August 2003 - Glasgow-haskell-users

a library for reifying values in GHC
by Bernard James POPE 15 Aug '03

15 Aug '03

Hi all, During my work on buddha (haskell debugger) I've had the need to print arbitrary values from a running program. Along the way I've written some code that works with GHC to do this. Just in case there are others who might benefit from this, I've ripped some code out of buddha and made it into somewhat of a library. You can download it from here: http://www.cs.mu.oz.au/~bjpop/code.html The main parts are: reify :: a -> IO Graph data Graph = ... prettyGraph :: Graph -> String The graph type is an ordinary data type: type Unique = Int -- a unique label for each node type Tag = Int -- what kind of node it is type NumKids = Int -- how many children it has data Graph = AppNode Unique String Tag NumKids [Graph] | CharNode Char | IntNode Int | IntegerNode Integer | FloatNode Float | DoubleNode Double | NullNode deriving Show The main features are: - it is conservative wrt to evaluation (lazy). It does not make its argument evaluate any further, - it detects cycles in the heap representation and makes them visible in the Graph representation (though the current pretty printer does not take advantage of this), - it knows about some "special" things like exceptions and some other oddities, - it ought to work on GHC 5 and 6, though I haven't tested it extensively on the latter Functions are a sore point (they all get mapped to the one thing, sigh). It makes use of the FFI and the nice API that GHC provides for the RTS (is that enough TLAs in one sentence?) Unfortunately to use the library you must compile with -prof. The reason is to trick GHC into keeping names of data constructors on the heap. I'd rather avoid this, and perhaps with the new HsDebug stuff in GHC there is a better way to get such names, but I haven't looked too hard. (Any ideas?) An example is below. Ooroo, Bernie. -------------------------------------------------------------------------------- Here's an example: {- demonstrating the use of ReifyHs.reify -} module Main where import ReifyHs (reify) import PrettyGraph (prettyGraph) import Data.Char (toUpper) main :: IO () main = do putStrLn $ "GHC version: " ++ show __GLASGOW_HASKELL__ let listTups = zip "abcdefghij" [1..] putStr "\n\nForce the list to be evaluated a bit:\n\n" print $ take 3 listTups graph <- reify listTups putStr "\n\nhere's the graph representation: \n\n" print graph putStr "\n\nhere's a pretty print of the above: \n\n" putStrLn $ prettyGraph graph putStr "\n\nForce the list to be evaluated a bit more:\n\n" print $ take 5 listTups graph <- reify listTups putStr "\n\nthe graph pretty printed again: \n\n" putStrLn $ prettyGraph graph -------------------------------------------------------------------------------- Running the example after "make" bjpop@bjpop2:/tmp/reify$ ./test GHC version: 504 Force the list to be evaluated a bit: [('a',1),('b',2),('c',3)] here's the graph representation: AppNode 1076636796 ":" 1 2 [AppNode 1076636776 "(,)" 1 2 [CharNode 'a', IntNode 1],AppNode 1076637368 ":" 1 2 [AppNode 1076637348 "(,)" 1 2 [CharNode 'b',IntNode 2],AppNode 1076637932 ":" 1 2 [AppNode 1076637912 "(,)" 1 2 [CharNode 'c',IntNode 3],AppNode (-1) "" 3 0 []]]] here's a pretty print of the above: [('a',1),('b',2),('c',3) .. ? Force the list to be evaluated a bit more: [('a',1),('b',2),('c',3),('d',4),('e',5)] the graph pretty printed again: [('a',1),('b',2),('c',3),('d',4),('e',5) .. ?

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AWARD NOTIFICATION.
by primitivalote＠netscape.net 13 Aug '03

13 Aug '03

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ASSISTANCE PLEASE
by johnmalanbo＠latinmail.com 13 Aug '03

13 Aug '03

Dear Greetings,I am John Malanbo Vaye {A Liberian}who has just gotten off the hands of Rebels fighting against the regime of President Charles Taylor. My Father who was then a minister in the Cabinet of President Taylor was his confidant in matter of diamond trade between the Sierra Leone authorities, and they usually smuggled them out through my country, Liberia with the help of PresidentTaylor and my father, who was killed by the Rebels about ten days ago. On the intervension of President Obasanjo, we were released and presently staying in a refugee camp in Ghana.Before my father's death, he notify me of a Huge amount he hurriedly deposited with a Security Company here in Ghana[during the war].He gave me the documents and Authority to claim the Consignment from the Company.The amount involve in the Consignmemt is $31.5m[Thirty one, million Five Hundred Thousand US Dollars] as well as some quantity of gold and diamond. He lodged it with the Company as Jeweleries. I got your contact,from an expartirate friend here in Ghana, who visited the refugee camp here, and normally travels on Business to your Country.I told him of my need for a foriegn Partner and my intensions to invest in Europe,Asia or USA.He told me of how reliable and trustworthy you are.This is how far he knows of my intensions. The Security Company is prepared to help me carry my consignment[Money] out of Africa.This Security Company Officials,do travel Abroad on official assignment and with Diplomatic Immunity.I want you to assist me and as my Partner to help me receive the Consignment over there and keep in a safe place.You will then send me a letter of Invitation,in other for me to get my Visa to join you up. I am also interested in buying a house as I will be coming to settle down there with my familly and you shall advice me on a profitable Business in yourCountry. For your assistant I'm prepared to compensate you with 10% of the money,5% will be set aside for Extra expenditure,during the cause of this transaction.While the rest will be for my investment. Please let me know your intension immedaitely by mail, as I do not have a phone yet. NOTE:please treat this as Confidential,as I have not told anybody except you even the friend who gave me your contact, and no one knows that I am here in Ghana, for security reasons. Waiting to hear from you, as I am afraid of the horrors in my country and this part of the world. Yours Truly, Bennard William Molanbo ( In Distress)

