- Haskell-Cafe - Haskell.org

re: Python
by Stijn De Saeger 31 May '05

31 May '05

> On 27/05/05, John Goerzen <jgoerzen(a)complete.org> wrote: > > Yes, but actually much of that is slated for removal from the Python > > language in future versions. See > > > > http://www.python.org/peps/pep-3000.html > > I still can't believe that Guido will get away with this... Yes. Many people I know state the functional part as a big reason why they chose python. Basically, before Python 3000 a number of scenarios are thinkable : - The python community will just bite their lip and take it. - There'll be some skirmishes and the proposal will get shot down after a small revolution. (not likely) - python will get a second -- more functional -- branch coexisting with the standard. I personally can see this last scenario happen, for some reason. I know it's not even being developed yet, but does anyone know what date python 3000 is aiming at? s.

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RE: [Haskell-cafe] Compiling GHC 6.2.2 without ghci
by Simon Marlow 31 May '05

31 May '05

On 25 May 2005 19:39, Jesper Louis Andersen wrote: > How do you compile GHC 6.2.2 without compiling the ghci (ghc > interactive)? I only need this as a stepping stone to GHC 6.4, so it > is really not needed, however great it might be. No ./configure > options seem to address the problem. Add the line 'GhcWithInterpreter=NO' to your mk/build.mk (create the file if you don't have it). Cheers, Simon

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Re: [Haskell-cafe] Re: Composition of Type Constructors
by Jan Christiansen 30 May '05

30 May '05

On Wednesday 25 May 2005 17:20, Chung-chieh Shan wrote: > Jan Christiansen <jac(a)informatik.uni-kiel.de> wrote in article <Pine.GSO.4.63.0505251243020.11488@arwen> in gmane.comp.lang.haskell.cafe: >> The problem is that I don't know how to express the composition of >> type constructors like the function (.) for ordinary functions. I know >> that (map1 . map2) is wrong but it states what I want to express, >> namely the composition of two type constructors. With this I would >> like to define an instance definition like the following. >> >> >> instance (Mapping map1 key1, Mapping map2 key2) >> => Mapping (map1 . map2) (key1, key2) where >> lookup (key1, key2) = lookup key2 . lookup key1 >> update (key1, key2) f = update key1 (update key2 f) > > You can define the type-level composition yourself. Something like > (untested): > > newtype Comp map1 map2 v = Comp (map1 (map2 v)) > instance (Mapping map1 key1, Mapping map2 key2) > => Mapping (Comp map1 map2) (key1, key2) where > lookup (key1, key2) (Comp map) = lookup key2 (lookup key1 map) > update (key1, key2) f (Comp map) = Comp (update key1 (update key2 f) > map) Thanks. That's a solution. There is no prettier way of doing this, is there. It's not allowed to make an instance of a type synonym and partially applied type synonyms are not allowed anyway. Is there a reason why partial application of type synonyms are forbidden?

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Python?
by Daniel Carrera 27 May '05

27 May '05

Hello, This might be a strange question to ask on a Haskell list, but I do want to hear your opinions. What do you think of Python? To explain where this question is comming from: I have a lady friend who wants to learn how to program. I just decided to teach her Python for practical reasons: 1) Python has a nice IDE-ish thing. It's called "idle". It includes both a shell and an editor. The interface is simple and clear. 2) I can't get Helium to compile (since I can't get ghc to run) on Solaris. 3) Python has some nice introductory documentation. The Haskell documentation is more advanced. 4) She's interested in writing an OOo plugin some day. Python can do that. But I do hesitate. I would like to teach her Haskell because I think it's a better language. But I just don't seem to have the tools to teach it to a complete beginner (idle, documentation). So I'm thinking that perhaps I can use Python, but try to teach her functional principles, like not changing the value of a variable and not letting her functions have side-effects. Given my circunstances, do you think that's a reasonable approach for teaching her how to program? Cheers, Daniel.

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idea's for a 3D modeller in Haskell
by Kenneth Hoste 27 May '05

27 May '05

Hello, I'm planning to start up a project to build a 3D modelling application in Haskell. I don't know which direction I would want to follow, hence this mail. I've set up a small wiki page @ http://haskell.org/hawiki/H3D. I'm looking for neat idea's, existing projects, articles, suggestions, anything that could help me getting in some direction. Currently, I'm considering using L-systems as a base, and maybe use Ogre3D as rendering engine. Feel free to add anything to the wiki or to reply. boegel

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Re: explicit signatures and default for integer literals
by Daniel Fischer 27 May '05

27 May '05

Am Freitag, 27. Mai 2005 15:00 schrieb Mirko Rahn: > Hi all, > > an explicit given signature causes ghc to choose the right types for > integer literals as in > > {-# OPTIONS -fglasgow-exts #-} > > import Data.Map > > f :: Ord a => [a] -> Map a Int > f xs = fromList $ zip xs [0..] > > Here the Literal 0 is threated as (0::Int). > > But the setting > > {-# OPTIONS -fglasgow-exts #-} > > import Data.Map > > class New a b where new :: a -> b > > instance Ord a => New [(a,b)] (Map a b) where new = fromList > > g :: Ord a => [a] -> Map a Int > g xs = new $ zip xs [0..] > > causes the error message > > Could not deduce (New [(a, b)] (Map a Int)) from the context (Ord a) > arising from use of `new' at Why.hs:10:7-9 > > ghc seems to be unable to threat the Literal 0 as (0::Int) this time but > I do not understand why :-( > > Can anyone explain it? > > Thanks, The problem is that ghc can't know that 0 ought to be Int, as it is, nothing prevents you declaring an instance Ord a => New [(a, Double)] (Map a Int) where new = ? and then it's clear that ghc wouldn't know which instance to choose. To solve the problem, I have three suggestions - write [0 :: Int .. ], so ghc knows that New [(a,Int)] (Map a Int) is the required instance - add a fundep: class New a b | [a -> b,] b -> a where ..., and ghc can again deduce the instance - add an expression type signature in 'g' g xs = (new :: Ord a => [(a,Int)] -> Map a Int) $ zip xs [0 .. ] any of these will do, depending on what you want,I recommend one of the first two. Cheers, Daniel

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ghc 6.4 import problem
by Shiqi Cao 27 May '05

