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  • F# - Function with no arguments?

    - by Rubys
    When thinking in a functional mindset, given that functions are supposed to be pure, one can conclude any function with no arguments is basically just a value. However, reallity gets in the way, and with different inputs, I might not need a certain function, and if that function is computationally expensive, I'd like to not evaluate it if it's not needed. I found a workaround, using let func _ = ... and calling it with func 1 or whatever, but that feels very non-idiomatic and confusing to the reader. This boils down to one question: In F#, Is there a proper way to declare a function with zero arguments, without having it evaluated on declaration?

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  • Is the FoldLeft function available in R?

    - by JSmaga
    Hi, I would like to know if there is an implementation of the foldLeft function (and foldRight?) in R. The language is supposed to be "rather" functional oriented and hence I think there should be something like this, but I could not find it in the documentation. To me, foldLeft function applies on a list and has the following signature: foldLeft[B](z : B)(f : (B, A) => B) : B It is supposed to return the following result: f(... (f(f(z, a0), a1) ...), an) if the list is [a0, a1, ..., an]. (I use the definition of the Scala List API) Does anybody know if such a function exists in R?

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  • Multiplying numbers on horizontal, vertial, and diagonal lines

    - by untwisted
    I'm currently working on a project Euler problem (www.projecteuler.net) for fun but have hit a stumbling block. One of the problem provides a 20x20 grid of numbers and asks for the greatest product of 4 numbers on a straight line. This line can be either horizontal, vertical, or diagonal. Using a procedural language I'd have no problem solving this, but part of my motivation for doing these problems in the first place is to gain more experience and learn more Haskell. As of right now I'm reading in the grid and converting it to a list of list of ints, eg -- [[Int]]. This makes the horizontal multiplication trivial, and by transposing this grid the vertical also becomes trivial. The diagonal is what is giving me trouble. I've thought of a few ways where I could use explicit array slicing or indexing, to get a solution, but it seems overly complicated and hackey. I believe there is probably an elegant, functional solution here, and I'd love to hear what others can come up with.

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  • How do we install Unity-2D and dependencies offline?

    - by Takkat
    We have installed 11.04 32-bit on an old machine that has no internet connection and with a graphics card that is not suitable for running Compiz or Unity. Still, we would like to run Unity-2D on this machine. We are aware of answers to this Question. Sadly Keryx will not run on 11.04 32-bit because of unmet dependencies. Building an offline repository is not an option because of limited storage capacity. Is there any convenient other way to find, download, install, and eventually update unity-2 and all dependencies (preferably from an OS independent download path)?

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  • March 21 EBS Webcast: A Functional and Technical Overview of Batch Layer Costing When Using Actual Costing

    - by Oracle_EBS
    ADVISOR WEBCAST: A Functional and Technical Overview of Batch Layer Costing When Using Actual CostingPRODUCT FAMILY: Process Manufacturing - EBS March 21, 2012 at 11 am ET, 9 am MT, 8 am PT This one-hour session is recommended for technical and functional users who use Actual Costing in OPM Financials. You will gain a better understanding of why layer costing was introduced, how it works, what benefits it provides, and how to get the the most out of this functionality.TOPICS WILL INCLUDE: Explain why Batch Layer Costing when using Actual Costing was introduced How this functionality works What benefits provided with Batch Layer Costing when using Actual Costing Tips to make this functionality work as desired Technical overview A short, live demonstration (only if applicable) and question and answer period will be included. Oracle Advisor Webcasts are dedicated to building your awareness around our products and services. This session does not replace offerings from Oracle Global Support Services. Current Schedule can be found on Note 740966.1 Post Presentation Recordings can be found on Note 740964.1

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  • Are lambda expressions/delegates in C# "pure", or can they be?

