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Re: [Haskell-cafe] Gtk2Hs and Glade Tutorial
by Duncan Coutts 14 Oct '06

14 Oct '06

On Fri, 2006-10-13 at 15:18 +0200, Hans van Thiel wrote: > Hello Duncan, > > Thanks for your reply, and here's the pdf. Thanks. > One of the things to be improved, which I note myself, is something on > how to do it on the Windows platform. It's much the same of course, but yes that would be nice. > (This is assuming there is a Glade for Windows.) There is. It comes with the dev flavour of the Gtk+ installer. > Another thing is the terminology, for example about handles, actions and > functions. Glade uses 'signals' and 'callback functions' and you can > specify them visually. I believe (I'll have to check this) you can look > up the names in a file 'callbacks.c'. Of course you have to substitute > those for the Gtk2Hs equivalents, but it might make it easier to find > the appropriate ones in the Gtk2Hs API. We do have slightly different terminology in a few places and usually for good reason. For example the idea of a callback function makes a lot of sense in C where you really do have to have a named function that gets called in response to a signal. I Haskell we don't need a named function of course we can just say: onClicked button $ do ... ... > I'll check out the link you provided in the next few days, and I'm > looking forward to your comments. I'll also have to wait and see what > Eddy Ahmed, the author of the Glade tutorial, thinks about this idea. > It would be nice to reuse that, and to put the Haskell version on his > more general web site as well. Why re-invent the wheel.. I'll send you some more comments when I've had a full read through. Perhaps we should use the haskell.org wiki for this. Duncan

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Porting content from the old wiki
by dons＠cse.unsw.edu.au 13 Oct '06

13 Oct '06

The main thing holding up porting of content from the old wiki is licensing. In order to help this, could people who've written for the old wiki, and are happy to have that work moved to the new wiki and relicensed, add their names to the list here: http://haskell.org/haskellwiki/HaWiki_migration Or email me and I'll add the name. Then anyone can move your work over, which should really speed things up. Thanks, Don

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quick trivial question on records
by Imam Tashdid ul Alam 13 Oct '06

13 Oct '06

I was reading Daan's paper on scoped labels and it struck me... has anyone tried a variation of the language where records are by dafault strict? and unboxed when appropriate? extended question: doesn't it makes more sense? laziness and partial applications go very well together, and the ADT constructors are often partially applied... __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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A type in search of a name...
by Brian Hulley 13 Oct '06

13 Oct '06

Hi, You'll never believe it but I've been struggling last night and all of today to try and think up a name for the following type and I'm still nowhere near a solution: data ??? = VarId | VarSym | ConId | ConSym this is part of a type to describe Haskell lexemes: data Token = TName !??? !ByteString.T | ... Here are some of my attempts to fill in ??? and my reasons for rejecting them: 1) VarConIdSym - the problem is that it's too long and the first letter is 'v' which could be confused with the letter 'V' in "VarId" or "VarSym" 2) Name - the problem is that this suggests the string itself rather than the VarId/VarSym/ConId/ConSym'ness of the token 3) NameType - I'm trying to avoid using the words "Type" "Kind" etc because I'll probably want to use these later for other things and in any case NameType suggests the type of a lexical name ie Token itself 4) Space - this can be confused with something to represent whitespace or the namespaces introduced by modules 5) Just using data Token = TVarId !BS.T | TVarSym !BS.T | ... -- explodes into too many different cases when you add tokens for qualified names and all their variations (since I'm also representing incomplete tokens like "Foo." and "Foo.where" (as a prefix of "Foo.whereas" etc since it can't stand by itself because "where" is a reserved word)) 6) Using Bool as in data Token = TName !Bool !Bool !BS.T -- problem is that then I won't get any help from the typechecker if I accidentally confuse the order of Bools when matching etc. I could use the record syntax but then code can become very clunky to look at and it would still allow the Bools to get confused when they are passed about Any ideas? I must say that trying to think up names for things is absolutely the most difficult task in programming imho. The problem is that once fixed down, a name gets used all over the place and becomes totally entrenched in the code and affects how one thinks about the code thereby influencing its whole future development in a very deep and pervasive way (think suffixes/ prefixes/ relationships with other concepts etc). I would also be satisfied with just good names for the following types: data ???1 = Var | Con data ???2 = Id | Sym data ???3 = Op | Plain (I just combined ???1 and ???2 in ??? to try and save some space in the representation but ideally they would be separate types if only there were a way to tell the compiler to represent each by 1 bit in a word at the machine level like C's struct {VarCon vc : 1; IdSym is : 1;}) Any suggestions welcome, Thanks, Brian. -- Logic empowers us and Love gives us purpose. Yet still phantoms restless for eras long past, congealed in the present in unthought forms, strive mightily unseen to destroy us. http://www.metamilk.com

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nightnightita
by George Brewster 13 Oct '06

13 Oct '06

hope you're feeing better too.

