- Glasgow-haskell-users

Pragma not recognised when wrapped in #ifdef
by Alistair Bayley 11 Feb '09

11 Feb '09

I have this little test program: {-# LANGUAGE CPP #-} #ifdef PRAGMA_DERIVE_TYPEABLE {-# LANGUAGE DeriveDataTypeable #-} #else {-# OPTIONS -fglasgow-exts #-} #endif -- This file is Test/Fail.hs. -- ghc --make -optP-DPRAGMA_DERIVE_TYPEABLE -XCPP Test.Fail module Test.Fail where import Data.Generics data Fail = Fail deriving Typeable If compile this wih the command ghc --make -optP-DPRAGMA_DERIVE_TYPEABLE -XCPP Test.Fail then I get this error from ghc-6.10.1: [1 of 1] Compiling Test.Fail ( Test\Fail.hs, Test\Fail.o ) Test\Fail.hs:11:26: Can't make a derived instance of `Typeable Fail' (You need -XDeriveDataTypeable to derive an instance for this class) In the data type declaration for `Fail' I've checked the preprocessor output with -E, and that looks fine. I can compile the preprocessor output with ghc without errors. Alistair

7 9

Byte in list
by Aswad, Mustafa K 10 Feb '09

10 Feb '09

Hi dear I need to calculate the size of alist consist of n element (("I(a*b)" , "I(b) , I(a)") in 32 bit machine ? -- Heriot-Watt University is a Scottish charity registered under charity number SC000278.

1 0

Re: How bad is the PowerPC backend?
by Tim Chevalier 10 Feb '09

10 Feb '09

On 2/9/09, David Brown <haskell(a)davidb.org> wrote: > > Which CPU is the x86? The modern x86 CPUs (such as Core2) will be > significantly faster than the PowerPC, even at comparable clock rates. > Have you just compared even C code tests? > I think that goes a long way towards explaining it... a simple C loop that I tried runs for 4.5s on the PC and 30s on the Mac. So probably this isn't GHC's fault. Thanks for the suggestion. Tim -- Tim Chevalier * http://cs.pdx.edu/~tjc * Often in error, never in doubt "In fact, a sense of essence is, in essence, the essence of sense, in effect." -- Douglas Hofstadter

1 0

How bad is the PowerPC backend?
by Tim Chevalier 09 Feb '09

09 Feb '09

Hello, For obscure reasons, I'm running some benchmarks both on an x86 machine (2.20 Ghz, 2 GB of RAM, Linux 2.6.22-15) and on a PowerPC Mac (1 Ghz, 512 MB of RAM, Mac OS 10.5). I noticed that even some pretty simple programs run much slower on the Mac than on the PC. For example, the following program (edited down from the "life" nofib benchmark): ------------------------------------------------- limit xs = go [] xs go acc (x:y:xs) | x==y = acc ++ [x] | otherwise = go (acc ++ [x]) (y:xs) go acc [x] = acc ++ [x] go acc [] = error "limit" main = print (length (limit (iterate (\ x -> if x == 10000 then x else (x+1)) 1))) --------------------------------------------------- runs in about 1.5 seconds on the PC, and 14 seconds on the Mac. This is with ghc -O2, version 6.10.1. The numbers are about the same on either machine whether I use -fvia-C or -fasm. The Mac does have a lot less RAM, but I can see that the program isn't swapping. So is the PPC backend really this bad, or should I be looking for something weird with the hardware or configuration on the Mac? Thanks, Tim -- Tim Chevalier * http://cs.pdx.edu/~tjc * Often in error, never in doubt "I don't like your I-can-use-anything-as-an-adjective attitude." -- Larry Wall

2 2

length of module name affecting performance??
by Daniel Gorín 09 Feb '09

09 Feb '09

Hi While trying to see if I could make some code run faster I stumbled upon something that looks weird to me: 2x-3x performance loss when a module is renamed to a longer name! Here's what I see with the attached examples: #diff long-modname-ver.hs short-modname-ver.hs 2c2 < import VeryLongModuleName --- > import ShortM #diff VeryLongModuleName.hs ShortM.hs 1c1 < module VeryLongModuleName --- > module ShortM #ghc --make -O2 -Wall long-modname-ver.hs #ghc --make -O2 -Wall short-modname-ver.hs #time -p ./long-modname-ver > /dev/null real 55.90 user 55.17 sys 0.51 #time -p ./short-modname-ver > /dev/null real 22.23 user 21.97 sys 0.10 I'm using GHC 6.10.1 on OS X. Any ideas on what may be going on? Thanks Daniel

