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  • The sieve of Eratosthenes in F#

    - by IVlad
    I am interested in an implementation of the sieve of eratosthenes in purely functional F#. I am interested in an implementation of the actual sieve, not the naive functional implementation that isn't really the sieve, so not something like this: let rec PseudoSieve list = match list with | hd::tl -> hd :: (PseudoSieve <| List.filter (fun x -> x % hd <> 0) tl) | [] -> [] The second link above briefly describes an algorithm that would require the use of a multimap, which isn't available in F# as far as I know. The Haskell implementation given uses a map that supports an insertWith method, which I haven't seen available in the F# functional map. Does anyone know a way to translate the given Haskell map code to F#, or perhaps knows of alternative implementation methods or sieving algorithms that are as efficient and better suited for a functional implementation or F#?

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  • Linear Recurrence for very large n

    - by Android Decoded
    I was trying to solve this problem on SPOJ (http://www.spoj.pl/problems/REC/) F(n) = a*F(n-1) + b where we have to find F(n) Mod (m) where 0 <= a, b, n <= 10^100 1 <= M <= 100000 I am trying to solve it with BigInteger in JAVA but if I run a loop from 0 to n its getting TLE. How could I solve this problem? Can anyone give some hint? Don't post the solution. I want hint on how to solve it efficiently.

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  • How to access a list in OCaml

    - by Erik
    I want to write a function that could check every item in a list is true or false. If at least one element is false, it will return true, so that: assert_eq "checkFalse [true; false; true]" (checkFalse [true; true; true]) false; assert_eq "checkFalse [false; false]" (checkFalse [false; true]) true; I am an absolute beginner in OCaml and I don't know how to approach this. I tried using a for loop, something like: let rec checkFalse (bools: bool list) : bool = for i = 0 to bools.length do if bools.length == false then false else... (I don't know how to continue) Then it said "Unbound record field...." I also tried using find like: if (find false bools != Not_found) then true else false But my ways did not work. I came from a Java background. Thank you very much!

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  • Problem with pattern matching in ocaml

    - by Antony
    I wrote the function used to decompose a Boolean function, the problem is that the compilation I get this : "Warning 5: this function application is partial, maybe some arguments are missing." How can I solve this problem? I've set wrong the patter matching or I can not run this operation with pattern matching The code is the following: let rec decomposition state_init state prec formula = match formula with And form -> (fun () -> let f1 = List.hd form in let f2 = And(List.tl form )in let new_state = Forms (state_init,f1) in decomposition state_init new_state state f1; decomposition state_init new_state state f2; Hashtbl.add graph new_state (("",false,state :: []) , []) ; let x = Hashtbl.find graph state in let succ = state :: snd x in let (desc,last,ptrs) = fst x in Hashtbl.replace graph state ( ("And-node",last,ptrs) , succ))

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  • Swing code in sockets

    - by asb
    I am learning swings for making GUI. I was thinking which is the best possible way in case of socket with swings. 1. The whole swing code goes in the server file. All the handlers and logic in on server side. Client only create socket. 2. The server have logic part. The code for the swing to display interface goes on client side. Client Creates stream to send / rec. data from server. Whch is the good way out of 2 ?

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  • mail function in windows application

    - by Ranjana
    i have used a mail function. after inserting every record simultaneously from multiple PC. I have set a timer which ticks for every 2 min. while it ticks it start to check the record and it send the mail. i have used background worker for that.in Bgdworker the mail fn will be called. private void timer_Startsendingemail_Tick(object sender, EventArgs e) { if (!bgw_startsendingemail.IsBusy) bgw_startsendingemail.RunWorkerAsync(); } private void bgw_startsendingemail_DoWork(object sender, DoWorkEventArgs e) { sendingMail(); sendingsms(); } in sendingmail() fn the datas fetch from database and send the mail based on email settings to all the inserted rec. but the prob is the timer triggered for 2 min often , and the process will be working fine and nothing there in log file but sometime the mail is not received by the clients.how to fix the prob. how to find out where it is strucked... its hard to find the problem. any idea over this??????????/

