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  • Haskell: type inference and function composition

    - by Pillsy
    This question was inspired by this answer to another question, indicating that you can remove every occurrence of an element from a list using a function defined as: removeall = filter . (/=) Working it out with pencil and paper from the types of filter, (/=) and (.), the function has a type of removeall :: (Eq a) => a -> [a] -> [a] which is exactly what you'd expect based on its contract. However, with GHCi 6.6, I get gchi> :t removeall removeall :: Integer -> [Integer] -> [Integer] unless I specify the type explicitly (in which case it works fine). Why is Haskell inferring such a specific type for the function?

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  • exceptions with python unicode encode/decode functions (why doesn't errors=ignore actually ignore th

    - by gatoatigrado
    Does anyone know why the string conversion functions throw exceptions when errors="ignore" is passed? How can I convert from regular Python string objects to unicode without errors being thrown? Thanks very much! python -c "import codecs; codecs.open('tmp', 'wb', encoding='utf8', errors='ignore').write('?????')" returns Traceback (most recent call last): File "", line 1, in File "/usr/lib/python2.6/codecs.py", line 686, in write return self.writer.write(data) File "/usr/lib/python2.6/codecs.py", line 351, in write data, consumed = self.encode(object, self.errors) UnicodeDecodeError: 'ascii' codec can't decode byte 0xd0 in position 0: ordinal not in range(128)

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  • bitset to dynamic bitset

    - by mr.bio
    Hi.. I have a function where i use bitset.Now i need to convert it to a dynamic bitset.. but i don't know how. Can somebody help me ? set<string> generateCandidates(set<string> ck,unsigned int k){ set<string> nk ; for (set<string>::const_iterator p = ck.begin( );p != ck.end( ); ++p){ for (set<string>::const_iterator q = ck.begin( );q != ck.end( ); ++q){ bitset<4> bs1(*p); bitset<4> bs2(*q); bs1|= bs2 ; if(bs1.count() == k){ nk.insert(bs1.to_string<char,char_traits<char>,allocator<char> >()); } } } return nk; }

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  • random() in python

    - by Arkapravo
    In python the function random() generates a random float uniformly in the semi-open range [0.0, 1.0). In principle can it ever generate 0.0 (i.e. zero) and 1.0 (i.e. unity)? What is the scenario in practicality?

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  • I'm having trouble with using std::stack to retrieve the values from a recursive function.

    - by Peter Stewart
    Thanks to the help I received in this post: http://stackoverflow.com/questions/2761918/how-do-i-use-this-in-a-member-function I have a nice, concise recursive function to traverse a tree in postfix order: void Node::postfix() { if (left != __nullptr) { left->postfix(); } if (right != __nullptr) { right->postfix(); } cout<<cargo<<"\n"; return; }; Now I need to evaluate the values and operators as they are returned. My problem is how to retrieve them. I tried the std::stack: #include <stack> stack <char*> s; void Node::postfix() { if (left != __nullptr) { left->postfix(); } if (right != __nullptr) { right->postfix(); } s.push(cargo); return; }; but when I tried to access it in main() while (!s.empty()) { cout<<s.top<<"\n"; s.pop; } I got the error: 'std::stack<_Ty::top': function call missing argument list; use '&std::stack<_Ty::top' to create a pointer to member' I'm stuck. Another question to follow shortly.

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  • Can't find applicationSupportDirectory?

    - by Frost Li
    There is always a pre-written function at AppDelegate: (NSString *)applicationSupportDirectory { NSArray *paths = NSSearchPathForDirectoriesInDomains(NSApplicationSupportDirectory, NSUserDomainMask, YES); NSString *basePath = ([paths count] > 0) ? [paths objectAtIndex:0] : NSTemporaryDirectory(); return [basePath stringByAppendingPathComponent:@"SyncFile"]; } However, I can't call this method outside this class: id _appDelegate = (SyncFile_AppDelegate *)[[NSApplication sharedApplication] delegate]; NSLog(@"%@", [_appDelegate applicationSupportDirectory]); The compiler warned me that it can't find method applicationSupportDirectory... Does anyone know what's wrong with my code? Thank you very much!