27 May '05

Hi, I tried to port some code from ghc 6.2 to ghc 6.4, but I got the following error PrelExts.lhs:41:25: Ambiguous occurrence `map' It could refer to either `GHC.Base.map', imported from Data.List at PrelExts.lhs:11:0-15 or `Data.Set.map', imported from Data.Set at PrelExts.lhs:10:0-14 The following is the first part of the code module PrelExts where import Data.FiniteMap import Data.Set import Data.List import IO There is no problem under ghc 6.2. What should I do? Shiqi Cao

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Re: working Edison, a couple of collection modules, and typing troubles
by oleg＠pobox.com 27 May '05

27 May '05

Samuel Bronson wrote: > I was trying my hand at writing some collection classes myself and I > can't figure out a good typing for map that will let me make Map an > instance of my Collection class... > I don't much like the head of Mapping. How about the following: > class Collection (d k e) (k, e) => Mapping d k e where > -- * Query > lookup :: (Monad m) => k -> d k e -> m e > > instance Ord k => Collection (M.Map k e) (k, e) where > null = M.null > empty = M.empty > <elided> > > instance Ord k => Mapping M.Map k e where > lookup = M.lookup A higher-ranked type constructor gets rid of functional dependencies. The drawback of course is trying to use something like Integer as a mapping from Int to Bool. We have to declare a wrapper > -- Integer as a collection of bits > newtype BitMap k e = BitMap Integer deriving Show > instance Collection (BitMap Int Bool) (Int, Bool) where > empty = BitMap 0 > fromList [] = empty > fromList ((b,v):r) = let BitMap br = (fromList r):: BitMap Int Bool > in BitMap ((if v then setBit else clearBit) br b) > > instance Mapping BitMap Int Bool where > lookup k (BitMap bm) = return $ testBit bm k This actually works (and efficiently: BitMap is a newtype, so no tagging is involved at run-time), but leaves the sense of dissatisfaction. The type BitMap k e appears polymorphic, yet the only permissible values for `k' is Int, and for `e' is Bool. Alas, this facts isn't expressed anywhere. We can add explicit constraints, or better, use GADT: > data BitMap k e where > BitMap :: Integer -> BitMap Int Bool the rest of the code is unchanged.

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working Edison, a couple of collection modules, and typing troubles
by Samuel Bronson 26 May '05

26 May '05

Whatever happened to Edison? I want to play with it and the one in the HFL cvs repository won't build for me (and uses flat names). I was trying my hand at writing some collection classes myself and I can't figure out a good typing for map that will let me make Map an instance of my Collection class... I'm attaching what I have so far. I don't much like the head of Mapping. I expect oleg will have some crazy type-system trick up his sleeve. -- Thankful-in-advance-ly yrs, Sam

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RE: [Haskell-cafe] RFE: Extensible algebraic user-defined data types?
by Simon Peyton-Jones 26 May '05

26 May '05

| Regarding reusing constructor names across several datatypes: is it | possible to qualify them with their enclosing datatype name, like | Maybe.Nothing where there is a name conflict? Then I might reuse | Nothing in my hypothetical data type, and it would be NEither.Nothing | if conflicting with Maybe.Nothing Yes, this'd occasionally be useful regardless of extensible data types, particularly constructor fields too. E.g. "T.x" could mean "field x from type T". There's a difficulty about parsing the name though. Does Neither.Nothing mean the constructor imported from module Neither or the constructor Nothing from type Neither In these days of lazy ambiguity resolution, though, it's not so bad. We could just say that "Neither.Nothing" names *both* of those things, and if both exist in the current scope, you need to disambiguate by adding further module qualifiers. This is one of those features that's hard to evaluate: modest gain in expressiveness, and modest increase in complexity. Simon

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Compiling GHC 6.2.2 without ghci
by Jesper Louis Andersen 25 May '05

25 May '05

Hi Cafe. How do you compile GHC 6.2.2 without compiling the ghci (ghc interactive)? I only need this as a stepping stone to GHC 6.4, so it is really not needed, however great it might be. No ./configure options seem to address the problem.

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Composition of Type Constructors
by Jan Christiansen 25 May '05

25 May '05

Hi! I would like to define a type class for a data structure that supports a lookup and an update function like the following one. class Mapping map key where lookup :: key -> map v -> v update :: key -> (v -> v) -> map v -> map v Now I want to lift this to a class instance for tuples of keys. This should be done by just using a map that contains another map as values. The problem is that I don't know how to express the composition of type constructors like the function (.) for ordinary functions. I know that (map1 . map2) is wrong but it states what I want to express, namely the composition of two type constructors. With this I would like to define an instance definition like the following. instance (Mapping map1 key1, Mapping map2 key2) => Mapping (map1 . map2) (key1, key2) where lookup (key1, key2) = lookup key2 . lookup key1 update (key1, key2) f = update key1 (update key2 f) I am not sure about the practical pertinence of this example cause I will probably only use one instance where the type of the keys is Int but I am curious if this is possible at all. thanks in advance, Jan

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RE: [Haskell-cafe] Question about classes from a Haskell newbie.
by Simon Peyton-Jones 25 May '05

25 May '05

http://research.microsoft.com/%7Esimonpj/Papers/type-class-design-space will fix manual Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of | Scott J. | Sent: 25 May 2005 13:29 | To: haskell-cafe | Subject: Re: [Haskell-cafe] Question about classes from a Haskell newbie. | | Hello, | | the web page http://research.microsoft.com/~simonpj/multi.ps.gz mentioned | in | | http://www.haskell.org/ghc/docs/latest/html/users_guide/type-extensions. html#multi-param-type- | classes | | is not reachable or does not exist anymore. | | Any hints how I can get my hands on this paper are welcome | | Jan | | | ----- Original Message ----- | From: "robert dockins" <robdockins(a)fastmail.fm> | To: <Jeff.Harper(a)handheld.com> | Cc: <haskell-cafe(a)haskell.org> | Sent: Tuesday, May 24, 2005 10:07 PM | Subject: Re: [Haskell-cafe] Question about classes from a Haskell newbie. | | | > | >> However, I didn't understand the syntax of the class declaration. | >> | >> Lemmih wrote: | >> > import Complex | >> > | >> > class ConvertibleToComplex a b | a -> b where | >> > toComplex :: RealFloat b => a -> Complex b | >> | >> I've looked at several sources to try to understand this declaration. I | >> can't find any examples where a class declaration takes two type | >> variables or uses the pipe symbol. One of the sources I used was | >> _Haskell 98 Language and Libraries The Revised Report_. I'm not an | >> expert at BNF notation, but the definitions for topdecl, tycls, and tyvar | >> in the grammar seems to exclude Lemmih's declaration. | >> | >> If someone could point me to some sources that explain this notation, I'd | >> be very grateful. | > | > This is a multi-parameter typeclass (with functional dependencies), which | > is not a part of Haskell 98, so its no surprise that you didn't find it in | > the Report. The Muli-parameter part is pretty easy to understand: the | > type class simply introduces more than one type variable. Functional | > dependencies let you say which types should determine which other types. | > Here are some pages on these ideas: | > | > http://www.haskell.org/ghc/docs/latest/html/users_guide/type-extensions. html#multi-param-type- | classes | > http://www.haskell.org/ghc/docs/latest/html/users_guide/type-extensions. html#functional- | dependencies | > http://haskell.org/hawiki/FunDeps | > | > In this particular instance, what the class definition means is that | > 'ConvertaibleToComplex' is a class which relates two types 'a' and 'b' AND | > the type 'a' uniquely determines the type 'b'. | > | > | > Hope that helps, | > Robert Dockins | > | > _______________________________________________ | > Haskell-Cafe mailing list | > Haskell-Cafe(a)haskell.org | > http://www.haskell.org/mailman/listinfo/haskell-cafe | > | | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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Question about classes from a Haskell newbie.
by Jeff.Harper＠handheld.com 25 May '05

