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  • Support for nested model and class validation with ASP.NET MVC 2.0

    - by Diep-Vriezer
    I'm trying to validate a model containing other objects with validation rules using the System.ComponentModel.DataAnnotations attributes was hoping the default MVC implementation would suffice: var obj = js.Deserialize(json, objectInfo.ObjectType); if(!TryValidateModel(obj)) { // Handle failed model validation. } The object is composed of primitive types but also contains other classes which also use DataAnnotications. Like so: public class Entry { [Required] public Person Subscriber { get; set; } [Required] public String Company { get; set; } } public class Person { public String FirstName { get; set;} [Required] public String Surname { get; set; } } The problem is that the ASP.NET MVC validation only goes down 1 level and only evaluates the properties of the top level class, as can be read on digitallycreated.net/Blog/54/deep-inside-asp.net-mvc-2-model-metadata-and-validation. Does anyone know an elegant solution to this? I've tried xVal, but they seem to use a non-recursive pattern (http://blog.stevensanderson.com/2009/01/10/xval-a-validation-framework-for-aspnet-mvc/). Someone must have run into this problem before right? Nesting objects in your model doesn't seem so weird if you're designing a web service.

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  • What's the "best" database for embedded?

    - by mawg
    I'm an embedded guy, not a database guy. I've been asked to redesign an existing system which has bottlenecks in several places. The embedded device is based around an ARM 9 processor running at 220mHz. There should be a database of 50k entries (may increase to 250k) each with 1k of data (max 8 filed). That's approximate - I can try to get more precise figures if necessary. They are currently using SqlLite 2 and planning to move to SqlLite 3. Without starting a flame war - I am a complete d/b newbie just seeking advice - is that the "best" decision? I realize that this might be a "how long is a piece of string?" question, but any pointers woudl be greatly welcomed. I don't mind doing a lot of reading & research, but just hoped that you could get me off to a flying start. Thanks. p.s Again, a total rewrite, might not even stick with embedded Linux, but switch to eCos, don't worry too much about one time conversion between d/b formats. Oh, and accesses should be infrequent, at most one every few seconds. edit: ok, it seems they have 30k entries (may reach 100k or more) of only 5 or 6 fields each, but at least 3 of them can be a search key for a record. They are toying with "having no d/b at all, since the data are so simple", but it seems to me that with multiple keys, we couldn't use fancy stuff like a quicksort() type search (recursive, binary search). Any thoughts on "no d/b", just data-structures? Btw, one key is 800k - not sure how well SqlLite handles that (maybe with "no d/b" I have to hash that 800k to something smaller?)

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  • Binary Trees in Scheme

    - by Javier
    Consider the following BNF defining trees of numbers. Notice that a tree can either be a leaf, a node-1 with one subtrees, or a node-2 with two subtrees. tree ::= (’leaf number) | (’node-1 tree) | (’node-2 tree tree) a. Write a template for recursive procedures on these trees. b. Define the procedure (leaf-count t) that returns the number of leaves in t > (leaf-count ’(leaf 5)) 1 > (leaf-count ’(node-2 (leaf 25) (leaf 17))) 2 > (leaf-count ’(node-1 (node-2 (leaf 4) (node-2 (leaf 2) (leaf 3))))) 3 Here's what I have so far: ;define what a leaf, node-1, and node-2 is (define leaf list) (define node-1 list) (define node-2 list) ;procedure to decide if a list is a leaf or a node (define (leaf? tree) (number? (car tree))) (define (node? tree) (pair? (car tree))) (define (leaf-count tree) (cond ((null? tree) 0) ((number? tree) 0) ((leaf? tree) 1) (else (+ (leaf-count (car tree)) (leaf-count (cdr tree)))))) It looks like it should run just fine, but when I try to run it using a simple test case like (leaf-count '(leaf 5)) I get the following error message: car: expects argument of type pair; given leaf What does this error message mean? I am defining a leaf as a list. But for some reason, it's not seeing that and gives me that error message.

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  • Shift-reduce: when to stop reducing?