9 12

Display of associated types in GHCi
by Douglas McClean 06 Feb '09

06 Feb '09

I have a question about the display of names for associated types in GHCi. I have a module with a matrix type constructor: > data (Natural r, Natural c) => Matrix r c t = Matrix [[t]] deriving (Eq) which uses type-level naturals to provide dimension checking. A type class for multiplication: > class Multiply a b where > type Product a b > times :: a -> b -> Product a b and an instance for matrix multiplication: > instance (Natural a, Natural b, Natural c, Num t) => Multiply (Matrix a b t) (Matrix b c t) where > type Product (Matrix a b t) (Matrix b c t) = Matrix a c t > times m1 m2 = ... All of this works really well, I get dimension checking (and inference), and lot of other goodies. My question has to do with the following GHCi session: *Main> let a = matrix two two [[1,1],[2,6]] *Main> :t a a :: Matrix Two Two Integer *Main> :t a `times` a a `times` a :: Product (Matrix Two Two Integer) (Matrix Two Two Integer) Am I correct that the type denoted by "Product (Matrix Two Two Integer) (Matrix Two Two Integer)" is always "Matrix Two Two Integer"? It certainly behaves that way in more complicated expressions, which is desirable. If so, could someone explain the reason why GHCi chooses not to simplify such types for display? Could it? Is there a reason why such simplification would be undesirable (when it is possible, I understand that it wouldn't be if type variables were present)? Thanks, Doug McClean

3 3

Temporarily overriding Data.Generic
by Deniz Dogan 06 Feb '09

06 Feb '09

Sorry for those who receive this who have already gotten it from haskell-cafe. --- Hi I'm currently working on "hacking" Data.Generics for my master thesis. I'm basically trying to find out whether it can be made any faster using e.g. rewrite rules. The problem I'm having is that I need an easy way to import my own modified version of Data.Generics (currently located in the same directory as my testing program) without unregistering or hiding syb-0.1.0.0 as base seems to depend on it. I've read the GHC user manual trying to find nice ways to do this using a bunch of different parameters to ghc, but I can't figure it out. Does anyone here know? Any help appreciated, Deniz

3 3

Error in building profiling
by Marco Túlio Gontijo e Silva 06 Feb '09

06 Feb '09

Hello, I'm trying to package ghc-paths for debian, and I got to this: $ ./setup configure --enable-library-profiling --disable-library-vanilla Configuring ghc-paths-0.1.0.5... $ ./setup build Preprocessing library ghc-paths-0.1.0.5... Building ghc-paths-0.1.0.5... /usr/bin/ar: creating dist/build/libHSghc-paths-0.1.0.5_p.a /usr/bin/ld: dist/build/GHC/Paths.o: No such file: No such file or directory I thought this could be a problem with this package, but I've tried with mtl, and I got the same result: /usr/bin/ld: dist/build/Control/Monad/Cont.o: No such file: No such file or directory I'm using ghc6 6.10.1+dfsg1-5 and binutils 2.19-1~exp1. I tried the same with ghc6 6.8.2dfsg1-1 and it worked. Greetings. -- marcot http://marcot.iaaeee.org/

1 0

Re: Ready for testing: Unicode support for Handle I/O
by Paolo Losi 04 Feb '09

04 Feb '09

Max Vasin wrote: > Wouldn't it be more correct to separate binary IO, which > return [Word8] (or ByteString) and text IO which return > [Char] and deal with text encoding? IIRC that was done in > Bulat Ziganshin's streams library. That's exactly what I meant. Text IO could be then implemented on top of binary IO. Would it be possible to envision a solution that enables composition of IO low level strategies vs binary <-> text conversion strategies? Pao

