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• Why is Lua considered a game language?

  - by Hoffmann

  I have been learning about Lua in the past month and I'm absolutely in love with the language, but all I see around that is built with lua are games. I mean, the syntax is very simple, there is no fuss, no special meaning characters that makes code look like regex, has all the good things about a script language and integrates so painlessly with other languages like C, Java, etc. The only down-side I saw so far is the prototype based object orientation that some people do not like (or lack of OO built-in). I do not see how ruby or python are better, surely not in performance ( http://shootout.alioth.debian.org/gp4/benchmark.php?test=all&lang=lua&lang2=python ). I was planning on writting a web app using lua with the Kepler framework and Javascript, but the lack of other projects that use lua as a web language makes me feel a bit uneasy since this is my first try with web development. Lua is considered a kids language, most of you on stackoverflow probably only know the language because of the WoW addons. I can't really see why that is... http://lua-users.org/wiki/LuaVersusPython this link provides some insights on Lua against Python, but this is clearly biased.

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• What's the Matlab equivalent of NULL, when it's calling COM/ActiveX methods?

  - by David M

  Hi, I maintain a program which can be automated via COM. Generally customers use VBS to do their scripting, but we have a couple of customers who use Matlab's ActiveX support and are having trouble calling COM object methods with a NULL parameter. They've asked how they do this in Matlab - and I've been scouring Mathworks' COM/ActiveX documentation for a day or so now and can't figure it out. Their example code might look something like this: function do_something() OurAppInstance = actxserver('Foo.Application'); OurAppInstance.Method('Hello', NULL) end where NULL is where in another language, we'd write NULL or nil or Nothing, or, of course, pass in an object. The problem is this is optional (and these are implemented as optional parameters in most, but not all, cases) - these methods expect to get NULL quite often. They tell me they've tried [] (which from my reading seemed the most likely) as well as '', Nothing, 'Nothing', None, Null, and 0. I have no idea how many of those are even valid Matlab keywords - certainly none work in this case. Can anyone help? What's Matlab's syntax for a null pointer / object for use as a COM method parameter? Update: Thanks for all the replies so far! Unfortunately, none of the answers seem to work, not even libpointer. The error is the same in all cases: Error: Type mismatch, argument 2 This parameter in the COM type library is described in RIDL as: HRESULT _stdcall OurMethod([in] BSTR strParamOne, [in, optional] OurCoClass* oParamTwo, [out, retval] VARIANT_BOOL* bResult); The coclass in question implements a single interface descending from IDispatch.

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• WCF Data Services - neither .Expand or .LoadProperty seems to do what I need

  - by TomK

  I am building a school management app where they track student tardiness and absences. I've got three entities to help me in this. A Students entity (first name, last name, ID, etc.); a SystemAbsenceTypes entity with SystemAbsenceTypeID values for Late, Absent-with-Reason, Absent-without-Reason; and a cross-reference table called StudentAbsences (matching the student IDs with the absence-type ID, plus a date, and a Notes field). What I want to do is query my entities for a given student, and then add up the number of each kind of Absence, for a given date range. I prepare my currentStudent object without a problem, then I do this... Me.Data.LoadProperty(currentStudent, "StudentAbsences") 'Loads the cross-ref data lblDaysLate.Text = (From ab In currentStudent.StudentAbsences Where ab.SystemAbsenceTypes.SystemAbsenceTypeID = Common.enuStudentAbsenceTypes.Late).Count.ToString ...and this second line fails, complaining it has no value for an object. I presume the problem is that while it DOES see that there are (let's say) four absences for the currentStudent (ie, currentStudent.StudentAbsences.Count = 4) -- it can't yet "peer into" each one of the absences to look at its type. How do I use .Expand or .LoadProperty to make this happen? I tried fiddling with .LoadProperty but it doesn't take a two-level syntax like so... Data.LoadProperty(currentStudent,"StudentAbsences.SystemAbsenceTypeID") or the like. Is there some other technique?

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• How to catch a carp-warning?

