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• What does your Lisp workflow look like?

  - by Duncan Bayne

  I'm learning Lisp at the moment, coming from a language progression that is Locomotive BASIC - Z80 Assembler - Pascal - C - Perl - C# - Ruby. My approach is to simultaneously: write a simple web-scraper using SBCL, QuickLisp, closure-html, and drakma watch the SICP lectures I think this is working well; I'm developing good 'Lisp goggles', in that I can now read Lisp reasonably easily. I'm also getting a feel for how the Lisp ecosystem works, e.g. Quicklisp for dependencies. What I'm really missing, though, is a sense of how a seasoned Lisper actually works. When I'm coding for .NET, I have Visual Studio set up with ReSharper and VisualSVN. I write tests, I implement, I refactor, I commit. Then when I'm done enough of that to complete a story, I write some AUATs. Then I kick off a Release build on TeamCity to push the new functionality out to the customer for testing & hopefully approval. If it's an app that needs an installer, I use either WiX or InnoSetup, obviously building the installer through the CI system. So, my question is: as an experienced Lisper, what does your workflow look like? Do you work mostly in the REPL, or in the editor? How do you do unit tests? Continuous integration? Packaging & deployment? When you sit down at your desk, steaming mug of coffee to one side and a framed photo of John McCarthy to the other, what is it that you do? Currently, I feel like I am getting to grips with Lisp coding, but not Lisp development ...

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• Liskov principle: violation by type-hinting

  - by Elias Van Ootegem

  According to the Liskov principle, a construction like the one below is invalid, as it strengthens a pre-condition. I know the example is pointless/nonsense, but when I last asked a question like this, and used a more elaborate code sample, it seemed to distract people too much from the actual question. //Data models abstract class Argument { protected $value = null; public function getValue() { return $this->value; } abstract public function setValue($val); } class Numeric extends Argument { public function setValue($val) { $this->value = $val + 0;//coerce to number return $this; } } //used here: abstract class Output { public function printValue(Argument $arg) { echo $this->format($arg); return $this; } abstract public function format(Argument $arg); } class OutputNumeric extends Output { public function format(Numeric $arg)//<-- VIOLATION! { $format = is_float($arg->getValue()) ? '%.3f' : '%d'; return sprintf($format, $arg->getValue()); } } My question is this: Why would this kind of "violation" be considered harmful? So much so that some languages, like the one I used in this example (PHP), don't even allow this? I'm not allowed to strengthen the type-hint of an abstract method but, by overriding the printValue method, I am allowed to write: class OutputNumeric extends Output { final public function printValue(Numeric $arg) { echo $this->format($arg); } public function format(Argument $arg) { $format = is_float($arg->getValue()) ? '%.3f' : '%d'; return sprintf($format, $arg->getValue()); } } But this would imply repeating myself for each and every child of Output, and makes my objects harder to reuse. I understand why the Liskov principle exists, don't get me wrong, but I find it somewhat difficult to fathom why the signature of an abstract method in an abstract class has to be adhered to so much stricter than a non-abstract method. Could someone explain to me why I'm not allowed to hind at a child class, in a child class? The way I see it, the child class OutputNumeric is a specific use-case of Output, and thus might need a specific instance of Argument, namely Numeric. Is it really so wrong of me to write code like this?

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• How do we keep dependent data structures up to date?

