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• Is it easier to write a recursive-descent parser using an EBNF or a BNF?

  - by Vivin Paliath

  I've got a BNF and EBNF for a grammar. The BNF is obviously more verbose. I have a fairly good idea as far as using the BNF to build a recursive-descent parser; there are many resources for this. I am having trouble finding resources to convert an EBNF to a recursive-descent parser. Is this because it's more difficult? I recall from my CS theory classes that we went over EBNFs, but we didn't go over converting them into a recursive-descent parser. We did go over converting BNF's into a recursive-descent parser. The reason I'm asking is because the EBNF is more compact. From looking at the EBNF's in general, I notice that terms enclosed between { and } can be converted into a while loop. Are there any other guidelines or rules?

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• F# Static Member Type Constraints

  - by Stephen Swensen

  I'm trying to define a function, factorize, which uses structural type constraints (requires static members Zero, One, +, and /) similar to Seq.sum so that it can be used with int, long, bigint, etc. I can't seem to get the syntax right, and can't find a lot of resources on the subject. This is what I have, please help. let inline factorize (n:^NUM) = ^NUM : (static member get_Zero: unit->(^NUM)) ^NUM : (static member get_One: unit->(^NUM)) let rec factorize (n:^NUM) (j:^NUM) (flist: ^NUM list) = if n = ^NUM.One then flist elif n % j = ^NUM.Zero then factorize (n/j) (^NUM.One + ^NUM.One) (j::flist) else factorize n (j + ^NUM.One) (flist) factorize n (^NUM.One + ^NUM.One) []

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• Python 3.1.1 Class Question

  - by Protean

  I'm a new Python programmer who is having a little trouble using 'self' in classes. For example: class data: def __init__(self): self.table = [] def add(self, file): self.table.append(file) data.add('yes') In this function I want to have table be a variable stored in the class data and use add to modify it. However, when I run this script it gives me the error: Traceback (most recent call last): File "/Projects/Python/sfdfs.py", line 7, in <module> data.add('yes') TypeError: add() takes exactly 2 positional arguments (1 given) I assume that I am trying to call the function the wrong way in this instance, as this syntax is very similar to an example in the python documentation: http://docs.python.org/3.1/tutorial/classes.html

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• Pretty print code to PDF

  - by Joel

  I'm searching for a tool that will take a source directory and produce a single PDF containing the source code, preferably with syntax highlighting. I would like to read the PDF on my phone, in order to get familiar with a code-base, or just to see what I can learn by reading a lot of code. I will most often be reading Ruby. I would prefer if the tool ran on Linux. I don't mind paying for a tool if it is particularly good. Any suggestions?

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• Using Objective-C blocks with old compiler

  - by H2CO3

  I'm using the opensource iPhone toolchain on Linux for developing for jailbroken iPhones. I'd like to take advantage of the new (4.0, 5.0) iOS SDK features, but I can't as my old build of GCC doesn't understand the ^ block syntax. I noticed that blocks are just of type id (struct objc_object *). I know this from two resources: first, class-dump reports them as id, second, Apple docs clarify that "blocks can be retained". My quiestion is, how can I take advantage of blocks using this knowledge? I thought of something like: // this is in SDK 4.x/5.x - (void) doSomethingWithBlock:((int)(^block)(int)); // and I modify it like: - (void) doSomethingWithBlock(id)block; the question is: HOW TO ACTUALLY CALL IT? How do I create blocks? I can, of course, create function pointers (IMPs in particular), but how to achieve the object-like memory layout?

