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please help
by David Savimbi 13 Jun '03

13 Jun '03

From: David Jonas Savimbi Johannesburg, South Africa Email: djsavimbi(a)phantomemail.com june 13th, 2003. Dear Sir, It is my humble pleasure to write you this letter irrespective of the fact that you do not know me. However, I got your name through your country business directory here in my search for a reliable and trustworthy person that can assist me confidently. My name is Mr.John Jonas Savimbi. I am the son of Late Dr. Jonas Savimbi from Angola. I am 29 years old and I have got two younger sisters of same blood. Our mother died almost a year ago. We are all fighting for political asylum in South Africa. We cannot find a home in Angola anymore because of the war that our late father fought with the government of Angola until he died in that war. The government of Angola is now mad at us because our late father also wanted to be president and caused the people to fight the war for him because he was the president of UNITA political movement of Angola. So now we are in South Africa and we are suffering too much because we don't have money and the government of South Africa will not give jobs to asylum seekers. I am much concerned about my younger sisters who are finding it very difficult to manage in the situation. But I know that we should not suffer this way. I know that I must not let my younger sisters get into trouble because of money. So after consideration I am hereby begging for your assistance to help me to recover the sum of USD $29 Million which is my inheritance from my late mother. My late mother had taken this money with her to Spain in a diplomatic metal box marked (Precious Stones). Subsequently she lodged the metal box (As precious Stones) with a Securities and Valuables Protection company in Spain. I am supposed to be the beneficiary in the event of her death. However, all effort I made to go Spain to claim was refused by the Spainish embassy. And this was while it was still possible for me to travel. Now I cannot travel anywhere anymore. So in the situation that we are facing now, I must find somebody who can go to the Spain on my behalf. I understand that I will have to transfer my beneficiary rights unto you. I am willing to do so in the hope that you are a God fearing person who will not abandon us after you have the money. So from the bottom of my heart I am giving you 20% of the all the money. Once we have enough to sustain us sufficiently, you may be come our fund manager and invest the rest wisely for us. If you will be kind to assist us, please inform me urgently. Kind regards to you and your family. Sincerely, David Jonas savimbi

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RE: Non-determinism, backtracking and Monads
by Simon Peyton-Jones 11 Jun '03

11 Jun '03

Check out "Embedding Prolog in Haskell", which explores exactly the topic you discuss. http://citeseer.nj.nec.com/272378.html Simon | -----Original Message----- | From: haskell-cafe-admin(a)haskell.org [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Graham | Klyne | Sent: 11 June 2003 08:38 | To: Jerzy Karczmarczuk; Haskell Cafe | Subject: Non-determinism, backtracking and Monads | | At 11:06 05/06/03 +0200, Jerzy Karczmarczuk wrote: | >I permit myself to observe that your powerset problem (and the restricted | >length problem, i.e. the combinations) is usually solved in Prolog, through | >backtracking, using reasoning/style which adopts this "individualistic" | >philosophy. | > | >powerset(<source>,<possible result>) --- is the pattern. And the | >solution is | > | >powerset([],[]). Since nothing else can be done. Otherwise you pick the item | > or not. | > | >powerset([X|Rest],L) :- powerset(Rest,L). | >powerset([X|Rest],[X|L) :- powerset(Rest,L). | > | >The xxx ++ map (x :) xxx solution in Haskell is a particular formulation | >(and optimization) of the straightforward transformation from a version | >using the non-deterministic Monad. This one is really almost a carbon copy | >of the Prolog solution, with appropriate "lifting" of operations from | >individuals to lazy lists. | | I was thinking some more about this comment of yours, and my own experience | with the ease of using lists to implement prolog-style generators, and | think I come to some better understanding. If I'm right, I assume the | following is common knowledge to experienced Haskell programmers. So, in | the spirit of testing my understanding... | | The common thread here is a non-deterministic calculation in which there | are several possible solutions for some problem. The goal is to find (a) | if there are any solutions, and (b) one, more or all of the solutions. | | Prolog does this, absent ! (cut), by backtracking through the possible | solutions. | | My first epiphany is that the Haskell idea of using a lazily evaluated list | for result of a non-deterministic computation is pretty much the same thing | (which is pretty much what you said? Is this what you mean by "the | non-deterministic monad"?). The mechanisms for accessing a list mean that | the solutions must be accessed in the order they are generated, just like | Prolog backtracking. | | So there seems to be a very close relationship between the lazy list and | non-deterministic computations, but what about other data structures? I | speculate that other structures, lazily evaluated, may also be used to | represent the results of non-deterministic computations, yet allow the | results to be accessed in a different order. And these, too, may be | (should be?) monads. If so, the Haskell approach might be viewed as a | generalization of Prolog's essentially sequential backtracking. | | In a private message concerning the powerset thread on this list, a | correspondent offered a program to evaluate the subsets in size order, | which I found particularly elegant: | | >ranked_powerset :: [a] -> [[[a]]] | >ranked_powerset = takeWhile (not . null) . foldr next_powerset ([[]] : | repeat []) | > | >next_powerset :: a -> [[[a]]] -> [[[a]]] | >next_powerset x r = zipWith (++) ([] : map (map (x:)) r) r | > | >powerset :: [a] -> [[a]] | >powerset = tail . concat . ranked_powerset | | They also pointed out that "ranked_powerset is handy since you can use it | to define combinatorial choice etc.": | | > choose :: Int -> [a] -> [[a]] | > choose k = (!! k) . ranked_powerset | | So here is an example of a different structure (a list of lists) also used | to represent a non-deterministic computation, and furthermore providing | means to access the results in some order other than a single linear | sequences (e.g. could be used to enumerate all the powersets containing the | nth member of the base set, *or* all the powersets of a given size, without | evaluating all of the other powersets). | | To test this idea, I think it should be possible to define a monad based on | a simple tree structure, which also can be used to represent the results of | a non-deterministic computation. An example of this is below, at the end | of this message, which seems to exhibit the expected properties. | | So if the idea of representing a non-deterministic computation can be | generalized from a list to a tree, why not to other data structures? My | tree monad is defined wholly in terms of reduce and fmap. Without going | through the exercise, I think the reduce function might be definable in | terms of fmap for any data type of the form "Type (Maybe a)", hence | applicable to a range of functors? In particular, I'm wondering if it can | be applied to any gmap-able structure over a Maybe type. | | I'm not sure if this is of any practical use; rather it's part of my | attempts to understand the relationship between functors and monads and | other things functional. | | #g | -- | | | [[ | -- spike-treemonad.hs | | data Tree a = L (Maybe a) | T { l,r :: Tree a } | deriving Eq | | instance (Show a) => Show (Tree a) where | show t = (showTree "" t) ++ "\n" | | showTree :: (Show a) => String -> Tree a -> String | showTree _ (L Nothing ) = "()" | showTree _ (L (Just a)) = show a | showTree i (T l r) = "( " ++ (showTree i' l) ++ "\n" ++ | i' ++ (showTree i' r) ++ " )" | where i' = ' ':' ':i | | instance Functor Tree where | fmap f (L Nothing) = L Nothing | fmap f (L (Just a)) = L (Just (f a)) | fmap f (T l r) = T (fmap f l) (fmap f r) | | reduce :: Tree (Tree a) -> Tree a | reduce (L Nothing) = L Nothing | reduce (L (Just (L Nothing ) )) = L Nothing | reduce (L (Just (L (Just a)) )) = L (Just a) | reduce (L (Just (T l r ) )) = T l r | reduce (T l r) = T (reduce l) (reduce r) | | instance Monad Tree where | -- L Nothing >>= k = L Nothing | t >>= k = reduce $ fmap k t | return x = L (Just x) | fail s = L Nothing | | -- tests | | t1 :: Tree String | t1 = T (L $ Just "1") | (T (T (T (L $ Just "211") | (L $ Just "311")) | (L Nothing)) | (L $ Just "22")) | | k1 :: a -> Tree a | k1 n = T (L $ Just n) (L $ Just n) | | r1 = t1 >>= k1 | | k2 :: String -> Tree String | k2 s@('1':_) = L $ Just s | k2 s@('2':_) = T (L $ Just s) (L $ Just s) | k2 _ = L Nothing | | r2 = t1 >>= k2 | | t3 = L Nothing :: Tree String | r3 = t3 >>= k1 | | r4 = t1 >>= k1 >>= k2 | r5 = (return "11") :: Tree String | r6 = r5 >>= k1 | | -- Check out monad laws | -- return a >>= k = k a | m1a = (return t1) >>= k1 | m1b = k1 t1 | m1c = m1a == m1b | | -- m >>= return = m | m2a = t1 >>= return | m2b = t1 | m2c = m2a == m2b | | -- m >>= (\x -> k x >>= h) = (m >>= k) >>= h | m3a = t1 >>= (\x -> k1 x >>= k2) | m3b = (t1 >>= k1) >>= k2 | m3c = m3a == m3b | ]] | | | ------------------- | Graham Klyne | <GK(a)NineByNine.org> | PGP: 0FAA 69FF C083 000B A2E9 A131 01B9 1C7A DBCA CB5E | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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Re: Non-determinism, backtracking and Monads
by Iavor Diatchki 11 Jun '03

11 Jun '03

hello, you might also want to take a look at the "new monad library" i am working on. it is based on the old one, but does some things slightly different. one of the differences is the "nondeterminism transformer" whose implementation is inbetween lists and continuations. it also resembles resumptions quite a bit. i came up with this particular implementation but i would not be surprised if people already know about it. it is also quite simillar to the "term implementation" of the backtracking transformer described by ralf heinze in his "deriving monad transformers" paper. i would also be interested in general comments on the library. it is in the haskell cvs repository in fptools/libraries/monads (you need to check out fpconfig frist). bye iavor

