May 2008 - Glasgow-haskell-users

partially applied type synonyms
by Arie Peterson 05 Mar '12

05 Mar '12

Dear list, Is there a good reason that partially applied type synonyms cannot be made instances of classes? - A simple example would be making the identity type 'Id' ("type Id x = x") instance of 'Monad'. This would eliminate the need for some silly occurrences of 'runIdentity', and perhaps narrow the gap between monads and monad transformers. - The reason I complain about this now is a more involved example, where introducing a newtype to work around the restriction is not an option. Well, not as far as I can see now, anyway. Partially applied type synonyms are, in a sense, the anonymous functions at the type level, and one might argue that they deserve the same 'first-class member status' as the lambda at the value level. Kind regards, Arie Peterson

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ANNOUNCE: GHC 6.8.3 Release Candidate
by Ian Lynagh 22 Sep '09

22 Sep '09

We are pleased to announce the Release Candidate phase for GHC 6.8.3. Snapshots beginning with 6.8.2.20080527 are release candidates for 6.8.3 You can download snapshots from here: http://www.haskell.org/ghc/dist/stable/dist/ Right now we have the source bundles: http://www.haskell.org/ghc/dist/stable/dist/ghc-6.8.2.20080527-src.tar.bz2 http://www.haskell.org/ghc/dist/stable/dist/ghc-6.8.2.20080527-src-extralib… Only the first of these is necessary. The "extralibs" package contains various extra packages that are often supplied with GHC - unpack the extralibs tarball on top of the source tree to add them, and they will be included in the build automatically. There is also currently an installer for i386/Windows and binary distributions for x86_64/Linux and i386/Linux. More may appear later. Please test as much as possible; bugs are much cheaper if we find them before the release! We expect to release in a few days, assuming no major issues are discovered. Thanks Ian, on behalf of the GHC team

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ghci and ghc -threaded broken with pipes & forking
by John Goerzen 29 Dec '08

29 Dec '08

Hi, I've been hitting my head against a wall for the past couple of days trying to figure out why my shell-like pipeline code kept hanging. I found fd leakage (file descriptors not being closed), which disrupts EOF detection and can lead to deadlocks. I just couldn't find the problem. I finally tried compiling my test with ghc instead of running it in ghci. And poof, it worked fine the first time. I tried asking on #haskell, and got the suggestion that ghci uses -threaded. I tried compiling my test program with ghc -threaded, and again, same deadlock. My program never calls forkIO or forkOS or any other threading code. You can see my test case with: darcs get '--tag=glasgow ml' http://darcs.complete.org/hsh ghc -fglasgow-exts --make -o test2 test2.hs That'll run fine. If you add -threaded, it will hang. Ideas? Thanks, -- John

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Arrow without `>>>'
by Valery V. Vorotyntsev 03 Sep '08

03 Sep '08

Hi, friends, I've built GHC from darcs, and... Could anybody tell me, what's the purpose of Arrow[1] not having `>>>' method? 1. http://darcs.haskell.org/packages/base/Control/Arrow.hs $ ghci GHCi, version 6.9.20080104: http://www.haskell.org/ghc/ :? for help Loading package base ... linking ... done. Prelude> :m + Control.Arrow Prelude Control.Arrow> :i Arrow class (Control.Category.Category a) => Arrow a where arr :: (b -> c) -> a b c pure :: (b -> c) -> a b c first :: a b c -> a (b, d) (c, d) second :: a b c -> a (d, b) (d, c) (***) :: a b c -> a b' c' -> a (b, b') (c, c') (&&&) :: a b c -> a b c' -> a b (c, c') -- Defined in Control.Arrow instance Arrow (->) -- Defined in Control.Arrow instance (Monad m) => Arrow (Kleisli m) -- Defined in Control.Arrow Prelude Control.Arrow> Leaving GHCi. I can't build[2] arrows-0.3 package without `>>>' in Arrow. 2. vvv@fun:~/src/arrows$ darcs w { hunk ./Control/Arrow/Operations.hs 36 +import Control.Category ((>>>)) hunk ./Control/Arrow/Transformer/CoState.hs 23 +import Control.Category ((>>>)) } vvv@fun:~/src/arrows$ runhaskell Setup build Preprocessing library arrows-0.3... Building arrows-0.3... [ 3 of 12] Compiling Control.Arrow.Transformer.CoState ( Control/Arrow/Transformer/CoState.hs, dist/build/Control/Arrow/Transformer/CoState.o ) Control/Arrow/Transformer/CoState.hs:29:7: `>>>' is not a (visible) method of class `Arrow' The question arises "should I?", but this is one of lambdabot's[3] depencies. 3. http://code.haskell.org/lambdabot/ Thanks a lot! -- vvv