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• How do I export a large table into 50 smaller csv files of 100,000 records each

  - by Eddie

  I am trying to export one field from a very large table - containing 5,000,000 records, for example - into a csv list - but not all together, rather, 100,000 records into each .csv file created - without duplication. How can I do this, please? I tried SELECT field_name FROM table_name WHERE certain_conditions_are_met INTO OUTFILE /tmp/name_of_export_file_for_first_100000_records.csv LINES TERMINATED BY '\n' LIMIT 0 , 100000 that gives the first 100000 records, but nothing I do has the other 4,900,000 records exported into 49 other files - and how do I specify the other 49 filenames? for example, I tried the following, but the SQL syntax is wrong: SELECT field_name FROM table_name WHERE certain_conditions_are_met INTO OUTFILE /home/user/Eddie/name_of_export_file_for_first_100000_records.csv LINES TERMINATED BY '\n' LIMIT 0 , 100000 INTO OUTFILE /home/user/Eddie/name_of_export_file_for_second_100000_records.csv LINES TERMINATED BY '\n' LIMIT 100001 , 200000 and that did not create the second file... what am I doing wrong, please, and is there a better way to do this? Should the LIMIT 0 , 100000 be put Before the first INTO OUTFILE statement, and then repeat the entire command from SELECT for the second 100,000 records, etc? Thanks for any help. Eddie

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• Can you return an assignable lvalue in Scala?

  - by Alex R

  (note, lvalue is actually a term from the C grammar, I don't know what it's called in Scala!) Trying to learn Scala... this evening I'm working on an internal DSL for a dynamically scoped language that might resemble PHP syntax. My REPL is: Welcome to Scala version 2.7.6.final (Java HotSpot(TM) Client VM, Java 1.6.0). I have some made-up example code: class $(any: Any) { def update(sym: Symbol, any: Any) { println("line 2 executed");} def -(sym: Symbol) : $ = { println("line 1 executed"); return this } def update(any: Any) { println("line 3 executed");} } The following works as expected: scala var a = new $(0) a: $ = $@19238ad scala a('x) = "blah" line 2 executed On the other hand, why does the following not invoke the 1-parameter update method? scala a = 1 :6: error: type mismatch; found : Int(1) required: $ a = 1 ^ Ultimately, I would like this to work: a-'x = "blah" Thanks

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• Why is there no IronPerl (Perl for .Net)?

  - by Renaud Bompuis

  I'm a bit disappointed that there doesn't seem to be any effort to make Perl a first-class citizen of the .Net world. I've read a few 'reasons' in the past but I don't see why they can't be overcome (different garbage collectors, hard-to-parse syntax, part of CPAN modules couldn't be ported, different communities, ...). Activestate has a Perl.Net product but it's a hack (in the good sense) around a standard interpreter and some syntactic sugar to interoperate with .Net assemblies. A few years ago they stopped they visual studio integration of Perl citing lack of interest. That was a while ago, before all the changes to .Net to make it more 'dynamic'. Am I the only one who yearns for IronPerl?

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• Middleware for MongoDB or CouchDB with jQuery Ajax/JSON frontend

  - by Tauren

  I've been using the following web development stack for a few years: java/spring/hibernate/mysql/jetty/wicket/jquery For certain requirements, I'm considering switching to a NoSQL datastore with an AJAX frontend. I would probably build the frontend with jQuery and communicate with the web application middleware using JSON. I'm leaning toward MongoDB because of more dynamic query capabilities, but am still considering CouchDB. I'm not sure what to use in the middle. Probably something RESTful? My preference is to stick with Java (or maybe Scala or Groovy) since I'm using tools like Drools for rules and Shiro for security. But then again, I want to pick something that is quick an easy to work with, so I'm open to other solutions. If you are building ajax/json/nosql solutions, I'd like to hear details about what tools you are using and any pros/cons you've found to using them. Thanks!

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• perl one liner alternative to this bash "chain"?

