- Haskell-Cafe - Haskell.org

Many broken links
by Henk-Jan van Tuyl 31 Dec '10

31 Dec '10

L.S., I find, quite often, links to haskell.org/xxx pages that have disappeared; isn't it possible to just copy all of these pages, to the original location, before the old server disappears? I used the W3C link checker[0] to check links from the GUI libraries page[1]; the following pages were reported missing: - http://haskell.org/FranTk - http://www.haskell.org/fruit/ - http://haskell.org/ObjectIO - http://haskell.org/graphics/ Other (sets of) pages that are missing: - http://haskell.org/gtk2hs/ - http://haskell.org/hdirect/ - http://www.haskell.org/~simonmar/ - http://www.haskell.org/sitewiki/ - http://www.haskell.org/all_about_monads - http://darcs.haskell.org/hfuse/ - http://darcs.haskell.org/yaht - http://haskell.org/haskore/ - http://www.haskell.org/yampa/ - http://darcs.haskell.org/~lemmih/ and probably many more. I suppose some of the maintainers have left, but the pages might still have some value. Some pages might be copied to the HaskellWiki, if the author gives permission to do so. It would also be good, to know which of these pages are obsolete, so that the links to these pages can be removed. Regards, Henk-Jan van Tuyl [0] http://validator.w3.org/checklink/ [1] http://www.haskell.org/haskellwiki/Applications_and_libraries/GUI_libraries -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html --

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Happy Parser problem
by Aaron Gray 31 Dec '10

31 Dec '10

I am trying to get a grammar where keywords are also valid identifiers. Been messing round with the following Happy grammar :- %token 'let' { TokenIdent "let" } 'in' { TokenIdent "in" } ident { TokenIdent $$ } int { TokenInt $$ } '=' { TokenEq } '+' { TokenPlus } '-' { TokenMinus } '*' { TokenTimes } '/' { TokenDiv } '(' { TokenOB } ')' { TokenCB } %% Exp : 'let' Var '=' Exp 'in' Exp { Let $2 $4 $6 } | Exp1 { Exp1 $1 } Exp1 : Exp1 '+' Term { Plus $1 $3 } | Exp1 '-' Term { Minus $1 $3 } | Term { Term $1 } Term : Term '*' Factor { Times $1 $3 } | Term '/' Factor { Div $1 $3 } | Factor { Factor $1 } Factor :: { Factor } : int { Int $1 } | ident { Var $1 } | '(' Exp ')' { Brack $2 } Var :: { Factor } : ident { Var $1 } | 'let' { Var "let" } Here 'Var' should be able to represent a 'let' identifier, as well as a keyword. Happy accepts the grammar but it does not parser the expected 'let let = x in let'. I have attached the full Happy grammar. I don't think this is an LR thing, but could be wrong. Many thanks in advance, Aaron

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A question regarding cmdargs package
by Ben Franksen 31 Dec '10

31 Dec '10

How can I disable the standard arguments 'help' and 'version'? Cheers

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Newbie Question
by Chionidis Ioannis 31 Dec '10

31 Dec '10

Hello everybody! I am quite new to haskell programming. I am trying to make a gui for a drumming project made in euterpea and I want to do something like this : > b <- button f [text := "Run!" , on command := (test mambo_orig)] "test mambo_orig" is executed from ghci but I want It to be able to execute each time the user presses the button. Hope I didn't mess it up in the explaination, Giannis Chionidis

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Fibonacci Heap without using Monad
by larry.liuxinyu 31 Dec '10

31 Dec '10

Hi, I checked the current Fibonacci Queue in Hackage DB: http://hackage.haskell.org/packages/archive/pqueue-mtl/1.0.7/doc/html/src/D… And a history email for Okasaki in 1995: http://darcs.haskell.org/nofib/gc/fibheaps/orig The hardest part is how to consolidate all unordered binomial trees in deleteMin. In imperative implementation, there is a elegant algorithm introduced in Chapter 20 of CLRS[1]. How to achieve it in Functional way is the key point of solve this problem. If we have a list of trees with rank [2, 1, 1, 4, 8, 1, 1, 2, 4], we need first meld the trees with same rank, and recursively doing that until there are no two trees with same rank. Here is a simple function can do this: consolidate:: (Num a)=>[a] -> [a] consolidate xs = foldl meld [] xs where meld :: (Num a)=>[a] -> a -> [a] meld [] x = [x] meld (x':xs) x = if x == x' then meld xs (x+x') else x:x':xs Generalize the `+` to link and `==` to compare rank yields the solution. Below are my literate source code with some description. For the details of Binomial heap, please refer to Okasaki's ``Purely Functional data structures''[2]. -- Definition -- Since Fibonacci Heap can be achieved by applying lazy strategy -- to Binomial heap. We use the same definition of tree as the -- Binomial heap. That each tree contains: -- a rank (size of the tree) -- the root value (the element) -- and the children (all sub trees) data BiTree a = Node { rank :: Int , root :: a , children :: [BiTree a]} deriving (Eq, Show) -- Different with Binomial heap, Fibonacci heap is consist of -- unordered binomial trees. Thus in order to access the -- minimum value in O(1) time, we keep the record of the tree -- which holds the minimum value out off the other children trees. -- We also record the size of the heap, which is the sum of all ranks -- of children and minimum tree. data FibHeap a = E | FH { size :: Int , minTree :: BiTree a , trees :: [BiTree a]} deriving (Eq, Show) -- Auxiliary functions -- Singleton creates a leaf node and put it as the only tree in the heap singleton :: a -> FibHeap a singleton x = FH 1 (Node 1 x []) [] -- Link 2 trees with SAME rank R to a new tree of rank R+1, we re-use the code -- for Binomial heaps link :: (Ord a) => BiTree a -> BiTree a -> BiTree a link t1@(Node r x c1) t2@(Node _ y c2) | x<y = Node (r+1) x (t2:c1) | otherwise = Node (r+1) y (t1:c2) -- Insertion, runs in O(1) time. insert :: (Ord a) => FibHeap a -> a -> FibHeap a insert h x = merge h (singleton x) -- Merge, runs in O(1) time. -- Different from Binomial heap, we don't consolidate the sub trees -- with the same rank, we delayed it later when performing delete- Minimum. merge:: (Ord a) => FibHeap a -> FibHeap a -> FibHeap a merge h E = h merge E h = h merge h1@(FH sz1 minTr1 ts1) h2@(FH sz2 minTr2 ts2) | root minTr1 < root minTr2 = FH (sz1+sz2) minTr1 (minTr2:ts2+ +ts1) | otherwise = FH (sz1+sz2) minTr2 (minTr1:ts1++ts2) -- Find Minimum element in O(1) time findMin :: (Ord a) => FibHeap a -> a findMin = root . minTree -- deleting, Amortized O(lg N) time -- Auxiliary function -- Consolidate unordered Binomial trees by meld all trees in same rank -- O(lg N) time consolidate :: (Ord a) => [BiTree a] -> [BiTree a] consolidate ts = foldl meld [] ts where meld [] t = [t] meld (t':ts) t = if rank t' == rank t then meld ts (link t t') else t:t':ts -- Find the tree which contains the minimum element. -- Returns the minimum element tree and the left trees as a pair -- O(lg N) time extractMin :: (Ord a) => [BiTree a] -> (BiTree a, [BiTree a]) extractMin [t] = (t, []) extractMin (t:ts) = if root t < root t' then (t, ts) else (t', t:ts') where (t', ts') = extractMin ts -- delete function deleteMin :: (Ord a) => FibHeap a -> FibHeap a deleteMin (FH _ (Node _ x []) []) = E deleteMin h@(FH sz minTr ts) = FH (sz-1) minTr' ts' where (minTr', ts') = extractMin $ consolidate (children minTr ++ ts) -- Helper functions fromList :: (Ord a) => [a] -> FibHeap a fromList xs = foldl insert E xs -- general heap sort function, can be re-used for any heap heapSort :: (Ord a) => [a] -> [a] heapSort = hsort . fromList where hsort E = [] hsort h = (findMin h):(hsort $ deleteMin h) -- test testFromList = fromList [16, 14, 10, 8, 7, 9, 3, 2, 4, 1] testHeapSort = heapSort [16, 14, 10, 8, 7, 9, 3, 2, 4, 1] Below are the test results in GHC. *FibonacciHeap> testFromList FH {size = 10, minTree = Node {rank = 1, root = 1, children = []}, trees = [Node {rank = 1, root = 2, children = []},Node {rank = 1, root = 4, children = []},Node {rank = 1, root = 3, children = []},Node {rank = 1, root = 7, children = []},Node {rank = 1, root = 9, children = []},Node {rank = 1, root = 8, children = []},Node {rank = 1, root = 10, children = []},Node {rank = 1, root = 14, children = []},Node {rank = 1, root = 16, children = []}]} *FibonacciHeap> testHeapSort [1,2,3,4,7,8,9,10,14,16] -- [1] Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest and Clifford Stein ``Introduction to Algorithms, Second Edition'. The MIT Press © 2001 (1180 pages) ISBN: [2] Chris Okasaki. ``Purely Functional Data Structures''. Cambridge university press, (July 1, 1999), ISBN-13: 978-0521663502

