[Haskell-cafe] Re: [Haskell] ANNOUNCE: HStringTemplate -- An Elegant, Functional, Nifty Templating Engine for Haskell
s.clover: HStringTemplate is a port of Terrence Parr’s lovely StringTemplate (http://www.stringtemplate.org) engine to Haskell. It is available, cabalized, at: darcs get http://code.haskell.org/HStringTemplate/ Looks very useful! Will this be on hackage.haskell.org soon? I can't wait to: cabal install HStringTemplate :) -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] All equations must have the same arity - why?
There is no technical reason for this. It's a matter of taste. As someone else pointed out, different arities is usually a bug. -- Lennart On Jan 13, 2008 3:12 PM, Neil Mitchell [EMAIL PROTECTED] wrote: Hi, It's nice to write functions in point free style: f = sort . nub But sometimes I have to add an extra case, on a certain value: f [] = [1] f = sort . nub But now these equations have different arities, and its rejected by Haskell. Why does this not simply desugar to: f [] = [1] f x = (sort . nub) x i.e. lift the arities to the longest argument list. Is there a reason this isn't done? Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Possibility to port vshaskell to VS2008?
Yes, the VS Shell indeed looks an attractive platform, because it's free. It'd be great if someone wanted to port Visual Haskell to the VS Shell. Simon | -Original Message- | From: Peter Verswyvelen | Sent: 13 January 2008 21:15 | Subject: Re: [Haskell-cafe] Possibility to port vshaskell to VS2008? | | It might be even better to port it to the freely available downloadable | Visual Studio Shell: | http://msdn2.microsoft.com/en-us/vsx2008/products/bb933751.aspx | | The F# plugin works for that environment, giving a very good free IDE. | | Cheers, | Peter (on Fedora 8 using, woohoo, my first steps on Linux :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Possibility to port vshaskell to VS2008?
Yes, would be really nice. And in the meanwhile update it to GHC 6.8.2 and add support for debugging/stepping now that GHC supports it :-) Peter On Mon, 2008-01-14 at 08:45 +, Simon Peyton-Jones wrote: Yes, the VS Shell indeed looks an attractive platform, because it's free. It'd be great if someone wanted to port Visual Haskell to the VS Shell. Simon | -Original Message- | From: Peter Verswyvelen | Sent: 13 January 2008 21:15 | Subject: Re: [Haskell-cafe] Possibility to port vshaskell to VS2008? | | It might be even better to port it to the freely available downloadable | Visual Studio Shell: | http://msdn2.microsoft.com/en-us/vsx2008/products/bb933751.aspx | | The F# plugin works for that environment, giving a very good free IDE. | | Cheers, | Peter (on Fedora 8 using, woohoo, my first steps on Linux :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Code folding in Emacs
It would be pretty neat for Haskell hacking if the Emacs Haskell mode
could do the following. Imagine you have written some code like so:
-- | The parse state.
data S = S {-# UNPACK #-} !B.ByteString -- current chunk
L.ByteString -- rest of the input
{-# UNPACK #-} !Int64 -- bytes read
-- | The 'Parser' monad is just a State monad carrying around the
-- input ByteString.
newtype Parser a = Parser { unParser :: S - Consumed (Reply a) }
-- | Match byte that fulfills predicate.
satisfy :: (Word8 - Bool) -- ^ Predicate that byte must fulfill.
- Parser Word8 -- ^ Matched byte.
satisfy p =
Parser $ \(S s ss pos) -
if B.null s
then (if L.null ss
then Empty (Error (ParseError pos))
else case L.splitAt 1 ss of
(consuming,rest) -
let now = B.concat . L.toChunks $ consuming
b = B.head now
in
if p b then
Consumed $ Ok b (S (B.tail now) rest (pos + 1))
else Empty $ Error $ ParseError pos
)
else let b = B.head s in
if p b then Consumed $ Ok (B.head s) (S (B.tail s) ss (pos + 1))
else Empty $ Error $ ParseError pos
Now you want an overview of your source file. One way would be to
replace all the implementation parts with ellipses, like so:
-- | The parse state.
data S = S {-# UNPACK #-} !B.ByteString -- current chunk
L.ByteString -- rest of the input
{-# UNPACK #-} !Int64 -- bytes read
-- | The 'Parser' monad is just a State monad carrying around the
-- input ByteString.
newtype Parser a = Parser { unParser :: S - Consumed (Reply a) }
-- | Match byte that fulfills predicate.
satisfy :: (Word8 - Bool) -- ^ Predicate that byte must fulfill.
- Parser Word8 -- ^ Matched byte.
satisfy p = ...
Binding a haskell-fold-source function to a key chain would enable you
to get a quick overview of your module showing only the comments and
type signatures. I've used the little function from
http://emacs.wordpress.com/2007/01/16/quick-and-dirty-code-folding/
but it doesn't work well together with indented type signatures like
in the example above.
Anyone with strong Emacs-fu that knows how one could implement such a function?
-- Johan
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Re: [Haskell-cafe] Computer Science Books using Haskell
Don Stewart writes: One textbook on algorithms with a functional approach is by Fethi Rabhi and Guy Lapalme: Algorithms: A functional programming approach published by Addison-Wesley, 235 pages, ISBN 0-201-59604-0 I'd imagine they wouldn't use many OCR unfriendly characters. I perhaps misunderstand this phrase, but if you suggest that it would be useful to snatch the code examples from within the book, I believe that no OCR is needed, they are here: http://www.iro.umontreal.ca/~lapalme/AlgoFP/code.html Jerzy Karczmarczuk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to add ENV variable in runhaskell shell script
only one argument is allowed after the #! on the first line. however the following should be portable if you must set the variable before runhaskell is executed: #!/bin/sh -- /dev/null 21; MYENV=foo runhaskell $_ import System.Environment main = getEnv MYENV = print -- John Meacham - ⑆repetae.net⑆john⑈ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] All equations must have the same arity - why?
