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  • Why do all procedures have to be defined before the compiler sees them?

    - by incrediman
    For example, take a look at this code (from tspl4): (define proc1 (lambda (x y) (proc2 y x))) If I run this as my program in scheme... #!r6rs (import (rnrs)) (define proc1 (lambda (x y) (proc2 y x))) I get this error: expand: unbound identifier in module in: proc2 ...This code works fine though: #!r6rs (import (rnrs)) (define proc2 +) (define proc1 (lambda (x y) (proc2 y x))) (display (proc1 2 3)) ;output: 5

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  • filtering elements from list of lists in Python?

    - by user248237
    I want to filter elements from a list of lists, and iterate over the elements of each element using a lambda. For example, given the list: a = [[1,2,3],[4,5,6]] suppose that I want to keep only elements where the sum of the list is greater than N. I tried writing: filter(lambda x, y, z: x + y + z >= N, a) but I get the error: <lambda>() takes exactly 3 arguments (1 given) How can I iterate while assigning values of each element to x, y, and z? Something like zip, but for arbitrarily long lists. thanks, p.s. I know I can write this using: filter(lambda x: sum(x)..., a) but that's not the point, imagine that these were not numbers but arbitrary elements and I wanted to assign their values to variable names.

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  • How to make negate_unary work with any type?

    - by Chan
    Hi, Following this question: How to negate a predicate function using operator ! in C++? I want to create an operator ! can work with any functor that inherited from unary_function. I tried: template<typename T> inline std::unary_negate<T> operator !( const T& pred ) { return std::not1( pred ); } The compiler complained: Error 5 error C2955: 'std::unary_function' : use of class template requires template argument list c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 223 1 Graphic Error 7 error C2451: conditional expression of type 'std::unary_negate<_Fn1>' is illegal c:\program files\microsoft visual studio 10.0\vc\include\ostream 529 1 Graphic Error 3 error C2146: syntax error : missing ',' before identifier 'argument_type' c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 222 1 Graphic Error 4 error C2065: 'argument_type' : undeclared identifier c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 222 1 Graphic Error 2 error C2039: 'argument_type' : is not a member of 'std::basic_ostream<_Elem,_Traits>::sentry' c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 222 1 Graphic Error 6 error C2039: 'argument_type' : is not a member of 'std::basic_ostream<_Elem,_Traits>::sentry' c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 230 1 Graphic Any idea? Update Follow "templatetypedef" solution, I got new error: Error 3 error C2831: 'operator !' cannot have default parameters c:\visual studio 2010 projects\graphic\graphic\main.cpp 39 1 Graphic Error 2 error C2808: unary 'operator !' has too many formal parameters c:\visual studio 2010 projects\graphic\graphic\main.cpp 39 1 Graphic Error 4 error C2675: unary '!' : 'is_prime' does not define this operator or a conversion to a type acceptable to the predefined operator c:\visual studio 2010 projects\graphic\graphic\main.cpp 52 1 Graphic Update 1 Complete code: #include <iostream> #include <functional> #include <utility> #include <cmath> #include <algorithm> #include <iterator> #include <string> #include <boost/assign.hpp> #include <boost/assign/std/vector.hpp> #include <boost/assign/std/map.hpp> #include <boost/assign/std/set.hpp> #include <boost/assign/std/list.hpp> #include <boost/assign/std/stack.hpp> #include <boost/assign/std/deque.hpp> struct is_prime : std::unary_function<int, bool> { bool operator()( int n ) const { if( n < 2 ) return 0; if( n == 2 || n == 3 ) return 1; if( n % 2 == 0 || n % 3 == 0 ) return 0; int upper_bound = std::sqrt( static_cast<double>( n ) ); for( int pf = 5, step = 2; pf <= upper_bound; ) { if( n % pf == 0 ) return 0; pf += step; step = 6 - step; } return 1; } }; /* template<typename T> inline std::unary_negate<T> operator !( const T& pred, typename T::argument_type* dummy = 0 ) { return std::not1<T>( pred ); } */ inline std::unary_negate<is_prime> operator !( const is_prime& pred ) { return std::not1( pred ); } template<typename T> inline void print_con( const T& con, const std::string& ms = "", const std::string& sep = ", " ) { std::cout << ms << '\n'; std::copy( con.begin(), con.end(), std::ostream_iterator<typename T::value_type>( std::cout, sep.c_str() ) ); std::cout << "\n\n"; } int main() { using namespace boost::assign; std::vector<int> nums; nums += 1, 3, 5, 7, 9; nums.erase( remove_if( nums.begin(), nums.end(), !is_prime() ), nums.end() ); print_con( nums, "After remove all primes" ); } Thanks, Chan Nguyen

