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ANNOUNCE: ZMachine 0.0
by Samuel Bronson 09 Dec '06

09 Dec '06

I've written a (partial) Z-machine interpreter in Haskell. It is missing lots of stuff, but I got it to the point where it doesn't cause actual pain to play with it ;-). It uses gtk2hs for the interface, though other interfaces could be implemented without actually changing the interpreter proper. (Though I suppose you'd want to get rid of all the trace output if you were going to write a curses UI.) You can either darcs get http://naesten.dyndns.org:8080/repos/ZMachine or grab a tarball at http://naesten.dyndns.org:8080/repos/ZMachine/ZMachine-0.0.tar.gz Patches and comments are greatly desired. (Except for "where is the status area". At least I don't have the stuff intended for the status area going to the main output area like it used to!)

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ANN: hpodder 0.99.1
by John Goerzen 08 Dec '06

08 Dec '06

Version 0.99.1 of hpodder is out. This version has been altered to be compatible with the new MissingH, ConfigFile, and hslogger packages. It also contains some minor bugfixes. hpodder has a new homepage: http://software.complete.org/hpodder

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ANN: MissingH 0.18.0
by John Goerzen 08 Dec '06

08 Dec '06

I'm pleased to announce release 0.18.0 of MissingH. This release implements the first part of the MissingH transition discussed on haskell-cafe. Detail on the planned changes can be found at http://software.complete.org/missingh/wiki/TransitionPlanning. Note that not all of those changes have been carried out with this release. The major changes are: * Most code from other sources that had been merged into MissingH has been split off * Stable, mostly standalone components of MissingH have been split off: hslogger, ftphs, ConfigFile, AnyDBM. * All modules renamed to more closely follow current Haskell naming practices MissingH is a large collection of assorted utility libraries for Haskell. Its primary audience is Haskell programmers that want to get practical things done fast. It also serves as a staging area of sorts for useful, general-purpose Haskell code. This could be code that may eventually wind up in base Haskell libraries, or it could grow into a library in its own and be forked off. Or it could remain in MissingH indefinately. You can find the MissingH homepage, which features a wiki, downloads, API reference, darcs repository viewer, and bug tracker, at: http://software.complete.org/missingh -- John Goerzen Author, Foundations of Python Network Programming http://www.amazon.com/exec/obidos/tg/detail/-/1590593715

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ANN: hslogger 1.0.0
by John Goerzen 08 Dec '06

08 Dec '06

hslogger 1.0.0 has been released. hslogger is a logging framework for Haskell. Here are some of its features: * Each log message has a priority and a source associated with it * Multiple log writers can be on the system * Configurable global actions based on priority and source * Extensible log writers (handlers) * Default handlers that write to the console, file handles, or syslog * Easy to use operation hslogger was previously a part of the MissingH library. The code in this release is unchanged from its state in MissingH, other than the changes necessary to make it a standalone package. You can find the hslogger homepage, which features a wiki, downloads, API reference, darcs repository viewer, and bug tracker, at: http://software.complete.org/hslogger

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ANN: ConfigFile 1.0.0
by John Goerzen 08 Dec '06

08 Dec '06

Hi, I'm pleased to announce version 1.0.0 of ConfigFile. ConfigFile is a parser and writer for handling sectioned config files in Haskell. The ConfigFile module works with configuration files in a standard format that is easy for the user to edit, easy for the programmer to work with, yet remains powerful and flexible. It is inspired by, and compatible with, Python's ConfigParser module. It uses files that resemble Windows .INI-style files, but with numerous improvements. ConfigFile provides simple calls to both read and write config files. It's possible to make a config file parsable by this module, the Unix shell, and make. ConfigFile was previously a part of the MissingH library where it was known as ConfigParser. The code in this release is unchanged from its state in MissingH, other than the changes necessary to make it a standalone package. You can find the ConfigFile homepage, which features a wiki, downloads, API reference, darcs repository viewer, and bug tracker, at: http://software.complete.org/configfile

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ANN: AnyDBM 1.0.0
by John Goerzen 08 Dec '06

08 Dec '06

AnyDBM 1.0.0 has been released today. AnyDBM is a generic DBM-type interface. It provides a generic infrastructure for supporting storage of hash-like items with String-to-String mappings. It can be used for in-memory or on-disk storage. Two simple backend drivers are included with this package: one that is RAM-only, and one that is persistent and disk-backed. The hdbc-anydbm package provides another driver, which lets you use simple tables in any SQL database to provide a DBM-like interface. MissingPy also provides a Python driver which lets you use any Python anydbm driver under Haskell AnyDBM. AnyDBM was previously a part of the MissingH library. The code in this release is unchanged from its state in MissingH, other than the changes necessary to make it a standalone package. You can find the AnyDBM homepage, which features a wiki, downloads, API reference, darcs repository viewer, and bug tracker, at: http://software.complete.org/anydbm

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ANN: ftphs
by John Goerzen 08 Dec '06

08 Dec '06

I'm pleased to announce the first standalone release of ftphs. ftphs is an FTP client and server library for Haskell. Its features include: * Easy to use operation * Full support of text and binary transfers * Optional lazy interaction * Server can serve up a real or a virtual filesystem tree * Standards compliant ftphs was previously a part of the MissingH library. The code in this release is unchanged from its state in MissingH, other than the changes necessary to make it a standalone package. You can find the ftphs homepage, which features a wiki, downloads, API reference, darcs repository viewer, and bug tracker, at: http://software.complete.org/ftphs