  - by Michael Mao

  Hello everyone: I am trying to comprehend Perl following the way describe in the book "Minimal Perl". I've uploaded all source txt files onto my own server : results folder I got the output from using several bash commands in a "chain" like this: cat run*.txt | grep '^Bank[[:space:]]Balance'| cut -d ':' -f2 | grep -E '\$[0-9]+' I know this is far from the most concise and efficient, but at least it works... As our uni subject now moves onto the Perl part, I'd like to know if there is a way to get the same results in one line? I am trying something like the following code but stuck in the middle: Chenxi Mao@chenxi-a6b123bb /cygdrive/c/eMarket/output $ perl -wlne 'print; if $n=~/^Bank Balance/' syntax error at -e line 1, near "if $n" Execution of -e aborted due to compilation errors.

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• Exception handling policy in libraries

  - by Asaf R

  When building a .NET library, what's your exception handling policy? In specific, what's your policy about handling exceptions inside library calls and exposing them to calling code? Would you treat a library function as any other, thus letting all exceptions it can't handle flow out of it as-is? Would you create a custom exception for that library? Would you catch all exceptions and throw the library's exception instead? Would you set the original exception as the library's exception internal exception? How would the library dependence on a DB affect your exception-handling policy? What other guidelines and rules would you suggest?

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• Logic / Probability Question: Picking from a bag

  - by Rosarch

  I'm coding a board game where there is a bag of possible pieces. Each turn, players remove randomly selected pieces from the bag according to certain rules. For my implementation, it may be easier to divide up the bag initially into pools for one or more players. These pools would be randomly selected, but now different players would be picking from different bags. Is this any different? If one player's bag ran out, more would be randomly shuffled into it from the general stockpile.

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• Invoke or BeginInvoke cannot be called on a control until the window handle has been created.

  - by blade3

  Hi I am trying to install SQL Server 2008 Developer Edition x64 on a Windows Server 2008 VM. I run the installer for a standalone installation and this works fine for the setup support rules bit. That passes ok but then I get this error: TITLE: SQL Server Setup failure. SQL Server Setup has encountered the following error: Invoke or BeginInvoke cannot be called on a control until the window handle has been created.. BUTTONS: OK How can I resolve this? I am getting 2008 R2 CTP but this is just a CTP. My download is from DreamSpark. Thanks

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• Remove characters after specific character in string, then remove substring?

  - by sah302

  I feel kind of dumb posting this when this seems kind of simple and there are tons of questions on strings/characters/regex, but I couldn't find quite what I needed (except in another language: http://stackoverflow.com/questions/2176544/remove-all-text-after-certain-point). I've got the following code: [Test] public void stringManipulation() { String filename = "testpage.aspx"; String currentFullUrl = "http://localhost:2000/somefolder/myrep/test.aspx?q=qvalue"; String fullUrlWithoutQueryString = currentFullUrl.Replace("?.*", ""); String urlWithoutPageName = fullUrlWithoutQueryString.Remove(fullUrlWithoutQueryString.Length - filename.Length); String expected = "http://localhost:2000/somefolder/myrep/"; String actual = urlWithoutPageName; Assert.AreEqual(expected, actual); } I tried the solution in the question above (hoping the syntax would be the same!) but nope. I want to first remove the queryString which could be any variable length, then remove the page name, which again could be any length. How can I get the remove the query string from the full URL such that this test passes?

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• Python Fabric error

  - by jwesonga

  I'm running fabric (Django deployment to apache) and everything seems to work fine until I get to the task for installing the site: def install_site(): "Add the virtualhost file to apache" require('release', provided_by=[deploy, setup]) sudo('cd %(path)/releases/%(release)/%(release); cp %(project_name)/%(virtualhost_path)/%(project_domain) /etc/apache2/sites-available/%(project_domain)s') sudo('cd /etc/apache2/sites-available; a2ensite %(project_domain)') I keep getting this error: [173.203.124.16] sudo: cd %(path)/releases/%(release)/%(release); [173.203.124.16] err: /bin/bash: -c: line 0: syntax error near unexpected token `(' [173.203.124.16] err: /bin/bash: -c: line 0: `cd %(path)/releases/%(release)/%(r elease);' Warning: sudo() encountered an error (return code 2) while executing 'cd %(path) /releases/%(release)/%(release);' I've gone through the fabfile.py over and over and I can't see why the error is coming...any ideas?