    - by Bob
    I recently asked about functional programs having no side effects, and learned what this means for making parallelized tasks trivial. Specifically, that "pure" functions make this trivial as they have no side effects. I've also recently been looking into LINQ and lambda expressions as I've run across examples many times here on StackOverflow involving enumeration. That got me to wondering if parallelizing an enumeration or loop can be "easier" in C# now. Are lambda expressions "pure" enough to pull off trivial parallelizing? Maybe it depends on what you're doing with the expression, but can they be pure enough? Would something like this be theoretically possible/trivial in C#?: Break the loop into chunks Run a thread to loop through each chunk Run a function that does something with the value from the current loop position of each thread For instance, say I had a bunch of objects in a game loop (as I am developing a game and was thinking about the possibility of multiple threads) and had to do something with each of them every frame, would the above be trivial to pull off? Looking at IEnumerable it seems it only keeps track of the current position, so I'm not sure I could use the normal generic collections to break the enumeration into "chunks". Sorry about this question. I used bullets above instead of pseudo-code because I don't even know enough to write pseudo-code off the top of my head. My .NET knowledge has been purely simple business stuff and I'm new to delegates and threads, etc. I mainly want to know if the above approach is good for pursuing, and if delegates/lambdas don't have to be worried about when it comes to their parallelization.

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  • How to iterate over modifed std::map values?

    - by Frank
    I have an std::map, and I would like to define an iterator that returns modified values. Typically, a std::map<int,double>::iterator iterates over std::pair<int,double>, and I would like the same behavior, just the double value is multiplied by a constant. I tried it with boost::transform_iterator, but it doesn't compile: #include <map> #include <boost/iterator/transform_iterator.hpp> #include <boost/functional.hpp> typedef std::map<int,double> Map; Map m; m[100] = 2.24; typedef boost::binder2nd< std::multiplies<double> > Function; typedef boost::transform_iterator<Function, Map::value_type*> MultiplyIter; MultiplyIter begin = boost::make_transform_iterator(m.begin(), Function(std::multiplies<double>(), 4)); // now want to similarly create an end iterator // and then iterate over the modified map The error is: error: conversion from 'boost ::transform_iterator< boost::binder2nd<multiplies<double> >, gen_map<int, double>::iterator , boost::use_default, boost::use_default >' to non-scalar type 'boost::transform_iterator< boost::binder2nd<multiplies<double> >, pair<const int, double> * , boost::use_default, boost::use_default >' requested What is gen_map and do I really need it? I adapted the transform_iterator tutorial code from here to write this code ...

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  • Learning Haskell maps, folds, loops and recursion

    - by Darknight
    I've only just dipped my toe in the world of Haskell as part of my journey of programming enlightenment (moving on from, procedural to OOP to concurrent to now functional). I've been trying an online Haskell Evaluator. However I'm now stuck on a problem: Create a simple function that gives the total sum of an array of numbers. In a procedural language this for me is easy enough (using recursion) (c#) : private int sum(ArrayList x, int i) { if (!(x.Count < i + 1)) { int t = 0; t = x.Item(i); t = sum(x, i + 1) + t; return t; } } All very fine however my failed attempt at Haskell was thus: let sum x = x+sum in map sum [1..10] this resulted in the following error (from that above mentioned website): Occurs check: cannot construct the infinite type: a = a -> t Please bear in mind I've only used Haskell for the last 30 minutes! I'm not looking simply for an answer but a more explanation of it. Thanks in advanced.

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  • Printing a field with additional dots in haskell

    - by Frank Kluyt
    I'm writing a function called printField. This function takes an int and a string as arguments and then then prints a field like this "Derp..." with this: printField 7 "Derp". When the field consists of digits the output should be "...3456". The function I wrote looks like this: printField :: Int -> String -> String printField x y = if isDigit y then concat(replicate n ".") ++ y else y ++ concat(replicate n ".") where n = x - length y This obviously isn't working. The error I get from GHC is: Couldn't match type `[Char]' with `Char' Expected type: Char Actual type: String In the first argument of `isDigit', namely `y' In the expression: isDigit y In the expression: if isDigit y then concat (replicate n ".") ++ y else y ++ concat (replicate n ".") I can't get it to work :(. Can anyone help me out? Please keep in mind that I'm new to Haskell and functional programming in general.

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  • How to use boost::transform_iterator to iterate over modifed std::map values?