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Network accept loop with graceful shutdown implementation
by Cat Dancer 08 Dec '06

08 Dec '06

I have a prospective implementation of a network accept loop with graceful shutdown. This email builds upon the previous discussion "Help needed interrupting accepting a network connection". In this code, just the accept loop part has been factored out and put into its own module. My hope is that if a fully correct version can be written, it will be useful to other projects. The source is available at http://code.catdancer.ws/acceptloop/ and is in the public domain. This AcceptLoop module is currently experimental, relying on an "either-or" guarantee for interruptible operations... which I don't know yet whether Haskell implementations provide -- or even intend to provide. Chris Kuklewicz provided several critical insights: * The return value of the 'accept' call can be passed out of the accept thread, allowing the code which implements accept with graceful shutdown to be separated from the code which handles the incoming client connection. * Inside of a 'block', interruptible operations may not (will not?) allow an asynchronous exception to be raised if the operation does not block. * Clarification for me of the desirable property that inside of a 'block', interruptible operations are either-or: either they allow an asynchronous operation to be raised, or they perform their operation, but not both. I made the following design decisions: In my original implementation, I used a custom datatype to throw a dynamic asynchronous exception to the thread calling 'accept'. In Chris' rewrite, he used 'killThread', which throws a 'ThreadKilled' asynchronous exception. I choose to continue to throw (and catch) only the specific, custom exception for the purpose of breaking out of the 'accept'. A robust implementation may need to catch other exceptions, however the desired behavior of the thread on receiving an *unexpected* exception may be different, and so I choose to leave handling of such an unexpected exception unimplemented for now. Chris uses STM instead of MVar's for communication with the accept thread. The challenge of writing code with STM or MVar's in the presence of asynchronous exceptions is exactly the same: either a call to 'atomically' or a call to an MVar operation such as 'putMVar' may allow an asynchronous exception to be raised inside of a 'block', and the code then needs to deal with that. It seems to me that MVar's could be implemented in terms of STM, and so the question is: are MVar's a more natural, higher level description of the desired semantics in this case, and would composable transactions be useful? A key insight is that in this implementation, a separate thread is used not for the purposes of concurrency, but solely to limit the scope of the thrown asynchronous exception. Once a result is available from the accept thread (either "Just" an incoming connection, or "Nothing" to say that the accept loop has shutdown), that result can then be used in a concurrent fashion, such as being handled in a child thread, passed into an STM transaction or written to a channel, etc. But there is no need to use composable transactions *inside* of the AcceptLoop module. Thus the only reason to use STM instead of MVar's inside the implementation is if it turns out that STM has the desired "either-or" behavior but MVar's don't. To avoid the "unlock (return ())" issue that Chris discovered, this implementation uses an additional MVar to indicate that a shutdown is in process. Thus (if the implementation is correct) the accept loop will shutdown either because of the MVar flag or by receiving the asynchronous exception inside of the 'accept'. To address the issue that Chris noticed of a race condition that new threads cannot be started in a 'block' state, yet another MVar is set by the accept thread to indicate that it is now inside of a 'block' and is ready to receive the asynchronous exception.

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Re: GHC Error question
by oleg＠pobox.com 07 Dec '06

07 Dec '06

Norman Ramsey wrote: > compile1 :: (Builder b box) => t -> Name -> Ir.ANF -> b t > compile1 f x body = do env <- compile body empty > wire (Arg W) (env x) > return f > class (Monad b) => Builder b box where > wire :: Source box -> Sink box -> b () > This program is rejected by GHC with the following message: > > Ccomp.hs:54:23: > Could not deduce (Builder b box1) from the context (Builder b box) > arising from use of `wire' at Ccomp.hs:54:23-42 He continued, [paraphrase] however, compile1 is accepted if the signature is removed. Furthermore, the inferred signature seems identical to the one given above. That is not a bug. We observe that in the explicitly given signature of compile1 > compile1 :: (Builder b box) => t -> Name -> Ir.ANF -> b t the type variable 'box' occurs only in the constraint Builder. The use of `wire' in the body of compile1 entails the constraint `Builder b1 box1' (we alpha-renamed the type variables). Now, we know that the result of the wire is the monadic value 'b1 ()', and compile1, according to the signature, produces the monadic value 'b t. So, the typechecker concludes that b = b1. However, there is nothing in the code that lets the typechecker conclude that box1 is the same as box. Hence the error: the given constraint (Builder b box) differs from the required (Builder b box1). What to do? If applicable, add a functional dependency (either per class or per instance) so to tell the typechecker that a particular 'b' (always, or in some cases) entails the particular 'box'. That will provide the missing improvement equation `box = box1'. Or, one may use the local type variable to the same end > compile1 :: forall b t box. (Builder b box) => t -> Name -> Ir.ANF -> b t > compile1 f x body = do env <- compile body empty > wire ((Arg W)::Source box) (env x) > return f the explicit `forall' binder is required.

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haddock-via-cabal: --prologue option?
by Conal Elliott 07 Dec '06

07 Dec '06

Is it possible to get haddock's --prologue flag passed in through cabal? Is there perhaps a way to get arbitrary options passed in? - Conal

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