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Announce: Pan release 2000-12-06
by Conal Elliott 08 Dec '00

08 Dec '00

There is a new release of Pan, a Haskell-embedded language and compiler for image synthesis, at http://research.microsoft.com/~conal/Pan I've also updated the Pan gallery with many new images for your enjoyment. The main features of this release, relative to 2000-10-04 are + Anti-aliasing for much smoother-looking images! + Render larger than the view. + ActiveX control for web pages or PowerPoint. + A recently given interactive presentation. Enjoy. - Conal ---- General description --- Pan is an experimental embedded language and compiler for image synthesis and manipulation, based on functional programming. You can get the compiler and do some Haskell programming do make your own effects, or get some of the precompiled effects and twiddle parameters to your heart's content. It's fun! The Pan compiler turns descriptions of images and image effects into efficient machine code for use with the Pan viewer program, web-page embedding (viewable with Internet Explorer 5.5 or later), or as a PhotoShop plug-in. All have automatically generated GUIs for control of the image synthesis/manipulation parameters with real-time redisplay. In the Pan viewer case the parameter settings may be saved into a small file for use later or sharing with others. See the Pan home page at http://research.microsoft.com/~conal/Pan, where you'll find a gallery of sample images and animations, papers on the language and implementation, instructions for use, and the binary and source releases. For now, Pan-generated effects run only on Windows. We welcome help in porting to other platforms. Also, the compiler assumes you have the Microsoft Visual C++, though we think it wouldn't be very hard to support other compilers and again we welcome help. Please let us know what you do with Pan, both trouble you run into and examples you construct with it (conal(a)microsoft.com)

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RE: GHCi, Hugs (was: Mixture ...)
by Simon Peyton-Jones 08 Dec '00

08 Dec '00

| This puzzles me a bit. From talking with people at the | Haskell Workshop, I understood that GHCi would only be an | interactive compiler. | | The disadvantage with that is that compilation time might be | very long. But it was said that that is the price we pay. | | The only advantage I can see with interpreted code is the | fact that it can be compiled (or "processed") much faster. | Will GHCi reach speeds up to Hugs level? It'll definitely be mixed compiled/interpreted. No, compiling won't be nearly as fast as Hugs, but it will, we earnestly hope be "fast enough". Execution should be faster than Hugs; apart from anything else you'll get compiled libraries. | One bad thing with Hugs is that, for large systems, the | loading/processing time gets longer, and, worse, is repeated | every time one loads the system. This is especially bad when | using "runhugs". Hopefully GHCi will work better in that | case! Yes, a lot better. The idea is only to recompile things that have changed. | Another thing that worries me is that Hugs will die. Not | only because I like Hugs a lot, but also that it is yet | another Haskell system that is dying. I think that is a very reasonable concern. I certainly want to see Hugs alive and kicking. Simon

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HaXml question
by Michael Zawrotny 08 Dec '00

08 Dec '00

This question is probably a bit low-brow compared to the normal discussions of type systems, rank-2 polymorphism... Anyway, here goes nothing. I'm working on getting up to speed on haskell in general and HaXml in particular. I read through the ICFP paper that came with the distribution, but it was a bit dense for a beginner. Is there anything out there that is more oriented towards people who are less fluent in haskell? I think that my problem may be a lack of understanding of the whole idea of what combinators are and how they work. What I would like to do is something like the Xtract tool that comes with HaXml, but to select an element based on the path criteria specified (as Xtract already does), but that also satisfies an arbitrary predicate function that I would specify (e.g. a function that normalizes case and then tests for equality, regexp match, etc.). If anybody can help out on either front, I would greatly appreciate it. Thanks, Mike

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Re: Mixture of Integer and Float arithmetic without "fromIntegral"?
by Christian Lescher 07 Dec '00

07 Dec '00

> OK, OK, I've just added -fno-monomorphism-restriction to GHC. Great! Will there also be a similar option for Stg Hugs? Christian