  - by sid_com

  I tried to catch a carp-warning ( carp "$start is $end" if (warnings::enabled()); ) with eval but it didn't work, so I looked in the eval-documentation and I discovered, that eval catches only syntax-errors, run-time-errors or executed die-statements. How could I catch a carp-warning? #!/usr/bin/env perl use warnings; use strict; use 5.012; use List::Util qw(max min); use Number::Range; my @array; my $max = 20; print "Input (max $max): "; my $in = <>; $in =~ s/\s+//g; $in =~ s/(?<=\d)-/../g; eval { my $range = new Number::Range( $in ); @array = sort { $a <=> $b } $range->range; }; if ( $@ =~ /\d+ is > \d+/ ) { die $@ }; # catch the carp-warning doesn't work die "Input greater than $max not allowed $!" if defined $max and max( @array ) > $max; die "Input '0' or less not allowed $!" if min( @array ) < 1; say "@array";

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• How to non-greedy multiple lookbehind matches

  - by ArtK

  Source: <prefix><content1><suffix1><prefix><content2><suffix2> Engine: PCRE RegEx1: (?<=<prefix>)(.*)(?=<suffix1>) RegEx2: (?<=<prefix>)(.*)(?=<suffix2>) Result1: <content1> Result2: <content1><suffix1><prefix><content2> The desired result for RegEx2 is just <content2> but it is obviously greedy. How do I make RegEx2 non-greedy and use only the last matching lookbehind? [I hope I have translated this correctly from the NoteTab syntax. I don't do much RegEx coding. The <prefix>, <content> & <suffix> terms are just meant to represent arbitrary strings. Only the "<" in the "?<=" lookbehind command is significant.] I suspect it is something simple but after too many hours of searching I'm giving up on solving it myself. Thanks for the help Art

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• Ultrawingrid - how to display #1/1/1800# as blank ( as if null )

  - by Charles Hankey

  Ultrawingrid 9.2 VS2008 .net 3.5 My wingrid uses a bindingsource. All datetimes which are null in SQL Server are delivered to the bindingsource as #1/1/1800# I would like Ultrawingrid to display this date as blank as it would a null from source. Also, if the date is null in the grid ( i.e. blanked out ) I would like to update the data source to the date #1/1/1800# ( the framework takes care of getting that date back into the backend as a null ) This seems like it should be a trivial matter but I can find no documentation on just where to intervene so the grid will see a particular date as a null and save a null as a particular date. This is the direction I've been headed but I don't think either is the right place and I can't even get the syntax to work in the BeforeRowUpdate as I cannot see how to set a value that is passed to the data binding without setting the value of control itself, which I think has to remain null in order to display as blank Private Sub ugPropMaster_BeforeRowUpdate(ByVal sender As Object, ByVal e As _ Infragistics.Win.UltraWinGrid.CancelableRowEventArgs) Handles _ ugPropMaster.BeforeRowUpdate If e.Row.Cells.Item("Exdate").Value Is Nothing Then e.Row.Cells("Exdate").Value = CDate(#1/1/1800#) End If End Sub Private Sub ugPropMaster_InitializeRow(ByVal sender As Object, ByVal e As _ Infragistics.Win.UltraWinGrid.InitializeRowEventArgs) Handles _ ugPropMaster.InitializeRow If CDate(e.Row.Cells.Item("Exdate").Value) = CDate(#1/1/1800#) Then e.Row.Cells.Item("Exdate").Value = Nothing End If End Sub Guidance much appreciated

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• Row Source - combo box, filtering what pops up in a combo box by date

  - by primus285

  so I have a combo box that I want to pop up when somebody wants to search by year. It will allow them to see in that combo box only results that happened in a certain year. so far I have something like SELECT DISTINCT Database_New.ASEC FROM Database_New WHERE (((Database_New.Date) >= DateValue('01/01/2001') AND (((Database_New.Date) <= DateValue('12/031/2001'))); or SELECT DISTINCT Database_New.ASEC FROM Database_New WHERE (((Database_New.Date) >= BETWEEN DateValue('01/01/2001') AND DateValue('12/31/2001’))); as you can see, the kicker is that I am already sorting the thing with SELECT DISTINCT under the ASEC field. But I want to filter it one more by year so a whole bunch of ASEC values that didnt happen in that year (and there are quite a few that happen rarely, or would onyl be associeted with one year) do not pop up as avalible. so far I get an error like "Syntax error in query expression '(((Database_New.Date) = DateValue('01/01/2001') AND (((Database_New.Date) <= DateValue('12/031/2001')))' and I am a VBA person, not quite as good at debuggin SQL. Is it something easy? or will it simply not work the way I have it set up.