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Fudgets
by Christian Buschmann 11 Jun '03

11 Jun '03

Hi! Is there any easy way to display an IO String with Fudgets? I know how to display a String: import Fudgets main :: IO () main = fudlogue (shellF "Prog" showMe) showMe = ("Hello " `labLeftOfF` displayF) >==< mapF getString >==< (buttonF "ClickMe!") getString :: Click -> String getString Click = "World!" But if I change the getString-function to: getString :: Click -> IO String getString Click = return "World!" --or any other kind of function which returns an IO String I get an error message. Is there any way, without using unsafePerformIO, to display my IO String? thanks Christian Buschmann

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Powerset
by oleg＠pobox.com 11 Jun '03

11 Jun '03

The following seems to be a faster version of powerset that delivers results strictly in the order of increasing cardinality (i.e., all sets of size 1 first, then of size 2, etc). It seems to run faster than any other ordered version of powerset posted so far. On GHCi, length $ powerset [1..22] is computed roughly 4 times faster than powerset3 given earlier. On Hugs, the powerset below also runs faster, with less memory consumption and in fewer GC cycles, up to a limit of 18 for the size of the input set. Then something happens. length $ powerset3 [1..19] runs out of memory on my (not current) version of Hugs too. The algorithm is more complex, though. Suppose we have a list xs Let powerset_n xs = filter (\p -> length p == n) $ powerset xs Let ps n i = powerset_n $ (tails xs)!!i that is, ps n 0 = powerset_n xs ps n (length(xs)-n) = [(tails xs)!!(length(xs)-n)] that is, i varies from 0 to (length(xs)-n) We observe that ps n (i-1) = ps n i ++ (map (x:) $ ps (n-1) i) where x = xs!!(i-1) Therefore, if we know ps (n-1) i for all i, we can compute ps n i from the base condition ps n (length(xs)-n) = [(tails xs)!!(length(xs)-n)] and then decrementing i. This recurrence is the instance of the right fold psn n psn1 = foldr (\ (psn1i,x) ps@(psni:_) -> (psni ++ (map(x:) psn1i)):ps) [[(tails xs)!!(length(xs)-n)]] $ zip (tail$init psn1) xs We can build ps n from n=0 onwards, given that ps 0 = map (const [[]]) (tails xs) we then observe that (tails xs)!!(length(xs)-n) === (reverse $ tails xs) !! n which, after a few simplifications, gives us import List powerset [] = [[]] powerset [x] = [[],[x]] powerset xs = [] : runit (tail rsxtails) ps0 where xstails = tails xs rsxtails = reverse xstails ps0 = map (const [[]]) $ tail xstails psn tn psn1 = foldr (\ xpsn1i ps@(psni:_) -> (xpsn1i++psni):ps) [[tn]] $ zipWith (\x psn1i -> map (x:) psn1i) xs (init $ psn1) runit [tn] _ = [xs] runit (tn:tns) psn1 = newps0 ++ (runit tns newps) where (newps0:newps) = psn tn psn1 There is still some room for improvement left. Actually, the following is a slightly faster version, showing off lazy evaluation: powerset [] = [[]] powerset [x] = [[],[x]] powerset xs = [] : runit (tail rsxtails) ps0 where xstails = tails xs rsxtails = reverse xstails ps0 = map (const [[]]) xstails psn tn psn1 = psnew where psnew = [tn]: (zipWith (++) (reverse (zipWith (\x psn1i -> map (x:) psn1i) xs (tail $ reverse$tail $ psn1))) psnew) runit [tn] _ = [xs] runit (tn:tns) psn1 = (last newps) ++ (runit tns newps) where newps = psn tn psn1

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RE: Powerset
by Simon Marlow 10 Jun '03

10 Jun '03

> The following seems to be a faster version of powerset that delivers > results strictly in the order of increasing cardinality (i.e., all > sets of size 1 first, then of size 2, etc). It seems to run faster > than any other ordered version of powerset posted so far. On GHCi, > length $ powerset [1..22] is computed roughly 4 times faster than > powerset3 given earlier. On Hugs, the powerset below also runs faster, > with less memory consumption and in fewer GC cycles, up to a limit of > 18 for the size of the input set. Just a word of warning: using GHCi or Hugs for comparison benchmarking will give unreliable results. Use GHC with -O. Cheers, Simon

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RE: Compiling hws with ghc 6
by Simon Marlow 10 Jun '03

10 Jun '03

> I'm trying to compile the haskell web server (from the > haskell-libs project > at sf.net) with ghc6 and I'm stuck on the last function in Util.hs: > > statMaybe filename = do > maybe_stat <- tryJust ioErrors (getFileStatus filename) > case maybe_stat of > Left e -> do > errno <- getErrorCode > if errno == eNOENT > then return Nothing > else ioError e > Right stat -> > return (Just stat) > > > What are the equivalents for getFileStatus and getErrorCode > these days? > > I suppose Foreign.C.Error.getErrno might substitute for > getErrorCode, but I'm stumped on getFileStatus. You're right about getErrno. getFileStatus is available from System.Posix. Cheers, Simon

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Bom dia haskell-cafe
by kandrak 10 Jun '03

10 Jun '03

Message to haskell-cafe(a)haskell.org Ola!!!! haskell-cafe GANHAMOS O PRÊMIO DE MELHOR SITE DO RAMO ======Estamos operando em Novo Formato====== Confira em: escuta21.kit.net ou http://www.escuta21.kit.net ei.... haskell-cafe Cuidado com o que fala ao Celular... ele tb tem ouvidos... para remover o haskell-cafe(a)haskell.org de nossa lista responda este e-mail e coloque remover nos perdoe o transtorno...ok? kandrak

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Re: on termination
by cwitty＠newtonlabs.com 10 Jun '03

10 Jun '03

"Cagdas Ozgenc" <co19(a)cornell.edu> writes: > This may be a little off topic, but I could not get much response from = > comp.theory, so here it goes: > > Is it possible to have a programming language that can be used to = > produce only the programs that terminate, but at the same time decide = > all recursive languages? Or does such limitation automatically reduce = > the class of languages that such a programming language decide to = > primitive-recursive? If you have any programming language (say Haskell), and if you have some formal system which is capable of proving termination properties of programs in your programming language (and in which proofs are machine-checkable), then you can create a new language "Terminating Haskell" simply by pairing each program with a proof of termination. Of course, if you start with a Turing-complete language, then your formal system is necessarily incomplete; this means there will be programs that do terminate but that you cannot prove terminate. So your programming language will include programs that decide all languages that you can prove recursive (in your formal system), but not all recursive languages. However, if your formal system is strong enough, it may be possible to prove termination of all the programs you really care about. Some theorem-proving systems (including ACL2 and PVS) are like this -- within the logic, you can write programs in a Turing-complete language, as long as you can prove termination. (More precisely, the language would be Turing-complete were it not for the termination requirement. In both cases, the "program" portion is fairly distinct from the "proof of termination" portion, so that it does make sense to talk about what the language would be like without the termination requirement.) It has long been a goal of mine to create a Haskell-like programming language where you could mark portions as being guaranteed to terminate. The compiler would prove termination whenever it could, but in cases where the termination proof was too complicated for automatic proofs, the programmer would be required to add an explicit proof of termination. Carl Witty

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Compiling hws with ghc 6
by Alistair Bayley 10 Jun '03

10 Jun '03

I'm trying to compile the haskell web server (from the haskell-libs project at sf.net) with ghc6 and I'm stuck on the last function in Util.hs: statMaybe filename = do maybe_stat <- tryJust ioErrors (getFileStatus filename) case maybe_stat of Left e -> do errno <- getErrorCode if errno == eNOENT then return Nothing else ioError e Right stat -> return (Just stat) What are the equivalents for getFileStatus and getErrorCode these days? I suppose Foreign.C.Error.getErrno might substitute for getErrorCode, but I'm stumped on getFileStatus.

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Please Help!
by David Savimbi 09 Jun '03

09 Jun '03

From: David Jonas Savimbi Johannesburg, South Africa Email: djsavimbi(a)phantomemail.com June 9th, 2003. Dear Sir, It is my humble pleasure to write you this letter irrespective of the fact that you do not know me. However, I got your name through your country business directory here in my search for a reliable and trustworthy person that can assist me confidently. My name is Mr.John Jonas Savimbi. I am the son of Late Dr. Jonas Savimbi from Angola. I am 29 years old and I have got two younger sisters of same blood. Our mother died almost a year ago. We are all fighting for political asylum in South Africa. We cannot find a home in Angola anymore because of the war that our late father fought with the government of Angola until he died in that war. The government of Angola is now mad at us because our late father also wanted to be president and caused the people to fight the war for him because he was the president of UNITA political movement of Angola. So now we are in South Africa and we are suffering too much because we don't have money and the government of South Africa will not give jobs to asylum seekers. I am much concerned about my younger sisters who are finding it very difficult to manage in the situation. But I know that we should not suffer this way. I know that I must not let my younger sisters get into trouble because of money. So after consideration I am hereby begging for your assistance to help me to recover the sum of USD $29 Million which is my inheritance from my late mother. My late mother had taken this money with her to Spain in a diplomatic metal box marked (Precious Stones). Subsequently she lodged the metal box (As precious Stones) with a Securities and Valuables Protection company in Spain. I am supposed to be the beneficiary in the event of her death. However, all effort I made to go Spain to claim was refused by the Spainish embassy. And this was while it was still possible for me to travel. Now I cannot travel anywhere anymore. So in the situation that we are facing now, I must find somebody who can go to the Spain on my behalf. I understand that I will have to transfer my beneficiary rights unto you. I am willing to do so in the hope that you are a God fearing person who will not abandon us after you have the money. So from the bottom of my heart I am giving you 20% of the all the money. Once we have enough to sustain us sufficiently, you may be come our fund manager and invest the rest wisely for us. If you will be kind to assist us, please inform me urgently. Kind regards to you and your family. Sincerely, David Jonas savimbi

