- Glasgow-haskell-users

Re: [Haskell-cafe] Default definitions for associated type synonyms
by Isaac Dupree 02 Jun '08

02 Jun '08

Dreixel wrote: > Hello, > > Does anyone know if it is possible to specify a default definition for an > associated type synonym? When I tried: > > class A a where >> type B a = a >> > > GHC (version 6.9.20080309) told me: "Type declaration in a class must be a > kind signature or synonym default". However, when I look at the parser I see > no way to specify such synonym default. Is this possible? I'm curious... so, cc'ing glasgow-haskell-users mailinglist because the question is more likely to be noticed by relevant people there. > Thanks, > Zé Pedro

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impredicative polymorphism: seen on HCAR
by Isaac Dupree 02 Jun '08

02 Jun '08

The May 2008 Haskell Communities and Activities Report, GHC <http://www.haskell.org/communities/05-2008/html/report.html#ghc>: > Impredicative polymorphism. We are not happy with GHC’s current > implementation of impredicative polymorphism, which is rather > complicated and ad hoc. Dimitrios (with Simon and Stephanie) > wrote a paper about a new and better approach: > http://research.microsoft.com/~simonpj/papers/boxy > . At the same time, Daan Leijen has been working on his > closely-related design: > http://research.microsoft.com/users/daan/pubs.html > . Daan’s design has a much simpler implementation, in exchange > for an (arguably) less-predictable specification. Which of these > two should we implement? Let us know! I read the papers... Dimitrios's *paper* is easier for me to understand than Daan's. In fact they seem quite similar. I have no idea of any examples where they would behave differently. I don't use impredicative polymorphism much (but maybe because of my perception that the existing implementations are poorly designed, and that it can usually be avoided by an amount of abstraction that's useful anyway). So I'd say, implement the easier solution. Is there a paper or documentation somewhere, presenting a practical argument for why impredicative polymorphism is important in real programs (beyond runST $) -- for example, a real program that uses it and has clearer code because of it? I don't really mind writing let/function type-signatures that have weird types (unless they're long and repeat information that doesn't need to be, which is a different problem). I wonder how often these proposals require type-signatures on lambdas passed to higher-order functions, though... A side-effect is for those of us who want to have any concern for future compatibility with non-GHC type systems (or the long future of GHC's, even), whether one of the proposals would be likely to be easier for someone else to implement in a different compiler. -Isaac

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Re: ANNOUNCE: GHC 6.8.3 Release Candidate
by Serge D. Mechveliani 02 Jun '08

02 Jun '08

On Sun, Jun 01, 2008 at 01:13:06AM +0100, Ian Lynagh wrote: > > Hi Serge, > > On Sat, May 31, 2008 at 12:54:50PM +0400, Serge D. Mechveliani wrote: > > This is a bug report for the ghc candidate of May 27, 2008 > > for ghc-6.8.3. > > A short program example for this bug candidate is on > > > > http://botik.ru/pub/local/Mechveliani/ghcBugs/candidateMay27-08-bug.zip > > Thanks, I've finally tracked this down. The problem is that when you > evaluate something like > f ^ 10 > in 6.8.2 the result was > res > while in 6.8.3 it is > 1 * res > > I think this is actually a bug in your class instances, but I will try > to look at http://hackage.haskell.org/trac/ghc/ticket/2306 before 6.8.3 > which should, as a side-effect, make it work again. ?? Probably, 6.8.3 is wrong. Because when res :: Num a => a, 1*res means ((fromInteger 1) :: a) * res in Haskell-98. Right? And (fromInteger n) :: a can be defined arbitrarily by the programmer. For example, DoCon has the instance instance CommutativeRing a => Num (Pol a) where ... fromInteger _ = error "No (fromInteger n) :: Pol _ !\ \Apply instead fromi <samplePolynomial> n." -- something of this kind. This is why res and 1*res are not equivalent in Haskell-98 for res :: Num a => a. Am I missing something? ----------------- Serge Mechveliani mechvel(a)botik.ru

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test for 6.8.3-may27
by Serge D. Mechveliani 01 Jun '08

01 Jun '08

About the 6.8.3 candidate of May 27, there remains the question: why it builds DoCon-2.11 considerably slower than ghc-6.8.2 (3 times, as I recall) and needs larger -M memory to build this DoCon ? Regards, ----------------- Serge Mechveliani mechvel(a)botik.ru

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Re: [Haskell-cafe] hint / ghc api and reloading modules
by Daniel Gorín 01 Jun '08