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• Writing fortran robust and "modern" code

  - by Blklight

  In some scientific environments, you often cannot go without FORTRAN as most of the developers only know that idiom, and there is lot of legacy code and related experience. And frankly, there are not many other cross-platform options for high performance programming ( C++ would do the task, but the syntax, zero-starting arrays, and pointers are too much for most engineers ;-) ). I'm a C++ guy but I'm stuck with some F90 projects. So, let's assume a new project must use FORTRAN (F90), but I want to build the most modern software architecture out of it. while being compatible with most "recent" compilers (intel ifort, but also including sun/HP/IBM own compilers) So I'm thinking of imposing: global variable forbidden, no gotos, no jump labels, "implicit none", etc. "object-oriented programming" (modules with datatypes + related subroutines) modular/reusable functions, well documented, reusable libraries assertions/preconditions/invariants (implemented using preprocessor statements) unit tests for all (most) subroutines and "objects" an intense "debug mode" (#ifdef DEBUG) with more checks and all possible Intel compiler checks possible (array bounds, subroutine interfaces, etc.) uniform and enforced legible coding style, using code processing tools C stubs/wrappers for libpthread, libDL (and eventually GPU kernels, etc.) C/C++ implementation of utility functions (strings, file operations, sockets, memory alloc/dealloc reference counting for debug mode, etc.) ( This may all seem "evident" modern programming assumptions, but in a legacy fortran world, most of these are big changes in the typical programmer workflow ) The goal with all that is to have trustworthy, maintainable and modular code. Whereas, in typical fortran, modularity is often not a primary goal, and code is trustworthy only if the original developer was very clever, and the code was not changed since then ! (i'm a bit joking here, but not much) I searched around for references about object-oriented fortran, programming-by-contract (assertions/preconditions/etc.), and found only ugly and outdated documents, syntaxes and papers done by people with no large-scale project involvement, and dead projects. Any good URL, advice, reference paper/books on the subject?

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• ExternalInterface

  - by Jesse

  Hey, so I'm having a bunch of trouble getting ExternalInterface to work, which is odd, because I use it somewhat often. I'm hoping it's something I just missed because I've been looking at it too long. The flash_ready function is correctly returning the objectID, and as far as I can tell, everything else is in order. Unfortunately, when I run it, I get an error (varying by browser) telling me that basically document.getElementById(<movename>).test() is not a valid method. Here's the code: javascript: function flash_ready(i){ document.getElementById(i).test('success!'); } Embed Html (Generated): <script type="text/javascript"> swfobject.embedSWF("/chainmaille/includes/media/flash/upload_image.swf", "/chainmaille/includes/media/flash/upload_image", "500", "50", "9.0.0","expressInstall.swf", {}, {allowScriptAccess:'always', wmode:'transparent'},{id:'uploader_flash',name:'uploader_flash'}); </script> <object type="application/x-shockwave-flash" id="uploader_flash" name="uploader_flash" data="/chainmaille/includes/media/flash/upload_image.swf" width="500" height="50"><param name="allowScriptAccess" value="always"><param name="wmode" value="transparent"></object> AS3 : package com.jesseditson.uploader { import flash.display.MovieClip; import flash.external.ExternalInterface; import flash.system.Security; public class UI extends MovieClip { // Initialization: public function UI() { Security.allowDomain('*'); ExternalInterface.addCallback("test", test); var jscommand:String = "flash_ready('"+ExternalInterface.objectID+"');"; var url:URLRequest = new URLRequest("javascript:" + jscommand + " void(0);"); navigateToURL(url, "_self"); } public function test(t){ trace(t); } } } Swfobject is being included via google code, and the flash embeds just fine, so that's not the problem. I've got a very similar setup working on another server, but can't seem to get it working on this one. It's a Hostgator shared server. Could it be the server's fault? Anybody see any obvious syntax problems? Thanks in advance!

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• Mixins, variadic templates, and CRTP in C++

  - by Eitan

  Here's the scenario: I'd like to have a host class that can have a variable number of mixins (not too hard with variadic templates--see for example http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.103.144). However, I'd also like the mixins to be parameterized by the host class, so that they can refer to its public types (using the CRTP idiom). The problem arises when trying to mix the too--the correct syntax is unclear to me. For example, the following code fails to compile with g++ 4.4.1: template <template<class> class... Mixins> class Host : public Mixins<Host<Mixins>>... { public: template <class... Args> Host(Args&&... args) : Mixins<Host>(std::forward<Args>(args))... {} }; template <class Host> struct Mix1 {}; template <class Host> struct Mix2 {}; typedef Host<Mix1, Mix2> TopHost; TopHost *th = new TopHost(Mix1<TopHost>(), Mix2<TopHost>()); With the error: tst.cpp: In constructor ‘Host<Mixins>::Host(Args&& ...) [with Args = Mix1<Host<Mix1, Mix2> >, Mix2<Host<Mix1, Mix2> >, Mixins = Mix1, Mix2]’: tst.cpp:33: instantiated from here tst.cpp:18: error: type ‘Mix1<Host<Mix1, Mix2> >’ is not a direct base of ‘Host<Mix1, Mix2>’ tst.cpp:18: error: type ‘Mix2<Host<Mix1, Mix2> >’ is not a direct base of ‘Host<Mix1, Mix2>’ Does anyone have successful experience mixing variadic templates with CRTP?