25 May '05

Thank you Pierre and Lemmih for answering my question about how to implement the toComplex function. Both of your answers were insightful. I understood Pierre's solution. Pierre wrote: > I think you misunderstand the meaning of the constraint ! > > toComplex :: (RealFloat b) => a -> Complex b > > means the type of "b" needs to be a "RealFloat" and that it will be > inferred from the context where the function "toComplex" is called ! "Inferring the type of a function based on the context where the function is called." is an idea that I'm going to have to wrap my mind around. Lemmih's solution is interesting too. I tried it. It seems to work well under Hugs. I'm under the impression that the return type of toComplex is inferred based on the argument passed to toComplex. However, I didn't understand the syntax of the class declaration. Lemmih wrote: > import Complex > > class ConvertibleToComplex a b | a -> b where > toComplex :: RealFloat b => a -> Complex b I've looked at several sources to try to understand this declaration. I can't find any examples where a class declaration takes two type variables or uses the pipe symbol. One of the sources I used was _Haskell 98 Language and Libraries The Revised Report_. I'm not an expert at BNF notation, but the definitions for topdecl, tycls, and tyvar in the grammar seems to exclude Lemmih's declaration. If someone could point me to some sources that explain this notation, I'd be very grateful. Thanks, Jeff

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Re: [Haskell] Beyond ASCII only editors for Haskell
by Scott Turner 24 May '05

24 May '05

[moved from haskell to haskell-cafe] On May 23 Monday, Mads Lindstrøm wrote: > This also means that I do think we should invent some symbols. > Like the (->) used in function signatures. And we can live with > the new notation, even though it is not intuitive, as it is used > very, very often. Programs are logical, and from that point of view the -> symbol is an excellent match with mathematical logic. I'd like to see more support for logical symbols in the type systems of programming languages. The Curry-Howard correspondence matches function types with logical implication, and provides a source for many more symbols.

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Question about classes from a Haskell newbie.
by Jeff.Harper＠handheld.com 23 May '05

23 May '05

Hi, I'm new to Haskell and even newer to this list. I have over 20 years of experience in C or C++. For fun, I decided to write a Fourier transform in Haskell. It would be convenient if I had a function that converts any real or complex number into a complex number. My attempt at doing this is below. Hugs produces errors when I try to load this code. Essentially, I'm trying to define a class called ConvertibleToComplex. There is a function in this class called toComplex. toComplex has the type: class ConvertibleToComplex a where toComplex :: RealFloat b => a -> Complex b I'd like some instances of toComplex to return a Complex Double while other instances return a Complex Float. Doing this sort of thing in C++ is fairly easy. However, I get the feeling that I'm pushing the Haskell type system to do something it isn't designed to do. Is there a way to define ConvertibleToComplex so that toComplex's return type is generic and a particular instance of ConvertibleToComplex decides what the return type is? Here is my attempt at doing this. If someone can give me some pointers on how to make this work, I'd appreciate it. module Main where import Complex -------------------------------------------------------------------------------- -- toComplex should convert a real or complex number to a complex number. -- -- Here's my goal for the type of toComplex. Given: -- f :: Float -- d :: Double -- cf :: Complex Float -- cd :: Complex Double -- -- When toComplex is applied to these, I'd like it to evaluate to the -- following types: -- -- toComplex f :: Complex Float -- toComplex d :: Complex Double -- toComplex cf :: Complex Float -- toComplex cd :: Complex Double class ConvertibleToComplex a where toComplex :: RealFloat b => a -> Complex b -- If I uncomment the following code, Hugs produces errors: -- ERROR "c:\tmp\test2.hs":29 - Inferred type is not general enough -- *** Expression : toComplex -- *** Expected type : (ConvertibleToComplex Float, RealFloat a) => Float -> Complex a -- *** Inferred type : (ConvertibleToComplex Float, RealFloat Float) => Float -> Complex Float {- instance ConvertibleToComplex Float where toComplex f = f :+ 0 instance ConvertibleToComplex Double where toComplex d = d :+ 0 instance ConvertibleToComplex (Complex a) where toComplex c = c -}

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Open mutable records
by Einar Karttunen 23 May '05

