[Haskell-cafe] ANNOUNCE: xmonad 0.7 released
http://xmonad.org The xmonad dev team is pleased to announce xmonad 0.7! The headlines: The 0.7 release of xmonad provides several improvements over 0.6, including improved integration with GNOME, more flexible "rules", various stability fixes, and of course, many new and interesting features in the extension library (general support for window decorations, utf8 support, scratch pad terminals, pointer control) and more! New GNOME support: Active, automated support for GNOME utilities. We know our users often like to use GNOME menus, tools and status bars, and we'd like to announce that xmonad actively supports GNOME! Extensions for communicating with and utilising gnome utilities come in the library suite, as well as extensive documentation and support. For more information see the GNOME/xmonad integration page on the wiki. A period of active development: In the past year, the xmonad development team received contributions from over 60 developers, making xmonad one of the largest window manager development teams around, and dwarfing other tiling window manager projects. Yet, at the same time, the core code base remains at around 1000 lines of code, with another 7000 lines in the extension library -- a significant achievment! Change logs: http://haskell.org/haskellwiki/Xmonad/Notable_changes_since_0.6 http://xmonad.org/changelog-0.7.txt http://xmonad.org/changelog-xmc-0.7.txt About: xmonad is a tiling window manager for X. Windows are arranged automatically to tile the screen without gaps or overlap, maximising screen use. Window manager features are accessible from the keyboard: a mouse is optional. xmonad is extensible in Haskell, allowing for powerful customisation. Custom layout algorithms, key bindings and other extensions may be written by the user in config files. Layouts are applied dynamically, and different layouts may be used on each workspace. Xinerama is fully supported, allowing windows to be tiled on several physical screens. Features: * Very stable, fast, small and simple. * Automatic window tiling and management * First class keyboard support: a mouse is unnecessary * Full support for tiling windows on multi-head displays * Full support for floating, tabbing and decorated windows * Full support for Gnome and KDE utilities * XRandR support to rotate, add or remove monitors * Per-workspace layout algorithms * Per-screens custom status bars * Compositing support * Powerful, stable customisation and reconfiguration * Large extension library * Excellent, extensive documentation * Large, active development team, support and community Get it! Information, screenshots, documentation, tutorials and community resources are available from the xmonad home page: http://xmonad.org The 0.7 release, and its dependencies, are available from hackage.haskell.org: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xmonad xmonad packages are available in the package systems of at least: Debian, Gentoo, Arch, Ubuntu, OpenBSD, NetBSD, FreeBSD, Gobo, NixOS, Source Mage, Slackware and 0.7 packages will appear in coming days (some are already available). On the fly updating to xmonad 0.7 is supported. You should be able to upgrade to xmonad 0.7 from 0.6 and earlier, transparently, without losing your session. Load the new code with mod-q and enjoy. Extensions: xmonad comes with a huge library of extensions (now more than 7 times the size of xmonad itself), contributed by viewers like you. Extensions enable pretty much arbitrary window manager behaviour to be implemented by users, in Haskell, in the config files. For more information on using and writing extensions see the webpage. The library of extensions is available from hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xmonad-contrib Full documentation for using and writing your own extensions: http://xmonad.org/contrib.html This release brought to you by the xmonad dev team: Spencer Janssen Don Stewart Jason Creighton David Roundy Brent YorgeyDevin Mullins Braden Shepherdson Roman Cheplyaka Lucas Mai Featuring code contributions from over 60 developers: Aaron DenneyAdam Vogt Alec Berryman Alex Tarkovsky Alexandre BuisseAndrea Rossato Austin SeippBas van Dijk Ben VouiBrandon Allbery Chris Mears Christian Thiemann Clemens Fruhwirth Daniel Neri Daniel Wagner Dave Harrison David Glasser David Lazar Dmitry KurochkinDominik Bruhn Dougal Stanton Eric Mertens Ferenc Wagner Gwern Branwen Hans Phil
Re: [Haskell-cafe] Equality constraints in type families
Hugo Pacheco: Yes, but doesn't the confluence problem only occur for type synonyms that ignore one or more of the parameters? If so, this could be checked... You can't check this easily (for the general case). Given type family G a b type FList a x = G a x type instance F [a] = FList a Does FList ignore its second argument? Depends on the type instances of G. Manuel On Fri, Mar 28, 2008 at 12:04 AM, Manuel M T Chakravarty <[EMAIL PROTECTED] > wrote: Hugo Pacheco: > Sorry, I meant > > type FList a x = Either One (a,x) > type instance F [a] = FList a We should not allow such programs. Manuel > > > On Thu, Mar 27, 2008 at 4:45 PM, Hugo Pacheco <[EMAIL PROTECTED]> > wrote: > > > The current implementation is wrong, as it permits > > type S a b = a > type family F a :: * -> * > type instance F a = S a > > Why do we need to forbid this type instance? Because it breaks the > confluence of equality constraint normalisation. Here are two > diverging normalisations: > > (1) > > F Int Bool ~ F Int Char > > ==> DECOMP > > F Int ~ F Int, Bool ~ Char > > ==> FAIL > > > (2) > > F Int Bool ~ F Int Char > > ==> TOP > > S Int Bool ~ S Int Char > > ==> (expand type synonym) > > Int ~ Int > > ==> TRIVIAL > > This does mean that a program such as > > type FList a = Either One ((,) a) > type instance F [a] = FList a > > will be disallowed in further versions? > Doesn't this problem occur only for type synonyms that ignore one or > more of the parameters? If so, this could be checked... > > hugo > > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Equality constraints in type families
