay/blob/master/src/Fay/Convert.hs#L54 https://github.com/lymar/hastache/blob/master/Text/Hastache/Context.hs#L321 All seem to use extQ to "choose" the right way to encode the values(I imagine it's because of the cast inside extQ?). So what am I missing here?

1 0

Error while using type and data constructor
by Nishant 15 May '15

15 May '15

Hi, I was writing some code for Tree. 1 : data Tree a = NULL | Node a (Tree a) (Tree a) works fine. But, 2 : data Tree a = NULL | Tree a (Node a) Tree a does not work. GHCI says Not in scope " type constructor or class 'Node'. Why is 2 declaration not valid though second definition looks much more closer to what a binary tree actually means ? Regards Nishant Verma

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CANCEL ME PLEASE
by Letizia Galli 15 May '15

15 May '15

-- Letizia Galli 0039 328 6917393 www.letiziagalli.it

2 1

cabal problem
by Roelof Wobben 15 May '15

15 May '15

Hello,, I want to use the module Digits which according to Hoogle is in Data.Digits But when I do cabal install Data.Digits I see this error message : cabal install Data.Digits cabal: The file does not exist 'Data.Digits' What do I do wrong ? Roelof --- Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware. http://www.avast.com

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Questions about optparse-applicative
by Mike Meyer 15 May '15

15 May '15

In trying to convert eddie (http://hackage.haskell.org/package/eddie) from CmdArgs optparse-applicative, I've run into a couple of problems. First question: I have options whose legality depends on other options: two that can't be specified together, and a couple that require one of the two, among other things. Is there some way to specify such constraints when building the parser? Maybe a way to print just the usage message if I check these myself? Maybe a better approach? It looks like if I replace main in test/Example/Hello.hs with: main = handleParseResult . Failure $ parserFailure (prefs idm) (info sample briefDesc) ShowHelpText mempty I should just get the Usage message output, but instead I get the full help text. Second, and possibly related, it's not at all clear what fullDesc does in that example program. In particular, removing it doesn't seem to change the program behavior. Is there some behavior I've missed, or is this an error?

1 0

can I have a case statement with a pattern matching
by Roelof Wobben 14 May '15

14 May '15

Hello, I try to make make the assignment of CIS194 where I must multiply every second item from the right by 2 So I thought this could be working : -- | Convert a digit to a reversed list for example 123 becomes [3,2,1] revtoDigits :: Integer -> [Integer] revtoDigits number | number <= 0 = [] | number > 0 = number`mod` 10 : revtoDigits (number `div` 10) -- | Convert a digit to a list for example 123 becomes [1,2,3] toDigits :: Integer -> [Integer] toDigits number | number <= 0 = [] | number > 0 = toDigitsAcc [] number toDigitsAcc:: [Integer] -> Integer -> [Integer] toDigitsAcc acc number | number <= 0 = acc | number > 0 = toDigitsAcc ((number `mod` 10) : acc) (number `div` 10) doubleEveryOther :: [Integer] -> [Integer] doubleEveryOther list = case (length list) `mod` 2 of 0 -> doubleEveryOther [] = [] doubleEveryOther (x:y:xs) = x*2 : y : xs (length list) `mod` 2 of 0 -> doubleEveryOther [] = [] doubleEveryOther (x:y:xs) = x : y*2 : xs -- | The main entry point. main = print $ doubleEveryOther [1,2,3] but apperantly you cannot have pattern matching after a case statement because I get a error on the = of a empty list Roelof --- Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware. http://www.avast.com

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