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RE: Mixture of Integer and Float arithmetic without "fromIntegral "?
by Simon Peyton-Jones 07 Dec '00

07 Dec '00

OK, OK, I've just added -fno-monomorphism-restriction to GHC. Simon | -----Original Message----- | From: Malcolm Wallace [mailto:Malcolm.Wallace@cs.york.ac.uk] | Sent: 07 December 2000 10:28 | To: haskell-cafe(a)haskell.org | Subject: Re: Mixture of Integer and Float arithmetic without | "fromIntegral"? | | | > > module Defs where | > > | > > n = 3 | > > x = 12.3 | > > | > > test = ceiling (x / n) | > | > There are people (including me) who think that the monomorphism | > restriction rule, which makes the above definitions without type | > signatures monomorphic and thus defaulted to concrete types, should | > be removed. | | If you want to experiment with an implementation that do not enforce | the monomorphism restriction, try nhc98. It happily infers the types | | n :: Num a => a | x :: Fractional a => a | | for the toplevel definitions shown. I don't think anyone has ever | complained about this feature. | | Regards, | Malcolm | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe |

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Mixture of Integer and Float arithmetic without "fromIntegral"?
by Christian Lescher 07 Dec '00

07 Dec '00

When defining expressions with arithmetic operations on a mixture of Integers and Floats (except literals), an explicit conversion by "fromIntegral" for the Integers is necessary, for example: ceiling (fromIntegral n / x) Is it possible to do the "fromInteger" conversion automatically? What's the best way to do it? (overloading of operators, etc.?) Christian

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RE: Rank-2 polymorphism & type inference
by Carlos Camarao de Figueiredo 06 Dec '00

06 Dec '00

Hello. < class C t where op :: t -> Bool < instance C [t] where op x = True < < p y = (let f :: c -> Bool; f x = op (y >> return x) in f, y ++ []) < q y = (y ++ [], let f :: c -> Bool; f x = op (y >> return x) in f) < <The definitions of p and q differ only in the order of the components in <the pair on their right-hand sides. And yet: < < ghc and "Typing Haskell in Haskell" reject p, but accept q; < Hugs rejects q, but accepts p; < hbc rejects both p and q; < nhc98 ... (Malcolm, can you fill in the blank for us!). System CT accepts both. No type signature is required. The types inferred for p and q are, resp.: Forall a,b. [a] -> (b -> Bool, [a]) and Forall a,b. [a] -> ([a], b -> Bool) You can run the attached "encoded" program (in which 'op' is overloaded, instead of having its type annotated in a type class) in CTinH (http://www.dcc.ufmg.br/~camarao/CT/CTinH.tar.gz) Type inference in system CT is explained in a paper available at http://www.dcc.ufmg.br/~camarao/CT/CT.ps.gz (see also homepage at http://www.dcc.ufmg.br/~camarao/CT) Carlos

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RE: Rank-2 polymorphism & type inference
by Mark P Jones 06 Dec '00

06 Dec '00

Johan Nordlander and I have been looking at these interesting examples, and would like to offer another entertaining variation to the collection: class C t where op :: t -> Bool instance C [t] where op x = True p y = (let f :: c -> Bool; f x = op (y >> return x) in f, y ++ []) q y = (y ++ [], let f :: c -> Bool; f x = op (y >> return x) in f) The definitions of p and q differ only in the order of the components in the pair on their right-hand sides. And yet: ghc and "Typing Haskell in Haskell" reject p, but accept q; Hugs rejects q, but accepts p; hbc rejects both p and q; nhc98 ... (Malcolm, can you fill in the blank for us!). The type signature for f forces context reduction to take place, and the results of this depend on whether or not the type of y is known, which in turn depends on which component of the pair the type checker analyzes first. I'm sure we will all continue to ponder this for some time to come ... All the best, Mark & Johan

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Haskell Module Browser
by Jan Skibinski 05 Dec '00