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• PHP: Get instance of static class by string value

  - by Tirithen

  I'm working on a php web api that was handed to me with a lot of code that needs to be refactored. The ones that wrote the code wanted to include a static configuration class to an api resource and then get an instance of that class something like this: <?php $obj = "User"; $confObjectSuffix = "_conf"; $confObject = $obj.$confObjectSuffix; if ($confObject::inst()->checkMethod($method)) { ..... This gives the error "Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM in ....." since $confObject is a string and not a object. I wrote some testcode: <?php $class = "User_conf"; echo "<pre>"; print_r($$class::Inst()); echo "</pre>"; class User_conf { private static $INSTANCE = null; public static function Inst() { if(User_conf::$INSTANCE === null) { User_conf::$INSTANCE = new User_conf(); } return User_conf::$INSTANCE; } } But can't get it to work with $$ either, is there some other way around this? I don't want to rewrite more than necessary.

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• How to force the build to be out of date, when a text file is modified?

  - by demoncodemonkey

  The Scenario My project has a post-build phase set up to run a batch file, which reads a text file "version.txt". The batch file uses the information in version.txt to inject the DLL with a version block using this tool. The version.txt is included in my project to make it easy to modify. It looks a bit like this: @set #Description="TankFace Utility Library" @set #FileVersion="0.1.2.0" @set #Comments="" Basically the batch file renames this file to version.bat, calls it, then renames it back to version.txt afterwards. The Problem When I modify version.txt (e.g. to increment the file version), and then press F7, the build is not seen as out-of-date, so the post-build step is not executed, so the DLL's version doesn't get updated. I really want to include the .txt file as an input to the build, but without anything actually trying to use it. If I #include the .txt file from a CPP file in the project, the compiler fails because it obviously doesn't understand what "@set" means. If I add /* ... */ comments around the @set commands, then the batch file has some syntax errors but eventually succeeds. But this is a poor solution I think. So... how would you do it?

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• Why can't I pass an argument to create this window using wxpython?

  - by somefreakingguy

  I am trying to learn how to make a GUI in python! Following an online tutorial, I found that the following code 'works' in creating an empty window: import wx from sys import argv class bucky(wx.Frame): def __init__(self, parent, id): wx.Frame.__init__(self, parent, id, 'Frame aka window', size=(300, 200)) if __name__=='__main__': app=wx.PySimpleApp() frame=bucky(parent=None,id=-1) frame.Show() app.MainLoop() That gives me a window, which is great. However, what if I want to get an argument passed onto the program to determine the window size? I thought something like this ought to do the trick: import wx from sys import argv script, x, y = argv class mywindow(wx.Frame): def __init__(self, parent, id): wx.Frame.__init__(self, parent, id, 'Frame aka window', size=(x, y)) if __name__=='__main__': app=wx.PySimpleApp() frame=mywindow(parent=None,id=-1) frame.Show() app.MainLoop() But, alas, that does not work! Nor does the raw_input() function pass on the value. I keep getting the following error: C:/Python26/pythonw.exe -u "C:/Documents and Settings/Owner/Desktop/wz.py" File "C:/Documents and Settings/Owner/Desktop/wz.py", line 8 wx.Frame.__init__(self, parent, id, 'Frame aka window', size=(x y)) ^ SyntaxError: invalid syntax Thanks for the help!

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• Why can't I build this Javascript object?

  - by Alex Mcp

  I have an object I'm trying to populate from another object (that is, iterate over a return object to produce an object with only selected values from the original). My code looks like this: var collect = {}; function getHistoricalData(username){ $.getJSON("http://url/" + username + ".json?params", function(data){ for (var i=0; i < data.length; i++) { console.log(i); collect = { i : {text : data[i].text}}; $("#wrap").append("<span>" + data[i].text + "</span><br />"); }; console.log(collect); }); } So I'm using Firebug for debugging, and here's what I know: The JSON object is intact console.log(i); is showing the numbers 1-20 as expected When I log the collect object at the end, it's structure is this: var collect = { i : {text : "the last iteration's text"}}; So the incrementer is "applying" to the data[i].text and returning the text value, but it's not doing what I expected, which is create a new member of the collect object; it's just overwriting collect.i 20 times and leaving me with the last value. Is there a different syntax I need to be using for assigning object members? I tried collect.i.text = and collect[i].text = and the error was that whatever I tried was undefined. I'd love to know what's going on here, so the more in-depth an explanation the better. Thanks!