    - by Joey Adams
    I'm trying to learn about shift-reduce parsing. Suppose we have the following grammar, using recursive rules that enforce order of operations, inspired by the ANSI C Yacc grammar: S: A; P : NUMBER | '(' S ')' ; M : P | M '*' P | M '/' P ; A : M | A '+' M | A '-' M ; And we want to parse 1+2 using shift-reduce parsing. First, the 1 is shifted as a NUMBER. My question is, is it then reduced to P, then M, then A, then finally S? How does it know where to stop? Suppose it does reduce all the way to S, then shifts '+'. We'd now have a stack containing: S '+' If we shift '2', the reductions might be: S '+' NUMBER S '+' P S '+' M S '+' A S '+' S Now, on either side of the last line, S could be P, M, A, or NUMBER, and it would still be valid in the sense that any combination would be a correct representation of the text. How does the parser "know" to make it A '+' M So that it can reduce the whole expression to A, then S? In other words, how does it know to stop reducing before shifting the next token? Is this a key difficulty in LR parser generation?

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  • Why is TransactionScope operation is not valid?

    - by Cragly
    I have a routine which uses a recursive loop to insert items into a SQL Server 2005 database The first call which initiates the loop is enclosed within a transaction using TransactionScope. When I first call ProcessItem the myItem data gets inserted into the database as expected. However when ProcessItem is called from either ProcessItemLinks or ProcessItemComments I get the following error. “The operation is not valid for the state of the transaction” I am running this in debug with VS 2008 on Windows 7 and have the MSDTC running to enable distributed transactions. The code below isn’t my production code but is set out exactly the same. The AddItemToDatabase is a method on a class I cannot modify and uses a standard ExecuteNonQuery() which creates a connection then closes and disposes once completed. I have looked at other posting on here and the internet and still cannot resolve this issue. Any help would be much appreciated. using (TransactionScope processItem = new TransactionScope()) { foreach (Item myItem in itemsList) { ProcessItem(myItem); } processItem.Complete(); } private void ProcessItem(Item myItem) { AddItemToDatabase(myItem); ProcessItemLinks(myItem); ProcessItemComments(myItem); } private void ProcessItemLinks(Item myItem) { foreach (Item link in myItem.Links) { ProcessItem(link); } } private void ProcessItemComments(Item myItem) { foreach (Item comment in myItem.Comments) { ProcessItem(comment); } } Here is top part of the stack trace. Unfortunatly I cant show the build up to this point as its company sensative information which I can not disclose. Hope this is enough information. at System.Transactions.TransactionState.EnlistPromotableSinglePhase(InternalTransaction tx, IPromotableSinglePhaseNotification promotableSinglePhaseNotification, Transaction atomicTransaction) at System.Transactions.Transaction.EnlistPromotableSinglePhase(IPromotableSinglePhaseNotification promotableSinglePhaseNotification) at System.Data.SqlClient.SqlInternalConnection.EnlistNonNull(Transaction tx) at System.Data.SqlClient.SqlInternalConnection.Enlist(Transaction tx) at System.Data.SqlClient.SqlInternalConnectionTds.Activate(Transaction transaction) at System.Data.ProviderBase.DbConnectionInternal.ActivateConnection(Transaction transaction) at System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject) at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection) at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) at System.Data.SqlClient.SqlConnection.Open()

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  • User Control SiteMap Provider Rendering Error

    - by Serexx
    I have created a Custom Server Control that renders the SiteMap as a pure UL for CSS styling. At run-time it renders properly but in VS2008 Design View VS shows this error: Error Rendering Control - menuMainAn unhandled exception has occurred. The provider 'AspNetXmlSiteMapProvider' specified for the defaultProvider does not exist in the providers collection. I have 'AspNetXmlSiteMapProvider' specified in web.config as per here : link text While I am happy that the code runs properly, the Designer error is bothersome if the underlying issue might cause the code to break in some circumstances so I need to understand what is going on... The code explicitly references the sitemap in the Render Method with : int level = 1; string ul = string.Format("<div class='{0}' id='{1}'>{2}</div>", CssClassName, this.ID.ToString(), EnumerateNodesRecursive(SiteMap.RootNode, level)); output.Write(ul); and the recursive method called referrences SiteMap.CurrentNode. Otherwise there are no explicit sitemap references in the code. Does anyone have any ideas why Deisgner is complaining?