    - by Frank
    I have an std::map, and I would like to define an iterator that returns modified values. Typically, a std::map<int,double>::iterator iterates over std::pair<int,double>, and I would like the same behavior, just the double value is multiplied by a constant. I tried it with boost::transform_iterator, but it doesn't compile: #include <map> #include <boost/iterator/transform_iterator.hpp> #include <boost/functional.hpp> typedef std::map<int,double> Map; Map m; m[100] = 2.24; typedef boost::binder2nd< std::multiplies<double> > Function; typedef boost::transform_iterator<Function, Map::value_type*> MultiplyIter; MultiplyIter begin = boost::make_transform_iterator(m.begin(), Function(std::multiplies<double>(), 4)); // now want to similarly create an end iterator // and then iterate over the modified map The error is: error: conversion from 'boost ::transform_iterator< boost::binder2nd<multiplies<double> >, gen_map<int, double>::iterator , boost::use_default, boost::use_default >' to non-scalar type 'boost::transform_iterator< boost::binder2nd<multiplies<double> >, pair<const int, double> * , boost::use_default, boost::use_default >' requested What is gen_map and do I really need it? I adapted the transform_iterator tutorial code from here to write this code ...

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  • Invoking code both before and after WebControl.Render method

    - by Dirk
    I have a set of custom ASP.NET server controls, most of which derive from CompositeControl. I want to implement a uniform look for "required" fields across all control types by wrapping each control in a specific piece of HTML/CSS markup. For example: <div class="requiredInputContainer"> ...custom control markup... </div> I'd love to abstract this behavior in such a way as to avoid having to do something ugly like this in every custom control, present and future: public class MyServerControl : TextBox, IRequirableField { public IRequirableField.IsRequired {get;set;} protected override void Render(HtmlTextWriter writer){ RequiredFieldHelper.RenderBeginTag(this, writer) //render custom control markup RequiredFieldHelper.RenderEndTag(this, writer) } } public static class RequiredFieldHelper{ public static void RenderBeginTag(IRequirableField field, HtmlTextWriter writer){ //check field.IsRequired, render based on its values } public static void RenderEndTag(IRequirableField field, HtmlTextWriter writer){ //check field.IsRequired , render based on its values } } If I was deriving all of my custom controls from the same base class, I could conceivably use Template Method to enforce the before/after behavior;but I have several base classes and I'd rather not end up with really a convoluted class hierarchy anyway. It feels like I should be able to design something more elegant (i.e. adheres to DRY and OCP) by leveraging the functional aspects of C#, but I'm drawing a blank.

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  • Help! I'm a Haskell Newbie

    - by Darknight
    I've only just dipped my toe in the world of Haskell as part of my journey of programming enlightenment (moving on from, procedural to OOP to concurrent to now functional). I've been trying an online Haskell Evaluator. However I'm now stuck on a problem: Create a simple function that gives the total sum of an array of numbers. In a procedural language this for me is easy enough (using recursion) (c#) : private int sum(ArrayList x, int i) { if (!(x.Count < i + 1)) { int t = 0; t = x.Item(i); t = sum(x, i + 1) + t; return t; } } All very fine however my failed attempt at Haskell was thus: let sum x = x+sum in map sum [1..10] this resulted in the following error (from that above mentioned website): Occurs check: cannot construct the infinite type: a = a -> t Please bear in mind I've only used Haskell for the last 30 minutes! I'm not looking simply for an answer but a more explanation of it. Thanks in advanced.

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  • How can I implement a splay tree that performs the zig operation last, not first?

    - by Jakob
    For my Algorithms & Data Structures class, I've been tasked with implementing a splay tree in Haskell. My algorithm for the splay operation is as follows: If the node to be splayed is the root, the unaltered tree is returned. If the node to be splayed is one level from the root, a zig operation is performed and the resulting tree is returned. If the node to be splayed is two or more levels from the root, a zig-zig or zig-zag operation is performed on the result of splaying the subtree starting at that node, and the resulting tree is returned. This is valid according to my teacher. However, the Wikipedia description of a splay tree says the zig step "will be done only as the last step in a splay operation" whereas in my algorithm it is the first step in a splay operation. I want to implement a splay tree that performs the zig operation last instead of first, but I'm not sure how it would best be done. It seems to me that such an algorithm would become more complex, seeing as how one needs to find the node to be splayed before it can be determined whether a zig operation should be performed or not. How can I implement this in Haskell (or some other functional language)?

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  • Can you dynamically combine multiple conditional functions into one in Python?