23 May '05

Hello I recently ended up hacking a quite concise implementation of mutable open (extensible) records in Haskell. Most of the ideas came from the HList-paper, but this seems like a very simple way of doing things. Run with ghci -fglasgow-exts -fallow-overlapping-instances. Import some stuff we are going to need later: > import Control.Monad.Reader > import Data.IORef > import System Monad for mutable record calculations - to get implisit this/self in the OO sense. > newtype OO t r = OO (ReaderT t IO r) deriving(Monad, MonadReader t, MonadIO) > > with :: s -> OO s a -> OO b a > with this (OO c) = liftIO (runReaderT c this) > > ooToIO :: OO s a -> IO a > ooToIO (OO c) = runReaderT c undefined Records First the record constructor - followed by the terminator. > data a :.: r = RC !a !r > infixr :.: > data END = END Next we define a field access method. > class Select r f t | r f -> t where (!) :: r -> f -> Ref t > instance Select (Field f t :.: r) f t where (!) (RC (F x) _) _ = x > instance Select r f t => Select (a :.: r) f t where (!) (RC _ t) = (!) t And finally the type of mutable fields. > type Ref a = IORef a > newtype Field name rtype = F (Ref rtype) Next we define a way to construct record values. > infixr ## > (##) :: v -> OO s r -> OO s ((Field f v) :.: r) > (##) v r = do { h <- liftIO (newIORef v); t <- r; return (RC (F h) t) } > end = return END :: OO s END Get the value of a field. > value :: Select s f t => f -> OO s t > value a = do x <- asks (\s -> s!a) > liftIO (readIORef x) Or set the value of a field. > (<-:) :: Select s f t => f -> t -> OO s () > a <-: b = do x <- asks (\s -> s!a) > liftIO (writeIORef x b) And as a convenience add value to an int field. > (+=) :: Select s f Int => f -> Int -> OO s Int > a += b = do x <- asks (\s -> s!a) > val <- liftIO (readIORef x) > let z = val+b > z `seq` liftIO (writeIORef x z) > return z Now implement the classic ocaml OO tutorial: > data X = X > type Point = Field X Int :.: END > > newPoint :: OO s Point > newPoint = 0 ## end > > getX :: Select s X t => OO s t > getX = value X > > move d = X += d > data Color = Color > type ColoredPoint = Field Color String :.: Point > > newColoredPoint :: String -> OO s ColoredPoint > newColoredPoint c = c ## 0 ## end > > color :: Select s Color t => OO s t > color = value Color The code looks in more complex examples like this: ((~=) is prepending into list fields.) newArrival :: Patient -> OO Hospital () newArrival patient = do with patient (HospitalVisits += 1) staff <- value FreeStaff if staff > 0 then do FreeStaff += (-1) Examination ~= patient with patient (do HospitalTime += 3 RemainingTime <-: 3) else do Triage ~= patient > main = ooToIO (do c1 <- newPoint > c2 <- newColoredPoint "green" > with c1 $ move 7 > with c2 $ move 4 > let p x = liftIO (print x) > p =<< with c1 getX > p =<< with c2 getX) - Einar Karttunen

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terrible Haskell pun
by Michael Vanier 23 May '05

23 May '05

I came up with a terrible Haskell pun that I had to share with this list: Haskell provides special syntactic support for monads in terms of the "do notation". There is a straightforward translation between this notation and the core language, which constitutes its "do-notational semantics", as it were. Sorry, Mike

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basic haskell question
by wenduan 22 May '05

22 May '05

hi, Anybody could please tell me that in the following two expressions what value does the [] take? foldl (/) 3 [] foldr (/) 3 [] when both of them are evaluated I got 3.0,but I thought I could get nothing out of there,cause its an empty list,does Haskell assume any default value for a empty list? -- ------------------------------------------------------------------------------------------------------- If you didn't succeed at the first attempt, you are just about average.

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Re: [Haskell-cafe] Python?
by karczma＠info.unicaen.fr 21 May '05

21 May '05

Tim Rowe writes: > On 5/11/05, Jerzy Karczmarczuk <karczma(a)info.unicaen.fr> wrote: > >> Give me one single language where [3-d arrays are] natural and immediate. > > I don't know how Matlab does it, but I find the C++ standard library > vector<vector<vector<float> > > > entirely intuitive (apart, perhaps, for the need for those two spaces)! Let's precise what I consider to be important in order to call it natural and immediate. And, in general, useful. 1. The definition of a concrete object, not just its type, but, say, the initialization with constants. Or/and, global initialization with zeros. 2. Easy synthesis of multi-dim matrices out of "planes", of submatrices of lesser dimensions; it can be an 'overlay', like, say, making a colour image out of three R/G/B planes, or making a 3D surfaces, or aking tensors through external products. 3. Easy indexing, and not only A[i][j][k], etc., but slicing, the extraction of sub-dimensional matrices, e.g., one column vector out of a 2D matrix in Matlab: A(3,:). Also, extracting parts (e.g. sub-images). Also, in mathematical context, "intelligent" indexing, e.g. treating a matrix as implicitly anti-symmetric. Here the CAS systems as Maple or Mathematica provide the adequate tools. C++ of course doesn't, unless you overload [] yourself. 4. Readable iterators, perhaps something more compact than insipid do-loops. 5. If those matrices are used as mathematical objects: tensors, etc., I want to have some simple notation for inner multiplications/ contractions, etc. This is not just the syntax problem, but the existence of good libraries as well... 6. Reshaping of those arrays. I thought that Matlab 'reshape' (or something similar in Numeric Python) is a baroque, rarely used construction. Now I use it quite often... So, plenty of things. That's why this is not so trivial... Jerzy Karczmarczuk

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forall in a lambda abstraction
by Scott J. 20 May '05

20 May '05

Hello, what's wrong with the code of test1 below. Ghci does complain with an error message that I don't understand. Thanks Jan id x = x test1 = \f ::(forall a. a -> a) -> (f True,f 'a') test = \f -> (f True,f False) h :: (forall a. a->a) -> (Bool,Char) --h :: (a.a -> a) -> (Bool,Char) h id = (id True, id 'a')

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RE: [Haskell-cafe] Tables in Haskell (data model /business app pr ototyping)
by Bayley, Alistair 20 May '05

20 May '05

> From: Rene de Visser [mailto:rene_de_visser@hotmail.com] > > I would rather use Haskell also for the persistency, global > constraint > maintanence, etc... rather than using an external database. > > The only thing I have found so far is HApps, but I haven't > figure out how > that works. > > Is there anything else? What do you mean by "external" database? If you just mean "on another server, accessed via a separately installed library or API" then you should consider Sqlite as a persistence storage solution. It's a doddle to install on common platforms, and consists of a single library which links to your program i.e. it runs in the same process-space. Both HSQL (and therefore HaskellDB, as it uses HSQL) and Takusen support Sqlite. http://haskelldb.sf.net/ http://cvs.sf.net/viewcvs.py/haskell-libs/libs/takusen/ Alistair. ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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Re: Why the instance declaration , passing on Hug but failing on GHC 6.2.1?
by Daniel Fischer 19 May '05

