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  • Haskell: foldl' accumulator parameter

    - by Clinton
    I've been asking a few questions about strictness, but I think I've missed the mark before. Hopefully this is more precise. Lets say we have: n = 1000000 f z = foldl' (\(x1, x2) y -> (x1 + y, y - x2)) z [1..n] Without changing f, what should I set z = ... So that f z does not overflow the stack? (i.e. runs in constant space regardless of the size of n) Its okay if the answer requires GHC extensions. My first thought is to define: g (a1, a2) = (!a1, !a2) and then z = g (0, 0) But I don't think g is valid Haskell.

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  • How do I map a macro across a list in Scheme?

    - by josh
    I have a Scheme macro and a long list, and I'd like to map the macro across the list, just as if it were a function. How can I do that using R5RS? The macro accepts several arguments: (mac a b c d) The list has (define my-list ((a1 b1 c1 d1) (a2 b2 c2 d2) ... (an bn cn dn))) And I'd like to have this: (begin (mac a1 b1 c1 d2) (mac a2 b2 c2 d2) ... (mac an bn cn dn)) (By the way, as you can see I'd like to splice the list of arguments too)

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  • strip version from package name using Bash

    - by cd1
    hi, I'm trying to strip the version out of a package name using only Bash. I have one solution but I don't think that's the best one available, so I'd like to know if there's a better way to do it. by better I mean cleaner, easier to understand. suppose I have the string "my-program-1.0" and I want only "my-program". my current solution is: #!/bin/bash PROGRAM_FULL="my-program-1.0" INDEX_OF_LAST_CHARACTER=`awk '{print match($0, "[A-Za-z0-9]-[0-9]")} <<< $PROGRAM_FULL` PROGRAM_NAME=`cut -c -$INDEX_OF_LAST_CHARACTER <<< $PROGRAM_FULL` actually, the "package name" syntax is an RPM file name, if it matters. thanks!

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  • Rails 2.3.5: How does one access code inside of lib/directory/file.rb?

    - by randombits
    I created a file so I can share a method amongst many models in lib/foo/bar_woo.rb. Inside of bar_woo.rb I defined the following: module BarWoo def hello puts "hello" end end Then in my model I'm doing something like: def MyModel < ActiveRecord::Base include Foo::BarWoo def some_method Foo::BarWoo.hello end end The interpreter is complaining that it expected bar_woo.rb to define Foo::BarWoo. The Agile Web Development with Rails book states that if files contain classes or modules and the files are named using the lowercase form of the class or module name, then Rails will load the file automatically. I didn't require it because of this.

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  • Can't use MySQL extract() function in the WHERE clause.

    - by UkraineTrain
    I've run the following query: UPDATE main_table, reference_table SET main_table.calc_column = (CASE WHEN main_table.incr = "6AM" THEN reference_table.col1+reference_table.col2+... WHEN main_table.incr = "12AM" THEN reference_table.col7+reference_table.col8+... WHEN main_table.incr = "6PM" THEN reference_table.col13+reference_table.col14+... ELSE reference_table.col19+reference_table.col20+...) WHERE main_table.month = extract(month from reference_table.thedate) AND main_table.day = extract(day from reference_table.thedate) I've used extract() function since my reference_table doesn't have month and day columns but has the date column named thedate. I've used the extract() function on the reference_table many times before successfully, so, I know that there's nothing wrong with my extract function syntax. However, in this instance, MySQL complains. It probably has to do with the fact that I've used in the WHERE clause. I know that this issue could get fixed if I added the month and day columns to the reference_table to avoid using the extract() function. However, I'm very reluctant to do that and would like to avoid it. How can I make it work?`

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  • Using iPhone Core Data to many Relationship

    - by BLeB
    When I define a to many relationship between entities in Xcode and then generate the data class from the entity I get a header with the following methods defined: @interface PriceList (CoreDataGeneratedAccessors) - (void)addItemsObject:(PriceListItem *)value; - (void)removeItemsObject:(PriceListItem *)value; - (void)addItems:(NSSet *)value; - (void)removeItems:(NSSet *)value; @end When I attempt to call addItemsObject with the following code a doesNotRecognizeSelector exception is thrown. PriceListItem *item = [NSEntityDescription insertNewObjectForEntityForName:@"PriceListItem" inManagedObjectContext:managedObjectContext]; item.cat = [attributeDict valueForKey:@"c"]; item.sel = [attributeDict valueForKey:@"s"]; [self addItemsObject:item]; From what I have read I do not have to implement these methods and that they are generated at runtime. Any ideas?

