- Haskell-Cafe - Haskell.org

Re: Re[2]: Tuple-like constructors
by Robert Dockins 08 Feb '06

08 Feb '06

[Moved to cafe; time to stop bothering the Haskell' committee...] On Feb 8, 2006, at 1:19 PM, Malcolm Wallace wrote: > Robert Dockins <robdockins(a)fastmail.fm> writes: > >> instance (Bin a,Bin b,Bin c,Bin d) => Bin (a,b,c,d) >> >> See the problem? Sooner or later (probably sooner) I'll get tired of >> typing. I have to write down an 'instance' declaration for each >> value of n. Clearly this can't generalize to all n. > > There has been a suggestion that the 'deriving' mechanism be de- > coupled > from the datatype declaration. Together with a generic default > definition, that means you could write something like > > deriving Bin for (,,,,,,,,,,,,,,,,,,,,) > > and hence not need to write the tedious instance header yourself, > since the compiler can easily infer it. Humm. That is nice, and it would help keep my fingers from cramping, but it doesn't solve the root objection. Consider machine-generated code using largish tuples. Should the generated code include the 'deriving' clause? If no, someone from outside has to supply it. If yes, I have to deal with overlapping instance from other generated code. If maybe, I have to know when to generate it and when not. Solvable? yes, but kind of ugly. Acceptable? probably. Now, (speculatively combining a whole host of language extensions) if I could write down: deriving Bin for (_::*) Which would mean "derive (as necessary) Bin for all types at kind * where the suitable preconditions can be found/derived" I'd be completely happy. Humph. That's more or less adding an axiom schema to the constraint solving system of the typehecker which could be realized at link-time via C++ style template thingies or at compile-time by whole-program analysis. I am simultaneously appalled by and attracted to this idea..... Rob Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG

2 1

Spotted in Haskell Weekly News: February 06, 2006
by Graham Klyne 08 Feb '06

08 Feb '06

Donald Bruce Stewart wrote: > Haskell Weekly News: February 06, 2006 : > Oleg says, "The implementation of RSA on the type level is left > for future work". Methinks this gives a whole new meaning to "type security". :) #g -- Graham Klyne For email: http://www.ninebynine.org/#Contact

1 0

Re: [Haskell-cafe] Why is $ right associative instead ofleftassociative?
by John Hughes 08 Feb '06

08 Feb '06

Lennart Augustsson wrote: > I now think :: for type signatures was a bad mistake. > I don't use lists very much. They are not the right data structure > for many things. So : is not as common as :: in my code. > I checked a small sample of code, about 20000 lines of Haskell. > It has about 1000 uses of ':' and 2000 of '::'. Just for interest, I analysed some of my code. Obviously my style is quite different to yours--my type specialiser of 3,500 lines has 240 conses, and only 22 occurrences of '::'. I seem to be using '::' a bit more lately, though, which I suspect is due to using classes much more. I also checked the Agda source code, about 14,000 lines, with about 500 occurrences of cons and 640 of '::'. I think the only conclusion one can draw is that style varies. > In my opinion all the special syntactic sugar for lists should go > away. I don't think lists are special enough to motivate it. What, no list comprehensions?? I'd disagree--sequencing is special, and lists represent it directly. Don't forget, also, that lists are also much more prevalent in beginners' code--and nice notation for beginners helps get people started on Haskell. > But this is not what Haskell' is about. It's supposed to be some > modest extensions to Haskell. Not designing a new perfect language. Right! John

8 10

does haskell have plist's ?
by raptor 08 Feb '06

08 Feb '06

does Haskell have a property lists. Like Lisp ? any pointer to examples ? tia

4 3

haskell reference card ?
by raptor 07 Feb '06

07 Feb '06

is there somewhre Haskell reference card ?

3 2

EclipseFP (Haskell IDE) 0.9.1 released
by Thiago Arrais 07 Feb '06

07 Feb '06

EclipseFP 0.9.1 has been released since last Friday. It is an open-source development environment for Haskell code. EclipseFP integrates GHC with an Haskell-aware code editor and also supports quick file browsing through an outline view, automatic building/compiling and quick one-button code execution. Downloads and more information are available on the project home page http://eclipsefp.sourceforge.net/ We are open for comments and general discussion. Actually we would really appreciate comments from both newbie and veteran Haskell programmers. This is open-source development and everyone on the Haskell community is welcome to participate. Cheers, Thiago Arrais

9 12

Re: [Haskell] Re: Streams: the extensible I/O library
by Bulat Ziganshin 07 Feb '06

07 Feb '06

Hello Peter, Monday, February 06, 2006, 10:24:01 PM, you wrote: moving to nescafe :) PS> > You can find further information about the library at the PS> > page http://haskell.org/haskellwiki/Library/Streams and PS> > download it as http://freearc.narod.ru/Streams.tar.gz PS> Is there any chance of running this code on a non-Windows PS> system? I tried to compile the example programs, but failed PS> for lack of a System.Win32 module. I might be able to port PS> the code, but I figured it would be wise to ask first. of course, it should work under other systems! it's my fault and you can fix this just by adding #ifdef around this import: #if defined(mingw32_HOST_OS) || defined(__MINGW32__) || defined(_MSC_VER) import System.Win32 #endif btw, my "wc" has about the same speed as yours :) thank you for the first bug-report! i re-uploaded the fixed version just now :) -- Best regards, Bulat mailto:bulatz@HotPOP.com

2 2

main features of functional programming paradigm
by Abigail 07 Feb '06

07 Feb '06

Hi, I would like to ask about what are tha main features of functional programming? Additionally, about FAD: A Functional Analysis and Design Methodology What kind of software can i develop with this methodology? thanks for your answers Abigail. __________________________________________________ Correo Yahoo! Espacio para todos tus mensajes, antivirus y antispam ¡gratis! Regístrate ya - http://correo.espanol.yahoo.com/

3 2

Re: [Haskell-cafe] Why is $ right associative instead ofleftassociative?
by John Hughes 06 Feb '06

06 Feb '06

> Quoting Paul Hudak <paul.hudak(a)yale.edu>: > >> Actually, one of the main reasons that we chose (:) is that that's what >> Miranda used. So, at the time at least, it was not entirely clear what >> the "de facto universal inter-language standard" was. > Phil Wadler argued for the ML convention at the time, and wrote a document containing a fair amount of sample code to illustrate what it would look like. We noticed something surprising: instead of (x:xs) and the like, Phil had consistently written (x :: xs) -- note the extra spaces. Somehow, using the longer operator name led him to feel spaces were needed around it. That in turn made his lines longer, encouraged him to split definitions across lines, and so on. When I read the thing, I realised after a while that I was skipping all the code fragments -- because they just looked too big and complicated to take in during a quick reading. It was at least partly that experience that convinced us that using :: for cons would impose a small cost, but a real one, on readability. It may seem trivial, but the sum of many such decisions is significant. The story does illustrate the importance of actually trying out syntactic ideas and seeing how they play--one can be surprised by the result. >> I don't think Haskell Prime should be about changing the look and >> feel of the language. It's about consolidating the most important extensions into the standard, isn't it? Changes that break existing code should be very, very well motivated--if porting code to Haskell Prime is too difficult, people just won't do it. John

11 16

Haskell to call Microsoft COM (Dispatch)
by Gracjan Polak 05 Feb '06

05 Feb '06

Hi all, Is there any library to make Haskell call Microsoft COM functions using Dispatch? E.g I don't need the full COM binary functionality, scripting is enough. Google didn't seem to find anything interesting... beside rolling my own using FFI :) Thanks in advance! -- Gracjan

5 6