March 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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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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ANN: ghc 6.8.2 from MacPorts
by Gregory Wright 06 May '08

06 May '08

After what many would consider an unconscionable delay, I am happy to announce that ghc 6.8.2 is available from MacPorts. The ghc 6.8.2 port is available for Tiger/ppc, Tiger/intel and Leopard/ intel. Users with Leopard/ppc are out of luck until for now, for reason discussed earlier on this list. In partial recompense for their patience, users will get a ghc with more patches than any previous MacPorts ghc. A few notes: The file locking bugs #1992 and #2134 are fixed. Bug #1992 was a simple lock logic error and should be killed dead. Bug #2134 was the result of a lazy readFile holding a lock for an unpredictable time. There may be more cases like this one, and I would appreciate a note from anyone who come across a lock error during building. Users on Leopard/intel must upgrade to 10.5.2 to avoid an OS bug which under unusual circumstances would repeatably (and mysteriously) crash the build. This was first noticed running the building in an eshell under Aquamacs. Archives were built without tables of contents because ranlib wasn't being run or wasn't running to completion. Builds in the usual Terminal.app didn't trip over this bug. OpenGL support is built by default. It can be turned off using the no_opengl variant. OpenAL support is disabled. Apple's OpenAL framework lacks ALUT support (needed for the ghc binding) but has name clashes with the freealut library from the OpenAL.org website. Fixing this is probably straightforward. If someone is interested, I can give them some pointers on getting started. MacPort's ghc ought to always link with the correct libgmp (the one provided by the gmp port). The latest versions of alex, happy, haddock and hs-Edison are also available. Best Wishes, Greg

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gmp
by Christian Maeder 16 Apr '08

16 Apr '08

I understand that gmp is needed for the certain libraries like the Prelude with Double and Integer. But I do not understand why gmp is so deeply buried in the rts. Are the basic types Int and Pointer not enough to write a compiler like ghc? Cheers Christian

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scope of header files
by Duncan Coutts 03 Apr '08

03 Apr '08

I was under the impression that with ghc, ffi import declarations like this do not escape the module: foreign import ccall unsafe "foo.h foo" foo :: IO () However it seems that this one does: foreign import ccall unsafe "curses.h & stdscr" stdscrp :: Ptr WINDOWptr from: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mage-1.0 perhapsPbecause it's a pointer import it gets treated differently? Is this correct and expected behaviour? It's hard to tell what header files need to be used globally and inherited by client packages and which can safely be used privately. Duncan

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ANN: prof2dot, a graphical profiling tool
by Gregory Wright 02 Apr '08

02 Apr '08

I am pleased to announce the first release of prof2dot, a graphical profiling tool for use with GHC. While GHC has in the past worked with graphical profiling tools, they have been heavyweight and/or proprietary. Prof2dot is a simple tool for converting profiling information into a graphical format, released under a BSD3 license. It is simple because it offloads all of the work of rendering the graph onto Graphviz. So you need to install the Graphviz tools in order to use it. The program is a filter that takes the profiling output generated by running a GHC-compiled program with the "+RTS -px -RTS" option and turns it into a dot file. (The "dot" format is a textual representation of a directed or undirected graph.) The dot file can rendered in any format supported by Graphviz's dot program, and the file itself can be post-processed or edited to adjust the layout. Features of prof2dot: * display either the call graph (default) or the call tree, * colorize by cost center count, time or allocations, * group cost centers in the same module. Prof2dot installs as a typical caballized application. Running "prof2dot -?" from the command line will give a short summary of how to use the program and its options. Rendering very large graphs can exceed the internal resource limits of dot. You may have to compile your own version of the Graphviz tools with higher limits to handle these cases. A example of a colorized profile of a medium sized project is shown on our company's web site: http://antiope.com/downloads.html. Click on the small image to download a pdf of the complete profile graph. Prof2dot is available from hackage or the link given above. -Greg

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simple CSE?
by Conal Elliott 01 Apr '08

01 Apr '08

I'd like to know if it's possible to get GHC to perform some simple CSE for function-level programming. Here's a simple example: liftA2 (*) sin sin :: Double -> Double which inlines and simplifies to \ t -> sin t * sin t A more realistic, equivalent, example: let b = sin <$> id in liftA2 (*) b b Can GHC be nudged into computing 'sin t' once rather than twice? Thanks, - Conal

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patch-applied messages
by Christian Maeder 01 Apr '08

01 Apr '08

(resent this request for cvs-ghc(a)haskell.org to glasgow-haskell-users) Hi, could the actual change-diff of patches also be posted via this list (or a web-link to the change)? I think this was the case with the old cvs repository. This would teach a bit Haskell programming and how to write expressive log messages. Currently I never look up changes, although the log messages make me curious sometimes. (I rarely use darcs.) Cheers Christian This is just an example (with an uninteresting diff) > Tue Mar 25 17:49:32 PDT 2008 Ian Lynagh <igloo(a)earth.li> > * Remove a redundant type sig > > M ./compiler/ghci/InteractiveUI.hs -1

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64-bit breakdown
by Jay Scott 31 Mar '08

31 Mar '08

I have a MacBook (which is a Core 2 Duo) running Mac OS X 10.4. On this platform, gcc makes 32-bit executables by default, but if you give it - m64 it makes them 64-bit. I've tried it, and it works. gcc gives its version as "i686-apple-darwin8-gcc-4.0.1 (GCC) 4.0.1 (Apple Computer, Inc. build 5367)" But 64-bit doesn't work with my ghc installation (6.8.2 from the binary distribution on the downloads page). If I compile a "Hello World" program with -fvia-c -optc-m64, it fails, saying -- Warning: retaining unknown function `_siC_entry.eh' in output from C compiler Warning: retaining unknown function `_Main_main_entry.eh' in output from C compiler Warning: retaining unknown function `_ZCMain_main_entry.eh' in output from C compiler Prologue junk?: _siC_entry: LFB142: subq $8, %rsp LCFI0: -- I don't need to solve this, but I thought I should make sure it's known. Jay

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