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  • How to open form action in Jquery Dialog

    - by user342391
    I have a form: <form style="display: inline;" action="/player.php" method="post"> <input type="hidden" name="recname" value="'.$row['name'].'"> <input type="hidden" name="recordingdesc" value="'.$row['description'].'"> <input type="hidden" name="reclink" value="$_SESSION['customerid'].'-'.$row['timestamp'].'.wav"> <button type="submit" class="tooltip table-button ui-state-default ui-corner-all" title=" rec"><span class="ui-icon ui-icon-volume-on"></span></button> </form> and i want player.php to open in a modal dialog and be able to display the post information how can this be done.

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  • Using an IN clause in Vb.net to save something to the database using SQL

    - by Rob
    I have a textbox and a button on a form. I wish to run a query (in Vb.Net) that will produce a query with the IN Values. Below is an example of my code myConnection = New SqlConnection("Data Source=sqldb\;Initial Catalog=Rec;Integrated Security=True") myConnection.Open() myCommand = New SqlCommand("UPDATE dbo.Recordings SET Status = 0 where RecID in ('" & txtRecID.Text & "') ", myConnection) ra = myCommand.ExecuteNonQuery() myConnection.Close() MsgBox("Done!", _ MsgBoxStyle.Information, "Done") When I enter a single value it works but when I enter values with commas it throws an error: "Conversion failed when converting the varchar value '1234,4567' to data type int." Could someone please help me to solve this or if there is an alternative way? Many Thanks

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  • Does the XML specification states that parser need to convert \n\r to \n always, even when \n\r appe

    - by mic.sca
    Hi, I've stumbled in a problem handling the \line-feed and \carriage-return characters in xml. I know that, according to http://www.w3.org/TR/REC-xml/#sec-line-ends, xml processors are required to replace any "\n\r" or lone "\r" sequences with "\n". The specification states that this has to be the behaviour for handling any "external parsed entity", does this apply to CDATA sections inside of an element as well? thank you, Michele I'm sure that msxml library for example converts every \n\r" or lone "\r" sequences to "\n", regardless of their being in a cdata section or not.

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  • Getting every nth Element of a Sequence

    - by Alexander Rautenberg
    I am looking for a way to create a sequence consisting of every nth element of another sequence, but don't seem to find a way to do that in an elegant way. I can of course hack something, but I wonder if there is a library function that I'm not seeing. The sequence functions whose names end in -i seem to be quite good for the purpose of figuring out when an element is the nth one or (multiple of n)th one, but I can only see iteri and mapi, none of which really lends itself to the task. Example: let someseq = [1;2;3;4;5;6] let partial = Seq.magicfunction 3 someseq Then partial should be [3;6]. Is there anything like it out there? Edit: If I am not quite as ambitious and allow for the n to be constant/known, then I've just found that the following should work: let rec thirds lst = match lst with | (_,_,x)::t -> x::thirds t | _ -> [] Would there be a way to write this shorter?

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  • Weird exception with OLEDB Parameter Insert

    - by Seamus MacKenzie
    Getting a strange error when trying to insert data into an Access database using parameters. the line where I am getting a problem is :- thisCommand.CommandText = "INSERT INTO Events (Venue_ID, Date_Start, Date_End, Time_Start, Time_End, Name, Description, Event_Type, Buy_Tickets_URL) VALUES (@VenID, @DStart, @DEnd, @evTime, @evTime, @Name, @Des, @EvType, @SysUrl);"; string desc = GetDesc(rec.EvName); thisCommand.Parameters.AddWithValue("@Des", desc); thisCommand.ExecuteNonQuery(); None of the other parameters cause a problem but when trying to insert data to the description field I get a database exception saying the field is too small to accept the amount of data. The problem is my program is only trying to insert 3 characters when it throws the error and the Description field is a memo so should be able to hold up to 65000+ characters. When inserting a value manually in the CommandText everything works fine so it must be something to do with the parameter properties.