1 0

Ready for testing: Unicode support for Handle I/O
by Simon Marlow 04 Feb '09

04 Feb '09

I've been working on adding proper Unicode support to Handle I/O in GHC, and I finally have something that's ready for testing. I've put a patchset here: http://www.haskell.org/~simonmar/base-unicode.tar.gz That is a set of patches against a GHC repo tree: unpack the tarball, and say 'sh apply /path/to/ghc/repo' to apply all the patches. Then clean your tree and build it from scratch (or if you're using the new GHC build system, just say 'make' ;-). It should validate, bar one or two minor failures. Oh, it doesn't work on Windows yet. That's the major thing left to do. If anyone else felt like tackling this I'd be delighted: all you have to do is implement a Win32 equivalent of the module GHC.IO.Encoding.Iconv (see below), everything else should work unchanged. Depending on whether any further changes are required, I may amend-record some of these patches, so treat them as temporary patches for testing only. Below is what will be the patch description in the patch for libraries/base. Comments/discussion please! Cheers, Simon Unicode-aware Handles ~~~~~~~~~~~~~~~~~~~~~ This is a significant restructuring of the Handle implementation with the primary goal of supporting Unicode character encodings. The only change to the existing behaviour is that by default, text IO is done in the prevailing encoding of the system. Handles created by openBinaryFile use the Latin-1 encoding, as do Handles placed in binary mode using hSetBinaryMode. We provide a way to change the encoding for an existing Handle: hSetEncoding :: Handle -> TextEncoding -> IO () and various encodings: latin1, utf8, utf16, utf16le, utf16be, utf32, utf32le, utf32be, localeEncoding, and a way to lookup other encodings: mkTextEncoding :: String -> IO TextEncoding (it's system-dependent whether the requested encoding will be available). Currently hSetEncoding is availble from GHC.IO.Handle, and the encodings are available from GHC.IO.Encoding. We may want to export these from somewhere more permanent; that's something for a library proposal. Thanks to suggestions from Duncan Coutts, it's possible to call hSetEncoding even on buffered read Handles, and the right thing happens. So we can read from text streams that include multiple encodings, such as an HTTP response or email message, without having to turn buffering off (though there is a penalty for switching encodings on a buffered Handle, as the IO system has to do some re-decoding to figure out where it should start reading from again). If there is a decoding error, it is reported when an attempt is made to read the offending character from the Handle, as you would expect. Performance is about 30% slower on "hGetContents >>= putStr" than before. I've profiled it, and about 25% of this is in doing the actual encoding/decoding, the rest is accounted for by the fact that we're shuffling around 32-bit chars rather than bytes in the Handle buffer, so there's not much we can do to improve this. IO library restructuring ~~~~~~~~~~~~~~~~~~~~~~~~ The major change here is that the implementation of the Handle operations is separated from the underlying IO device, using type classes. File descriptors are just one IO provider; I have also implemented memory-mapped files (good for random-access read/write) and a Handle that pipes output to a Chan (useful for testing code that writes to a Handle). New kinds of Handle can be implemented outside the base package, for instance someone could write bytestringToHandle. A Handle is made using mkFileHandle: -- | makes a new 'Handle' mkFileHandle :: (IODevice dev, BufferedIO dev, Typeable dev) => dev -- ^ the underlying IO device, which must support -- 'IODevice', 'BufferedIO' and 'Typeable' -> FilePath -- ^ a string describing the 'Handle', e.g. the file -- path for a file. Used in error messages. -> IOMode -- ^ The mode in which the 'Handle' is to be used -> Maybe TextEncoding -- ^ text encoding to use, if any -> IO Handle This also means that someone can write a completely new IO implementation on Windows based on native Win32 HANDLEs, and distribute it as a separate package (I really hope somebody does this!). This restructuring isn't as radical as previous designs. I haven't made any attempt to make a separate binary I/O layer, for example (although hGetBuf/hPutBuf do bypass the text encoding). The main goal here was to get Unicode support in, and to allow others to experiment with making new kinds of Handle. We could split up the layers further later. API changes and Module structure ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NB. GHC.IOBase and GHC.Handle are now DEPRECATED (they are still present, but are just re-exporting things from other modules now). For 6.12 we'll want to bump base to version 5 and add a base4-compat. For now I'm using #if __GLASGOW_HASKEL__ >= 611 to avoid deprecated warnings. I split modules into smaller parts in many places. For example, we now have GHC.IORef, GHC.MVar and GHC.IOArray containing the implementations of IORef, MVar and IOArray respectively. This was necessary for untangling dependencies, but it also makes things easier to follow. The new module structurue for the IO-relatied parts of the base package is: GHC.IO Implementation of the IO monad; unsafe*; throw/catch GHC.IO.IOMode The IOMode type GHC.IO.Buffer Buffers and operations on them GHC.IO.Device The IODevice and RawIO classes. GHC.IO.BufferedIO The BufferedIO class. GHC.IO.FD The FD type, with instances of IODevice, RawIO and BufferedIO. GHC.IO.Exception IO-related Exceptions GHC.IO.Encoding The TextEncoding type; built-in TextEncodings; mkTextEncoding GHC.IO.Encoding.Types GHC.IO.Encoding.Iconv Implementation internals for GHC.IO.Encoding GHC.IO.Handle The main API for GHC's Handle implementation, provides all the Handle operations + mkFileHandle + hSetEncoding. GHC.IO.Handle.Types GHC.IO.Handle.Internals GHC.IO.Handle.Text Implementation of Handles and operations. GHC.IO.Handle.FD Parts of the Handle API implemented by file-descriptors: openFile, stdin, stdout, stderr, fdToHandle etc.

4 6