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Recursive functions and constant parameter closures (inlining/strictness analyzer question)
by Tyson Whitehead 25 Jun '08

25 Jun '08

main = print $ foldl' (+) 0 [1..] with foldl' f y xs = foldl' y xs where foldl' y [] = y foldl' y (x:xs) = foldl' (f y x) xs runs indefinitely with very little memory consumption, while foldl' f y [] = y foldl' f y (x:xs) = foldl' f (f y x) xs rapidly consumes all the machine's memory and dies. Running ghc with -ddump-stranal shows the outer foldl' of the first gets inlined into main as a call to the following specialized version of the inner foldl': foldl'_sSY [ALWAYS LoopBreaker Nothing] :: GHC.Num.Integer -> [GHC.Num.Integer] -> GHC.Num.Integer [Arity 2 Str: DmdType SS] foldl'_sSY = \ (y_aj7 [ALWAYS Just S] :: GHC.Num.Integer) (ds_dQl [ALWAYS Just S] :: [GHC.Num.Integer]) -> case ds_dQl of wild_XH [ALWAYS Just A] { [] -> y_aj7; : x_aja [ALWAYS Just S] xs_ajb [ALWAYS Just S] -> foldl'_sSY (GHC.Num.plusInteger y_aj7 x_aja) xs_ajb } Doing the same with the second foldl' shows it to remains non-inlined and fully polymorphic: foldl'_sQN [ALWAYS LoopBreaker Nothing] :: forall t_auW t_av2. (t_av2 -> t_auW -> t_av2) -> t_av2 -> [t_auW] -> t_av2 [Arity 3 Str: DmdType LLS] foldl'_sQN = \ (@ t_auW) (@ t_av2) (f_aj0 [ALWAYS Just L] :: t_av2 -> t_auW -> t_av2) (y_aj1 [ALWAYS Just L] :: t_av2) (ds_dQg [ALWAYS Just S] :: [t_auW]) -> case ds_dQg of wild_XK [ALWAYS Just A] { [] -> y_aj1; : x_aj5 [ALWAYS Just L] xs_aj6 [ALWAYS Just S] -> foldl'_sQN @ t_auW @ t_av2 f_aj0 (f_aj0 y_aj1 x_aj5) xs_aj6 } Forcing it inline with {-# INLINE foldl' #-} just specialized it: foldl'_sSS [ALWAYS LoopBreaker Nothing] :: (GHC.Num.Integer -> GHC.Num.Integer -> GHC.Num.Integer) -> GHC.Num.Integer -> [GHC.Num.Integer] -> GHC.Num.Integer [Arity 3 Str: DmdType LLS] foldl'_sSS = \ (f_aj0 [ALWAYS Just L] :: GHC.Num.Integer -> GHC.Num.Integer -> GHC.Num.Integer) (y_aj1 [ALWAYS Just L] :: GHC.Num.Integer) (ds_dQg [ALWAYS Just S] :: [GHC.Num.Integer]) -> case ds_dQg of wild_XI [ALWAYS Just A] { [] -> y_aj1; : x_aj5 [ALWAYS Just L] xs_aj6 [ALWAYS Just S] -> foldl'_sSS f_aj0 (f_aj0 y_aj1 x_aj5) xs_aj6 } I thought this was interesting. Is it to be expected? Am I right in interpreting this to mean it was just too much for the strictness analyzer. I believe the first ultimately produces significantly superior code, so should one always write their recursive functions such that the constant (functional?) parameters are first captured in a closure? In that vein, would it be useful if the compiler automatically transformed the second into the first? Thanks! -Tyson

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Building ndp Problem
by Dominic Steinitz 09 Jun '08