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  • Array of paths to html lists

    - by dmsk
    I wrote a recursive function, which returns an array with the paths to all files/folders in a given path. An array is already sorted and returns the exact information i want, but i struggle to display it properly in html lists. Array_of_paths = ( [0] => /path/to/folderA/ [1] => /path/to/folderA/subfolderAA/ [2] => /path/to/folderB/ [3] => /path/to/folderB/subfolderBB/ [4] => /path/to/folderB/subfolderBB/fileBB.txt [5] => /path/to/folderB/fileB.txt [6] => /path/to/folderC/ ... ) I want to put these paths in <ul>,<li> tags to see something like this: <ul> <li>/path/to/folderA/ <ul> <li>/path/to/folderA/folderAA/</li> </ul> </li> <li>/path/to/folderB <ul> <li>/path/to/folderB/subfolderBB/ <ul> <li>/path/to/folderB/subfolderBB/fileBB.txt</li> </ul> </li> <li>/path/to/folderB/fileB.txt</li> </ul> </li> <li>/path/to/folderC/</li> </ul> = /path/to/folderA/ /path/to/folderA/folderAA/ /path/to/folderB /path/to/folderB/subfolderBB/ /path/to/folderB/subfolderBB/fileBB.txt /path/to/folderB/fileB.txt /path/to/folderC/ I managed to find a couple of similars questions, but the answers were in Ruby language. So, what's the problem solving idea behind this?

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  • Debugging Key-Value-Observing overflow.

    - by Paperflyer
    I wrote an audio player. Recently I started refactored some of the communication flow to make it fully MVC-compliant. Now it crashes, which in itself is not surprising. However, it crashes after a few seconds inside the Cocoa key-value-observing routines with a HUGE stack trace of recursive calls to NSKeyValueNotifyObserver. Obviously, it is recursively observing a value and thus overflowing the NSArray that holds pending notifications. According to the stack trace, the program loops from observeValueForKeyPath to setMyValue and back. Here is the according code: - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { if ([keyPath isEqual:@"myValue"] && object == myModel && [self myValue] != [myModel myValue]) { [self setMyValue:[myModel myValue]; } } and - (void)setMyValue:(float)value { myValue = value; [myModel setMyValue:value]; } myModel changes myValue every 0.05 seconds and if I log the calls to these two functions, they get called only every 0.05 seconds just as they should be, so this is working properly. The stack trace looks like this: -[MyDocument observeValueForKeyPath:ofObject:change:context:] NSKeyValueNotifyObserver NSKeyValueDidChange -[NSObject(NSKeyValueObserverNotification) didChangeValueForKey:] -[MyDocument setMyValue:] _NSSetFloatValueAndNotify …repeated some ~8k times until crash Do you have any idea why I could still be spamming the KVO queue?

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  • Parsec: backtracking not working

    - by Nathan Sanders
    I am trying to parse F# type syntax. I started writing an [F]Parsec grammar and ran into problems, so I simplified the grammar down to this: type ::= identifier | type -> type identifier ::= [A-Za-z0-9.`]+ After running into problems with FParsec, I switched to Parsec, since I have a full chapter of a book dedicated to explaining it. My code for this grammar is typeP = choice [identP, arrowP] identP = do id <- many1 (digit <|> letter <|> char '.' <|> char '`') -- more complicated code here later return id arrowP = do domain <- typeP string "->" range <- typeP return $ "("++domain++" -> "++range++")" run = parse (do t <- typeP eof return t) "F# type syntax" The problem is that Parsec doesn't backtrack by default, so > run "int" Right "int" -- works! > run "int->int" Left "F# type syntax" unexpected "-" expecting digit, letter, ".", "`" or end of input -- doesn't work! The first thing I tried was to reorder typeP: typeP = choice [arrowP, identP] But this just stack overflows because the grammar is left-recursive--typeP never gets to trying identP because it keeps trying arrowP over and over. Next I tried try in various places, for example: typeP = choice [try identP, arrowP] But nothing I do seems to change the basic behaviours of (1) stack overflow or (2) non-recognition of "-" following an identifier. My mistake is probably obvious to anybody who has successfully written a Parsec grammar. Can somebody point it out?

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  • Undefined symbols compiling apache module mod_transform on Mac OS X