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  • Providing *implicit* conversion operator for template specialization

    - by Neil G
    I have a templated sparse_vector<T> class, and I am also using Boost UBLAS. How would I provide implicit conversions between sparse_vector<double> and boost::numeric::ublas::compressed_vector<double>? I would also like to provide similar conversions between std::vector<double> and boost::numeric::ublas::vector<double>. (I am using gcc 4.4 with C++0x enabled.)

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  • Lifetime of implicitly casted temporaries

    - by Answeror
    I have seen this question. It seems that regardless of the cast, the temporary object(s) will "survive" until the fullexpression evaluated. But in the following scenario: void foo(boost::tuple<const double&> n) { printf("%lf\n", n.get<0>()); } int main() { foo(boost::tuple<const double&>(2));//#1 foo(boost::make_tuple(2));//#2 return 0; } 1 run well, but 2 do not. And MSVC gave me a warning about 2: "reference member is initialized to a temporary that doesn't persist after the constructor exits" Now I am wondering why they both make a temporary "double" object and pass it to boost::tuple<const double&> and only 2 failed.

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  • C++ creating generic template function specialisations

    - by Fire Lancer
    I know how to specialise a template function, however what I want to do here is specialise a function for all types which have a given method, eg: template<typename T> void foo(){...} template<typename T, if_exists(T::bar)>void foo(){...}//always use this one if the method T::bar exists T::bar in my classes is static and has different return types. I tried doing this by having an empty base class ("class HasBar{};") for my classes to derive from and using boost::enable_if with boost::is_base_of on my "specialised" version. However the problem then is that for classes that do have bar, the compiler cant resolve which one to use :(. template<typename T> typename boost::enable_if<boost::is_base_of(HasBar, T>, void>::type f() {...} I know that I could use boost::disable_if on the "normal" version, however I do not control the normal version (its provided by a third party library and its expected for specialisations to be made, I just don't really want to make explicit specialisations for my 20 or so classes), nor do I have that much control over the code using these functions, just the classes implementing T::bar and the function that uses it. Is there some way to tell the compiler to "always use this version if possible no matter what" without altering the other versions?

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  • How do i pass a number from a list as a parameter in scheme?

    - by wyatt
    I need to take a number from a list and convert it to a number so that i can pass it as a parameter. im trying to make a 1-bit adder in scheme. i've written the code for the or gate and the xor gate and also the half adder and now im trying to combine them all to make a full adder. im not sure if im going about it the right way. any input will be appreciated thank you. (define or-gate (lambda (a b) (if (= a 1) 1 (if (= b 1) 1 0)))) (define xor-gate (lambda (a b) (if (= a b) 0 1))) (define ha (lambda (a b) (list (xor-gate a b)(and-gate a b)))) (define fa (lambda (a b cin) (or-gate (cdr(ha cin (car (ha a b))))(cdr(ha a b))))) the issue i get when i run the program is that the half adder (ha) function outputs a list as a value and that makes the values incompatible with my other procedures because they require numbers and not lists. i feel like there is a simple solution but i dont know it.

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  • Header Files Cross Project

    - by Mike
    So I have two projects, A and B, where B is dependent on A (A is a library, while B is a console application). A uses the boost library, and has been configured to include the header and library files, but B has not. Visual studio throws an error saying the Boost Header files cannot be found (in project B). For example: error C1083: Cannot open include file: 'boost/asio.hpp': No Such file or directory [Project: B] My question is: Is there a way such that B does not have to include the Boost library as well?

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  • Batch crop PDF pages?

    - by boost
    I have a PDF document containing pages which have crop marks on them. I'd like to copy these pages to another PDF without the crop marks. I'm assuming I have to crop-out the crop marks but is there any way to do this in batch rather than interactively?

