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RE: container for different types, avoiding boiler plate
by Hal Daume 20 Aug '03

20 Aug '03

I use my 'DynamicMap' type to handle this sort of thing. However, I don't really recommend this approach unless you're very careful. You basically lose out on all nice type checking properties and enter a world of dynamic typing (more or less). Anyway, you can find it at: http://www.isi.edu/~hdaume/DynamicMap.hs it uses "NLP.FiniteMap", but you can replace this with "Data.FiniteMap". You can then do things like: data Gender = Masc | Fem | Neutr deriving Typeable data Number = First | Second | Third deriving Typeable let dm = addToDM (addToDM emptyDM Masc) Second case lookupDM dm of Just Masc -> "is a guy" Just _ -> "is not a guy" _ -> "i don't know gender" case lookupDM dm of Just First -> "is first" Just Second -> "is second" _ -> "either i don't know or is third" of course 'deriving Typeable' means you need GHC6; otherwise you can write the instances by hand. -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume > -----Original Message----- > From: haskell-admin(a)haskell.org > [mailto:haskell-admin@haskell.org] On Behalf Of > Markus.Schnell(a)infineon.com > Sent: Wednesday, August 20, 2003 5:01 AM > To: haskell(a)haskell.org > Subject: container for different types, avoiding boiler plate > > > I think similar things have been asked before, but I couldn't > find anything > specific. > I have a data type with attributes. These attributes have > different types. > Right now I'm using a lot of boilerplate like that: > > > > data Gender = Masc | Fem | Neutr > > ... > > data Attr = Gender Gender | Cat Cat | Graph Graph | ... > > data Type = TypeCat | TypeGender | ... deriving Eq > > > > myTypeOf (Gender _) = TypeGender > > myTypeOf (Cat _) = TypeCat > > ... > > myTypeOf _ = TypeError > > > > data Segment = Seg { attrs :: [Attr] } > > > > attr f seg = seg { attrs = f (attrs seg) } > > > > gattr :: Type -> [Attr] -> Maybe Attr > > gattr theType [] = fail "attribute not found" > > gattr theType (a:as) = if myTypeOf a == theType then return > a else gattr > theType as > > > > cat :: Cat -> Segment -> Segment > > cat c = attr ((Cat c):) -- set value > > > > gcat :: Segment -> Maybe Cat -- get value > > gcat = deCat . gattr TypeCat . attrs > > where deCat (Just (Cat c)) = c > > deCat x = x > > ... > > Does anyone have some suggestions for making this more concise? > Generic Haskell? Tricky type classes? > > Thanks, > Markus > > -- > Markus Schnell > Infineon Technologies AG, CPR ET > Tel +49 (89) 234-20875 > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell >

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'Forest inversion'?
by Marnix Klooster 20 Aug '03

20 Aug '03

Hi all, Recently I've discovered an inversion operation on forests that transforms 'wide' forests into 'deep' onces and vice versa. I'm sure that this operation is already known, however, I could not find any information on it. (Largely because I don't know under what name to look for it.) You Haskell guys know about data structures, so you should know more. :-) Example (use a fixed with font to view): the single-tree forest A /|\ B C D | | |\ E F G H | | I J | K is inverted to the forest A B E /| |\ C F I K / \ D G / \ H J and vice versa. In an implementation where every node has two pointers, one to its first child and one to its right-hand sibling, the inversion means that in every node those two pointers are swapped. In Haskell the algorithm looks like this: > data Forest a = Forest {trees :: [(a, Forest a)]} deriving (Show, Eq) > > inv :: Forest a -> Forest a > inv (Forest []) = Forest [] > inv (Forest ((a,f) : g)) = Forest ((a, inv (Forest g)) : trees (inv f)) and it is easy to prove that for every f :: Forest a, inv (inv f) = f. What would I want to do with it? Well, deep trees are difficult to navigate using existing tree controls. Example: Suppose I want to let the user play a text adventure, but I allow 'undo'. Then I can show him the tree of moves that he already tried, and let him backup to a previous state, and try something else at that point. This results often in a deep tree. So showing a wide tree instead (using the above inversion) might help the user. Especially if the children of a node are 'ordered' in the sense that the first child node is most important. So: is this 'forest inversion' known, under which name, what are the known uses, etc.? Thanks in advance! Groetjes, <>< Marnix -- Marnix Klooster mklooster(a)baan.nl

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GPCE 03 Call for Participation
by Akos Ledeczi 20 Aug '03