On Sun, Mar 30, 2008 at 3:54 AM, Manuel M T Chakravarty < [EMAIL PROTECTED]> wrote: > Hugo Pacheco: > > Yes, but doesn't the confluence problem only occur for type synonyms > > that ignore one or more of the parameters? If so, this could be > > checked... > > You can't check this easily (for the general case). > I was most interested in knowing that this assumption was enough, and it looks like it does. > > Given > > type family G a b >type FList a x = G a x >type instance F [a] = FList a > > Does FList ignore its second argument? Depends on the type instances > of G. > > Manuel > I haven't thought of that, thanks for the example. hugo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Equality constraints in type families
Anyway, do you think it is feasible to have a flag such as -fallow-unsafe-type-families for users to use at their own risk? (supposing we know how to guarantee these constraints). I speak for my own, there are currently some nice thinks that I can only accomplish with partially applied type synonyms in type families, otherwise code starts to get dummier in terms of type contexts and context variables. Thanks, hugo On Sun, Mar 30, 2008 at 4:14 AM, Hugo Pacheco <[EMAIL PROTECTED]> wrote: > On Sun, Mar 30, 2008 at 3:54 AM, Manuel M T Chakravarty < > [EMAIL PROTECTED]> wrote: > > > Hugo Pacheco: > > > Yes, but doesn't the confluence problem only occur for type synonyms > > > that ignore one or more of the parameters? If so, this could be > > > checked... > > > > You can't check this easily (for the general case). > > > > I was most interested in knowing that this assumption was enough, and it > looks like it does. > > > > > > Given > > > > type family G a b > >type FList a x = G a x > >type instance F [a] = FList a > > > > Does FList ignore its second argument? Depends on the type instances > > of G. > > > > Manuel > > > > I haven't thought of that, thanks for the example. > > hugo > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] compilation succeeds -- execution fails
Bertram Felgenhauer <[EMAIL PROTECTED]> wrote: > Jason Dusek wrote: > > It compiles fine and loads fine -- but it doesn't run fine: > > unknown symbol `___stginit_cedictzm0zi1zi1_DataziCharziCEDICTziMatter_' > > This is a cabal pitfall. Thank you -- this tip saved my bacon. -- _jsn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] compilation succeeds -- execution fails
Stefan O'Rear <[EMAIL PROTECTED]> wrote: > The only type that you are allowed to assume corresponds to a C int is > CInt, in the Foreign.C.Types module. This probably isn't the problem, > but it could make problems of its own on a 64-bit or otherwise weird > system. So say I turn everything back to pointers to CInt, what is the accepted way to convert from CInt to Int and CInt to Char? Is relying on the fact that CInt always wraps a Haskell integer an okay way to go? I might was well learn these things now, before I get into bad habits. -- _jsn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] announce: hgdbmi (GDB/MI interface)
Just in case someone else needed this, here you go: GDB/MI lets programs drive GDB. It can be used, for example, by GDB frontends. This module wraps attaching GDB to a process and parsing the (surprisingly complicated) GDB/MI output. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hgdbmi ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] compilation succeeds -- execution fails
On Sat, Mar 29, 2008 at 10:21:32PM -0700, Jason Dusek wrote: > Stefan O'Rear <[EMAIL PROTECTED]> wrote: > > The only type that you are allowed to assume corresponds to a C int is > > CInt, in the Foreign.C.Types module. This probably isn't the problem, > > but it could make problems of its own on a 64-bit or otherwise weird > > system. > > So say I turn everything back to pointers to CInt, what is the > accepted way to convert from CInt to Int Same as any other pair of whole-number types - fromIntegral. > and CInt to Char? fromIntegral and toEnum > Is relying on the fact that CInt always wraps a Haskell integer an > okay way to go? What do you mean by wraps? It's an opaque type... Stefan signature.asc Description: Digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parsec Expected Type
