January 2011 - Haskell-Cafe

GHC.Paths (libDir)
by Serguey Zefirov 04 Jan '11

04 Jan '11

I am looking at GHC API examples page: http://www.haskell.org/haskellwiki/GHC/As_a_library One of examples use "import GHC.Paths ( libDir)" and mentions that it needs "-package ghc-paths" option. I tried the second example with latest Haskell Platform (Windows). I commented out libDir = "/usr..." as it is not applicable to my case and inserted GHC.Paths import. So I run it like "ghci -package ghc -package ghc-paths A.hs" and get an error that "<command line>: cannot satisfy -package ghc-paths". When I do not use -package ghc-paths, it fails to load a module "GHC.Paths". What should I do to obtain libDir?

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How about Haskell Golf just like vimgolf.com
by C K Kashyap 04 Jan '11

04 Jan '11

Hi, First of all, happy new year. I found this site called http://vimgolf.com/ ... the idea there is that people come up with challenges and try to come up with the least number of keystrokes to get it done. Perhaps a similar thing for Haskell would be interesting. Just a thought. Regards, Kashyap

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GHC > 6.8.2 on IA64-Linux platform (Itanium)
by Karel Gardas 04 Jan '11

04 Jan '11

Hello, [sorry for cross-post, I assume Itanium interest is quite rare these days so to grab attention of Itanium/Haskell people I send to both haskell-cafe and ghc list] I'd like to compile more recent than 6.8.2 GHC on itanium-linux system I do have access to, but I'm kind of unlucky with this. I'm trying unregisterised build (of 6.12.3 and 6.10.4) and it always fails with: "inplace/bin/ghc-stage2" -H32m -O -package-name dph-base-0.4.0 -hide-all-packages -i -ilibraries/dph/dph-base/. -ilibraries/dph/dph-base/dist-install/build -ilibraries/dph/dph-base/dist-install/build/autogen -Ilibraries/dph/dph-base/dist-install/build -Ilibraries/dph/dph-base/dist-install/build/autogen -Ilibraries/dph/dph-base/include -optP-include -optPlibraries/dph/dph-base/dist-install/build/autogen/cabal_macros.h -package array-0.3.0.1 -package base-4.2.0.2 -package ghc-prim-0.2.0.0 -package random-1.0.0.2 -Odph -funbox-strict-fields -haddock -fcpr-off -XTypeFamilies -XGADTs -XRankNTypes -XBangPatterns -XMagicHash -XUnboxedTuples -XTypeOperators -O2 -XGenerics -fno-warn-deprecated-flags -Wwarn -odir libraries/dph/dph-base/dist-install/build -hidir libraries/dph/dph-base/dist-install/build -stubdir libraries/dph/dph-base/dist-install/build -hisuf hi -osuf o -hcsuf hc -c libraries/dph/dph-base/./Data/Array/Parallel/Base/Hyperstrict.hs -o libraries/dph/dph-base/dist-install/build/Data/Array/Parallel/Base/Hyperstrict.o ghc-stage2: internal error: evacuate: strange closure type 15 (GHC version 6.12.3 for ia64_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug make[1]: *** [libraries/dph/dph-base/dist-install/build/Data/Array/Parallel/Base/Hyperstrict.o] Aborted make: *** [all] Error 2 I even attempted unoptimized build with mk/build.mk containing this: GhcUnregisterised=YES GhcWithNativeCodeGen=NO SplitObjs=NO SRC_HC_OPTS = -H64m -O0 GhcStage1HcOpts = -O0 GhcStage2HcOpts = -O0 GhcLibHcOpts = -O0 but this time ghc segfaults while compiling: "inplace/bin/ghc-stage2" -H64m -O0 -package-name dph-base-0.4.0 -hide-all-packages -i -ilibraries/dph/dph-base/. -ilibraries/dph/dph-base/dist-install/build -ilibraries/dph/dph-base/dist-install/build/autogen -Ilibraries/dph/dph-base/dist-install/build -Ilibraries/dph/dph-base/dist-install/build/autogen -Ilibraries/dph/dph-base/include -optP-include -optPlibraries/dph/dph-base/dist-install/build/autogen/cabal_macros.h -package array-0.3.0.1 -package base-4.2.0.2 -package ghc-prim-0.2.0.0 -package random-1.0.0.2 -Odph -funbox-strict-fields -haddock -fcpr-off -XTypeFamilies -XGADTs -XRankNTypes -XBangPatterns -XMagicHash -XUnboxedTuples -XTypeOperators -O0 -fno-warn-deprecated-flags -Wwarn -odir libraries/dph/dph-base/dist-install/build -hidir libraries/dph/dph-base/dist-install/build -stubdir libraries/dph/dph-base/dist-install/build -hisuf hi -osuf o -hcsuf hc -c libraries/dph/dph-base/./Data/Array/Parallel/Base/Hyperstrict.hs -o libraries/dph/dph-base/dist-install/build/Data/Array/Parallel/Base/Hyperstrict.o make[1]: *** [libraries/dph/dph-base/dist-install/build/Data/Array/Parallel/Base/Hyperstrict.o] Segmentation fault I've also seen, the last available GHC in Debian for IA64 platform is 6.8.2 -- which I'm using for bootstrap btw so debian will not help me here with some clever patch which would change recent ghc to be buildable... So, I'd like to ask here: is there anybody who was lucky enough to find appropriate set of options or any other magic way how to compile more recent GHC sources to the _stable_ compiler binary on IA64/Linux? If so, please let me know. Thanks a lot, Karel

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What's the motivation for η rules?
by David Sankel 04 Jan '11

04 Jan '11

TIA, David -- David Sankel Sankel Software www.sankelsoftware.com

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Re: [Haskell-cafe] [Haskell] ANNOUNCE: haskell-src-meta 0.3
by Felipe Almeida Lessa 03 Jan '11

03 Jan '11

On Tue, Jan 4, 2011 at 1:49 AM, Ben Millwood <haskell(a)benmachine.co.uk> wrote: > haskell-src-meta is a package originally written by Matt Morrow to > provide a translation from the syntax tree provided by > haskell-src-exts to template haskell syntax. Essentially this allows > TH code to be parsed from a string, and is used in several quasiquoter > libraries. Are the purposes of haskell-src-meta and haskell-src-exts-qq the same? What are the main differences? Cheers! =) -- Felipe.