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• Moving a large number of files in one directory to multiple directories

  - by Axsuul

  I am looking to create a Windows batch script to move about 2,000 files and splitting them up so that there are 10 files per folder. I have attempted creating a batch script but the syntax really boggles my mind. Here is what I have so far @echo off :: Config parameters set /a groupsize = 10 :: initial counter, everytime counter is 1, we create new folder set /a n = 1 :: folder counter set /a nf = 1 for %%f in (*.txt) do ( :: if counter is 1, create new folder if %n% == 1 ( md folder%nf% set /a n += 1 ) :: move file into folder mv -Y %%f folder%nf%\%%f :: reset counter if larger than group size if %n% == %groupsize% ( set /a n = 1 ) else ( set /a n += 1 ) ) pause Basically what this script does is loop through each .txt file in the directory. It creates a new directory in the beginning and moves 10 files into that directory, then creates a new folder again and moves another 10 files into that directory, and so on. However, I'm having problems where the n variable is not being incremented in the loop? I'm sure there's other errors too since the CMD window closes on me even with pause. Any help or guidance is appreciated, thanks for your time!

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• Treetop basic parsing and regular expression usage

  - by ucint

  I'm developing a script using the ruby Treetop library and having issues working with its syntax for regex's. First off, many regular expressions that work in other settings dont work the same in treetop. This is my grammar: (myline.treetop) grammar MyLine rule line string whitespace condition end rule string [\S]* end rule whitespace [\s]* end rule condition "new" / "old" / "used" end end This is my usage: (usage.rb) require 'rubygems' require 'treetop' require 'polyglot' require 'myline' parser = MyLineParser.new p parser.parse("randomstring new") This should find the word new for sure and it does! Now I wont to extend it so that it can find new if the input string becomes "randomstring anotherstring new yetanother andanother" and possibly have any number of strings followed by whitespace (tab included) before and after the regex for rule condition. In other words, if I pass it any sentence with the word "new" etc in it, it should be able to match it. So let's say I change my grammar to: rule line string whitespace condition whitespace string end Then, it should be able to find a match for: p parser.parse("randomstring new anotherstring") So, what do I have to do to allow the string whitespace to be repeated before and after condition? If I try to write this: rule line (string whitespace)* condition (whitespace string)* end , it goes in an infinite loop. If i replace the above () with [], it returns nil In general, regex's return a match when i use the above, but treetop regex's dont. Does anyone have any tips/points on how to go about this? Plus, since there isn't much documentation for treetop and the examples are either too trivial or too complex, is there anyone who knows a more thorough documentation/guide for treetop?

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• Understanding F# Asynchronous Programming

  - by Yin Zhu

  I kind of know the syntax of asynchronous programming in F#. E.g. let downloadUrl(url:string) = async { let req = HttpWebRequest.Create(url) // Run operation asynchronously let! resp = req.AsyncGetResponse() let stream = resp.GetResponseStream() // Dispose 'StreamReader' when completed use reader = new StreamReader(stream) // Run asynchronously and then return the result return! reader.AsyncReadToEnd() } In F# expert book (and many other sources), they say like let! var = expr simply means "perform the asynchronous operation expr and bind the result to var when the operation completes. Then continue by executing the rest of the computation body" I also know that a new thread is created when performing async operation. My original understanding was that there are two parallel threads after the async operation, one doing I/O and one continuing to execute the async body at the same time. But in this example, I am confused at let! resp = req.AsyncGetResponse() let stream = resp.GetResponseStream() What happens if resp has not started yet and the thread in the async body wants to GetResponseStream? Is this a possible error? So maybe my original understanding was wrong. The quoted sentences in the F# expert book actually means that "creating a new thread, hang the current thread up, when the new thread finishes, wake up the body thread and continue", but in this case I don't see we could save any time. In the original understanding, the time is saved when there are several independent IO operations in one async block so that they could be done at the same time without intervention with each other. But here, if I don't get the response, I cannot create the stream; only I have stream, I can start reading the stream. Where's the time gained?

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• Problem with Zend Project

  - by Fincha

  Hello, i write a script and it works perfectly, on my local server. I have uploaded it on my server and now I getting this Problem Parse error: syntax error, unexpected '{' in /homepages/46/d319011794/htdocs/suche/public/index.php on line 18 an here is my index.php <?php error_reporting(E_ALL || E_STRICT); define('APPLICATION_PATH', realpath(dirname(__FILE__)) . '/../application'); set_include_path( APPLICATION_PATH . '/../library' . PATH_SEPARATOR . '../application/models' . PATH_SEPARATOR . get_include_path() ); require_once 'Zend/Loader.php'; Zend_Loader::registerAutoload(); new App_Connect(); try { //Line 18 require '../application/bootstrap.php'; } catch(Exception $exception) { echo "<html><body>Fehler beim bootstraping"; if(defined('APPLICATION_ENVIROMENT') && APPLICATION_EVIROMENT != 'production') { echo "<br><br>" . $exception->getMessage() . "<br>" . "<div align='left'>Stack Trace: " . "<pre> " . $exception->getTraceAsString() . "</pre></div>"; } echo "</body></html>"; exit(1); } Zend_Controller_Front::getInstance()->dispatch(); This is a Zend Project... so may be some one know what to do...

