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• What exactly is a Monad?

  - by WeNeedAnswers

  Can someone please explain to me what a Monad is. I think I grasp Monoids and I grasp that they basically control the input of state into a system. I just look at the text in Haskell and glaze over. A simple example in python would be great. My current understanding is that a Monoid is a procedural piece of code that needs to be read from top to bottom in sequence with the output being the input for the function. I think that I may even got that wrong, but hey I am here to learn.

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• Code understanding, reverse engineering, best concepts and tools. Java.

  - by core07

  One of most demanding tasks for any programmer, architect is understanding other's code. E.g. I am contractor, hired to rescue some project very quickly. Fix bugs, plan global refactoring and therefore I need most efficient way to understand the code. What is the list of concepts, their priority and best tools for this? Of what I know: reverse code engineering to create object models (creating of diagram per package is not so convenient), create sequence diagrams (the tool connects in debug mode to the system and generates diagrams from runtime). Some visualizing techniques, using some tools to work not just with .java but also with e.g. JPA implementors like Hibernate. Generate diagram for not all the codebase, but add some class and then classes used by it. Is Sparx Enterprise Architect state of the art in reverse engineering or far from that. Any other better tools? Ideally would be that tool makes me understand the code as if I wrote it myself :)

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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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• CORE DATA objectId changes constantly

  - by mongeta

  Hello, I have some data that I export into an XML file and put in a remote FTP Server. I have to identified each object with a unique attribute, it doesn't matter wich is, but must be persistent always = it can never change. I don't want to create a unique attribute, sequence, serial, etc. I'm using the objectID but every time I use it a get a new reference. I know that before the object has been saved, it has a 'temporal id', but once it's saved, it gets the definitive. I'm not seeing this, never. When I export, just fetch all data and loop, and always I get a new reference: NSURL *objectID = [[personalDataObject objectID] URIRepresentation]; // some of id received for the SAME OBJECT (no changes made, saved, ...) // 61993296 // 62194624 thanks, r. edit I was using %d instead of %@, now the returned data is: x-coredata://F46F3300-8FED-4876-B0BF-E4D2A9D80913/DataEntered/p1 x-coredata://F46F3300-8FED-4876-B0BF-E4D2A9D80913/DataEntered/p2

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• What adapter to use for ExpandableListView with non-TextView views?

  - by David

  I have an ExpandableListView in which I'd like to have controls other than TextView. Apparently, SimpleExandableListViewAdapter assumes all the controls are TextViews. A cast exception is generated if they are not. What is the recommended solution? Options I can think of include: - Use some other included adapter. But I can't tell if they all have the same assumption. - Create my own adapter. Is there a doc which describes the contract, ie the sequence of method calls an adapter will encounter? I expected the existing adapters to require the views to conform to some interface to allow any conforming view to be used, rather than hardcode to textview and limit where they can be used.

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• Tkinter Gui to read in csv file and generate buttons based on the entries in the first row

  - by Thomas Jensen

  I need to write a gui in Tkinter that can choose a csv file, read it in and generate a sequence of buttons based on the names in the first row of the csv file (later the data in the csv file should be used to run a number of simulations). So far I have managed to write a Tkinter gui that will read the csv file, but I am stomped as to how I should proceed: from Tkinter import * import tkFileDialog import csv class Application(Frame): def __init__(self, master = None): Frame.__init__(self,master) self.grid() self.createWidgets() def createWidgets(self): top = self.winfo_toplevel() self.menuBar = Menu(top) top["menu"] = self.menuBar self.subMenu = Menu(self.menuBar) self.menuBar.add_cascade(label = "File", menu = self.subMenu) self.subMenu.add_command( label = "Read Data",command = self.readCSV) def readCSV(self): self.filename = tkFileDialog.askopenfilename() f = open(self.filename,"rb") read = csv.reader(f, delimiter = ",") app = Application() app.master.title("test") app.mainloop() Any help is greatly appreciated!

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• Hibernate: same generated value in two properties

  - by Markos Fragkakis

  Hi, I have an entity A with fields: aId (the system id) bId I want the first to be generated: @Id @Column(name = "PRODUCT_ID", unique = true, nullable = false, precision = 12, scale = 0) @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "PROD_GEN") @BusinessKey public Long getAId() { return this.aId; } I want the bId to be initially exactly as the aId. One approach is to insert the entity, then get the aId generated by the DB (2nd query) and then update the entity, setting the bId to be equal to aId (3rd query). Is there a way to get the bId to get the same generated value as aId? Note that afterwards, I want to be able to update bId from my gui. If the solution is JPA, even better.