    - by erich
    I'm curious if it's possible to take several conditional functions and create one function that checks them all (e.g. the way a generator takes a procedure for iterating through a series and creates an iterator). The basic usage case would be when you have a large number of conditional parameters (e.g. "max_a", "min_a", "max_b", "min_b", etc.), many of which could be blank. They would all be passed to this "function creating" function, which would then return one function that checked them all. Below is an example of a naive way of doing what I'm asking: def combining_function(max_a, min_a, max_b, min_b, ...): f_array = [] if max_a is not None: f_array.append( lambda x: x.a < max_a ) if min_a is not None: f_array.append( lambda x: x.a > min_a ) ... return lambda x: all( [ f(x) for f in f_array ] ) What I'm wondering is what is the most efficient to achieve what's being done above? It seems like executing a function call for every function in f_array would create a decent amount of overhead, but perhaps I'm engaging in premature/unnecessary optimization. Regardless, I'd be interested to see if anyone else has come across usage cases like this and how they proceeded. Also, if this isn't possible in Python, is it possible in other (perhaps more functional) languages?

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  • How can I write simulations in Erlang?

    - by rick
    Hi guys, I want to do some numerical stuff in Erlang like this: You've got an array with the following values: [2,3,4] In each iteration, you calculate 0.1 * [n-1] + 0.7 *[n] + 0.2 * [n+1] This becomes the new [n]. If n == 0 then [n-1] = 0. If [n] == length of array then [n] = 0. So I try an example: [2,3,4] calculations: 0.1 * 0 + 0.7 * 2 + 0.2 * 3 = 2 0.1 * 2 + 0.7 * 3 + 0.2 * 4 = 3.1 0.1 * 3 + 0.7 * 4 + 0.2 * 0 = 3.1 So [2,3,4] becomes to [2, 3.1, 3.1] after one iteration. I know how to write this in a non-functional language like C. But I have difficulties to imagine, how this could be done in Erlang. I found some tutorials on how you read a file to a list. So this is not the problem. How can I spawn different Erlang processes that each process has one element of the list? How can I do calculations by communicating with 'the neighbors', so that the neighbors know where their neigbors are generically, without specifying each? How can I collect the data into a list? Eventually, is it possible to solve that problem in Erlang at all? Thanks for your help.

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  • Assign a static function to a variable in PHP

    - by Felipe Almeida
    I would like to assign a static function to a variable so that I can send it around as a parameter. For example: class Foo{ private static function privateStaticFunction($arg1,$arg2){ //compute stuff on the args } public static function publicStaticFunction($foo,$bar){ //works $var = function(){ //do stuff }; //also works $var = function($someArg,$someArg2){ //do stuff }; //Fatal error: Undefined class constant 'privateStaticFunction' $var = self::privateStaticMethod; //same error $var = Foo::privateStaticFunction; //compiles, but errors when I try to run $var() somewhere else, as expected //Fatal error: Call to private method Foo::privateStaticMethod() from context '' $var = function(){ return Foo::privateStaticMethod(); }; } } I've tried a few more variations but none of them worked. I don't even expect this sort of functional hacking to work with PHP but hey, who knows? Is it possible to do that in PHP or will I need to come up with some hack using eval? P.S.: LawnGnome on ##php mentioned something about it being possible to do what I want using array('Foo','privateStaticMethod') but I didn't understand what he meant and I didn't press him further as he looked busy.

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  • HintPath vs ReferencePath in Visual Studio

    - by toasteroven
    What exactly is the difference between the HintPath in a .csproj file and the ReferencePath in a .csproj.user file? We're trying to commit to a convention where dependency DLLs are in a "releases" svn repo and all projects point to a particular release. Since different developers have different folder structures, relative references won't work, so we came up with a scheme to use an environment variable pointing to the particular developer's releases folder to create an absolute reference. So after a reference is added, we manually edit the project file to change the reference to an absolute path using the environment variable. I've noticed that this can be done with both the HintPath and the ReferencePath, but the only difference I could find between them is that HintPath is resolved at build-time and ReferencePath when the project is loaded into the IDE. I'm not really sure what the ramifications of that are though. I have noticed that VS sometimes rewrites the .csproj.user and I have to rewrite the ReferencePath, but I'm not sure what triggers that. I've heard that it's best not to check in the .csproj.user file since it's user-specific, so I'd like to aim for that, but I've also heard that the HintPath-specified DLL isn't "guaranteed" to be loaded if the same DLL is e.g. located in the project's output directory. Any thoughts on this?