Hello Neil, Monday, January 14, 2008, 2:12:52 AM, you wrote: But sometimes I have to add an extra case, on a certain value: f [] = [1] f = sort . nub Is there a reason this isn't done? this may be also due an error, and in most cases it actually will be due an error. then it makes type inference trickier and will led to very strange error messages instead of simple different amount of arguments. so, we will buy power but lose simplicity -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Code folding in Emacs
On 1/14/08, Johan Tibell [EMAIL PROTECTED] wrote: It would be pretty neat for Haskell hacking if the Emacs Haskell mode could do the following. Imagine you have written some code like so: [...] Binding a haskell-fold-source function to a key chain would enable you to get a quick overview of your module showing only the comments and type signatures. I've used the little function from http://emacs.wordpress.com/2007/01/16/quick-and-dirty-code-folding/ but it doesn't work well together with indented type signatures like in the example above. AFAIU the problem, .. data StupidTypeNameIntendedToBeLong = Foo functionWithLngName :: Foo - Bar functionWithLngName = undefined .. you don't like the way haskell-mode indents the `- Bar' line. If this is the case, you could `newline-and-indent' (`C-j') right after `::'. anotherFunctionWithLongName :: Foo - Bar anotherFunctionWithLongName = undefined And what's this haskell-fold-source function you were talking about? -- vvv ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [newbie question] Memoization automatic in Haskell?
On Sun, Jan 13, 2008 at 12:25:53AM +0100, Henning Thielemann [EMAIL PROTECTED] wrote a message of 28 lines which said: Caching is not the default, but you can easily code this by yourself: Define an array and initialize it with all function values. Because of lazy evaluation the function values are computed only when they are requested and then they persist in the array. It works only if the argument of the function is an integer or an enumerated type. If the argument is a string and you do not know the string values in advance, you cannot use the array. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Code folding in Emacs
Johan Tibell wrote: Anyone with strong Emacs-fu that knows how one could implement such a function? This looks like a straightforward application of outline mode. I believe it might be as simple as setting up a regex and enabling the mode, but check the LISP source for outline mode or perhaps the emacs manual. Joe Buehler ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [IETF Apps meeting] A Theory of Templating Languages
I did find one paper that makes a start at such work, Enforcing Strict Model-View Separation in Template Engines, but the theory is a little weak and it focuses on the nebulous idea of separation of model and view, as opposed to a classification of capabilities and limitations. When I did the research for my template engine paper, that was also the most theoretically-inclined paper I could find. In fact, it was almost the only paper focusing on template languages. That entire area, of considerable importance in practice, seems to be completely ignored by computer science. My own work was more on the practical side, but its first section may be of some interest for its (sadly informal) pointing out of relationships between template engines and functional programming. The paper and the slides can be found at: http://www.idealliance.org/papers/extreme/proceedings/html/2007/Blazevic01/EML2007Blazevic01.xml Good luck. -- Mario Blazevic [EMAIL PROTECTED] Stilo Corporation This message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure, copying, or distribution is strictly prohibited. If you are not the intended recipient(s) please contact the sender by reply email and destroy all copies of the original message and any attachments. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Code folding in Emacs
On Jan 14, 2008 2:30 PM, Valery V. Vorotyntsev [EMAIL PROTECTED] wrote: On 1/14/08, Johan Tibell [EMAIL PROTECTED] wrote: It would be pretty neat for Haskell hacking if the Emacs Haskell mode could do the following. Imagine you have written some code like so: [...] Binding a haskell-fold-source function to a key chain would enable you to get a quick overview of your module showing only the comments and type signatures. I've used the little function from http://emacs.wordpress.com/2007/01/16/quick-and-dirty-code-folding/ but it doesn't work well together with indented type signatures like in the example above. AFAIU the problem, .. data StupidTypeNameIntendedToBeLong = Foo functionWithLngName :: Foo - Bar functionWithLngName = undefined .. you don't like the way haskell-mode indents the `- Bar' line. If this is the case, you could `newline-and-indent' (`C-j') right after `::'. No, I like the way haskell-mode indents. :) However the simple folding snippet I linked to above doesn't work with it since that code simple collapses everything that's indented. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: All equations must have the same arity - why?