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Haddock: generate documentation for all functions?
by Edward Amsden 03 Jan '11

03 Jan '11

When using Java, one can tell javadoc to generate documentation for all members of a class, including private and protected members. This is useful for generating internal documentation (for instance). Is there a similar way in Haddock to produce documentation for functions and types that are not exported as a part of a module? -- Edward Amsden Undergraduate Computer Science Rochester Institute of Technology www.edwardamsden.com

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Lazy cons, Stream-Fusion style?
by Stephen Tetley 03 Jan '11

03 Jan '11

Hello all Can a lazy cons be implemented for (infinite) Streams in the Stream-Fusion style? I'm trying to make a Stream library, hopefully efficient enough for audio synthesis in the style of Jerzy Karczmarczuk's Clarion. As performance is important, the obvious model is the Stream-Fusion library, but 'cons' is problematic in this style. With the normal, inductive definition of Streams (vis Wouter Swierstra's Stream library), streams are sufficiently lazy: data Stream a = a :< Stream Using the laziness means that this definition of 'ones' is productive: demo01 = take 10 ones where ones = 1 <:> ones -- (<:>) is stream-cons However with Stream-Fusion, streams are not inductively defined, instead they are unfold-like pair of a stepper function and a start state: -- Some details removed... -- data Stream a = forall st. Stream !(st -> Step a st) !st For infinite Streams the Done constructor can be removed from the Step type, a truly infinite is never done: data Step a s = Yield a !s | Skip !s | Done Cons is strict - (:!:) is the constructor for a Strict pair, but the strictness of the pair is irrelevant here (I think). Even with a lazy pair the definition is too strict to be useful for 'ones' defined above as it won't "stream" (S1 and S2 are the constructors of counting / flag datatype used to encode which state the iteration is in): cons :: a -> Stream a -> Stream a cons w (Stream next0 s0) = Stream next (S2 :!: s0) where {-# INLINE next #-} next (S2 :!: s) = Yield w (S1 :!: s) next (S1 :!: s) = case next0 s of Done -> Done Skip s' -> Skip (S1 :!: s') Yield x s' -> Yield x (S1 :!: s') Here's a running example: > {-# LANGUAGE PackageImports #-} > module SFrec where > import qualified "stream-fusion" Data.Stream as S -- -- The S.append1 construct is used to unwind a Stream -- to a list so it can be printed -- > bad_loopy :: [Int] > bad_loopy = S.append1 (S.take 10 v) [] > where > v = 1 `S.cons` v > good_productive :: [Int] > good_productive = S.append1 (S.take 10 v) [] > where > v = S.repeat 1 Thanks Stephen

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Happstack related problem with templates/class methods
by Markus Barenhoff 03 Jan '11

03 Jan '11

Hi! I'am trying to express a happstack component like the simplified one here: https://gist.github.com/763597 What exactly is the problem for the compiler? Is there a better way to describe such a "abstract" or parametrized component? Regards alios

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A good video on monad
by C K Kashyap 03 Jan '11

03 Jan '11

Hi, I found this nice video on monads (although for clojure). http://www.youtube.com/watch?v=ObR3qi4Guys Question - in the video, if I understood right, the guy implements "return" as a function that takes a value and returns a function (action) that takes nothing and returns that value. And upon executing the action (essentially invoking the function that takes void) you get the value. So, what is the correct way of thinking about the similarity(if any) between a function taking 0 parameters and a single parameter type constructor? Regards, Kashyap

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HaXml installation trouble
by Matthew Fairtlough 03 Jan '11

03 Jan '11

Still very new here. I'm trying to install HaXml and I've updated cabal. I see that a similar issue was posted recently as a bug http://hackage.haskell.org/trac/ghc/ticket/4513 but one that's supposedly fixed; do I need to wait for something or can this be fixed some other way? I think I've posted all necessary version numbers below: ~ $ sudo cabal install HaXml-1.20.2 --global Resolving dependencies... Downloading haskell98-1.1.0.0... Configuring haskell98-1.1.0.0... Preprocessing library haskell98-1.1.0.0... ...info deleted... [24 of 30] Compiling Directory ( Directory.hs, dist/build/Directory.o ) Directory.hs:34:38: Not in scope: `setOwnerReadable' Directory.hs:35:38: Not in scope: `setOwnerWritable' Directory.hs:36:38: Not in scope: `setOwnerExecutable' Directory.hs:37:38: Not in scope: `setOwnerSearchable' Directory.hs:38:57: Not in scope: `emptyPermissions' cabal: Error: some packages failed to install: HaXml-1.20.2 depends on haskell98-1.1.0.0 which failed to install. haskell98-1.1.0.0 failed during the building phase. The exception was: ExitFailure 1 polyparse-1.4 depends on haskell98-1.1.0.0 which failed to install. ~ $ cabal --version cabal-install version 0.8.2 using version 1.8.0.6 of the Cabal library ~ $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.12.3 ~ $ sw_vers ProductName: Mac OS X ProductVersion: 10.6.5 BuildVersion: 10H574

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