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• Create many constrained, random permutation of a list

  - by Eyal

  I need to make a random list of permutations. The elements can be anything but assume that they are the integers 0 through x-1. I want to make y lists, each containing z elements. The rules are that no list may contain the same element twice and that over all the lists, the number of times each elements is used is the same (or as close as possible). For instance, if my elements are 0,1,2,3, y is 6, and z is 2, then one possible solution is: 0,3 1,2 3,0 2,1 0,1 2,3 Each row has only unique elements and no element has been used more than 3 times. If y were 7, then 2 elements would be used 4 times, the rest 3.

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• GDI+ is giving me errors

  - by user146780

  I want to use GDI + just to load a png. I included the headers and lib file then I do: Bitmap b; b.fromfile(filename); I get this from the compiler though. Error 1 error C2146: syntax error : missing ';' before identifier 'b' c:\users\josh\documents\visual studio 2008\projects\vectorizer project\vectorizer project\vectorizer project.cpp 23 Error 2 error C4430: missing type specifier - int assumed. Note: C++ does not support default-int c:\users\josh\documents\visual studio 2008\projects\vectorizer project\vectorizer project\vectorizer project.cpp 23 Error 3 error C4430: missing type specifier - int assumed. Note: C++ does not support default-int c:\users\josh\documents\visual studio 2008\projects\vectorizer project\vectorizer project\vectorizer project.cpp 23 Error 4 error C2440: '=' : cannot convert from 'const char [3]' to 'WCHAR *' c:\users\josh\documents\visual studio 2008\projects\vectorizer project\vectorizer project\vectorizer project.cpp 172 Error 5 error C2228: left of '.FromFile' must have class/struct/union c:\users\josh\documents\visual studio 2008\projects\vectorizer project\vectorizer project\vectorizer project.cpp 179 What is the correct way to do this? Thanks

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• passing a fortran int array to C++ by calling C++ function in fortran

  - by cppb

  hi, I am trying to call a C++ function in FORTRAN subroutine. This C+ function is supposed to update an integer array. Here is a non-working code I wrote. Can someone please let me know what the issue is: ! FORTRAN function that calls a C++ function subroutine my_function() integer(4) ar(*) integer(4) get_filled_ar ! Need correct syntax here. ar = get_filled_ar() end // C++ function: extern "C" { void get_filled_ar(int *ar){ ar[0] = 1; ar[1] = 10; ar[3] = 100; } }

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• Shopping Portal based on XML Data - XSLT or PHP?

  - by buggy1985

  For my bachelor thesis I want to implement a shopping (price comparison) portal prototype based on XML Data. The main requirement is to get a very clear and customizable HTML template, which should be hosted by the customer on his own webserver. I'm not very sure if XSLT meets this requirements, as it generates a lot of xsl-related code. It is not easy to understand for people with little HTML skills. I have some experience with the PHP templating engine Smarty. The syntax is much better, but I'm not sure if it's a good idea to parse the XML data with PHP, as it is very complex. Which language should I choose for a web application with high complexity? XSLT or PHP?

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• Hibernate: Parent/Child relationship in a single-table

  - by Dee

  I hardly see any pointer on the following problem related to Hibernate. This pertains to implementing inheritance using a single database table with a parent-child relationship to itself. For example: CREATE TABLE Employee ( empId BIGINT NOT NULL AUTO_INCREMENT, empName VARCHAR(100) NOT NULL, managerId BIGINT, CONSTRAINT pk_employee PRIMARY KEY (empId) ) Here, the managerId column may be null, or may point to another row of the Employee table. Business rule requires the Employee to know about all his reportees and for him to know about his/her manager. The business rules also allow rows to have null managerId (the CEO of the organisation doesn't have a manager). How do we map this relationship in Hibernate, standard many-to-one relationship doesn't work here? Example code would be appreciated.