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  • Rails app w/ 2.2.0 embedd how to use ruby 1.8 vice 1.9

    - by Barb
    Hello all, I have just downloaded an app that is based on Rail 2.2.0 which is included in the app. I have just upgraded to Ruby 1.9 and I still have Ruby 1.8 on my machine. Is there a way I can tell this app to use Ruby 1.8 vice 1.9? Would it be easier to decouple the app from Rails 2.2.0 and upgrade it to Rails 2.3.6? If changing the rails would be easier, how do I do that?

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  • Microsoft C Compiler: Inline variable declaration?

    - by Rosarch
    I'm writing C in Visual Studio 2010. The compiler doesn't seem to want to let me use inline variable declarations. The following code produces an error: unsigned int fibonacci_iterative(unsigned int n) { if (n == 0) { return 0; } if (n == 1) { return 1; } unsigned int prev_prev = 0; // error unsigned int prev = 1; // error unsigned int next = 0; // error for (int term_number = 0; term_number < n; term_number++) { unsigned int temp = prev_prev + prev; prev = next; prev_prev = prev; next = temp; } return next; } Error: error C2143: syntax error : missing ';' before 'type' error C2143: syntax error : missing ';' before 'type' error C2143: syntax error : missing ';' before 'type' Why is this happening? Is there a setting to make the compiler not so strict?

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  • Python string manipulation

    - by paradox
    I'm trying to split a string into a int list for further processing. But somehow I can't remove certain whitespaces in between elements of the list. The string x is supposed to have a length of 1000 instead of 1019. I tried reading the documentation for python and saw the function strip() for stripping whitespaces from strings. However, it only works for trailing and leading whitespaces. How should I go about removing these whitespaces and also how do I convert a str list to a int list? My code is as follows : import array x = """73167176531330624919225119674426574742355349194934 96983520312774506326239578318016984801869478851843 85861560789112949495459501737958331952853208805511 12540698747158523863050715693290963295227443043557 66896648950445244523161731856403098711121722383113 62229893423380308135336276614282806444486645238749 30358907296290491560440772390713810515859307960866 70172427121883998797908792274921901699720888093776 65727333001053367881220235421809751254540594752243 52584907711670556013604839586446706324415722155397 53697817977846174064955149290862569321978468622482 83972241375657056057490261407972968652414535100474 82166370484403199890008895243450658541227588666881 16427171479924442928230863465674813919123162824586 17866458359124566529476545682848912883142607690042 24219022671055626321111109370544217506941658960408 07198403850962455444362981230987879927244284909188 84580156166097919133875499200524063689912560717606 05886116467109405077541002256983155200055935729725 71636269561882670428252483600823257530420752963450""" y=[] for i in range(0,len(x)): #String is now in a string list if x[i]!='': y.append(x[i]) print(y[i]) print(len(x))

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  • how to calculate a bill from several tables on mysql?

    - by Audel
    I'm using mysql to create an hotel booking system, but i am struggling a little bit to calculate the final bill. I need a SELECT command to get data from several tables and make some calculations. Basically I just need to get the 'night cost' from a table called 'room_types'. Then, use DATEDIFF function to get the difference of days between the 'checkin' and 'checkout' columns in the table 'room_booking' and multiply the difference with the night cost and display the total. These are the tables I would be using: are room_booking, room_types, booking, and room. One booking may have several room bookings, so Im looking for a table that looks something like this: +------------+------------+---------------+------------------+ | bookingid | Room price | nights stayed | total room price | +------------+------------+---------------+------------------+ | B001 | 30.00 | 4 | 120.00 | +------------+------------+---------------+------------------+ | B001 | 40.00 | 3 | 120.00 | +------------+------------+---------------+------------------+ booking id comes from table 'booking' room price from 'room_types', 'nights stayed' is calculated from the table room_booking, using the datediff command between checkin and checkout . I hope i was clear