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URGENT ASSISTANCE
by anthonysanedmunds＠eudoramail.com 12 Aug '03

12 Aug '03

ANTHONY EDMUNDS. EMAILl: anthonysanedmunds(a)eudoramail.com FAX:+34 MADRID-SPAIN: Dear Sir AN APPEAL FOR ASSISTANCE My name is Anthony Edmundo a liberian nacional I was a former minister in the Government of President Charles Taylor. I am on the run due to the iminent collapse of the Government in liberia as a result of the war. My purpose of writing you is to solicit assistance from you for the safe keeping of some money which I was able to bring out of liberia. This money,a total of $ 21.5m (twenty_one million,five hundred thousand U.S. Dollars)only,is part of the proceeds we made from illegal sale of diamonds while in government. I already have this money in a safe deposit with a security company here in Madrid. The company has agreed to help me set up an account where I could deposit the Fund,but for security reasons I can not set up such bank account in my name now. Your country being my final destination with my family,it therefore became natural for Me to look for someone trustworthy in the your country who can keep custody of the fund until my entire family is out of liberia and finally settle in your country I find it convinient to provide all logistics for a smooth trnasfer of the ownership of the fund to you,and the subsequent transfer to your bank account, I will reward you very handsomly with 17% of the total sum upon completion. I would therefore propose a meeting in Madrid with you in order to discuss and also draw a working agreement between the two of us.If you are satisfied with the agreement,we may conclude the transfer of ownership at the same time, so that the money could be transfered to your account pending my arrival in there for final disbursement. I look forward to hearing your decision on this matter very quick . Please I beg of you to keep this piece of information with you and treat it with maximum confidentiality even in the event that you are not able to assist me. Thank you and God blees . Yours sincerely, Anthony Edmunds.

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URGENT ASSISTANCE
by anthonyedmunds＠excite.com 12 Aug '03

12 Aug '03

ANTHONY EDMUNDS. EMAILl: anthonyedmunds(a)exite.com FAX:+34 MADRID-SPAIN: Dear Sir AN APPEAL FOR ASSISTANCE My name is Anthony Edmundo a liberian nacional I was a former minister in the Government of President Charles Taylor. I am on the run due to the iminent collapse of the Government in liberia as a result of the war. My purpose of writing you is to solicit assistance from you for the safe keeping of some money which I was able to bring out of liberia. This money,a total of $ 21.5m (twenty_one million,five hundred thousand U.S. Dollars)only,is part of the proceeds we made from illegal sale of diamonds while in government. I already have this money in a safe deposit with a security company here in Madrid. The company has agreed to help me set up an account where I could deposit the Fund,but for security reasons I can not set up such bank account in my name now. Your country being my final destination with my family,it therefore became natural for Me to look for someone trustworthy in the your country who can keep custody of the fund until my entire family is out of liberia and finally settle in your country I find it convinient to provide all logistics for a smooth trnasfer of the ownership of the fund to you,and the subsequent transfer to your bank account, I will reward you very handsomly with 17% of the total sum upon completion. I would therefore propose a meeting in Madrid with you in order to discuss and also draw a working agreement between the two of us.If you are satisfied with the agreement,we may conclude the transfer of ownership at the same time, so that the money could be transfered to your account pending my arrival in there for final disbursement. I look forward to hearing your decision on this matter very quick . Please I beg of you to keep this piece of information with you and treat it with maximum confidentiality even in the event that you are not able to assist me. Thank you and God blees . Yours sincerely, Anthony Edmunds.