19 May '05

Am Donnerstag, 19. Mai 2005 10:39 schrieb Stefan Holdermans: > Wukaichen, > > > data People = A | B | C | D | E | F deriving (Show, Eq, Ord, Enum) > > data Pair a = Pair a a deriving Eq > > > > instance Show (Pair People) where > > show (Pair x y) = "<" ++ show x ++ ", " ++ show y ++ ">" > > GHC is right, actually. Haskell 98 requires instance declarations to > have the form > > instance (...) => C (T a1 ... an) > > where a1 are type variables, not type constructors as in your example. > > However, you can use the Glasgow extensions to get rid of this > restrictions. For example by adding > > {-# OPTIONS -fglasgow-exts#-} > > to the top of your file. > > HTH, > > Stefan > Alternatively, one might define instance Show a => Show (Pair a) where ... By the way, the original code also needs the '-98' option for hugs, so the behaviour isn't really different. Cheers, Daniel

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www.haskell.org
by Colin Paul Adams 19 May '05

19 May '05

I'm trying to download a darcs client, but I get: "The connection was refused when trying to connect to www.haskell.org" from Firefox on Linux. -- Colin Adams Preston Lancashire

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Bit fiddling
by Florian Weimer 19 May '05

19 May '05

I'm toying a bit with Haskell and wondering what's the best way to implement bit fiddling. Most of my applications involve serializing and deserializing small blobs (IP packets, for instance), and after browsing the GHC library documentation, I'm not sure which appraoch I should use. That's why I'd appreciate pointers to sample code. Portability beyond GHC is not required. It's not necessary to update blobs, only to parse them, and serialize new ones. And in the beginning, I'd like to write the boilerplate manually. 8-)

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Data types and Haskell classes
by Jens Blanck 18 May '05

18 May '05

How would I introduce number classes that are extended with plus and minus infinity? I'd like to have polymorphism over these new classes, something like a signature f :: (Real a, Extended a b) => b -> b which clearly is not part of the current syntax, but I hope you get the picture. What are the elegant ways of doing this? Somewhat related (I think), I have a class of dyadic numbers, it is clearly in Num and Real, but not in Fractional. Now, I would like to have intervals, both dyadic and rational, providing operations like lower and upper end point, centre, diameter, the partial order of interval inclusion, and membership for a dyadic/rational number. All these operations can be computed on dyadic numbers (only division by 2 is needed). Could I make the rational numbers belong to a class of "averageable numbers" or something like that so that I can get actual dyadic numbers returned when they happen to be dyadic? Jens

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Haskell-related Job Posting, Portland OR area
by Isaac Jones 17 May '05

17 May '05

Galois Connections does most of its development in Haskell, and this job may involve some Haskell development, so I felt it was on topic for this list. Senior Test Engineer Galois Connections, Inc., located near Portland, Oregon, designs and develops high confidence software for critical applications using cutting edge methods and technology. Innovative and highly creative problem-solving in the demanding application areas of security, information assurance and cryptography has earned Galois a reputation of excellence in both private and government sectors. Are you seeking an intellectually challenging position in which you'll own a mission-critical piece of a mission-critical product? Do you aspire to work with a team that shares your level of commitment and enthusiasm to develop tomorrow's high-assurance technology today? If so, you might be just the person we're looking for. Galois has recently opened a position for a Senior Test Engineer who will have end-to-end responsibility for the QA process, including planning, QA infrastructure, and assessments. This person will work in a highly cooperative and collaborative team setting and will be responsible for ensuring that our high-assurance projects deliver robust and fully functional systems according to client expectations and potential certifying agencies. For more details about this exciting opportunity please go to: http://www.galois.com/job_testengineer.php To learn more about Galois visit our website at http://www.galois.com

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Text search
by Gracjan Polak 17 May '05

17 May '05

Hi, Simple question: I need a function that matches string in another string. Something like: find (isSuffixOf "needle") (inits "haystack") This one is beautiful, but not very practical. Could anybody point me to some haskell library that does some searching, using KMP for example? -- Gracjan

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RE: [Haskell-cafe] RE: Haskell-Cafe Digest, Vol 21, Issue 31
by Bayley, Alistair 17 May '05

17 May '05

> From: Atwood, John Wesley [mailto:john.atwood@hp.com] > > Under my Linux install, with ghc6.4, it doesn't throw an > exception, but > also doesn't return a correct result; > it returns Just []. Under WindowsXP, ghc6.4, I get the exception you > get; under hugs, it can't find subRegex, but > matchRegex returns Just []. What does seem to work is > > import Text.Regex.Posix > > > > p1 = do > > r <- regcomp "\\." 0 > > b <- regexec r "foo.bar" > > putStr (show b) > > why it's in the IO monad, I don't know. > Where would I find the source? I browsed the ghc cvs at > haskell.org, but > can't find Text.Regex. > > > John http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/libraries/base/Text/Regex. hs?rev=1.15 ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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RE: Haskell-Cafe Digest, Vol 21, Issue 31
by Atwood, John Wesley 17 May '05

17 May '05

> Date: Wed, 11 May 2005 17:22:25 -0400 (Eastern Standard Time) > From: "S. Alexander Jacobson" <alex(a)alexjacobson.com> > Subject: [Haskell-cafe] subRegex bug? > > Am I misunderstanding the regex docs? > > *MyMod> subRegex (mkRegex "\\." ) "foo.bar" "blah" > "foo*** Exception: Text.Regex.Posix.regcomp: error in pattern > Under my Linux install, with ghc6.4, it doesn't throw an exception, but also doesn't return a correct result; it returns Just []. Under WindowsXP, ghc6.4, I get the exception you get; under hugs, it can't find subRegex, but matchRegex returns Just []. What does seem to work is > import Text.Regex.Posix > > p1 = do > r <- regcomp "\\." 0 > b <- regexec r "foo.bar" > putStr (show b) why it's in the IO monad, I don't know. Where would I find the source? I browsed the ghc cvs at haskell.org, but can't find Text.Regex. John

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RE: Re[2]: [Haskell-cafe] Text search
by Bayley, Alistair 17 May '05

17 May '05

> From: Bulat Ziganshin [mailto:bulatz@HotPOP.com] > > if you really need KMP, you can find it at > http://haskell.org/hawiki/RunTimeCompilation > > > find (isSuffixOf "needle") (inits "haystack") > > find (isPrefixOf "needle") (tails "haystack") > > if you need an index - add it with zip: > > find (isPrefixOf "needle".snd) (zip [0..] (tails "haystack")) Or: findIndex (isPrefixOf "bla") (tails "dfvbdbblaesre") (I asked for something similar a few weeks ago: http://www.haskell.org//pipermail/haskell-cafe/2005-April/009690.html ) ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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Re: [Haskell-cafe] NumberTheory library
by Yitzchak Gale 17 May '05