Paul Keir wrote: > What I'd like is to parse either the string "parameter", or the > string ":". I'm using 'reserved' and 'symbol' because they seem to > correspond well to the concepts in the language I'm parsing. You may consider using reservedOp for ":", depending on how ":+" should be parsed: for ":+" use reservedOp for ":" "+" use symbol If you use reserved, then ":name" will be parsed as ":name" not ":" "name" as you probably expect. generally, reserved is for identifier-like keywords, and reservedOp for operator-like keywords. > Perhaps I'd express my confusion better if I ask: Why are 'reserved' > and 'symbol' different types? I have no idea. They aren't in the Parsec manual on Daans site: http://legacy.cs.uu.nl/daan/download/parsec/parsec.html You can fix this by defining reserved name = ParsecToken.reserved tokenParser name >> return name instead of reserved = ParsecToken.reserved tokenParser to "import" the reserved component from the tokenParser to the toplevel. Now, reserved :: String -> CharParser st String Another option is to fix it the other way, by defining symbol name = ParsecToken.symbol tokenParser name >> return () or to fix it in a ad-hoc manner, by defining ignored = (>> return ()) and using it in the approbiate places, like parameterOrColon = reserved "parameter" <|> ignored (symbol ":") Tillmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [GSoC] Porting HaRe to use the GHC API
Chaddaï Fouché wrote: Comments, reactions ? You can also propose refactoring, if I complete the port early, I'll try to add some refactoring to HaRe. Comment: Yes please ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: HTTP client libraries
Hi, On Fri, Mar 28, 2008 at 6:42 AM, John Goerzen <[EMAIL PROTECTED]> wrote: > On 2008-03-28, Don Stewart <[EMAIL PROTECTED]> wrote: > > paulrbrown+haskell-cafe: > > > And we have a curl binding, already in wide use. > > > > http://code.haskell.org/curl.git/ > > > > a release to hackage is imminent. > > Do you mean this? > > http://hackage.haskell.org/cgi-bin/hackage-scripts/package/curl-1.3.1 > > Looks like it's not quite as current as your Git repo. Is this surprising? Hackage is not a revision control system. The curl package on hackage is a fairly recent version of the git repo. -Iavor ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] compilation succeeds -- execution fails
Jason Dusek wrote: Stefan O'Rear <[EMAIL PROTECTED]> wrote: The only type that you are allowed to assume corresponds to a C int is CInt, in the Foreign.C.Types module. This probably isn't the problem, but it could make problems of its own on a 64-bit or otherwise weird system. So say I turn everything back to pointers to CInt, what is the accepted way to convert from CInt to Int and CInt to Char? Type class methods: -- for numbers like Int, CInt fromIntegral :: (Num b, Integral a) => a -> b -- for Char fromEnum :: (Enum a) => a -> Int toEnum :: (Enum a) => Int -> a > Is relying on the fact that CInt always wraps a Haskell integer an okay way to go? I don't know what you mean by this. > I might was well learn these things now, before I get into bad habits. Hope this helps, Claude -- http://claudiusmaximus.goto10.org ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] compilation succeeds -- execution fails
On 29 Mar 2008, at 10:21 PM, Jason Dusek wrote: Stefan O'Rear <[EMAIL PROTECTED]> wrote: The only type that you are allowed to assume corresponds to a C int is CInt, in the Foreign.C.Types module. This probably isn't the problem, but it could make problems of its own on a 64-bit or otherwise weird system. So say I turn everything back to pointers to CInt, what is the accepted way to convert from CInt to Int Use fromIntegral to go CInt -> Int, Int -> CInt. This only depends on CInt being an Integral type. and CInt to Char? Use toEnum . fromIntegral jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] announce: Glome.hs raytracer
On Thu, Mar 27, 2008 at 02:49:35AM +, Ian Lynagh wrote: > On Wed, Mar 26, 2008 at 02:33:20PM -0700, Jim Snow wrote: > > > > -Memory consumption is atrocious: 146 megs to render a scene that's a > > 33k ascii file. Where does it all go? A heap profile reports the max > > heap size at a rather more reasonable 500k or so. (My architecture is > > 64 bit ubuntu on a dual-core amd.) > > I haven't looked properly yet, but it looks like something is leaking > memory that shouldn't be. Bug filed here: http://hackage.haskell.org/trac/ghc/ticket/2185 Thanks Ian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Announce: Decimal arithmetic package
I've just uploaded version 0.1.0 of a decimal arithmetic package to Hackage. Decimal numbers are stored as an Integral mantissa and a Word8 exponent, where the number stored is mantissa * 10^(-exponent). In other words the exponent is the number of decimal places stored. There are also routines for partitioning a value such that the sum of the parts is equal to the original value. This is useful in financial arithmetic. This came out of my ongoing work on an AMQP binding for Haskell. Version 0-10 of the AMQP spec includes decimal fractions defined in this way for financial applications, so I thought I'd make a proper job of it. A darcs repository will be set up shortly. Paul. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monad instance for Data.Set
On Tue, 25 Mar 2008, Ryan Ingram wrote: settest :: S.Set Int settest = runSetM $ do x <- mplus (mplus mzero (return 2)) (mplus (return 2) (return 3)) return (x+3) -- fromList [5,6] What this does under the hood is treat the computation on each element of the set separately, except at programmer-specified synchronization points where the computation result is required to be a member of the Ord typeclass. It's like working in the List monad mainly, collapsing duplicates from time to time, right? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Usage of Read Class
Hello,
I would like to ask something that results in when I have the following
commands