    - by Laurence Rowe
    I'm trying to compile mod_transform on Mac OS X 10.6, but get an ld error while running make. Thanks to diciu I have added some CFLAGS which resolve most of the linking problems, but I still am unable to get the apreq2 linking to work $ CFLAGS="-lxml2 -lxslt -L/opt/local/lib -lapreq2" ./configure --with-apr=/opt/local/bin/apr-1-config --with-apr-util=/opt/local/bin/apu-1-config --with-apxs=/opt/local/apache2/bin/apxs --with-apreq2=/opt/local/bin/apreq2-config ...snip... $ make $ make Making all in src /opt/local/share/apr-1/build/libtool --tag=CC --mode=link gcc -Wall -I../include -I/usr/local/include -I/usr/local/include/libxml2 -O2 -arch x86_64 -I/opt/local/include -DDARWIN -DSIGPROCMASK_SETS_THREAD_MASK -no-cpp-precomp -I/opt/local/apache2/include -I/opt/local/include/apr-1 -I/opt/local/include/apr-1 -I/opt/local/include -O2 -arch x86_64 -I/opt/local/include -DDARWIN -DSIGPROCMASK_SETS_THREAD_MASK -no-cpp-precomp -I/opt/local/apache2/include -I/opt/local/include/apr-1 -I/opt/local/include -I/opt/local/include/apr-1 -I/opt/local/include/apreq2 -I/opt/local/include/apr-1 -I/opt/local/include -lxml2 -lxslt -L/opt/local/lib -lapreq2 -module -export-dynamic -avoid-version -no-undefined /opt/local/lib/libapreq2.la -L/opt/local/lib -laprutil-1 -L/opt/local/lib/db46 -L/opt/local/lib -lapr-1 -lpthread -ldb-4.6 -lexpat -liconv -o http.la -rpath /opt/local/apache2/modules/mod_transform http_la-http.lo /usr/bin/gcc-4.2 -o .libs/http.so -bundle .libs/http_la-http.o -lxml2 -lxslt -L/opt/local/lib /opt/local/lib/libapreq2.dylib -L/opt/local/lib/db46 /opt/local/lib/libaprutil-1.dylib /opt/local/lib/libapr-1.dylib -lpthread /opt/local/lib/db46/libdb-4.6.dylib /opt/local/lib/libexpat.dylib /opt/local/lib/libiconv.dylib -arch x86_64 -arch x86_64 Undefined symbols: "_apreq_handle_apache2", referenced from: _transform_run_begin in http_la-http.o _filter_init in http_la-http.o ld: symbol(s) not found collect2: ld returned 1 exit status make[1]: *** [http.la] Error 1 make: *** [all-recursive] Error 1 Anyone have any other tweaks to fix this? This is mod_transform from http://svn.outoforder.cc/svn/mod%5Ftransform/trunk/ Laurence

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  • Bubble Breaker Game Solver better than greedy?

    - by Gregory
    For a mental exercise I decided to try and solve the bubble breaker game found on many cell phones as well as an example here:Bubble Break Game The random (N,M,C) board consists N rows x M columns with C colors The goal is to get the highest score by picking the sequence of bubble groups that ultimately leads to the highest score A bubble group is 2 or more bubbles of the same color that are adjacent to each other in either x or y direction. Diagonals do not count When a group is picked, the bubbles disappear, any holes are filled with bubbles from above first, ie shift down, then any holes are filled by shifting right A bubble group score = n * (n - 1) where n is the number of bubbles in the bubble group The first algorithm is a simple exhaustive recursive algorithm which explores going through the board row by row and column by column picking bubble groups. Once the bubble group is picked, we create a new board and try to solve that board, recursively descending down Some of the ideas I am using include normalized memoization. Once a board is solved we store the board and the best score in a memoization table. I create a prototype in python which shows a (2,15,5) board takes 8859 boards to solve in about 3 seconds. A (3,15,5) board takes 12,384,726 boards in 50 minutes on a server. The solver rate is ~3k-4k boards/sec and gradually decreases as the memoization search takes longer. Memoization table grows to 5,692,482 boards, and hits 6,713,566 times. What other approaches could yield high scores besides the exhaustive search? I don't seen any obvious way to divide and conquer. But trending towards larger and larger bubbles groups seems to be one approach Thanks to David Locke for posting the paper link which talks above a window solver which uses a constant-depth lookahead heuristic.

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  • How would you answer Joel's sample programming questions?

    - by Khorkrak
    I recently interviewed a candidate for a new position here. I wish though that I'd read Joel's Guerrilla Guide to Interviewing prior to that interview - naturally I happened upon it the night afterwards :P http://www.joelonsoftware.com/articles/GuerrillaInterviewing3.html So I tried answering the easy questions myself - yeah I used the python interpreter to type stuff in and tested the results a bit - I didn't look up any solutions beforehand though and I also thought about how long it took me to come up with answers for each one and what I'd look for the next time I interview someone. I'd let them type stuff into the interpreter and see how did used python's introspection capabilities too to find out things like what's the re module's method for building a regex etc. Here are my answers - these are in python of course - what are yours in your favourite language? Do you see any issues with the answers I came up with - i.e. how could they be improved upon - what did I miss? Joel's example questions: Write a function that determines if a string starts with an upper-case letter A-Z. import re upper_regex = re.compile("^[A-Z]") def starts_with_upper(text): return upper_regex.match(text) is not None Write a function that determines the area of a circle given the radius. from math import pi def area(radius): return pi * radius**2 Add up all the values in an array. sum([1, 2, 3, 4, 5]) Harder Question: Write an example of a recursive function - so how about the classic factorial one: def factorial(num): if num > 1: return num * factorial(num - 1) else: return 1

