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  • Prolog: using the sort/2 predicate

    - by Øyvind Hauge
    So I'm trying to get rid of the wrapper clause by using the sort library predicate directly inside split. What split does is just generating a list of numbers from a list that looks like this: [1:2,3:2,4:6] ---split-- [1,2,3,2,4,6]. But the generated list contains duplicates, and I don't want that, so I'm using the wrapper to combine split and sort, which then generates the desired result: [1,2,3,4,6]. I'd really like to get rid of the wrapper and just use sort within split, however I keep getting "ERROR: sort/2: Arguments are not sufficiently instantiated." Any ideas? Thanks :) split([],[]). split([H1:H2|T],[H1,H2|NT]) :- split(T,NT). wrapper(L,Processed) :- split(L,L2), sort(L2,Processed).

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  • Has anyone "learned how to program in 21 days?"

    - by Sheehan Alam
    I'm not a fan of these learn how to program in X amount of days books. Some even boast, learn how to program in 24 hours. This is a joke and an insult to me as a software engineer who went through a rigorous discipline in computer science and mathematics. So a question to the community, have you benefited from these become a programmer quick books?

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  • What applications is Python optimal for?

    - by Alan
    I'm already a professional J2EE developer by day, and Rails developer by night. I'm planning on adding Python to my list of skills. I'm already convinced a language is just a tool, so I'm not interested in a religious war. I agree with the Pragmatic Programmers that learning one language/year is a good thing for your professional development So, in your considered opinion, what kinds of applications does Python hit the sweet spot? And why? What advantages does it have, and why do these advantages outweigh the costs in adopting Python? ADD: I also plan on learning a pure functional language like Scheme.

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  • F# - core benefits

    - by David Neale
    Since the release of VS 2010 I've seen F# more strongly advertised by Microsoft. What are the core benefits of using this language? What problems does it most naturally lend itself to? What is the learning curve like?

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  • Is PHP still basically Procedural Overall?

    - by coffeeaddict
    I know PHP 5 has some object oriented similarities but it's not a true OOP environment still right? Also does it have a true compiler? I see compiling of scripts which still means procedural. I assume it's not a real compiler in that any PHP compilers out there do not create assemblies?

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  • C# functional quicksort is failing

    - by Rubys
    I'm trying to implement quicksort in a functional style using C# using linq, and this code randomly works/doesn't work, and I can't figure out why. Important to mention: When I call this on an array or list, it works fine. But on an unknown-what-it-really-is IEnumerable, it goes insane (loses values or crashes, usually. sometimes works.) The code: public static IEnumerable<T> Quicksort<T>(this IEnumerable<T> source) where T : IComparable<T> { if (!source.Any()) yield break; var pivot = source.First(); var sortedQuery = source.Skip(1).Where(a => a.CompareTo(source.First()) <= 0).Quicksort() .Concat(new[] { pivot }) .Concat(source.Skip(1).Where(a => a.CompareTo(source.First()) > 0).Quicksort()); foreach (T key in sortedQuery) yield return key; } Can you find any faults here that would cause this to fail?

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  • How to Format Code in Research Reports

    - by RoseOfJericho
    I am currently writing a formal research report, and I'll be including code with this report. Question: Is there an accepted way of displaying code in research reports? I'm thinking both in terms of font, spacing, et cetera, and whether the code should be displayed inside the document, or in an appendix. The code will be JavaScript and PHP. None of the sections of code will be more than 25 lines (so they're mere snippets). There will be approx. half a dozen snippets. Each of the snippets will have a couple of paragraphs explaining what is happening in the code, and a discussion on its pros/cons. I have no contact with the body the report will be submitted to, and they have no published guidelines on how to format code (please do not question these points). Any help considered and appreciated.

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  • How to get an internship with a low GPA?

    - by Jason Baker
    A lot of changed majors and some other mitigating circumstances have left me with a pretty low GPA. My GPA in the last couple of semesters hasn't been stellar, but my grades have gotten a LOT better. I want to try and start putting in some resumes to get a good internship this summer. I do think that I have some decent experience for someone at my level, but I see my GPA being a pretty big potential stumbling block. Is there anything I can do to help my chances of getting a good internship? (For the record, the mitigating circumstances aren't something I'd feel comfortable discussing with a potential employer. I'd prefer getting a job by proving my merit, not making excuses.)