data Color = Red | Green | Blue | Indigo | Violet deriving (Enum,Show,Read)
(read.show) x
:1:1:
Ambiguous type variable `a' in the constraint:
`Read a' arising from a use of `read' at :1:1-4
Probable fix: add a type signature that fixes these type variable(s)
I also receive the same message with the following:
*Test > let x = Branch (Branch (Branch (Leaf 'a') (Leaf 'b')) (Leaf 'c') )
(Leaf 'd')
*Test > x
<<<'a'|'b'>|'c'>|'d'>
*Test > (read.show) x
:1:1:
Ambiguous type variable `a' in the constraint:
`Read a' arising from a use of `read' at :1:1-4
Probable fix: add a type signature that fixes these type variable(s)
data Tree a = Leaf a | Branch (Tree a) (Tree a)
--type ShowS = String -> String
showsTree :: (Show a) => Tree a -> ShowS
showsTree (Leaf x) = shows x
showsTree (Branch l r) = ('<':).showsTree l . ('|':) . showsTree r . ('>':)
--type ReadS a = String -> [(a,String)]
readsTree :: (Read a) => ReadS (Tree a)
readsTree s = [(Branch l r, x) | ("<",t) <- lex s,
(l,u) <- readsTree t,
("|",v) <- lex u,
(r,w) <- readsTree v,
(">",x) <-lex w]
++
[(Leaf x, t) | (x,t) <- read s]
instance Show a=> Show (Tree a) where
showsPrec _ x = showsTree x
instance Read a => Read (Tree a) where
readsPrec _ s = readsTree s
Why is this happen? Maybe an example with a simple application of the Class
Read would be helpful.
Thanks
--
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[Haskell-cafe] lexicographic order
Hello everyone, I would like to ask something that I found in the ebook "a Gentle Introduction to Haskell". http://haskell.org/tutorial/stdclasses.html#sect8.4 data Tree a = Leaf a | Branch (Tree a) (Tree a) instance (Ord a) => Ord (Tree a) where (Leaf _) <= (Branch _) = True (Leaf x) <= (Leaf y)= x <= y (Branch _) <= (Leaf _)= False (Branch l r) <= (Branch l' r') = l == l' && r <= r' || l <= l' The latter specifies a lexicographic order: Constructors are ordered by the order of their appearance the data declaration, and the arguments of a constructor are compared from left to right. Although I have tried to make sense what lexicographic order means I haven't figured out. Maybe an example with a simple application of this would be helpful. To be honest I can't understand what the symbol <= really means. Thanks -- View this message in context: http://www.nabble.com/lexicographic-order-tp16381434p16381434.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Usage of Read Class
> I would like to ask something that results in when I have the following > commands > data Color = Red | Green | Blue | Indigo | Violet deriving (Enum,Show,Read) > (read.show) x > > :1:1: > Ambiguous type variable `a' in the constraint: > `Read a' arising from a use of `read' at :1:1-4 > Probable fix: add a type signature that fixes these type variable(s) What the error message says is, it doesn't know which type to read to. read has the type Read a => String -> a, and unless you tell it what 'a' is going to be, how would it know? If you say '(read.show) x :: Color' it should work just fine. Cheers, /Niklas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lexicographic order
> Although I have tried to make sense what lexicographic order means I haven't > figured out. Maybe an example with a simple application of this would be > helpful. To be honest I can't understand what the symbol <= really means. <= means "less than or equal to". Normally, lexicograpic order is the order in which words would appear in a lexicon. This can be generalized to other data types than strings by the kind of comparison done here, by specifying an ordering of the constructors (in this case Leaf < Branch). Cheers, /Niklas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lexicographic order
Hello Simeon, Monday, March 31, 2008, 12:45:54 AM, you wrote: > The latter specifies a lexicographic order: Constructors are ordered by the > order of their appearance the data declaration, and the arguments of a > constructor are compared from left to right. > Although I have tried to make sense what lexicographic order means I haven't > figured out. Maybe an example with a simple application of this would be > helpful. To be honest I can't understand what the symbol <= really means. i'm not sire that i understood your question (are you really never seen less-or-equal comparison? :), but i can say about lex. order: if you can compare chars and 'a' < 'b', then *lists* of chars compared in lexicographic order will be "aaa" < "aab" "aab" < "aba" "baa" < "abb" and so on - i.e. it finds *left-most* pair of non-equal chars and returns result based on it comparison the same principle used for comparison of these trees - any Leaf smaller than any Branch, if the same constructors are used then their parameters are compared, from left to right although the last alternative, (Branch l r) <= (Branch l' r') = l == l' && r <= r' || l <= l' seems suspicious to me. isn't it the same as (Branch l r) <= (Branch l' r') = l <= l' ? -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Usage of Read Class