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• Hibernate: Parent/Child relationship in a single-table

  - by Dee

  I hardly see any pointer on the following problem related to Hibernate. This pertains to implementing inheritance using a single database table with a parent-child relationship to itself. For example: CREATE TABLE Employee ( empId BIGINT NOT NULL AUTO_INCREMENT, empName VARCHAR(100) NOT NULL, managerId BIGINT, CONSTRAINT pk_employee PRIMARY KEY (empId) ) Here, the managerId column may be null, or may point to another row of the Employee table. Business rule requires the Employee to know about all his reportees and for him to know about his/her manager. The business rules also allow rows to have null managerId (the CEO of the organisation doesn't have a manager). How do we map this relationship in Hibernate, standard many-to-one relationship doesn't work here? Example code would be appreciated.

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• if_attribute on declarative authorization

  - by Victor Martins

  I have a many-to-many relationship like this: A user has_many organizations through affiliations and vice-versa. I'm using declarative organizations and I only want a user to edit a particular organization if he is affiliated and the affiliationtype attribute of affiliation is a particular value. So affiliations has 3 columns , user_id, organization_id and affiliationtype_id I can do: o = Organization.find(:first) o.affiliatons[0].user and get the user now I wish to do this: has_permission_on [:organizations], :to => :edit do if_attribute (...) end That if_attribute should see if the current user is the organization.affiliation[?].user and if the organization.affiliation[?].affiliationtype_id = "3" I hope this is syntax issue ... I really need to get this working.

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• jQuery datepicker getMinDate '+1d'

  - by Adrian Adkison

  Once I have set the minDate property of a datepicker with the convenient string syntax $(elem).datepicker('option','minDate','+1d +3m'); how can I get the date object of the minDate? To help illustrate, there is a method $(elem).datepicker('getDate'); which returns the date that is entered in the input in the format of a date object. I would like the same thing but for datepicker('getMinDate'). There is an option like this $(elem).datepicker('option','minDate'); but this returns '+1d +3m' which is not helpful. I need the actual date object to compare with another date object. Any ideas?

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• MIPS assembly: how to declare integer values in the .data section?

  - by Barney

  I'm trying to get my feet wet with MIPS assembly language using the MARS simulator. My main problem now is how do I initialize a set of memory locations so that I can access them later via assembly language instructions? For example, I want to initialize addresses 0x1001000 - 0x10001003 with the values 0x99, 0x87, 0x23, 0x45. I think this can be done in the data declaration (.data) section of my assembly program but I'm not sure of the syntax. Is this possible? Alternatively, in the .data section, how do I specify storing the integer values in some memory location (I don't care where, but I just want to reference them somewhere). So I'm looking for the C equivalent of "int x = 20, y=30, z=90;" I know how to do that using MIPS instructions but is it possible to declare something like that in the .data section of a MIPS assembly program?

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• Assign table values to multiple variables using a single SELECT statement and CASE?

  - by Darth Continent

  I'm trying to assign values contained in a lookup table to multiple variables by using a single SELECT having multiple CASE statements. The table is a lookup table with two columns like so: [GreekAlphabetastic] SystemID Descriptor -------- ---------- 1 Alpha 2 Beta 3 Epsilon This is my syntax: SELECT @VariableTheFirst = CASE WHEN myField = 'Alpha' THEN tbl.SystemID END, @VariableTheSecond = CASE WHEN myField = 'Beta' THEN tbl.SystemID END, @VariableTheThird = CASE WHEN myField = 'Epsilon' THEN tbl.SystemID END FROM GreekAlphabetastic tbl However, when I check the variables after this statement executes, I expected each to be assigned the appropriate value, but instead only the last has a value assigned. SELECT @VariableTheFirst AS First, @VariableTheSecond AS Second, @VariableTheThird AS Third Results: First Second Third NULL NULL 3 What am I doing wrong?

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