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"record" types and unique names
by Aaron Gray 30 Dec '10

30 Dec '10

Given a Haskell "record type" :- data Test = Test { name :: String, value :: Int } test = Test { name = "test", value = 1 } main :: IO () main = do putStrLn (name test) Are "name" and "value" in the global name space, as the following gives an error "Multiple declarations of `name'" :- name :: String -> String name s = s Is there any way round this ? Many thanks in advance, Aaron

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Not in scope: type constructor or class `Map'
by michael rice 30 Dec '10

30 Dec '10

Not sure what's going on here. Doesn't like line 5, the type statement. And what's with the semicolons in that line and in function main? Michael ========= From: http://www.haskell.org/ghc/docs/6.10.3/html/libraries/mtl/Control-Monad-Rea… import Control.Monad.Reader import qualified Data.Map as Map import Data.Maybe type Bindings = Map String Int; -- Returns True if the "count" variable contains correct bindings size. isCountCorrect :: Bindings -> Bool isCountCorrect bindings = runReader calc_isCountCorrect bindings -- The Reader monad, which implements this complicated check. calc_isCountCorrect :: Reader Bindings Bool calc_isCountCorrect = do count <- asks (lookupVar "count") bindings <- ask return (count == (Map.size bindings)) -- The selector function to use with 'asks'. -- Returns value of the variable with specified name. lookupVar :: String -> Bindings -> Int lookupVar name bindings = fromJust (Map.lookup name bindings) sampleBindings = Map.fromList [("count",3), ("1",1), ("b",2)] main = do putStr $ "Count is correct for bindings " ++ (show sampleBindings) ++ ": "; putStrLn $ show (isCountCorrect sampleBindings); ========== Prelude> :l monad5 [1 of 1] Compiling Main ( monad5.hs, interpreted ) monad5.hs:5:16: Not in scope: type constructor or class `Map' Failed, modules loaded: none.

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";" in do
by Daryoush Mehrtash 30 Dec '10

30 Dec '10

Why do people put ";" in do {}, or "," in data fields, at the beginning of the line? -- Daryoush Weblog: http://onfp.blogspot.com/

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Incorrectly inferring type [t]
by william murphy 30 Dec '10

30 Dec '10

Hi All, I've spent a lot of time trying to write a version of concat, which concatenates lists of any "depth": So: concat'' [[[1,2],[3,4]],[[5]]] would return: [1,2,3,4,5] The code is: concat'' :: [a] -> [b] concat'' ((y:ys):xs) = (concat'' (y:ys)) ++ (concat'' xs) concat'' [] = [] concat'' (x:xs) = (x:xs) And the inevitable error is: test.hs:298:12: Couldn't match expected type `a' against inferred type `[t]' `a' is a rigid type variable bound by the type signature for `concat''' at test.hs:297:13 In the pattern: y : ys In the pattern: (y : ys) : xs In the definition of `concat''': concat'' ((y : ys) : xs) = (concat'' (y : ys)) ++ (concat'' xs) test.hs:300:24: Couldn't match expected type `b' against inferred type `[t]' `b' is a rigid type variable bound by the type signature for `concat''' at test.hs:297:20 In the first argument of `(:)', namely `x' In the expression: (x : xs) In the definition of `concat''': concat'' (x : xs) = (x : xs) Failed, modules loaded: none. Any help or advice would be appreciated. Will

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Lambda Calculus: Bound and Free formal definitions
by Mark Spezzano 30 Dec '10

30 Dec '10

Hi, Presently I am going through AJT Davie's text "An Introduction to Functional Programming Systems Using Haskell". On page 84, regarding formal definitions of FREE and BOUND variables he gives Defn 5.2 as The variable X is free in the expression E in the following cases a) <omitted> b) If E is a combination E1 E2 then X is free in E if and only if X is free in E1 or X is free in E2 c) <omitted> Then in Defn 5.3 he states The variable X is bound in the expression E in the following cases a) <omitted> b) If E is a combination E1 E2 then X is free in E if and only if X is free in E1 or X is free in E2. c) <omitted> Now, are these definitions correct? They seem to contradict each other....and they don't make much sense on their own either (try every combination of E1 and E2 for bound and free and you'll see what I mean). If it is correct then please give some examples of E1 and E2 showing exactly why. Personally I think that there's an error in the book. You can see the full text on Google Books (page 84) Thanks for reading! Mark Spezzano

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SampleVar semantics, documentation vs. source
by Eric Stansifer 30 Dec '10

30 Dec '10

Hi, doc: http://www.haskell.org/ghc/docs/7.0-latest/html/libraries/base-4.3.0.0/Cont… source: http://www.haskell.org/ghc/docs/7.0-latest/html/libraries/base-4.3.0.0/src/… The documentation for Control.Concurrent.SampleVar implies that a SampleVar is either "filled" or "empty". The source code suggests that there are three possible states: "full" (when readers == 1), "empty" (when readers == 0), and "empty with blocked readers" (when readers < 0). In particular, the isEmptySampleVar function, isEmptySampleVar :: SampleVar a -> IO Bool isEmptySampleVar (SampleVar svar) = do (readers, _) <- readMVar svar return (readers == 0) returns false in the third state, when readers < 0. Can someone clarify the semantics of SampleVar? Thanks, Eric

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what is the status of haskell's mail libraries?
by Günther Schmidt 30 Dec '10

30 Dec '10

Hi all, I was just looking for mail libraries on hackage. You know libraries where I can construct an email, or retrieve on from the server. With retrieving an email I mean something with a bit more structure than a String, or, God help me, a ByteString. Where are we on this subject? I really cannot tell from the first glance. Günther

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How to make such code?
by Magicloud Magiclouds 30 Dec '10

30 Dec '10

Hi, In Haskell's way, normally, we write: if condition then expression_true else expression_false But I just heard that, in fancy way, we could do: do ifNeedToDo >> doIt bluh May I have any clue here? -- 竹密岂妨流水过山高哪阻野云飞

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Re: [Haskell-cafe] [Haskell-beginners] Tying the knot
by Antoine Latter 30 Dec '10