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  • Recursively adding threads to a Java thread pool

    - by Leith
    I am working on a tutorial for my Java concurrency course. The objective is to use thread pools to compute prime numbers in parallel. The design is based on the Sieve of Eratosthenes. It has an array of n bools, where n is the largest integer you are checking, and each element in the array represents one integer. True is prime, false is non prime, and the array is initially all true. A thread pool is used with a fixed number of threads (we are supposed to experiment with the number of threads in the pool and observe the performance). A thread is given a integer multiple to process. The thread then finds the first true element in the array that is not a multiple of thread's integer. The thread then creates a new thread on the thread pool which is given the found number. After a new thread is formed, the existing thread then continues to set all multiples of it's integer in the array to false. The main program thread starts the first thread with the integer '2', and then waits for all spawned threads to finish. It then spits out the prime numbers and the time taken to compute. The issue I have is that the more threads there are in the thread pool, the slower it takes with 1 thread being the fastest. It should be getting faster not slower! All the stuff on the internet about Java thread pools create n worker threads the main thread then wait for all threads to finish. The method I use is recursive as a worker can spawn more worker threads. I would like to know what is going wrong, and if Java thread pools can be used recursively.

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  • StackOverFlowException - but oviously NO recursion/endless loop

    - by user567706
    Hi there, I'm now blocked by this problem the entire day, read thousands of google results, but nothing seems to reflect my problem or even come near to it... i hope any of you has a push into the right direction for me. I wrote a client-server-application (so more like 2 applications) - the client collects data about his system, as well as a screenshot, serializes all this into a XML stream (the picture as a byte[]-array]) and sends this to the server in regular intervals. The server receives the stream (via tcp), deserializes the xml to an information-object and shows the information on a windows form. This process is running stable for about 20-25 minutes at a submission interval of 3 seconds. When observing the memory usage there's nothing significant to see, also kinda stable. But after these 20-25 mins the server throws a StackOverflowException at the point where it deserializes the tcp-stream, especially when setting the Image property from the byte[]-array. I thoroughly searched for recursive or endless loops, and regarding the fact that it occurs after thousands of sucessfull intervals, i could hardly imagine that. public byte[] ImageBase { get { MemoryStream ms = new MemoryStream(); _screen.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg); return ms.GetBuffer(); } set { if (_screen != null) _screen.Dispose(); //preventing well-known image memory leak MemoryStream ms = new MemoryStream(value); try { _screen = Image.FromStream(ms); //<< EXCEPTION THROWING HERE } catch (StackOverflowException ex) //thx to new CLR management this wont work anymore -.- { Console.WriteLine(ex.Message + Environment.NewLine + ex.StackTrace); } ms.Dispose(); ms = null; } } I hope that more code would be unnecessary, or it could get very complex... Please help, i have no clue at all anymore thx Chris

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  • Beginner problems with references to arrays in python 3.1.1