05 Dec '00

A prototype of this tool is shown here: www.numeric-quest.com/haskell/explorer/browser.html Jan

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RE: Rank-2 polymorphism & type inference
by Simon Peyton-Jones 05 Dec '00

05 Dec '00

| reported the bug several months ago.) Sorry! The bug has been fixed, but our nhc98 installation hasn't been rebuilt. | If your nhc98 compiler | was built by gcc, hbc, or nhc98 itself, then it gives a proper error | message here, viz: | | Couldn't simplify the context ((_180#) _171). | Possible sources for the problem are:11:20 No cigar! What is Joe Programmer going to do with that? But seriously, it's interesting that nhc fails in the same way as GHC and Hugs. Simon

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RE: Rank-2 polymorphism & type inference
by Malcolm Wallace 05 Dec '00

05 Dec '00

> Both GHC and Hugs reject this module if the type signature for > test is omitted. NHC (v1.00, 2000-09-15) falls over completely, with > Fail: Prelude.chr: bad argument Rushing to the defence of nhc98 (as always!), I should point out that nhc98 actually falls over here because of a bug in ghc. (I reported the bug several months ago.) If your nhc98 compiler was built by gcc, hbc, or nhc98 itself, then it gives a proper error message here, viz: Couldn't simplify the context ((_180#) _171). Possible sources for the problem are:11:20 However, this is totally unrelated to the question of interest regarding type inference. Regards, Malcolm

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List types
by Eric Allen Wohlstadter 04 Dec '00

04 Dec '00

Is there a way to make a list that contains multiple types? If not, why, and isn't this a serious restriction? I would like to be able to say: map show ['a',5] Since both Char and Num derive Show it seems like a reasonable thing to do. I realise classes in haskell don't work this way so I guess my question is, why not? Could I do something like this in O'Haskell, Clean, or some other functional language? In particular I am interested in exploring software engineering implications of monadic IO, separation of concerns, etc... Eric Wohlstadter UCDavis Software Engineering

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RE: Beginner: error when using multiple where stmts in hugs98
by Mark P Jones 01 Dec '00

01 Dec '00

| I've been trying some examples in functional programming. Most things | work fine, but I have trouble with expressions with 'where' clauses | that define more then one local definition. | ... | For example: | ... | mydiff f = f' | where f' x = ( f (x+h) - f x) / h | h = 0.0001 The second line in the where clause (your attempt to define local variable h) will be treated as if it were part of the first definition (for the variable f'). Why? Because that's what the layout/indentation in your code specifies. In fact, to a Haskell compiler, your input looks a lot like the following, clearly incorrect definition: mydiff f = f' where f' x = ( f (x+h) - f x) / h h = 0.0001 If you want h to be defined as a local variable at the same level as f', then you should make sure the two definitions start with the same indentation: mydiff f = f' where f' x = ( f (x+h) - f x) / h h = 0.0001 The indentation you've actually used suggests that you might have intended the definition of h to be local to f'. In that case, you should add an extra "where" keyword: mydiff f = f' where f' x = ( f (x+h) - f x) / h where h = 0.0001 All the best, Mark

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RE: a trap for the unwary
by Mark P Jones 01 Dec '00

01 Dec '00

Hi Malcolm, | Today, I thought I had discovered a bug in ghc. Then I tried hbc | and Hugs, and they also rejected my program with the same error. | nhc98 alone accepts it without complaint. I looked up the Report, | and it seems that the program is indeed incorrect. | | > f x = y | > where | > y | isSpace x = True | > y | otherwise = False For what it's worth, older versions of Hugs would have accepted this too. Only quite recently was it changed to conform to the report. Incidentally, although the above is not valid Haskell, the following should work just fine: f x = y where y | isSpace x = True | otherwise = False The difference is that I haven't repeated the left hand side of the definition in the second equation, which means that it's treated as one definition, not two. All the best, Mark (PS. An even nicer way to write this definition: f = isSpace :-)

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Type classes diagram?
by Kurt 30 Nov '00

30 Nov '00

Has anyone seen a downloadable diagram of the relationships between all of the Haskell type classes? If so, could you post a link? TIA, Kurt.