30 Dec '10

On Wed, Dec 29, 2010 at 7:22 PM, aditya siram <aditya.siram(a)gmail.com> wrote: > My brain turns into strange braid when I see this kind of thing. I > don't quite understand it and I've never used it in real world code > but I'll try and explain anyway. Caveat emptor. > Once when I was parsing a group of source files into an AST, the source files included 'copy' directives that allowed pieces of syntax to be a clone of some other piece of syntax - even across source files. So I did the whole process of parsing in the Reader monad, which was parametrized over the result of parsing all of the files. When I hit a copy directive, I simply called 'ask' and looked up the element I wanted to copy. It doesn't allow for separate processing of source files, but I didn't really need it. Antoine > First forget about 'labelLeaves' and think a function that only > returned the leaf count: > count :: Tree a -> Int > count tree = c > where > c = count' tree > > count' (Branch a b) = na+nb > where > na = count' a > nb = count' b > count' (Leaf _) = 1 > >> count $ Branch (Leaf "hello") (Leaf "world") > 2 > > Now look at 'n' and imagine it was a memory location. Mentally > substitute some hex address (like 0x0000) if it makes it easier. > Here's what the function looks like now: > > labelLeaves :: Tree a -> Tree Int > labelLeaves tree = tree' > where > (0x0000, tree') = label 0x0000 tree -- n is both result and argument! > > label 0x0000 (Branch a b) = (na+nb, Branch a' b') > where > (na,a') = label 0x0000 a > (nb,b') = label 0x0000 b > label 0x0000 (Leaf _) = (1, Leaf 0x0000) > > So if labelLeaves is given (Branch (Leaf "hello") (Leaf "world")) as > an argument, and we continue to think of 'n' as a memory location the > function returns something like: > (Branch (Leaf 0x0000) (Leaf 0x0000)) > > The part of the function where the leaves are counted up is exactly > like my 'count' example above, but when the function is done instead > of just returning it this line: > (n,tree') = label n tree > assigns the final count to 'n'. If 'n' is a memory location the final > leaf count would be sitting in 0x0000. Subbing the value at that > location into the result we get: > (Branch (Leaf 2) (Leaf 2)) > > > -deech > > On Wed, Dec 29, 2010 at 4:52 PM, Patrick LeBoutillier > <patrick.leboutillier(a)gmail.com> wrote: >> Heinrich, >> >>> A canonical example is the following solution to the problem of labeling all >>> the leaves in a tree with the total leaf count: >>> >>> data Tree a = Branch (Tree a) (Tree a) | Leaf a >>> >>> labelLeaves :: Tree a -> Tree Int >>> labelLeaves tree = tree' >>> where >>> (n, tree') = label n tree -- n is both result and argument! >>> >>> label n (Branch a b) = (na+nb, Branch a' b') >>> where >>> (na,a') = label n a >>> (nb,b') = label n b >>> label n (Leaf _) = (1, Leaf n) >>> >> >> This looks completely freaky to me... how does it work? Is it the >> laziness that allows the sum to be calculated first while preserving >> the structure (as thunks?), and then once the value of n is known it >> is propagated back down the tree and the actual tree values >> constructed? Anyways this is really amazing to my newbie eyes... >> >> Patrick >> -- >> ===================== >> Patrick LeBoutillier >> Rosemère, Québec, Canada >> >> _______________________________________________ >> Beginners mailing list >> Beginners(a)haskell.org >> http://www.haskell.org/mailman/listinfo/beginners >> > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://www.haskell.org/mailman/listinfo/beginners >

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What are these comments for {-# SCC "Mangler" #-}
by Aaron Gray 30 Dec '10

30 Dec '10

What are these comments for in Happy ? {-# SCC "Mangler" #-} Many thanks in advance, Aaron

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Reader monad
by michael rice 30 Dec '10

30 Dec '10

From: Control.Monad.Reader type Reader r = ReaderT r IdentityThe parameterizable reader monad. Computations are functions of a shared environment. The return function ignores the environment, while >>= passes the inherited environment to both subcomputations ============ Is there an unparameterizable reader monad? Michael

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Manatee-0.1.6 release!
by Andy Stewart 30 Dec '10

30 Dec '10

Hi all, Manatee-0.1.6 release, sorry for late, I was tired of the many trivial this month. http://www.youtube.com/watch?v=weS6zys3U8k hackage.haskell.org/package/manatee New version Manatee support customize and hot-swap, like elisp for Emacs, but much much fast and safe. Please look http://www.flickr.com/photos/48809572@N02/5304662424/lightbox/ to understand hot-swap framework. Example, copy IrcClient.hs (https://patch-tag.com/r/AndyStewart/manatee-ircclient/snapshot/current/cont… IrcClient.hs) to directory ~/.manatee/config/ then you can modify IrcClient.hs when manatee-ircclient is running, you just need press C-u to dynamic loading new version to *running* manatee-ircclient and won't lose state. Because GHC won't release memory after you dynamic-linking new version, so i recommend use this features as *develop mode* to accelerate develop. Once you adjust finish, you can press C-i to compile current configure file to build new manatee-ircclient. Next step, I will focus my time on IDE features.... Enjoy! -- Andy

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The IO monad is 45 years old
by oleg＠okmij.org 30 Dec '10

30 Dec '10

The unabated debate about exactly how much category theory one needs to know to understand that strange beast of IO prompts a thought if monads, like related continuations, are the things that are destined to be rediscovered time and time again. An old (1994) paper on category theory monads and functional programming included an interesting historical side-note. It turns out that the RealWorld-passing trick underlying the implementation of the IO monad, the trick that made it possible to embed truly side-effecting operations into pure Haskell -- the trick is 45 years old. It has been first published in February 1965. That 1965 paper also anticipated State and Writer monad, call/cc, streams and delayed evaluations, relation of streams with co-routines, and even stream fusion. First, here is the historical aside, cited from Jonathan M. D. Hill and Keith Clarke An Introduction to Category Theory, Category Theory Monads, and Their Relationship to Functional Programming. 1994 http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.53.6497 [blockquote] 3 An historical aside Monads are typically equated with single-threadedness, and are therefore used as a technique for incorporating imperative features into a purely functional language. Category theory monads have little to do with single-threadedness; it is the sequencing imposed by composition that ensures single-threadedness. In a Wadler-ised monad this is a consequence of bundling the Kleisli star and flipped compose into the bind operator. There is nothing new in this connection. Peter Landin in his Algol 60 used functional composition to model semi-colon. Semi-colon can be thought of as a state transforming operator that threads the state of the machine throughout a program. The work of Peyton-Jones and Wadler has turned full circle back to Landin's earlier work as their use of Moggi's sequencing monad enables real side-effects to be incorporated into monad operations such as print. This is similar to Landin's implementation of his sharing machine where the assignandhold function can side-effect the store of the sharing machine because of the sequencing imposed by functional composition. Landin defined that `Imperatives are treated as null-list producing functions' [In Landin's paper, () is the syntactic representation of the empty list and not the unit.]. The assignandhold imperative is subtly different in that it enables Algol's compound statements to be handled. The function takes a store location and a value as its argument, and performs the assignment to the store of the sharing machine, returning the value assigned as a result of the function. Because Landin assumed applicative order reduction, the K combinator was used to return (), and the imperative was evaluated as a side effect by the unused argument of the K-combinator. Statements are formed by wrapping such an imperative in a lambda expression that takes () as an argument. Two consecutive Algol-60 assignments would be encoded in the lambda calculus as: Algol 60 | Lambda Calculus x:= 2; | ( (\() -> K () (assignandhold x 2)) . x:= -3; | (\() -> K () (assignandhold x (-3))) ) () By using a lambda with () as its parameter, () can be thought of as the `state of the world' that is threaded throughout a program by functional composition. [/blockquote] Peter Landin's paper is remarkable indeed: P. J. Landin. A correspondence between ALGOL 60 and Church's lambda notation. Communications of the ACM, 8(2):89-101, February 1965. (Part 2 in CACM Vol 8(2) 1965, pages 158-165.) http://portal.acm.org/citation.cfm?id=363749 First the reader will notice the `where' notation. Peter Landin even anticipated the debate on `let' vs `where', saying ``The only consideration in choosing between `let' and `where' will be the relative convenience of writing an auxiliary definition before or after the expression it qualifies.'' The ()-passing trick is described in full on p100, with remarkable clarity: ``Statements. Each statement is rendered as a 0-list- transformer, i.e. a none-adic function producing the nullist for its result. It achieves by side-effects a transformation of the current state of evaluation. ... Compound statements are considered as functional products (which we indicate informally by infixed dots).'' A remark ``However, input/output devices can be modeled as named lists, with special, rather restricted functions associated. ... Writing is modeled by a procedure that, operates on a list, and appends a new final segment derived from other variables. (Alternatively, a purely functional approach can be contrived by including the transformed list among the results.)'' anticipated the State and Writer monads as well. Another remark, in the section on Streams, ``This correspondence [laws of head/tail/cons] serves two related purposes. It enables us to perform operations on lists (such as generating them, mapping them, concatenating them) without using an `extensive,' item-by-item representation of the intermediately resulting lists; and it enables us to postpone the evaluation of the expressions specifying the items of a list until they arc actually needed. The second of these is what interests us here.'' and footnote 6, ``It appears that in stream-transformers we have a functional analogue of what Conway [12] calls "co-routines." show that Peter Landin understood streams, on-demand evaluation and even stream fusion.