> > :1:1: > > Ambiguous type variable `a' in the constraint: > > `Read a' arising from a use of `read' at :1:1-4 > > Probable fix: add a type signature that fixes these type variable(s) > > What the error message says is, it doesn't know which type to read to. > read has the type Read a => String -> a, and unless you tell it what > 'a' is going to be, how would it know? If you say '(read.show) x :: > Color' it should work just fine. Just to sharpen the point: read cannot know from the string it processes which type to deliver. For example, try the following at the ghci prompt: read "3" -> Yields the same error as above read "3" + 3 -> 6 read "3" + 3.3-> 6.3 read "3.3" + 3.3 -> 6.6 read "3.3" + 3-> Error: no parse What's happening is that the type of the expression is determined by the literal on the _right_side_ of the + sign, and not by the contents of the string on the left side. The last example is a bit tricky. ghci sees 3 on the rhs, which can be of any type in the Num class (as opposed to 3.3, which has to be of a Fractional type). If unresolved, it will default to Integer (or Int?), and try to parse "3.3" as such -- which will of course fail. -- Ariel J. Birnbaum ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] lexicographic order
Hello Bulat, Monday, March 31, 2008, 1:16:35 AM, you wrote: > if you can compare chars and 'a' < 'b', then *lists* of chars compared > in lexicographic order will be > "aaa" < "aab" > "aab" < "aba" > "baa" < "abb" as it was mentioned by Niklas Broberg, the last sentence should be reversed: "abb" < "baa" sorry for +1 confusion :) -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lexicographic order
2008/3/30, Bulat Ziganshin <[EMAIL PROTECTED]>: > although the last alternative, >(Branch l r) <= (Branch l' r') = l == l' && r <= r' || l <= l' > seems suspicious to me. isn't it the same as >(Branch l r) <= (Branch l' r') = l <= l' Yes, it should be : (Branch l r) <= (Branch l' r') = l < l' || l == l' && r <= r' Lexical order for a tuple (a,b) is : (a,b) <= (a',b') iff (a < a' or (a == a' and b <= b')) The same idea can be applied to list (where Nil is strictly less than anything else) or other datatypes. -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] compilation succeeds -- execution fails
Thanks for your answers, everybody. -- _jsn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monad instance for Data.Set
On Sun, Mar 30, 2008 at 1:09 PM, Henning Thielemann <[EMAIL PROTECTED]> wrote: > It's like working in the List monad mainly, collapsing duplicates from > time to time, right? Sort of. You can look at it that way and get a basic understanding of what's going on. A slightly more accurate analysis of what is going on is that it is working in ContT Set for a variation of ContT that doesn't require the underlying object to be a full monad, but only a restricted one. In such a monad you could define > mplus :: ContT Set a -> ContT Set a -> ContT Set a > mplus x y = lift $ union (runContT x id) (runContT y id) (not valid haskell code) However, what is actually happening is that we are defining a set of "side-effectful" computations using Prompt, and then observing those computations in a "Set" environment. With this definition you can actually implement the interface for any monad you want; just define the operations in your data type. In this case: > data OrdP m a where >PZero :: OrdP m a >PRestrict :: Ord a => m a -> OrdP m a >PPlus :: Ord a => m a -> m a -> OrdP m a > type SetM = RecPrompt OrdP Every monad provides at least the same operations as the Identity monad; this definition says that SetM is a monad that provides those operations, plus three additional operations: "prompt PZero", "prompt $ PRestrict x", and "prompt $ PPlus x y" of the types shown in the definition of "OrdP". You can then interpret those operations however you want; runSetM defines an observation function that runs the computation and returns its results in a Set, given the restriction that the computation itself returns an Ord type. In order to really understand this, you need to understand the type of "runPromptC": runPromptC :: (r -> ans) -- "pure" result handler -> (forall a. p a -> (a -> ans) -> ans) -- "side effect" handler that gets a continuation -> Prompt p r -- computation to run -> ans "runPromptC" is (almost) just the case operation for a structure of this type: data Prompt p r = Return r | forall a. BindEffect (p a) (a -> Prompt p r) except with the recursive call to runPromptC inlined within BindEffect; given this data type you can define runPromptC easily: runPromptC ret _ (Return r) = ret r runPromptC _ prm (BindEffect p k) = prm p (\a -> runPromptC ret prm (k a)) This definition makes it obvious that the "pure" continuation "ret" is called at the end of the computation, and the "effectful" continuation prm is called to handle any side effects. Exercise 1: Define the function "prompt :: p a -> Prompt p a" on this datatype. Exercise 2: Define an instance of Monad for this datatype. Now you should be able to understand the observation function "runSetM": > runSetM :: Ord r => SetM r -> S.Set r > runSetM = runPromptC ret prm . unRecPrompt where >-- ret :: r -> S.Set r >ret = S.singleton >-- prm :: forall a. OrdP SetM a -> (a -> S.Set r) -> S.Set r >prm PZero _ = S.empty >prm (PRestrict m) k = unionMap k (runSetM m) >prm (PPlus m1 m2) k = unionMap k (runSetM m1 `S.union` runSetM m2) "ret" handles the result of pure computations; that is, those that could have just as easily run in the Identity monad. "prm" handles any effects; in this case the three effects "PZero", "PRestrict" and "PPlus". You could write a different observation/interpretation function that treated the elements as a List, or Maybe, or whatever. Let me know if this makes sense, or if you have any other questions. -- ryan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Possible to automatically determine typeclass membership?