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  • Fibonacci Numbers in Haskell

    - by boraer
    Hi everbody I need to change my F# code to Haskell code but I am so new in Haskell and I can not this My code simply read data from keyboard if data not an integer return an error message then calculate the n fibonacci number then writes to a list after that writes the list into a txt file Here is my code open System let rec fib n = match n with |0->0 |1->1 |2->1 |n->fib(n-1)+fib(n-2);; let printFibonacci list = for i=0 to (List.length list)-1 do printf "%d " (list.Item(i));; let writeToFile list = let file = System.IO.File.Create("C:\out2.txt") let mutable s ="" let writer = new System.IO.StreamWriter(file) try for i=0 to (List.length list)-1 do s <- list.Item(i).ToString() writer.Write(s+" ") finally writer.Close() file.Dispose() printfn "Writed To File" let mutable control = true let mutable num = 0 while control do try printfn "Enter a Number:" num <- Convert.ToInt32(stdin.ReadLine()) let listFibonacci = [for i in 0 .. num-1->fib(i)] printFibonacci(listFibonacci) printfn "\n%A"(listFibonacci) writeToFile(listFibonacci) control<-false with | :? System.FormatException->printfn "Number Format Exception"; Console.ReadKey true|>ignore

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  • F# operator over-loading question

    - by jyoung
    The following code fails in 'Evaluate' with: "This expression was expected to have type Complex but here has type double list" Am I breaking some rule on operator over-loading on '(+)'? Things are OK if I change '(+)' to 'Add'. open Microsoft.FSharp.Math /// real power series [kn; ...; k0] => kn*S^n + ... + k0*S^0 type Powers = double List let (+) (ls:Powers) (rs:Powers) = let rec AddReversed (ls:Powers) (rs:Powers) = match ( ls, rs ) with | ( l::ltail, r::rtail ) -> ( l + r ) :: AddReversed ltail rtail | ([], _) -> rs | (_, []) -> ls ( AddReversed ( ls |> List.rev ) ( rs |> List.rev) ) |> List.rev let Evaluate (ks:Powers) ( value:Complex ) = ks |> List.fold (fun (acc:Complex) (k:double)-> acc * value + Complex.Create(k, 0.0) ) Complex.Zero

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  • how to get a sub list from a list in ocaml

    - by romerun
    Hi, I'm looking at the List document. It seems the library does not provide a sublist function. I'm trying to get list of elements from i to j. Now I have to write it as: let rec sublist list i j = if i j then [] else (List.nth list i) :: (sublist list (i+1) j) which is quite concise but I'm questioning the efficiency of List.nth, because if it's O(n), I would rather have to write it in a less concise way. I'm wondering why didn't they provide List.sublist func, if List.nth is not O(1), because it's such a quite common operation..

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  • Function which returns itself

    - by Juliet
    As a purely academic exercise (read "because I have no life"), I'm trying to write a function f which accepts another function g, executes g for its side effect, and returns itself. So I have this: let rec f g x = ignore(g x) fun y -> f g y F# complains: fun y -> f g y;; -------------^^^^^ C:\Users\Juliet\AppData\Local\Temp\stdin(8,14): error FS0001: Type mismatch. Expecting a 'a but given a 'b -> 'a The resulting type would be infinite when unifying ''a' and ''b -> 'a' If it works the way I intend, then I could write: let printer = f (printfn "%s") printer("this")("is")("so")("useless")("its")("awesome!") // prints: // this // is // so // useless // its // awesome Is it possible to write a function like this?

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  • Whhether or not it is an elegant way in such a situation?

    - by z_axis
    There are some text files which needed to be manipulated line by line. I wrote a withFile function as below: let withFile fn handle = let rec iter_lines fh = try handle (input_line fh); iter_lines fh with _ -> close_in fh in iter_lines (open_in fn);; So i can manipulate each file as : withFile "file1.txt" (fun line -> (*...*)) withFile "file2.txt" (fun line -> (*...*)) ... But i amnot sure how to exit elehantly when i donot want to handle all lines. For example: withFile "file3.txt" (fun line -> (*when the line meets some condition, i will exit without handling other lines*) ); Any suggestion is appreciated !