17 May '05

> As promised, here's the first attempt: > > darcs get http://andrew.bromage.org/darcs/numbertheory/ A few small comments about the function "factor" in Prime.hs: o I think you are testing w' * w' < n each time, even when you are repeating factors of the same prime p. You only need to do that when you move to the next p. o You can use divMod (or quotRem) instead of using div and then multiplying. (That's an ancient trick from C. It may not make a difference on modern CPUs.) o You are using the old functional programming trick of artificially creating state with extra function parameters. Nowadays we don't need that in Haskell - it is much simpler just to use the State monad. o I personally would much prefer a function that only returns prime numbers, not -1, 0, or 1. o I think that in most of the places where you fix the type as Int or Integer, you could leave it polymorphic and avoid a lot of coercing. Below is a version of "factor" that implements the above (except the last two, so that I preserve your interface). Regards, Yitz import Control.Monad.State -- ...etc. -- An infinite list of possible prime factors wheel :: Integral a => [a] wheel = iVerySmallPrimes ++ [f + d | d <- [0,iWheelModulus..], f <- wheelSettings] where iWheelModulus = fromIntegral wheelModulus iVerySmallPrimes = map fromIntegral verySmallPrimes wheelSettings = [f | f <- [z,z+2..iWheelModulus+1], null [p | p <- iVerySmallPrimes, f `mod` p == 0]] z = last iVerySmallPrimes + 2 -- |Factorize a number. factor :: Integral a => a -> [a] factor 0 = [0] factor 1 = [1] factor n | n < 0 = -1 : factor (-n) | otherwise = evalState (factorS n) wheel -- Factorize n with wheel as state factorS :: Integral a => a -> State [a] [a] factorS 1 = return [] factorS n = do p <- gets head if p * p > n then return [n] else factorPS n p -- Factorize n at a given prime p factorPS :: Integral a => a -> a -> State [a] [a] factorPS n p | rem == 0 = do ps <- factorPS quot p return (p:ps) | otherwise = do modify tail factorS n where (quot, rem) = n `quotRem` p

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concatMap generalizes to msumMap?
by S. Alexander Jacobson 16 May '05

16 May '05

What is the name of the monadic generalization of concatMap? In which lib is it located? -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

3 4

Type system extension
by Thomas Davie 16 May '05

16 May '05

Hi, I'd just been writing some code and an interesting idea for an extension to Haskell's type system sprang into my head. I have no idea if people have played with it, but it looked vaguely useful to me, so I thought I'd see what everyone else thought. Supposing you have these types: type Export = String data SCode = SModule String [Export] | SUnknown It would be useful to specify a function as so: doSomethingToAModule :: SCode(SModule) -> SomeRandomOtherType which would specify, not only that the first argument was of type SCode, but more specifically, that it used the SModule constructor. This would then allow you to safely only write a case for the SModule constructor, and not worry about a runtime error when pattern matching failed on an SUnknown (as this would be checked at compile time). I hope this makes sense What does anyone think of the idea, and is there an obvious flaw in the plan? Thanks Tom Davie

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fptools in darcs now available
by John Goerzen 16 May '05

16 May '05

Hello, I am pleased to announce that I have used tailor.py to successfully convert the entire history of fptools HEAD branch, dating back to 1996, from CVS to darcs. For those of you that don't know, fptools represents the development area for the GHC Haskell compiler as well as many other related projects. It contains 21,949 changesets. You may check out the darcs repository by running: darcs get --partial http://darcs.complete.org/fptools *IMPORTANT REQUEST* PLEASE use --partial when you download this. If you really want a full copy of the repo to play with, contact me offline and I can give you a tar.bz2 somewhere. This server is not really set up to handle requests for 21,000 individual files. Currently, there is one checkpoint, made near the present time. I am going to try to add some more at various points in history if that would be useful. I'm not quite sure how to checkpoint old versions in a repo yet, though, so if anyone has tips... send 'em my way. Anyway, comments welcome. I intend to sync this up with the CVS sources every few days until either 1) the fptools people adopt darcs, or 2) it becomes apparent that it's not being useful for people. -- John

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NumberTheory library
by Bo Herlin 15 May '05

15 May '05

Hi I've been running Hugs for a couple of weeks now and I'm slowly starting to get the Haskell idea, and I certanly like it! But there are functions that I cant find and that I assume others before me must have missed and then perhaps also implemented them. Is there any standard library with functions like: binomial isCatalan nthCatalan nextCatalan isPrime nthPrime nextPrime factorize isFibonacci nthFibonacci nextFibonacci and possibly/hopefully other essential functions as well? (and of course better naming...) /Bo

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Re: Should inet_ntoa Be Pure?
by Dominic Steinitz 14 May '05

14 May '05

On Monday 09 May 2005 11:45 am, you wrote: > On 07 May 2005 11:59, Dominic Steinitz wrote: > > Does anyone know why these are in the IO monad? Aren't they pure > > functions converting between dotted-decimal strings and a 32-bit > > network byte ordered binary value? > > > > Dominic. > > http://www.haskell.org/ghc/docs/latest/html/libraries/network/Network.So > cket.html#v%3Ainet_addr > > http://www.haskell.org/ghc/docs/latest/html/libraries/network/Network.So > cket.html#v%3Ainet_ntoa > > Clearly it should be pure. To avoid breaking the interface, we could > add: > > showHostAddress :: HostAddress -> String > > and deprecate inet_ntoa? > > Cheers, > Simon I haven't followed the thread on this carefully but as a pragmatic approach, how about: hostAddress :: HostAddress -> (Word8,Word8,Word8,Word8) inetAddress :: (Word8,Word8,Word8,Word8) -> HostAddress then there shouldn't be any errors to deal with as all the addresses are valid in both representations. And if you want to show the address you can always do: showHostAddress x = concat $ intersperse "." (map show [first x, second x, third x, fourth x]) where first (a,_,_,_) = a second (_,b,_,_) = b third (_,_,c,_) = c fourth (_,_,_,d) = d Dominic.