  - by Geo

  Suppose you have a parse tree, an abstract syntax tree, and a control flow graph, each one logically derived from the one before. In principle it is easy to construct each graph given the parse tree, but how can we manage the complexity of updating the graphs when the parse tree is modified? We know exactly how the tree has been modified, but how can the change be propagated to the other trees in a way that doesn't become difficult to manage? Naturally the dependent graph can be updated by simply reconstructing it from scratch every time the first graph changes, but then there would be no way of knowing the details of the changes in the dependent graph. I currently have four ways to attempt to solve this problem, but each one has difficulties. Nodes of the dependent tree each observe the relevant nodes of the original tree, updating themselves and the observer lists of original tree nodes as necessary. The conceptual complexity of this can become daunting. Each node of the original tree has a list of the dependent tree nodes that specifically depend upon it, and when the node changes it sets a flag on the dependent nodes to mark them as dirty, including the parents of the dependent nodes all the way down to the root. After each change we run an algorithm that is much like the algorithm for constructing the dependent graph from scratch, but it skips over any clean node and reconstructs each dirty node, keeping track of whether the reconstructed node is actually different from the dirty node. This can also get tricky. We can represent the logical connection between the original graph and the dependent graph as a data structure, like a list of constraints, perhaps designed using a declarative language. When the original graph changes we need only scan the list to discover which constraints are violated and how the dependent tree needs to change to correct the violation, all encoded as data. We can reconstruct the dependent graph from scratch as though there were no existing dependent graph, and then compare the existing graph and the new graph to discover how it has changed. I'm sure this is the easiest way because I know there are algorithms available for detecting differences, but they are all quite computationally expensive and in principle it seems unnecessary so I'm deliberately avoiding this option. What is the right way to deal with these sorts of problems? Surely there must be a design pattern that makes this whole thing almost easy. It would be nice to have a good solution for every problem of this general description. Does this class of problem have a name?

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• Licensing issues with using code from samples coming with SDK

  - by Andrey

  Samples coming with SDK are intended to provide best practices. So logically it looks perfectly valid to take code from them. But usually samples come under licenses, for example a lot of samples from Microsoft are released under Microsoft Public License (MS-PL). Samples are usually published to provide best practices and common reusable code. But how can I use code from samples if they are under rather strict licenses?

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• Task Management - How important it is for a entry level developer?

  - by Naveen Kumar

  I hold masters in CS & now I'm mobile apps developer (Entry Level) , I always start to plan things when starting or doing any project both at work & projects i do at Home (for passion) - as I can deliver the project on time but sometimes i m running out of time like 10 tasks a day vs my time forecast will take 2 on that day? As I'm beginner level, I want your suggestions on How important is Task Management for a person like me & for achieving my goals? My target for the next 3 year will be a Project Manager or Similiar Role - i belive which these time managing skills will be a needed quality.

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• Class instance clustering in object reference graph for multi-entries serialization

  - by Juh_

  My question is on the best way to cluster a graph of class instances (i.e. objects, the graph nodes) linked by object references (the -directed- edges of the graph) around specifically marked objects. To explain better my question, let me explain my motivation: I currently use a moderately complex system to serialize the data used in my projects: "marked" objects have a specific attributes which stores a "saving entry": the path to an associated file on disc (but it could be done for any storage type providing the suitable interface) Those object can then be serialized automatically (eg: obj.save()) The serialization of a marked object 'a' contains implicitly all objects 'b' for which 'a' has a reference to, directly s.t: a.b = b, or indirectly s.t.: a.c.b = b for some object 'c' This is very simple and basically define specific storage entries to specific objects. I have then "container" type objects that: can be serialized similarly (in fact their are or can-be "marked") they don't serialize in their storage entries the "marked" objects (with direct reference): if a and a.b are both marked, a.save() calls b.save() and stores a.b = storage_entry(b) So, if I serialize 'a', it will serialize automatically all objects that can be reached from 'a' through the object reference graph, possibly in multiples entries. That is what I want, and is usually provides the functionalities I need. However, it is very ad-hoc and there are some structural limitations to this approach: the multi-entry saving can only works through direct connections in "container" objects, and there are situations with undefined behavior such as if two "marked" objects 'a'and 'b' both have a reference to an unmarked object 'c'. In this case my system will stores 'c' in both 'a' and 'b' making an implicit copy which not only double the storage size, but also change the object reference graph after re-loading. I am thinking of generalizing the process. Apart for the practical questions on implementation (I am coding in python, and use Pickle to serialize my objects), there is a general question on the way to attach (cluster) unmarked objects to marked ones. So, my questions are: What are the important issues that should be considered? Basically why not just use any graph parsing algorithm with the "attach to last marked node" behavior. Is there any work done on this problem, practical or theoretical, that I should be aware of? Note: I added the tag graph-database because I think the answer might come from that fields, even if the question is not.