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  • Help me to explain the F# Matrix transpose function

    - by Kev
    There is a Matrix transpose function: let rec transpose = function | (_::_)::_ as M -> List.map List.head M :: transpose (List.map List.tail M) | _ -> [] [[1; 2; 3]; [4; 5; 6]; [7; 8; 9]] |> transpose |> printfn "%A" It works fine. What does ( _ :: _ ) :: _ mean? I don't understand the whole code! Who can explain it? Thank You!

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  • F# match char values

    - by rwallace
    I'm trying to match an integer expression against character literals, and the compiler complains about type mismatch. let rec read file includepath = let ch = ref 0 let token = ref 0 use stream = File.OpenText file let readch() = ch := stream.Read() let lex() = match !ch with | '!' -> readch() | _ -> token := !ch ch has to be an int because that's what stream.Read returns in order to use -1 as end of file marker. If I replace '!' with int '!' it still doesn't work. What's the best way to do this?

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  • What's some simple F# code that generates the .tail IL instruction?

    - by kld2010
    I'd like to see the .tail IL instruction, but the simple recursive functions using tail calls that I've been writing are apparently optimized into loops. I'm actually guessing on this, as I'm not entirely sure what a loop looks like in Reflector. I definitely don't see any .tail opcodes though. I have "Generate tail calls" checked in my project's properties. I've also tried both Debug and Release builds in Reflector. The code I used is from Programming F# by Chris Smith, page 190: let factorial x = // Keep track of both x and an accumulator value (acc) let rec tailRecursiveFactorial x acc = if x <= 1 then acc else tailRecursiveFactorial (x - 1) (acc * x) tailRecursiveFactorial x 1 Can anyone suggest some simple F# code which will indeed generate .tail?

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  • Looking for Haskell `group` alternative in F#

    - by Heather
    Haskell group descripted there: http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html#v:group example : group "Mississippi" = ["M","i","ss","i","ss","i","pp","i"] Is there simple F# way of doing it? I can implement something alike let rec sameCounter (data : list<float>) el same (ss : list<float * int>) = if data.Length > (el + 1) then if data.[el] = data.[el + 1] then sameCounter data (el + 1) <| same + 1 <| ss else if same > 0 then sameCounter data (el + 1) <| 0 <| (data.[el], same) :: ss else sameCounter data (el + 1) <| 0 <| ss else ss let group d = sameCounter d 0 0 [] but it's a bit ugly way I think, is there better variant?

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  • Writing lambda functions in Scala

    - by user2433237
    I'm aware that you can write anonymous functions in Scala but I'm having trouble trying to convert a piece of code from Scheme. Could anyone help me convert this to Scala? (define apply-env (lambda (env search-sym) (cases environment env (empty-env () (eopl:error 'apply-env "No binding for ~s" search-sym)) (extend-env (var val saved-env) (if (eqv? search-sym var) val (apply-env saved-env search-sym))) (extend-env-rec (p-name b-var p-body saved-env) (if (eqv? search-sym p-name) (proc-val (procedure b-var p-body env)) (apply-env saved-env search-sym)))))) Thanks in advance

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  • Home Networking Questions

    - by Eddie Parker
    Hello: I'm looking to wire my home with CAT-X (where X is probably going to be CAT-6, unless someone can convince me differently. ;) ). I'm seeking advice on what equipment I'll need for the job, and any things I should watch out for. It's a two story half-duplex I'll be wiring, roughly about 1800 sq ft. Here's what I believe I need so far: Bulk CAT-6 Ethernet cabling CM Rated Gigabit switch(es?) Patch panel Equipment for cutting, terminating wire, fishing through walls, etc Wall outlet covers, etc. Questions I have: Does it matter the MHz rating on the Ethernet cable? If so, why? I have two gigabit switches currently, an 8-port and a 5-port. Should I buy one massive switch to cover all the connections I need, or should I just chain the two together and buy a switch for however many other connections I need? Do I really need a patch panel? I understand it keeps the cables looking cleaner than coming out of a hole in the wall, but is there some other product I can use, perhaps combining a switch with a patch panel or some such? Ideally I'll have all this running out of a relatively small closet, so the less components (or smaller) the better. Any advice, links, or suggested product to use/avoid would be appreciated!