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• Oracle - Is there any effects of not having a primary key on a table ?

  - by Sathya

  We use sequence numbers for primary keys on the tables. There are some tables where we dont really use the primary key for any querying purpose. But, we have Indexes on other columns. These are non-unique indexes. The queries use these non-primary key columns in the WHERE conditions. So, I dont really see any benefit of having a primary key on such tables. My experience with SQL 2000 was that, it used to replicate tables which had some primary key. Otherwise it would not. I am using Oracle 10gR2. I would like to know if there are any such side-effects of having tables that dont have primary key.

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• Database Modelling - Conceptually different entities but with near identical fields

  - by Andrew Shepherd

  Suppose you have two sets of conceptual entities: MarketPriceDataSet which has multiple ForwardPriceEntries PoolPriceForecastDataSet which has multiple PoolPriceForecastEntry Both different child objects have near identical fields: ForwardPriceEntry has MarketPriceDataSetId (foreign key to parent table) StartDate EndDate SimulationItemId ForwardPrice PoolPriceForecastEntry has PoolPriceForecastDataSetId (foreign key to parent table) StartDate EndDate SimulationItemId ForecastPoolPrice If I modelled them as separate tables, the only difference would be the foreign key, and the name of the price field. There has been a debate as to whether the two near identical tables should be merged into one. Options I've thought of to model this is: Just keep them as two independent, separate tables Have both sets in the one table with an additional "type" field, and a parent_id equalling a foreign key to either parent table. This would sacrifice referential integrity checks. Have both sets in the one table with an additional "type" field, and create a complicated sequence of joining tables to maintain referential integrity. What do you think I should do, and why?

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• openCV usage cvFindDominantPoints

  - by rsinha

  Hi, Does anyone know how to use the cvFindDominantPoints API of openCV? I basically have a 1 channel, binary image from which I get a set of contours. Judging from the image, I seem to be getting the correct contours. Now, I am selecting one of these contours to get dominant points of. This contour has about 60 vertices. However, the API call to cvFindDominantPoints is giving me a sequence of points (about 15) that does not even lie on the contour. It is quite far from it. Any insight? my usage: CvSeq *dominantpoints = cvFindDominantPoints(targetSeq, tristorage, CV_DOMINANT_IPAN, 7, 9, 9, 150);

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• Template Matching 2 ROI in a single video capture in real time

  - by YS

  Hi, I am working on a project to perform template matching on a video captured via my webcam. I am able to create 2 template from the webcam capture, but I am unable to perform template matching for both. The program can run only with either template matching, but not both. My program sequence is: Capture from webcam get template 1 get template 2 perform template 1 matching with webcam capture then perform template 2 matching with webcam capture if fail, stop. Can any expert advice me on this?

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• Linq to Entities, checking for specific foreign key id?

  - by AaronLS

  I am trying to get rows where the foreign key ParentID == 0, and this is what I am trying but I get a NotSupportedException because it can't translate the ArrayIndex [0]: IQueryable<ApplicationSectionNode> topLevelNodeQuery = from n in uacEntitiesContext.ApplicationSectionNodeSet where (int)n.Parent.EntityKey.EntityKeyValues[0].Value == 0 orderby n.Sequence select n; So I need to pull that ArrayIndex out of the query so that the runtime can successfully translate the query. I'm not sure how to do that though. How does one query a specific object via it's primary key or set of objects via foreign key? Edit: Note that there is not actually a row in the table with NodeId == 0, the 0 is a magic value(not my idea) to indicate top level nodes. So I can't do n.Parent.NodeId == 0

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• MySQL locking problem

  - by teehoo

  I have a simple setup of a set of writers and a set of readers working with a MySQL ISAM table. The writers are only inserting rows while the readers are only checking for new rows. OK, so I know that I don't need a lock in this situation, since I'm not modifying existing rows. However my Writers are accessing one more table that does need a lock. I piece of information seems irrelevant except for the following limitation stated in the MySQL documentation: A session that requires locks must acquire all the locks that it needs in a single LOCK TABLES statement. While the locks thus obtained are held, the session can access only the locked tables. For example, in the following sequence of statements, an error occurs for the attempt to access t2 because it was not locked in the LOCK TABLES statement: So to access the table I want to insert rows into, I NEED to lock it, which is causing me performance problems. Any suggestions of how to get around this?