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  • Python read multiline JSON

    - by Paul W
    I have been trying to use JSON to store settings for a program. I can't seem to get Python 2.6 's JSON Decoder to decode multi-line JSON strings... Here is example input: .settings file: """ {\ 'user':'username',\ 'password':'passwd',\ }\ """ I have tried a couple other syntaxes for this file, which I will specify below (with the traceback they cause). My python code for reading the file in is import json settings_text = open(".settings", "r").read() settings = json.loads(settings_text) The Traceback for this is: Traceback (most recent call last): File "json_test.py", line 4, in <module> print json.loads(text) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/json/__init__.py", line 307, in loads return _default_decoder.decode(s) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/json/decoder.py", line 322, in decode raise ValueError(errmsg("Extra data", s, end, len(s))) ValueError: Extra data: line 1 column 2 - line 7 column 1 (char 2 - 41) I assume the "Extra data" is the triple-quote. Here are the other syntaxes I have tried for the .settings file, with their respective Tracebacks: "{\ 'user':'username',\ 'pass':'passwd'\ }" Traceback (most recent call last): File "json_test.py", line 4, in <module> print json.loads(text) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/json/__init__.py", line 307, in loads return _default_decoder.decode(s) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/json/decoder.py", line 319, in decode obj, end = self.raw_decode(s, idx=_w(s, 0).end()) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/json/decoder.py", line 336, in raw_decode obj, end = self._scanner.iterscan(s, **kw).next() File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/json/scanner.py", line 55, in iterscan rval, next_pos = action(m, context) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/json/decoder.py", line 155, in JSONString return scanstring(match.string, match.end(), encoding, strict) ValueError: Invalid \escape: line 1 column 2 (char 2) '{\ "user":"username",\ "pass":"passwd",\ }' Traceback (most recent call last): File "json_test.py", line 4, in <module> print json.loads(text) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/json/__init__.py", line 307, in loads return _default_decoder.decode(s) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/json/decoder.py", line 319, in decode obj, end = self.raw_decode(s, idx=_w(s, 0).end()) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/json/decoder.py", line 338, in raw_decode raise ValueError("No JSON object could be decoded") ValueError: No JSON object could be decoded If I put the settings all on one line, it decodes fine.

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  • python simple function error ?

    - by abhilashm86
    Here's a simple function to do simple math operations, when i call this from other program using import, output i get is none. When i remove def function, everything is working fine. What's the problem with defining this function? I'm new to python. def calci(a, op, b): if op == '+': c = a + b elif op == '-': c = a-b elif op == '*': c= a*b elif op =='/': if(b == 0): print('can\'t divide') c = a/b print('value is',c) return c result = calci(12,'+', 12) print(result) nter code here

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  • C# Process flow - Datastream, XML and datagrid

    - by Farstucker
    Im looking for some advice/suggestions on how I should setup the work flow of a small application Im building. When the application is launched the datagrid will be populated via the XML file. Once running the application will receive a datastream that I hope to update the file and datagrid. So Im curious what you would suggest on how I setup the workflow (ie, split the data from the data stream and simultaneously populate the file and grid or would you suggest populating the XML file first and setting up a timer to have the grid read the file?) Im really looking for optimal performance.

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  • Perl file test operator help

    - by Aaron Moodie
    This is a really basic issue, but I'm new to perl and cannot work out what the issue is. I'm just trying to isolate the files in a directory, but the -d operator keeps treating all the folder contents as files ... @contents is my array, and when I run this: foreach $item(@contents) { if (-d $item) { next; } print"$item is a file\n"; } I keep getting both folders and files. Alternatively, if I use -f, I get nothing. edit: this is the output - file01.txt is a file folder 01 is a file folder 02 is a file Screen shot 2010-04-18 at 1.26.17 PM.png is a file I'm running this on OSX

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  • Unreachable statement when using return in finally?

