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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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  • 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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  • What language is this???

    - by Misha Koshelev
    Dear All: I thought this was Javascript... but parser is giving me trouble. Any ideas? Thank you! Misha for (;;); {"error":0,"errorSummary":"","errorDescription":"","errorIsWarning":false,"silentError":0,"payload":{"collections": [{"name":"bcm","type":"flp","filter":"flp_662923563701","value":"662923563701","editable":true,"deletable":true,"members": ["1319651388","539562714","710814793","569071038","1553739575","2413243"]}, {"name":"mstp","type":"flp","filter":"flp_715806870131","value":"715806870131","editable":true,"deletable":true,"members": ["1263807225","1159429816","508447486","508005223","1234906348","642723993","552875889","23401888","10701320","8302901","7931988","3007490","1286522890","1128447272","1076062553","775679867","737520202","640799498","224400055","224400048","14211567","7909445","3005965","2404364","218216","660037273","224400089","73306230","9603033","1111694","1034418884","775680513" ,"704526828","518753881","512477182","224400016","24904610","19000876","5403952","3005641","2100348","100000421128298","1445411167","691445174","1020020100","795471177","683724539","682441089","532450522","224400129","224400005","3006522","2246813","1302265","7197","1900494", "100000474978266","2533582","1205125","1384091677","1260996959","710814793","514951289","224400164","224400156","173601800","13304723","7938844","3004783","3001379","302817","716739950 ","706849","1418109424","562676898","82501644","3007569","13173"]}, {"name":"mystery","type":"flp","filter":"flp_687949656211","value":"687949656211","editable":true,"deletable":true,"members": ["100001286464748","508123007","100001161894460","1148567030","1048974191","769992391","831734347","15347","1297180076","756692945","3005266","733396195","34410910","100000940154241"," 748426280","569417581","1318922027","100000164920046","1475269609","1436536592","10000016210 8385","754095305","100000421128298","537833189","100000692471928","7920231","673753496","3006217","1221878","8365333","1128447272","224400133","218216","505457123","1421958541","183829 5926","2349408","1622810085","1201640391","510959992","23429895","542118016","1017385668","586225579","625100539","100000474886633","26404148","1384091677","224400156","806908635","843 187401","400435","768261176","7901808","748496482","1541469473","2511982","25401573","503715 506","1226000844","559195162","41400094","1099436201","409816","1584400985","1577092523","100000349351880","199301581"]},{"name":"SMS Subscriptions","type":"ms","filter":"ms","value":"3","editable":true,"deletable":false,"members":[]}],"current_view":false}}

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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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  • problems with cut (unix)

    - by lego69
    hello everybody, I've got strange problem with cut I wrote script, there I have row: ... | cut -d" " -f3,4 >! out cut recieves this data (I checked it with echo) James James 033333333 0 0.00 but I recieve empty lines in out, can somebody explain why?

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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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  • How can I define a verb in J that applies a different verb alternately to each atom in a list?

    - by Gregory Higley
    Imagine I've defined the following name in J: m =: >: i. 2 4 5 This looks like the following: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 I want to create a monadic verb of rank 1 that applies to each list in this list of lists. It will double (+:) or add 1 (>:) to each alternate item in the list. If we were to apply this verb to the first row, we'd get 2 3 6 5 10. It's fairly easy to get a list of booleans which alternate with each item, e.g., 0 1 $~{:$ m gives us 0 1 0 1 0. I thought, aha! I'll use something like +:`>: @. followed by some expression, but I could never quite get it to work. Any suggestions? UPDATE The following appears to work, but perhaps it can be refactored into something more elegant by a J pro. poop =: monad define (($ y) $ 0 1 $~{:$ y) ((]+:)`(]:) @. [)"0 y )

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  • Supporting Piping (A Useful Hello World)