Is it possible in Haskell + GHC extensions to use reflection techniques to determine typeclass membership? I'm thinking of things like the following: Idea 1: > data MaybeEq a = NoEq a | Eq a => HasEq a > checkEq :: (some typeclass constraint) => a -> MaybeEq a (such that checkEq x returns HasEq x if and only if x has an Eq instance.) Idea 2: > data HTrue > data HFalse > class MaybeEq a b | a -> b > instance Eq a => MaybeEq a HTrue > instance (otherwise) => MaybeEq a HFalse -- ryan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Functional dependencies with Type Classes
Henning Günther: suppose there are two (identical) classes: class Res a b | a -> b where getRes :: a -> b and class Res2 t where type Member t getRes2 :: t -> Member t It is easy to automatically make every instance of Res2 an instance of res: instance Res2 a => Res a (Member a) where getRes x = getRes2 x However, declaring every instance of Res an instance of Res2 seems impossible, as the following doesn't compile instance Res a b => Res2 a where type Member a = b getRes2 x = getRes x Question is: How to do this? The reason I need it is because I use a library which uses functional dependencies, but my classes shall be type families. The last definition is invalid as the right-hand side of a type family instance can only depend on its parameters. However, in type Member a = b you pull 'b' out of thin air. Remember that associated types (ie, type families as part of classes) are only syntactic sugar for sparate type family and class declarations. Obviously, it would be imposible to pull the type instance out of the class in your definition. (The mismatch between FDs and TFs here really is due to FDs being tied to classes and TFs being separable - in that sense TFs are more general than FDs, and hence, you cannot always simulate TFs with FDs.) However, you can wrap an FD library into a TF interface with some additional effort. Using your example for illustration, define the type family and class separately: type family Member a class Res2 a where getRes2 :: a -> Member a Then, implement the catch all class instance as follows: instance Res a (Member a) => Res2 a where getRes2 x = getRes x (This needs -fundecidable-instances. It is perfectly decidable if your FD class is, but GHC doesn't know that.) Now, the additional overhead is that you need to define the type family instances separately; ie, for every class instance of the FD class, such as instance Res Int Bool where getRes x = x == 0 you need to repeat the type mapping: type instance Member Int = Bool I hope this is not too much of a burden in your application. Manuel PS: Hmm, maybe this should go onto the wiki...___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wumpus World
On 28 Mar 2008, at 10:59 pm, Benjamin L. Russell wrote: The commercial SICStus Prolog is also substantially more expensive (see http://www.sics.se/isl/sicstuswww/site/index.html), at 153 euros for a Personal License (see http://www.sics.se/isl/sicstuswww/site/order4.html). Prices for Academic, Single-User Commercial, and Multi-User Commercial licenses are even more expensive, at 1560, 1980, and 7800 euros, respectively. An Evaluation License is only valid for 30 days. Not all students and researchers can afford a Personal License. Let me contrast SICStus Prolog with GHC. I *have* a personal copy of SICStus on my SunBlade 100/Solaris 2.10 system which installed absolutely trouble free. I *did* have a copy of GHC, but trying to install GHC 6.4 took a great deal of my time and now I don't have a working GHC any more. So for me, GHC is by far the more expensive: I've spent considerably more than 500 Euros of my time and got nothing for it. Much though I admire Jan, I've also had such a lot of trouble installing SWI Prolog on various machines that SICStus was *really* cheaper than the "free" Prolog after all. I do wish people would remember that not all the world is Linux. 153 Euros (why did the Europeans name their currency after the Common Wallaroo?) is NZD 303 or about the price of two textbooks. (Three copies of Bird's introduction to functional programming would do it, if they shipped free.) You're telling me that *researchers* can't afford the price of a couple of books? The academic licence isn't that unreasonable. 1560 Euros is NZD 3091, which is about one month of a TA's pay. Another 880 Euros gives you the right to give your students free binaries, however many students you have, year after year after year. Can you recommend an alternative, fast Prolog development system under a free licensing agreement, such as GPL/GLPL? There is, after all, GNU Prolog. The last time I saw any benchmarks, it was substantially faster than SWI, while not quite as good as SICStus. See http://gprolog.inria.fr/ or http://www.gprolog.org/ For what it's worth, GNU Prolog's developers *do* realise that not all the world's linux. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Equality constraints in type families
Hugo Pacheco: Anyway, do you think it is feasible to have a flag such as -fallow- unsafe-type-families for users to use at their own risk? (supposing we know how to guarantee these constraints). Sorry, but it doesn't seem like a good idea to enable an unsound type system even by an explicit option. Manuel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [GSoC] Porting HaRe to use the GHC API