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  • Buttons size not equal in IE and Firefox

    - by Anurag
    I have few buttons on my jsp page and I am using the style as : .buttonblue { background-color: #003366; border-color: #99CCFF; color: #FFFFFF; font-family: Verdana,Arial,Helvetica; font-size: 8pt; font-weight: bold; height: 20px; display:inline; line-height: 1.2; text-align: center; margin-top: 2px; } In Firefox the buttons are bit smaller than IE6. I can not define the size of buttons as the caption changes the button size changes accordingly. I tried with width:auto but no success. Also, with overflow:visible the buttons in IE becomes bit smaller. Please help.

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  • SWIG interface file questions

    - by morpheous
    I am writing a C/C++ extension module for other languages and I am using SWIG to generate the bindings. I have two questions Can I include more than 1 header file in the declaration part of the interface file e.g.: /* Declarations exposed to wrapper: */ > %{ > #define SWIG_FILE_WITH_INIT > #include "a.h" > #include "b.h" > #include "c.h" %} In all of the examples I have seen so far, after the header include declaration (as shown above), the functions declared in the header are then declared again in the interface file. Is this really necessary, as it means there are two copies of the function declarations that need to be maintained. Note: I can appreciate that some functions/methods declaration may need to be 'decorated' with the 'newobject' declaration so these obviously need to be in the interface file, to avoid memory leaks - however, I would have though that it would be sufficient to include the headers and then ONLY the declarations of the functions/methods that need to be declared with 'newobject' - is this recommended way of doing things?

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  • Best way to search a point across several polygons

    - by user1474341
    I have a requirement whereby I need to match a given point (lat,lon) against several polygons to decide if there is a match. The easiest way would be to iterative over each polygon and apply the point-in-polygon check algorithm, but that is prohibitively expensive. The next optimization that I did was to define a bounding rectangle for each polygon (upper bound, lower bound) and iteratively check the point against the bounding box (fewer comparisons as against checking all the points in the polygon). Is there any other optimization possible? Would a spatial index on the bound rectangle points or a geohash help ? Any guidance would be greatly appreciated. Thanks!

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  • Mapping LINQ to SQL table to another very similar table without iterating through every one

    - by Daniel Coffman
    Apologies for the vague question. Here it is: I have a table object created by LINQ to SQL. I am copying entries from one table to an "archive" table that has all the columns of the original, plus a couple extra ones. It feels sloppy to iterate through every object and manually define the mapping like: foreach (oldTable in dbContextOldTables) { var newTable = new NewTable(); newTable.TableID = oldTable.ID; newTable.Title = oldTable.Title; ... (repeat for twenty columns) newTable.ColumnThatIsntInOldTable = "Data that will be the same for every row"; dbContext.NewTables.InsertOnSubmit(newTable); } dbContext.SubmitChanges(); Is there a clever way to do this?

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  • Jquery UI modal (popup box) control size and hide by default

    - by user782104
    jsfddle page I am currently using bootstrap modal , which is a jquery plugin to create a popup box, here is its documentation, only few lines, so it takes a minute to read only I encountered problem in 3 aspect : How can i define the size of the modal(pop up box)? I tried: <div class="modal" id="myModal" style="width:800px;height:900px;"> but it does not display correctly. And how can i hide the modal by default, it currently display when i enter the page I tried the method in doucment $(document).ready(function() { $('#myModal').modal("hide"); } ); but not working as well. Thank you

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  • 3rd party applications API / Framework Q for PHP user site

    - by Ryan
    So we are defining out functional requirements for a user content site and would like to enable: 1) 3rd party developers to develop applications that users can use on their profile 2) Enable users to export content to other sites meaning share their photos on the net. So we were told we need to use APIs for this & it's merely changing data permissions. Is that the only thing we need? Is there a framekwrok we need to build out, or what is the process functioanlly to define out to make these happen? Platform is being built on MySQL and Cake php.

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  • Javascript Inheritance and Arrays

    - by Inespe
    Hi all! I am trying to define a javascript class with an array property, and its subclass. The problem is that all instances of the subclass somehow "share" the array property: // class Test function Test() { this.array = []; this.number = 0; } Test.prototype.push = function() { this.array.push('hello'); this.number = 100; } // class Test2 : Test function Test2() { } Test2.prototype = new Test(); var a = new Test2(); a.push(); // push 'hello' into a.array var b = new Test2(); alert(b.number); // b.number is 0 - that's OK alert(b.array); // but b.array is containing 'hello' instead of being empty. why? As you can see I don't have this problem with primitive data types... Any suggestions?