Jonathan Cast [EMAIL PROTECTED] wrote: On 13 Jan 2008, at 5:49 PM, Achim Schneider wrote: Jonathan Cast [EMAIL PROTECTED] wrote: On 13 Jan 2008, at 5:27 PM, Achim Schneider wrote: Answer #2: Because you can't write f x = case x of [] - [1] - sort.nub But why not? Because arities aren't lifted to the longest argument list. I think you lost the point of my question... I'm glad you are capable of ever so nobly assigning the purest imaginable motives to me. You are a true inspiration. Treating case as syntax sugar for a higher-order function, so that all binding occurrences of lambdas in the unsugared code are associated with lambdas, is a good thing, and offers a natural way of desugaring the above, one case at a time. What about f x = [1] f - = sort.nub ? You could also do things like f - x = (foo x).bar with it. No more rewriting of pointfree code because of added arguments... So `-' as a pattern means `implicitly apply the RHS to whatever this pattern matches'? I like it. Yes. I suppose _ is a better idea, or something else beginning with _, as the rest of the characters could be functions. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: 0/0 1 == False
On Fri, Jan 11, 2008 at 07:10:20PM -0800, Jonathan Cast wrote: On 11 Jan 2008, at 10:12 AM, Achim Schneider wrote: David Roundy [EMAIL PROTECTED] wrote: Prelude let x=1e-300/1e300 Prelude x 0.0 Prelude x/x NaN The true answer here is that x/x == 1.0 (not 0 or +Infinity), but there's no way for the computer to know this, so it's NaN. Didn't catch this the first time around, but: only to a physicist. I don't understand what you're saying below. Do you mean that the true answer is not 1.0, or that it's not reasonable for the computer to call it NaN? Since 1.0 is the answer you get for high-precision computations, it's hard to see how you can argue that it's a wrong answer. (I mean no disrespect to the author of darcs, but nevertheless the point stands). Back in the real world, 0 / 0 may be defined arbitrarily, or left undefined. (Defining it breaks the wonderful property that, if lim (xn) = x, lim (yn) = y, and x/y = z, then lim (xn / yn) = z. This is considered a Bad Thing by real mathematicians). In fact, in integration theory 0 * inf = 0 for certain 'multiplications', which gives the lie to 0 / 0. -- David Roundy Department of Physics Oregon State University ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Computer Science Books using Haskell
PR Stanley wrote: Can the list recommend books that use Haskell - or any FP language but preferably Haskell - to illustrate the principles of compilers and/or algorithms? Try Andrew Appel's Modern Compiler Implementation in ML http://www.cs.princeton.edu/~appel/modern/ml/ which, as it uses SML for everything, should translate quite readily to Haskell. b ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] cabal and hpc?
Has the Haskell Program Coverage tool been integrated into Cabal? That is, is there anything like runhaskell Setup.hs coverage to generate a coverage report? Thanks, Greg ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] cabal and hpc?
garious: Has the Haskell Program Coverage tool been integrated into Cabal? That is, is there anything like runhaskell Setup.hs coverage to generate a coverage report? Not yet, but definitely on the todo list (its a variant of the test target, that would add -fhpc to each compile, so might be a bit tricky). Until then, you can hook hpc into your testsuite. I'd also recommend linking to the hpc coverage logs from your cabal file's 'description' field., until hackage can compute hpc results automatically. Bring on the code quality! -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Getting frantic with FranTk
On Jan 13, 2008 5:54 AM, Torsten Otto [EMAIL PROTECTED] wrote: Howdy, with a just-in-time-learning approach I managed to teach my class of advanced high schoolers the basics of functional programming using Haskell (I had only used Scheme before). Now to show them that Haskell That is awesome. I commend you. I only ever learned BASIC in school. I have Hugs installed at /opt/local/bin/hugs in MacOS 10.4/10.5. What do I do to get Hugs to recognize FranTk? I have downloaded it, but I can't even get the demo to work, none of the imports can be found: I don't know much about Hugs and less about FranTk. You should probably verify that FranTk is still compatible with recent versions of Hugs. If they are, maybe try putting all the libraries in your current directory and then look for command line options to force hugs to look for them there? Justin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Yi editor tutorial
On 2008.01.14 13:34:42 +, Andrew Birkett [EMAIL PROTECTED] scribbled 0.8K characters: [EMAIL PROTECTED] wrote: I'm going through them now, and I like them a lot. (Maybe I'll finally begin doing stuff with Yi!) Is there any particular reason you didn't put your tutorials on the Haskell wiki? I'd think they'd be good there. Cool, thanks. :-) I agree it'll be a good idea to move it to the wiki, and I'll do that soon. On my own site, I can make lots of little changes locally and then atomically (well, quickly at least!) rsync the new version up onto the server. It makes life easier when I'm likely to change around the top level structure. The wiki makes a lot of sense though, because it's central and other people can extend the tutorial and fix bugs. I'd say editing a wiki is even easier. :) But if you want to wait until you've gotten it to a state where you're happy with it, that's good too. It's also nice to be able to check the server logs and gauge interest too (about 5000 hits since yesterday). Andrew True, but the interest won't last forever; so maybe after the Reddit links go quiescent? -- gwern rico Glock telex million propellants Warfare Ortega CNN 8182 Vauxhall pgpokedMhOryB.pgp Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: MonadPrompt + Gtk2Hs = ?
On Jan 13, 2008 6:49 PM, apfelmus [EMAIL PROTECTED] wrote:
K. Claessen. Poor man's concurrency monad.
http://www.cs.chalmers.se/~koen/pubs/jfp99-monad.ps
P. Li, S. Zdancewic. Combining events and threads for scalable
network services.
http://www.seas.upenn.edu/~lipeng/homepage/papers/lz07pldi.pdf
Two great papers! Thanks for pointing them out!
Eventually this feature rang some bells: you can save not only when you
want to undo, but also when you want to ask something to the user.
Unfortunately, I still haven't come up with a nice higher order function
that generalizes this work without reinventing Prompt on an isomorphic type.
Oh, what kind of generalization do you have in mind?
