- Glasgow-haskell-users

class default method proposal
by Duncan Coutts 13 Dec '07

13 Dec '07

I'd just like to float an idea that's related to the Class Alias proposal[1] but is perhaps somewhat simpler. We all know that Functor should have been a superclass of Monad, and indeed we now know that Applicative should be too. Making such a change would break lots of things however so the change does not happen. However in this case the Monad operations can be used to implement the Functor and Applicative class methods. So it would be nice if we could get them for free if the author did not choose to write the Functor and Applicative instances. So my suggestion is that we let classes declare default implementations of methods from super-classes. class Functor m => Monad m where {- the ordinary bits -} fmap f m = m >>= return . f So if there already is a Functor instance for m then the default implementation of fmap is not used. Does this proposal have any unintended consequences? I'm not sure. Please discuss :-) Duncan [1] http://repetae.net/recent/out/classalias.html

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GHC 6.8.1 on Mac OS 10.5 Leopard (Intel) - Configure fails
by Carsten Keßler 12 Dec '07

12 Dec '07

Hi, I know this issue has been discussed on the list before, but I have not found a solution in the archives. Running ./configure on Mac OS 10.5 (Intel) is aborted with this error message: checking build system type... i386-apple-darwin9.1.0 checking host system type... i386-apple-darwin9.1.0 checking target system type... i386-apple-darwin9.1.0 Which we'll further canonicalise into: i386-apple-darwin checking for path to top of build tree... dyld: Library not loaded: GMP.framework/Versions/A/GMP Referenced from: /Users/Carsten/Desktop/ghc-6.8.1/utils/pwd/pwd Reason: image not found configure: error: cannot determine current directory Any ideas how to get around this issue? Thanks, Carsten

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Installing on Leopard
by Johan Tibell 11 Dec '07

11 Dec '07

I have some problems installing 6.8.1 on Mac OS X Leopard. First I installed readline using ports: $ sudo port install readline <snip> Then GHC $ ./configure --prefix=$HOME && make install make -C rts install DOING_BIN_DIST=YES cc -E -undef -traditional -P -DINSTALLING \ -DIMPORT_DIR='"/Users/tibell/lib/ghc-6.8.1/imports"' \ -DLIB_DIR='"/Users/tibell/lib/ghc-6.8.1"' \ -DINCLUDE_DIR='"/Users/tibell/lib/ghc-6.8.1/include"' \ -DDATA_DIR='"/Users/tibell/share/ghc-6.8.1"' \ -DHTML_DIR='"/Users/tibell/share/ghc-6.8.1/html/libraries/rts"' \ -DHADDOCK_IFACE='"/Users/tibell/share/ghc-6.8.1/html/libraries/rts/rts.haddock"' \ -I../includes \ -x c -DGMP_INCLUDE_DIRS='' -DGMP_LIB_DIRS='' -I -Iinclude -DPACKAGE=rts -DVERSION= -DPKG_LIBDIR='"/Users/tibell/lib/ghc-6.8.1"' -DPKG_DATADIR='"/Users/tibell/share/ghc-6.8.1"' package.conf.in \ | grep -v '^#pragma GCC' \ | sed -e 's/""//g' -e 's/:[ ]*,/: /g' \ | /Users/tibell/Downloads/ghc-6.8.1/utils/ghc-pkg/ghc-pkg.bin --global-conf /Users/tibell/lib/ghc-6.8.1/package.conf update - --force dyld: Library not loaded: /opt/local/lib/libgmp.3.dylib Referenced from: /Users/tibell/Downloads/ghc-6.8.1/utils/ghc-pkg/ghc-pkg.bin Reason: image not found /bin/sh: line 1: 60782 Done cc -E -undef -traditional -P -DINSTALLING -DIMPORT_DIR='"/Users/tibell/lib/ghc-6.8.1/imports"' -DLIB_DIR='"/Users/tibell/lib/ghc-6.8.1"' -DINCLUDE_DIR='"/Users/tibell/lib/ghc-6.8.1/include"' -DDATA_DIR='"/Users/tibell/share/ghc-6.8.1"' -DHTML_DIR='"/Users/tibell/share/ghc-6.8.1/html/libraries/rts"' -DHADDOCK_IFACE='"/Users/tibell/share/ghc-6.8.1/html/libraries/rts/rts.haddock"' -I../includes -x c -DGMP_INCLUDE_DIRS='' -DGMP_LIB_DIRS='' -I -Iinclude -DPACKAGE=rts -DVERSION= -DPKG_LIBDIR='"/Users/tibell/lib/ghc-6.8.1"' -DPKG_DATADIR='"/Users/tibell/share/ghc-6.8.1"' package.conf.in 60783 | grep -v '^#pragma GCC' 60784 | sed -e 's/""//g' -e 's/:[ ]*,/: /g' 60786 Trace/BPT trap | /Users/tibell/Downloads/ghc-6.8.1/utils/ghc-pkg/ghc-pkg.bin --global-conf /Users/tibell/lib/ghc-6.8.1/package.conf update - --force make[1]: *** [install] Error 133 make: *** [install] Error 2 ------------------- I thought GHC shipped with its own GMP lib. -- Johan