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  • c++ macros with memory?

    - by anon
    Is it possible to define macros write_foo(A); and read_foo(); so that: WRITE_FOO(hello); code_block_1; READ_FOO(); code_block_2; READ_FOO(); WRITE_FOO(world); code_block_3; READ_FOO(); code_block_4; READ_FOO(); expands into: code_block_1; hello; code_block_2; hello; code_boock_3; world; code_block_4; world; ? Thanks!

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  • Can I reproduce Scala's behavior for == ?

    - by JPP
    In Programming in Scala, I can read that the == operator behaves as if it was defined like this: final def == (that: Any): Boolean = if (null eq this) {null eq that} else {this equals that} But there must actually be compiler magic to avoid null pointer exceptions, right? Is there any way for me to replicate this behavior with pure Scala; i.e., have an operator/method return one thing if the receiver is null and another one if it isn't? What I mean is an actual implementation of null eq this. I suppose I can write a "pimp" and then define the method on the wrapper class, but is there a more direct way to do this?

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  • will destroyed() be emitted if the constructor of a class derived from QObject throws?

    - by PorkyBrain
    Ive seen Qt GUI syntax like the following all over the place: myDialog::myDialog(QWidget *parent, Qt::WFlags flags):QDialog(parent, flags) { QPushButton *button = new QPushButton("&Download", this); QVBoxLayout *layout = new QVBoxLayout(this); //something that can throw here layout ->addWidget(button ); setLayout(layout); } I've always wondered if this can leak in the event of an exception because the "this" I'm giving as a parent to button and layout is not fully constructed so it might not destroy its children. I tried it out in MSVC2010 Qt4.8.3 and it looks like as soon as the base QObject class is fully created (which is done first of course) it is ok to pass "this" to other objects in the constructor, they will destroyed correctly. I haven't found the spot in the Qt docs guaranteeing this though, can someone point me to it so I have assurance that this will not change in the future?

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  • Learn C++ after learning C#

    - by RichK
    I'm developing a library in C# at the moment and recently bought a great book to help me out but the code snippets are in C++. Does anyone have a link to a site/PDF that'll give me a crash course in C++? (mainly the syntax rather than pros/cons etc) because I'll be developing in C# but things like -, ::, &, **, are giving me the shivers. Obviously the languages aren't 100% compatible but if I know what the C++ is doing from a 'theoretical' point of view I can make a stab at rewriting it in C#. I've had a Google to find the answer but all the sites seem to be "Should I use C++ or C#?", which isn't any good to me. Thanks in advance.

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  • how does [<Literal>] differ from other constants in F#

    - by Mitzh
    I am a bit confused by the Literal keyword and why it is necessary in F#. Reading the docs, it sounds to me that [<Literal>] is used to define a constant, however I am a bit confused how this constant differs from all other constants in F#.. Values that are intended to be constants can be marked with the Literal attribute. This attribute has the effect of causing a value to be compiled as a constant. When I think of a constant, I think of something which is immutable.... let x = "a" + "b" //this is a immutable value, its value is constant [<Literal>] let y = "a" + "b" //this is also a immutable value, but why is this a special constant? Is it because the 'normal' F# values are evaluated lazily and the [<Literal>] is not evaluated lazily..? is that what they mean with 'compiled as constant'..? or is there something else to it?

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  • Hibernate entities: columns without entity properties

    - by lewap
    Is there a way to "magically" persist a column which is not represented as a property in an entity? Concretely I want to add audit info to an entity without having the audit info on the entity. The audit values are not stored in the entity, but are retrieved from the environment at the time of persisting the entity. This happens in a AuditInfoUserType. The nullSafeSet gets the info from the SecurityContext, instead of reading from the entity. In the hibernate mapping, however, the audit info properties have to be defined. Is there a way in hibernate to define columns without properties?

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  • Avaliable parallel technologies in .Net

    - by David
    I am new to .Net platform. I did a search and found that there are several ways to do parallel computing in .Net: Parallel task in Task Parallel Library, which is .Net 3.5. PLINQ, .Net 4.0 Asynchounous Programming, .Net 2.0, (async is mainly used to do I/O heavy tasks, F# has a concise syntax supporting this). I list this because in Mono, there seem to be no TPL or PLINQ. Thus if I need to write cross platform parallel programs, I can use async. .Net threads. No version limitation. Could you give some short comments on these or add more methods in this list? Thanks.