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ghc +RTS -M and -A behaving strange
by Johannes Waldmann 29 Dec '10

29 Dec '10

Hello. When I run a program compiled with ghc-6.12.3 like this: ... +RTS -A2G -M8G -s I get as an answer: Heap exhausted; Current maximum heap size is 0 bytes (0 MB); use `+RTS -M<size>' to increase it. and when I put the options ... +RTS -A2000M -M8000M -s I get Heap exhausted; Current maximum heap size is 4093640704 bytes (3904 MB); use `+RTS -M<size>' to increase it. and both numbers look strange. The behaviour of the program is also strange (instead of "heap exhausted" I'd expect it to do some smore garbage collections, which it does indeed without the -A option)

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Re: [Haskell-cafe] Incrementially updating an array
by Henning Thielemann 29 Dec '10

29 Dec '10

On Wed, 29 Dec 2010, Robert Clausecker wrote: > Am Mittwoch, den 29.12.2010, 13:29 +0100 schrieb Henning Thielemann: >> >> I don't know, I hope it's doing its best. :-) You might compare speed of >> Array.accum with a manually written foldl with (//). > > At a glance onto it's sourcecode it actually does, but there are > actually other problems now, as my program now runs out of stack space. > (The list to accumulate contains about 1000000 elements). I guess it's > all about that the garbage collector can't handle such things very well. The pure number of 1000000 elements should not be a problem. You may post the failing code. I guess it has something to do with: http://www.haskell.org/haskellwiki/Stack_overflow

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Re: [Haskell-cafe] [Haskell] haskell.org migration complete
by Henning Thielemann 29 Dec '10

29 Dec '10

Thomas Schilling schrieb: > I created http://www.haskell.org/haskellwiki/MigratingWikiContent to > list known issues and workarounds. Please feel free to extend that > page where needed. I liked to add that the Category link on each Wiki page is missing. How about an alternate CSS layout for the old Wiki style? Btw. unfortunately also in Konqueror CSS selections are not preserved across sessions. I did not like to add these items while having to log in over unsecure HTTP connection. Formerly I could just replace "http:" by "https:" which is no longer possible.

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multi type addition
by william murphy 29 Dec '10

29 Dec '10

We were trying to make an addition function that, unlike the library one, could add numbers of different types from the typeclass 'Num.' We originally ran into a problem when trying to add (5 :: Integer) + 4.8, and were trying to define a new function that would be able to get that: (+') :: (Num a, Num b) => a -> b -> Float x +' b = d + e where d :: Float d = x e :: Float e = b This gave us the error: Couldn't match expected type `Float' against inferred type `b' `b' is a rigid type variable bound by the type signature for `pl' at test.hs:9:18 In the expression: b In the definition of `e': e = b In the definition of `pl': pl x b = d + e where d :: Float d = x e :: Float e = b Failed, modules loaded: none.

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Having trouble with ftphs module
by aXqd 29 Dec '10

29 Dec '10

Hi all: I'm new to Haskell, and I ran into this problem recently while I am using ftphs module downloaded from hackage. Prelude> :m Network.FTP.Client Prelude Network.FTP.Client> h <- easyConnectFTP "xxx.xxx.xxx.xxx" *** Exception: FTP: "(unknown)" (line 2, column 1): unexpected "\r" expecting "\r\n" or Code 220 I am not the administrator of this FTP server. Hence all I've been told is that it is a "Microsoft FTP Server". I want to know 1. if this should be regarded as a bug of ftphs or not? 2. is there any other workaround other than the one below? Possible workaround: Implement another BAT script to do the FTP work and use system() to invoke it. Thanks in advance. -- Best regards, -Tian

1 0

Incrementially updating an array
by Robert Clausecker 28 Dec '10

28 Dec '10

Hi folks! I have the following problem. As code is most time easier to understand, let give an example what I try to do in C: unsigned int i,j; unsigned int r[100]; for (i = 0; i < 1000000; i++) { j = makeResult(); //j is known to be smaller than 100. r[j] = r[j] + 1; } (My C is poor, so please don't laugh) Currently I'm using a Data.Map for this, but as the result is bounded in this area, an array seems to be more appropreate. I don't want to mess with mutable arrays, but I can't find anything which does the same like Data.Map.insertWith for arrays in a reasonable way. In my example, the input comes from a lazy list and is than folded into the Map by insertWith (+) j 1 r. Is there any nice, quick way to do this with Arrays without using mutable ones? Yours, Robert Clausecker

3 2

Re: [Haskell-cafe] DFAs and self-referential data
by oleg＠okmij.org 28 Dec '10

28 Dec '10

Maxime Henrion wrote: > I've been playing with some code to work with DFAs, but I'm now faced > with an implementation problem. In order to have states that can > transition to themselves, it seems I would need self-referential data; > otherwise I would need to separate those transitions from the rest and > handle them specially in the code. Perhaps an old article http://okmij.org/ftp/misc.html#ccard-transform might be of some help. The article describes not only running a finite automaton (represented as a cyclic graph) on given input but also printing the automaton out and determinizing it: converting NFA to an equivalent DFA. The latter operation converts one cyclic graph to another.

2 1

How to "instance MonadIO Identity"?
by Magicloud Magiclouds 28 Dec '10

28 Dec '10

Hi, From another thread in this list, I got code as: > instance MonadIO Identity where > liftIO = id Well, it does not work for me as: Message.hs:22:12: Couldn't match expected type `Identity a' with actual type `IO a' Expected type: IO a -> Identity a Actual type: IO a -> IO a In the expression: id In an equation for `liftIO': liftIO = id -- 竹密岂妨流水过山高哪阻野云飞

3 5

instance for (Show ([(String, Int)] -> Int))
by Aaron Gray 28 Dec '10

28 Dec '10

How do I code an 'instance' declaration for '(Show ([(String, Int)] -> Int))'. I am new to instance declarations and am following the Happy examples :- http://www.haskell.org/happy/doc/html/sec-using.html#sec-other-datatypes The compiler is requesting an instance declaration for Show :- expr-eval.hs:334:23: No instance for (Show ([(String, Int)] -> Int)) arising from a use of `print' at expr-eval.hs:334:23-27 Possible fix: add an instance declaration for (Show ([(String, Int)] -> Int)) In the first argument of `(.)', namely `print' In the second argument of `(>>=)', namely `print . calc . lexer' In the expression: getContents >>= print . calc . lexer Many thanks in advance, Aaron

3 8

ANNOUNCE: yackage 0.0.0
by Michael Snoyman 27 Dec '10

27 Dec '10

Hi all, I was speaking with my coworker Yitz[1] about a project he's working on. Basically, he's going to end up with about 16 cabal packages that are not going to be deployed to Hackage, and wanted us to set up a Hackage server for our company to deploy these kinds of things. However, getting all the pieces of Hackage aligned properly for such a simple use case seemed a bit overkill. I then realized that I had the exact same problem during Yesod development: before I make a major release, I usually end up with about 10-15 packages that are not yet live on Hackage. It gets to be a real pain when suddenly wai-extra is depending on network 2.3 and authenticate requires network 2.2, and suddenly I need to manually recompile 10 packages. So I decided to write up a simple web service to act as a local Hackage server. It has no security (anyone with access can upload a package), doesn't build haddocks, doesn't show package descriptions, etc. All it does is: Show a list of uploaded packages/versions Links to the tarballs Allows you to upload new versions, which will automatically overwrite existing packages Provides the 00-index.tar.gz file needed by cabal-install, as well as the tarballs for all the packages In order to use this, just do the following: cabal install yackage run "yackage" Upload your packages Add remote-repo: yackage:http://localhost:3500/ to your ~/.cabal/config file cabal update Install your packages are usual You'll need to leave yackage running whenever you want to run an update or download new packages. A few other usage notes: If you overwrite a package, your cache folder will still have the old version. You might want to just wipe our your cache folder on each usage. Running cabal update will download the update for both yackage and the main hackage server; the latter can be a long process depending on your internet connection. Here's a little shell script that will disable the Hackage repo, wipe our the Yackage cache, update and re-enable the Hackage repo: #!/bin/sh CABAL_DIR=~/.cabal cp $CABAL_DIR/config $CABAL_DIR/config.sav sed 's/^remote-repo: hackage/--remote-repo: hackage/' < $CABAL_DIR/config.sav > $CABAL_DIR/config rm -rf $CABAL_DIR/packages/yackage cabal update cp $CABAL_DIR/config.sav $CABAL_DIR/config I hope others find this tool useful. Michael [1] http://www.haskellers.com/user/Yitz_Gale/

3 3

ANNOUNCE: greg-client - a scalable distributed logger with a high-precision global time axis
by Eugene Kirpichov 27 Dec '10