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Re: class default method proposal
by apfelmus 11 Dec '07

11 Dec '07

Jules Bean wrote: > David Menendez wrote: >> Duncan Coutts wrote: >>> So my suggestion is that we let classes declare default >>> implementations of methods from super-classes. >> >> It creates ambiguity if two classes declare defaults for a common >> superclass. >> >> My standard example involves Functor, Monad, and Comonad. Both Monad >> and Comonad could provide a default implementation for fmap. But let's >> say I have a type which is both a Monad and a Comonad: which default >> implementation gets used? >> >> I'm disappointed to see this objection isn't listed on the wiki. > > Doesn't sound like a very big problem. That would just be a compile time > error ("More than one default for fmap possible for Foo, please reslve > ambiguity"). And how would you resolve that ambiguity? module Control.Functor.UsefulStuff (hylo) where hylo :: Functor f => (a -> f a) -> (f b -> b) -> a -> b hylo f g = g . fmap (hylo f g) . f module BANG where import Foo (Foo) import Foo.Is.Monad import Foo.Is.Comonad import Control.Functor.UsefulStuff (hylo) bar :: Bar -> Foo Bar baz :: Foo Baz -> Baz bang = hylo bar baz The problem is that the ambiguity may arise by just importing different modules while not having access to the offending call to fmap . Also note that as much as I'd like explicit import/export of type class instances, the current implicit and global export is no accident, it's crucial for well-definedness. See also the second half of http://article.gmane.org/gmane.comp.lang.haskell.general/15471 In other words, the main problem of all those superclass/explicit import/export proposals is that there are no proofs of the fact that they only allow well-defined programs. The homework isn't done yet, discussing adoption is too early. Regards, apfelmus