1 0

resolving missing class instances @ compile time
by Greg Buchholz 13 May '05

13 May '05

Here's a little quirk I ran into recently. While making a little vector data type in class Num (code below), I didn't implement an instance of "fromInteger" (thinking I didn't need it). Well as you can probably guess, it turns out I did need it, and subsequently got a run time exception. Which surprised me a little, since it seems like it could have been caught at compile time. (Although I did ignore a warning). This has probably been answered a thousand times, but could someone point me in the direction of documentation explaining why it compiled? Thanks, Greg Buchholz --uncomment out "fromInteger" to get a working program instance Num Vec where (V a b c) + (V x y z) = (V (a+x) (b+y) (c+z)) (V a b c) - (V x y z) = (V (a-x) (b-y) (c-z)) --fromInteger 0 = V 0.0 0.0 0.0 instance Eq Vec where (V a b c) == (V x y z) = (a==x) && (b==y) && (c==z) data Vec = V !Double !Double !Double deriving Show main = print $ sum [(V 1.0 2.0 3.0), (V 4.0 5.0 6.0)]

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ANNOUNCE: Haskell Communities & Activities Report (8th ed., May 2005)
by Andres Loeh 13 May '05

13 May '05

On behalf of the many, many contributors, I am pleased to announce that the Haskell Communities and Activities Report (8th edition, May 2005) http://www.haskell.org/communities/ is now available from the Haskell Communities home page in several formats: PDF, for screenreading as well as printing, HTML, for those of you who prefer not to deal with plugins or external viewers, and PostScript, for those of you who have nice quick printers that do not grok PDF. Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. I hope you will find it as interesting a read as we did. If you haven't encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and well in time for the actual deadline ;) ) to the call. The editor collects all the contributions into a single report and feeds that back to the community. When we try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ---------------------------------------- End of October 2005: target deadline for contributions to the November 2005 edition of the HC&A Report ---------------------------------------- Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to `register' with the editor for a simple e-mail reminder in the middle of October (you could point us to them as well, and we can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! Andres Loeh <hcar at haskell.org> <andres at cs.uu.nl> -- Haskell Communities and Activities Report (http://haskell.org/communities)

1 0

rank 2 polymorphism example
by Scott J. 12 May '05

12 May '05

Hi, can someone give me an example of an arbitrary rank polymorphism function? Thanks Jan

1 0

subRegex bug?
by S. Alexander Jacobson 11 May '05

11 May '05

Am I misunderstanding the regex docs? *MyMod> subRegex (mkRegex "\\." ) "foo.bar" "blah" "foo*** Exception: Text.Regex.Posix.regcomp: error in pattern -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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Re: Haskell-Cafe Digest, Vol 21, Issue 27
by Stijn De Saeger 11 May '05

11 May '05

Quinn Dunkan <qdunkan(a)gmail.com> wrote : > ... It is very natural to > write in a somewhat functional style, especially in regards to > sequence processing: higher order functions and listcomps provide the > processing and its built in generators and iterator protocol provide > some of the benefits of laziness. Its elementary pattern matching > encourages you to return as many values from a function as you need > and use zip() (another haskell steal) to iterate over parallel > sequences (all pattern matches are irrefutable, though). I'm confused... Python has pattern matching ? s.

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RE: [Haskell-cafe] Tables in Haskell (data model /business app pr ototyping)
by Bayley, Alistair 11 May '05

11 May '05

> From: Rene de Visser [mailto:rene_de_visser@hotmail.com] > > >What do you mean by "external" database? If you just mean "on another > > I would like to write my views and constraints in Haskell, > and not in a > seperate database language. > > i.e. I want to use Haskell also as declarative active > database language to > define the business logic and rules. This would seem to me > to be a lot > easier when the database is written in Haskell itself and > part of the same > program. > > Rene. Well, in that case, HaskellDB is probably about as good as it's gonna get. Were you looking for something similar to an existing system that you're familiar with? (Datalog? Kliesli?) Alistair. ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

1 0

and what about AliceML?
by fred 11 May '05

11 May '05

Hi, As long as this group seems to tolerate "What about Haskell and language X?" has anyone had any experience with AliceML? My initial impression is that it might be a nice tool for teaching fundamental concepts. ---fred

2 1

Type classes and definite types
by Bryn Keller 11 May '05

11 May '05

Hi folks, I set out to perform a (seemingly) simple experiment last night. I thought I'd try to get used to the HSQL library by writing a little app that would take an SQL query on the command line, run it, and print the results. So far, this seems to be impossible. I'd like to know if there's a way around this problem, or if this is actually insurmountable (short of generating and compiling new Haskell programs for each query). The HSQL library works quite well for queries whose types you know in advance, as in printRow stmt = do (id :: Int) <- getFieldValue stmt "ID" (code :: String) <- getFieldValue stmt "Code" (name :: String) <- getFieldValue stmt "Name" putStrLn (unwords [show id, show code, show name]) however, it doesn't work at all if you can't specify the types at compile time: printRow' (names,types,nulls) stmt = do values <- mapM (getFieldValue stmt) names putStrLn $ unwords (map show values) The problem is that getFieldValue returns a value of type (SqlBind a) => a. That is, there's no type information associated with this return value other than it's a valid SQL value. There are no operations in the SqlBind class, it's just a marker as near as I can tell. So when you call getFieldValue, the exact type has to be fixed in some way (by annotations in this example). If the type is not fixed, it can't be used, as shown by the fact that printRow' won't compile. I think this is just the same problem we have with other type classes, e.g., (show (read s)), not anything new. The question is, what can be done about it? Is there anything I, the user can do about it, or can only the library authors solve this problem? Is there something we can change in Haskell to make this sort of thing possible? Thanks, Bryn import Database.HSQL import Database.HSQL.ODBC import System.Environment (getArgs) main = do (connString:sql:_) <- getArgs conn <- connect connString "" "" putStrLn "Connected" stmt <- query conn sql putStrLn $ "Ran query " ++ sql let info = unzip3 $ getFieldsTypes stmt putStrLn (show info) forEachRow' printRow stmt printRow stmt = do (id :: Int) <- getFieldValue stmt "ID" (code :: String) <- getFieldValue stmt "Code" (name :: String) <- getFieldValue stmt "Name" putStrLn (unwords [show id, show code, show name]) printRow' (names,types,nulls) stmt = do values <- mapM (getFieldValue stmt) names putStrLn $ unwords (map show values)

3 5

Tables in Haskell (data model /business app prototyping)
by Rene de Visser 11 May '05

11 May '05

Hello, I have been thinking about using Haskell for prototyping of business apps. I would rather use Haskell also for the persistency, global constraint maintanence, etc... rather than using an external database. The only thing I have found so far is HApps, but I haven't figure out how that works. Is there anything else? I guess I could just use lists for the relations, and the state monad. I would extend the record types witha deleted flag and a transaction number (i.e. simple multi version control). Then updates would just consist of pushing a new record onto the front of the list, and rollbacks and commits come for free. The only disadvantage I see that I always need to scan through the whole list all the time, which will get long, and might even be too slow for prototyping. The lists might also get too large memory wise. Any suggestions? Any libraries? Any experiences with HApps or prototyping business apps with haskell in general? Rene.