Chaddaï Fouché wrote: > My proposal for the SoC is to port HaRe (its parsing and refactoring) > to use the GHC API instead of Programmatica. This is an appealing idea, and it has the kind of tight scope that makes it plausible as a summer project. Excellent! http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell job opening
MindIQ Corporation is looking for a Haskell programmer. Details can be found at http://cdsmith.twu.net/jobposting.html. This isn't "officially" announced yet, but it will be in a few days. >From the announcement: Why You Want This Job * You can program in Haskell and get a salary for it. * Work from home. Choose your hours. Travel only if you want to. * Build a new software application from scratch. * Chance to work some (but not entirely) on open source stuff. * Small company, no bureaucracy, but quite stable (around since 1986). * You will be "Lead Software Developer" within a very short time. Hope this is of interest. -- Chris Smith Lead Software Developer, MindIQ Corporation ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: SoC project: Python-Haskell bridge - request for feedback
On 2008.03.27 14:07:23 -0700, Dan Weston <[EMAIL PROTECTED]> scribbled 0.7K characters: > I did not see MissingPy on Hackage (presumably it would be next to > MissingH?) Remember, Hackage is alphabetical by category and then by title; I personally would not stick MissingH in the Unclassified category but something like Development. Anyway, I doubt you'll see MissingPy on Hackage soon; note that the installation procedure requires you to use a python script to generate an appropriate cabal file. (It doesn't build for me anyway, but that's a separate issue.) > I found it (listed on http://www.complete.org/jgoerzen/softindex.html) at > http://darcs.complete.org/missingpy > > Is this the right place to get it? > > Dan I think so. That's the host I recognize from HSH, at least. -- gwern Brown virtual DDR&E B83 Kwajalein Team IMF CANSLO Watergate MOD pgpD6EyGSgW1h.pgp Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Possible to automatically determine typeclass membership?
Hello,
> Is it possible in Haskell + GHC extensions to use reflection
> techniques to determine typeclass membership? I'm thinking of things
> like the following:
>
I think the short answer is not in general; i.e. I don't think there is any
way to access the members of an arbitrary typeclass (but I'd love to be
proved wrong).
However, you could always explicitly list the members of a typeclass you are
interested in (this is similar to your Idea 2):
{-# OPTIONS_GHC -fglasgow-exts -fallow-undecidable-instances
-fallow-overlapping-instances #-}
class InEq a b | a -> b where inEq :: a -> Bool
instance TypeCast b HFalse => InEq a b where inEq _ = False
instance InEq Int HTrue where inEq _ = True
instance InEq a b => InEq [a] b where inEq _ = inEq (undefined :: a)
data HTrue
data HFalse
class TypeCast a b | a -> b, b-> a where typeCast :: a -> b
class TypeCast' t a b | t a -> b, t b -> a where typeCast' :: t -> a -> b
class TypeCast'' t a b | t a -> b, t b -> a where typeCast'' :: t -> a -> b
instance TypeCast' () a b => TypeCast a b where typeCast x = typeCast' () x
instance TypeCast'' t a b => TypeCast' t a b where typeCast' = typeCast''
instance TypeCast'' () a a where typeCast'' _ x = x
You can also do an arguably nicer, more flexible version of the previous by
recreating some of the typeclass machinery yourself; Oleg has several
examples of this such as: //okmij.org/ftp/Haskell/poly2.txt
-Jeff
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Re: [Haskell-cafe] Wumpus World
--- "Richard A. O'Keefe" <[EMAIL PROTECTED]> wrote: > [snip] > > Let me contrast SICStus Prolog with GHC. > I *have* a personal copy of SICStus on my SunBlade > 100/Solaris 2.10 > system which installed absolutely trouble free. > I *did* have a copy of GHC, but trying to install > GHC 6.4 took > a great deal of my time and now I don't have a > working GHC any more. > So for me, GHC is by far the more expensive: I've > spent considerably > more than 500 Euros of my time and got nothing for > it. Much though > I admire Jan, I've also had such a lot of trouble > installing SWI Prolog > on various machines that SICStus was *really* > cheaper than the "free" > Prolog after all. I do wish people would remember > that not all the > world is Linux. Sorry to hear about your troubles with GHC. Have you tried documenting your problems and sending an inquiry to the Glasgow-haskell-bugs mailing list (see http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs)? That mailing list is dedicated to GHC-related bugs, and they tend to be quite responsive. FWIW, I have GHC 6.8.2, which installed trouble-free, running on a Windows XP (Service Pack 2) system at work. I did customize it (after installation) to restore the original banner, but that was a customization, not a bug-fix, and I haven't encountered any bugs per se with it so far. > > 153 Euros (why did the Europeans name their currency > after the > Common Wallaroo?) is NZD 303 or about the price of > two textbooks. > (Three copies of Bird's introduction to functional > programming > would do it, if they shipped free.) > > You're telling me that *researchers* can't afford > the price of > a couple of books? It's more than that, actually, because, in my case, I also want to study it at home on a PPC-based PowerBook running Mac OS X 10.2.8 Jaguar, soon-to-be-upgraded