1 0

Which ghc versions can build ghc-6.8.1?
by Gregory Wright 11 Dec '07

11 Dec '07

Hi, I'm the process of updating MacPort's ghc to 6.8.1 and adding support for Leopard (OS X 10.5) and have been having] some trouble. The first task is just to get 6.8.1 running on Tiger (10.4). On PPC, I use ghc 6.4 as a bootstrap compiler and on Intel ghc 6.6. I am traveling with only a PPC PowerBook G4/OS X 10.4, so that's all I've been able to test with. The problem is that ghc 6.4 can not build 6.8.1. It seems related to Cabal. Using the 6.4 bootstrap compiler (with the version of Cabal that it shipped with) I get: ranlib libHSrts_thr_debug.a ------------------------------------------------------------------------ == Finished recursively making `all' for ways: p debug thr thr_p thr_debug ... PWD = /opt/local/var/macports/build/_Users_gwright_src_macports- trunk_dports_lang_ghc/work/ghc-6.8.1/rts ------------------------------------------------------------------------ make -C libraries boot rm -f -rf bootstrapping.Cabal cp -R Cabal bootstrapping.Cabal /usr/bin/find bootstrapping.Cabal $ -name "*.o" -o -name "*.hi" $ \ -exec rm -f -f {} \; touch stamp/bootstrapping.Cabal rm -f -rf bootstrapping.filepath cp -R filepath bootstrapping.filepath /usr/bin/find bootstrapping.filepath $ -name "*.o" -o -name "*.hi" $ \ -exec rm -f -f {} \; touch stamp/bootstrapping.filepath rm -f -rf ifBuildable mkdir ifBuildable cp ifBuildable.hs ifBuildable/ cd ifBuildable && /opt/local/var/macports/build/ _Users_gwright_src_macports-trunk_dports_lang_ghc/work/ghc-bootstrap/ bin/ghc -Wall --make ifBuildable -o ifBuildable Chasing modules from: ifBuildable Compiling Main ( ifBuildable.hs, ifBuildable.o ) Linking ... ld: warning prebinding disabled because dependent library: /opt/local/ lib/libgmp.3.dylib is not prebound rm -f -rf base/setup mkdir base/setup cp base/Setup.*hs base/setup cd base/setup && /opt/local/var/macports/build/ _Users_gwright_src_macports-trunk_dports_lang_ghc/work/ghc-bootstrap/ bin/ghc -Wall -cpp --make Setup.*hs -o Setup \ -DCABAL_VERSION=1,2,2,0 -i../../ bootstrapping.Cabal -i../../bootstrapping.filepath Chasing modules from: Setup.hs Compiling System.FilePath.Posix ( ../../bootstrapping.filepath/System/ FilePath/Posix.hs, ../../bootstrapping.filepath/System/FilePath/ Posix.o ) Compiling System.FilePath ( ../../bootstrapping.filepath/System/ FilePath.hs, ../../bootstrapping.filepath/System/FilePath.o ) Compiling Main ( Setup.hs, Setup.o ) Setup.hs:19:18: Not in scope: `buildHook' Setup.hs:21:30: Not in scope: `buildHook' Setup.hs:22:18: Not in scope: `makefileHook' Setup.hs:24:33: Not in scope: `makefileHook' Setup.hs:25:18: Not in scope: `instHook' Setup.hs:26:29: Not in scope: `instHook' Setup.hs:33:12: Not in scope: `compilerFlavor' Setup.hs:33:45: Not in scope: data constructor `GHC' make[1]: *** [base/setup/Setup] Error 1 make: *** [stage1] Error 2 If I upgrade the bootstrap compiler's Cabal to 1.1.6.2, the build still fails. (The old version of Cabal was unregistered according the instructions for working with older versions of ghc & Cabal.) ranlib libHSrts_thr_debug.a ------------------------------------------------------------------------ == Finished recursively making `all' for ways: p debug thr thr_p thr_debug ... PWD = /Users/gwright/Desktop/ghc-6.8.1/rts ------------------------------------------------------------------------ make -C libraries boot rm -f -rf bootstrapping.Cabal cp -R Cabal bootstrapping.Cabal /usr/bin/find bootstrapping.Cabal $ -name "*.o" -o -name "*.hi" $ \ -exec rm -f -f {} \; touch stamp/bootstrapping.Cabal rm -f -rf bootstrapping.filepath cp -R filepath bootstrapping.filepath /usr/bin/find bootstrapping.filepath $ -name "*.o" -o -name "*.hi" $ \ -exec rm -f -f {} \; touch stamp/bootstrapping.filepath rm -f -rf ifBuildable mkdir ifBuildable cp ifBuildable.hs ifBuildable/ cd ifBuildable && /opt/local/bin/ghc -Wall --make ifBuildable -o ifBuildable Chasing modules from: ifBuildable Compiling Main ( ifBuildable.hs, ifBuildable.o ) Linking ... rm -f -rf base/setup mkdir base/setup cp base/Setup.*hs base/setup cd base/setup && /opt/local/bin/ghc -Wall -cpp --make Setup.*hs -o Setup \ -DCABAL_VERSION=1,2,2,0 -i../../ bootstrapping.Cabal -i../../bootstrapping.filepath Chasing modules from: Setup.hs Compiling System.FilePath.Posix ( ../../bootstrapping.filepath/System/ FilePath/Posix.hs, ../../bootstrapping.filepath/System/FilePath/ Posix.o ) Compiling System.FilePath ( ../../bootstrapping.filepath/System/ FilePath.hs, ../../bootstrapping.filepath/System/FilePath.o ) Compiling Main ( Setup.hs, Setup.o ) Setup.hs:22:18: Not in scope: `makefileHook' Setup.hs:24:33: Not in scope: `makefileHook' make[1]: *** [base/setup/Setup] Error 1 make: *** [stage1] Error 2 With my installed 6.6.1 (and the Cabal 1.1.6.2 shipped with it) I was able to build 6.8.1. I tried adding "-ignore-package Cabal" to the lines BOOTSTRAP_INC_1_UP = -DCABAL_VERSION=1,2,2,0 $(addprefix -i../ bootstrapping.,$(BOOTSTRAP_LIBS)) BOOTSTRAP_INC_2_UP = -DCABAL_VERSION=1,2,2,0 $(addprefix -i../../ bootstrapping.,$(BOOTSTRAP_LIBS)) in libraries/Makefile and was able to compile all of the Setup files, but the "setup configure" failed in libraries/base, complaining that Setup could not determine the version of ghc-inplace. (It also printed a message that to build libraries/base the ghc version needs to be at least 6.2. This at the least is different than the distribution web page, which only mentions that ghc => 6.0 is needed.) For comparison, the same part of the build log building 6.8.1 using the 6.6.1 installed by MacPorts: ranlib libHSrts_thr_debug.a ------------------------------------------------------------------------ == Finished recursively making `all' for ways: p debug thr thr_p thr_debug ... PWD = /Users/gwright/Desktop/ghc-6.8.1/rts ------------------------------------------------------------------------ make -C libraries boot rm -f -rf bootstrapping.Cabal cp -R Cabal bootstrapping.Cabal /usr/bin/find bootstrapping.Cabal $ -name "*.o" -o -name "*.hi" $ \ -exec rm -f -f {} \; touch stamp/bootstrapping.Cabal rm -f -rf bootstrapping.filepath cp -R filepath bootstrapping.filepath /usr/bin/find bootstrapping.filepath $ -name "*.o" -o -name "*.hi" $ \ -exec rm -f -f {} \; touch stamp/bootstrapping.filepath rm -f -rf ifBuildable mkdir ifBuildable cp ifBuildable.hs ifBuildable/ cd ifBuildable && /opt/local/bin/ghc -Wall --make ifBuildable -o ifBuildable [1 of 1] Compiling Main ( ifBuildable.hs, ifBuildable.o ) Linking ifBuildable ... rm -f -rf base/setup mkdir base/setup cp base/Setup.*hs base/setup cd base/setup && /opt/local/bin/ghc -Wall -cpp --make Setup.