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• Inserting null fields with dbi:Pg

  - by User1

  I have a Perl script inserting data into Postgres according to a pipe delimited text file. Sometimes, a field is null (as expected). However, Perl makes this field into an empty string and the Postgres insert statement fails. Here's a snippet of code: use DBI; #Connect to the database. $dbh=DBI-connect('dbi:Pg:dbname=mydb','mydb','mydb',{AutoCommit=1,RaiseError=1,PrintError=1}); #Prepare an insert. $sth=$dbh-prepare("INSERT INTO mytable (field0,field1) SELECT ?,?"); while (<){ #Remove the whitespace chomp; #Parse the fields. @field=split(/\|/,$_); print "$_\n"; #Do the insert. $sth-execute($field[0],$field[1]); } And if the input is: a|1 b| c|3 EDIT: Use this input instead. a|1|x b||x c|3|x It will fail at b|. DBD::Pg::st execute failed: ERROR: invalid input syntax for integer: "" I just want it to insert a null on field1 instead. Any ideas? EDIT: I simplified the input at the last minute. The old input actually made it work for some reason. So now I changed the input to something that will make the program fail. Also note that field1 is a nullable integer datatype.

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• Compiled Haskell libraries with FFI imports are invalid when imported into GHCI

  - by John Millikin

  I am using GHC 6.12.1, in Ubuntu 10.04 When I try to use the FFI syntax for static storage, only modules running in interpreted mode (ie GHCI) work properly. Compiled modules have invalid pointers, and do not work. I'd like to know whether anybody can reproduce the problem, whether this an error in my code or GHC, and (if the latter) whether it's a known issue. I'm using sys_siglist because it's present in a standard library on my system, but I don't believe the actual storage used matters (I discovered this while writing a binding to libidn). If it helps, sys_siglist is defined in <signal.h> as: extern __const char *__const sys_siglist[_NSIG]; I thought this type might be the problem, so I also tried wrapping it in a plain C procedure: #include<stdio.h> const char **test_ffi_import() { printf("C think sys_siglist = %X\n", sys_siglist); return sys_siglist; } However, importing that doesn't change the result, and the printf() call prints the same pointer value as show siglist_a. My suspicion is that it's something to do with static and dynamic library loading. Update: somebody in #haskell suggested this might be 64-bit specific; if anybody tries to reproduce it, can you mention your architecture and whether it worked in a comment? Code as follows: -- A.hs {-# LANGUAGE ForeignFunctionInterface #-} module A where import Foreign import Foreign.C foreign import ccall "&sys_siglist" siglist_a :: Ptr CString -- -- B.hs {-# LANGUAGE ForeignFunctionInterface #-} module B where import Foreign import Foreign.C foreign import ccall "&sys_siglist" siglist_b :: Ptr CString -- -- Main.hs {-# LANGUAGE ForeignFunctionInterface #-} module Main where import Foreign import Foreign.C import A import B foreign import ccall "&sys_siglist" siglist_main :: Ptr CString main = do putStrLn $ "siglist_a = " ++ show siglist_a putStrLn $ "siglist_b = " ++ show siglist_b putStrLn $ "siglist_main = " ++ show siglist_main peekSiglist "a " siglist_a peekSiglist "b " siglist_b peekSiglist "main" siglist_main peekSiglist name siglist = do ptr <- peekElemOff siglist 2 str <- maybePeek peekCString ptr putStrLn $ "siglist_" ++ name ++ "[2] = " ++ show str I would expect something like this output, where all pointer values identical and valid: $ runhaskell Main.hs siglist_a = 0x00007f53a948fe00 siglist_b = 0x00007f53a948fe00 siglist_main = 0x00007f53a948fe00 siglist_a [2] = Just "Interrupt" siglist_b [2] = Just "Interrupt" siglist_main[2] = Just "Interrupt" However, if I compile A.hs (with ghc -c A.hs), then the output changes to: $ runhaskell Main.hs siglist_a = 0x0000000040378918 siglist_b = 0x00007fe7c029ce00 siglist_main = 0x00007fe7c029ce00 siglist_a [2] = Nothing siglist_b [2] = Just "Interrupt" siglist_main[2] = Just "Interrupt"

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• Can I use a property placeholder with Spring EL?