20 Aug '03

GPCE'03: 2nd International Conference on Generative Programming and Component Engineering In Cooperation with ACM SIGPLAN and SIGSOFT and co-located at NetObjectDays'03 September 22-25, 2003, Erfurt, Germany http://gpce.org/GPCE03 GPCE is the premier forum for dissemination and discussion of ideas on domain-specific languages, generative programming, model-based development, and component engineering. It brings together software engineering and programming language researchers and practitioners interested in key technologies for automating program development. This second conference will be co-located with NetObjectDays'03, one of the largest main-stream software development conferences in Germany. GPCE'03 program features 2 invited talks, by Olivier Danvy and Peri Tarr 21 papers featuring latest research in - Domain-Specific Languages - Staged Programming - Modeling-Based Development - Aspect-Orientation - Meta-Programming and Language Extension - Domain-Specific Code Generation 4 workshops - Reflectively Extensible Programming Languages and Systems - Product Line Engineering - The early steps: Planning, Managing, and Modeling - Component Engineering Methodology - GPCE Young Researchers Workshop 6 tutorials - Executable UML - Domain-Specific Languages - Multi-Staged Programming - Generatrive Programming - Model-Driven Development - Model-Driven Architecture 6 tool demonstrations of tools for - Metamodeling - Model-Driven Architecture - Generative development GPCE'03 attendees will have access to all NetObjectDays'03 events including Keynote Addresses by Steve Mellor, Jim Odell, and Dave Weiss. Poster submissions and submissions to the Product Line Engineering Workshop are still being solicited. For details of the conference program please refer to http://gpce.org/GPCE03.

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Weighted Automata: Workshop Announcement
by Sandra Grossmann 20 Aug '03

20 Aug '03

[apologies if you receive multiple copies of this message] ----------------------------------------------------------- Weighted Automata: Theory and Applications Dresden University of Technology, June 1 - 5, 2004 The workshop will cover all aspects of weighted automata, ranging from the theory of formal power series to max-plus- algebra and applications as e.g. in digital image processing or algebraic optimization of networks. The aim is to present tutorials and survey lectures by outstanding scientists in this area. Moreover, we encourage everybody to participate in this workshop and present their own technical contribution in this area. Tutorials: P. Butkovic (Birmingham) U. Montanari (Pisa) J. Kari (Iowa City) J. Sakarovitch (Paris) Survey lectures: J. Albert (Wuerzburg) F. Katritzke (Siegen) S. Bozapalidis (Thessaloniki) W. Kuich (Wien) Z. Esik (Szeged) M. Mohri (AT&T, New Jersey) P. Gastin (Paris) L. Staiger (Halle) All lecturers are asked to give a survey on their field of interest followed by recent research results. Submission: If you wish to present a technical contribution, please send us an abstract (preferably of at most one page) before February 15, 2004. Authors will be informed about acceptance of their submission before March 15, 2004. There will be a special issue of the Journal of Automata, Languages, and Combinatorics (JALC) on the topic of this workshop. The deadline for submission of papers is July 15, 2004. All submissions will be refereed according to the usual journal standards. Registration: Interested participants are most welcome. There are no conference fees. Participants from central/eastern european countries can apply for financial support. Important Dates: deadline for submission of abstracts February 15, 2004 notification of acceptance March 15, 2004 registration April 1, 2004 submission of papers July 15, 2004 Further Information: http://www.orchid.inf.tu-dresden.de/gk-spezifikation/wata4.html --------------------------------------------------------------- Manfred Droste Heiko Vogler Dresden University of Technology Dresden University of Technology Institute of Algebra Inst. of Theor. Computer Science D-01062 Dresden, Germany D-01062 Dresden, Germany Tel.: +49-351-463-33908 Tel.: +49-351-463-38232 Fax: +49-351-463-34235 Fax: +49-351-463-37959 E-Mail: droste(a)math.tu-dresden.de E-Mail: vogler(a)inf.tu-dresden.de

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container for different types, avoiding boiler plate
by Markus.Schnell＠infineon.com 20 Aug '03

20 Aug '03

I think similar things have been asked before, but I couldn't find anything specific. I have a data type with attributes. These attributes have different types. Right now I'm using a lot of boilerplate like that: > data Gender = Masc | Fem | Neutr > ... > data Attr = Gender Gender | Cat Cat | Graph Graph | ... > data Type = TypeCat | TypeGender | ... deriving Eq > > myTypeOf (Gender _) = TypeGender > myTypeOf (Cat _) = TypeCat > ... > myTypeOf _ = TypeError > > data Segment = Seg { attrs :: [Attr] } > > attr f seg = seg { attrs = f (attrs seg) } > > gattr :: Type -> [Attr] -> Maybe Attr > gattr theType [] = fail "attribute not found" > gattr theType (a:as) = if myTypeOf a == theType then return a else gattr theType as > > cat :: Cat -> Segment -> Segment > cat c = attr ((Cat c):) -- set value > > gcat :: Segment -> Maybe Cat -- get value > gcat = deCat . gattr TypeCat . attrs > where deCat (Just (Cat c)) = c > deCat x = x > ... Does anyone have some suggestions for making this more concise? Generic Haskell? Tricky type classes? Thanks, Markus -- Markus Schnell Infineon Technologies AG, CPR ET Tel +49 (89) 234-20875

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ANNOUNCE: New Chameleon version (03-08)
by Martin Sulzmann 20 Aug '03