*hs -o Setup \ -DCABAL_VERSION=1,2,2,0 -i../../ bootstrapping.Cabal -i../../bootstrapping.filepath [ 1 of 42] Compiling Distribution.Simple.GHC.Makefile ( ../../ bootstrapping.Cabal/Distribution/Simple/GHC/Makefile.hs, ../../ bootstrapping.Cabal/Distribution/Simple/GHC/Makefile.o ) [ 2 of 42] Compiling Distribution.Simple.PreProcess.Unlit ( ../../ bootstrapping.Cabal/Distribution/Simple/PreProcess/Unlit.hs, ../../ bootstrapping.Cabal/Distribution/Simple/PreProcess/Unlit.o ) [ 3 of 42] Compiling Distribution.System ( ../../bootstrapping.Cabal/ Distribution/System.hs, ../../bootstrapping.Cabal/Distribution/ System.o ) [ 4 of 42] Compiling Distribution.Verbosity ( ../../ bootstrapping.Cabal/Distribution/Verbosity.hs, ../../ bootstrapping.Cabal/Distribution/Verbosity.o ) [ 5 of 42] Compiling Distribution.Compat.ReadP ( ../../ bootstrapping.Cabal/Distribution/Compat/ReadP.hs, ../../ bootstrapping.Cabal/Distribution/Compat/ReadP.o ) [ 6 of 42] Compiling Distribution.Compat.RawSystem ( ../../ bootstrapping.Cabal/Distribution/Compat/RawSystem.hs, ../../ bootstrapping.Cabal/Distribution/Compat/RawSystem.o ) [ 7 of 42] Compiling Distribution.Compat.Exception ( ../../ bootstrapping.Cabal/Distribution/Compat/Exception.hs, ../../ bootstrapping.Cabal/Distribution/Compat/Exception.o ) [ 8 of 42] Compiling Distribution.Compat.Directory ( ../../ bootstrapping.Cabal/Distribution/Compat/Directory.hs, ../../ bootstrapping.Cabal/Distribution/Compat/Directory.o ) [ 9 of 42] Compiling Distribution.Compat.Map ( ../../ bootstrapping.Cabal/Distribution/Compat/Map.hs, ../../ bootstrapping.Cabal/Distribution/Compat/Map.o ) [10 of 42] Compiling Distribution.GetOpt ( ../../bootstrapping.Cabal/ Distribution/GetOpt.hs, ../../bootstrapping.Cabal/Distribution/ GetOpt.o ) [11 of 42] Compiling Language.Haskell.Extension ( ../../ bootstrapping.Cabal/Language/Haskell/Extension.hs, ../../ bootstrapping.Cabal/Language/Haskell/Extension.o ) [12 of 42] Compiling Distribution.Version ( ../../bootstrapping.Cabal/ Distribution/Version.hs, ../../bootstrapping.Cabal/Distribution/ Version.o ) [13 of 42] Compiling Distribution.Configuration ( ../../ bootstrapping.Cabal/Distribution/Configuration.hs, ../../ bootstrapping.Cabal/Distribution/Configuration.o ) [14 of 42] Compiling Distribution.Package ( ../../bootstrapping.Cabal/ Distribution/Package.hs, ../../bootstrapping.Cabal/Distribution/ Package.o ) [15 of 42] Compiling Distribution.License ( ../../bootstrapping.Cabal/ Distribution/License.hs, ../../bootstrapping.Cabal/Distribution/ License.o ) [16 of 42] Compiling Distribution.Compiler ( ../../ bootstrapping.Cabal/Distribution/Compiler.hs, ../../ bootstrapping.Cabal/Distribution/Compiler.o ) [17 of 42] Compiling Distribution.ParseUtils ( ../../ bootstrapping.Cabal/Distribution/ParseUtils.hs, ../../ bootstrapping.Cabal/Distribution/ParseUtils.o ) [18 of 42] Compiling Distribution.InstalledPackageInfo ( ../../ bootstrapping.Cabal/Distribution/InstalledPackageInfo.hs, ../../ bootstrapping.Cabal/Distribution/InstalledPackageInfo.o ) [19 of 42] Compiling Distribution.Simple.Compiler ( ../../ bootstrapping.Cabal/Distribution/Simple/Compiler.hs, ../../ bootstrapping.Cabal/Distribution/Simple/Compiler.o ) [20 of 42] Compiling System.FilePath.Posix ( ../../ bootstrapping.filepath/System/FilePath/Posix.hs, ../../ bootstrapping.filepath/System/FilePath/Posix.o ) [21 of 42] Compiling System.FilePath ( ../../bootstrapping.filepath/ System/FilePath.hs, ../../bootstrapping.filepath/System/FilePath.o ) [22 of 42] Compiling Distribution.Compat.TempFile ( ../../ bootstrapping.Cabal/Distribution/Compat/TempFile.hs, ../../ bootstrapping.Cabal/Distribution/Compat/TempFile.o ) [23 of 42] Compiling Distribution.Simple.Utils ( ../../ bootstrapping.Cabal/Distribution/Simple/Utils.hs, ../../ bootstrapping.Cabal/Distribution/Simple/Utils.o ) [24 of 42] Compiling Distribution.PackageDescription ( ../../ bootstrapping.Cabal/Distribution/PackageDescription.hs, ../../ bootstrapping.Cabal/Distribution/PackageDescription.o ) [25 of 42] Compiling Distribution.Simple.Program ( ../../ bootstrapping.Cabal/Distribution/Simple/Program.hs, ../../ bootstrapping.Cabal/Distribution/Simple/Program.o ) [26 of 42] Compiling Distribution.Simple.Setup ( ../../ bootstrapping.Cabal/Distribution/Simple/Setup.hs, ../../ bootstrapping.Cabal/Distribution/Simple/Setup.o ) [27 of 42] Compiling Distribution.Simple.InstallDirs ( ../../ bootstrapping.Cabal/Distribution/Simple/InstallDirs.hs, ../../ bootstrapping.Cabal/Distribution/Simple/InstallDirs.o ) [28 of 42] Compiling Distribution.Simple.LocalBuildInfo ( ../../ bootstrapping.Cabal/Distribution/Simple/LocalBuildInfo.hs, ../../ bootstrapping.Cabal/Distribution/Simple/LocalBuildInfo.o ) [29 of 42] Compiling Distribution.Simple.JHC ( ../../ bootstrapping.Cabal/Distribution/Simple/JHC.hs, ../../ bootstrapping.Cabal/Distribution/Simple/JHC.o ) [30 of 42] Compiling Distribution.Simple.NHC ( ../../ bootstrapping.Cabal/Distribution/Simple/NHC.hs, ../../ bootstrapping.Cabal/Distribution/Simple/NHC.o ) [31 of 42] Compiling Distribution.Simple.PreProcess ( ../../ bootstrapping.Cabal/Distribution/Simple/PreProcess.hs, ../../ bootstrapping.Cabal/Distribution/Simple/PreProcess.o ) [32 of 42] Compiling Distribution.Simple.Hugs ( ../../ bootstrapping.Cabal/Distribution/Simple/Hugs.hs, ../../ bootstrapping.Cabal/Distribution/Simple/Hugs.o ) [33 of 42] Compiling Distribution.Simple.SrcDist ( ../../ bootstrapping.Cabal/Distribution/Simple/SrcDist.hs, ../../ bootstrapping.Cabal/Distribution/Simple/SrcDist.o ) [34 of 42] Compiling Distribution.Simple.Haddock ( ../../ bootstrapping.Cabal/Distribution/Simple/Haddock.hs, ../../ bootstrapping.Cabal/Distribution/Simple/Haddock.o ) [35 of 42] Compiling Distribution.Simple.GHC.PackageConfig ( ../../ bootstrapping.Cabal/Distribution/Simple/GHC/PackageConfig.hs, ../../ bootstrapping.Cabal/Distribution/Simple/GHC/PackageConfig.o ) [36 of 42] Compiling Distribution.Simple.GHC ( ../../ bootstrapping.Cabal/Distribution/Simple/GHC.hs, ../../ bootstrapping.Cabal/Distribution/Simple/GHC.o ) [37 of 42] Compiling Distribution.Simple.Install ( ../../ bootstrapping.Cabal/Distribution/Simple/Install.hs, ../../ bootstrapping.Cabal/Distribution/Simple/Install.o ) [38 of 42] Compiling Distribution.Simple.Register ( ../../ bootstrapping.Cabal/Distribution/Simple/Register.hs, ../../ bootstrapping.Cabal/Distribution/Simple/Register.o ) [39 of 42] Compiling Distribution.Simple.Configure ( ../../ bootstrapping.Cabal/Distribution/Simple/Configure.hs, ../../ bootstrapping.Cabal/Distribution/Simple/Configure.o ) [40 of 42] Compiling Distribution.Simple.Build ( ../../ bootstrapping.Cabal/Distribution/Simple/Build.hs, ../../ bootstrapping.Cabal/Distribution/Simple/Build.o ) [41 of 42] Compiling Distribution.Simple ( ../../bootstrapping.Cabal/ Distribution/Simple.hs, ../../bootstrapping.Cabal/Distribution/ Simple.o ) [42 of 42] Compiling Main ( Setup.hs, Setup.o ) Linking Setup ... Can 6.4 build 6.8.1? Or is a later version required? If possible, I want to use the existing bootstrap compiler for OS X < 10.5, since building a new one is a lot of work, especially to root out unnecessary dependencies. And it would mean terminating support for Panther (10.3). We only promise support for the most recent two OS version, so dropping Panther is not a big deal, but I try not to gratuitously drop support for older version if I can avoid it. If a later version bootstrap compiler is needed, we should take the opportunity to update the documentation. Best Wishes, Greg