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RE: Naive question on lists of duplicates
by Stecher, Jack 08 Jun '03

08 Jun '03

Thanks so much for the reply. On Thu, Jun 06, 2003 at 08:06 PM, Dylan Thurston wrote: > Was there actually a problem with the efficiency of your first code? No -- it was untested, and as I developed more of the code in Haskell, I found that there were slight differences between what I thought we needed to do and what my co-worker had in mind. So, even if my co-worker goes back to writing things in SAS, this has already been helpful for clarifying requirements. In particular, it turns out that he needs to know when promotions overlap for the same SKU, as this is an indication that the data we've received are invalid. I tested the mergeSort to make sure I didn't have any errors, though I used the fairly standard one. It was much faster than a sort in SAS, at least with a PROC SQL, though I ran into size limitations because I had to compile on the Windows side. (We don't have gcc installed on our UNIX side, so ghci will work but ghc won't compile my code.) Since I'm analyzing roughly 600MB of data, I will probably add a step or two in order to chunk the data. In any case, I'm not noticing any obvious inefficiencies, but my Haskell programming is self-taught, and this is my first attempt at solving a real problem at work using Haskell, so I figured I'd get feedback from the list. > (Unless this is really a one-shot deal, I suspect using Ints for dates > is a bad decision...) When I first read this message, I thought, "Well, this really is only a one-shot deal." However, as I thought more about this, I decided that I should write this so that we can use it in case another client comes along with similar data for us to analyze on another project. So I will change this and define a date type, or else I'll read the ghc documentation and learn how to use what's in the time library. > import List(sortBy, insertBy) > > data PromotionRec = PR {sku :: String, store :: String, startDate :: Int, endDate :: Int, amount::Float} As it turns out, the same promotions are always on across all stores. Thus, each SKU/startDate/endDate will seem to have a duplicate promotion. Also, I don't need the amount information, so I wrote the import function so that it would ignore the amount information. One further change: the SKU and store are identified by their number, not their descriptions. The new data type is like this: data PromoRec = PR {startDate, endDate, skuID, storeID :: Int} deriving Show though I will likely implement a better show function and will, as noted above, change the dates to a date type. The file is a fixed-width file, so I just do this: loadData :: Handle -> IO [String] loadData handle = do s <- hGetContents handle return (lines s) toPromoRecs :: [String] -> [PromoRec] toPromoRecs [] = [] toPromoRecs (x:xs) = (PR (read (take 8 x)) (read (take 8 (drop 8 x))) (read (take 20 (drop 16 x))) (read (take 20 (drop 36 x)))) : toPromoRecs xs There's probably a much more clever way to do this, but it seems fairly fast. The file allowed 20 spaces for the SKU and store numbers, but they're at most 7 digits long. Again, I'll need to change the first and second reads to some function that converts a string in the form yyyymmdd into a date type (or I'll need to write one). > compareStart, compareEnd :: PromotionRec -> PromotionRec -> Ordering > compareStart x y = compare (startDate x) (startDate y) > compareEnd x y = compare (endDate x) (endDate y) This is helpful; I'll also need to add a function like this: compareSku :: PromoRec -> PromoRec -> Ordering compareSku x y = compare (skuID x) (skuID y) > overlap :: [PromoRec] -> [[PromoRec]] > overlap l = filter (lambda l. length l > 1) > (overlap' [] (sortBy compareStart l)) > > overlap' _ [] = [] > overlap' active (x:xs) = > let {active' = dropWhile (lambda y. endDate y < startDate x) active} in > (x:active') : overlap' (insertBy compareEnd x active') xs Okay; I see what additional modifications I should make. I need to add a step sort by store and delete duplicate stores where the SKU, start date, and end date are the same. But I should be able to get there from here. > The key is that, by keeping a list of the currently active promotions > in order sorted by the ending date, we only need to discared an > initial portion of the list. Good insight. Many thanks. > You could get a moderately more efficient implementation by keeping > the active list as a heap rather than a list. I had thought about that, and took the BinomialHeap.hs file from Okasaki, but I must have a typo somewhere, because I was having typing clashes that I couldn't easily clarify. At least, when I loaded the BinomialHeap.hs into Hugs, it didn't complain, but when I tried to create an empty heap using the heapEmpty function, Hugs screamed at me. I got scared and fled the scene, retreating into the safety of lists. Thanks again, Jack

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Naive question on lists of duplicates
by Stecher, Jack 07 Jun '03

07 Jun '03

Hi, all. I have an exceedingly simple problem to address, and am wondering if there are relatively straightforward ways to improve the efficiency of my solution. The task is simply to look at a lengthy list of stock keeping units (SKUs -- what retailers call individual items), stores, dates that a promotion started, dates the promotion ended, and something like sales amount; we want to pull out the records where promotions overlap. I will have dates in yyyymmdd format, so there's probably no harm in treating them as Ints. My suggestion went something like this (I'm not at my desk so I don't have exactly what I typed): > data PromotionRec = PR {sku :: String, store :: String, startDate :: Int, endDate :: Int, amount::Float} > > match :: PromotionRec -> [PromotionRec] -> [PromotionRec] > match _ [] = [] > match x (x:xs) = filter (meet x) xs > > nomatch :: PromoRec -> [PromotionRec] -> [PromotionRec] > nomatch _ [] = [] > nomatch x (x:xs) = filter (nomeet x) xs > > meet :: PromoRec -> PromoRec -> Bool > meet x y = and [startDate x <= endDate y, startDate y <= startDate x] > > nomeet :: PromoRec -> PromoRec -> Bool > nomeet x y = not (meet x y) > > overlaps :: [PromoRec] -> [[PromoRec]] > overlaps [] = [] > overlaps (x:xs) = (x : match x xs) : (overlaps (nomatch x xs)) > > overlap :: [PromoRec] -> [[PromoRec]] > overlap [] = [] > overlap (x:xs) = filter g1 (overlaps (x:xs)) where > g1 ys = (length ys) > 1 What I sent might have been slightly different, and I might have some typos in the above (as I'm composing from memory at the keyboard), but that's the rough idea: treat this like a quicksort, pulling out the records that overlap the first record, consing the first record onto the list, and then consing the resulting list onto the same function applied to the records that didn't overlap. As a last step, delete the records that were not on promotion while anything else was on promotion. I'm pretty confident that this will be more efficient than my colleague's SAS code, as he was comparing each record to every other record (giving n (n-1) comparisons). It seems like this, in the worst case where everything is on promotion at distinct times, will compare the first record to (n-1) records, the second to (n-2) records, etc., giving n (n-1)/2 comparisons. Thus, while this is worst-case O(n^2), it seems like it should have at most half as much work to do as the earlier approach in SAS. On the other hand, in the best case, when everything is on promotion at the same time, there should be something like n-1 comparisons made and then that should be it. So it seems like, depending on how frequently promotions co-occur for this retailer, the above should be somewhere between O(n) and O(n^2) time complexity. Since these people are always having some sale or other, I suspect this won't be much worse than O(n log n). Is there anything that is an obvious improvement in efficiency -- some clever tricks with the fold functions, some way of loading the data into some sort of convenient structure first, etc -- that I could easily implement? Please share your thoughts. Many thanks, Jack Stecher jack.stecher(a)retek.com

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Re: Collecting values from Functors?
by Graham Klyne 07 Jun '03

07 Jun '03

[Moved to haskell-cafe] At 20:40 04/06/03 +0200, Tomasz Zielonka wrote: > > > > I'm trying to figure if there's any way I can use (say) monads to > collect > > > > values from a Functor. > > > > > > > > For example, suppose I have a tree of some values that supports > fmap, is > > > > there any way I can use the fmap function to collect a list of all > the node > > > > values? > > > > > > No, you need a fold to do that. > > > Or a variant of Functor constructor class that I have proposed some time > > ago on comp.lang.functional: > > > > class FunctorM t where > > fmapM :: Monad m => (a -> m b) -> (t a -> m (t b)) > > fmapM_ :: Monad m => (a -> m b) -> (t a -> m ()) > > fmapM_ f t = fmapM f t >> return () > > > > instance FunctorM [] where > > fmapM = mapM > > fmapM_ = mapM_ I've done a little playing with this, which seems to work on a small scale, and am just wanting to check if I am properly understanding your idea... 'Arc' is a small part of a data structure I am playing with, which is currently a Functor. I've made this an instance of FunctorM, defining fmapM which has some recognizable similarity with fmap. Finally, there's a monad type CollectNodes using Control.Monad.State and constructor function mungeNode to actually apply the transformation and collect results. It seems to work -- is this roughly what you envisaged? [[ -- spike-FunctorM.hs import Control.Monad.State class FunctorM t where fmapM :: Monad m => (a -> m b) -> (t a -> m (t b)) fmapM_ :: Monad m => (a -> m b) -> (t a -> m ()) fmapM_ f t = fmapM f t >> return () data Arc lb = Arc { asubj, apred, aobj :: lb } deriving (Eq, Show) instance Functor Arc where fmap f (Arc s p o) = Arc (f s) (f p) (f o) instance FunctorM Arc where -- fmapM :: (lb -> m l2) -> Arc lb -> m (Arc l2) fmapM f (Arc s p o) = do { s' <- f s ; p' <- f p ; o' <- f o ; return $ Arc s' p' o' } -- CollectNodes a b is a state transformer on a state of -- type '[a]', which additionally returns a value of type 'b'. type CollectNodes a b = State [a] b -- constructor State { runState :: (s -> (a, s)) } -- runState :: State s a -> s -> (a, s) -- evalState :: State s a -> s -> a -- execState :: State s a -> s -> s -- mapState :: ((a, s) -> (b, s)) -> State s a -> State s b -- withState :: (s -> s) -> State s a -> State s a -- instance MonadState s (State s) -- get :: m s -- (CollectNodes a b) [a] -- put :: s -> m () -- modify :: (MonadState s m) => (s -> s) -> m () -- gets :: (MonadState s m) => (s -> a) -> m a mungeNode :: lb -> CollectNodes lb (Maybe lb) mungeNode lab = do { modify (lab:) -- accumulate labels ; return (Just lab) -- return modified label } a1 = Arc "s1" "p1" "o1" r1 = runState ( fmapM mungeNode a1 ) [] ]] I think, but haven't worked out the details, that one could define fmap in terms of fmapM. (I read somewhere about an identity Monad, but can't recall the reference -- I think that might do it.) I'm also harbouring a suspiscion that this FunctorM framework might be subsumed by gmap and friends, but I'll leave that for another day. #g ------------------- Graham Klyne <GK(a)NineByNine.org> PGP: 0FAA 69FF C083 000B A2E9 A131 01B9 1C7A DBCA CB5E