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  • Functional languages & support for memoization

    - by Joel
    Do any of the current crop of popular functional languages have good support for memoization & if I was to pick one on the strength of its memoisation which would you recommend & why? Update: I'm looking to optimise a directed graph (where nodes could be functions or data). When a node in the graph is updated I would like the values of other nodes to be recalculated only if they depend the node that changed. Update2: require free or open-source language/runtime.

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  • How to automatically run in the background?

    - by Hun1Ahpu
    I'm not sure that it's not implemented yet, I hope that it is. But I know that in .Net programmers should manually run time-consuming task in the background thread. So every time we handle some UI event and we understand that this will take some time we also understand that this will hang UI thread and our application. And then we make all this Background work things and handle callbacks or whatever. So my question is: Is there in some language/platform a mechanism that will automatically run time-consuming tasks in the background and will do all related work itself? So we just write the code for handling specific UI event and this code will be somehow detected as time-consuming and will be executed in background. And if there isn't, then why?

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  • Regarding grep in solaris

    - by Arav
    I want grep for a particular work in multiple files. Multiple files are stored in variable testing. TESTING=$(ls -tr *.txt) echo $TESTING test.txt ab.txt bc.txt grep "word" "$TESTING" grep: can't open test.txt ab.txt bc.txt Giving me an error. Is there any other way to do it other than for loop

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  • distributing R package with optional S4 syntax sugar

    - by mariotomo
    I've written a small package for logging, I'm distributing it through r-forge, recently I received some very interesting feedback on how to make it easier to use, but this functionality is based on stuff (setRefClass) that was added to R in 2.12. I'd like to keep distributing the package also for R-2.9, so I'm looking for a way to include or exclude the S4 syntactical sugar automatically, and include it when the library is loaded on a R = 2.12 system. one other option I see, that is to write a small S4 package that needs 2.12, imports the simpler logging package and exports the syntactically sugared interface... I don't like it too much, as I'd need to choose a different name for the S4 package.

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  • Error in merging two sequences of timestamps to yield strings

    - by AruniRC
    The code sorts two input sequences - seq01 and seq02 - on the basis of their timestamp values and returns a sequence that denotes which sequence is to be read for the values to be in order. For cases where seq02's timestamp value is lesser than seq01's timestamp value we yield a "2" to the sequence being returned, else a "1". These denote whether at that point seq01 is to be taken or seq02 is to be taken for the data to be in order (by timestamp value). let mergeSeq (seq01:seq<_>) (seq02:seq<_>) = seq { use iter01 = seq01.GetEnumerator() use iter02 = seq02.GetEnumerator() while iter01.MoveNext() do let _,_,time01 = iter01.Current let _,_,time02 = iter02.Current while time02 < time01 && iter02.MoveNext() do yield "2" yield "1" } To test it in the FSI created two sequences a and b, a={1;3;5;...} and b={0;2;4;...}. So the expected values for let c = mergeSeq a b would have been {"2","1","2","1"...}. However I am getting this error: error FS0001: The type ''a * 'b * 'c' does not match the type 'int' EDIT After correcting: let mergeSeq (seq01:seq<_>) (seq02:seq<_>) = seq { use iter01 = seq01.GetEnumerator() use iter02 = seq02.GetEnumerator() while iter01.MoveNext() do let time01 = iter01.Current let time02 = iter02.Current while time02 < time01 && iter02.MoveNext() do yield "2" yield "1" } After running this, there's another error: call MoveNext. Somehow the iteration is not being performed.

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  • Sparse linear program solver

    - by Jacob
    This great SO answer points to a good sparse solver, but I've got constraints on x (for Ax = b) such that each element in x is >=0 an <=N. The first thing which comes to mind is an LP solver for large sparse matrices. Any ideas/recommendations?