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  • How exactly do you use json_decode to pass a javascript array to php?

    - by Adam
    This is how I got my php array to javascript echo 'var daysofweek = '.json_encode($daysofweek).';'; Now I am aware that json_decode can do the opposite, however the problem is I don't know the syntax to do so. I tried: <script> var array_days = new Array(); array_days[] = "psdfo"; array_days[] = "bsdf"; <?php $array_days = json_decode(?>array_days<?php);?> </script> yes im clueless. I forgot to mention that I want to send an array through post, having all my information regarding all the form values dynamically created by javascript. Otherwise, I wouldn't know which name="" to look for as it will be decided by the user. Unless someone else has an alternative solution...

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  • C++: use array of strings wrapped in namespace?

    - by John D.
    I got the following code, wishing to wrap a group of strings nicely in a namespace: namespace msgs { const int arr_sz = 3; const char *msg[arr_sz] = {"blank", "blank", "blank" }; msg[0] = "Welcome, lets start by getting a little info from you!\n"; msg[1] = "Alright, bla bla bla.."; msg[2] = "etc."; } The code inside works nicely inside a function, but I don't know how to return an array from it. The namespace idea LOOKS fine, but it returns on the last three lines: error: expected constructor, destructor, or type conversion before ‘=’ token Why can't I define the array inside a namespace, do I need to do something first? It's nice because I can call it like printf(msgs::msg[1]) etc. I want to do this I just can't wrap my head around what's wrong :(

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  • Objective C - Custom Getter with inheritance

    - by anhdat
    Recently I have worked with Core Data. When I want to set a default value for some fields, I came up with this problem: So I made a simple represent: We have 2 class Parent and Child, in which Child inherit from Parent. // Parent.h @interface Parent : NSObject @property (strong, nonatomic) NSString *lastName; // Child.h @interface Child : Parent In Parent class, I made a custom getter to set a default value when nothing is set: // Parent.h - (NSString *)lastName { if (_lastName) { return _lastName; } else { return @"Parent Default Name"; } } But I cannot make a custom default value for the field "name" which Child inherits from its Parent. // Child.h @implementation Child - (NSString *)lastname { if (super.lastName) { return super.lastName; } else { return @"Child Default Name"; } } Apparently, this method is never called. So my question here is: How can I set a custom getter for the field the Child class inherits from Parent without define an overriding property?

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  • How do I use a graphics method to pass parameters? Example is below.

    - by sonny5
    private static void getCorners(out float Wx, out float Wy, out float Vx, out float Vy) { // note-- I don't know how to flip the Y axis using this method... this is not a "graphics" method // In other words, I should use something like: // flipY(object sender, System.EventArgs e); // but don't know the syntax or whatever // I tried to do this: //Graphics g = this.CreateGraphic //Matrix myMatrix2 = new Matrix(1, 0, 0, -1, 0, 0); // flip Y axis //g.Transform = myMatrix2; //g.TranslateTransform(0, 480, MatrixOrder.Append); // ...but I get the error: // error CS0026: Keyword 'this' is not valid in a static property, static method, or // static field initializer Wx = 1.00F; Wy = 1.00F; // make this 1.00 (not 3.00F) down from the TOP since cannot get Y flipped Vx = ((Wx- WXmin)*((VXmax-VXmin)+VXmin)/(WXmax-WXmin)); Vy = ((Wy-WYmin)*(VYmax-VYmin)/(WYmax-WYmin)+VYmin); } thanks, Sonny5

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  • Beginner Access VBA SQL INSERT Question

    - by Josh K
    Syntax question: I am using the code below to call a query in Access VBA strSQL = "INSERT INTO tblLoanDetails ([ServerName]) VALUES ('Test') WHERE [ID]=3" Call CurrentDb.Execute(strSQL) And i am getting a runtime error of "3067: Query must contain atleast one table or query." the insert statement string looks like this (Threw the var into a text box): INSERT INTO tblLoanDetails ([ServerName]) VALUES ('Test') WHERE [ID]=3 I also tried adding a semi-colon to the end but with no luck. I also double checked to make sure my table is called tblLoanDetails and my Column names are ServerName, and ID Appreciate any help.

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