  - by David Easley

  Before upgrading to Spring 3 I had this in my applicationContext.xml file: <bean class="com.northgateis.pole.ws.PolePayloadValidatingInterceptor"> <property name="validateRequest" value="${validateRequest}" /> <property name="validateResponse" value="${validateResponse}" /> </bean> where ${validateRequest) and ${validateRequest) refer to properties that may or may not be defined in my properties file. In Spring 2, if these proeprties were not present in the properties file the setters on the bean were not called and so the defaults hard-coded in PolePayloadValidatingInterceptor were used. After upgrading to Spring 3, it seems the behaviour is different: If the properties are not present in the properties file I get the following exception: SEVERE: Exception sending context initialized event to listener instance of class org.springframework.web.context.ContextLoaderListener org.springframework.beans.factory.BeanDefinitionStoreException: Invalid bean definition with name 'annotationMapping' defined in class path resource [com/northgateis/pole/ws/applicationContext-ws.xml]: Could not resolve placeholder 'validateRequest' at org.springframework.beans.factory.config.PropertyPlaceholderConfigurer.processProperties(PropertyPlaceholderConfigurer.java:272) at org.springframework.beans.factory.config.PropertyResourceConfigurer.postProcessBeanFactory(PropertyResourceConfigurer.java:75) at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:640) at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:615) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:405) at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:272) I tried dabbling with Spring EL but the following doesn't seem to work: <bean class="com.northgateis.pole.ws.PolePayloadValidatingInterceptor"> <property name="validateRequest" value="${validateRequest?:true}" /> <property name="validateResponse" value="${validateResponse?:false}" /> </bean> The value after the Elvis operator is always used, even when the properties are defined in the proeprties file. Interesting that the syntax is accepted. Any suggestions?

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• How to refactor these generic methods?

  - by Steve Crane

  I have written two nearly identical generic extension methods and am trying to figure out how I might refactor them into a single method. They differ only in that one operates on List and the other on List, and the properties I'm interested in are AssetID for AssetDocument and PersonID for PersonDocument. Although AssetDocument and PersonDocument have the same base class the properties are defined in each class so I don't think that helps. I have tried public static string ToCSVList<T>(this T list) where T : List<PersonDocument>, List<AssetDocument> thinking I might then be able to test the type and act accordingly but this results in the syntax error Type parameter 'T' inherits conflicting constraints These are the methods that I would like to refactor into a single method but perhaps I am simply going overboard and they would besat be left as they are. I'd like to hear what you think. public static string ToCSVList<T>(this T list) where T : List<AssetDocument> { var sb = new StringBuilder(list.Count * 36 + list.Count); string delimiter = String.Empty; foreach (var document in list) { sb.Append(delimiter + document.AssetID.ToString()); delimiter = ","; } return sb.ToString(); } public static string ToCSVList<T>(this T list) where T : List<PersonDocument> { var sb = new StringBuilder(list.Count * 36 + list.Count); string delimiter = String.Empty; foreach (var document in list) { sb.Append(delimiter + document.PersonID.ToString()); delimiter = ","; } return sb.ToString(); }

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• Destructuring assignment in JavaScript

  - by Anders Rune Jensen

  As can be seen in the Mozilla changlog for JavaScript 1.7 they have added destructuring assignment. Sadly I'm not very fond of the syntax (why write a and b twice?): var a, b; [a, b] = f(); Something like this would have been a lot better: var [a, b] = f(); That would still be backwards compatible. Python-like destructuring would not be backwards compatible. Anyway the best solution for JavaScript 1.5 that I have been able to come up with is: function assign(array, map) { var o = Object(); var i = 0; $.each(map, function(e, _) { o[e] = array[i++]; }); return o; } Which works like: var array = [1,2]; var _ = assign[array, { var1: null, var2: null }); _.var1; // prints 1 _.var2; // prints 2 But this really sucks because _ has no meaning. It's just an empty shell to store the names. But sadly it's needed because JavaScript doesn't have pointers. On the plus side you can assign default values in the case the values are not matched. Also note that this solution doesn't try to slice the array. So you can't do something like {first: 0, rest: 0}. But that could easily be done, if one wanted that behavior. What is a better solution?

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• clojure.algo.monad strange m-plus behaviour with parser-m - why is second m-plus evaluated?