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Re: [Haskell-cafe] Python?
by Donn Cave 11 May '05

11 May '05

Quoth Daniel Carrera <dcarrera(a)digitaldistribution.com>: ... | I have a lady friend who wants to learn how to program. I just decided | to teach her Python for practical reasons: I think when you factor in practical reasons, it makes a lot of sense. Python's simplicity and suitability for beginners is vastly overrated, but it's no worse than any of its competition and better than many. It has good exception handling and the top level handler prints out a traceback, I think that's very instructive. As for Objective CAML, it is as someone suggested somewhere in the more practical direction (I haven't checked, but likely enough it does build just fine on Solaris.) And it's a bona fide FPL, plus an interesting OOP layer. Has a lot going for it, but for me it's just no fun. The syntax has something to do with that. | So I'm thinking that perhaps I can use Python, but try to teach her | functional principles, like not changing the value of a variable and not | letting her functions have side-effects. You'll teach her to resent these restrictions. Haskell is built to make the most of that style of programming, Python isn't. It does have some of that, though -- e.g., you can't modify a string. But the first principle of FP might be "use functions", and that you can impart. Python programmers often could stand to break their code out into functions. You won't get to compose functions as you would in Haskell (though it isn't clear to me that it's a big win with beginners anyway), but Python does have the basics for functional usage inasmuch as it can return multiple values, GC storage etc. In the end though it's a classic OOPL and a rather feeble FPL, and it seems to me kind of like teaching horsemanship with an oxe. Donn

1 0

Specify array or list size?
by Daniel Carrera 10 May '05

10 May '05

Hello, Right now I'm using type declarations like: f :: Int -> [Int] So f returns a list of Ints. Is there a way to tell Haskell that a list or array must have exactly (say) 256 elements? I'd love to have Haskell make sure that the array I build is the correct size. Cheers, Daniel.

20 50

hackage, cabal-get, and security
by Isaac Jones 10 May '05

10 May '05

Followups to libraries(a)haskell.org, please. I'm working with Lemmih on the designs for Hackage and Cabal-Get. He's a real trooper, since I'm a total "customer" and have hardly written a line of code for these tools, but keep coming up with new requirements. The basic interaction we would like is this: 1) upload a tarball of a cabal-ized tool to the web site 2) the tarball gets unpacked, the .cabal file is read and added to the database 3) Now, an end user can say "cabal-get pkgname" and it'll download pkgname and all of its build-depends, compile and install them. Use the --user flag if you want to install it all locally. Yay! This actually already works :) The big problem actually is that this is in no way secure, and just begging to be exploited. Boo. I was assuming that we'd add some kind of package signing similar to what Debian does in its apt-secure tool (since I was one of the authors on that tool, I have a good idea about what we need), but I figured we could do that later. But now I'm thinking that this is a stupid idea, and it needs to be secure from the get-go. So here's the new sequence of steps: 1) Generate a gnupg key. preferably get it signed by someone in my web of trust (I'll try to organize a keysigning party at ICFP). We have a core group already by virtue of Debian's web of trust. 2) use cabal-put to sign and upload a package (or get someone with a key to upload your package) 2.a) if you try to upload a new version of a package that's signed by someone else's key, you're out of luck. You'll have to get me to over-ride it or get the original uploader to upload the new version. 3) cabal-get can then be used to download and install as before, but first it checks the signatures of all the packages. If any of them are untrusted signatures (as defined by the cabal-get keyring), then warn the end user. It'll be harder to upload packages, but at least now exploits won't be trivial, and for signed packages, we have something approaching Real Security! What do folks think of that? peace, isaac

1 0

FW: GHC.Prim.realWorld
by Simon Peyton-Jones 09 May '05

09 May '05

| I'd like to know what the function GHC.Prim.realWorld does exactlly | in the STG code below: Think of it as a fixed value. We want the join point $w$j to be a function, with at least one argument, otherwise it'll be evaluated eagerly (since it has a primitive type), which is semantically wrong. It's rather like saying (\().e), only cheaper, because passing () requires you to actually pass a value, whereas the 'realword' token has a type that says "you don't need to pass anything at runtime". GHC.Prim is a built-in module for functions and types that can't be defined in Haskell. The functions in GHC.Prim are enumerated in ghc/compiler/prelude/primops.txt.pp Simon | | PrelBase.divInt# = | \r [x# y#] | let-no-escape { | $w$j = | sat-only \r [w] | case <# [x# 0] of wild { | GHC.Base.False -> quotInt# [x# y#]; | GHC.Base.True -> | case ># [y# 0] of wild1 { | GHC.Base.True -> | case +# [x# 1] of sat_s10t { | __DEFAULT -> | case quotInt# [sat_s10t y#] of sat_s10w { | __DEFAULT -> -# [sat_s10w 1]; | }; | }; | GHC.Base.False -> quotInt# [x# y#]; | }; | }; | } in | case ># [x# 0] of wild { | GHC.Base.False -> $w$j GHC.Prim.realWorld#; | GHC.Base.True -> | case <# [y# 0] of wild1 { | GHC.Base.True -> | case -# [x# 1] of sat_s10I { | __DEFAULT -> | case quotInt# [sat_s10I y#] of sat_s10L { | __DEFAULT -> -# [sat_s10L 1]; | }; | }; | GHC.Base.False -> $w$j GHC.Prim.realWorld#; | }; | }; | | Finally, where is the module GHC.Prim defined ? I've looked for it | in GHC source directories but I haven't found it. Is it part of the | runtime system ? | | Thanks in advance, | | -- | ________________________________ | Monique Louise B.Monteiro | Msc Student in Computer Science | Center of Informatics | Federal University of Pernambuco

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