09 Jun '08

I wanted to try out data parallel haskell. I followed the instructions on http://haskell.org/haskellwiki/Data_Parallel_Haskell/PackageNDP but I get the following error: > dom@lagrange:~/ghc/libraries> make make.library.ndp > make: *** No rule to make target `build.library.ndp', needed by `make.library.ndp'. Stop. BTW when I built ghc, I had the following problem with happy (and alex). It kept telling me I needed dvips but dvips is already installed. In the end I used --nodeps. > dom@lagrange:~/happy> rpmbuild -ta happy-1.17.tar.gz > error: Failed build dependencies: > dvips is needed by happy-1.17-1.i586 > dom@lagrange:~/happy> rpmlocate dvips > /usr/bin/dvips > dom@lagrange:~/happy> rpm --query -f /usr/bin/dvips > texlive-2007-69 > dom@lagrange:~/happy> dvips --version > dvips(k) 5.96 > kpathsea version 3.5.6 > Copyright (C) 2005 Radical Eye Software. > There is NO warranty. You may redistribute this software > under the terms of the GNU General Public License > and the Dvips copyright. > For more information about these matters, see the files > named COPYING and dvips.h. > Primary author of Dvips: T. Rokicki; -k maintainer: T. Kacvinsky/ S. Rahtz. > rpmbuild -ta --nodeps happy-1.17.tar.gz

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*BSD support in 6.8.3
by Simon Marlow 07 Jun '08

07 Jun '08

Hi Folks, 6.8.3 is nearing release, and we have an outstanding bug affecting the GHCi on the BSDs: http://hackage.haskell.org/trac/ghc/ticket/2013 We need someone to help out with this. The patch in the ticket apparently works, but can't be committed as is because it isn't correctly #ifdef'd and will presumably break other platforms. Also it needs to be tested on OpenBSD/NetBSD in addition to FreeBSD. I don't have access to a *BSD machine right now, and I don't have the time available to set one up. If someone can donate a temporary account then that would be helpful, but most helpful would be if someone could work with us to get this bug fixed in time for 6.8.3 (i.e. the next few days). Otherwise, we have to release with the bug still in, which would be bad. Cheers, Simon

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GHC rewrite rules pragma
by Jan Jakubuv 30 May '08

30 May '08

Hi, I'm trying to find out how the GHC rewrite rules pragma work, but I'm not able to make it working. I have this simple example, where I would like to specialize the function gen to spec on strings: {-# OPTIONS -O2 -fglasgow-exts #-} gen :: [a] -> a gen = head {-# RULES "gen/Char" gen=spec #-} spec :: [Char] -> Char spec x = 'x' main :: IO () main = putStr (gen "aaa":"\n") -- EOF I compile it as: ghc -O2 -fglasgow-exts spec.hs but as a result, is always prints 'a' while I expect 'x'. Is it right? What is the problem here? I would be glad for any answer. I'm using GHC 6.8.2. Sincerely, Jan.

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Re: darcs-2 executable for PowerPC Macintosh
by Christian Maeder 30 May '08

30 May '08

I was able to statically link in libgmp.a by changing my installation: 1. I've copied libgmp.a into <prefix>/lib/ghc-6.8.2 2. I've changed <prefix>/lib/ghc-6.8.2/package.conf manually: changed: ], frameworkDirs = [], frameworks = ["GMP"], to: ,"-lgmp"], frameworkDirs = [], frameworks = [], so that "-lgmp" is in ldOptions and frameworks are empty 3. called ghc with the additional flags: -optl-Xlinker -optl-search_paths_first HTH Christian zooko wrote: > Here is a darcs-2 executable for PowerPC Mac. It was built on Mac OS > 10.4, and this tarball includes the "GMP.framework", which > (unfortunately) you have to copy into /Library/Frameworks or ~/ > Library/Frameworks before darcs will run. > > If any Haskell experts can tell me how to statically link or remove > this dependency on this GMP.framework I would like to know, and then > I can build a darcs binary which doesn't require such a step during > installation. > > https://zooko.com/darcs-2-mac-powerpc.tar.bz2 > > Regards, > > Zooko

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SCC "ab cd"
by Serge D. Mechveliani 29 May '08

29 May '08

Dear GHC developers, ghc-6.8.2 compiles {-# SCC "ab cd" #-} as all right. And the GHC candidate of May 27, 2008 reports the error: "spaces are not allowed in SCC". Do you think that this latter has more sense? Is not this a matter of the programmer to give string names to SCC points? Regards, ----------------- Serge Mechveliani mechvel(a)botik.ru

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