Welcome to issue 57 of HWN, a weekly newsletter covering developments in the Haskell community.

Lots of news to report after a break due to Hac '07 and POPL.


lhs2tex 1.12. Andres Loeh announced lhs2TeX version 1.12, a preprocessor to generate LaTeX code from literate Haskell sources. lhs2TeX includes the following features: highly customized output; liberal parser; generate multiple versions of a program or document from a single source; active documents: call Haskell to generate parts of the document (useful for papers on Haskell); a manual explaining all the important aspects of lhs2TeX.

hscom. Krasimir Angelov announced the hscom library. This is a FFI library for Microsoft COM. It is far from complete and it doesn't have automatic IDL to Haskell translator but if you have ever thought to start writing you own COM library for Haskell then please take a look. It is designed to be as close as possible to the standard FFI library for C.

DeepArrow 0.0: Arrows for 'deep application'. Conal Elliott announced the birth of DeepArrow, a Haskell library for composable 'editors' of pure values. DeepArrow enables 'deep function application' in two senses: deep application of functions and application of deep functions. These tools generalize beyond values and functions, via the DeepArrow subclass of the Arrow type class.

Phooey 0.1: functional user interface library. Conal Elliott announced version 0.1 of Phooey, an arrow-based functional user interface library. New in version 0.1: documentation, text input, boolean input/output, mtl. Phooey is now used in TV.

TV 0.0: Tangible Values. Conal Elliott announced TV, a library for composing tangible values (TVs): values that carry along external interfaces. In particular, TVs can be composed to create new TVs, and they can be directly executed with a friendly GUI, a process that reads and writes character streams, or many other kinds interfaces. Values and interfaces are combined for direct use, and separable for composability. See the project page.

polyparse 1.00. Malcolm Wallace announced the release of PolyParse, a collection of parser combinator libraries in Haskell. They were all previously distributed as part of HaXml, but are now split out to make them more widely available.

Data.Binary: binary serialisation. The Binary Strike Force announced the release of Binary, a high performance, pure binary serialisation library for Haskell. It is available from Hackage and darcs. The 'binary' package provides efficient serialisation of Haskell values to and from lazy ByteStrings. ByteStrings constructed this way may then be written to disk, written to the network, or further processed (e.g. stored in memory directly, or compressed in memory with zlib or bzlib).

DrIFT 2.2.1: support for Data.Binary. John Meacham announced that DrIFT 2.2.1 is out and now has support for the Data.Binary module.

A History of Haskell. Simon Peyton-Jones mentioned that the paper 'A History of Haskell: being lazy with class', authored by Paul Hudak, John Hughes, Phil Wadler and Simon, is finally done. You can get a copy now!

piggybackGHC 0.1. Martin Grabmueller announced the release 0.1 of piggybackGHC, a small utility package for using GHC for lexing and parsing Haskell source code. The library uses the GHC library for all the hard stuff, so all supported GHC extensions are available.

regex-tdfa 0.20. Chris Kuklewicz announced regex-tdfa, a 'tagged' DFA regular expression backend in pure Haskell, along with a suite of updates to the existing regex packages.

hpaste.org. Eric Mertens announced 'hpaste', the Haskell Pastebin. Developed over a few days by many of the members of the Haskell irc channel, it provies a reliable paste bot with Haskell-specific capabilities.


This section covers the Haskell' standardisation process.


This week's proposals and extensions to the standard libraries.


Beautiful concurrency. Simon Peyton-Jones announced that the revised draft of 'Beautiful concurrency' is now online, and feedback is welcome.

Even higher-order abstract syntax: typeclasses vs GADT. Oleg Kiselyov demonstrated a typeclass implementation of the canonical use case for GADTs: a higher-order abstract-syntax-based embedding of a language in Haskell, with implement static and dynamic semantics of the language. The interpreter of the language is tagless and statically assured: only well-typed terms may be evaluated, and the evaluation of those does not get stuck.

JHC call for volunteers. John Meacham mentioned that Jhc has recently gotten a ghc back end, making it much closer to mainstream use as an optimizing 'front end' to ghc. In addition to some of jhc's crazy optimizations, it implements several extensions to the language which will likely prove interesting to play with to some. John would like to welcome any volunteers who would like to help develop the ghc back end while I work on improving the grin back end and optimizations in general, to make JHC a viable alternative compiler for Haskell.

State monad strictness. Yitzchak Gale pondered strictness in State monads.

Using PAPI to measure performance with CPU events. Alexey Yakushev described how to use the new PAPI library together with GHC to gather performance information from your CPU (cache misses, branch misprediction). At present only cache miss information is supported in a platform independent way (though not tested). Also, this implementation separates the performance information for the garbage collector and the mutator so it is quite useful if you are implementing an optimisation.

Simple proof-carrying code in Haskell 98. Oleg Kiselyov demonstrated a datatype `Terminates' that can hold only an assuredly terminating (strongly normalizable) term in untyped lambda-calculus. Furthermore, the values of the datatype `Terminates' contain all and only those untyped lambda-calculus terms with that property. To create the value `Terminates', the user submits the term in question and the proof of its termination. The proof will be verified -- and if it holds, the Terminates certificate will be created.

Article review: Category Theory. David House mentioned that he's written a chapter for the Wikibook that attempts to teach some basic Category Theory in a Haskell hacker-friendly fashion.

IO is not a monad. Yitzchak Gale sparked a long thread on issues of parametricity and polymorphic seq in the IO monad

Monad laws for fail. Ulf Norrel wondered about what properties 'fail' should satisify


Postdoctoral Research Fellow at St Andrews. Kevin Hammond announced a vacancy for a postdoctoral research fellow, working with the Hume language developed jointly with Heriot-Watt University. Knowledge of Haskell and other functional programming technologies is a distinct advantage.

Blog noise

Haskell news from the blogosphere.

Quotes of the Week

Code Watch

Thu Jan 11 05:13:59 PST 2007. Pepe Iborra. Added the new :breakpoint continue option. Previously, when in a breakpoint, :quit was used to continue execution. This is not the right thing to do, so this patch restores :quit to its original meaning whether or not ghci is in an inferior session. The continue behavior is now provided by ':breakpoint continue'. I added a synonim command in :continue because it is much shorter, but this is optional

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