    - by Protean
    As part of the last assignment in a beginner python programing class, I have been assigned a traveling sales man problem. I settled on a recursive function to find each permutation and the sum of the distances between the destinations, however, I am have a lot of problems with references. Arrays in different instances of the Permute and Main functions of TSP seem to be pointing to the same reference. from math import sqrt class TSP: def __init__(self): self.CartisianCoordinates = [['A',[1,1]], ['B',[2,2]], ['C',[2,1]], ['D',[1,2]], ['E',[3,3]]] self.Array = [] self.Max = 0 self.StoredList = ['',0] def Distance(self, i1, i2): x1 = self.CartisianCoordinates[i1][1][0] y1 = self.CartisianCoordinates[i1][1][1] x2 = self.CartisianCoordinates[i2][1][0] y2 = self.CartisianCoordinates[i2][1][1] return sqrt(pow((x2 - x1), 2) + pow((y2 - y1), 2)) def Evaluate(self): temparray = [] Data = [] for i in range(len(self.CartisianCoordinates)): Data.append([]) for i1 in range(len(self.CartisianCoordinates)): for i2 in range(len(self.CartisianCoordinates)): if i1 != i2: temparray.append(self.Distance(i1, i2)) else: temparray.append('X') Data[i1] = temparray temparray = [] self.Array = Data self.Max = len(Data) def Permute(self,varray,index,vcarry,mcarry): #Problem Class array = varray[:] carry = vcarry[:] for i in range(self.Max): print ('ARRAY:', array) print (index,i,carry,array[index][i]) if array[index][i] != 'X': carry[0] += self.CartisianCoordinates[i][0] carry[1] += array[index][i] if len(carry) != self.Max: temparray = array[:] for j in range(self.Max):temparray[j][i] = 'X' index = i mcarry += self.Permute(temparray,index,carry,mcarry) else: return mcarry print ('pass',mcarry) return mcarry def Main(self): out = [] self.Evaluate() for i in range(self.Max): array = self.Array[:] #array appears to maintain the same reference after each copy, resulting in an incorrect array being passed to Permute after the first iteration. print (self.Array[:]) for j in range(self.Max):array[j][i] = 'X' print('I:', i, array) out.append(self.Permute(array,i,[str(self.CartisianCoordinates[i][0]),0],[])) return out SalesPerson = TSP() print(SalesPerson.Main()) It would be greatly appreciated if you could provide me with help in solving the reference problems I am having. Thank you.

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  • PostgreSQL: Auto-partition a table

    - by Adam Matan
    Hi, I have a huge database which holds pairs of numbers (A,B), each ranging from 0 to 10,000 and stored as floats. e.g., (1, 9984.4), (2143.44, 124.243), (0.55, 0), ... Since the PostgreSQL table which stores these pairs grew quite large, I have decided to partition it into inheriting sub-tables. I intend to create 100 such tables, each storing a range of 1000x1000. The problem is that these numbers tend to come in large chunks of nearby numbers. It means that in the future, some tables will be nearly empty and some will hold a very large portion of the database. Unfortunately, the distribution of future pairs is yet unknown. I am looking for a way to automatically repartition my table. That means that if a certain subtable holds more than a specific number of pairs, it will be automatically partitioned into four sub-sub tables, and so on. My questions are: Is recursive partitioning and inheritance possible in PostgreSQL 8.3? Will indexes and query plans understand it? What's the best way to split a subtable once it grew too large? I should point out that this isn't a live database, so a downtime of few hours every week is totally acceptable. Thanks in advance, Adam

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  • Scheme Infix to Postfix

    - by Cody
    Let me establish that this is part of a class assignment, so I'm definitely not looking for a complete code answer. Essentially we need to write a converter in Scheme that takes a list representing a mathematical equation in infix format and then output a list with the equation in postfix format. We've been provided with the algorithm to do so, simple enough. The issue is that there is a restriction against using any of the available imperative language features. I can't figure out how to do this in a purely functional manner. This is our fist introduction to functional programming in my program. I know I'm going to be using recursion to iterate over the list of items in the infix expression like such. (define (itp ifExpr) ( ; do some processing using cond statement (itp (cdr ifExpr)) )) I have all of the processing implemented (at least as best I can without knowing how to do the rest) but the algorithm I'm using to implement this requires that operators be pushed onto a stack and used later. My question is how do I implement a stack in this function that is available to all of the recursive calls as well?

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  • Reordering arguments using recursion (pro, cons, alternatives)

    - by polygenelubricants
    I find that I often make a recursive call just to reorder arguments. For example, here's my solution for endOther from codingbat.com: Given two strings, return true if either of the strings appears at the very end of the other string, ignoring upper/lower case differences (in other words, the computation should not be "case sensitive"). Note: str.toLowerCase() returns the lowercase version of a string. public boolean endOther(String a, String b) { return a.length() < b.length() ? endOther(b, a) : a.toLowerCase().endsWith(b.toLowerCase()); } I'm very comfortable with recursions, but I can certainly understand why some perhaps would object to it. There are two obvious alternatives to this recursion technique: Swap a and b traditionally public boolean endOther(String a, String b) { if (a.length() < b.length()) { String t = a; a = b; b = t; } return a.toLowerCase().endsWith(b.toLowerCase()); } Not convenient in a language like Java that doesn't pass by reference Lots of code just to do a simple operation An extra if statement breaks the "flow" Repeat code public boolean endOther(String a, String b) { return (a.length() < b.length()) ? b.toLowerCase().endsWith(a.toLowerCase()) : a.toLowerCase().endsWith(b.toLowerCase()); } Explicit symmetry may be a nice thing (or not?) Bad idea unless the repeated code is very simple ...though in this case you can get rid of the ternary and just || the two expressions So my questions are: Is there a name for these 3 techniques? (Are there more?) Is there a name for what they achieve? (e.g. "parameter normalization", perhaps?) Are there official recommendations on which technique to use (when)? What are other pros/cons that I may have missed?

