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• A compiler for automata theory

  - by saadtaame

  I'm designing a programming language for automata theory. My goal is to allow programmers to use machines (DFA, NFA, etc...) as units in expressions. I'm confused whether the language should be compiled, interpreted, or jit-compiled! My intuition is that compilation is a good choice, for some operations might take too much time (converting NFA's to equivalent DFA's can be expensive). Translating to x86 seems good. There is one issue however: I want the user to be able to plot machines. Any ideas?

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• How can I replace only the last occurence of an number in a string with php?

  - by Shawn

  How would you change this: a-10-b-19-c into something like this: a-10-b-20-c using regular expressions in PHP? The only solution I've found so far is: reverse the original string - "c-91-b-01-a" find the first number - "91" reverse it - "19" turn in into a number (parseInt) - 19 add 1 to it (+1) - 20 turn it into a string again (toString) - "20" reverse it again - "02" replace the original match with this new number - "c-02-b-01-a" reverse the string - "a-10-b-20-c" I was hoping someone on SO would have a simpler way to do this... Anyone?

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• Expression Tree : C#

  - by nettguy

  My understanding of expression tree is : Expression trees are in-memory representation of expression like arithmetic or boolean expression.The expressions are stored into the parsed tree.so we can easily transalate into any other language. Linq to SQL uses expression tree.Normally when our LINQ to SQL query compiler translates it to parsed expression trees.These are passed to Sql Server as T-SQL Statements.The Sql server executes the T-SQL query and sends down the result back.That is why when you execute LINQ to SQL you gets IQueryable<T> not IEnumetrable<T>.Because IQuerybale contains public IQueryable:IEnumerable { Type Element {get;} Expression Expression {get;} IQueryaleProvider Provider {get;} } Questions : Microsoft uses Expression trees to play with LINQ-to-Sql.What are the different ways can i use expression trees to boost my code. Apart from LINQ to SQL,Linq to amazon ,who used expression trees in their applications? Linq to Object return IEnumerable,Linq to SQL return IQueryable ,What does LINQ to XML return?

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• Using C# and gppg, how would I construct an abstract syntax tree?

  - by Rupert

  Is there a way to do this almost out-of-the-box? I could go and write a big method that would use the collected tokens to figure out which leaves should be put in which branches and in the end populate a TreeNode object, but since gppg already handled everything by using supplied regular expressions, I was wondering if there's an easier way? Even if not, any pointers as to how best to approach the problem of creating an AST would be appreciated. Apologies if I said anything silly, I'm only just beginning to play the compiler game. :)

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• How to handle subclasses in JasperReports?

  - by gotch4

  I've two classes (A and B) that extend a base class BASE. I need to make a report that takes an array of such classes and the prints the fields of A or B. I tought of using conditional expressions, then casting to one or another (depending on a field value). But I can't cast, because I don't know how to refere to the current bean. To do this I am using a JRBeanCollectionDataSource filled with a List<BASE>. How do I cast every bean to A or B in a report (or subreport)? I tried: ((A)this) but it says basically that this contains the report instance, not the current bean and gives error.

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• Why does Excel expose an 'Evaluate' method at all?

  - by jtolle

  A few questions have come up recently involving the Application.Evaluate method callable from Excel VBA. The old XLM macro language also exposes an EVALUATE() function. Both can be quite useful. Does anyone know why the general expression evaluator is exposed, though? My own hunch is that Excel needed to give people a way to get ranges from string addresses, and to get the value of named formulas, and just opening a portal to the expression evaluator was the easiest way. But of course you don't need the ability to evaluate arbitrary expressions just to do that. Application.Evaluate seems kind of...unfinished. It isn't very well documented, and there are quite a few quirks and limitations (as described by Charles Williams here: http://www.decisionmodels.com/calcsecretsh.htm) with what is exposed. I suppose the answer could be simply "why not expose it?", but I'd be interested to know what design decisions led to this feature. Failing that, I'd be interested to hear other hunches.

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• Why is this logical expression in python False?

  - by W3ctor

  My question is, why are these expressions False? Python 2.6.4 (r264:75706, Dec 7 2009, 18:45:15) [GCC 4.4.1] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> num = raw_input("Choose a number: ") Choose a number: 5 >>> print num 5 >>> print ( num < 18 ) False >>> print ( num == 5 ) False Because if i try this: >>> print ( num > 0 ) True The expression works fine. Thank you for the help!