Leaking Prompt(..) in the export list to the GUI code seems wrong to
me, I like 'runPromptM' because it hides the Prompt(..) data type from
the user [module]. But after some rest I think I found a nice
corresponding function:
contPromptM :: Monad m = (r - m ())
- (forall a. p a - (a - m ()) - m ())
- Prompt p r - m ()
contPromptM done _ (PromptDone r) = done r
contPromptM done cont (Prompt p c) = cont p (contPromptM done cont . c)
This way all the Prompts get hidden so that 'lastAttempt' may be coded as
lastAttempt' :: AttemptCode
lastAttempt' showInfo entry button = guessGameNew = contPromptM done cont
where
cont :: forall a. GuessP a - (a - IO ()) - IO () -- signature needed
cont (Print s) c = showInfo s c ()
cont Guess c = do
mfix $ \cid -
onClicked button $ do {signalDisconnect cid;
guess - entryGetText entry;
c (read guess)}
return ()
done attempts = showInfo $ You took ++ show attempts ++ attempts.
Nice and clean, and much better to read as well. Now the only question
unanswered for me is if there are any relations between
(forall a. p a - (a - m ()) - m ()) -- from contPromptM
and
(ContT r m a - (a - m r) - m r) -- from runContT
besides the fact that both carry a continuation. I have a feeling that
I am missing something clever here.
Cheers,
--
Felipe.
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[Haskell-cafe] Strange GLFW linker problem on Linux
Because apparently GHC works much better on Linux than Windows, I switched to that platform. I'm currently trying Fedora 8. So now I'm completely alone in the dark: no experience with Haskell, no experience with Linux; I left decades of experience with Microsoft products behind me ;-) I tried compiling GFLW (used by SOE) and a Haskell test app on my laptop, and that worked fine. Then I installed Fedora on my desktop, installed all development tools, and GLFW (both the C library and Haskell wrapper) also compiled and linked fine, but when trying to link the test app to GLFW, I got linker errors (see below). It seems these symbols are defined in libXrandr, but I have both the binary as the devel package installed: [EMAIL PROTECTED] dev]# yum list installed | grep Xrandr libXrandr.i386 1.2.2-1.fc8installed libXrandr-devel.i386 1.2.2-1.fc8installed So I have no idea what to do. The main difference between the laptop and desktop is that I installed the NVidia drivers on the desktop manually (first installed the kernel-devel package, and then downloaded and installed the linux driver from the nvidia website) Any hints? Thanks, Peter Linker errors reported by ghc --make Main.hs: /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_window.o): In function `_glfwPlatformRefreshWindowParams': x11_window.c:(.text+0x803): undefined reference to `XRRGetScreenInfo' x11_window.c:(.text+0x80d): undefined reference to `XRRConfigCurrentRate' x11_window.c:(.text+0x81b): undefined reference to `XRRFreeScreenConfigInfo' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_window.o): In function `_glfwPlatformCloseWindow': x11_window.c:(.text+0xb7a): undefined reference to `XRRGetScreenInfo' x11_window.c:(.text+0xb9d): undefined reference to `XRRSetScreenConfig' x11_window.c:(.text+0xba6): undefined reference to `XRRFreeScreenConfigInfo' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_window.o): In function `_glfwPlatformPollEvents': x11_window.c:(.text+0x115b): undefined reference to `XRRUpdateConfiguration' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_window.o): In function `_glfwPlatformOpenWindow': x11_window.c:(.text+0x1fa5): undefined reference to `XRRSelectInput' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_fullscreen.o): In function `_glfwPlatformGetVideoModes': x11_fullscreen.c:(.text+0x1ca): undefined reference to `XRRGetScreenInfo' x11_fullscreen.c:(.text+0x1db): undefined reference to `XRRConfigSizes' x11_fullscreen.c:(.text+0x219): undefined reference to `XRRFreeScreenConfigInfo' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_fullscreen.o): In function `_glfwSetVideoModeMODE': x11_fullscreen.c:(.text+0x329): undefined reference to `XRRGetScreenInfo' x11_fullscreen.c:(.text+0x344): undefined reference to `XRRConfigCurrentConfiguration' x11_fullscreen.c:(.text+0x394): undefined reference to `XRRSetScreenConfigAndRate' x11_fullscreen.c:(.text+0x3ac): undefined reference to `XRRSetScreenConfig' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_fullscreen.o): In function `_glfwGetClosestVideoMode': x11_fullscreen.c:(.text+0x3fa): undefined reference to `XRRGetScreenInfo' x11_fullscreen.c:(.text+0x408): undefined reference to `XRRConfigSizes' x11_fullscreen.c:(.text+0x48f): undefined reference to `XRRConfigRates' x11_fullscreen.c:(.text+0x4dc): undefined reference to `XRRFreeScreenConfigInfo' x11_fullscreen.c:(.text+0x512): undefined reference to `XRRFreeScreenConfigInfo' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_fullscreen.o): In function `_glfwSetVideoModeMODE': x11_fullscreen.c:(.text+0x3be): undefined reference to `XRRFreeScreenConfigInfo' /usr/local/lib/GLFW-0.1/ghc-6.8.2/libHSGLFW-0.1.a(x11_init.o): In function `_glfwPlatformInit': x11_init.c:(.text+0xea): undefined reference to `XRRQueryExtension' collect2: ld returned 1 exit status ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] First Israel Haskell Event
Hello all, A Haskell gathering will take place for the first time in Israel: Friday, January 18 2008 at 11:00 AM Village Green, 33 Jaffa Rd, (corner of Rivlin St), Jerusalem This will be an informal event where everyone can introduce themselves and talk about their thoughts on Haskell. Everyone and anyone are invited. If you are in the area then please stop by, and email me with any questions. Looking forward to an enlightening time, Benny ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Strange GLFW linker problem on Linux