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  • SEO Copywriting - Tips on Making Sense to Humans and Google

    This article covers a range of handy tips that you can implement to boost your search engine ratings. It deals with striking the balance between optimising for search engines like Google and making sense to your human visitors. You'll learn a whole range of writing techniques to boost your ranking, along with some behind the scenes tips.

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  • C# Dev - I've tried Lisps, but I don't get it.

    - by Jonathan Mitchem
    After a few months of learning about and playing with lisps, both CL and a bit of Clojure, I'm still not seeing a compelling reason to write anything in it instead of C#. I would really like some compelling reasons, or for someone to point out that I'm missing something really big. The strengths of a Lisp (per my research): Compact, expressive notation - More so than C#, yes... but I seem to be able to express those ideas in C# too. Implicit support for functional programming - C# with LINQ extension methods: mapcar = .Select( lambda ) mapcan = .Select( lambda ).Aggregate( (a,b) = a.Union(b) ) car/first = .First() cdr/rest = .Skip(1) .... etc. Lambda and higher-order function support - C# has this, and the syntax is arguably simpler: "(lambda (x) ( body ))" versus "x = ( body )" "#(" with "%", "%1", "%2" is nice in Clojure Method dispatch separated from the objects - C# has this through extension methods Multimethod dispatch - C# does not have this natively, but I could implement it as a function call in a few hours Code is Data (and Macros) - Maybe I haven't "gotten" macros, but I haven't seen a single example where the idea of a macro couldn't be implemented as a function; it doesn't change the "language", but I'm not sure that's a strength DSLs - Can only do it through function composition... but it works Untyped "exploratory" programming - for structs/classes, C#'s autoproperties and "object" work quite well, and you can easily escalate into stronger typing as you go along Runs on non-Windows hardware - Yeah, so? Outside of college, I've only known one person who doesn't run Windows at home, or at least a VM of Windows on *nix/Mac. (Then again, maybe this is more important than I thought and I've just been brainwashed...) The REPL for bottom-up design - Ok, I admit this is really really nice, and I miss it in C#. Things I'm missing in a Lisp (due to a mix of C#, .NET, Visual Studio, Resharper): Namespaces. Even with static methods, I like to tie them to a "class" to categorize their context (Clojure seems to have this, CL doesn't seem to.) Great compile and design-time support the type system allows me to determine "correctness" of the datastructures I pass around anything misspelled is underlined realtime; I don't have to wait until runtime to know code improvements (such as using an FP approach instead of an imperative one) are autosuggested GUI development tools: WinForms and WPF (I know Clojure has access to the Java GUI libraries, but they're entirely foreign to me.) GUI Debugging tools: breakpoints, step-in, step-over, value inspectors (text, xml, custom), watches, debug-by-thread, conditional breakpoints, call-stack window with the ability to jump to the code at any level in the stack (To be fair, my stint with Emacs+Slime seemed to provide some of this, but I'm partial to the VS GUI-driven approach) I really like the hype surrounding Lisps and I gave it a chance. But is there anything I can do in a Lisp that I can't do as well in C#? It might be a bit more verbose in C#, but I also have autocomplete. What am I missing? Why should I use Clojure/CL?

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  • Two routers, one off-site, same ISP-assigned static IP. A recipe for conflict?

    - by boost
    This is the situation I've inherited: There are two routers, one off-site. Both are connected to the ISP. The ISP assigns both of them the same static IP (or so it seems). Presumably, the network problems we're having are related to the idea that you can't have two instances of the same IP. So we rang up the folk off-site and told them to turn off the router. Now everything's working okay here. How do I get around this? Get another static IP? Figure out how to get the router to ask for a dynamic IP (as we're not using the static IP for anything)?

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  • Does the powershell cmdlet add to or replace out-of-office settings in Exchange 2007?

    - by boost
    When using Powershell to set Out-of-Office in Exchange 2007 (e.g.), do multiple commands containing -StartTime and -EndTime add to some internal list that Exchange maintains or does each successive command replace the previous command? For example we have a staffer who is only in the office Tuesdays and Fridays. We'd like to set up Exchange to send an Out-of-Office message to all internal senders on those days when he's not in. How is this best done?

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  • Is it possible to get a google voice number without already having a phone number?