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  • Call a function from another Class - Obj C

    - by AndrewDK
    I'm trying to figure out how I can call a function from another one of my classes. I'm using a RootViewController to setup one of my views as lets say AnotherViewController So in my AnotherViewController im going to add in on the .h file @class RootViewController And in the .m file im going to import the View #import "RootViewController.h" I have a function called: -(void)toggleView { //do something } And then in my AnotherViewController I have a button assigned out as: -(void)buttonAction { //} In the buttonAction I would like to be able to call the function toggleView in my RootViewController. Can someone clarify on how I do this. I've tried adding this is my buttonAction: RootViewController * returnRootObject = [[RootViewController alloc] init]; [returnRootObject toggleView]; But I dont think that's right. Thanks in advanced.

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  • How can I pass methods in javascript?

    - by peterjwest
    I often need to pass methods from objects into other objects. However I usually want the method to be attached to the original object (by attached I mean 'this' should refer to the original object). I know a few ways to do this: a) In the object constructor: ObjectA = function() { var that = this; var method = function(a,b,c) { that.abc = a+b+c }} b) In objectA which has been passed objectB: objectB.assign(function(a,b,c) { that.method(a,b,c) }) c) Outside both objects: objectB.assign(function(a,b,c) { objectA.method(a,b,c) }) I want to know if there is a simpler way to pass methods attached to their original objects.

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  • Help me write my LISP :) LISP environments, Ruby Hashes...

    - by MikeC8
    I'm implementing a rudimentary version of LISP in Ruby just in order to familiarize myself with some concepts. I'm basing my implementation off of Peter Norvig's Lispy (http://norvig.com/lispy.html). There's something I'm missing here though, and I'd appreciate some help... He subclasses Python's dict as follows: class Env(dict): "An environment: a dict of {'var':val} pairs, with an outer Env." def __init__(self, parms=(), args=(), outer=None): self.update(zip(parms,args)) self.outer = outer def find(self, var): "Find the innermost Env where var appears." return self if var in self else self.outer.find(var) He then goes on to explain why he does this rather than just using a dict. However, for some reason, his explanation keeps passing in through my eyes and out through the back of my head. Why not use a dict, and then inside the eval function, when a new "sub-environment" needs to be created, just take the existing dict and update the key/value pairs that need to be updated, and pass that new dict into the next eval? Won't the Python interpreter keep track of the previous "outer" envs? And won't the nature of the recursion ensure that the values are pulled out from "inner" to "outer"? I'm using Ruby, and I tried to implement things this way. Something's not working though, and it might be because of this, or perhaps not. Here's my eval function, env being a regular Hash: def eval(x, env = $global_env) ........ elsif x[0] == "lambda" then ->(*args) { eval(x[2], env.merge(Hash[*x[1].zip(args).flatten(1)])) } ........ end The line that matters of course is the "lambda" one. If there is a difference, what's importantly different between what I'm doing here and what Norvig did with his Env class? If there's no difference, then perhaps someone can enlighten me as to why Norvig uses the Env class. Thanks :)

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  • Haskell map function with predicate

    - by Paul
    I feel like this should be fairly obvious, or easy, but I just can't get it. What I want to do is apply a function to a list (using map) but only if a condition is held. Imagine you only wanted to divide the numbers which were even: map (`div` 2) (even) [1,2,3,4] And that would give out [1,1,3,2] since only the even numbers would have the function applied to them. Obviously this doesn't work, but is there a way to make this work without having to write a seperate function that you can give to map? Filter is almost there, except I also want to keep the elements which the condition doesn't hold for, and just not apply the function to them. Thanks

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  • book with good examples for each implementation?

    - by ajsie
    i've read about design patterns and it seems that there are a lot of different design patterns to use. i wonder if there are some books that acts like a reference. "you want to build a framework, then consider this, this and this pattern". also giving some examples. then jumps to another implementation eg. search engine and gives some patterns and concrete examples to use. in this way you learn about the weakness and strength about each pattern and where they will fit, instead of just reading about every design pattern decoupled from each other. are there good "reference sheets" or other tutorials good for a beginner at this? thanks

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