    - by blastthisinferno
    I am trying to write a collection of simple C++ programs that follow the basic Unix philosophy by: Make each program do one thing well. Expect the output of every program to become the input to another, as yet unknown, program. I'm having an issue trying to get the output of one to be the input of the other, and getting the output of one be the input of a separate instance of itself. Very briefly, I have a program add which takes arguments and spits out the summation. I want to be able to pipe the output to another add instance. ./add 1 2 | ./add 3 4 That should yield 6 but currently yields 10. I've encountered two problems: The cin waits for user input from the console. I don't want this, and haven't been able to find a simple example showing a the use of standard input stream without querying the user in the console. If someone knows of an example please let me know. I can't figure out how to use standard input while supporting piping. Currently, it appears it does not work. If I issue the command ./add 1 2 | ./add 3 4 it results in 7. The relevant code is below: add.cpp snippet // ... COMMAND LINE PROCESSING ... std::vector<double> numbers = multi.getValue(); // using TCLAP for command line parsing if (numbers.size() > 0) { double sum = numbers[0]; double arg; for (int i=1; i < numbers.size(); i++) { arg = numbers[i]; sum += arg; } std::cout << sum << std::endl; } else { double input; // right now this is test code while I try and get standard input streaming working as expected while (std::cin) { std::cin >> input; std::cout << input << std::endl; } } // ... MORE IRRELEVANT CODE ... So, I guess my question(s) is does anyone see what is incorrect with this code in order to support piping standard input? Are there some well known (or hidden) resources that explain clearly how to implement an example application supporting the basic Unix philosophy? @Chris Lutz I've changed the code to what's below. The problem where cin still waits for user input on the console, and doesn't just take from the standard input passed from the pipe. Am I missing something trivial for handling this? I haven't tried Greg Hewgill's answer yet, but don't see how that would help since the issue is still with cin. // ... COMMAND LINE PROCESSING ... std::vector<double> numbers = multi.getValue(); // using TCLAP for command line parsing double sum = numbers[0]; double arg; for (int i=1; i < numbers.size(); i++) { arg = numbers[i]; sum += arg; } // right now this is test code while I try and get standard input streaming working as expected while (std::cin) { std::cin >> arg; std::cout << arg << std::endl; } std::cout << sum << std::endl; // ... MORE IRRELEVANT CODE ...

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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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  • Why are functional languages considered a boon for multi threaded environments?

    - by Billy ONeal
    I hear a lot about functional languages, and how they scale well because there is no state around a function; and therefore that function can be massively parallelized. However, this makes little sense to me because almost all real-world practical programs need/have state to take care of. I also find it interesting that most major scaling libraries, i.e. MapReduce, are typically written in imperative languages like C or C++. I'd like to hear from the functional camp where this hype I'm hearing is coming from....

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  • sending data packet just before closing socket

    - by xopht
    Before disconnect the client, the server wants to send some info to the client - why do I(server) disconnect you(client). If I send packet to the info and close the client socket immediately, closesocket() returns -1 and if I use linger option to work closesocket() successfully, the info cannot be sent completely. How can I complete this and is it possible to know socket buffer is empty(means my packet sent all)? thx.

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  • Array: Recursive problem cracked me up

    - by VaioIsBorn
    An array of integers A[i] (i 1) is defined in the following way: an element A[k] ( k 1) is the smallest number greater than A[k-1] such that the sum of its digits is equal to the sum of the digits of the number 4* A[k-1] . You need to write a program that calculates the N th number in this array based on the given first element A[1] . INPUT: In one line of standard input there are two numbers seperated with a single space: A[1] (1 <= A[1] <= 100) and N (1 <= N <= 10000). OUTPUT: The standard output should only contain a single integer A[N] , the Nth number of the defined sequence. Input: 7 4 Output: 79 Explanation: Elements of the array are as follows: 7, 19, 49, 79... and the 4th element is solution. I tried solving this by coding a separate function that for a given number A[k] calculates the sum of it's digits and finds the smallest number greater than A[k-1] as it says in the problem, but with no success. The first testing failed because of a memory limit, the second testing failed because of a time limit, and now i don't have any possible idea how to solve this. One friend suggested recursion, but i don't know how to set that. Anyone who can help me in any way please write, also suggest some ideas about using recursion/DP for solving this problem. Thanks.

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  • Simple IF statement question

    - by JGreig
    How can I simply the below if statements? if ( isset(var1) & isset(var2) ) { if ( (var1 != something1) || (var2 != something2) ) { // ... code ... } } Seems like this could be condensed to only one IF statement but am not certain if I'd use an AND or OR

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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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  • Using Cases to change background colour | Visual Studio 2008

    - by Simon
    I really need help working with cases, I'm only learning it so far, but just can't get a drop down menu to work that would change the background of a Textbox. Private Sub cbColours_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cbColours.SelectedIndexChanged Select Case colours Case Is = "Red" txtSpace.BackColor = Color.Red Case Is = "Blue" txtSpace.BackColor = Color.Blue Case Is = "Green" txtSpace.BackColor = Color.Green End Select End Sub It isn't doing anything at all... In the dropdown menu, it has Red, Blue and Green one per line When the value (e.g. Green) is clicked, it will then change the Textbox to the colour selected. Many help appreciated :)

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  • MySQL: Get only count of result set.

    - by Varun
    I am using MVC with PHP/MySQL. Suppose I am using 10 functions with different queries for fetching details from the database. But at other times I may want to get only the count of the result that will be returned by the query. What is the standard way to handle such situation. Should I write 10 more functions which duplicate almost whole query and return only the count. Or Should I always return the count also with the result set Or I can pass a flag to indicate that the function should return count only, and then based on the flag I will dynamically generate the (select part of) query. Or Is there a better way?

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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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