    - by boost
    I'm sorry if this is the wrong place to post this, but I couldn't find a more suitable website in the stackexchange network. I currently have no phone number; I can make outgoing calls via the widget in gmail, but I cannot receive calls (as far as I know). I know that you can set up a google voice number to forward to google chat, and this is exactly what I want. The problem is, I can't get a google voice number in the first place, because it first requires that I have an existing phone number, even if I wouldn't use it. So, it is possible to skip providing an existing phone number, and just get a google voice number that forwards to google chat? Alternatively, is there any free phone service that can be used without a phone and lets you receive calls from any number? I realize I'm kind of asking for free candy, but, if it's out there, I'd be a fool

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  • Online Content Distribution is a Valuable SEO Tool

    Online content distribution is quite possibly one of the best and easiest ways to boost your search engine rankings if done properly. It is quite common however to overlook the importance this strategy can play in our optimization efforts. Read on to see 5 ways in which using content can boost your SEO efforts leading to even more exposure and traffic.

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  • What would a new web development tool need to succeed?

    - by boost
    If one wanted to bring a new web development tool to market, what would it have to be able to do that would differentiate it enough from all the others to attract people's attention? In what areas are all the other frameworks and languages falling down, such that if a new product addressed those issues, it would stand a chance of being adopted by significant user community?

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  • StructureMap Autowiring with two different instances of the same interface

    - by Lambda
    For the last two days, i tried my best to learn something about StructureMap, using an old project of mine as an concrete implementation example. I tried to simplify my question as much as possible. While i will post my examples in vb.net, answers with examples in C# are also okay. The project includes an interfaces called IDatabase which connects itself to a Database. The important part looks like this. Public Interface IDatabase Function Connect(ByVal ConnectionSettings As ConnectionSettings) As Boolean ReadOnly Property ConnectionOpen As Boolean [... more functions...] End Interface Public Class MSSQLConnection Implements IDatabase Public Function Connect(ByVal ConnectionSettings As ConnectionSettings) As Boolean Implements IDatabase.Connect [... Implementation ...] End Function [... more implementations...] End Class ConnectionSettings is a structure that has all the information needed to connect to a Database. I want to open the Database Connection once and use it for every single connection in the project, so i register a instance in the ObjectFactory. dim foo = ObjectFactory.GetInstance(Of MSSQLConnection)() dim bar as ConnectionSettings foo.connect(bar) ObjectFactory.Configure(Sub(x) x.For(Of IDatabase).Use(foo)) Up until this part, everything works like a charm. Now, i get to a point where i hav e classes that need an additional instance of IDatabase because they connect to a second database. Public Class ExampleClass Public Sub New(ByVal SameOldDatabase as IDatabase, ByVal NewDatabase as IDatabase) [...] Magic happens here [...] End Sub End Class I want this second IDatabase to behave much like the first one. I want it to use a concrete, single instance and want to connect it to a different database invoking Connect with a different ConnectionSettings. The problem is: While i'm pretty sure it's somewhow possible, (my initial idea was registering ExampleClass with alternative constructor arguments), i actually want to do it without registering ExampleClass. This probably involves more configuration, but i have no idea how to do it. So, basically, it comes down to this question: How do i configurate the ObjectFactory in a way that the autowiring always invokes the constructor with object Database1 for the first IDatabase parameter and object Database2 for the second one (if there is one?)

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  • Base64 Android encode to PHP decode make error

    - by studio lambda
    I'm a french guy, so, I'm sorry for my english... I'm developing an Android App which communicate with a PHP REST service. So, when I try to encode an image file into Base64 like this : InputStream fileInputStream = context.getContentResolver().openInputStream(uri); BufferedInputStream in = new BufferedInputStream(fileInputStream); StringWriter out = new StringWriter(); int b; while ((b = in.read()) != -1) out.write(b); out.flush(); out.close(); in.close(); String encoded = new String(android.util.Base64.encode(out.toString() .getBytes(), android.util.Base64.DEFAULT)); On server side, I make : $data=base64_decode(chunk_split($base64BinaryData)); The result is that my image file is corrupted! INFO : the image is made by an Intent to android.provider.MediaStore.ACTION_IMAGE_CAPTURE Activity in Emulator mode (avd 5554) I've already read lots of discussions about similar problem but nothing fix my bug. thanks for help Regards,

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  • Error with python-setuptools doing "sudo easy_install python-graph-core"