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• Listing mysql row entries from tags into one single row

  - by Derrick

  Hi guys, Ive got two tables, one a listings and another representing a list of tags for the listing table. In the listings table the tag ids are stored in a field called tags as 1-2-3- this has worked out very well for me regular expressions and joins to seperate and display the data, BUT... I now need to pull the titles of those tags into a single row. See below. listings table id tags 1 1-2-3- 2 4-5-6- tags table id title 1 pig 2 dog 3 cat 4 mouse 5 elephant 6 duck And what I need to produce out of the listings table is: id tags 2 mouse, elephant, duck any suggestions?

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• How can I remove sensitive data from the debug_backtrace function?

  - by RenderIn

  I am using print_r(debug_backtrace(), true) to retrieve a string representation of the debug backtrace. This works fine, as print_r handles recursion. When I tried to recursively iterate through the debug_backtrace() return array before turning it into a string it ran into recursion and never ended. Is there some simple way I can remove certain sensitive key/value pairs from the backtrace array? Perhaps some way to turn the array to a string using print_r, then back to an array with the recursive locations changed to the string RECURSION, which I could the iterate through. I don't want to execute regular expressions on the string representation if possible.

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• Regex pattern for searches with include and exclude

  - by alex-kravchenko-zmeyp

  I am working on a Regex pattern for searches that should allow optional '+' sign to include in the search and '-' sign to exclude from the search. For example: +apple orange -peach should search for apples and oranges and not for peaches. Also the pattern should allow for phrases in double quotes mixed with single words, for example: "red apple" -"black grape" +orange - you get the idea, same as most of the internet searches. So I am running 2 regular expressions, first to pick all the negatives, which is simple because '-' is required: (?<=[\-]"?)((?<=")(?<exclude>[^"]+)|(?<exclude>[^\s,\+\-"]+)) And second to pick positives, and it is a little more complex because '+' is optional: ((?<=[\+\s]")(?<include>[^\s"\+\-][^"]+))|(?<include>(?<![\-\w]"?)([\w][^,\s\-\+]+))(?<!") Positive search is where I am having a problem, it works fine when I run it in RegexBuddy but when I try in .Net the pattern picks up second word from negative criteria, for example in -"black grape" it picks up word 'grape' even though it ends with double quote. Any suggestions?

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• How to handle an "infinite" IEnumerable?

  - by Danvil

  A trivial example of an "infinite" IEnumerable would be IEnumerable<int> Numbers() { int i=0; while(true) { yield return i++; } } I know, that foreach(int i in Numbers().Take(10)) { Console.WriteLine(i); } and var q = Numbers(); foreach(int i in q.Take(10)) { Console.WriteLine(i); } both work fine (and print out the number 0-9). But are there any pitfalls when copying or handling expressions like q? Can I rely on the fact, that they are always evaluated "lazy"? Is there any danger to produce an infinite loop?

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• How to validate expression on button click in asp.net C#

  - by Hamad

  I am making a website and I have made a form fields like email field and validation expressions associated with it. Validation is initiated on text change. But i want it t execute on "submit" button click event. I have searched but could not locate the solution to my problem. Please tel me why is this happening and how can i make it right. I am new to this web development field, So need help from you guys. Thanks in advance!!! Hamad

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• How do I use Eval() to reference values in a SortedDictionary in an asp Repeater?

  - by MatthewMartin

  I thought I was clever to switch from the memory intensive DataView to SortedDictionary as a memory efficient sortable data structure. Now I have no idea how get the key and value out of the datasource in the <%# or Eval() expressions. SortedDictionary<int, string> data = RetrieveNames(); rCurrentTeam.DataSource = data; rCurrentTeam.DataBind(); <asp:Repeater ID="rNames" runat="server"> <ItemTemplate> <asp:Label ID="lblName" runat="server" Text='<%# Eval("what?") %>' /> </ItemTemplate> </asp:Repeater> Any suggestions?

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• What is the purpose of Java's unary plus operator?

  - by Syntactic

  Java's unary plus operator appears to have come over from C, via C++. As near as I can tell, it has the following effects: promotes its operand to int, if it's not already an int or wider unboxes its operand, if it's a wrapper object complicates slightly the parsing of evil expressions containing large numbers of consecutive plus signs It seems to me that there are better (or, at least, clearer) ways to do all of these things. In this SO question, concerning the counterpart operator in C#, someone said that "It's there to be overloaded if you feel the need." But in Java, one cannot overload any operator. So does this operator exist in Java just because it existed in C++?