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  • Maintain one to one mapping between objects

    - by Rohan West
    Hi there, i have the following two classes that provide a one to one mapping between each other. How do i handle null values, when i run the second test i get a stackoverflow exception. How can i stop this recursive cycle? Thanks [TestMethod] public void SetY() { var x = new X(); var y = new Y(); x.Y = y; Assert.AreSame(x.Y, y); Assert.AreSame(y.X, x); } [TestMethod] public void SetYToNull() { var x = new X(); var y = new Y(); x.Y = y; y.X = null; Assert.IsNull(x.Y); Assert.IsNull(y.X); } public class X { private Y _y; public Y Y { get { return _y; } set { if(_y != value) { if(_y != null) { _y.X = null; } _y = value; if(_y != null) { _y.X = this; } } } } } public class Y { private X _x; public X X { get { return _x; } set { if (_x != value) { if (_x != null) { _x.Y = null; } _x = value; if (_x != null) { _x.Y = this; } } } } }

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  • How to use Common Table Expression and check no duplication in sqlserver

    - by vodkhang
    I have a table references to itself. User table: id, username, managerid and managerid links back to id Now, I want to get all the managers including direct manager, manager of direct manager, so on and so forth... The problem is that I do not want to have a unstop recursive sql. So, I want to check if an id alreay in a list, I will not include it anymore. Here is my sql for that: with --the relation for all the subparts of ozsolar including itself all_managers (id, username, managerid, idlist) as ( --seed that is the ozsola part select u1.id, u1.username, u1.managerid, ' ' from users u1, users u2 where u1.id = u2.managerid and u2.id = 6 UNION ALL select u.id, u.username, u.managerid, idlist + ' ' + u.id from all_managers a, users u where a.managerid = u.id and charindex(cast(u.id as nvarchar(5)), idlist) != 0 ) --select the total number of subparts and group by subpart select id, username from all_managers; The problem is that in this line: select u1.id, u1.username, u1.managerid, ' ' The sqlserver complains with me that I can not put ' ' as the initialized for idlist. nvarchar(40) does not work as well. I do not know how to declare it inside a common table expression like this one. Usually, in db2, I can just put varchar(40)

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  • Can I copy/clone a function in JavaScript?

    - by Craig Stuntz
    I'm using jQuery with the validators plugin. I would like to replace the "required" validator with one of my own. This is easy: jQuery.validator.addMethod("required", function(value, element, param) { return myRequired(value, element, param); }, jQuery.validator.messages.required); So far, so good. This works just fine. But what I really want to do is call my function in some cases, and the default validator for the rest. Unfortunately, this turns out to be recursive: jQuery.validator.addMethod("required", function(value, element, param) { // handle comboboxes with empty guids if (someTest(element)) { return myRequired(value, element, param); } return jQuery.validator.methods.required(value, element, param); }, jQuery.validator.messages.required); I looked at the source code for the validators, and the default implementation of "required" is defined as an anonymous method at jQuery.validator.messages.required. So there is no other (non-anonymous) reference to the function that I can use. Storing a reference to the function externally before calling addMethod and calling the default validator via that reference makes no difference. What I really need to do is to be able to copy the default required validator function by value instead of by reference. But after quite a bit of searching, I can't figure out how to do that. Is it possible? If it's impossible, then I can copy the source for the original function. But that creates a maintenance problem, and I would rather not do that unless there is no "better way."

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  • What is the right way to make a new XMLHttpRequest from an RJS response in Ruby on Rails?