27 Dec '10

Hi cafe, Let me bring to your attention this package developed by me and Dmitry Astapov: http://hackage.haskell.org/package/greg-client It is a Haskell binding to the "greg" logger ( http://code.google.com/p/greg , http://github.com/jkff/greg - "global registrator" ). You can read the project's description and motivation at the homepage http://code.google.com/p/greg , but here are some highlights: * It's designed for debugging lattency bottlenecks or synchronization issues in distributed systems. I've been using it on small and large clusters, Dmitry has been using it for debugging haskell-mpi if I'm correct (Dmitry, can you elaborate a bit?). * It's a client/server logger - you launch a server and clients log messages to it * It provides a high-precision global time axis by computing clock offset between server and each client (this allows to register events with their occurence timestamps, not arrival-to-server timestamps) * It's very fast (I squeezed 400,000 messages/sec = 20Mb/s out of the Java binding) * It can handle a huge number of clients (a much less scalable implementation was tested on a 2000-core cluster) * It's robust to intermittent deaths of clients, server or the link between them * It's very lightweight - no persistence infrastructure, piles of config files or whatever - just send him the messages, it will align them on the global axis and log them to console I found it especially useful in conjunction with the log visualization tools described here http://slideshare.net/jkff/two-visualization-tools . P.S. How to use it (while hackage hasn't yet rebuilt the docs): import System.Log.Greg main = withGregDo defaultConfiguration $ do .... ...logMessage "Something happened"... -- Eugene Kirpichov Senior Software Engineer, Grid Dynamics http://www.griddynamics.com/

1 0

global, modifiable variable for debugging
by briand＠aracnet.com 27 Dec '10

27 Dec '10

Hi, I have a program with a debug flag in it (Strangely I've yet to be able to write bug-free code). I'd like to change the state of the debug flag based on command line args. I looked at IOVar but that would cause all the pure procedures to get swallowed by the IO Monad. Is a better way to get this behavior ? Thanks, Brian

5 4

The Bay Area Haskell Hackathon is coming up: Feb 11-13, 2011
by Bryan O'Sullivan 27 Dec '10

27 Dec '10

Mark Lentczner and I are organizing, and it will be held at Hacker Dojo in Mountain View<http://maps.google.com/maps/place?cid=2122486601784397611&q=hacker+dojo&gl=…> . If you plan to attend, please fill in our sign-up form<https://spreadsheets.google.com/viewform?formkey=dEc5cW1fa3hjQ3JheVF5dHAwdT…>so we know we'll have room. Also, please consider joining the Hackathon's Google group<http://groups.google.com/group/bayhac> . We look forward to seeing you!

2 2

UTF-8 in Haskell.
by Magicloud Magiclouds 27 Dec '10

27 Dec '10

Hi, Recently, I am reading ssh hackage (http://hackage.haskell.org/package/ssh) When at the part of deal with string, I got confused. I am not sure if this is a bug for the hackage, or I am just misunderstanding. An ascii char takes a Word8. So this works (LBS stands for Data.ByteString.Lazy): toLBS :: String -> LBS.ByteString toLBS = LBS.pack . map (fromIntegral . fromEnum) But a UTF-8 char takes a Int (Word32). Then I think the above code would break the data, right? If so, OK, then I think I could make a packInt which turns an Int into 4 Word8 first. Thus under all situation (ascii, UTF-8, or even UTF-32), my program always send 4 bytes through the network. Is that OK? -- 竹密岂妨流水过山高哪阻野云飞

5 7

Internship in Tokyo
by employment 27 Dec '10

27 Dec '10

Tsuru Capital will be taking on interns again in 2011. The internship period is three months. There should be a position available again from January. The position is in Tokyo in a English speaking team of around 6 people. The company does algorithmic options market-making. The exact roles are not fixed yet but the projects will be something supportive to the trading activity. We are looking for Haskell programmers and preference will go to those with experience in Haskell programming. Without any experience it is unlikely that you will be selected. Our interns typically work on projects relating to reporting and statistics, using databases, web interfaces and iteratees on Linux systems. Performance tuning, optimization and testing are very important to us. We should emphasise that although we are doing trading the intern positions will be just tangential to the activity and we are really looking for people who want to do programming more than people who want to do finance. Those looking for actual trading experience may be disappointed. At the current time we are not looking expand the team working on the trading itself. Compensation would be a small package including flights and accommodation. If interested please send a resume to jobs(a)tsurucapital.com You can see more details about the company at tsurucapital.com and at the company page on LinkedIn For those who have applied before but would like to be considered again it may be worth just sending a reminder mail, giving the dates you are available.

1 0

Intro to monad transformers
by michael rice 27 Dec '10

27 Dec '10

I lifted the code below from here: http://en.wikibooks.org/wiki/Haskell/Monad_transformers Since the wiki page doesn't say what needs to be imported, I'm guessing. Not sure what is happening. Maybe someone can tell me. Michael ============== import Control.Monad import Control.Monad.Trans.Class import Data.Char newtype (Monad m) => MaybeT m a = MaybeT { runMaybeT :: m (Maybe a) } instance Monad m => Monad (MaybeT m) where return = MaybeT . return . Just x >>= f = MaybeT $ do maybe_value <- runMaybeT x case maybe_value of Nothing -> return Nothing Just value -> runMaybeT $ f value instance Monad m => MonadPlus (MaybeT m) where mzero = MaybeT $ return Nothing mplus x y = MaybeT $ do maybe_value <- runMaybeT x case maybe_value of Nothing -> runMaybeT y Just value -> runMaybeT x instance MonadTrans MaybeT where lift = MaybeT . (liftM Just) instance Show (MaybeT m a) getValidPassword :: MaybeT IO String getValidPassword = do s <- lift getLine guard (isValid s) return s isValid :: String -> Bool isValid s = (length s > 8) && ((filter isAlphaNum s) == s) && any isDigit s && any isAlpha s askPassword :: MaybeT IO () askPassword = do lift $ putStrLn "Insert your new password:" value <- getValidPassword lift $ putStrLn "Storing in database..." ============= [michael@localhost ~]$ ghci GHCi, version 6.12.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Prelude> :l test5 [1 of 1] Compiling Main ( test5.hs, interpreted ) Ok, modules loaded: Main. *Main> askPassword Loading package transformers-0.2.2.0 ... linking ... done. *** Exception: stack overflow *Main>

5 8

Matlab Style Logic Operations ala V1.*(V2>0) on Vectors and Matrices with HMatrix ??
by gutti 26 Dec '10

26 Dec '10

Hi all, In Matlab the following line of code: V3 = V1.*(V2>0) (V2>0) gives a Bool-Vector with ones (trues) and zero's where elements of V2 are > 0; Then this Bool vector is used to multiply all elements in V1 to zero where the condition V2>0 is not fulfilled. How can I do that in Haskell ? (I haven't seen bol operations or mapping functions into vectors, arrays in the HMatrix.pdf). . -- Many thanks in advance Phil -- View this message in context: http://haskell.1045720.n5.nabble.com/Matlab-Style-Logic-Operations-ala-V1-V… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

3 12

command line options using ghc -e
by briand＠aracnet.com 26 Dec '10

26 Dec '10

Hi, for example : ghc -e main foo.hs these should be treated as args for argv I'm wondering if there is a magic option to indicate that everything after this option is an arg option. Thanks Brian P.S. yes I know about :main args in ghci.

2 1

Re: [Haskell-cafe] Intro to monad transformers
by Antoine Latter 26 Dec '10

26 Dec '10

On Dec 26, 2010 2:01 PM, "michael rice" <nowgate(a)yahoo.com> wrote: > > I lifted the code below from here: > > http://en.wikibooks.org/wiki/Haskell/Monad_transformers > > Since the wiki page doesn't say what needs to be imported, I'm guessing. > > Not sure what is happening. Maybe someone can tell me. > > Michael > I haven't had a chance to dig into your example, but you might want to try the maybeT library: http://hackage.haskell.org/package/MaybeT That way you could try to narrow down where the error is coming from. Take care, Antoine > ============== > > import Control.Monad > import Control.Monad.Trans.Class > import Data.Char > > newtype (Monad m) => MaybeT m a = MaybeT { runMaybeT :: m (Maybe a) } > > instance Monad m => Monad (MaybeT m) where > return = MaybeT . return . Just > x >>= f = MaybeT $ do maybe_value <- runMaybeT x > case maybe_value of > Nothing -> return Nothing > Just value -> runMaybeT $ f value > > instance Monad m => MonadPlus (MaybeT m) where > mzero = MaybeT $ return Nothing > mplus x y = MaybeT $ do maybe_value <- runMaybeT x > case maybe_value of > Nothing -> runMaybeT y > Just value -> runMaybeT x > > instance MonadTrans MaybeT where > lift = MaybeT . (liftM Just) > > instance Show (MaybeT m a) > > getValidPassword :: MaybeT IO String > getValidPassword = do s <- lift getLine > guard (isValid s) > return s > > isValid :: String -> Bool > isValid s = (length s > 8) && > ((filter isAlphaNum s) == s) && > any isDigit s && > any isAlpha s > > askPassword :: MaybeT IO () > askPassword = do lift $ putStrLn "Insert your new password:" > value <- getValidPassword > lift $ putStrLn "Storing in database..." > > ============= > > [michael@localhost ~]$ ghci > GHCi, version 6.12.3: http://www.haskell.org/ghc/ :? for help > Loading package ghc-prim ... linking ... done. > Loading package integer-gmp ... linking ... done. > Loading package base ... linking ... done. > Loading package ffi-1.0 ... linking ... done. > Prelude> :l test5 > [1 of 1] Compiling Main ( test5.hs, interpreted ) > Ok, modules loaded: Main. > *Main> askPassword > Loading package transformers-0.2.2.0 ... linking ... done. > *** Exception: stack overflow > *Main> > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