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RE: Network.CGI
by Simon Peyton-Jones 06 Jun '03

06 Jun '03

If anyone cares to write some (Haddockised), we'd be happy to paste it into the source code. Simon | -----Original Message----- | From: haskell-cafe-admin(a)haskell.org [mailto:haskell-cafe-admin@haskell.org] On | Behalf Of Thomas L. Bevan | Sent: 04 June 2003 08:29 | To: haskell-cafe(a)haskell.org | Subject: Network.CGI | | Can anyone point me to some documentation on the Network.CGI package? | | The wrapper fn is clear enough but I'm not sure what | pwrapper is for or the nature of the contract in connectToCGIScript | | Tom | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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RE: How do I create an IOError exception?
by Bayley, Alistair 05 Jun '03

05 Jun '03

Ahh... I see now (thanks). This advice (in the documentation for System.IO.Error.ioError) threw me: "The ioError variant should be used in preference to throw to raise an exception within the IO monad because it guarantees ordering with respect to other IO operations, whereas throw does not." After reading this I assumed that I should also use the exceptions in System.IO.Error i.e. the IOError type. But of course this is not the case; ioError has type Exception -> IO a. -----Original Message----- From: Hal Daume III [mailto:hdaume@ISI.EDU] Sent: 04 June 2003 16:32 To: Bayley, Alistair Cc: haskell-cafe(a)haskell.org Subject: Re: How do I create an IOError exception? In Control.Exception, there's: > data Exception = ... > | DynException Dynamic > | ... and > throwIO :: Exception -> IO a so, what you want is probably something like: > if rc < 0 > then throwIO (DynException (toDyn ("Err", rc))) > else ... and then when you catch, use fromDyn(amic) to get the value out if you can predict its type... HTH. - Hal -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume On Wed, 4 Jun 2003, Bayley, Alistair wrote: > (I know I'm asking some noddy questions, but hey, that's what this list is > for...) > > How do I create IOError exceptions? System.IO.Error has two functions that > create IOErrors: userError and mkIOError. However, both of them take a > String (I assume containing a description of the problem), and mkIOError > takes optional Handle and FilePath args. > > http://www.haskell.org/ghc/docs/latest/html/base/System.IO.Error.html > > What I'd like to do is stuff some more information into the exception (a bit > like Java exceptions), along the lines of: > > > mkIOError :: a -> IOError > > where I could choose to use it like this (ociHandleAlloc is a foreign C > function): > > > handleAlloc2 handleType env ptr = do > > rc <- ociHandleAlloc env ptr handleType 0 0 > > if rc < 0 > > then ioError (mkIOError ("Couldn't allocate handle", rc)) > > else peek ptr > > > When I catch the exception (currently in main) I would like to interrogate > it to get the values I stuffed in it (in this case a (String, Int) tuple), > and then do some error reporting by calling another function which decodes > the error number. > > Is this the wrong way to go about error handling? Or is it relatively simple > to create your own IOErrors? Have I missed something in the docs? > ***************************************************************** The information in this email and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal professional or other privilege or may otherwise be protected by work product immunity or other legal rules. It must not be disclosed to any person without our authority. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. *****************************************************************

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FFI Help
by Matthew Donadio 05 Jun '03

05 Jun '03

Hi all, I am just starting to experiment with FFI, and am running into a problem. I was to create an FFI to the lgamma(3) found in many of the newer libm implementations. My code follows the sig. The lgamma function works. The gamma function core dumps (I am using ghc 5.04.3) on me. gdb reports a SIGSEGV in signgam(), but I'm not sure why. I believe that I need to use the monad because signgam is only valid after lgamma returns. Does anyone have an idea what I am doing wrong? Thanks. -- Matthew Donadio <m.p.donadio(a)ieee.org> > module Gamma (gamma, lgamma) where > import System.IO.Unsafe > foreign import ccall "math.h lgamma" lgammaC :: Double -> IO Double > foreign import ccall "math.h signgam" signgamC :: IO Int > lgamma :: Double -> Double > lgamma x = unsafePerformIO $ lgammaC x > gamma :: Double -> Double > gamma x = unsafePerformIO $ gammaIO x > gammaIO :: Double -> IO Double > gammaIO x = do lg <- lgammaC x > s <- signgamC > return $ fromIntegral s * exp lg

3 4

How do I create an IOError exception?
by Bayley, Alistair 04 Jun '03

04 Jun '03

(I know I'm asking some noddy questions, but hey, that's what this list is for...) How do I create IOError exceptions? System.IO.Error has two functions that create IOErrors: userError and mkIOError. However, both of them take a String (I assume containing a description of the problem), and mkIOError takes optional Handle and FilePath args. http://www.haskell.org/ghc/docs/latest/html/base/System.IO.Error.html What I'd like to do is stuff some more information into the exception (a bit like Java exceptions), along the lines of: > mkIOError :: a -> IOError where I could choose to use it like this (ociHandleAlloc is a foreign C function): > handleAlloc2 handleType env ptr = do > rc <- ociHandleAlloc env ptr handleType 0 0 > if rc < 0 > then ioError (mkIOError ("Couldn't allocate handle", rc)) > else peek ptr When I catch the exception (currently in main) I would like to interrogate it to get the values I stuffed in it (in this case a (String, Int) tuple), and then do some error reporting by calling another function which decodes the error number. Is this the wrong way to go about error handling? Or is it relatively simple to create your own IOErrors? Have I missed something in the docs? ***************************************************************** The information in this email and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal professional or other privilege or may otherwise be protected by work product immunity or other legal rules. It must not be disclosed to any person without our authority. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. *****************************************************************

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RE: Help: writing ffi bindings to a C library
by Bayley, Alistair 04 Jun '03

04 Jun '03

Thanks. This is very helpful. I'm making much better progress now. Is alloca the idiomatic technique when you want to create a pointer to a pointer? Or are there other ways? Initially I tried to pass a Ptr (Ptr SomeType), but I couldn't because Ptr has no constructors To create values of type Ptr I must use the functions in Foreign.Marshal.Alloc (and Foreign.Marshal.Utils). Correct? -----Original Message----- From: Marcin 'Qrczak' Kowalczyk [mailto:qrczak@knm.org.pl] Sent: 02 June 2003 10:46 To: haskell-cafe(a)haskell.org Subject: Re: Help: writing ffi bindings to a C library Dnia pon 2. czerwca 2003 09:58, Bayley, Alistair napisał: > Yes, I had considered this (writing an abstraction layer in C). I have > decided initially to try doing it in Haskell, because I thought that > Haskell would be a better choice for writing abstraction layers (not as > verbose as C). You can write it in Haskell too and I would recommend that - unless the C library uses some passing convention Haskell cannot handle (e.g. passing structs by value, or having variable argument count, or relying heavily on macros). > Getting back to my question, can I use functions that take twice-deref'ed > pointers as args? This is a function that effectively returns some of its > work in "out" arguments Sure. You can use libraries documented in the Haskell FFI proposal. > e.g. a C function like this: > > int someCFunction(SomeType **ptrptr, int i) > > (It would create an opaque structure and point *ptrptr at it. If it fails > then it would return a negative value.) > > Is it simply a case of declaring it like this (in ghc): > > data SomeType > > type SomeTypeRef = Ptr SomeType > > foreign import ccall "blah.h someCFunction" someCFunction :: > > Ptr SomeTypeRef -> Int -> Int foreign import ccall "blah.h someCFunction" someCFunction :: Ptr SomeTypeRef -> CInt -> IO CInt haskellWrapper :: Int -> IO (Maybe SomeTypeRef) haskellWrapper arg = alloca $ \ptr -> do res <- someCFunction ptr (fromIntegral arg) if res < 0 then return Nothing else liftM Just (peek ptr) You can raise an IO error instead. You can wrap the result in a ForeignPtr if it should be finalized when it's garbage collected. You can use hsc2hs to access integer constants, enumeration values and structs from Haskell, or write C wrappers inline inside Haskell source (e.g. to turn macros into functions). -- __("< Marcin Kowalczyk \__/ qrczak(a)knm.org.pl ^^ http://qrnik.knm.org.pl/~qrczak/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ***************************************************************** The information in this email and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal professional or other privilege or may otherwise be protected by work product immunity or other legal rules. It must not be disclosed to any person without our authority. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. *****************************************************************