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  • m2eclipse workspace resolution

    - by Bartosz Radaczynski
    Hi all, I am using m2eclipse for managing maven projects in eclipse. It seems that in the previous release that I was using (0.9.8) the workspace resolution did not work at all, but right now it also does not work quite as I would expect. Namely, when the "resolve dependencied from workspace" setting for a project is not checked, the project turns red and cannot be build. The message says: artifact xxx x.y-SNAPSHOT cannot be found int local repository (or something to that extent). The trouble is that m2eclipse is putting information about workspace project into my local repo. Is there a way to change this behaviour? P.S. The workaround for this is to close the xxx project, then m2eclipse resolved the dependency to whatever version I've had previously in the local repository (i.e. the non-snapshot version).

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  • How to extend an 'unloadable' Rails plugin?

    - by Vitaly Kushner
    I'm trying to write a plugin that will extend InheritedResources. Specifically I want to rewrite some default helpers. And I'd like it to "just work" once installed, w/o any changes to application code. The functionality is provided in a module which needs to be included in a right place. The question is where? :) The first attempt was to do it in my plugin's init.rb: InheritedResources::Base.send :include, MyModule It works in production, but fails miserably in development since InheritedResource::Base declared as unloadable and so its code is reloaded on each request. So my module is there for the first request, and then its gone. InheritedResource::Base is 'pulled' in again by any controller that uses it: Class SomeController < InheritedResource::Base But no code is 'pulling in' my extension module since it is not referenced anywhere except init.rb which is not re-loaded on each request So right now I'm just including the module manually in every controller that needs it which sucks. I can't even include it once in ApplicationController because InheritedResources inherites from it and so it will override any changes back. update I'm not looking for advice on how to 'monkey patch'. The extension is working in production just great. my problem is how to catch moment exactly after InheritedResources loaded to stick my extension into it :) update2 another attempt at clarification: the sequence of events is a) rails loads plugins. my plugin loads after inherited_resources and patches it. b) a development mode request is served and works c) rails unloads all the 'unloadable' code which includes all application code and also inherited_resources d) another request comes in e) rails loads controller, which inherites from inherited resources f) rails loads inherited resources which inherit from application_controller g) rails loads application_contrller (or may be its already loaded at this stage, not sure) g) request fails as no-one loaded my plugin to patch inherited_resources. plugin init.rb files are not reloaded I need to catch the point in time between g and h

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  • How to extend an 'unloadable' Rails plugin?

    - by Vitaly Kushner
    I'm trying to write a plugin that will extend InheritedResources. Specifically I want to rewrite some default helpers. And I'd like it to "just work" once installed, w/o any changes to application code. The functionality is provided in a module which needs to be included in a right place. The question is where? :) The first attempt was to do it in my plugin's init.rb: InheritedResources::Base.send :include, MyModule It works in production, but fails miserably in development since InheritedResource::Base declared as unloadable and so its code is reloaded on each request. So my module is there for the first request, and then its gone. InheritedResource::Base is 'pulled' in again by any controller that uses it: Class SomeController < InheritedResource::Base But no code is 'pulling in' my extension module since it is not referenced anywhere except init.rb which is not re-loaded on each request So right now I'm just including the module manually in every controller that needs it which sucks. I can't even include it once in ApplicationController because InheritedResources inherites from it and so it will override any changes back.

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  • How to manually disable/blacklist Maven repository

    - by cetnar
    In my base project I use dependency of JasperReports which has non-existent repository declaration in its pom. When I run every Maven commad there is dependency looking for commons-collection in this Jasper repository so I need to wait for timeout. This is my base project and is used as dependency in my others projects so again I need to wait for timeout. Is there are a way to move this repository to blacklisted or override this settings? Notes: 1.Why it search in Jasper repository, maybe bacause of ranges <dependency> <groupId>commons-collections</groupId> <artifactId>commons-collections</artifactId> <version>[2.1,)</version> <scope>compile</scope> </dependency> 2.My idea to resolve this problem is to change jasper pom and use proxy repository, but I looking to another option. 3.I use jasperreports 1.3.3 version and I'd like don't change it.

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  • C# Putting the required DLLs somewhere other than the root of the output

    - by aip.cd.aish
    I am using EmguCV for a project and when our program runs it needs some dlls like "cxcore.dll" etc. (or it throws runtime exceptions). At the moment, I put the files in the root of the output folder (selected "Copy Always" in the file's properties in Visual Studio). However it looks a bit messy, to have about 10 different dlls just there. Is there someway where I can move it to a subfolder in the output folder and it'll still find it.

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