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• Pros and Cons of Different macro function / inline methods in C

  - by Robert S. Barnes

  According to the C FAQ, there are basically 3 practical methods for "inlining" code in C: #define MACRO(arg1, arg2) do { \ /* declarations */ \ stmt1; \ stmt2; \ /* ... */ \ } while(0) /* (no trailing ; ) */ or #define FUNC(arg1, arg2) (expr1, expr2, expr3) To clarify this one, the arguments are used in the expressions, and the comma operator returns the value of the last expression. or using the inline declaration which is supported as an extension to gcc and in the c99 standard. The do { ... } while (0) method is widely used in the Linux kernel, but I haven't encountered the other two methods very often if at all. I'm referring specifically to multi-statement "functions", not single statement ones like MAX or MIN. What are the pros and cons of each method, and why would you choose one over the other in various situations?

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• Cannot understand NullPointerException with custom adapter

  - by ganesh

  hi, I am trying to create a list view which as TextView that can display html content , an WebView and other basic TextViews.I tried to extend SimpleAdapter but i struck with the problem ,I will be glad if someone can point out the mistake i am doing. In onCreate method ArrayList mylist= resultfromXmlparser(); adap = new MyAdapter(TourLandingPage.this, mylist, R.layout.row, new String[] {"Name", "desc","Duration","Price","imgurl"}, new int[] {R.id.productname,R.id.des,R.id.duration,R.id.pricefrom,R.id.photo}); setListAdapter(adap); My custom Adapter looks like this private class MyAdapter extends SimpleAdapter { ArrayList<HashMap<String,String>> elements; Context ctx; public MyAdapter(Context context, ArrayList<HashMap<String,String>> mylist,int textViewResourceId,String[] names,int[] resouceid) { super(context, mylist,textViewResourceId, names,resouceid); this.elements=mylist; this.ctx=context; } @Override public int getCount() { return elements.size(); } @Override public Object getItem(int position) { return elements.get(position); } @Override public long getItemId(int position) { return position; } @Override public View getView(int position, View convertView, ViewGroup parent) { RelativeLayout rowLayout; if (convertView == null) { rowLayout = (RelativeLayout) LayoutInflater.from(ctx).inflate(R.layout.rowfor_tourlist, parent, false); } else { rowLayout = (RelativeLayout) convertView; } TextView in = (TextView)rowLayout.findViewById(R.id.introduction); TextView du = (TextView)rowLayout.findViewById(R.id.duration); TextView pf = (TextView)rowLayout.findViewById(R.id.pricefrom); TextView pn = (TextView)rowLayout.findViewById(R.id.productname); WebView wv=(WebView)rowLayout.findViewById(R.id.photo); in.setText(Html.fromHtml(mylist.get(position).get("desc"))); du.setText(mylist.get(position).get("Duration")); pf.setText(mylist.get(position).get("Price")); pn.setText(mylist.get(position).get("Name")); wv.getSettings().setJavaScriptEnabled(true); wv.loadUrl(mylist.get(position).get("imgurl")); return convertView; } }//class and my row.xml file looks like RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" TextView android:id="@+id/productname" ...... LinearLayout android:layout_width="wrap_content" android:layout_height="60dip" android:layout_margin="5dip" android:layout_below="@id/productname" android:orientation="horizontal" android:id="@+id/lay1" WebView android:id="@+id/photo" .... TextView android:id="@+id/introduction" ...... LinearLayout TextView android:id="@+id/duration" .... TextView android:id="@+id/pricefrom" ..... RelativeLayout The error i was getting was 04-28 19:46:17.749: ERROR/AndroidRuntime(976): Uncaught handler: thread main exiting due to uncaught exception 04-28 19:46:17.769: ERROR/AndroidRuntime(976): java.lang.NullPointerException 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.ListView.setupChild(ListView.java:1693) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.ListView.makeAndAddView(ListView.java:1671) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.ListView.fillDown(ListView.java:637) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.ListView.fillFromTop(ListView.java:694) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.ListView.layoutChildren(ListView.java:1521) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.AbsListView.onLayout(AbsListView.java:1113) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.view.View.layout(View.java:6831) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1119) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.LinearLayout.layoutHorizontal(LinearLayout.java:1108) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.LinearLayout.onLayout(LinearLayout.java:920) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.view.View.layout(View.java:6831) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1119) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:998) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.LinearLayout.onLayout(LinearLayout.java:918) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.view.View.layout(View.java:6831) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.FrameLayout.onLayout(FrameLayout.java:333) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.view.View.layout(View.java:6831) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1119) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:998) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.LinearLayout.onLayout(LinearLayout.java:918) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.view.View.layout(View.java:6831) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.widget.FrameLayout.onLayout(FrameLayout.java:333) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.view.View.layout(View.java:6831) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.view.ViewRoot.performTraversals(ViewRoot.java:996) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.view.ViewRoot.handleMessage(ViewRoot.java:1633) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.os.Handler.dispatchMessage(Handler.java:99) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.os.Looper.loop(Looper.java:123) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at android.app.ActivityThread.main(ActivityThread.java:4338) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at java.lang.reflect.Method.invokeNative(Native Method) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at java.lang.reflect.Method.invoke(Method.java:521) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 04-28 19:46:17.769: ERROR/AndroidRuntime(976): at dalvik.system.NativeStart.main(Native Method) 04-28 19:46:17.789: INFO/Process(52): Sending signal. PID: 976 SIG: 3 04-28 19:46:17.799: INFO/dalvikvm(976): threadid=7: reacting to signal 3 04-28 19:46:17.829: INFO/dalvikvm(976): Wrote stack trace to '/data/anr/traces.txt'