    - by abson
    this compiles class ex1 { public int show() { try { int a=10/10; return 10; } catch(ArithmeticException e) { System.out.println(e); } finally { System.out.println("Finally"); } System.out.println("hello"); return 20; } } on the other hand this doesn't class ex15 { public int show() { try { int a=10/0; return 10; } catch(ArithmeticException e) { System.out.println(e); } finally { System.out.println("Finally"); return 40; } System.out.println("hello"); return 20; } } and gives unreachable statement System.out.println("hello"); error. why is it so?

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  • Unable to connect on socket across different networks.

    - by maleki
    I am having trouble connecting my online application to others across another network. I am able to give them the hostAddress to connect when we are on the same network but when we are doing it across the internet the generated host address doesn't allow a connection, nor does using the ip address gotten from online sites such as whatismyip.com My biggest issue isn't debugging this code, because it works over intra-network but The server doesn't see attempts when we try to move to different networks. Also, the test ip I am using is 2222. InetAddress addr = InetAddress.getLocalHost(); String hostname = addr.getHostName(); System.out.println("Hostname: " + hostname); System.out.println("IP: " + addr.getHostAddress()); I display the host to the server when it is starting if (isClient) { System.out.println("Client Starting.."); clientSocket = new Socket(host, port_number); } else { System.out.println("Server Starting.."); echoServer = new ServerSocket(port_number); clientSocket = echoServer.accept(); System.out.println("Warning, Incoming Game.."); }

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  • Trying to manually recreate a simple generate/scaffolding script

    - by montooner
    I'm trying to understand Rails from the ground up. I want to learn how to manually create basic show-all/show-single/CRUD functionality in the framework. I currently am working on the display-all functionality, but am stopped by an error when I try to request all items in the Products db Here are the steps I've taken so far: script/generate controller Products script/generate model Products rake db:migrate modified products_controller.rb to add: def index() { @products = Product.all} (error: uninitialized constant ProductsController::Product) ideally, dump all orders in the view What's the fix?

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  • Why is my NSMutableArray returning nill?

    - by lampShade
    I have a very simple task: add the contents of a textField to an NSMutableArray.The Problem is the array is returning nill. I believe that it has something to do with the fact that the array I'm using is declared as an instance variable. /* IBOutlet NSTextField *textField; IBOutlet NSTabView *tableView; IBOutlet NSButton *button; NSMutableArray *myArray; */ #import "AppController.h" @implementation AppController -(IBAction)addNewItem:(id)sender { NSString *string = [textField stringValue]; NSLog(@"%@",string); [myArray addObject:string]; NSLog(@"%d",[myArray count]);//this outputs 0 why is that? }

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  • Java: dangerous self-returning-recursive function by IOException?

    - by HH
    I had very errorsome Exception handling with if-clauses. An exception occurs if not found path. An exception returns the function again. The function is recursive. Safe? $ javac SubDirs.java $ java SubDirs Give me an path. . HELLO com TOASHEOU google common annotations base collect internal Give me an path. IT WON'T FIND ME, SO IT RETURNS ITSELF due to Exception caught Give me an path. $ cat SubDirs.java import java.io.*; import java.util.*; public class SubDirs { private List<File> getSubdirs(File file) throws IOException { List<File> subdirs = Arrays.asList(file.listFiles(new FileFilter() { public boolean accept(File f) { return f.isDirectory(); } })); subdirs = new ArrayList<File>(subdirs); List<File> deepSubdirs = new ArrayList<File>(); for(File subdir : subdirs) { deepSubdirs.addAll(getSubdirs(subdir)); } subdirs.addAll(deepSubdirs); return subdirs; } public static void search() { try{ BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); String s; System.out.println("Give me an path."); while ((s = in.readLine()) != null && s.length() != 0){ SubDirs dirs = new SubDirs(); List<File> subDirs = dirs.getSubdirs(new File(s)); for ( File f : subDirs ) { System.out.println(f.getName()); } System.out.println("Give me an path."); } }catch(Exception e){ // Simple but is it safe? search(); } } public static void main(String[] args) throws IOException { search(); } }

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