Peter Verswyvelen [EMAIL PROTECTED] wrote: Any hints? Look at ghc --make -v and make sure that ghc uses the right -l and -L options when it calls the linker. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Getting frantic with FranTk
Thank you for the encouragement, Justin. Unfortunately I did try that. But it may also be where my basic understanding is missing: the libraries - do I have to somehow compile all the source or can I just use it? The source is Haskell, but it all comes with makefiles - are these for use with GHC or something more? I have a feeling I have to compile something somehow into some special location. I guess I'll just keep mucking around until I find a clue somewhere... All I know so far is how to use modules in Hugs which is enough for High School, but there is so much more out there... The Readme points out for the underlying Tcl: *** If on unix compile up the TclPrim.so library and run the tclexe script, with hugs as the argument program ie ../bin/tclexe hugs *** Ok, I can find tclexe, but how do I compile up the TclPrim? Probably pretty standard, I'm working on that (hints would still be appreciated...). I'm confused at the point where the demo imports FranTk allright, but then I've hunted the web for missing modules which left me with something else missing: Hugs :l Demos.lhs ERROR ./Utils.hs - Error while importing DLL ./Utils.so: dlopen(./Utils.so, 9): image not found Foreign.Marshal.Alloc I don't begin to understand what this is telling me... If I get it to work, I'll put in on the Web for others to find. Torsten ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell and GUI
Seeing my woes with FranTk - what else is out there that people use if a (simple) GUI is desired for a Haskell app? Just a few textboxes and a button or two would do me. Thanks in advance! Regards, Torsten ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell and GUI
Hi Torsten, Seeing my woes with FranTk - what else is out there that people use if a (simple) GUI is desired for a Haskell app? Just a few textboxes and a button or two would do me. Gtk2hs in GHC: http://www.haskell.org/gtk2hs/ Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Getting frantic with FranTk
On Sun, 2008-01-13 at 14:54 +0100, Torsten Otto wrote: Howdy, with a just-in-time-learning approach I managed to teach my class of advanced high schoolers the basics of functional programming using Haskell (I had only used Scheme before). Now to show them that Haskell is not a weirdo esoteric command line only language, I thought I'd end the class with spoken output (easy enough with the System module and say in Mac OS) and a GUI for input using FranTk. Honestly, if you could get FranTk to work I'd be very impressed. My impression is that it is extremely bitrotted. I would suggest trying one of the other GUI libs that has seen some maintenance this century. (I'm not joking - http://haskell.org/FranTk/ says it works with ghc-4.04 which was released in 1999) That also probably means using ghc rather than hugs since most of the modern GUI libs only work with ghc. The only exception is HGL, which is rumoured to still work wit hugs (though again it has seen little to no maintenance in recent years). So I'd recommend the new SOE, OpenGL, Gtk2Hs or wxHaskell. All of those come with some demos you can show off. SOE and OpenGL are purely for doing drawings and animation (OpenGL is 3D of course). The other two are full blown GUI toolkits. http://haskell.org/soe http://haskell.org/haskellwiki/Opengl http://haskell.org/gtk2hs http://wxhaskell.sourceforge.net/ Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: MonadPrompt + Gtk2Hs = ?
Felipe Lessa wrote:
apfelmus wrote:
Oh, what kind of generalization do you have in mind?
Leaking Prompt(..) in the export list to the GUI code seems wrong to
me, I like 'runPromptM' because it hides the Prompt(..) data type from
the user [module]. But after some rest I think I found a nice
corresponding function:
contPromptM :: Monad m = (r - m ())
- (forall a. p a - (a - m ()) - m ())
- Prompt p r - m ()
contPromptM done _ (PromptDone r) = done r
contPromptM done cont (Prompt p c) = cont p (contPromptM done cont . c)
This way all the Prompts get hidden so that 'lastAttempt' may be coded as
lastAttempt' :: AttemptCode
lastAttempt' showInfo entry button = guessGameNew = contPromptM done cont
where
cont :: forall a. GuessP a - (a - IO ()) - IO () -- signature needed
cont (Print s) c = showInfo s c ()
cont Guess c = do
mfix $ \cid -
onClicked button $ do {signalDisconnect cid;
guess - entryGetText entry;
c (read guess)}
return ()
done attempts = showInfo $ You took ++ show attempts ++ attempts.
Nice and clean, and much better to read as well.
The type of contPromptM is even more general than that:
casePromptOf' :: (r - f b)
- (forall a,b. p a - (a - f b) - f b)
- Prompt p r - f b
casePromptOf' done cont (PromptDone r) = done r
casePromptOf' done cont (Prompt p c ) = cont p (casePromptOf' done
cont . c)
In other words, it's (almost) the case expression / dual for the Prompt
data type. So, only exporting this function and not the Prompt
constructors is like exporting only
either :: (a - c) - (b - c) - Either a b - c
instead of Left and Right for pattern matching. This way, you can do
(simulated) pattern matching with them, but may not use them for
construction. Which is probably what you want here.
Except that there is a subtle difference, namely that c in Prompt p c
has type
c :: a - Prompt p r
whereas the argument to casePromptOf' expects it as
c' = casePromptOf' done cont . c :: a - f b
This means that not exporting constructors could reduce the number of
programs that are possible to implement, but I can't (dis-)prove it.
(That's basically the question at the end of
http://thread.gmane.org/gmane.comp.lang.haskell.cafe/31842/focus=32218).
Of course, you can just change the argument type to
(forall a,b. p a - (a - Prompt p b) - f b)
for the full flexibility.