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• How to extract URL parameters from a URL with Ruby or Rails?

  - by Flackou

  Hi, I have some URLs, like http://www.example.com/something?param1=value1&param2=value2&param3=value3, and I would like to extract the parameters from these URLs and get them in a Hash. Obviously, I could use regular expressions, but I was just wondering if there was easier ways to do that with Ruby or Rails. I haven't found anything in the Ruby Module 'URI' but perhaps I missed something. In fact, I need a method that would do that : extract_parameters_from_url("http://www.example.com/something?param1=value1&param2=value2&param3=value3") => {:param1 => 'value1', :param2 => 'value2', :param3 => 'value3'} Would you have some advices? Thanks in advance. Julien

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• Are Scala "continuations" just a funky syntax for defining and using Callback Functions?

  - by Alex R

  And I mean that in the same sense that a C/Java for is just a funky syntax for a while loop. I still remember when first learning about the for loop in C, the mental effort that had to go into understanding the execution sequence of the three control expressions relative to the loop statement. Seems to me the same sort of effort has to be applied to understand Continuations (in Scala and I guess probably other languages). And then there's the obvious follow-up question... if so, then what's the point? It seems like a lot of pain (language complexity, programmer errors, unreadable programs, etc) for no gain.

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• Can't create admin user on Heroku