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  • USB To Serial under OpenSuse 11.3

    - by Lars
    I have a LogiLink USB-To-Serial adapter. This has the PL2303 chip inside. When I insert the device: [26064.927083] usb 7-1: new full speed USB device using uhci_hcd and address 9 [26065.076090] usb 7-1: New USB device found, idVendor=067b, idProduct=2303 [26065.076099] usb 7-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0 [26065.076105] usb 7-1: Product: USB-Serial Controller [26065.076110] usb 7-1: Manufacturer: Prolific Technology Inc. [26065.079181] pl2303 7-1:1.0: pl2303 converter detected [26065.091296] usb 7-1: pl2303 converter now attached to ttyUSB0 So the device is recognized and the converter is attached to ttyUSB0. When I do screen /dev/ttyUSB0 9600 I get the error: bash: /dev/ttyUSB0: Permission denied So I went looking in the file permissions. ls -l from the /dev folder reports: crw-rw---- 1 root dialout 188, 0 2011-04-26 15:47 ttyUSB0 I added my user lars to the dialout group. When I use the commands groups under lars it shows that I'm in the group. Though I still recieve the permissions denied error, as lars, and as root. I'm trying to connect to a console cable to configure some Cisco switches. My OS is OpenSuse 11.3 x86_64 with kernel version 2.6.34.7-0.7-desktop.

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  • Any Recommendations for a Web Based Large File Transfer System?

    - by Glen Richards
    I'm looking for a server software product that: Allows my users to share large files with: The general public securely to 1 or more people (notification via email, optionally with a token that gives them x period of time to download) Allows anyone in the general public to share files with my users. Perhaps by invitation. Has to be user friendly enough to allow my users to use this with out having to bug me as the admin. It needs to be a system that we can install on our own server (we don't want shared data sitting on anyone else's server) A web based solution. Using some kind or secure comms channel would be good too, eg, ssh Files to share could be over 1 GB. I found the question below. WebDav does not sound user friendly enough: http://serverfault.com/questions/86878/recommendations-for-a-secure-and-simple-dropbox-system I've done a lot of searching, but I can't get the search terms right. There are too many services that provide this, but I want something we can install on our own server. A last resort would be to roll my own. Any ideas appreciated. Glen EDIT Sorry Tom and Jeff but Glen specifically says that he's looking for a 'product' so given that I specialise in this field thought that my expertise in this area may have been of use to him. I don't see how him writing services is going to be easy for him to maintain going forward (large IT admin overhead) or simple for his users and the general public to work with.

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  • USB Hardware vs. Software Write Lock

    - by TreyK
    I'm in the market for a USB flash drive, and remember this cool feature a tiny 32MB flash drive of mine had: a write lock switch. This seemed like it would be an amazing feature to have as a shield against any nastiness happening to the drive on an unfamiliar computer. However, very few drives on the market offer this feature. Instead, it seems that forms of software protection are the more prominent method. This software protection causes me a bit of uneasiness, as it seems like this software wouldn't be nearly as bulletproof as a physical switch. Also, levels of protection seem to vary from product to product. Being able to protect certain folders from reading and/or writing would be nice, but is the security trade-off worth it? Just how effective can this software protection be? Wouldn't a simple format be able to clean any drive with software protection? My drive must also be compatible with Windows XP, Vista, and 7, as well as Linux and Mac. What would be the best way forward for getting a well-sized (~8GB) flash drive with a strong write protection implementation, for little or no more than a regular drive? Thanks.

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