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Nim Game in Haskell - Someone plz?
by Luis Felipe 13 Oct '06

13 Oct '06

Hi, I need help to develop an implementation of nim game in Haskell. Could anyone send me a implementation of this game in haskell?? thanks -- Luis

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Having typing problem with "tan" function.
by Edward Ing 13 Oct '06

13 Oct '06

Hi, I am new to Haskell, so the following problem is probably easy for you to spot but difficult for me. Any pointers would be appreciated. In GHCI on a load I am getting the following message: SSnowflake.hs:41:45: No instance for (Floating Int) arising from use of `pi' at Snowflake.hs:41:45-46 Probable fix: add an instance declaration for (Floating Int) In the first argument of `(/)', namely `pi' In the first argument of `tan', namely `(pi / 3)' In the second argument of `(*)', namely `(tan (pi / 3))' Failed, modules loaded: none. When I put the expression "tan ( pi / 3)" at the GHCI interpreter prompt I get a value, but this is not accepted on a load the code. Here is the code: >>>> code triangle :: Window -> (Point,Point) -> Int -> IO () triangle window ((x1,y1), (x2,y2)) size = let height = fromIntegral(y2 - y1) * 3 / 2 halfWidth = height * (tan (pi / 3 )) in drawInWindow window (withColor (sizeColorMap size) (polygon [(x1,y1),( x1 - halfWidth, height ), (x1 + halfWidth, height)] ))

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Is Haskell a Keynesian language?
by Henning Thielemann 12 Oct '06

12 Oct '06

Here is another approach of questionable classification of languages. :-) A lazy functional program is demand driven, an imperative program is supply driven. That is, if I request some information by calling a function in GHCi or Hugs, the interpreter develops a plan a how to produce the information I need and then executes the necessary steps. In contrast to that, an imperative program executes what's next on the schedule, whether it is need or not. So is Haskell a Keynesian language and C++ a Say language?

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tail-recursing through an associative list
by Seth Gordon 12 Oct '06

12 Oct '06

In my first posting, I mentioned that I was going to try to translate some of our code to Haskell and see how it worked. Well, I don't have a stunning demonstration of the power of pure functional programming, but I do have an interesting problem. I chose to port a program that we use in our build system that takes a table of geographic data and groups the rows in the table according to [REDACTED]. The description of what the existing program does takes up only a few paragraphs, but the source code is eight pages of dense C++ that has obviously been optimized up the wazoo (and beyond the point where a mortal like myself can understand what's going on). On one of our servers, it can process 200,000 rows in about three minutes. My Haskell translation is three and a half pages of gorgeous lucid almost-entirely-functional code ... that in its first draft, took about three seconds to process 2,000 rows, eight minutes to process 20,000 rows, and overflowed a 1-MB stack when processing 200,000 rows. Oops. After banging together a version that took input from stdin instead of the database (it was easier to do that then to learn enough about Cabal to get HSQL recompiled with profiling), I profiled the code and observed that the most-called-upon function in the program (200 million entries for those 20,000 rows) was structured like this: type AList = [(Key, [MetaThingies])] myFunction :: AList -> Thingie -> AList myFunction [] x = [(key x, [meta x])] myFunction ((k, v):tail) x | matchKeys k (key x) = case tryJoining v x of Nothing -> (k, v) : (myFunction tail x) Just v' -> (k', v') : tail where v' = bestKey k (key x) | otherwise = (k, v) : (myFunction tail x) I'm wondering if the slowness of the program can be attributed to that case statement in the middle--perhaps unwrapping the Maybe type returned by tryJoining is preventing the function from being properly tail-recursive, or something. (I tried making the list construction strict by replacing "(k, v) : (myFunction tail x)" et al. with "(:) (k, v) $! (myFunction tail x)", and it actually slowed the program down, so either I'm not understanding how to improve things with strictness or laziness isn't the problem here.) Any advice from the gurus?

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Gtk2Hs and Glade Tutorial
by Hans van Thiel 12 Oct '06

12 Oct '06

Hello, There is a very nice tutorial on the Glade Interface Designer at http://www.writelinux.com/glade and I've been using it with 'An Introduction to Gtk2Hs, A Haskell GUI Library', by Kenneth Hoste at http://haskell.org/~shae/memory.pdf to learn Gtk2Hs and Glade. The 'Gtk2Hs Introduction', however, is not really aimed at the absolute beginner and so I've written down my experience as an 'appendix' to the glade tutorial, which really is for getting started. I've just asked the author, Eddy Ahmed, for permission to 'translate' his tutorial to Haskell Gtk2Hs, but meanwhile I'd like to submit my separate concept (attached) for comments. Thanks, Hans van Thiel

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