2 1

Network.CGI
by Thomas L. Bevan 04 Jun '03

04 Jun '03

Can anyone point me to some documentation on the Network.CGI package? The wrapper fn is clear enough but I'm not sure what pwrapper is for or the nature of the contract in connectToCGIScript Tom

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Please help me
by David Savimbi 03 Jun '03

03 Jun '03

From: David Jonas Savimbi Johannesburg, South Africa Email: djsavimbi(a)phantomemail.com June 3rd, 2003. Dear Sir, It is my humble pleasure to write you this letter irrespective of the fact that you do not know me. However, I got your name through your country business directory here in my search for a reliable and trustworthy person that can assist me confidently. My name is Mr.John Jonas Savimbi. I am the son of Late Dr. Jonas Savimbi from Angola. I am 29 years old and I have got two younger sisters of same blood. Our mother died almost a year ago. We are all fighting for political asylum in South Africa. We cannot find a home in Angola anymore because of the war that our late father fought with the government of Angola until he died in that war. The government of Angola is now mad at us because our late father also wanted to be president and caused the people to fight the war for him because he was the president of UNITA political movement of Angola. So now we are in South Africa and we are suffering too much because we don't have money and the government of South Africa will not give jobs to asylum seekers. I am much concerned about my younger sisters who are finding it very difficult to manage in the situation. But I know that we should not suffer this way. I know that I must not let my younger sisters get into trouble because of money. So after consideration I am hereby begging for your assistance to help me to recover the sum of USD $29 Million which is my inheritance from my late mother. My late mother had taken this money with her to Spain in a diplomatic metal box marked (Precious Stones). Subsequently she lodged the metal box (As precious Stones) with a Securities and Valuables Protection company in Spain. I am supposed to be the beneficiary in the event of her death. However, all effort I made to go Spain to claim was refused by the Spainish embassy. And this was while it was still possible for me to travel. Now I cannot travel anywhere anymore. So in the situation that we are facing now, I must find somebody who can go to the Spain on my behalf. I understand that I will have to transfer my beneficiary rights unto you. I am willing to do so in the hope that you are a God fearing person who will not abandon us after you have the money. So from the bottom of my heart I am giving you 20% of the all the money. Once we have enough to sustain us sufficiently, you may be come our fund manager and invest the rest wisely for us. If you will be kind to assist us, please inform me urgently. Kind regards to you and your family. Sincerely, David Jonas savimbi

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Please help me
by David Savimbi 03 Jun '03

03 Jun '03

From: David Jonas Savimbi Johannesburg, South Africa Email: djsavimbi(a)phantomemail.com June 3rd, 2003. Dear Sir, It is my humble pleasure to write you this letter irrespective of the fact that you do not know me. However, I got your name through your country business directory here in my search for a reliable and trustworthy person that can assist me confidently. My name is Mr.John Jonas Savimbi. I am the son of Late Dr. Jonas Savimbi from Angola. I am 29 years old and I have got two younger sisters of same blood. Our mother died almost a year ago. We are all fighting for political asylum in South Africa. We cannot find a home in Angola anymore because of the war that our late father fought with the government of Angola until he died in that war. The government of Angola is now mad at us because our late father also wanted to be president and caused the people to fight the war for him because he was the president of UNITA political movement of Angola. So now we are in South Africa and we are suffering too much because we don't have money and the government of South Africa will not give jobs to asylum seekers. I am much concerned about my younger sisters who are finding it very difficult to manage in the situation. But I know that we should not suffer this way. I know that I must not let my younger sisters get into trouble because of money. So after consideration I am hereby begging for your assistance to help me to recover the sum of USD $29 Million which is my inheritance from my late mother. My late mother had taken this money with her to Spain in a diplomatic metal box marked (Precious Stones). Subsequently she lodged the metal box (As precious Stones) with a Securities and Valuables Protection company in Spain. I am supposed to be the beneficiary in the event of her death. However, all effort I made to go Spain to claim was refused by the Spainish embassy. And this was while it was still possible for me to travel. Now I cannot travel anywhere anymore. So in the situation that we are facing now, I must find somebody who can go to the Spain on my behalf. I understand that I will have to transfer my beneficiary rights unto you. I am willing to do so in the hope that you are a God fearing person who will not abandon us after you have the money. So from the bottom of my heart I am giving you 20% of the all the money. Once we have enough to sustain us sufficiently, you may be come our fund manager and invest the rest wisely for us. If you will be kind to assist us, please inform me urgently. Kind regards to you and your family. Sincerely, David Jonas savimbi

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RE: Networking : PortNumber
by Simon Marlow 03 Jun '03

03 Jun '03

> Sorry, > > I've just worked it out. > > PortNumber is an instance of the class Enum > so we can use > > toEnum :: Int -> a It's also an instance of the Integral class, which means you can just write integral constants of type PortNumber. eg. (80 :: PortNumber) is valid. Also, the universal integral conversion function 'fromIntegral' can be used for converting values of other integral types into PortNumbers (this is preferable to toEnum). Cheers, Simon

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Networking : PortNumber
by Thomas L. Bevan 03 Jun '03

03 Jun '03

Hi, How can I take some input and convert this into a PortID ? I don't quite understand why the constructor PortNumber doesn't have the signature PortID = PortNumber Int | ... Instead it is PortID = PortNumber PortNumber where PortNumber is not a member of the Read class. Tom

1 1

a readFile problem
by Naudts, Guido 02 Jun '03

02 Jun '03

Hallo, I have the following problem: my program asks the user for a command, when the command is executed a new command is asked (this is no problem ; an example is in the HUgs distribution namely Main.hs in the Prolog example. However one of the commands is: read filename i.e. read a file and display it. I do not succeed in implementing this. Could anyone give an example of: reading commands in a loop where one of the commands is the read command mentionned above. Or is it not possible in Haskell? I have already wated a lot of time on this, so if anyone gives me an answer I will be very gratefull. Greetings,

3 2

RE: Help: writing ffi bindings to a C library
by Bayley, Alistair 02 Jun '03

02 Jun '03

Yes, I had considered this (writing an abstraction layer in C). I have decided initially to try doing it in Haskell, because I thought that Haskell would be a better choice for writing abstraction layers (not as verbose as C). The idea was to write the Haskell-C bindings at as low a level as possible (i.e. directly to the OCI libraries), and then build up from there. Although the bindings may be ugly, I thought it would have been easier to build higher layers in Haskell rather than C. However, if you think it's probably better to build the first layer in C, then I'll do that. Getting back to my question, can I use functions that take twice-deref'ed pointers as args? This is a function that effectively returns some of its work in "out" arguments e.g. a C function like this: int someCFunction(SomeType **ptrptr, int i) (It would create an opaque structure and point *ptrptr at it. If it fails then it would return a negative value.) Is it simply a case of declaring it like this (in ghc): > data SomeType > type SomeTypeRef = Ptr SomeType > foreign import ccall "blah.h someCFunction" someCFunction :: Ptr SomeTypeRef -> Int -> Int Or must C functions that are to be called from Haskell return results only in the return value? -----Original Message----- From: Ronald Legere [mailto:rjljr2@yahoo.com] Sent: 31 May 2003 15:25 To: Bayley, Alistair; 'haskell-cafe(a)haskell.org' Subject: RE: Help: writing ffi bindings to a C library One strategy is to wrap that funtion in another function (in C) that encapsulates the 'typical' call you want to make. THen import this function into haskell. In any event, start with something simpler, to get the hang of it. Try to write a function (in C) that adds two integers,or prints something and import that in to haskell. There are some examples floating around to get you started, but I can't find them at the moment on the CVS tree. Anyone? Also, read "Tackling the awkward squad" (Google it) Ron --- "Bayley, Alistair" <Alistair_Bayley(a)ldn.invesco.com> wrote: > So... > > I'm still trying to write this Oracle OCI ffi > binding. Can anyone tell me > how to declare the Haskell type for this function: > > sword OCIEnvCreate (OCIEnv **envp, ub4 mode, dvoid > *ctxp, > dvoid *(*malocfp)(dvoid *ctxp, > size_t size), > dvoid *(*ralocfp)(dvoid *ctxp, > dvoid *memptr, size_t > newsize), > void (*mfreefp)(dvoid *ctxp, > dvoid *memptr), > size_t xtramem_sz, dvoid > **usrmempp); > > Note that when I use it, I'm passing 0 (NULL) into > almost all of the args, > so the usage in C is typically: > > rc = OCIEnvCreate(&envhp, OCI_DEFAULT, 0, 0, 0, 0, > 0, 0); > > i.e. I don't care about most of the args, so that > should make the Haskell > declaration simpler. Some of the arguments are > pointers to functions, for > example. > > What I can't figure out is how to declare the type > of the first arg. Is is > Ptr (Ptr OCIEnv) ? > > Here's what I have so far (not much, I know): > > > module Main where > > import Foreign > > import Foreign.C.Types > > import Foreign.C.String > > import Foreign.Ptr > > > data OCIEnv > > > foreign import ccall "oci.h OCIEnvCreate" > ociEnvCreate :: Ptr OCIEnv -> > Int -> Int -> Int -> Int -> Int -> Int -> Int -> Int > ***************************************************************** The information in this email and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal professional or other privilege or may otherwise be protected by work product immunity or other legal rules. It must not be disclosed to any person without our authority. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. *****************************************************************

2 1

How to... use haskell 'functions' in C(++) sources ?
by Antoine Utonium 02 Jun '03

02 Jun '03

Everything is in the title. I like "simplicity" of Haskell and would like to use what i write in my c/c++ programs. Thanks a lot by advance.