Now the only question unanswered for me is if there are any
relations between
(forall a. p a - (a - m ()) - m ()) -- from contPromptM
and
(ContT r m a - (a - m r) - m r) -- from runContT
besides the fact that both carry a continuation. I have a feeling that
I am missing something clever here.
The link to ContT m a = (forall b . (a - m b) - m b) is apparent in
the case of casePromptOf' and is no surprise: you can omit p a and
Prompt p r entirely and implement them directly as continuations
(thereby loosing the ability to use it with different m, which would
defeat the whole point here.) See also
Implementing the State Monad.
http://article.gmane.org/gmane.comp.lang.haskell.cafe/31486
for the details.
Regards,
apfelmus
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[Haskell-cafe] Re: Re: Displaying # of reductions after eachcomputation in ghci?
Lennart Augustsson wrote: What is a reduction anyway? I am not an expert but I thought in lambda calculus one has primitive rules for evaluation, e.g. beta reduction. So a reduction is a 'smallest step' in reducing an expression to normal form, no? Cheers Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell and GUI
On Jan 14, 2008 10:09 PM, Torsten Otto [EMAIL PROTECTED] wrote: Seeing my woes with FranTk - what else is out there that people use if a (simple) GUI is desired for a Haskell app? Just a few textboxes and a button or two would do me. Thanks in advance! I like wxHaskell. It seems that GTK2HS is more active though, but I never did manage to install it on windows. -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Displaying # of reductions after eachcomputation in ghci?
Ben Franksen wrote: Lennart Augustsson wrote: What is a reduction anyway? I am not an expert but I thought in lambda calculus one has primitive rules for evaluation, e.g. beta reduction. So a reduction is a 'smallest step' in reducing an expression to normal form, no? Yes and no, a single beta reduction step like (\x.c(d(e(f(x) g = c(d(e(f(g may take 5 steps in some reduction strategies since you have to walk down the expression tree to find the variable and replace it with its value. In the end, seconds are a better measure for time :) Regards, apfelmus ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] QuickCheck properties: export or not?
paul: I was recently sent a patch for my Ranged Sets library which exported all the QuickCheck properties. I'd left them unexported on the grounds that they clutter up the documentation (although simplified versions are included in the documentation) and you can easily run them with the standard quickcheck script. The contributor, [EMAIL PROTECTED] suggested an explicit test harness instead. I'm not unduly bothered one way or the other, but I thought I'd ask the community: what is the best practice here? Most libs seem to include an external Properties.hs or similar file. The only tension there is how much do you need to test thoroughly. You might still end up exporting more than you wish to. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Why purely in haskell?
[EMAIL PROTECTED] wrote: Wolfgang Jeltsch wrote: My impression is that staying close to math is good from a software technology point of view. And it has the advantage of less confusion for the user. What does it mean close to math? How close? Does math raise exceptions upon the division by zero? Does *MATH* answer the question what is: (0/0)==(0/0) ? Nope! Exactly. So why try to give an answer in Haskell? MATH says: the expression 0/0 is undefined, thus comparing (0/0)==(0/0) is undefined, too. I would expect Haskell to say the same. Cheers Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] QuickCheck properties: export or not?
I was recently sent a patch for my Ranged Sets library which exported all the QuickCheck properties. I'd left them unexported on the grounds that they clutter up the documentation (although simplified versions are included in the documentation) and you can easily run them with the standard quickcheck script. The contributor, [EMAIL PROTECTED] suggested an explicit test harness instead. I'm not unduly bothered one way or the other, but I thought I'd ask the community: what is the best practice here? Paul. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] QuickCheck properties: export or not?
ndmitchell: Hi standard quickcheck script. The contributor, [EMAIL PROTECTED] suggested an explicit test harness instead. Unless you have a test harness (ideally through Cabal), the properties will go out of sync, and you'll forget to run them. Tests are good, they should be able to be invoked as standard. Every time I've *not* done a test harness, and then relied on manually remembering things or putting them in the documentation, it has gone wrong very quickly! I usually have a main = runTests file, and then use darcs to ensure the tests are up to date: $ cat _darcs/prefs/prefs test ghc -no-recomp -Onot -fasm -itests tests/Unit.hs --make -odir /tmp tests/Unit darcs will run the testsuite, and it needs to pass, before a commit will be accepted. We do a similar thing for xmonad. The test command to run on every commit can be set via, darcs setpref test my test command -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Why purely in haskell?
[EMAIL PROTECTED] wrote: When math says that something is undefined, in my little brain I understand that there is no answer. NO answer. Math doesn't say that something is undefined, but tells you that you did something that's illegal, i.e. impossible, in the system you're working with. Trying to divide by zero is like trying to break out of a mental asylum with a banana: It's neither a good tool to fight your way free, as well as using it will get you back into the asylum, by system-inherent laws. The mathematically right, and only really sane way to handle such things is not to do them at all, which would change Haskell's semantics rather drastically. There just is no unsafePerformMath :: Math a - a. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Why purely in haskell?
