September 2006 - 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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Replacement for GMP: Update
by Peter Tanski 23 Jan '07

23 Jan '07

Simon PJ, Simon, Esa and John, Here is an update on what I have been doing so far in making a grand attempt to replace GMP. (1) evaluate replacement libraries LibTomMath: Pros- * has all the operators GMP offered Cons- * slow; about half as fast as OpenSSL in my tests for simple mathematical operations, much slower if you account for time to write or resize memory. (There is another MP library, which LibTomMath is based on, that is also very slow--student work) * not even reentrant; needs significant modification * beta-release; needs a bit of work to get it to production level * configuration needs to be written (not really portable, messy) ARPREC: Pros- * very fast (essentially does everything through the Floating Point Unit of a CPU) * complex mathematical operations * very precise * already thread safe (through C++ thread-safe statics) Cons- * no bitwise operations (not even left and right-shifts) * difficult configuration (everything runs by setting a precision level; ("precision level" ~= number of words (doubles) in array) it does not automatically resize memory; conversion from MP Real to Integer relies specially on careful precision-level) * memory inefficient (underestimates the number of real digits you can fit into a double, i.e., a 64-bit double has 48 bits of precision, holding about 9.6 digits per byte, resulting in an 848-byte array to hold an MP number with 1000 digits). OpenSSL: Crypto++ (http://www.eskimo.com/~weidai/cryptlib.html) Botan (http://botan.randombit.net/) Pros- * all of these are fast, since all use Integers to support cryptography; (Crypto++ and Botan are C++ crypto-libraries, all licenses good) * all of these provide most basic mathematical operations Cons- * none of these provide &, |, ^(xor) bitwise operators * Botan has least mathematical operators of the three * none provide lcm operator * all would realistically have to have the Integer libraries stripped out of the distribution and repackaged for GHC Summary: I finally settled on modifying OpenSSL, since that would be the easiest to work with under GHC's hood (plain C code, not C++). I have to: a. make OpenSSL's BN thread-safe (add thread local storage, at least) b. optimally add configure-conditional parallelism to BN (through PVM) c. add &, |, ^, lcm and a few other operations d. separate the BN from the rest of OpenSSL and rename the symbols to avoid conflicts (necessary because I have to modify the library anyway) (2) work on GHC: * finally understand C--; know what I need to modify * work through Makefiles: touch and go; I haven't mapped out all the variable settings from configure.in on down when it comes to DLLs Comment: for the Makefile in ghc/rts, in lines 300-346, GC_HC_OPTS += -optc-O3 --isn't this problematic? gcc, from -O2 on includes -fgcse which may *reduce* runtime performance in programs using computed gotos; -fgcse is actually run twice, because -frerun-cse-after-loop is also set at -O2. Would it be better to pass individual flags, such as -funroll-loops and -falign-loops=16 (ppc, Intel setting)? (3) I have been looking at how to implement a dual-constructor-in-a- pointer for Integer (i.e., merge constructors of small Integers and big Integers into the Int#). Would that solution be workable or might it break current Haskell programs? Just a thought. -Peter

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RE: [Haskell] Deferred instance declarations (serialization ofexistential boxes)
by Simon Peyton-Jones 10 Nov '06

10 Nov '06

[redirecting to GHC users, since it's a GHC-specific question] Misha | I asked this question on haskell-cafe once, but my post didn't get any | responses, so I try once again here explaining a bit more where my | problem comes from. I was at ICFP. | Suppose I have a monomorphic datatype, say T and want to do something | with it, which depends on an instance of class C being defined for T. | However I can only provide this instance later, in a different module. | So I would like to write something like | | > f :: C T => T -> T | or | > instance C T => C T' where | > -- a body that uses functions from C T There is no reason in principle why this isn't ok. But there is a practical reason why things are the way they are. Generally, GHC tries to share constraints as much as possible, so that a (C T) constraint in one function right hand side is satisfied by the same binding as another (C T) constraint from another right hand side. So in general, GHC "floats" constraints outwards if they don't mention any type variables bound by the forall's of the type signature. The whole question of the interaction of type signatures and constraints is quite delicate, and I rather doubt I'll change this behaviour soon. (And no one else has asked for it before, I think.) But I think the case is stronger for top-level constraints, and I will bear it in mind. If you would like to open a Trac feature request, please do so. Concerning your application | I am having a box like | > data Box = forall a. Cxt a => Box a | and want to write a Read instances for it. I don’t see how it helps to defer the Read instance. Reading existentials is bound to be difficult, or even impossible. I guess it depends what is in Cxt. Simon

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GHC 6.4.1 and Win32 DLLs: Bug in shutdownHaskell?
by Michael Marte 24 Oct '06