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Re: Eval in Haskell
by Lauri Alanko 02 Jun '03

02 Jun '03

[Moving to cafe, this is only barely Haskell-related.] On Sun, Jun 01, 2003 at 04:16:36PM -0700, oleg(a)pobox.com wrote: > Eval of the kind > let x = 1 in eval "x" > is plainly an abomination. I agree, though not because of the optimization issues but rather as a matter of principle: a closed variable should be _closed_, it should not be visible to anything but the body of the let-expression that binds it. And an externally acquired eval-able expression is definitely "anything but". Nevertheless, this abomination is supported even by some scheme implementations: guile> (define local-environment (procedure->syntax (lambda (exp env) env))) guile> (define (eval-where-x-bound exp) ... (let ((x 'foo)) (local-eval exp (local-environment)))) guile> (eval-where-x-bound '(list 'x x)) (x foo) > Incidentally, restricting eval to top-level or "standard" bindings is > not a significant limitation. It is, in general, a very good practice > to apply eval to closed expressions only. This depends entirely on what you want to achive with eval, so I don't think the "in general" is justified. If you just want to evaluate closed expressions whose results are printable and readable, then you really just have an embedded interpreter which happens to read the same language as your source code. On the other hand, it is common for perl programs and especially shell scripts to eval configuration files with the explicit purpose that the configuration file may alter variables which are bound in the main program. For such usage, it is essential that the main program and the evaled file access the same enviroment. (Naturally a configuration file shouldn't be allowed to mess with _everything_ in the main program, but I don't think perl allows detailed adjustment of the bindings in the environment. Some schemes do, though.) Lauri Alanko la(a)iki.fi

2 2

RE: Help: writing ffi bindings to a C library
by Bayley, Alistair 31 May '03

31 May '03

So... I'm still trying to write this Oracle OCI ffi binding. Can anyone tell me how to declare the Haskell type for this function: sword OCIEnvCreate (OCIEnv **envp, ub4 mode, dvoid *ctxp, dvoid *(*malocfp)(dvoid *ctxp, size_t size), dvoid *(*ralocfp)(dvoid *ctxp, dvoid *memptr, size_t newsize), void (*mfreefp)(dvoid *ctxp, dvoid *memptr), size_t xtramem_sz, dvoid **usrmempp); Note that when I use it, I'm passing 0 (NULL) into almost all of the args, so the usage in C is typically: rc = OCIEnvCreate(&envhp, OCI_DEFAULT, 0, 0, 0, 0, 0, 0); i.e. I don't care about most of the args, so that should make the Haskell declaration simpler. Some of the arguments are pointers to functions, for example. What I can't figure out is how to declare the type of the first arg. Is is Ptr (Ptr OCIEnv) ? Here's what I have so far (not much, I know): > module Main where > import Foreign > import Foreign.C.Types > import Foreign.C.String > import Foreign.Ptr > data OCIEnv > foreign import ccall "oci.h OCIEnvCreate" ociEnvCreate :: Ptr OCIEnv -> Int -> Int -> Int -> Int -> Int -> Int -> Int -> Int -----Original Message----- From: Ronald Legere [mailto:rjljr2@yahoo.com] Sent: 21 May 2003 20:32 To: 'haskell-cafe(a)haskell.org' Subject: Re: Help: writing ffi bindings to a C library Agreeing with David, but I like to use types rather than (). YOu can do this because, in ghc, you can write: data Blah with no rhs, and it is understood to be an 'opaque' type. Ghc beleives any claims you make about passing Ptr Blah back and forth to C in your foreign import declarations <* Grin *>. As for passing structures back and forth, and accessing the components, you can do it from Haskell or from the "c-side"... I can send you a sample of doing it from haskell if you wish. Ron --- David Roundy <droundy(a)abridgegame.org> wrote: > On Wed, May 21, 2003 at 04:27:10PM +0100, Bayley, > Alistair wrote: > > construct a Ptr a? What type should "a" be?). > > Unless you actually need to ever access their > contents, I'd just define the > pointers to be of type Ptr (), essentially like a > void * pointer in C. No > need to use Storable if they are only ever accessed > through C functions > (which I would hope would be the case). > -- ***************************************************************** The information in this email and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal professional or other privilege or may otherwise be protected by work product immunity or other legal rules. It must not be disclosed to any person without our authority. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. *****************************************************************

2 1

RE: how to break up a large module?
by Simon Peyton-Jones 30 May '03

30 May '03

A non-exported function can be inlined, and its definition deleted. If there is only one call site, it can be inlined no matter how big it is. S | -----Original Message----- | From: haskell-cafe-admin(a)haskell.org [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Jerzy | Karczmarczuk | Sent: 30 May 2003 14:04 | To: haskell-cafe(a)haskell.org | Subject: Re: how to break up a large module? | | Simon Marlow wrote: | | > Be careful about accidental overloading: | ... | | > Be careful with exports. Prune export lists to just those functions | > which need to be exported. | | | How a too long export list can slow-down the target program? | | Jerzy Karczmarczuk | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

2 1

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by tony2003＠yahoo.ca 30 May '03

30 May '03

1 0

RE: how to break up a large module?
by Simon Marlow 30 May '03

30 May '03

> I recently spent a couple of hours breaking up a large module > (2.5k lines) > into several smaller modules. When I finally got it working, > I found that > my program took about 60% longer to run. This was running ghc with -O > optimization. > > Any suggestions how to go about breaking up a module in such > a way that it > doesn't slow things down? Do I just have to go adding INLINE > directives to > all my functions? Or is there some other trick I could use? Be careful about accidental overloading: GHC will specialise if it can see the uses of a function within a single module, but not when the function is in another module. Put type signatures on everything, and consider using SPECIALISE pragmas to eliminate overloading. Be careful with exports. Prune export lists to just those functions which need to be exported. Cheers, Simon

2 1

RE: how to break up a large module?
by Simon Peyton-Jones 30 May '03

30 May '03

60% longer is a lot. I'm surprised. I'd try compiling the whole thing both ways with profiling on and see if that reveals anything S | -----Original Message----- | From: haskell-cafe-admin(a)haskell.org [mailto:haskell-cafe-admin@haskell.org] On Behalf Of David | Roundy | Sent: 30 May 2003 13:06 | To: haskell-cafe(a)haskell.org | Subject: how to break up a large module? | | I recently spent a couple of hours breaking up a large module (2.5k lines) | into several smaller modules. When I finally got it working, I found that | my program took about 60% longer to run. This was running ghc with -O | optimization. | | Any suggestions how to go about breaking up a module in such a way that it | doesn't slow things down? Do I just have to go adding INLINE directives to | all my functions? Or is there some other trick I could use? | | For the moment I've reverted to my single big file method, but it certainly | would be handy to be able to break that up so that it wouldn't take so long | to recompile. | -- | David Roundy | http://www.abridgegame.org | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

1 0

how to break up a large module?
by David Roundy 30 May '03

30 May '03

I recently spent a couple of hours breaking up a large module (2.5k lines) into several smaller modules. When I finally got it working, I found that my program took about 60% longer to run. This was running ghc with -O optimization. Any suggestions how to go about breaking up a module in such a way that it doesn't slow things down? Do I just have to go adding INLINE directives to all my functions? Or is there some other trick I could use? For the moment I've reverted to my single big file method, but it certainly would be handy to be able to break that up so that it wouldn't take so long to recompile. -- David Roundy http://www.abridgegame.org

1 0

Immediate business proposal
by DR MICHAEL KAGIDA 30 May '03

30 May '03

DR MICHAEL KAGIDA LAGOS-NIGERIA A very good day to you. We have an immediate business proposal that involves US$ 30,000,000.00 Million Dollars which we will like to invest under your custody.Once I receive a message from you notifying me of your interest, the details of the transaction/the terms and condition of sharing regarding the business would then be brought to your knowledge. Your urgent response will be highly appreciated and will swiftly bring us to the commencement of the transaction. We hope to conclude. this transaction within 10-14 working days Do not forget to contact me on the receipt of this e-mail address. And please you have to maintain absolute confidentiality as regards this pending transaction. You have to send me your phone and fax numbers so I can contact you. I urgently await your response. Best Regards, Dr MICHAEL KAGIDA NB:PLEASE QUOTE REFERENCE NUMBER FM/01 IN YOUR RESPONSE.

1 0

Hello haskell-cafe !
by DR MICHAEL KAGIDA 30 May '03

30 May '03

DR MICHAEL KAGIDA LAGOS-NIGERIA A very good day to you. We have an immediate business proposal that involves US$ 30,000,000.00 Million Dollars which we will like to invest under your custody.Once I receive a message from you notifying me of your interest, the details of the transaction/the terms and condition of sharing regarding the business would then be brought to your knowledge. Your urgent response will be highly appreciated and will swiftly bring us to the commencement of the transaction. We hope to conclude. this transaction within 10-14 working days Do not forget to contact me on the receipt of this e-mail address. And please you have to maintain absolute confidentiality as regards this pending transaction. You have to send me your phone and fax numbers so I can contact you. I urgently await your response. Best Regards, Dr MICHAEL KAGIDA NB:PLEASE QUOTE REFERENCE NUMBER FM/01 IN YOUR RESPONSE.