    - by Dan
    Using easy_install, part of the python-setuptools, I get the following error: $ sudo easy_install python-graph-core [sudo] password for dan: Searching for python-graph-core Reading http://pypi.python.org/simple/python-graph-core/ Reading http://code.google.com/p/python-graph/ Reading http://code.google.com/p/python-graph/downloads/list?can=1 Reading http://code.google.com/p/python-graph/downloads/list Best match: python-graph-core 1.7.0 Downloading http://python-graph.googlecode.com/files/python-graph-core-1.7.0.tar.gz Processing python-graph-core-1.7.0.tar.gz Running python-graph-core-1.7.0/setup.py -q bdist_egg --dist-dir /tmp/easy_install-GwpYiM/python-graph-core-1.7.0/egg-dist-tmp-1yqbyV setup.py:8: Warning: 'as' will become a reserved keyword in Python 2.6 Traceback (most recent call last): File "/usr/bin/easy_install", line 8, in <module> load_entry_point('setuptools==0.6c9', 'console_scripts', 'easy_install')() File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 1671, in main with_ei_usage(lambda: File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 1659, in with_ei_usage return f() File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 1675, in <lambda> distclass=DistributionWithoutHelpCommands, **kw File "/usr/lib/python2.5/distutils/core.py", line 151, in setup dist.run_commands() File "/usr/lib/python2.5/distutils/dist.py", line 974, in run_commands self.run_command(cmd) File "/usr/lib/python2.5/distutils/dist.py", line 994, in run_command cmd_obj.run() File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 211, in run self.easy_install(spec, not self.no_deps) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 446, in easy_install return self.install_item(spec, dist.location, tmpdir, deps) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 476, in install_item dists = self.install_eggs(spec, download, tmpdir) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 655, in install_eggs return self.build_and_install(setup_script, setup_base) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 930, in build_and_install self.run_setup(setup_script, setup_base, args) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 919, in run_setup run_setup(setup_script, args) File "/usr/lib/python2.5/site-packages/setuptools/sandbox.py", line 27, in run_setup lambda: execfile( File "/usr/lib/python2.5/site-packages/setuptools/sandbox.py", line 63, in run return func() File "/usr/lib/python2.5/site-packages/setuptools/sandbox.py", line 29, in <lambda> {'__file__':setup_script, '__name__':'__main__'} File "setup.py", line 8 except ImportError as ie: ^ SyntaxError: invalid syntax Any suggestions to what I may be doing wrong? Thanks, Dan

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  • Compiling Gearman PHP Library for CentOS 5.8

    - by Andrew Ellis
    I've been trying to get Gearman compiled on CentOS 5.8 all afternoon. Unfortunately I am restricted to this version of CentOS by my CTO and how he has our entire network configured. I think it's simply because we don't have enough resources to upgrade our network... But anyways, the problem at hand. I have searched through Server Fault, Stack Overflow, Google, and am unable to locate a working solution. What I have below is stuff I have pieced together from my searching. Searches have told said to install the following via yum: yum -y install --enablerepo=remi boost141-devel libgearman-devel e2fsprogs-devel e2fsprogs gcc44 gcc-c++ To get the Boost headers working correctly I did this: cp -f /usr/lib/boost141/* /usr/lib/ cp -f /usr/lib64/boost141/* /usr/lib64/ rm -f /usr/include/boost ln -s /usr/include/boost141/boost /usr/include/boost With all of the dependancies installed and paths setup I then download and compile gearmand-1.1.2 just fine. wget -O /tmp/gearmand-1.1.2.tar.gz https://launchpad.net/gearmand/1.2/1.1.2/+download/gearmand-1.1.2.tar.gz cd /tmp && tar zxvf gearmand-1.1.2.tar.gz ./configure && make -j8 && make install That works correctly. So now I need to install the Gearman library for PHP. I have attempted through PECL and downloading the source directly, both result in the same error: checking whether to enable gearman support... yes, shared not found configure: error: Please install libgearman What I don't understand is I installed the libgearman-devel package which also installed the core libgearman. The installation installs libgearman-devel-0.14-3.el5.x86_64, libgearman-devel-0.14-3.el5.i386, libgearman-0.14-3.el5.x86_64, and libgearman-0.14-3.el5.i386. Is it possible the package version is lower than what is required? I'm still poking around with this, but figured I'd throw this up to see if anyone has a solution while I continue to research a fix. Thanks!

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