    - by Yuri Baranov
    I'm trying to come closer to a solution for the problem of my previous question. The scheme I would like to try is following: User requests an action from RoR controller. Action makes some database queries, makes some calculations, sets some session variable(s) and returns some RJS code as the response. This code could either update a progress bar and make another ajax request. display the final result (e.g. a chart grahic) if all the processing is finished The browser evaluates the javascript representation of the RJS. It may make another (recursive? Is recursion allowed at all?) request, or just display the result for the user. So, my question this time is: how can I embed a XMLHttpRequest call into rjs code properly? Some things I'd like to know are: Should I create a new thread to avoid stack overflow. What rails helpers (if any) should I use? Have anybody ever done something similar before on Rails or with other frameworks? Is my idea sane?

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  • dynamic ul with sub-levels

    - by Y.G.J
    i have this recursive code <ul> <% sql="SELECT * FROM cats ORDER BY orderid " rs.Open sql,Conn dim recArray If Not rs.EOF Then recArray = rs.getRows() dim i for i=0 to uBound(recArray,2) if recArray(1,i)=0 then call showMessage(i) end if next End If function showMessage(index) %><li><%=recArray(2,index)%></li><% for a=0 to uBound(recArray,2) if recArray(1,a) = recArray(0,index) Then %><ul><% call showMessage(a) %></ul><% end if next %></li><% end function %> </ul> inside the loop in the function i have the for the sub(s) but after each line of li it will close the ul how can i have that dynamic and to have the output like this <ul> <li></li> <li></li> <li> <ul> <li></li> <li></li> <li></li> </ul> </li> <li></li> </ul> and not like this <ul> <li></li> <li></li> <li> <ul><li></li></ul> <ul><li></li></ul> <ul><li></li></ul> </li> <li></li> </ul>

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  • process of connecting RTP with SIP via SDP & land lines

    - by TacB0sS
    Hello to everyone, I have a problem with starting a media session and to combine it with my SIP client. I've designed a recursive SIP client that reuse the same request template to send the next requests to server, according to the acceptable sequences noted in the RFC's, and examples that I read. as far as I could tell the SIP part is working fine registers to server invites, and authenticates. I didn't complete any calls to clients yet because of the content header needs to be filled up (which I didn't yet so I get a 503 from the server which is OK I guess). for a long time I didn't know where to start with the media session, and slowly learned how to use the JMF and I've constructed an object that handles RTP transmitting, now I'm standing at the cross road, on the one hand I have my SIP signaling but it needs the SDP content header to complete the invite, and on the other I have the RTP which is knows how to p2p. For me to complete my design I require your help with the following questions: Is there an easy//a simple//an implemented way to convert the Audio/Video format from the JMF into SDP media headers? or even a generator that I would input all the parameters for the content header, and it would generate a content header fast, or do I have to implement this myself? Once I've finished constructing the SDK and the SIP is up and running and I get an OK response from the server (after ringing and all), how do I start the media session? do I connect p2p according to caller details I send in the SIP invite? If 2 is correct, then how does a connection to land lines would be? does land lines knows that once they send an OK back to server they listen/start RTP session on a specific port? Or did I get everything wrong? :-/ I really appreciate any help I could I get, I looked every where for answers but they are not clear, they ignore question 2 as if it was an obvious thing, but for me it just isn't. Thank in advance, Adam Zehavi.

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  • PyGTK/GIO: monitor directory for changes recursively

    - by detly
    Take the following demo code (from the GIO answer to this question), which uses a GIO FileMonitor to monitor a directory for changes: import gio def directory_changed(monitor, file1, file2, evt_type): print "Changed:", file1, file2, evt_type gfile = gio.File(".") monitor = gfile.monitor_directory(gio.FILE_MONITOR_NONE, None) monitor.connect("changed", directory_changed) import glib ml = glib.MainLoop() ml.run() After running this code, I can then create and modify child nodes and be notified of the changes. However, this only works for immediate children (I am aware that the docs don't say otherwise). The last of the following shell commands will not result in a notification: touch one mkdir two touch two/three Is there an easy way to make it recursive? I'd rather not manually code something that looks for directory creation and adds a monitor, removing them on deletion, etc. The intended use is for a VCS file browser extension, to be able to cache the statuses of files in a working copy and update them individually on changes. So there might by anywhere from tens to thousands (or more) directories to monitor. I'd like to just find the root of the working copy and add the file monitor there. I know about pyinotify, but I'm avoiding it so that this works under non-Linux kernels such as FreeBSD or... others. As far as I'm aware, the GIO FileMonitor uses inotify underneath where available, and I can understand not emphasising the implementation to maintain some degree of abstraction, but it suggested to me that it should be possible. (In case it matters, I originally posted this on the PyGTK mailing list.)

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