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RE: preemptive getLine on cygwin?
by Simon Marlow 12 Aug '03

12 Aug '03

> So that's a third variant of runtime behaviour, then, for the same > trivial program (probably cygwin on a more modern windows?)!? > > What do other GHC versions say? And, more importantly, what > _should_ they do? GHC 5.04.3 behaves as I'd expect, except that it defaults to BlockBuffering for stdin/stdout in a cygwin window. In a DOS window it defaults to LineBuffering as expected. This appears to be because mingw's implementation of isatty() only detects DOS windows, which is reasonable. > Strangely, with Blockbuffering the program > seems to be slightly better behaved than with LineBuffering in > cygwin, so the "cat"-hack helps a bit ("strangely", because I'm > reading lines, so I'd usually explicitly set LineBuffering.., and > "slightly better", because it's still not quite as I would have > expected). > > I'd still like to understand what's going on and how to get my > Haskell programs to behave (this arises in a debugging mode of > a larger app and means that, at the moment, I can't easily use this > for debugging, which makes life slightly difficult, but at least it > doesn't seem to cause the bug*..). I think just upgrading your GHC should fix things. If not, we'll look into it. Cheers, Simon

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RE: preemptive getLine on cygwin?
by Simon Marlow 12 Aug '03

12 Aug '03

> I seem to have some problems understanding preemptive getLine > behaviour on cygwin, and wonder whether this is a known/fixed > bug/feature (I haven't switched to ghc-6.. yet), or whether anyone > has experience with this (behaviour on solaris, with an even older > ghc is more or less as expected). You're running a fairly old version of GHC. With 5.04.3 here I get different behaviour, although strangely it seems that stdin and stdout don't default to LineBuffering in a cygwin shell window. Cheers, Simon

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Data.Tree.Tree Show instance
by Tomasz Zielonka 12 Aug '03

12 Aug '03

Hi! The Tree datatype in new Data.Tree module has a Show instance that works like shown below: Prelude Data.Tree> print (Node 'a' [Node 'b' [], Node 'c' []]) - 'a' -+- 'b' | `- 'c' I use a similar module for Trees in conjunction with WASH for generating web pages. WASH session management relies on the ability to read back previously showed values. Writing a Read instance for such Show would be a weird thing to do. I think it would be better to derive Show instance for Tree instead of providing a pretty printing one. Then it would be possible to have a complementing Read instance. The pretty printing function could be provided under a different name (eg. drawTree). The other tiny problem is that the current instance is not recursion-proof: Prelude Data.Tree> let f x = Node x [Node x [], Node x []] Prelude Data.Tree> print (f (f 1)) - - 1 -+- 1 | `- 1 -+- - 1 -+- 1 | `- 1 | `- - 1 -+- 1 | `- 1 Best regards, Tom -- .signature: Too many levels of symbolic links

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Hello
by MR.DAVID OKOLO 12 Aug '03

12 Aug '03

Dear Sir/Madam, I have been instructed by my colleagues to look for partners who can assist us execute an urgent business transaction involving huge profits and international cooperation. We are interested in the importation of Solar Panels,Agricultural equipment and computer accessories.We need a foreign partner who can assist us with the transaction involving US$31, 000 000.00,which has been set-aside in an escrow account. We have resolved that a negotiable percentage will be your commission for participating in this transaction on our behalf and any other assistance you may give in this deal. A percentage will also be set aside from the entire sum to settle any expenses we may incur in the cause on these transactions. My colleagues and I are civil servants and as such, it is not,possible for any of us to operate a foreign account directly,hence we are soliciting your support. We propose to finalize the transaction in ten working days. If this proposal is accepted please respond to us via e-mail to enable us provide you with the detailed modalities for the successful completion of the project. I would also suppose you'd prefer a voice contact which requires sending your telephone and fax numbers to facilitate the various processes. There is no risk involved we just need an international contact.Moreso,it will be of great importance you provide me with your telephone/fax details,so we can have a more detailed conversation regarding the whole project.This is my private email address(david_okolo(a)thepostmaster.net) of which i will like you to send your reply. Finally, if you are not interested in this proposal,I apologize on behalf of myself and my colleagues for any inconvenience. Yours Sincerely, David Okolo(Dr)

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Timing repeated function calls
by Jeffrey A. Scofield 11 Aug '03

11 Aug '03

Greetings. Using GHC 6.0 on Mac OS X (10.2.6), I'm trying to do some timing tests of something that doesn't take very long. So, I want to call a function repeatedly (1000s of times). It appears, however, that the compiler is figuring out that there's no need to call the function more than once since it's pure. Is there anything simple I can do to get the compiler to call a function repeatedly? Here is a snippet of code showing what I am trying right now: main = do t0 <- getClockTime times 1000 t1 <- getClockTime . . . times :: Int -> IO () times 0 = return () times n = do let [a,b,c,d] = take 4 (myFunction) Control.Exception.evaluate a Control.Exception.evaluate b Control.Exception.evaluate c Control.Exception.evaluate d times $! n - 1 myFunction :: [Int] myFunction = . . . (There may be some absurd stuff in this code; I've left in the remnants of several failed attempts.) Regards, Jeff Scofield

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