1 0

Re: GHCi ASCII art
by andrew cooke 29 May '03

29 May '03

there's a program that generates these things - it's called "figlet" and you can waste hours trying different fonts etc.. _ _ __ _| |__ ___(_) / _` | '_ \ / __| | | (_| | | | | (__| | \__, |_| |_|\___|_| |___/ andrew [moved to cafe] John Sincock <jss(a)au.mensa.org> writes: > since the content of this list is in general so completely beyond > my feeble Haskell comprehension, I feel I must make a nuisance of > myself with some inane criticism of the GHCi ASCII art ... ! -- http://www.acooke.org

7 6

Question about Haskell lexer and parser.
by Serguey Zefirov 28 May '03

28 May '03

Hello haskell-cafe, Question is really about layout rules. If the first lexeme of a module is not a "module" keyword, we insert {n}, where n is the indentation of first lexeme. Then we apply function L to the list of lexemes and stack of layouts: L ({n}:lexemes) [] One of first case definitions of L covers this situation: L ({n}:ts) [] | n>0 = {:L ts [n] -- n>0 means that layout isn't explicit. It's obvious that after our first {n} comes usual lexeme, like Var. This situaiton is covered in the following L rule: L (t:ts) (m:ms) | m /= 0 = }:L (t:ts) ms -- Haskell Report says that we here -- should recognize parsing errors -- but how we can do that in lexer? So we finally get {:}:...lexemes... Is it right? I think this situation is wrong. -------------------------- What I do. I just try to entertain and educate myself trying to implement Haskell interpreter or compiler (what will come first). My approach is to get highly modular and declarative structure of a system (current Haskell lexer uses monads, which I found unsatisfable). -- Best regards, Serguey mailto:sz@uc.ru

1 0

how to track down out-of-bounds error?
by David Roundy 28 May '03

28 May '03

In some code which uses UArrays, I'm getting the following error: Fail: Ix{Int}.index: Index (3723) out of range ((0,3722)) Presumably this means I'm trying to access one beyond the end of an array. The problem is trying to figure out where I'm doing this. Unfortunately, I have only been able to see this error on a rather large test repository, where it takes seven minutes for the test to show up. Any suggestions how I might most easily track this bug down? -- David Roundy http://www.abridgegame.org

4 3

Why is this program leaking memory ?
by Ahn Ki-yung 28 May '03

28 May '03

I'm playing with the lazy abstract machine of 1997 Sestoft's paper. I implemented this with haskell using ghc 5.04.3. I lambda lifted the original input expression to prevent memory leak of "Lazy Abstarc Machine", and it works fine. I tested with the leaky program example of the Sestoft 97 paper. [kyagrd@OBIWAN transform]$ cat test.txt let ff = \n.let i=\x.x in ff i in ff ff I printed the 4 tuples (Heap, Exp, Env, Stack) each step. It goes on and on like this. [kyagrd@OBIWAN transform]$ ./main.exe < test.txt let "ff"=\"n".let "i"=\"x"."x" in "ff" "i" in "ff" "ff" let 1=\2.let 3=\4.4 in 1 3 in 1 1 let -1=\2.-1 -3 -3=\4.4 in -1 -1 let -1=\2.-1 -3 -3=\4.4 in -1 -1 let 0=\0.1 2 0=\0.0 in 0 0 ([],let 0=\0.1 2 0=\0.0 in 0 0,[],[]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],0 0,[2,1],[]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],0,[2,1],[2]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],\0.1 2,[2,1],[2]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],1 2,[2,2,1],[]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],1,[2,2,1],[1]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],\0.1 2,[2,1],[1]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],1 2,[1,2,1],[]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],1,[1,2,1],[1]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],\0.1 2,[2,1],[1]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],1 2,[1,2,1],[]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],1,[1,2,1],[1]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],\0.1 2,[2,1],[1]) ([(2,(\0.1 2,[2,1])),(1,(\0.0,[2,1]))],1 2,[1,2,1],[]) ... But Strangely the Haskell heap memory leaks if I omit printing every step but only print the result. [kyagrd@OBIWAN transform]$ ./main.exe < test.txt let "ff"=\"n".let "i"=\"x"."x" in "ff" "i" in "ff" "ff" let 1=\2.let 3=\4.4 in 1 3 in 1 1 let -1=\2.-1 -3 -3=\4.4 in -1 -1 let -1=\2.-1 -3 -3=\4.4 in -1 -1 let 0=\0.1 2 0=\0.0 in 0 0 c:\MyDoc\iFolder\kyagrd\LAZY\transform\main.exe: fatal error: RTS exhausted max heap size (268435456 bytes) I attach my source code except for the parser and lexer stuff. I switched between two main' and main fucntion. Why, in the Main module, "printNreduce" do not leak but while "printeval" leaks ? Can't understand this behavior. module Main where import Syntax import Parser import Lazyeval import MonadST printeval q = if q'==q then print q' else printeval q' where q' = reduce q printNreduce q = if q'==q then print q' else (print q >> printNreduce q') where q' = reduce q -- print every step does not leak main = do s <- getContents let e = parser s e' <- printNpreprocess e printNreduce ([],e',[],[]) -- print only result leak !! main' = do s <- getContents let e = parser s e' <- printNpreprocess e printeval ([],e',[],[]) printNpreprocess e = print e >> print e1 >> print e2 >> print e3 >> print e' >> return e' where ((ns,[]),e1) = evalST ([1..],[]) (uniqueify e) e2 = lambdalift negate e1 (ns3,e3) = evalST ns (normalize e2) e' = bruijnize e3 {- Syntax.hs preprocessing of lazy language for evaluation Ahn Ki-yung -} module Syntax where import MonadST import List data Lambda id = Var id | App (Lambda id) (Lambda id) | Lam id (Lambda id) | Let [(id,Lambda id)] (Lambda id) -- deriving (Eq, Ord) deriving (Eq, Ord, Read) instance Show a => Show (Lambda a) where show (Var s) = show s show (Lam s e) = '\\':show s ++ '.':show e show (App e e') = showParenExpr e ++ ' ' : showParenExpr e' where showParenExpr e@(Var s) = show e showParenExpr e = '(':show e++")" show (Let h e) = "let" ++ concat [' ':show s++'=':show e|(s,e)<-h] ++ " in " ++ show e instance Functor Lambda where fmap f (Var x) = Var (f x) fmap f (App e e') = App (fmap f e) (fmap f e') fmap f (Lam x e) = Lam (f x) (fmap f e) fmap f (Let ds e) = Let [(f x,fmap f e)|(x,e)<-ds] (fmap f e) transform (getId,putId,popId) = trans where newId x = putId x >> getId x trans (Var x) = do { x'<-getId x; return (Var x') } trans (App e e1) = do { e'<-trans e; e1'<-trans e1; return (App e' e1') } trans (Lam x e) = do { x'<-newId x; e'<-trans e; popId x; return (Lam x' e') } trans (Let ds e) = do let (xs,es) = unzip ds xs'<-mapM newId xs es'<-mapM trans es let ds' = zip xs' es' e'<-trans e mapM popId xs return (Let ds' e') uniqueify :: (Eq a, Eq b) => Lambda a -> StateTrans ([b],[(a,b)]) (Lambda b) uniqueify = transform (getId,putId,popId) where getId x = do (_,l) <- readST let Just (_,n) = find ((x==).fst) l return n putId x = do (n:ns,l) <- readST writeST (ns,(x,n):l) popId x = do (ns,l) <- readST writeST (ns,deleteBy (\p-> \q->fst p==fst q) (x,head ns) l) normalize :: Lambda a -> StateTrans [a] (Lambda a) normalize = normExpr where newvar = do (x:xs) <- readST writeST xs return x normExpr (Var x) = return (Var x) normExpr (Lam x e) = do e' <- normExpr e return (Lam x e') normExpr (App e (Var x)) = do e' <- normExpr e return (App e' (Var x)) normExpr (App e1 e2) = do x <- newvar e1' <- normExpr e1 e2' <- normExpr e2 return (Let [(x,e2')] (App e1' (Var x))) normExpr (Let ds e) = do let (vs,es) = unzip ds es' <- mapM normExpr es let ds' = zip vs es' e' <- normExpr e return (Let ds' e') (f,g)@@(x,y) = (f x, g y) -- assumes uniquified normalized e lambdalift topv e = Let ds (subsfree [] topv d' e') where d' = delcombs [] d ds = [ (topv x, foldr Lam (subsfree fv topv d' e) fv) | (x,fv,e)<-d' ] (d,fv,e') = llift e delcombs combs d = if combs/=combs' then delcombs combs' [(x,fv\\combs',e) | (x,fv,e)<-d] else d where combs' = [x | (x,[],_)<-d] -- assumes uniquified and no lets -- done llift subsfree bv topv d e = subs e where var' = Var . topv subs (Var x) = case find (\(y,_,_)->x==y && not (elem x bv)) d of Just (_,fv,_) -> foldl App (var' x) (map var' fv) _ -> Var x subs (App e e') = App (subs e) (subs e') subs (Lam x e) = Lam x (subs e) -- assumes uniquified llift (Var x) = ([], [x], Var x) llift (App e e') = (d1++d2, union fv1 fv2, App e1 e2) where (d1,fv1,e1) = llift e (d2,fv2,e2) = llift e' llift (Lam x e) = (d, fv\\[x], Lam x e') where (d, fv, e') = llift e llift (Let ds e) = (dd++d', fv, e') where (d, fv, e') = llift e xds = map ((id,llift)@@) ds dd = [ (x, fv\\[x], e) | (x,(d,fv,e))<-xds ] d' = foldr (++) d [d | (_,(d,_,_))<-xds] bruijnize e = bruijn [] e elemIndex' x xs = (\(Just i)->i) $ elemIndex x xs bruijn xs (Var x) = Var (elemIndex' x xs) bruijn xs (Lam x e) = Lam 0 (bruijn (x:xs) e) bruijn xs (App e e') = App (bruijn xs e) (bruijn xs e') bruijn xs (Let ds e) = Let [(0,bruijn xs' e) | e<-es] (bruijn xs' e) where (vs,es) = unzip ds xs' = vs ++ xs module Lazyeval where import Syntax import List data StackElem = Update Int | Point Int deriving Eq instance Show StackElem where show (Update i) = '#':show i show (Point i) = show i getHeap p = (\(Just x)->snd x) . find ((p==).fst) setHeap t@(p,e) = insertBy (mapF2 fst $ flip compare) t . deleteBy (mapF2 fst (==)) t where mapF2 g f2 x y = f2 (g x) (g y) reduce (h,App e (Var i),env,s) = (h,e,env,Point(env!!i):s) reduce (h,Lam _ e,env,Point p:s) = (h,e,p:env,s) reduce (h,Var i,env,s) = (h,e',env',s') where s' = case e' of Lam _ _ ->s; _->Update p:s (e',env') = getHeap p h p = env!!i reduce (h,Lam x e,env,Update p:s) = (setHeap (p,(Lam x e,env)) h,Lam x e,env,s) reduce (h,Let ds e,env,s) = (h',e,env',s) where es = snd (unzip ds) h' = newhs ++ h env' = newps ++ env newhs = zip newps [(e,env')|e<-es] newps = take n [m+n,m+n-1..] m = if null h then 0 else (head . fst . unzip) h n = length es reduce q = q fix f x = if x'==x then x else fix f x' where x' = f x eval = fix reduce module MonadST (readST, writeST, applyST, evalST, valueST, stateST, StateTrans) where data StateTrans s a = ST { st :: s -> (s,a) } instance Monad (StateTrans a) where return x = ST (\s -> (s, x)) m >>= f = ST (\s -> let (s',x) = st m s in st (f x) s') readST = ST (\s -> (s, s)) writeST s' = ST (\s -> (s', ())) applyST f = ST (\s -> (f s, ())) evalST s m = st m s valueST s = snd . evalST s stateST s = fst . evalST s