01 Jun '08

(Since this can be of interest to those using the ghc-api I'm cc-ing the ghc users' list.) Hi, Evan The odd behavior you spotted happens only with hint under ghc-6.8. It turns out the problem was in the session initialization. Since ghc-6.8 the newSession function no longer receives a GhcMode. The thing is that, apparently, if one was passing the Interactive mode to newSession under ghc-6.6, now you ought to set the ghcLink dynflag to LinkInMemory instead. I couldn't find this documented anywhere (except for this patch http://www.haskell.org/pipermail/cvs-ghc/2007-April/034974.html) but it is what ghci is doing and after patching hint to do this the reloading of modules works fine. I'll be uploading a fixed version of hint to hackage in the next days. Thanks, Daniel On May 31, 2008, at 2:46 PM, Evan Laforge wrote: > I'm using "hint", but since it's basically a thin wrapper around the > GHC API, this is probably a GHC api question too. Maybe this should > go to cvs-ghc? Let me know and I'll go subscribe over there. > > It's my impression from the documentation that I should be able to > load a module interpreted, make changes to it, and then reload it. > This is, after all what ghci does. It's also my impression that the > other imported modules should be loaded as object files, if the .hi > and .o exist, since this is also what ghci does. > > However, if I load a module and run code like so (using hint): > > GHC.loadModules ["Cmd.LanguageEnviron"] > GHC.setTopLevelModules ["Cmd.LanguageEnviron"] > GHC.setImports ["Prelude"] > cmd_func <- GHC.interpret (mangle_code text) (GHC.as :: LangType) > > It works fine until I change LanguageEnviron. If I make a change to a > function, I don't see my changes in the output, as if the session is > only getting partially reset. If I insert a syntax error, then I do > see it, so it is recompiling the file in some way. However, if I > *rename* the function and call it with the new name, I get a > GhcException: > > During interactive linking, GHCi couldn't find the following symbol: > ... etc. > > So I examined the code in hint for loadModules and the code in > ghci/InteractiveUI.hs:/loadModule, and they do look like they're doing > basically the same things, except a call to rts_revertCAFs, which I > called too just for good measure but it didn't help (I can't find its > source anywhere, but the ghci docs imply it's optional, so I suspect > it's a red herring). > > Here's a condensed summary of what hint is doing: > -- reset > GHC.setContext session [] [] > GHC.setTargets session [] > GHC.load session GHC.LoadAllTargets > -- rts_revertCAFs > > -- load > targets <- mapM (\f -> GHC.guessTarget f Nothing) fs > GHC.setTargets session targets > GHC.load session GHC.LoadAllTargets > > -- interpret > let expr_typesig = "($expr) :: xyz" > expr_val <- GHC.compileExpr session expr_typesig > return (GHC.Exts.unsafeCorce# expr_val :: a) > > -- GHC.compileExpr > maybe_stuff <- hscStmt hsc_env ("let __cmCompileExpr = "++expr) > ([n],[hv]) <- (unsafeCoerce# hval) :: IO [HValue] > return (Just hv) > > > and then ghci does: > -- load > GHC.setTargets session [] > GHC.load session LoadAllTargets > > targets <- io (mapM (uncurry GHC.guessTarget) files') > GHC.setTargets session targets > GHC.load session LoadAllTargets > > rts_revertCAFs > putStrLn "Ok, modules loaded: $modules" > > -- interpret > GHC.runStmt session stmt step > > -- GHC.runStmt > Just (ids, hval) <- hscStmt hsc_env' expr > coerce hval to (IO [HValue]) and run it carefully > > > So it *looks* like I'm doing basically the same thing as ghci... > except obviously I'm not because ghci reloads modules without any > trouble. Before I go start trying to make hint even more identical to > ghci, is there anything obviously wrong here that I'm doing? > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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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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large binary footprint ?
by HP Wei 28 May '08

28 May '08

machine: Sun Sparc, with SunOS 5.10 ghc version --- 6.8.2 [ solaris-binaries downloaded from ghc site ] The Question: I compiled the code: putStr "Hello World!\n" ghc -o hello -L../lib hello.hs where ../lib contains the libgmp.so The resulting binary code size is 3.9 Mbytes I had the impression that it should be of the order of 500 Kbytes. How can I reach that number ? Thanks HP

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static linking
by Peter Gammie 28 May '08

28 May '08

Hello, I am having a bit of trouble static linking my program using GHC 6.8.2. In brief: "rt" uses "pthread", but -lrt is the final thing on the command line passed to the linker, and so the pthread symbols are not resolved. Manually moving -lpthread to the end of the collect2 command line does the trick. The question is how to do this using ghc. This is on Debian, using the 6.8.2-5 from unstable. I can provide the command lines if that is helpful. Note the same setup worked fine under GHC 6.6.1. cheers peter

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