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Encoding Lists with Lengths by Type Family
by Shin-Cheng Mu 11 Dec '07

11 Dec '07

Hi, I understand that the type family is still an experimental feature in GHC. This is just a confirmation whether it is a bug, or is what the designers intended. I am curious how much "dependent type" programming I can emulate using GADT and type family. Therefore I started with the typical "list with length" example. List a n is a list of elements a and length n encoded by singleton types Zero and Suc, as was done in the paper Towards Open Type Functions for Haskell: > data Zero = Zero > data Suc a = Suc a > data List a n where > Nil :: List a Zero > Cons :: a -> List a n -> List a (Suc n) Concatenation effortlessly type checks! > cat :: List a m -> List a n -> List a (Plus m n) > cat Nil y = y > cat (Cons a x) y = Cons a (cat x y) However, I was not able to convince GHC that the following function revcat, list reversal using an accumulating parameter, is type correct: > revcat :: List a m -> List a n -> List a (Plus m n) > revcat Nil y = y > revcat (Cons a x) y = > subst incAssocL (revcat x (Cons a y)) In the recursive case, (Cons a x) has type List a (Suc m) and y has type List a n. The recursive call to revcat is supposed to yield a list of type: List a (Plus m (Suc n)) while we want the return type to be List a (Plus (Suc m) n) Therefore I shall provide a conversion proving that they are actually the same thing. Currently I give the types only and will think about how to implement them later: > subst :: (m -> n) -> List a m -> List a n > subst = undefined > incAssocL :: Plus m (Suc n) -> Plus (Suc m) n > incAssocL = undefined However, GHCi (run with options -XTypeFamilies -XGADTs) gave me the following error message: Couldn't match expected type `Plus n3 n2' against inferred type `Plus m n1' Expected type: Plus m (Suc n1) -> Plus (Suc n3) n2 Inferred type: Plus m (Suc n1) -> Plus (Suc m) n1 In the first argument of `subst', namely `incAssocL' In the expression: subst incAssocL (revcat x (Cons a y)) For some reason GHC wanted me to return the more general type Plus (Suc n3) n2 where n2 and n3 are fresh, rather than unifying n2 with m and n2 with n. Why is that? sincerely, Shin