Ben Franksen writes: [EMAIL PROTECTED] wrote: ... Does *MATH* answer the question what is: (0/0)==(0/0) ? Nope! Exactly. So why try to give an answer in Haskell? MATH says: the expression 0/0 is undefined, thus comparing (0/0)==(0/0) is undefined, too. I would expect Haskell to say the same. I don't know whether you are serious, or you are pulling my leg... Let's suppose that it is serious. When math says that something is undefined, in my little brain I understand that there is no answer. NO answer. Is this the undefined you want to have? The bottom non-termination? Now, this is obviously the *worst* possible reaction of the system, the IEEE indefinite is much better, at least you know what had happened. Would you propose the non-termination as the issue of all errors, such as negative argument to the real sqrt, etc? Well, as you wish... But don't write medical software, please... Jerzy Karczmarczuk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell and GUI
There's also the HOC (Haskell Objective-C bridge), which lets you use Apple's Cocoa APIs. Bob On 14 Jan 2008, at 22:09, Torsten Otto wrote: Seeing my woes with FranTk - what else is out there that people use if a (simple) GUI is desired for a Haskell app? Just a few textboxes and a button or two would do me. Thanks in advance! Regards, Torsten ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Why purely in haskell?
Achim Schneider writes: [EMAIL PROTECTED] wrote: When math says that something is undefined, in my little brain I understand that there is no answer. Math doesn't say that something is undefined, but tells you that you did something that's illegal, i.e. impossible, in the system you're working with. Yeah, sure. Thanks God, we have on this list a fellow who gets direct telephone calls from her Majesty the Queen Mathematics. And knows better. Go tell to all people who use the word 'undefined' in math that they are stupid. At least, more stupid than you. http://mathworld.wolfram.com/Undefined.html http://en.wikipedia.org/wiki/Defined_and_undefined http://mathforum.org/library/drmath/view/53336.html http://encarta.msn.com/encyclopedia_761568582/Calculus_(mathematics).html etc. Jerzy Karczmarczuk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Why purely in haskell?
On Jan 15, 2008 12:29 AM, [EMAIL PROTECTED] wrote: Ben Franksen writes: [EMAIL PROTECTED] wrote: ... Does *MATH* answer the question what is: (0/0)==(0/0) ? Nope! Exactly. So why try to give an answer in Haskell? MATH says: the expression 0/0 is undefined, thus comparing (0/0)==(0/0) is undefined, too. I would expect Haskell to say the same. I don't know whether you are serious, or you are pulling my leg... Let's suppose that it is serious. When math says that something is undefined, in my little brain I understand that there is no answer. NO answer. I'm not sure if I'm agreeing or disagreeing with you here. Depends on exactly what you mean by no answer. When I was a TA for calculus 2, students were presented with something like the following problem: Find the limit: lim (sin x / x) x-0 And proceeding, they would reduce this to: sin 0 / 0 0 / 0 Look in the book that said 0/0 is undefined, and write undefined on the paper as if that were the answer. For the calculus uninclined (I figure that is a vast minority on this list), the answer is 1. In that case, undefined meant you did the problem wrong. And the error was precisely when they wrote 0 on the bottom of the division sign. To me, when math says undefined... let me stop there. Math doesn't say undefined. Instead, when mathematicians say undefined, they usually mean not that the question has no answer, but that the question you're asking doesn't even make sense as a question. For example, division is only defined when the denominator is not 0. Asking what the answer to 0/0 is is like asking what happens when I move the king across the board in chess?. That operation doesn't even make sense with those arguments. However, Haskell is not blessed (cursed?) with dependent types, so it is forced to answer such questions even though they don't make sense. But looking to math (at least with a classical interpretation of numbers) is just not going to work. Personally, I loathe the existence of NaN and +-Infinity in floating point types. Someone here made an enlightinging point encouraging us to think of floating point numbers not as numbers but as intervals. That makes me slightly more okay with the infinities, but NaN still bugs me. I'd prefer an error: Haskell's way of saying you did the problem wrong. That would be most useful in the kinds of things I do with floating point numbers (games). But there are probably other areas where the IEEE semantics are more useful. Well... that paragraph was just a long-winded way of saying I have an opinion, but I don't think it's very important Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Why purely in haskell?
[EMAIL PROTECTED] wrote: Achim Schneider writes: [EMAIL PROTECTED] wrote: When math says that something is undefined, in my little brain I understand that there is no answer. Math doesn't say that something is undefined, but tells you that you did something that's illegal, i.e. impossible, in the system you're working with. Yeah, sure. Thanks God, we have on this list a fellow who gets direct telephone calls from her Majesty the Queen Mathematics. And knows better. Go tell to all people who use the word 'undefined' in math that they are stupid. At least, more stupid than you. That's funny, you just proved that I am more stupid than myself, as I use the term. For things that are illegal or impossible in the system I'm working with. It's not that I posted it because I didn't agree with what you said. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] fast fractional part of floating point number - modf?
On Sun, Jan 13, 2008 at 01:08:49AM +0100, Henning Thielemann wrote: Is there a fast and reliable way to compute the fraction of a floating point number? no, and this has bothered me to the point I consider it a bug in the language spec that all 'rounding' style functions give back an integral type. These sort of operations are often used on floating point values when you want the same type out you put in, and in particular you want it to handle things like infinities and nan's properly which the conversion through integral does not (plus, these usually coorespond to a single machine instruction so are more 'primitive' in a sense and thus better building blocks for a RealFrac class). To alleviate this I added the following to the RealFrac class in jhc -- TODO Doubles class (Real a, Fractional a) = RealFrac a where ... -- new stuff added by jhc properFractionf :: a - (a,a) truncatef, roundf :: a - a ceilingf, floorf :: a - a truncatef x = m where (m,_) = properFractionf x roundf x = fromInteger (round x) ceilingf x= if r 0 then n + 1 else n where (n,r) = properFractionf x floorf x = if r 0 then n - 1 else n where (n,r) = properFractionf x the meaning should be clear, they perform the same operation as their non f counterparts but maintain the same type. John -- John Meacham - ⑆repetae.net⑆john⑈ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: 0/0 1 == False
On 14 Jan 2008, at 9:56 AM, David Roundy wrote: On Fri, Jan 11, 2008 at 07:10:20PM -0800, Jonathan Cast wrote: On 11 Jan 2008, at 10:12 AM, Achim Schneider wrote: David Roundy [EMAIL PROTECTED] wrote: Prelude let x=1e-300/1e300 Prelude x 0.0 Prelude x/x NaN The true answer here is that x/x == 1.0 (not 0 or +Infinity), but there's no way for the computer to know this, so it's NaN. Ah. My apologies. Must remember to read first, then flame... You are right that, in Ratio Integer, you get this result. But you can't get that answer in Double. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: MonadPrompt + Gtk2Hs = ?