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• sorting content of a text file in python

  - by rabidmachine9

  I have this small script that sorts the content of a text file # The built-in function `open` opens a file and returns a file object. # Read mode opens a file for reading only. try: f = open("tracks.txt", "r") try: # Read the entire contents of a file at once. # string = f.read() # OR read one line at a time. #line = f.readline() # OR read all the lines into a list. lines = f.readlines() lines.sort() f = open('tracks.txt', 'w') f.writelines(lines) # Write a sequence of strings to a file finally: f.close() except IOError: pass the only problem is that the text is displayed at the bottom of the text file everytime it's sortened... I assume it also sorts the blank lines...anybody knows why? thanks in advance

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• Javascript: window.onload problem

  - by Matrym

  This isn't working in IE (although it does work in FFX). Why? Using HTML in the header: <script type="application/javascript"> // And finally, let's call the code ourselves. window.onload = lbp.init; </script> And then the script: // lbp is the script's universal variable, which retains everything var lbp = {}; // The sequence of functions to trigger lbp.init = function() { alert('hi'); } Thanks in advance for your help =)

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• Using XSD file in VS2005

  - by xt_20

  Hello all I want to write an XML file. I have created an XSD file named XMLSchema.xsd, and run the command 'xsd /c XMLSchema.xsd' which generated a c# class file. Now, how do I use this file to generate XML files? Part of my code: <?xml version="1.0" encoding="utf-8"?> <xs:schema id="XMLSchema" targetNamespace="http://tempuri.org/XMLSchema.xsd" elementFormDefault="qualified" xmlns="http://tempuri.org/XMLSchema.xsd" > <xs:element name="root"> <xs:complexType> <xs:sequence> <xs:element name="Audit"> <xs:complexType> ... which generates a c# class 'root'. How do I call 'root' from my C# web program? Thanks

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• Activation rectangle

  - by Knowing me knowing you

  Making UML sequence diagram in VS 2010RC I've observed that there is no activation rectangle in first object. Is this correct? Not according to my tutor and I have to quote him: "Finally, you have no activation rectangle for the userInterface instance, so the initial message could never have been sent." But I'm thinking that if guys from VS did that it must/should be correct. Another thing he is picking me at is and I'm quoting him: "In class diagram the generalisation arrow heads should be open triangles." In my opinion there isn't strictly said that they must be open triangles especially when software lets you choose their form. Looking forward to hear your opinions. Thanks for answers.

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• JTextField that has inner fields or preformated format, something like the ip field in windows

  - by dimitar

  Hello guys, i want to create a text field that will be for date and will have dd.mm.YYYY format. Now what i want to do is the user to type only the numbers, not the dots to. So the field would be like: _ _. _ _ . _ _ _ _ So when the user wants to type the date: 15.05.2010 for example, he will only type the numbers in the sequence 15052010. Also i would like, when he preses on left or right arrow, the cursor to go from one field(not JTextField, but field in the JTextField). So lets say i have JTextField with text in it: 15.05.2010, so if user is on the beginning and he preses right arrow, the cursor to go to the .05 field. I hope you understand me 'cos right now i don't any idea how to make this, or at least how to look for it on google. Thank you.

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• Find and replace text in a string using C#

  - by Joey Morani

  Anyone know how I would find & replace text in a string? Basically I have two strings: string firstS = "/9j/4AAQSkZJRgABAQEAYABgAAD/2wBDABQODxIPDRQSERIXFhQYHzMhHxwcHz8tLyUzSkFOTUlBSEZSXHZkUldvWEZIZoxob3p9hIWET2ORm4+AmnaBhH//2wBDARYXFx8bHzwhITx/VEhUf39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f3//"; string secondS = "abcdefg2wBDABQODxIPDRQSERIXFh/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/abcdefg"; I want to search firstS to see if it contains any sequence of characters that's in secondS and then replace it. It also needs to be replaced with the number of replaced characters in squared brackets: [NUMBER-OF-CHARACTERS-REPLACED] For example, because firstS and secondS both contain "2wBDABQODxIPDRQSERIXFh" and "/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/f39/" they would need to be replaced. So then firstS becomes: string firstS = "/9j/4AAQSkZJRgABAQEAYABgAAD/[22]QYHzMhHxwcHz8tLyUzSkFOTUlBSEZSXHZkUldvWEZIZoxob3p9hIWET2ORm4+AmnaBhH//2wBDARYXFx8bHzwhITx/VEhUf39[61]f3//"; Hope that makes sense. I think I could do this with Regex, but I don't like the inefficiency of it. Does anyone know of another, faster way?