  - by Nick5a1

  I am new to rails and I have gone through Kevin Skoglund's Ruby on Rails 3 Essential Training course on Lynda.com. Through the course you set up a simple cms, which I did. It doesn't cover Git or deployment but I've pushed my simple cms to github (https://github.com/nick5a1/Simple_CMS) and deployed to Heroku (http://nkarrasch.herokuapp.com/). In order to deploy to Heroku I followed the Heroku setup guide (https://devcenter.heroku.com/articles/rails3) and switched my database from MySQL to PostgreSQL. As instructed I changed gen'mysql2' to gen 'sqlite3' in my Gemfile and ran bundle install before pushing. I then ran heroku run rake db:migrate. I'm running into 2 problems. When I try to log in (http://nkarrasch.herokuapp.com/access) I get an error "We're sorry, but something went wrong". I should instead be getting a flash message with invalid username/password combination. This is what I'm getting on my test environment on my local machine. Secondly, when I log into the Heroku console to create and create an admin user, when I try to save that user I get the following error: irb(main):004:0> user.save (1.2ms) BEGIN AdminUser Exists (1.9ms) SELECT 1 AS one FROM "admin_users" WHERE "admin_users"."username" = 'Nick5a1' LIMIT 1 (1.7ms) ROLLBACK => false Any advice on how to troubleshoot would be greatly appreciated :). Thanks very much, Nick EDIT: Here are my Heroku logs: 2012-06-27T20:36:44+00:00 heroku[slugc]: Slug compilation started 2012-06-27T20:37:34+00:00 heroku[api]: Add shared-database:5mb add-on by [email protected] 2012-06-27T20:37:34+00:00 heroku[api]: Release v2 created by [email protected] 2012-06-27T20:37:34+00:00 heroku[api]: Add RAILS_ENV, LANG, PATH, RACK_ENV, GEM_PATH config by [email protected] 2012-06-27T20:37:34+00:00 heroku[api]: Release v3 created by [email protected] 2012-06-27T20:37:34+00:00 heroku[api]: Release v4 created by [email protected] 2012-06-27T20:37:34+00:00 heroku[api]: Deploy 1d82839 by [email protected] 2012-06-27T20:37:35+00:00 heroku[slugc]: Slug compilation finished 2012-06-27T20:37:36+00:00 heroku[web.1]: Starting process with command `bundle exec rails server -p 45450` 2012-06-27T20:37:40+00:00 app[web.1]: DEPRECATION WARNING: You have Rails 2.3-style plugins in vendor/plugins! Support for these plugins will be removed in Rails 4.0. Move them out and bundle them in your Gemfile, or fold them in to your app as lib/myplugin/* and config/initializers/myplugin.rb. See the release notes for more on this: http://weblog.rubyonrails.org/2012/1/4/rails-3-2-0-rc2-has-been-released. (called from <top (required)> at /app/config/environment.rb:5) 2012-06-27T20:37:40+00:00 app[web.1]: DEPRECATION WARNING: You have Rails 2.3-style plugins in vendor/plugins! Support for these plugins will be removed in Rails 4.0. Move them out and bundle them in your Gemfile, or fold them in to your app as lib/myplugin/* and config/initializers/myplugin.rb. See the release notes for more on this: http://weblog.rubyonrails.org/2012/1/4/rails-3-2-0-rc2-has-been-released. (called from <top (required)> at /app/config/environment.rb:5) 2012-06-27T20:37:40+00:00 app[web.1]: DEPRECATION WARNING: You have Rails 2.3-style plugins in vendor/plugins! Support for these plugins will be removed in Rails 4.0. Move them out and bundle them in your Gemfile, or fold them in to your app as lib/myplugin/* and config/initializers/myplugin.rb. See the release notes for more on this: http://weblog.rubyonrails.org/2012/1/4/rails-3-2-0-rc2-has-been-released. (called from <top (required)> at /app/config/environment.rb:5) 2012-06-27T20:37:44+00:00 app[web.1]: => Rails 3.2.6 application starting in production on http://0.0.0.0:45450 2012-06-27T20:37:44+00:00 app[web.1]: => Call with -d to detach 2012-06-27T20:37:44+00:00 app[web.1]: => Booting WEBrick 2012-06-27T20:37:44+00:00 app[web.1]: Connecting to database specified by DATABASE_URL 2012-06-27T20:37:44+00:00 app[web.1]: => Ctrl-C to shutdown server 2012-06-27T20:37:44+00:00 app[web.1]: [2012-06-27 20:37:44] INFO WEBrick 1.3.1 2012-06-27T20:37:44+00:00 app[web.1]: [2012-06-27 20:37:44] INFO ruby 1.9.2 (2011-07-09) [x86_64-linux] 2012-06-27T20:37:44+00:00 app[web.1]: [2012-06-27 20:37:44] INFO WEBrick::HTTPServer#start: pid=2 port=45450 2012-06-27T20:37:45+00:00 heroku[web.1]: State changed from starting to up 2012-06-27T20:39:44+00:00 heroku[run.1]: Awaiting client 2012-06-27T20:39:44+00:00 heroku[run.1]: Starting process with command `bundle exec rake db:migrate` 2012-06-27T20:39:44+00:00 heroku[run.1]: State changed from starting to up 2012-06-27T20:39:51+00:00 heroku[run.1]: Process exited with status 0 2012-06-27T20:39:51+00:00 heroku[run.1]: State changed from up to complete 2012-06-27T20:41:05+00:00 heroku[run.1]: Awaiting client 2012-06-27T20:41:05+00:00 heroku[run.1]: Starting process with command `bundle exec rails console` 2012-06-27T20:41:05+00:00 heroku[run.1]: State changed from starting to up 2012-06-27T20:46:09+00:00 heroku[run.1]: Process exited with status 0 2012-06-27T20:46:09+00:00 heroku[run.1]: State changed from up to complete