24 Oct '06

Hello *, before filing a bug report, I want others to comment on my problem. Maybe it's my fault, not ghc's. I wrapped up some Haskell modules in a Win32 DLL. Loading the DLL dynamically (with LoadLibrary) works fine. However, whether I actually use the library or not, the program (an application with MFC GUI) crashes upon termination. To find the reason for the crash, I added a new function for unloading the DLL using FreeLibrary. FreeLibrary works fine, however the program crashes when it returns to the main event loop. Interestingly, when I reload the library (FreeLibrary followed by LoadLibrary) the program continues working. However, every reload cycle causes the virtual size of the process to increase by about 300K and the fourth reload fails with the error message "getMBlock: VirtualAlloc failed with: 8" (appears in a message window) accompanied by many repetitions of the message "Timer proc: wait failed -- error code: 6" (appears on stderr) and followed by the message "getMBlocks: misaligned block returned" (again in a message window). Then the programm crashes. Development takes place on Windows XP Professional using MS Visual Studio 6.0 SP 5 and ghc 6.4.1. There are no references from the C++ side to the Haskell heap. I build the DLL using the command ghc --mk-dll -optdll--def -optdllFoo.def -o Foo.dll Foo.o Foo_stub.o dllMain.c dllMain.c looks as follows: #include <windows.h> #include <Rts.h> extern void __stginit_EUzu3820zu85(void); static char* args[] = { "ghcDll", NULL }; /* N.B. argv arrays must end with NULL */ BOOL STDCALL DllMain(HANDLE hModule, DWORD reason, void* reserved) { if (reason == DLL_PROCESS_ATTACH) { /* By now, the RTS DLL should have been hoisted in, but we need to start it up. */ startupHaskell(1, args, __stginit_Foo); return TRUE; } else if (reason == DLL_PROCESS_DETACH) { shutdownHaskell(); } return TRUE; } I played around with hs_exit instead of shutdownHaskell, I moved initialization and clean-up from DllMain to my library loader, nothing helps. Even doing no clean-up whatsoever does not change the behaviour. Any ideas? Michael

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6.4.3 and threaded RTS problems
by Simon Marlow 16 Oct '06

16 Oct '06

Hi Folks, Roman Leshchinskiy and I looked into the 6.4.3 crashes on Sparc/Solaris yesterday. I think we may have found the problem, and it seems likely that this is the same problem affecting 6.4.3 on MacOS X. The threaded RTS is assuming in a couple of places that pthread_cond_wait() doesn't spuriously wake up, which is apparently the case on Linux but not true in general. I don't think this bug affects 6.6. I could be wrong, however. Does anyone on MacOS X have a recent testsuite run with the HEAD? I'll try to put together a fix for 6.4.3 when the 6.6 release cycle has died down. Cheers, Simon

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UTF-8 decoding error
by Christian Maeder 10 Oct '06

10 Oct '06

How can I convince ghc version 6.5.20060919 to accept latin1 characters in literals? I wish to keep source files (containing umlauts in strings) that can be compiled by either ghc-6.4.2 and ghc-6.6. Christian

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building GHC (head) on windows MINGW: HsRegexPosixConfig.h: No such file or directory
by Rene de Visser 05 Oct '06

05 Oct '06

Hello, What do I need to install for the regex library support on MINGW? It looks like the regex library needs the posix library, and in my MINGW / MSYS installation I don't find one (and neither does configure). Rene.

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GHC on MacOS
by Simon Peyton-Jones 03 Oct '06

03 Oct '06

Folks Quite a few of you are using GHC on MacOS -- for example, there were lots of Macs at the GHC Hackathon earlier this month. However, we don't have access to a machine running MacOS, so it's pretty difficult for us to deal with bug reports. So this message is to ask: a) Can anyone give us remote access to a Mac? b) Does anyone feel able to help look after GHC's Mac port? Simon, Simon, and Ian

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Map.genericSize
by Serge D. Mechveliani 02 Oct '06

02 Oct '06

Dear GHC developers, Can you, please, provide Map.genericSize :: Map -> Integer in addition to Map.size :: Map -> Int ? For I use `Map.size', a bit, and need its variant which is both O(1) and Integer (because Int is less reliable). Probably, this is not hard to arrange. The same request is for Data.Set. What do you think of this? ----------------- Serge Mechveliani mechvel(a)botik.ru

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more fixups for GHC docs
by Bulat Ziganshin 01 Oct '06

01 Oct '06

Hello glasgow-haskell-users, 1. section 7.11.6 contains small typo - both %note are "%note foo" while CORE pragmas use "foo" and "bar" 2. section 7.13 notes that generic classes was broken in GHC 5.02. afaik, they worked at least in GHC 6.4 also it will be great if each paragraph of Release Notes will link to corresponding section in documentation for further reading. now we don't have links for impredicative polymorphism, bang patterns, GC improvements (we can point to http://hackage.haskell.org/trac/ghc/ticket/650) -I RTS flag, -split-objs flag (and also it will be great to mention here that its using allows to reduce size of binaries) i think that it should be mentioned here that parallel arrays support is omitted in 6.6 despite this support was never documented one more small suggestion - in GHC 6.4.3 add "-A5m" RTS flag to compiler itself in order to make it faster and last question - i don't like inclusion of unix and win32 in a list of core libs. why they are here? may be it's possible to include small modules with functionality required for compiler itself in GHC.* hierarchy and then move the rest into extra libraries? -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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