  - by Mark Fisher

  I'm getting unexpected behaviour in some monads I'm writing. I've created a parser-m monad with (def parser-m (state-t maybe-m)) which is pretty much the example given everywhere (here, here and here) I'm using m-plus to act a kind of fall-through query mechanism, in my case, it first reads values from a cache (database), if that returns nil, the next method is to read from "live" (a REST call). However, the second value in the m-plus list is always called, even though its value is disgarded (if the cache hit was good) and the final return is that of the first monadic function. Here's a cutdown version of the issue i'm seeing, and some solutions I found, but I don't know why. My questions are: Is this expected behaviour or a bug in m-plus? i.e. will the 2nd method in a m-plus list always be evaluated if the first item returns a value? Minor in comparison to the above, but if i remove the call _ (fetch-state) from checker, when i evaluate that method, it prints out the messages for the functions the m-plus is calling (when i don't think it should). Is this also a bug? Here's a cut-down version of the code in question highlighting the problem. It simply checks key/value pairs passed in are same as the initial state values, and updates the state to mark what it actually ran. (ns monods.monad-test (:require [clojure.algo.monads :refer :all])) (def parser-m (state-t maybe-m)) (defn check-k-v [k v] (println "calling with k,v:" k v) (domonad parser-m [kv (fetch-val k) _ (do (println "k v kv (= kv v)" k v kv (= kv v)) (m-result 0)) :when (= kv v) _ (do (println "passed") (m-result 0)) _ (update-val :ran #(conj % (str "[" k " = " v "]"))) ] [k v])) (defn filler [] (println "filler called") (domonad parser-m [_ (fetch-state) _ (do (println "filling") (m-result 0)) :when nil] nil)) (def checker (domonad parser-m [_ (fetch-state) result (m-plus ;; (filler) ;; intitially commented out deliberately (check-k-v :a 1) (check-k-v :b 2) (check-k-v :c 3))] result)) (checker {:a 1 :b 2 :c 3 :ran []}) When I run this as is, the output is: > (checker {:a 1 :b 2 :c 3 :ran []}) calling with k,v: :a 1 calling with k,v: :b 2 calling with k,v: :c 3 k v kv (= kv v) :a 1 1 true passed k v kv (= kv v) :b 2 2 true passed [[:a 1] {:a 1, :b 2, :c 3, :ran ["[:a = 1]"]}] I don't expect the line k v kv (= kv v) :b 2 2 true to show at all. The first function to m-plus (as seen in the final output) is what is returned from it. Now, I've found if I pass a filler into m-plus that does nothing (i.e. uncomment the (filler) line) then the output is correct, the :b value isn't evaluated. If I don't have the filler method, and make the first method test fail (i.e. change it to (check-k-v :a 2) then again everything is good, I don't get a call to check :c, only a and b are tested. From my understanding of what the state-t maybe-m transformation is giving me, then the m-plus function should look like: (defn m-plus [left right] (fn [state] (if-let [result (left state)] result (right state)))) which would mean that right isn't called unless left returns nil/false. I'd be interested to know if my understanding is correct or not, and why I have to put the filler method in to stop the extra evaluation (whose effects I don't want to happen). Apologies for the long winded post!

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• CStdioFile Undeclared Identifier

  - by Eric Regnier

  I am unable to compile my code when using a CStdioFile type. I have included the afx.h header file but I am still receiving errors. What I am trying to do is write a cstring that contains an entire xml document to file. This cstring contains comments inside of it, but when I use other objects such as wofstream to write it to file, these comments are striped out for some reason. So that is why I am trying to write this to file using CStdioFile now. If anyone can help me out as to why I cannot compile my code using CStdioFile, or any other way to write a cstring that contains xml comments to file, please let me know! Below is my code using CStdioFile: CStdioFile xmlFile; xmlFile.Open( "c:\\test.txt", CFile::modeCreate | CFile::modeWrite | CFile::typeText ); xmlFile.WriteString( m_sData ); xmlFile.Close(); And my errors: error C2065: 'CStdioFile' : undeclared identifier error C2065: 'modeCreate' : undeclared identifier error C2065: 'modeWrite' : undeclared identifier error C2065: 'typeText' : undeclared identifier error C2065: 'xmlFile' : undeclared identifier error C2146: syntax error : missing ';' before identifier 'xmlFile' error C2228: left of '.Close' must have class/struct/union type type is ''unknown-type'' error C2228: left of '.Open' must have class/struct/union type type is ''unknown-type'' error C2228: left of '.WriteString' must have class/struct/union type type is ''unknown-type'' error C2653: 'CFile' : is not a class or namespace name error C2653: 'CFile' : is not a class or namespace name error C2653: 'CFile' : is not a class or namespace name error C3861: 'xmlFile': identifier not found, even with argument-dependent lookup error C3861: 'xmlFile': identifier not found, even with argument-dependent lookup error C3861: 'xmlFile': identifier not found, even with argument-dependent lookup

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