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RE: Question about Haskell lexer and parser.
by Simon Marlow 28 May '03

28 May '03

> Question is really about layout rules. > If the first lexeme of a module is not a "module" keyword, we insert > {n}, where n is the indentation of first lexeme. Then we apply > function L to the list of lexemes and stack of layouts: > > L ({n}:lexemes) [] > > One of first case definitions of L covers this situation: > L ({n}:ts) [] > | n>0 = {:L ts [n] -- n>0 means that layout isn't explicit. > It's obvious that after our first {n} comes usual lexeme, like Var. > This situaiton is covered in the following L rule: > > L (t:ts) (m:ms) > | m /= 0 = }:L (t:ts) ms -- Haskell Report says that we here > -- should recognize parsing errors > -- but how we can do that in lexer? This rule only applies if there is a parse error on the next token (t). The report explains what this means in "Note 5". It does mean that layout processing can't be done entirely in the lexer, the parser has to be involved too. This is what makes parsing layout in Haskell hard. Take a look at some of the existing Haskell parsers to see how it can be done: there are two in GHC's source tree (one in GHC itself, another in libraries/haskell-src). Hugs's parser is written in C but uses similar techniques. nhc98's parser uses parsing combinators IIRC. Cheers, Simon

2 1

Re: Haskell Employers
by David Barton 27 May '03

27 May '03

Ashley Yakeley writes: > So are there companies that pay people to write in Haskell, or indeed in > any functional language? I do know of Galois Connections in Oregon; are > there others? > > As a Haskell developer looking for a job, this would certainly be useful > information... I can't say we are using Haskell (well, we have for a small thing or two, but not enough to justify hiring someone for it). However, I think that the use of higher level languages in general are increasing. We'll be looking for someone soon to develop, not only in C++ or Java, but also in a new systems design language called Rosetta (http://www.sldl.org) I predict that the use of such languages will increase in the next few years --- slowly at first, then faster --- particularly in the systems and hardware design arenas, even more than in software. Dave Barton EDAptive Computing

1 0

Happy
by Pablo Dejuan 27 May '03

27 May '03

Hi. I've just started using haskell and I've some problems with the generated file of happy, the example.hs. When I try to load it, It complains that isAlpha, isDigit and isSpace are variables not in scope. This means I should import a particular module to do so? TIA

2 1

failure notice
by MAILER-DAEMON＠foshan.net 27 May '03

27 May '03

Hi. This is the qmail-send program at foshan.net. I'm afraid I wasn't able to deliver your message to the following addresses. This is a permanent error; I've given up. Sorry it didn't work out. <hauj(a)foshan.net>: Sorry, no mailbox here by that name. vpopmail (#5.1.1) --- Below this line is a copy of the message. Return-Path: <haskell-cafe(a)haskell.org> Received: (ctmail 25865 invoked from network); 27 May 2003 09:57:10 -0000 Received: from unknown (HELO hauj) (218.13.218.251) by 0 with SMTP; 27 May 2003 09:57:10 -0000 From: "haskell-cafe" <haskell-cafe(a)haskell.org> Subject: =?GB2312?B?VE+jumhhdWpAZm9zaGFuLm5ldLvh1LHK1SE=?= 17:52:54:7 To: hauj(a)foshan.net Content-Type: text/html;charset="GB2312" Sender: haskell-cafe <haskell-cafe(a)haskell.org> Reply-To: wangxiao1999(a)163.com Date: Tue, 27 May 2003 17:52:54 +0800 X-Priority: 4 X-Mailer: Microsoft Outlook Express 5.50.4133.2400 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; charset=gb2312"> <META content="MSHTML 6.00.2462.0" name=GENERATOR></HEAD> <BODY>     ÄúºÃ£¡     CCTV-2£º·ÇµäŽÙœø¡¢ÉýÎÂÐÅÏ¢»¯£¬µç×ÓÉÌÎñÐÎÊÆŽóºÃ£¬ÄúžÐÊÜÏ²ÔÃÁËÂð£¿     ÔÚÖøÃûÉÌÃ³ÍøÕŸÖÐÇáËÉÑ°ÕÒÂò·œÓëÂô·œµÄÁªÏµ·œÊœ£š¹«ËŸ¡¢µç»°¡¢Ž«Õæ¡¢ÁªÏµÈË¡¢ÓÊŒþ¡¢µØÖ·µÈ£©£¬²¢ÓëÎŽÀŽ¿Í»§È¡µÃÁªÏµ£¬ÊÇ×îÓÐÐ§¡¢×î¿ìœÝ¡¢×îµÍ³É±ŸµÄÓªÏú·œ·š¡£     ÉÌÖÇµç×ÓÉÌÎñÈíŒþŸÍÄÜ°ïÄúÊµÏÖÍêÃÀ£¡Íš¹ý»¥ÁªÍøÀŽ»ñÈ¡ÒµÎñ¶©µ¥µÄµç×ÓÉÌÎñÓÅÐãÈíŒþ£¬ÄÜÊ¹ÄúÔ¶Àë·ÇµäÀ§ÈÅ£¬Íš¹ý»¥ÁªÍøÀŽÊµÏÖÓ¯Àû£¡     Ö»ÐèŒž·ÖÖÓ£¬ÉÌÖÇµç×ÓÉÌÎñÈíŒþ¿Éœ«ÄúµÄ²úÆ·»òÏîÄ¿ÐÅÏ¢ÔÚ1554ŒÒ¹©ÇóÐÅÏ¢ÆœÌš·¢²Œ¡¢2147ŒÒÍøÕŸÖÐËÑË÷ÄúÎŽÀŽµÄ¿Í»§¡£ÒÔ×îµÍµÄ³É±Ÿ¡¢ÓÃ×î¹ãµÄ×ÊÔŽ¡¢ŽŽ×îºÃµÄÐ§Òæ.ÈíŒþ×¢²áºÅ£ºÉîÛÚDGY-2002-0321     »¶ÓÏÂÔØÈíŒþÊÔÓÃ£¬Ãâ·ÑË÷È¡ÓÃ»§ÃûÓëÃÜÂë.³ÏÕ÷ºÏ×÷»ï°é¡£     ÇëÓÊŒþ»òÔÚÏßQQ:39398668 3203821 33669329  ÍõÐ¡œã Â¬ÏÈÉú</BODY></HTML> ÉÌÖÇµç×ÓÉÌÎñÈíŒþÉÌÎñ×ÉÑ¯

1 0

I am just starting out
by Andy Schmidt 27 May '03

27 May '03

Hi, my name is Andy Schmidt and I stumbled across this website as I started my quest for the best programming language. I am only in college and I am trying to learn as many languages as I can. I hope haskell will be the one I stick with. -Andy _________________________________________________________________ Help STOP SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail

11 16

Re:For All Educational Personnel
by epcinquire＠epcparts.com 27 May '03

27 May '03

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1 0

re: re: 你好
by 高明 26 May '03

26 May '03

1 0

Italian-crafted Rolex - only $65 - $140!! Free SHIPPING ! !
by james＠hello.com 26 May '03

26 May '03

1 0

monomorphism restriction
by John Meacham 24 May '03

24 May '03

Just a random thought, What would be the effect of lifting the monomorphism restriction under the condition that assignments which would normally be subject to the restriction must be memoized on the class constraint parameter by the implementation? it seems that this would solve the problems which inspired the monomorphism restriction since the value can be shared among all instantiations when the type is the same. I am posting this to haskell-cafe because it might just be half-baked. John -- --------------------------------------------------------------------------- John Meacham - California Institute of Technology, Alum. - john(a)foo.net ---------------------------------------------------------------------------

1 0

Shooting yourself in the foot, a contribution
by Alain Cremieux 23 May '03

23 May '03

Hi, If I may contribute to the language definitions (http://burks.brighton.ac.uk/burks/language/index.htm) concerning *Haskell* : You shoot yourself in the foot. The gun fires half an hour later (lazy evaluation), blows your hand instead of your foot (polymorphism), and leaves you in a state of total amnesia (memory leaks). Alain

8 8