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RE: Will Haskell be commercialized in the future?
by Doug Ransom 29 Nov '00

29 Nov '00

Development tools for OO now are as good as smalltalk-80. I expect the benefits of FP to be widely adopted in industry by 2020. XSLT is kind of cool and taking off. Not exactly functional but there is no destructive assignment. A lot of the things Haskell excells at (IMO) inferior tools are being used in place. For example, microsoft has build good XSLT translators and two new compilers (C#, VB7) in the last couple years. Unfortunately, C#, not Haskell, will probably be "the" language for the next decade. Fortunately, C++ will not be the language of the next decade. > -----Original Message----- > From: Christian Lescher [mailto:christian@lescher.de] > Sent: Thursday, November 23, 2000 10:14 PM > To: haskell-cafe(a)haskell.org > Subject: Will Haskell be commercialized in the future? > > > In my opinion there are many more real world problems, that > can be most > efficiently solved with functional languages like Haskell, as > (software) > industry can think of at the moment; they only know their C/C++, Java, > etc. but can't even think of the power of functional programming or at > least don't take languages like Haskell for full. (Of corse, there are > exceptions to the rule, too.) > > What do you think: Will Haskell (the related compilers/tools) be > "commercialized" in the future? > > Christian > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Re: Will Haskell be commercialized in the future?
by Ashley Yakeley 28 Nov '00

28 Nov '00

At 2000-11-27 19:52, Tyson Dowd wrote: >On 27-Nov-2000, Adrian Hey <ahey(a)iee.org> wrote: >> On Mon 27 Nov, Fergus Henderson wrote: >> > Do you think that Haskell would be better without `unsafePerformIO'? >> >> Well, a sceptic like me is bound to wonder why such a non-function is >> provided in a purely functional language. What really worries me is >> that the damage isn't localised. If you allow such things you can never be >> sure that any function really is a function, without careful scrutiny of all >> the code it's dependent on. > >This is an issue, but it arises in any "pure" language with a foreign >language interface. Not necessarily, the functions just need to be typed correctly. In the case of a non-safe or imperative function, that's going to be of the form "a -> IO b" (or "IO a -> IO b" if you prefer the more powerful arrow model). No safety needs to be sacrificed. -- Ashley Yakeley, Seattle WA

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unsubscribe haskell-cafe
by Wooseok Yang 25 Nov '00

25 Nov '00

unsubscribe haskell-cafe

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Will Haskell be commercialized in the future?
by Christian Lescher 24 Nov '00

24 Nov '00

In my opinion there are many more real world problems, that can be most efficiently solved with functional languages like Haskell, as (software) industry can think of at the moment; they only know their C/C++, Java, etc. but can't even think of the power of functional programming or at least don't take languages like Haskell for full. (Of corse, there are exceptions to the rule, too.) What do you think: Will Haskell (the related compilers/tools) be "commercialized" in the future? Christian

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(no subject)
by Chris Angus 24 Nov '00

24 Nov '00

I was wondering if Has anybody had access to a Haskell -> Java compiler/translator. ----------------------------------------- Chris Angus Armature Enterprise House 1 Apex View Leeds LS11 9BH +44 113 2595253 cangus(a)armature.com

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Re: Will Haskell be commercialized in the future?
by Friedrich Dominicus 24 Nov '00

24 Nov '00

Christian Lescher <christian(a)lescher.de> writes: > In my opinion there are many more real world problems, that can be most > efficiently solved with functional languages like Haskell, as (software) > industry can think of at the moment; they only know their C/C++, Java, > etc. but can't even think of the power of functional programming or at > least don't take languages like Haskell for full. (Of corse, there are > exceptions to the rule, too.) > > What do you think: Will Haskell (the related compilers/tools) be > "commercialized" in the future? Let me counter with another question. Do you think people will pay for it and enough to keep the vendors going? Regards Friedrich