On Jan 14, 2008 2:28 PM, Felipe Lessa [EMAIL PROTECTED] wrote:
lastAttempt' :: AttemptCode
lastAttempt' showInfo entry button = guessGameNew = contPromptM done cont
where
cont :: forall a. GuessP a - (a - IO ()) - IO () -- signature needed
cont (Print s) c = showInfo s c ()
cont Guess c = do
mfix $ \cid -
onClicked button $ do {signalDisconnect cid;
guess - entryGetText entry;
c (read guess)}
return ()
done attempts = showInfo $ You took ++ show attempts ++ attempts.
Excellent work; I love it.
I'll definitely have to give this a try when I get back from vacation.
I'd been wondering what the best way to interface with GUI code is
and it's nice to have a sample to work from.
-- ryan
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[Haskell-cafe] Re: [Haskell] ANNOUNCE: HStringTemplate -- An Elegant, Functional, Nifty Templating Engine for Haskell
I'm absolutely planning to get it up there, but it needs a bit more work first. Just today, gwern sent a bunch of very nice patches that cleaned up some -Wall messages, and fixed a build issue with 6.8. And then, thanks to an email from Martin Lütke, I realized that I had foolishly not exported a function to query groups, because I was too worried about functions to compose them! So yeah, letting your baby out into the world is a bit scary, but everyone's been quite helpful and supportive so far, and hopefully I'll feel ready to get it on hackage in the next week or two. (Of course, after that, I'm now puzzling over the best typesafe ways to represent html entity encoding and url escaping, planning to pull together some more documentation on all the loveliness of the stringtemplate grammar, there are more quickcheck properties to be written, you know.. the usual. :-) ) --S On Jan 14, 2008, at 3:09 AM, Don Stewart wrote: s.clover: HStringTemplate is a port of Terrence Parr’s lovely StringTemplate (http://www.stringtemplate.org) engine to Haskell. It is available, cabalized, at: darcs get http://code.haskell.org/HStringTemplate/ Looks very useful! Will this be on hackage.haskell.org soon? I can't wait to: cabal install HStringTemplate :) -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Re: Displaying # of reductions after eachcomputation in ghci?
In lambda calculus you can take a beta reduction as the step. But Haskell is not normally implemented by lambda calculus so you have to pick something else. There are measures of reduction that you can come up with but they will vary, e.g., by compiler, optimization level, etc. I think time is a much more interesting measure, since that's what you really care about in the end. On Jan 14, 2008 2:03 PM, Ben Franksen [EMAIL PROTECTED] wrote: Lennart Augustsson wrote: What is a reduction anyway? I am not an expert but I thought in lambda calculus one has primitive rules for evaluation, e.g. beta reduction. So a reduction is a 'smallest step' in reducing an expression to normal form, no? Cheers Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ErrorT and catchError question
Hi, I'm trying to use ErrorT transformer based on Don Stewart's Shell example: http://cgi.cse.unsw.edu.au/~dons/blog/2007/03/10#programmable-semicolons It's probably a trivial question, but I cannot figure out how to implement the catchError function in: instance MonadError String Shell where throwError = error . (Shell failed: ++) catchError l h = ??? Thanks for help, Adam ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] QuickCheck properties: export or not?
I think that type classes with nontrivial requirements should export QuickCheck properties that test those requirements. For example, the Data.Monoid module (http://haskell.org/ghc/docs/latest/html/libraries/base/Data-Monoid.html) could export properties that check the monoid laws (for an Arbitrary Monoid with Eq). That would serve as a formal specification of the requirements, and allow any user to check that their implementation is right. -- I'm doing Science and I'm still alive. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ErrorT and catchError question
On Jan 15, 2008, at 0:28 , Adam Smyczek wrote: It's probably a trivial question, but I cannot figure out how to implement the catchError function in: instance MonadError String Shell where throwError = error . (Shell failed: ++) catchError l h = ??? Take a look at Control.Exception.catch for starters. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] fast fractional part of floating point number - modf?
On Mon, 14 Jan 2008, John Meacham wrote: On Sun, Jan 13, 2008 at 01:08:49AM +0100, Henning Thielemann wrote: Is there a fast and reliable way to compute the fraction of a floating point number? no, and this has bothered me to the point I consider it a bug in the language spec that all 'rounding' style functions give back an integral type. I find returning an Integral is appropriate. The type expresses perfectly what kind of values you can expect. Sure, there should be some optimization rule like fromInteger (round x) = roundf x . However, the 'fraction' function gets a fraction and returns a fraction and doesn't care about the type of the integer part. As I see this is also missing from your RealFrac class extension. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
