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Improvements to crypto-API: CTR CMAC and SIV modes
by klondike 04 Apr '11

04 Apr '11

Hi, The attached files provide some preliminary support for the CTR, CMAC and SIV modes of operation on the crypto-api for both strict and lazy bytestrings. My main worries here are that the implementations may be vulnerable to timing attacks, and that the code in CPolys may be subject to copyright restrictions since it may be a derivative work from "Table of Low-Weight Binary Irreducible Polynomials" by Gadiel Seroussi (since all I did was apply transformations to the original PDF to get the data). As a side note, if I have time I'll improve the dbl and shift operations so they can work directly over the bytestrings which may be faster than converting and back. I'll also try both parallelizing the implementation of the counter mode and make it work with transformations other than adding one.

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Haskell programs as specifications
by Patrick Browne 03 Apr '11

03 Apr '11

Hi, Attached are two programs that represent one-way and two-way traffic on a road. I can get the programs to produce reasonable results that match our intuitive ideas of roads. However, I have 2 question about the programs: 1)I cannot get the result suggested by the author that t1 should give true in prog1 and false in prog2. 2)My second question is more theoretical. It is stated by the author that type checking and excitability provide verification. In this case verification probably means checking that an instance is consistent with its type class. Does verification using these techniques in Haskell have any firmer logical foundation than say doing the verification in Java? I am aware that Haskell uses inference for type checking, but is the net result superior to compilers that do not use inference? Also, is Haskell execution based purely on logic? Regards, Pat This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie

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fundeps => type family
by Tad Doxsee 03 Apr '11

03 Apr '11

Hi All, Last week I asked a question with the subject "object oriented technique". I got a lot very helpful answers and I thank all who contributed. At the end of my question, I alluded to some problems that I was having with what I wanted to do next, which was to add additional polymorphism. I figured out a solution, which is: ------------------------------------------------- {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE FunctionalDependencies #-} data Rectangle a = MkRectangle { rx, ry, rw, rh :: a } deriving (Eq, Show) drawRect :: Show a => Rectangle a -> String drawRect r = "Rect (" ++ show (rx r) ++ ", " ++ show (ry r) ++ ") -- " ++ show (rw r) ++ " x " ++ show (rh r) data Circle a = MkCircle {cx, cy, cr :: a} deriving (Eq, Show) drawCirc :: Show a => Circle a -> String drawCirc c = "Circ (" ++ show (cx c) ++ ", " ++ show (cy c)++ ") -- " ++ show (cr c) r1 = MkRectangle 0 0 3 2 r2 = MkRectangle 1 1 4 5 c1 = MkCircle 0 0 5 c2 = MkCircle 2 0 7 class ShapeC a s | s -> a where draw :: s -> String copyTo :: s -> a -> a -> s {- -- GADT version data ShapeD a where MkShapeD :: ShapeC a s => s -> ShapeD a -} -- Existential Quantification version data ShapeD a = forall s . ShapeC a s => MkShapeD s instance ShapeC a (ShapeD a) where draw (MkShapeD s) = draw s copyTo (MkShapeD s) x y = MkShapeD (copyTo s x y) mkShape :: ShapeC a s => s -> ShapeD a mkShape s = MkShapeD s instance Show a => ShapeC a (Rectangle a) where draw = drawRect copyTo (MkRectangle _ _ rw rh) x y = MkRectangle x y rw rh instance Show a => ShapeC a (Circle a) where draw = drawCirc copyTo (MkCircle _ _ r) x y = MkCircle x y r r1s = MkShapeD r1 r2s = MkShapeD r2 c1s = MkShapeD c1 c2s = MkShapeD c2 shapes1 = [r1s, r2s, c1s, c2s] drawing1 = map draw shapes1 shapes2 = map mkShape rs ++ map mkShape cs drawing2 = map draw shapes2 -- copy the shapes to the origin then draw them shapes3 = map (\s -> copyTo s 0 0) shapes2 drawing3 = map draw shapes3 ------------------------------------------------- The main difference with my previous version is that the above is polymorphic in the type for the origin and dimensions. (I used a Double previously.) Also, the above version uses existential quantification instead of GADTs, only because some said that that method is more "standard". I had to use functional dependencies in the defintion of class ShapeC to get it to compile and run. Ed Yang's excellent post (http://blog.ezyang.com/2011/03/type-tech-tree) says that type families are equivalent to multiparameter type classes + functional dependencies, so I tried to rewrite the above using type families, but I got stuck. Also the GHC documentaton (http://www.haskell.org/ghc/docs/7.0-latest/html/users_guide/type-families.h…) says that "Equality constraints ... enable a simple translation of programs using functional dependencies into programs using family synonyms instead. So I tried: class (T s ~ a) => ShapeC a s where type T s :: * draw :: s -> String copyTo :: s -> T s -> T s -> s but got a compile error: Alas, GHC 7.0 still cannot handle equality superclasses: T s ~ a So my question is, how does one convert the above code to use type families instead of functional dependencies? Is one technique preferable over another? Thanks, Tad