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FP & Python
by Manuel M. T. Chakravarty 24 Nov '00

24 Nov '00

The following article featuring an interview with the authors of alternative Python implementations might be interesting to some of you, as it features the use of FP technology in the context of a popular language: http://www-4.ibm.com/software/developer/library/l-pyth7.html?open&l=666,t=g… Vyper might actually be of interest for Phil's page about real-world applications of FP. Cheers, Manuel

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haskell editor..
by John Meacham 17 Nov '00

17 Nov '00

so while randomly surfing the realm of haskell space I came across the Alfa Proof assistant. (http://www.cs.chalmers.se/~hallgren/Alfa/) All I can say is WOW, this thing is fun to play with, (and to think I have been doing my proofs with pencil and paper all these years). The interactive editor in particular I found quite enjoyable to use, I was wondering if someone has ever made or considered making a similar editor for haskell programs themselves? On first thought it seems that such a thing should not be too difficult as the type system of haskell is based on the same theories and haskell programs are similar to declarative proofs. It seems like an editor of that sort coupled with a class browser would be a powerful authoring tool.. (and this coming from a vi user :) ) The other thing that Alfa made me want to try out was programming with Fudgets. however as far as I can tell Fudgets has bit-rotted away... at least I have been unable to find a version which compiles with my prefered setup (ghc 4.08.1)... I was wondering if there is anyone working on bringing Fudgets up to date? There must be some setup that can compile it as Alfa still appears to be actively developed, From a lookover of the sources probably all that would need to be done is to replace the Xlib layer with one based on FFI so as to be portable to all the modern platforms and bring the code up to haskell98 compliance... perhaps somebody has already done this but it is not well publicised or is there some other reason Fudgets has not been developed recently like the existence of an accepted better GUI API? just some random thoughts.... John -- -------------------------------------------------------------- John Meacham http://www.ugcs.caltech.edu/~john/ California Institute of Technology, Alum. john(a)foo.net --------------------------------------------------------------

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Re: List types
by Scott Turner 13 Nov '00

13 Nov '00

You could make a type like this: data C a b = Raw b | Cooked ( a -> C a b ) ap :: C a b -> a -> C a b ap (Cooked f) v = f v cook :: C a (a -> t) -> C a t cook (Cooked f) = Cooked g where g a = cook (f a) cook (Raw f) = Cooked g where g a = Raw (f a) foo x y z = x <= y && y <= z f3 = cook $ cook $ cook $ Raw foo test = f3 `ap` 1 `ap` 2 `ap` 3 Though you could do something similar with a list-based approach. -- Scott At 20:12 2000-11-12 -0800, you wrote: >I would like to be able to make a list that contains functions which take >arguments of a certain type 'a'. However I don't know how many 'a' >arguments there are. For example I'd like to be able to make a list of >f,g, and h. > >f::a->b >g::a->a->b >h::a->a->a->b >[f,g,h] > >I want to be able to curry the a's one at a time. -- Scott Turner p.turner(a)computer.org http://www.ma.ultranet.com/~pkturner

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List types
by Eric Allen Wohlstadter 13 Nov '00

13 Nov '00

I would like to be able to make a list that contains functions which take arguments of a certain type 'a'. However I don't know how many 'a' arguments there are. For example I'd like to be able to make a list of f,g, and h. f::a->b g::a->a->b h::a->a->a->b [f,g,h] Now I could make a function l that takes a list of 'a'. l::[a]->b However, I want to be able to curry the a's one at a time. My solution so far is declare a type Element like this: data Element a b c d = One a | Two b | Three c | Four d and then I can make my list like this, [One f,Two g,Three h] This gets very ugly. Do you guys have any ideas? Eric Wohlstadter UCDavis Software Engineering

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(no subject)
by Luciano Caixeta Moreira 26 Oct '00