to the PPC version of Mac OS X 10.5.x Leopard, soon-to-be-replaced by an Intel-based MacBook Pro running the Intel version of Mac OS X 10.5.x Leopard. And this is alongside studying it at work. Granted, SICStus Prolog does appear to be an extremely easy-to-install, fast, well-documented, stable, industrial-grade version of Prolog. It would probably provide an extremely pleasant and rewarding Prolog experience. It is probably well-supported as well. However, the Personal License of SICStus Prolog is only valid for a single computer running a single copy at any one time. So I would actually need to purchase a minimum of two licenses if I used it at both work and home and then went through the trouble of uninstalling each version of SICStus Prolog every time I upgraded my OS at home (which I usually don't do, because it costs already purchased time), and a maximum of four licenses if I chose not to uninstall. Now, 4 * 153 euros = 612 euros which is much more than the price of a couple books. > > The academic licence isn't that unreasonable. 1560 > Euros is > NZD 3091, which is about one month of a TA's pay. > Another 880 > Euros gives you the right to give your students free > binaries, > however many students you have, year after year > after year. > > > Can you recommend an alternative, fast > > Prolog development system under a free licensing > > agreement, such as GPL/GLPL? > > There is, after all, GNU Prolog. The last time I > saw any benchmarks, > it was substantially faster than SWI, while not > quite as good as > SICStus. > > See http://gprolog.inria.fr/ or > http://www.gprolog.org/ Yes, GNU Prolog does seem one alternative. Thank you for providing the link. I'll have to compare and contrast it with SICStus Prolog and SWI-Prolog. Although the ease of installation of SICStus Prolog does seem enticing, the need to purchase a new license every time I use a different computer seems a little frightening. What happens if one day, my boss suddenly tells me I'm fired and prohibits access to my work PC for "security" reasons, thereby preventing me from uninstalling SICStus Prolog at work, and I then need to continue studying it on a different PC at a new job? Wouldn't I need to purchase another Personal License, at another 153 euros? There is no such thing as real job "security" in the current job market. This could happen without warning at any time, for any reason or even lack of reason. > > For what it's worth, GNU Prolog's developers *do* > realise that not all > the world's linux. Yes, but I'm not quite sure what you mean by this, since SWI-Prolog is also available on Windows, and I don't use Linux, either--I use Mac OS X. So who is it that believes that all the world is Linux? Benjamin L. Russell ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lexicographic order
Chaddaï Fouché-2 wrote: > > 2008/3/30, Bulat Ziganshin <[EMAIL PROTECTED]>: >> although the last alternative, >>(Branch l r) <= (Branch l' r') = l == l' && r <= r' || l <= l' >> seems suspicious to me. isn't it the same as >>(Branch l r) <= (Branch l' r') = l <= l' > > Yes, it should be : > (Branch l r) <= (Branch l' r') = l < l' || l == l' && r <= r' > > Lexical order for a tuple (a,b) is : > (a,b) <= (a',b') iff (a < a' or (a == a' and b <= b')) > The same idea can be applied to list (where Nil is strictly less than > anything else) or other datatypes. > > -- > Jedaï > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > Chaddaï Fouché-2 wrote: > > 2008/3/30, Bulat Ziganshin <[EMAIL PROTECTED]>: >> although the last alternative, >>(Branch l r) <= (Branch l' r') = l == l' && r <= r' || l <= l' >> seems suspicious to me. isn't it the same as >>(Branch l r) <= (Branch l' r') = l <= l' > > Yes, it should be : > (Branch l r) <= (Branch l' r') = l < l' || l == l' && r <= r' > > Lexical order for a tuple (a,b) is : > (a,b) <= (a',b') iff (a < a' or (a == a' and b <= b')) > The same idea can be applied to list (where Nil is strictly less than > anything else) or other datatypes. > > -- > Jedaï > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > Quoted from: http://www.nabble.com/lexicographic-order-tp16381434p16388762.html Thanks for your help...I feel so embarrassed. With all of these symbolos in Haskell like -> (for types), => (in classes) etc I couldn't imagine that <= means less than or equal to!!!:clap: >Yes, it should be : >(Branch l r) <= (Branch l' r') = l < l' || l == l' && r <= r' >Lexical order for a tuple (a,b) is : >(a,b) <= (a',b') iff (a < a' or (a == a' and b <= b')) I have tested it and I have found that it is the same with (Branch l r) <= (Branch l' r') = (l == l' && r <= r') || l < l' The problem with the previous is that the compiler during the parsing takes as right (Branch l r) <= (Branch l' r') = l == l' && (r <= r') || l < l') since the infix operator && needs two operands,i.e. one on the left and the other on the right Though I can't understand why both (Branch l r) <= (Branch l' r') = l < l' || l == l' && r <= r' (Branch l r) <= (Branch l' r') = l <= l' || l == l' && r <= r' give the same results and why I should take as right (a,b) <= (a',b') iff (a < a' or (a == a' and b <= b')) and not (a,b) <= (a',b') iff (a <= a' or (a == a' and b <= b')) The latter seems more logical, doesn't it? -- View this message in context: http://www.nabble.com/lexicographic-order-tp16381434p16392557.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