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[ANNOUNCE] Data-flow based graph algorithms
by Mitar 03 Apr '11

03 Apr '11

Hi! Based on my Etage data-flow framework: http://hackage.haskell.org/package/Etage I have made a package to show how to implement graph algorithms on top of it: http://hackage.haskell.org/package/Etage-Graph I invite everybody to take a look and see how it is possible to implement known control-flow algorithms in a data-flow manner. For now, only shortest paths search is implemented (from all to all nodes). The nice feature is that such approach is easily parallelized. It quite heavily uses Haskell threads so it is also useful to benchmark and test them, especially for graphs with many nodes (> 300). There is documentation, but because of this bug it is not visible: http://hackage.haskell.org/trac/hackage/ticket/656 Mitar

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Unboxing CFloat and GLfloat
by Jason Dagit 03 Apr '11

03 Apr '11

First a bit of background. Sometimes I would like to be able to create unboxed arrays of CFloats and GLfloats. Both of these are defined as newtypes around types that can be unboxed (e.g., Float). I'm assuming GHC here. As far as I can tell, the newtyping is there to help programmers pick a representation that matches the C compiler's representation on their platform without having to use CPP in their Haskell code. Would it be possible to add instances like these? instance MArray (STUArray s) GLfloat (ST s) instance MArray IOUArray GLfloat IO instance MArray (STUArray s) CFloat (ST s) instance MArray IOUArray CFloat IO I would also want instances for the other C types that map to Haskell types that are unboxed and the other GL types too. For example, in my program I imported all the right libraries and added this instance as an experiment: instance MArray (STUArray s) GLfloat (ST s) where {-# INLINE getBounds #-} getBounds (STUArray l u _ _) = return (l,u) {-# INLINE getNumElements #-} getNumElements (STUArray _ _ n _) = return n {-# INLINE unsafeNewArray_ #-} unsafeNewArray_ (l,u) = unsafeNewArraySTUArray_ (l,u) fLOAT_SCALE {-# INLINE newArray_ #-} newArray_ arrBounds = newArray arrBounds 0 {-# INLINE unsafeRead #-} unsafeRead (STUArray _ _ _ marr#) (I# i#) = ST $ \s1# -> case readFloatArray# marr# i# s1# of { (# s2#, e# #) -> (# s2#, unsafeCoerce (F# e#) #) } {-# INLINE unsafeWrite #-} unsafeWrite (STUArray _ _ _ marr#) (I# i#) e = ST $ \s1# -> let F# e# = unsafeCoerce e in case writeFloatArray# marr# i# e# s1# of { s2# -> (# s2#, () #) } I had to use an unsafeCoerce because the constructor for GLfloat is not exposed, and realToFrac has terrible performance because the following rules (suggested by Andy Gill) are missing from the OpenGL bindings: {-# RULES "realToFrac/a->GLfloat" realToFrac = \x -> GLfloat (realToFrac x) #-} {-# RULES "realToFrac/GLfloat->a" realToFrac = \(GLfloat x) -> realToFrac x #-} Even if I had those rules, I would still need to get access to the underlying representation (the e#) to have the right kind. GLfloat is defined in terms of CFloat which is defined in terms of other things. On my machine, CFloat happens to correspond to Float, although in general this need not be the case. So to do this instance correctly I would need to know, in general, what the underlying type is for CFloat. I think that means I would need to use the same macros as GHC, although I don't think that requires this instance to appear in base. I could just borrow the macros once I figure out the corresponding instance for CFloat. While the GLfloat instances don't need to be in base, the CFloat instance probably should be in base. Is this something I should make a library proposal for and submit patches? Is there an easier way to get these instances? Has someone already done this? Thanks, Jason

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Call for contributions: Second edition of the Typeclassopedia
by Brent Yorgey 03 Apr '11

03 Apr '11

Hi all, It's time for a second edition of the Typeclassopedia [1], and I'd love to have your suggestions and contributions. You can send me suggestions and darcs patches [2] by email. For more detailed information, see my blog post [3]. -Brent [1] http://www.haskell.org/wikiupload/8/85/TMR-Issue13.pdf [2] http://code.haskell.org/~byorgey/typeclassopedia/ [3] http://byorgey.wordpress.com/2011/04/03/call-for-contributions-second-editi…