2 1

New woes regarding ghc-6.8.1 on FreeBSD-amd64
by Wilhelm B. Kloke 11 Dec '07

11 Dec '07

Some days ago I announced having success in porting ghc-6.8.1 to FreeBSD-7.0-amd64. As the compiler seemed to be able to compile itself, I was confident to make the binary package available to the public. Now I have found out that the port is rooten in a very weird way. >From the files in testsuite (6.6.1) it has 4707 expected passes vs. 669 unexpected failures. Among the most unexpected of these is the failure of arith003 (conversions between Int and Integer near 64bit boundary). It seems there is still some 32/64-bit confusion left from the building process. Still worse is, that any attempt to use the partially usable compiler as bootstrap tool fails for some reasons. On a freshly configure 6.8.1 tree (with ./configure --with-gmp-includes=/usr/local/include --with-gmp-libraries=/usr/local/lib ) the build process fails at libraries/base/Control/Concurrent.hs because gmp.h is not found by ghc-inplace I fixed this by copying /usr/local/include/gmp.h to ghc-6.8.1/includes. This is, of course, a risk of confusing the 32/64bit version of this library. Anyway, the resulting compiler in stage2/ghc-6.8.1 dumps core. Perhaps I can get better results, if I use the most conservative settings possible for stage1 build, but I have no idea what they are. The recommended porting process (via .hc files) fails, too. I am going to make a separate bug report about this. -- Dipl.-Math. Wilhelm Bernhard Kloke Institut fuer Arbeitsphysiologie an der Universitaet Dortmund Ardeystrasse 67, D-44139 Dortmund, Tel. 0231-1084-257 PGP: http://vestein.arb-phys.uni-dortmund.de/~wb/mypublic.key

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Re: HUnit 1.2.0.0 on 6.8.1 vs 1.1.1 on 6.6.1
by Greg Fitzgerald 11 Dec '07

11 Dec '07

> >> > "abc" @=? "efg" > >> Loading package HUnit-1.2.0.0 ... linking ... done. > >> *** Exception: (unknown) > > On Dec 3, 2007 7:23 AM, Ian Lynagh <igloo(a)earth.li> wrote: > > This is caused by a change in the HUnit library, from > > assertFailure msg = ioError (userError (hunitPrefix ++ msg)) > > to > > assertFailure msg = E.throwDyn (HUnitFailure msg) I've had no luck contacting Dean Herington using the email address posted on the HUnit page. > They just use the latest version in the darcs repositories at the time that they are built Sounds like this is the first case where the latest version isn't a stable one (Go Haskell!). Is it much trouble for package maintainers to package GHC with HUnit.1.1.1? To keep it simple, maybe there should be an HUnitStable branch where 1.1.1 is the latest version? Thanks, Greg

2 1

GHC 6.8.2, Haddock not finding std libs
by Greg Fitzgerald 10 Dec '07

10 Dec '07

> Please test as much as possible One difference between 6.8.1 and 6.8.2 that I see is in running "runhaskell Setup.hs haddock" with Haddock 0.8 on Windows XP. Haddock is no longer able to resolve the names from the standard libraries. Running Haddock for Xyz-0.1... Warning: Xyz: the following names could not be resolved: FilePath Show Eq String Maybe Bool Char Int Thanks, Greg

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Re: type equality symbol
by Johannes Waldmann 10 Dec '07

10 Dec '07

On Fri, 7 Dec 2007, Manuel M T Chakravarty wrote: > The problem is that Haskell 98 already messed that up. > If type functions are to use lower-case letters, [...] Yes. The broken thing is that the upper/lower case distinction has syntactic importance in the language definition at all. I guess this was introduced to avoid writing out some declarations. This is a bad design goal, especially so for a declarative language. Reminds me of ancient Fortran using the first letter of an identifier for implicit typing (I .. N for integer, others for real). Best regards, -- -- Johannes Waldmann -- Tel/Fax (0341) 3076 6479/80 -- ---- http://www.imn.htwk-leipzig.de/~waldmann/ -------

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