2 1

Character encoding?
by michael rice 26 Dec '10

26 Dec '10

How are characters encoded? *Main System.Random Control.Monad.State.Lazy> random (mkStdGen 0) :: (Char,StdGen) ('\64685',40014 40692) *Main System.Random Control.Monad.State.Lazy> random (snd it) :: (Char,StdGen) ('\1052295',1601120196 1655838864) *Main System.Random Control.Monad.State.Lazy> random (snd it) :: (Char,StdGen) ('\639025',1346387765 2103410263) *Main System.Random Control.Monad.State.Lazy> random (snd it) :: (Char,StdGen) ('\625672',439883729 1872071452) Michael

3 3

ANNOUNCE: storable-endian
by Eugene Kirpichov 26 Dec '10

26 Dec '10

Hi cafe, I've released "storable-endian" http://hackage.haskell.org/package/storable-endian It defines types like {{Int,Word}{16,32,64},Double,Float}{LE,BE} (for example Int32BE) etc. with a corresponding Storable instance. It is needed for binary interoperability with libraries or network protocols with fixed endianness. Hope you find it useful. -- Eugene Kirpichov Senior Software Engineer, Grid Dynamics http://www.griddynamics.com/

7 20

DFAs and self-referential data
by Maxime Henrion 26 Dec '10

26 Dec '10

Hello all, I've been playing with some code to work with DFAs, but I'm now faced with an implementation problem. In order to have states that can transition to themselves, it seems I would need self-referential data; otherwise I would need to separate those transitions from the rest and handle them specially in the code. I tried to exploit laziness in order to get self-referential data as shown in the 'self' function below: module DFA where import Data.Map (Map) import qualified Data.Map as M data DFA a = DFA (Map a (DFA a)) -- The set of transitions functions Bool -- Is this a final state? accept :: Ord a => DFA a -> [a] -> Bool accept (DFA _ f) [] = f accept (DFA ts f) (x:xs) = maybe False (`accept` xs) (M.lookup x ts) empty :: Bool -> DFA a empty = DFA M.empty path :: Ord a => a -> DFA a -> DFA a -> DFA a path x d' (DFA ts f) = DFA (M.insert x d' ts) f self :: Ord a => a -> DFA a -> DFA a self x d = let d' = path x d' d in d' test :: String -> Bool test = accept s1 where s1 = path '0' s2 . self '1' $ empty True s2 = path '0' s1 . self '1' $ empty False The automaton I construct in the 'test' function is the example one from the wikipedia page (http://en.wikipedia.org/wiki/Deterministic_finite_automaton) on DFAs. It should accept any string formed with ones and zeros that contain an even number of zeros (or, equivalently, strings that match the regular expression "1*(0(1*)0(1*))*"). Unfortunately, this doesn't seem to give the desired effect: *DFA> test "0" False *DFA> test "00" True *DFA> test "000" False *DFA> test "0000" True *DFA> test "1" True *DFA> test "11" True *DFA> test "111" True *DFA> test "11100" False Anyone knows what I'm doing wrong here? I suspect my attempt at having self-referential data is somehow buggy; do I need to treat transitions to the same state differently? Cheers, Maxime

2 3

Compiling a DSL on the shoulders of GHC
by Patai Gergely 26 Dec '10

26 Dec '10

Hello all, I'm trying to reuse as much of the sweat and tear put into GHC as possible to derive a compiler for a language highly similar to Haskell in many aspects. The difference is that instead of constructing an expression of type IO (), the programmer has to provide a stream processor on the top level - whether this is an arrow structure or just a pure function mapping input to output is not decided yet. In other words, I want to allow the programmer to use full Haskell as a metaprogramming language to create an expression of a much more limited language. My idea was to move the relevant types into a module, and make my combinators simple data constructors behind the scene, so the Haskell phase would effectively build an AST. The tricky bit is that I don't necessarily want to make everything an explicit data constructor. For instance, I'd like to allow Haskell functions in the tree. Using the GHC API, I can get the Core representation of the metaprogram. What I'd like at this point is to evaluate the top level expression and still have a representation open to analysis (traversal, pretty printing, interpretation etc.), including lambdas; if this evaluation takes more time than some well-defined limit, I could treat it as a compile-time error. Basically, I want the constant that is the main program to be folded completely if possible during compile time, and signal an error in case it isn't or doesn't seem to be. The resulting structure would be transformed further by a separate application instead of the existing GHC backends. Unfortunately the GHC API is not very approachable for the uninitiated, so it's not clear to me whether this is even possible. Or is it simply such a bad idea that it's not even worth considering in the face of more conventional approaches? Gergely -- http://www.fastmail.fm - Same, same, but different...

6 17

Re: [Haskell-cafe] [darcs-users] Darcs failure
by Andrew Coppin 26 Dec '10

26 Dec '10

On 24/12/2010 09:58 AM, Miles Gould wrote: > Hi Andrew, > > Others have probably told you this, Actually no... > but you should look into the pkill > command, which allows you to kill processes (including sending signals > other than SIGTERM) by name. It's installed by default on Ubuntu. Mmm, OK. Thanks for the tip. Gotta love the way that this is THE MOST COMMON USE CASE for kill, and yet kill itself doesn't support doing this. But still, that's the Unix methodology; why have one application that does what you want when you could split it into a dozen smaller applications and force everybody yo reinvent the wheel every single time they need it? PS. No, I'm not bitter. Not at all...

3 2

How to reload module that package has linked in memory?
by Andy Stewart 26 Dec '10

