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• Code golf: Reverse Polish notation (postfix) evaluator

  - by Dario

  After having had code-golf contests on ordinary mathematical expressions, I just thought it would also be quite interesting how short an evaluation function for postfix notation (RPN) can be. Examples for RPN: 1 2 + == 3 1 2 + 3 * == 9 0 1 2 3 + + - 2 6 * + 3 / 1 - == 1 3 2 / 2.0 + == 3.5 To make things shorter, only +, -, * and /, all just in their binary version, must be supported. Operators/Operands are delimited by one space, divsions by zero don't have to be handled. The resulting code should be a function that takes the postfix string as input and returns the resulting number.

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• Regular Expression Help - Brackets within brackets

  - by adbox

  Hello I'm trying to develop a function that can sort through a string that looks like this: Donny went to the {park|store|{beach with friends|beach alone}} so he could get a breath of freash air. What I intend to do is search the text recursively for {} patterns where there is no { or } inside the {}, so only the innermost sandwiched text is selected, where I will then run a php to array the contents and select one at random, repeating process until the whole string has been parsed, showing a complete sentence. I just cannot wrap my head around regular expressions though. Appreciate any help!

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• Translate a webpage in PHP

  - by Rob

  I'm looking to translate a webpage in PHP 5 so I can save the translation and make it easily accessible via mydomain.com/lang/fr/category/article.html rather than users having to go through google translate. I've found various easy ways to translate text via CURL, however what i'd really like to be able to do is translate an entire webpage but obviously ignore the tags. The problem is that Google Translate messes up all the HTML tags, class names etc Does anyone know of a php class that can translate an entire webpage whilst ignoring the tags? I'm guessing it may be possible via advanced regular expressions or something like that, but i'm not sure. I can't just curl Google's response as i'll have all the extra JS that they put in. Any ideas?

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• Numbering Regex Submatches

  - by gentlylisped

  Is there a canonical ordering of submatch expressions in a regular expression? For example: What is the order of the submatches in "(([0-9]{3}).([0-9]{3}).([0-9]{3}).([0-9]{3}))\s+([A-Z]+)" ? a. (([0-9]{3})\.([0-9]{3})\.([0-9]{3})\.([0-9]{3}))\s+([A-Z]+) (([0-9]{3})\.([0-9]{3})\.([0-9]{3})\.([0-9]{3})) ([A-Z]+) ([0-9]{3}) ([0-9]{3}) ([0-9]{3}) ([0-9]{3}) b. (([0-9]{3})\.([0-9]{3})\.([0-9]{3})\.([0-9]{3}))\s+([A-Z]+) (([0-9]{3})\.([0-9]{3})\.([0-9]{3})\.([0-9]{3})) ([0-9]{3}) ([0-9]{3}) ([0-9]{3}) ([0-9]{3}) ([A-Z]+) or c. somthin' else.

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• Bug in Mathematica's Integrate with PrincipalValue->True

  - by Janus

  It seems that Mathematica's handling of principal value integrals fails on some corner cases. Consider these two expressions (which should give the same result): Integrate[UnitBox[x]/(x0 - x), {x, -Infinity, Infinity}, PrincipalValue -> True, Assumptions -> {x0 > 0}] /. x0 -> 1 // Simplify Integrate[UnitBox[x]/(x0 - x) /. x0 -> 1, {x, -Infinity, Infinity}, PrincipalValue -> True] In Mathematica 7.0.0 I get I Pi+Log[3] Log[3] Has this been fixed in later versions? Does anybody have an idea for a (more or less) general workaround?

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• Regular expression to match one of two video ID's in a Google Video URL

  - by Baldur

  I need to grab the video ID from a Google Video URL. There are two different types of URLs that I need to be able to match: http://video.google.com/videoplay?docid=-3498228245415745977# where I need to be able to match -3498228245415745977 (note the dash; -), and video.google.com/videoplay?docid=-3498228245415745977#docid=2728972720932273543 where I need to match 2728972720932273543. Is there any good regular expression that can match this? This is what I've got so far: @"docid=(-?\d{19}+)" since the video ID seems to be 19 characters except when it's prefixed with the dash. I'm using C# (of which I have very little experience) if that changes anything. P.s. I would also appreciate you review my regular expressions for YouTube (@"[\?&]v=([^&#])";), RedTube (@"/(\d{1,6})") and Vimeo (@"/(\d*)"). I do not expect users to enter the full URL and thus do not match the ^http://\\.?sitename+\\.\\w{2,3}.

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• Efficient data structure design

  - by Sway

  Hi there, I need to match a series of user inputed words against a large dictionary of words (to ensure the entered value exists). So if the user entered: "orange" it should match an entry "orange' in the dictionary. Now the catch is that the user can also enter a wildcard or series of wildcard characters like say "or__ge" which would also match "orange" The key requirements are: * this should be as fast as possible. * use the smallest amount of memory to achieve it. If the size of the word list was small I could use a string containing all the words and use regular expressions. however given that the word list could contain potentially hundreds of thousands of enteries I'm assuming this wouldn't work. So is some sort of 'tree' be the way to go for this...? Any thoughts or suggestions on this would be totally appreciated! Thanks in advance, Matt

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• Functional languages targeting the LLVM

  - by Matthew

  Are there any languages that target the LLVM that: Are statically typed Use type inference Are functional (i.e. lambda expressions, closures, list primitives, list comprehensions, etc.) Have first class object-oriented features (inheritance, polymorphism, mixins, etc.) Have a sophisticated type system (generics, covariance and contravariance, etc.) Scala is all of these, but only targets the JVM. F# (and to some extent C#) is most if not all of these, but only targets .NET. What similar language targets the LLVM?

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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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• Math with interpolated variables?

  - by Idan Gazit

  Consider the following sass: $font-size: 18; $em: $font-size; $column: $font-size * 3; // The column-width of my grid in pixels $gutter: $font-size * 1; // The gutter-width of my grid in pixels $gutter-em: #{$gutter / $em}em; // The gutter-width in ems. $column-em: #{$column / $em}em; // The column-width in ems; $foo = $gutter-em / 2; // This results in a value like "1em/2". :( $bar = ($gutter-em / 2); // this doesn't work either, same as above. How can I generate a $foo that works, and that I can reuse further in other expressions?

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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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• Python regular expression help

  - by dlw

  Hi SO, I can't seem to create the correct regular expression to extract the correct tokens from my string. Padding the beginning of the string with a space generates the correct output, but seems less than optimal: >>> import re >>> s = '-edge_0triggered a-b | -level_Sensitive c-d | a-b-c' >>> re.findall(r'\W(-[\w_]+)',' '+s) ['-edge_0triggered', '-level_Sensitive'] # correct output Here are some of the regular expressions I've tried, does anyone have a regex suggestion that doesn't involve changing the original string and generates the correct output >>> re.findall(r'(-[\w_]+)',s) ['-edge_0triggered', '-b', '-level_Sensitive', '-d', '-b', '-c'] >>> re.findall(r'\W(-[\w_]+)',s) ['-level_Sensitive'] Thanks -- DW

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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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• 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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• 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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• 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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• 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 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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• 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 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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• 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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• 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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• 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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