26 Oct '00

unsubscribe luti(a)linkexpress.com.br

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Re: Haskell Programming Environment
by C.Reinke 25 Oct '00

25 Oct '00

> One of the emacs modes for Haskell gives the type of the identifier > the cursor is in in the modeline. It does this by examining the type > signatures in the current file, and having the prelude type signatures > built-in. This is quite helpful, if incomplete, and fairly easy to > implement. Similar shortcuts are possible for other aspects, and might help to produce something useful within the constraints of an MSc project. Finding a reasonable compromise between producing something for an MSc and producing something that will remain in use and that others could build on later would be the first challenge, I think. Personally, I couldn't care less about yet another non-portable IDE demo bound to one specific, non-standard, smallish editor and one specific graphics library with one specific OS. It might get a small user base, but is likely to be out of date before it can grow to a functionality that could attract more users. But that's just my personal opinion.. The results of this survey and your own thoughts about what the specific issues in a Haskell Programming Environment might be, what functionality should be provided, and how, have a greater likelihood to be of lasting value. If you want to produce anything "real", you will want to reuse the language knowledge built into existing implementations. If you then want to remain portable, a good route would be to define an interface between the HPE and some Haskell implementation, specifying exactly which functionality the HPE would want to access, and how. Examples: - syntax-awareness. Experience with syntax-directed editors shows that users don't like to be locked into the syntax, they want some leeway for errors in intermediate stages. Also, many programmers don't want to drop their favourite, productive, proven and portable editor for the ones built into IDEs. Still, the editor should be aware of the syntax of the current language (those regular-expression-based syntax-highlighters are nothing but a stop-gap measure). Having a standard interface to the implementation's parser (where is the next subexpression? where is next enclosing context? where and what is the next syntax error?..). - scope&type awareness. A natural extension of the above with an interface to the implementation's symbol table (where is the binding occurence for this variable? what the type of this expression? what are the constructors/class instances for this type? which identifiers with which types are exported from this module?..) - other language-specific interactions. (evaluate current expression in current environment; browse module graph; browse class graph; compile&run; instrument for debugging;..) Have a look at the functionality provided in Hugs and try to define an interface that could support that functionality from within a standard editor, without being dependent on Hugs. There used to be an idea of having a more modular Haskell implementation with interfaces between all parts, including an interface between Hugs-like frontend and background compiler and runtime system (part of the Haskell Execution Platform, HEP;-). That got rescheduled to low priority, but might still be a useful starting point (http://www.haskell.org/ghc/docs/papers/hep.ps.gz) Of course, that would be only one side of a modular HPE. The other half would be to make sure that standard programmer editors (Emacs, VIM, ..) get the necessary stub functionality to make use of the interfaces. And finally, both Haskell implementers and Editor developers would need to be convinced to support those interfaces.. After that, implementing and adding functionality using the editor and implementation interfaces would be the lesser problem. The really good IDEs are either built on meta-programming and reflective facilities in the underlying programming language or integrated into one particular implementation. Trying to guess types and syntax is either a lot of work (duplicating what has gone into existing implementations) or just a hack. Claus

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RE: Haskell Programming Environment
by Doug Ransom 25 Oct '00