26 Dec '10

Hi all, I'm working on how to dynamic loading library into *running* program. I can dynamic loading/update module into *running* program if have *new* package installed. Example, when program *startup* and loading package foo-0.0.1 with function : api :: String -> String api = reverse then, i change `api` and install by foo-0.0.2: api :: String -> String api = show . length and dynamic-linking foo-0.0.2 works fine, i change api's value in *runtime*. And problem is, my solution just work when you install *new* package in Cabal/GHC database (foo-0.0.1 => foo-0.0.2), if i just change `api` value and don't install *new* package, my code can't work. I use Linker.linkPackages and Linker.getHValue to get symbol value, but looks Linker.getHValue can't get *update* value once current package has linked in memory. So how to make Linker.getHValue can get *update* value and don't need install *new* package in Cabal/GHC database? How to *reload* module with current version package? Or any GHC-API missing? Below is my source code, you just need look function `load`. Thanks! :) -- Andy ------------------------------> source code start <------------------------------ module System.Dynload ( PackageVersion (..), dynload ) where import Control.Monad (forM_) import Data.IORef import GHC.Paths (libdir) import MonadUtils (liftIO) import Data.List import Data.Ord import Distribution.Package import qualified DynFlags import qualified Exception import qualified GHC import qualified HscTypes import qualified IOEnv import qualified Linker import qualified LoadIface import qualified Maybes import qualified Module import qualified Name import qualified OccName import qualified Outputable import qualified PackageConfig as PC import qualified Packages import qualified SrcLoc import qualified TcRnTypes import qualified UniqSupply import qualified Unique data PackageVersion = Newest | Version String deriving (Ord, Show, Eq) dynload :: (String, PackageVersion, String, [(String, Linker.HValue -> IO ())]) -> IO () dynload (packageName, packageVersion, moduleName, loadList) = GHC.defaultErrorHandler DynFlags.defaultDynFlags $ GHC.runGhc (Just libdir) $ do -- Update Flags of session. sessionFlags <- GHC.getSessionDynFlags GHC.setSessionDynFlags sessionFlags -- this is ncessary, otherwise get GHC error -- Initialise package information. (flags, _) <- liftIO $ Packages.initPackages sessionFlags -- Search packages that export modules. let packages = map fst $ filter snd $ Packages.lookupModuleInAllPackages flags (Module.mkModuleName moduleName) exportError pName mName = "# Package " ++ pName ++ " not exist or not export module " ++ mName result = case packages of [] -> Left $ "# No package export module : " ++ moduleName _ -> let matchPackages = filter (\x -> packageConfigName x == packageName) packages in case matchPackages of [] -> Left $ exportError packageName moduleName _ -> case packageVersion of Version pv -> let pName = packageName ++ "-" ++ pv versions = map packageConfigVersion matchPackages in if pv `elem` versions then Right pName else Left $ exportError pName moduleName Newest -> case findNewestPackage matchPackages of Nothing -> Left "# dynload : Impossible reach here" Just packageConfig -> Right $ packageConfigIdString packageConfig case result of Left err -> liftIO $ putStrLn err Right packageNameStr -> do liftIO $ putStrLn $ "* Use package : " ++ packageNameStr -- Initialise the dynamic linker. liftIO $ Linker.initDynLinker flags hscEnv <- GHC.getSession forM_ loadList $ \ (symbolName, loadFun) -> do -- Because symbol perhaps re-export from external module. -- So we need parse symbol to find define location. parseResult <- liftIO $ parseSymbol (packageNameStr, moduleName, symbolName) hscEnv flags case parseResult of Just args -> load args flags loadFun Nothing -> return () -- | Internal load function for pdynload. load :: (GHC.GhcMonad m) => (String, String, String) -> GHC.DynFlags -> (Linker.HValue -> IO ()) -> m () load (packageName, moduleName, symbolName) flags loadFun = Exception.ghandle (\(GHC.CmdLineError _) -> -- Catch package error. liftIO $ putStrLn $ "# Unknown package " ++ packageName) (do -- Debug code. -- liftIO $ Linker.showLinkerState -- Link exactly the specified packages, and their dependents -- (unless of course they are already linked). -- The dependents are linked automatically, -- and it doesn't matter what order you specify the input packages. let packageId = Module.stringToPackageId packageName liftIO $ Linker.linkPackages flags [packageId] Exception.ghandle (\(GHC.ProgramError err) -> liftIO $ putStrLn $ "# " ++ err) (do liftIO $ putStrLn $ "* Linking " ++ packageName ++ ":" ++ moduleName ++ "." ++ symbolName ++ " ..." -- Get current session. session <- GHC.getSession -- Create a name which definitely originates in the given module. let name = Name.mkExternalName (Unique.mkBuiltinUnique 0) (Module.mkModule packageId (Module.mkModuleName moduleName)) (OccName.mkVarOcc symbolName) SrcLoc.noSrcSpan -- Get the HValue associated with the given name. -- May cause loading the module that contains the name. result <- liftIO $ Linker.getHValue session name liftIO $ loadFun result)) -- | Parse symbol whether defined in current module. -- If symbol is re-export other module, parse recursively, -- until found the define location of symbol. parseSymbol :: (String, String, String) -> HscTypes.HscEnv -> GHC.DynFlags -> IO (Maybe (String, String, String)) parseSymbol (packageName, moduleName, symbolName) hscEnv flags = do putStrLn $ "* Parse " ++ packageName ++ ":" ++ moduleName ++ "." ++ symbolName ++ " ..." -- Build unique supply to build environment. uniqueSupply <- UniqSupply.mkSplitUniqSupply 'a' uniqueSupplyIORef <- newIORef uniqueSupply -- Initialise. let packageId = Module.stringToPackageId packageName module' = Module.mkModule packageId $ Module.mkModuleName moduleName environment = TcRnTypes.Env { TcRnTypes.env_top = hscEnv, TcRnTypes.env_us = uniqueSupplyIORef, TcRnTypes.env_gbl = (), TcRnTypes.env_lcl = ()} -- Find and read interface file. iface <- IOEnv.runIOEnv environment $ LoadIface.findAndReadIface Outputable.empty module' False case iface of -- Return Nothing if can't found interface file. Maybes.Failed _ -> do putStrLn $ "# Can't found interface file of " ++ packageName ++ ":" ++ moduleName ++ "." ++ symbolName return Nothing -- Parse symbol. Maybes.Succeeded (moduleInterface, hiFile) -> do putStrLn $ "* Scan interface file " ++ hiFile ++ " ..." -- Export list of current module let ifaceExport = HscTypes.mi_exports moduleInterface -- [(ModuleName, [type])] exports = map (\ (mod, items) -> (Module.moduleNameString $ Module.moduleName mod ,concatMap (\item -> case item of HscTypes.Avail name -> [OccName.occNameString name] HscTypes.AvailTC _ list -> map OccName.occNameString list ) items) ) ifaceExport -- Partition current module and external module. (currentExports, otherExports) = partition (\ (mName, _) -> mName == moduleName) exports case findSymbolInExportList currentExports symbolName of -- Return current module if found symbol in export list of current module. Just _ -> do putStrLn $ "* '" ++ symbolName ++ "' defined in " ++ packageName ++ ":" ++ moduleName return $ Just (packageName, moduleName, symbolName) Nothing -> -- Parse recursively if symbol is re-export from external module. case findSymbolInExportList otherExports symbolName of Just mn -> do putStrLn $ "* '" ++ symbolName ++ "' is re-export from module " ++ mn -- Lookup new package of external module. newPackageName <- do putStrLn $ "* Lookup package of module " ++ mn lookupPackageName flags mn case newPackageName of -- Parse symbol in new package. Just npn -> parseSymbol (npn, mn, symbolName) hscEnv flags -- Return Nothing if package not found. Nothing -> return Nothing -- Return Nothing if can't found symbol in interface file. -- If reach this, interface file is incorrect. Nothing -> do putStrLn $ "# Can't found symbol " ++ symbolName ++ " in " ++ hiFile return Nothing -- | Lookup package name from ghc database. lookupPackageName :: DynFlags.DynFlags -> String -> IO (Maybe String) lookupPackageName flags moduleName -- Return Nothing when no package found. | packageNum == 0 = do putStrLn $ "# Can't found module " ++ show moduleName return Nothing | packageNum == 1 = do let (packageConfig, isExpose) = head packages pName = packageConfigIdString packageConfig if isExpose -- Return package name when package expose module. then return $ Just pName -- Return Nothing if module hide in package. else do putStrLn $ "# Module " ++ show moduleName ++ " hide in package " ++ pName return Nothing -- Return Nothing if no package expose module. | null exposePackages = do putStrLn $ "# Can't found module " ++ show moduleName return Nothing -- Return first match package when found module in multiple packages. | otherwise = case findNewestPackage exposePackages of Nothing -> do putStrLn "# lookupPackageName: Impossible reach here" return Nothing Just packageConfig -> do let pName = packageConfigIdString packageConfig putStrLn $ "# Module " ++ moduleName ++ " expose in multiple packages." putStrLn $ "* Use package : " ++ pName return $ Just pName where packages -- search package that *contain* module. = Packages.lookupModuleInAllPackages flags (Module.mkModuleName moduleName) packageNum -- length of package list = length packages exposePackages -- filter package that *export* module = map fst $ filter snd packages -- | Find symbol in export list of module. -- Return module name when found symbol in export list. -- Otherwise return Nothing. findSymbolInExportList :: Eq b => [(a, [b])] -> b -> Maybe a findSymbolInExportList [] _ = Nothing findSymbolInExportList ((moduleName, symList) :xs) sym | sym `elem` symList = Just moduleName | otherwise = findSymbolInExportList xs sym -- | Get PackageConfig id string. packageConfigIdString :: PC.PackageConfig -> String packageConfigIdString = Module.packageIdString . PC.packageConfigId -- | The package name of PC. packageConfigName :: PC.PackageConfig -> String packageConfigName packageConfig = packageName where (PackageName packageName) = PC.pkgName $ PC.sourcePackageId packageConfig -- | The package version of PC. packageConfigVersion :: PC.PackageConfig -> String packageConfigVersion = showVersion . PC.versionBranch . PC.pkgVersion . PC.sourcePackageId -- | Find newest package. findNewestPackage :: [PC.PackageConfig] -> Maybe PC.PackageConfig findNewestPackage [] = Nothing findNewestPackage [a] = Just a findNewestPackage xs = Just $ maximumBy (comparing (PC.pkgVersion . PC.sourcePackageId)) xs -- | Convert version [x,y,z] to "x.y.z". showVersion :: [Int] -> String showVersion [] = "" showVersion [x] = show x showVersion (x:xs) = (show x ++ ".") ++ showVersion xs ------------------------------> source code end <------------------------------