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• Play Video on Safari iTouch

  - by dave cohen

  I have a web site that opens iframe for video on page, page uses ajax to pull in videos from selected menu. As expected and understood, on iTouch after selecting video it shows a play button, which brings up video in another screen. However, when the video completes, it returns browser to page prior to one where video was played from. Sequence: - open Page1 - go to Page2 which offers videos to play, in iframe - play video - video completes, returns to Page1, not Page2!! Only happens on iTouch, so must be issue with how control is returned on video completion. Any suggestions? If this is not a known problem, I can work up example (currently, need account on site). Thanks Dave

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• Xcode 5 new bug

  - by user2874675

  Since the recent IOS update last month I have been having issues with this new bug that has hampered my program. The bug is as follows: using a UIButton and I want to insert a value into it, only after my execution ends does a letter actually appear. But if I create a method during execution to tell me, using NSLog, what my properties contain then that letter I added never shows up. I'm thinking I need to find a way to refresh a property during execution instead in the end. For example: Let's say you want to insert the letter F into a UIButton. Immediately after writing F into that UIButton, look to see that F hasn't isn't in there. But it will only show up after that particular execution sequence finishes. Any help would be great. Thanks in advance.

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• MS Access Mark Duplicates in order of appearance - using the function RankOfDup: (SELECT Count(*) ...)

  - by veska stoyanova

  I'm trying to create Ranking that shows the sequence of agreements for the two fields Customers and Agreements. The number for agreements must be unique, whereas customers can repeat. The formula RankOfDup: (SELECT Count(*) FROM Data a WHERE a.customer=Data.customer And a.agreement >= Data.agreement) Works beautifully but after this query with columns Agreement, Customer and RankofDup, I need to create crosstab that transposes the RankofDub. It works when I make the table first and then create query but my data is too large so I'm trying to put the select query with the ranking in a crosstab query. However, when I try to do this Access gives error message that microsoft jet ... doesn't recognise Data.customer? Any ideas how I can fix this?

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• Does replacing statements by expressions using the C++ comma operator could allow more compiler opti

  - by Gabriel Cuvillier

  The C++ comma operator is used to chain individual expressions, yielding the value of the last executed expression as the result. For example the skeleton code (6 statements, 6 expressions): step1; step2; if (condition) step3; return step4; else return step5; May be rewritten to: (1 statement, 6 expressions) return step1, step2, condition? step3, step4 : step5; I noticed that it is not possible to perform step-by-step debugging of such code, as the expression chain seems to be executed as a whole. Does it means that the compiler is able to perform special optimizations which are not possible with the traditional statement approach (specially if the steps are const or inline)? Note: I'm not talking about the coding style merit of that way of expressing sequence of expressions! Just about the possible optimisations allowed by replacing statements by expressions.

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• Regular expressions and matching URLs with metacharacters

  - by James P.

  I'm having trouble finding a regular expression that matches the following String. Korben;http://feeds.feedburner.com/KorbensBlog-UpgradeYourMind?format=xml;1 One problem is escaping the question mark. Java's pattern matcher doesn't seem to accept \? as a valid escape sequence but it also fails to work with the tester at myregexp.com. Here's what I have so far: ([a-zA-Z0-9])+;http://([a-zA-Z0-9./-]+);[0-9]+ Any suggestions? Edit: The original intent was to match all URLs that could be found after the first semi colon.

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• DbMetal chokes on repeated foreign key references in SQLite - any ideas?

  - by DanM

  I've been struggling to get DbMetal to process my SQLite database. I finally isolated the problem. It won't allow a table to have two foreign key references to the same column. For example, a SQLite database with these two tables will fail: CREATE TABLE Person ( Id INTEGER PRIMARY KEY, Name TEXT NOT NULL ); CREATE TABLE Match ( Id INTEGER PRIMARY KEY, WinnerPersonId INTEGER NOT NULL REFERENCES Person(Id), LoserPersonId INTEGER NOT NULL REFERENCES Person(Id) ); I get this error: DbMetal: Sequence contains more than one matching element If I get rid of the second foreign key reference, no error occurs. So, this works: CREATE TABLE Match ( Id INTEGER PRIMARY KEY, WinnerPersonId INTEGER NOT NULL REFERENCES Person(Id), LoserPersonId INTEGER NOT NULL ); But I really need both "person" columns to reference the person table. I submitted a bug report for this, but I could use a workaround in the meantime. Any ideas?

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