25 Oct '00

I would like to be able to inspect the type of things easily by hovering my mouse over an expression. As a beginner, I find it hard sometimes to get types correct in Haskell since often variables are not declared as a specific type. > -----Original Message----- > From: Jan Skibinski [mailto:jans@numeric-quest.com] > Sent: Wednesday, October 25, 2000 1:28 AM > To: Pawel Kot > Cc: haskell-cafe(a)haskell.org > Subject: Re: Haskell Programming Environment > > > > > On Wed, 25 Oct 2000, =?ISO-8859-2?Q? Pawe=B3?= Kot wrote: > > > Hello, > > > > I'm writing my master thesis. Its subject is 'Haskell Programming > > Environment'. It is (or rather will be) an extended text > editor working in > > graphical (XFree86) environment designed for Haskell > programmers. It will be > > implemented using Fudgets library. > > I'm wondering what features would you like to find in such > environment. What > > should be neccessary, what would help, what would make > writing programs > > easier, etc. > > I have some concepts, but I would like to hear some > suggestions from you. > > A module/class/instance/library browser perhaps? > Acquiring its information from standard libraries > and other user defined directories? Extracting comments, > module comments, class comments, and implementation > details to present them in some consistent way? Supporting > incremental compilation, a'la hmake? With intelligent use of > colorization, or other useful hints for programmers, > for a start? Intelligent inspectors? > > In short - something that exists for ages in Smalltalk, > or in Eiffel development environment, but with Haskell's > extra capabilities, limitations and goals in view? > > I once did something of this sort for Java: > + Java browser for Xcoral editor - in C > + Bongo based class hierarchy browser - in Java > You can find more about it on our web pages. > > Jan > > > > > > > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Re: Haskell Programming Environment
by Adrian Hey 25 Oct '00

25 Oct '00

Hello, On Wed 25 Oct, Pawe³ Kot wrote: > I have some concepts, but I would like to hear some suggestions from you. How about being able to type check partially written modules? Carlos Camarao posted a link to an implementation of type system CT in Haskell.. http://www.dcc.ufmg.br/~camarao/CT/CTinH.tar.gz Of course you don't really want to use a different type sytem from that currently used by Haskell. I believe this system makes use of 'principal typings' to infer the types of free variables from the context they are used, so it can be used to type check incomplete modules/programs. I can't think why such a system should be incompatible with the current Haskell type system. It seems quite appropriate for an interactive development environment and should be able to give more intelligent error reports. Regards -- Adrian Hey

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Re: Haskell Programming Environment
by Jan Skibinski 25 Oct '00

25 Oct '00

On Wed, 25 Oct 2000, =?ISO-8859-2?Q? Pawe=B3?= Kot wrote: > Hello, > > I'm writing my master thesis. Its subject is 'Haskell Programming > Environment'. It is (or rather will be) an extended text editor working in > graphical (XFree86) environment designed for Haskell programmers. It will be > implemented using Fudgets library. > I'm wondering what features would you like to find in such environment. What > should be neccessary, what would help, what would make writing programs > easier, etc. > I have some concepts, but I would like to hear some suggestions from you. A module/class/instance/library browser perhaps? Acquiring its information from standard libraries and other user defined directories? Extracting comments, module comments, class comments, and implementation details to present them in some consistent way? Supporting incremental compilation, a'la hmake? With intelligent use of colorization, or other useful hints for programmers, for a start? Intelligent inspectors? In short - something that exists for ages in Smalltalk, or in Eiffel development environment, but with Haskell's extra capabilities, limitations and goals in view? I once did something of this sort for Java: + Java browser for Xcoral editor - in C + Bongo based class hierarchy browser - in Java You can find more about it on our web pages. Jan

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RE: Num class
by Tom Pledger 20 Oct '00

20 Oct '00

Mark P Jones writes: > [...] > > Defaulting only kicks in if (a) at least one class is numeric, and > (b) all classes are standard. [...] Defaulting was designed to > work in this way so that (i) it would catch and deal with the most > common problems occurring with numeric literals, and (ii) it would > not be used too often; defaulting is in general undesirable because > it can silently change the semantics. Again, defaulting is an > example of a compromise in the design of Haskell. Ideally, you'd > do without it all together, but if you went that way, you'd end up > having to write more type information in your programs. And again, > I don't suppose there is a universally satisfactory point on this > spectrum. A language extension for subtyping would be of some use there. For example, if Int is set up as a subtype of Integer, meaning that an Int value is acceptable anywhere an Integer value is expected (with the typechecker inserting the conversion code), the literal 42 can unambiguously be assigned the type Int. (This is a reprise of an airy suggestion I've posted before, hence the move to the haskell-cafe list. I'm still at the reading-about- related-work stage of doing something more thorough about it.) Regards, Tom