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GHC-7.01 and intrinsic operations
by Pavel Perikov 25 Dec '10

25 Dec '10

Is it possible to make GHC-7.0.1 to generate intrinsic instructions instead of calls to C library to compute trigonometric functions? > main = do > a <- readLn > print $ sin a I tried -O -msse2 -fllvm and their combinations. Generating assembly always contains calls for computation of sin Pavel

2 2

(Co/Contra)Functor and Comonad
by Mario Blažević 25 Dec '10

25 Dec '10

Why are Cofunctor and Comonad classes not a part of the base library? I recently defined a data type (Control.Cofunctor.Ticker in monad-coroutine on Hackage) that happens to be a co-functor, or contra-functor if you prefer. In other words, it can implement the following function: > cofmap :: (a -> b) -> cf b -> cf a I wanted to define a proper instance for it, but to my surprise I discovered that I couldn't. Not only is the class not defined in base, the only package I could find on Hackage that defines it is category-extras. This is a huge package I'd rather not have as a dependency, so I opted not to declare any instance. Later on I found that this question has been raised before by *Conal Elliott*, nearly four years ago. http://www.haskell.org/pipermail/libraries/2007-January/006740.html The result was the TypeCompose package, which presents a decent solution. I still can't think of any harm in having a proper class declaration in the base library: if you don't need it, you don't need to know it. But without the class declaration in the base library (or in some other obvious package) every other released library must either lack the instance declarations or declare the class itself and risk clashes. This is not some obscure class you've never encountered, by the way: any "consumer" of data is a cofunctor. All regexp data types, for example, are cofunctor instances - or would be if there was a class to declare them instances of. The same question extends to Comonad. I am not too familiar with this area so there may be fewer potential instances of the class, but I remember there was quite a bit of buzz around comonads a few years ago. Judging by a cursory Hayoo search, if anything the situation is worse than with Cofunctor: there are multiple incompatible declarations of the class scattered in various libraries that need it: ad, category-extras, data-category, rope. There is also evidence of undeclared Comonad instances: see the ListZipper and value-supply libraries. So, is it time to add these two classes to the base library?

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Re: [Haskell-cafe] (Co/Contra)Functor and Comonad
by Mario Blažević 25 Dec '10

25 Dec '10

On Thu, Dec 23, 2010 at 11:25 PM, Tony Morris <tonymorris(a)gmail.com> wrote: > > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > ...regardless of the utility of a contravariant functor type-class, I > strongly advocate for calling it Contrafunctor and not Cofunctor. I > have seen numerous examples of confusion over this, particularly in > other languages. > I don't personally care what's it called, as long as it's available. Can anybody point to an authoritative source for the terminology, though? Wikipedia claims that cofunctor is a contravariant functor. Also, is there anything in category theory equivalent to the Functor -> Applicative -> Monad hierarchy , but with a Cofunctor/Contrafunctor at the base? I'm just curious, I'm not advocating adding the entire hierarchy to the base library. ;)

3 3

Cabal message problem.
by Magicloud Magiclouds 25 Dec '10

25 Dec '10

Hi, I see this kind of information a lot when I using cabal to install package. Or sometimes same packages both exist in global and user space, which is a "shadowed by" message. How to resolve that? Thanks. Resolving dependencies... <command line>: cannot satisfy -package Cabal-1.10.0.0: Cabal-1.10.0.0-9ac678c7f1e4f8dd31bac0e19f600698 is unusable due to missing or recursive dependencies: process-1.0.1.4-24e3819e5c17aaf49bfec6a0ab739420 (use -v for more information) -- 竹密岂妨流水过山高哪阻野云飞

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GHC 7.0.1 developer challenges
by John D. Ramsdell 24 Dec '10

24 Dec '10

A quick review of GHC 7.0.1 revealed two challenges for developers. I downloaded the GHC 7.0.1 sources, configured for a home directory install, and built and installed the compiler. Very close to the end, my machine froze, perhaps due to memory exhaustion. In any event, a reboot allowed me to complete the installation. I tested the new compiler on an application I distribute, CPSA. The algorithm implemented by the program is not guaranteed to terminate, and it's hard to predict when non-termination is inevitable. Sometimes the way it terminates is to allocate all the memory in swap space and freeze the machine. It's an ugly crash. So in my documentation, I recommend people supply a runtime flag limiting memory usage. Due to a security concern, GHC 7.0.1 disables all runtime flags unless a new flag is provided during linking. Since limiting memory usage is so important, many developers will modify their cabal files to add the linker flag or prepare for complaints from users that the developer's program caused their machine to freeze and lose their work. The irony of this situation is deep. CPSA is a program that analyzes cryptographic protocols in an effort to expose security flaws. To ensure that the program does not crash a user's machine, I have to use a linker option that may expose the user to some security problems. There is one more disappointment in GHC 7.0.1 for developers. Cabal sdist is still hosed. Since ten months ago, cabal sdist fails to preserve the file mode bits of the source files put into the tarball being generated (Ticket #627 reported by draconx). An executable shell script and a source file world readable both have a mode of 600 in the tarball! So developers, continue to keep GHC 6.10.4 around so you can create source distributions. That's what I do. John

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ANN: xmobar 0.12 released
by Jose A. Ortega Ruiz 24 Dec '10

24 Dec '10

I'm happy to announce a new relase of xmobar, the text-based monitor bar. You can read everything about xmobar and this release at our new web address (http://projects.haskell.org/xmobar/) or see below for a summary of what's new (cf. http://projects.haskell.org/xmobar/releases.html) ## Version 0.12 xmobar has a new [maintainer], a new [website], a new [mailing list] and uses a new [source code repository]. Many thanks to Andrea Rossato, xombar's author and maintainer so far, for creating xmobar in the first place, and for giving me the chance to become its maintainer. And a big thanks to Ben Boeckel, Petr Rockai and Norbert Zeh for their patches. [website]: http://projects.haskell.org/xmobar/ [mailing list]: http://projects.haskell.org/cgi-bin/mailman/listinfo/xmobar [source code repository]: https://github.com/jaor/xmobar [maintainer]: http://hacks-galore.org/jao/ _New features_ - Window borders: configuration options `border` and `borderColor` allow drawing borders around xmobar's window. - New monitor, `Uptime`, showing the system uptime. - New monitor argument (`-S`) to enable displaying the `%` symbol in percentages or other suffixes (e.g., units in Uptime and Network); the symbol is now never included by default. - New 'run once' commands, by specifying a 0 refresh rate in `Run Com` ([issue 26]). - MPD monitor: updated to libmpd 1.5. New fields `ppos` (playlist position) and `remaining` (remaining time). New configuration options to specify MPD's host, user name and password. - Battery monitor: new `watts` and `timeleft` fields (Petr Rockai), and specific arguments to control coloring and thresholds of the former. - MultiCPU monitor: new `auto*` fields that automatically detect all present CPUs (Ben Boeckel). - CpuFreq monitor uses just one decimal digit for GHz values (Petr Rockai). - Mail plugin expands paths starting with "~/" (Ben Boeckel). Ditto MBox. - Weather monitor now skips not retrieved fields, instead of displaying a long error message. - New compilation flag, `all_extensions`. - Documentation and website updates. _Bug fixes_ - [issue 23]: Wireless monitor is now compatible with iwlib 29. - [issue 24]: Swap monitor's used ratio display fixed. - [issue 25]: Percentages only include `%` if requested using `-P`. - [issue 31]: MPD monitor now respects `-W` argument. - Fixes in CPU frequency formatting, string alignment and colour boxes in monitors (Norbert Zeh). - TopMem and TopProc now use the `-L` and `-H` options correctly for memory template fields. - MBox skips non-existent mbox paths instead of hanging.

1 0

List of numbers to list of ranges
by C K Kashyap 24 Dec '10

24 Dec '10

Hi all, Here's my attempt to convert a list of integers to a list of range tuples - Given [1,2,3,6,8,9,10], I need [(1,3),(6,6),8,10)] My attempt using foldl yields me the output in reverse. I can ofcourse reverse the result, but what would be a better way? f xs = foldl ff [] xs where [] `ff` i = [(i,i)] ((s,e):ns) `ff` i = if i == e+1 then (s,i):ns else (i,i):(s,e):ns Regards, Kashyap

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