20 Aug '03

Latest version can be downloaded via http://www.comp.nus.edu.sg/~sulzmann/chameleon/ You might also want to check out http://www.comp.nus.edu.sg/~sulzmann/chr/publications.html - The Chameleon Type Debugger (Tool Demonstration) - Interactive Type Debugging in Haskell Martin

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Announce: HWordNet - A Haskell Interface to WordNet
by Hal Daume III 19 Aug '03

19 Aug '03

Briefly, http://www.isi.edu/~hdaume/HWordNet/ HWordNet is a Haskell binding to the WordNet database. You will actually need to have WordNet installed to use the Haskell interface, but you won't need any of the source (the Haskell interface is 100% pure Haskell; no crummy FFI bindings here!). However, it does of course use the WordNet database files, so you'll need those. See http://www.cogsci.princeton.edu/~wn/ for more about WordNet This interface doesn't cover all of WordNet -- for instance, it doesn't yet do morphology. This will be available in a release soon. Also, it does use implicit parameters, so you've got to have GHC or Hugs or some other compiler that supports those. - Hal -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume

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RE: more unsafePerformIO questions ([...])
by Simon Marlow 19 Aug '03

19 Aug '03

> On Tuesday, 2003-08-19, 13:18, Simon Marlow wrote: > > [...] > > > Yes, I agree that one shouldn't rely on the "no duplication of work" > > property. However, folloing this argument we arrive at the > conclusion that > > hGetContents is an invalid use of unsafePerformIO. (which > is something I've > > been saying for a while now :-). > > Can't hGetContents be implemented without unsafePerformIO but with > unsafeInterleaveIO? Wouldn't this be valid? Am I'm missing > something here? unsafeInterleaveIO = return . unsafePerformIO Well, almost. unsafeInterleaveIO should also give you the guarantee that the IO in its argument can't be performed *before* the unsafeInterleaveIO is executed, but I don't think this distinction is important to the present discussion. Actually I dislike unsafeInterleaveIO even more than unsafePerformIO, because it has an implicit laziness assumption. The only purpose of unsafeInterleaveIO is to "delay" some IO until it is "demanded". But Haskell lacks a precise definition of "demand", prefering to leave the evaluation order up to the implementation. Hence, unsafeInterleaveIO is left in limbo - it might do something useful, but that depends entirely on your implementation. GHC doesn't guarantee much about unsafeInterleaveIO at all. Cheers, Simon

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RE: more unsafePerformIO questions (is it safe to use with ReadMode Handles)?
by Simon Marlow 19 Aug '03

19 Aug '03

> >> Isn't there the possibility of inlining causing a read to > >> happen twice even if it only appears to happen once? > > > >In theory that would be a valid transformation, but in practice no > >compiler would duplicate arbitrary computations. GHC > certainly doesn't. > > I was thinking of a situation like > > let x = unsafePerformIO readFooFromDB in x+x > > I see from your "Secrets of the GHC inliner" paper that x wouldn't be > inlined by GHC, but it seems to me like a serious abuse of > the principle of > referential transparency to write programs that _assume_ that. Yes, I agree that one shouldn't rely on the "no duplication of work" property. However, folloing this argument we arrive at the conclusion that hGetContents is an invalid use of unsafePerformIO. (which is something I've been saying for a while now :-). Cheers, Simon

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RE: more unsafePerformIO questions (is it safe to use with ReadMode Handles)?
by Simon Marlow 19 Aug '03

19 Aug '03

> I'm finishing up my Haskell interface to WordNet > (http://www.cogsci.princeton.edu/~wn/) and have a standard > unsafePerformIO question :). > > Basically, the interface functions by first calling an initialization > function, 'initializeWordNet :: IO WordNetEnv'. WordNetEnv is > essentially just a record of a lot of Handles which we will be reading > from and doing binary search in. > > All the functions which use the WordNetEnv (i.e., every other function > in the interface) basically do the following: > > - take one handle from the WordNetEnv and do binary search > in it, read a line. > > - use that line to read another line from another of the handles > > - parse that last one > > of course, therefore, all of these functions have type '... -> IO > something'. > > However, one of the "rules of thumb" for using unsafePerformIO is when > you can imagine a functional interface doing the same thing. I can: > simply read in all the databases in initializeWordNet and then do > Data.List.lookup on the results. Does this mean it's safe to wrap all > these functions in unsafePerformIO? It sounds like your interface is pure, as long as you don't expect the contents of any of the databases to change during the run of your program. That is, it doesn't matter whether you do all the IO at the start or lazilly on demand. If the databases *do* change over time, then there are two possibilities: 1. the contents change due to external factors only 2. the contents change because this program doing the writing in (1), you can still pretend the interface is pure, by imagining that all the changes happened earlier. This works as long as you only read the external data once. In (2), you have a truly impure interface, so using unsafePerformIO would be wrong. Cheers, Simon

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