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RE: Num class
by Simon Peyton-Jones 19 Oct '00

19 Oct '00

[I'm sending this reply to haskell-cafe. This one could run and run!] | > The defaulting mechanism works as follows: If there is an unresolved | > overloading error on a type variable a, which has as an *only* | > constraint (Num a), then we take a to be the suitable default. | | This is not what the Haskell 98 Report says. Section 4.3.4: | | "In situations where an ambiguous type is discovered, an ambiguous | type variable is defaultable if at least one of its classes is a | numeric class (that is, Num or a subclass of Num) and if all of its | classes are defined in the Prelude or a standard library (Figures 6--7 | show the numeric classes, and Figure 5 shows the classes defined in | the Prelude.)" | | I see no good reason for Show superclass of Num. Quite so. It's nothing to do with defaulting, and you could legitimately complain about it. | I agree that the default mechanism is ugly, and that at least the | restriction about classes defined in standard libraries should | be removed. This was quite a conscious decision by the Haskell committee. Defaulting decisions are made silently, and they affect the meaning of the program. So we consciously imposed quite heavy constraints to make sure that silent defaulting doesn't happen much. (GHC has a flag that warns you when it is happening.) You can always write your program by adding an explicit type signature. You can argue that this was a poor decision. Almost certainly there will be programs for which a more liberal choice would be much more convenient; perhaps Koen's is one. So I'm not trying to say "we got it right", only to explain why it is the way it is. Making Show a superclass of Num wasn't nearly as conscious a choice. Simon

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RE: documentation for Hugs-GHC extension libraries
by Simon Marlow 13 Oct '00

13 Oct '00

> I can't seem to find an easily printable (i.e., not > HTML-in-many-pieces) > version of the documentation for the Hugs-GHC extension > libraries. Have > I overlooked it? There's a huge PDF file containing GHC's User Guide and the Library documentation, of which the "lang" section of the Libraries is what used to be the Hugs-Ghc extension libraries, here: http://www.haskell.org/ghc/docs/latest/set.pdf Cheers, Simon

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documentation for Hugs-GHC extension libraries
by Dean Herington 13 Oct '00

13 Oct '00

I can't seem to find an easily printable (i.e., not HTML-in-many-pieces) version of the documentation for the Hugs-GHC extension libraries. Have I overlooked it? Thanks. Dean Herington heringto(a)cs.unc.edu

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Haskell Problem
by Graeme Turner 11 Oct '00

11 Oct '00

Hello, I am e-mailing you to see if you could offer me a bit of assistance. I have chosen to use Haskell in a minor assignment at my University, Heriot Watt in Edinburgh. The basic aim is to read in a file of data, sort it and then display it. I have managed to get a sort to function properly but I am having trouble with reading in the data from the file. I have managed to use the hGetContents and hGetLine methods of the IO library to read the data in but when it is read in, it is stored as an IO String type. I would like to convert the input from the file into one large string so I can process it before sorting it. After reading the whole file into a variable, how do I then convert that IO String to a String? I would be very grateful if you could offer me some assistance in this matter. Thanks Graeme Turner

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Doh!! Still don't quite understand
by Graeme Turner 10 Oct '00

10 Oct '00

Hi, I e-mailed earlier about the IO String input but am still unable to get anything to work Thanks for the e-mails back but I still haven't got a grasp of what to do.Here is a more detailed explanation as I may have been rather vague last time! I have a file of the following format :- Surname , Forename , Age , Height e.g. <String>, <String>, <Int> , <Int> I have a tuple called Person which is defined as (String,String,Int,Int) as you would expect. What I want to do is to create a function which will 1 take a line from the file 2 create a Person tuple from the read information I have defined functions to perform an insertion sort given a tuple of the above specification. Thanks for your time in explaining this to me Graeme Turner

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