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error to Fail Conversion
by Anwar Bari 03 Apr '11

03 Apr '11

HI Cafe I have problem with this function value :: Theorm-> [(String,Int)] -> Tem -> Int value _ env (Var s) = maybe (error "Unknown variable.") id (lookup s env) value mdl env (OP s _ _ l) = maybe (error "Function not defined.") id (lookup (map (value mdl env) l) (S.toList $ maybe (error "Uknown function.") id (fmap snd (multiLookup s (operations mdl))))) This function is working fine, but I want to change error function to fail function to be able use it in my GUI application. I can't change the output of value function to IO Int,any idea will help. Thanks Nour.

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Can't connect to local yackage server
by Yitzchak Gale 03 Apr '11

03 Apr '11

On Mac OS X 10.6.7, after upgrading to yackage 0.1.0.1: After running yackage -l, I cannot connect to it even directly from localhost. I get the message: This Yackage server only talks to local clients On a Linux server it seems to work fine though. On the Mac, when I do "telnet localhost" I get: Trying ::1... Could it be that yackage 0.1.0.1 doesn't recognize the IPv6 notion of localhost? Thanks, Yitz

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7th Ghent Functional Programming Group meeting on Tuesday, April 26
by Jasper Van der Jeugt 03 Apr '11

03 Apr '11

Dear all, We are very glad to announce an exciting program for the 7th meeting of the Ghent Functional Programming Group, especially since we are celebrating our first year of existence today. Our program features no less than three interesting functional programming languages: Erlang, Haskell and Scheme. The meeting will take place on Tuesday, April 26 in the Technicum building of Ghent University (Sint-Pietersnieuwstraat 41, 9000 Gent) at 19h30. As before, to enter the building, you should go to the automatic sliding door on the far left of the building and dial the phone number that is provided on the note taped to the door. Someone will then open the door for you. Our program is as follows: 1. Tom Van Custem - Experiments with MapReduce in Erlang MapReduce is a programming model for large data processing popularized by, and in daily use at Google. The MapReduce model builds strongly on key tenets of functional programming such as higher-order functions and side-effect free execution. In this talk, we summarize this programming model and describe a didactic implementation in Erlang. Invented at Ericsson's research labs, Erlang is known for its massively concurrent programming model, and itself builds on a functional core language. The talk will not focus on Erlang as such, but we will describe its key features as needed to understand the MapReduce abstraction. 2. Tom Schrijvers - How you could have won the VPW 2011 contest with Haskell We all know that Functional Programming is great for writing concise solutions for programming problems. With some skill this can even be done quickly! Yet, there was little evidence of this at the 3rd edition of the Flemish Programming Contest (VPW 2011) that took place on March 23. Not so before the contest: The jury stress-tested all questions by writing various solutions in different languages. Haskell was used to solve most problems and invariably produced short solutions. In this talk I present my own Haskell solutions to several of this year's problems and discuss alternative solution strategies with the audience. After the talk you will be all set for winning next year's edition -- or at least enjoying it -- using Haskell. 3. Pieter Audenaert - Functional Geometry and a Graphical Language We will discuss a simple language for drawing images. During the presentation we will illustrate the power of data abstraction and algebraic closure, meanwhile using higher order procedures in an essential manner. The language has been designed to easy experimenting with patterns such as those appearing in typical M.C. Escher drawings where the artist repeats the pattern both moving it across the drawing and scaling it when applicable. In the language we use procedures to represent the data objects that will be combined in the final drawing and we make sure that all operations conducted on these procedures are algebraically closed. These features allow generating patterns of any complexity. For our implementation, we use the LISP functional programming language -- more accurately, the Scheme dialect. The presentation is based on "Structure and Interpretation of Computer Programs", Abelson & Sussman Hope to see you there! The GhentFPG organizing committee, Andy Georges Jeroen Janssen Jasper Van der Jeugt

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using IO monad in Iteratee
by Dmitry Olshansky 03 Apr '11

03 Apr '11

Dear collegues, I use Iteratee with Monad Transformer stack in this way: type MyMonad a b = Iteratee a (StateT StateType IO) b I've wrote some Enumeratees using this type. Then I want to compose it with standard enumerator like Data.Enumerator.Binary.enumFile. But enumFile use IO monad instead of MonadIO class. I didn't see (maybe I'm blind...) a way to compose my Enumeratees with enumFile. How I can do that? Is it possible to change enumFile to using MonadIO class? Best regards, Dmitry

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