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• Merging MySQL row entries into a single row

  - by Derrick

  I've got two tables, one for listings and another representing a list of tags for the listings table. In the listings table the tag ids are stored in a field called tags as 1-2-3-. This has worked out very well for me (regular expressions and joins to separate and display the data), but I now need to pull the titles of those tags into a single row. See below. listings table id tags 1 1-2-3- 2 4-5-6- tags table id title 1 pig 2 dog 3 cat 4 mouse 5 elephant 6 duck And what I need to produce out of the listings table is: id tags 2 mouse, elephant, duck

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• Adding two Set[Any]

  - by Alex Boisvert

  Adding two Set[Int] works: Welcome to Scala version 2.8.1.final (Java HotSpot(TM) Server VM, Java 1.6.0_23). Type in expressions to have them evaluated. Type :help for more information. scala> Set(1,2,3) ++ Set(4,5,6) res0: scala.collection.immutable.Set[Int] = Set(4, 5, 6, 1, 2, 3) But adding two Set[Any] doesn't: scala> Set[Any](1,2,3) ++ Set[Any](4,5,6) <console>:6: error: ambiguous reference to overloaded definition, both method ++ in trait Addable of type (xs: scala.collection.TraversableOnce[Any])scala.collection.immutable.Set[Any] and method ++ in trait TraversableLike of type [B >: Any,That](that: scala.collection.TraversableOnce[B])(implicit bf: scala.collection.generic.CanBuildFrom[scala.collection.immutable.Set[Any],B,That])That match argument types (scala.collection.immutable.Set[Any]) Set[Any](1,2,3) ++ Set[Any](4,5,6) ^ Any suggestion to work around this error?

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• What's the point of lambda in scheme?

  - by incrediman

  I am learning scheme. I know how to use both lambda and let expressions. However I'm struggling to figure out what the point is of using lambda. Can't you do everything with let that you can with lambda? It would be especially helpful to see an example of a situation where a lambda expression is a better choice than let. One other thing - are there also situations where let is more useful than lambda? If so such an example would be nice as well. Thanks!

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• How to implement arrays in an interpreter?

  - by Ray

  I have managed to write several interpreters including Tokenizing Parsing, including more complicated expressions such as ((x+y)*z)/2 Building bytecode from syntax trees Actual bytecode execution What I didn't manage: Implementation of dictionaries/lists/arrays. I always got stuck with getting multiple values into one variable. My value structure (used for all values passed around, including variables) looks like this, for example: class Value { public: ValueType type; int integerValue; string stringValue; } Works fine with integers and strings, but how could I implement arrays? (From now on with array I mean arrays in my experimental language, not in C++) How can I fit the array concept into the Value class above? Is it possible? How should I make arrays able to be passed around just as you could pass around integers and strings in my language, using the class above? Accessing array elements or memory allocation wouldn't be the problem, I just don't know how to store them.

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• Python: Elegant way to check if at least one regex in list matches a string

  - by houbysoft

  Hi. I have a list of regexes in python, and a string. Is there an elegant way to check if the at least one regex in the list matches the string? By elegant, I mean something better than simply looping through all of the regexes and checking them against the string and stopping if a match is found. Basically, I had this code: list = ['something','another','thing','hello'] string = 'hi' if string in list: pass # do something else: pass # do something else Now I would like to have some regular expressions in the list, rather than just strings, and I am wondering if there is an elegant solution to check for a match to replace if string in list:. Thanks in advance.

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• C# Lambda Problem

  - by Chris Klepeis

  Probably something simple, but as I'm new to lambda expressions, the problem evades me: m => m.contactID == contactID && m.primaryAddress == true && (m.addressTypeID == 2 || m.addressTypeID == 3) I tried to use that lambda expression but I receive an invalid operator. Is there a way to simplify this so that it would work? Edit: The equivolent sql query would be: SELECT * FROM Contact WHERE contactID = 3 AND primaryAddress = 1 AND (addressTypeID = 2 OR addressTypeID = 3) I have a repository function defined like so: public E Single(Expression<Func<E, bool>> where) { return objectSet.Single<E>(where); } I'm passing the lambda expression above into this function. Invalid operator error.

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