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• Quantifying the value of refactoring in commercial terms

  - by Myles McDonnell

  Here is the classic scenario; Dev team build a prototype. Business mgmt like it and put it into production. Dev team now have to continue to deliver new features whilst at the same time pay the technical debt accrued when the code base was a prototype. My question is this (forgive me, it's rather open ended); how can the value of the refactoring work be quantified in commercial terms? As developers we can clearly understand and communicate the value in technical terms, such a the removal of code duplication, the simplification of an object model and so on. But this means little to an executive focussed on the commercial elements. What will mean something to this executive is the dev. team being able to deliver requirements at faster velocity. Just making this statement without any metrics that clearly quantify return on investment (increased velocity in return for resource allocated to refactoring) carries little weight. I'm interested to hear from anyone who has had experience, positive or negative, in relation to the above. ----------------- EDIT ---------------- Thanks for the responses so far, all of which I think are good. What I want to develop is a metric that proves (or disproves!) all of these statements. A report that ties velocity to refactoring and shows a positive effect.

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• How does one handle an incorrect resource file?

  - by AedonEtLIRA

  I'm starting the parser that will handle one of the key features of my app and realizing exactly who easy it would be for me to screw up a resource file that is provided to the application. For example, a simple resource that I provide to my app is a JSON file that contains an entity layout (name, fascia, location etc...). It would be easy for me to leave out the name of the entity or misspell the JSON key. Obviously catastrophic failures during parsing are to be handled in a try/catch, but how would subtle failures (such as a dyslexic spelling of name) be handled?

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• Do certain corporations hold more weight on a resume?

  - by Ryan

  Would a developer/tester position at Google, Apple, Microsoft, etc. (any large tech. company of which most people have heard) be more valuable on a resume than working as a developer/tester somewhere where tech. isn't the main objective (shipping company, restaurant chain, insurance company, etc.)? Let's say you have two offers, and you only plan to stay with whichever company for 5 years, before trying to get a better position at a different company. One at Google that has a starting salary of $60,000, and one at some insurance company that has a starting salary of $80,000. I guess what I'm trying to say is... with university's, if someone graduates from MIT or Carnegie Mellon, they can pretty much get a job anywhere. Does someone seem more valuable after having worked at a company like Google, Apple, Microsoft, etc.? In other words, would taking the lower paying job be better in the long run since it's at Google, or would it be better to take the higher paying job at the insurance company?

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• How is this number calculated?

  - by Hamid

  I have numbers; A == 0x20000000 B == 18 C == (B/10) D == 0x20000004 == (A + C) A and D are in hex, but I'm not sure what the assumed numeric bases of the others are (although I'd assume base 10 since they don't explicitly state a base. It may or may not be relevant but I'm dealing with memory addresses, A and D are pointers. The part I'm failing to understand is how 18/10 gives me 0x4. Edit: Code for clarity: *address1 (pointer is to address: 0x20000000) printf("Test1: %p\n", address1); printf("Test2: %p\n", address1+(18/10)); printf("Test3: %p\n", address1+(21/10)); Output: Test1: 0x20000000 Test2: 0x20000004 Test3: 0x20000008

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• Gödel, Escher, Bach - Gödel's string

  - by Brad Urani

  In the book Gödel, Escher, Bach: An Eternal Golden Braid by Douglas Hofstadter, the author gives us a representation of the precursor to Gödel's string (Gödel's string's uncle) as: ~Ea,a': (I don't have the book in front of me but I think that's right). All that remains to get Gödel's string is to plug the Gödel number for this string into the free variable a''. What I don't understand is how to get the Gödel number for the functions PROOF-PAIR and ARITHMOQUINE. I understand how to write these functions in a programming language like FlooP (from the book) and could even write them myself in C# or Java, but the scheme that Hofstadter defines for Gödel numbering only applies to TNT (which is just his own syntax for natural number theory) and I don't see any way to write a procedure in TNT since it doesn't have any loops, variable assignments etc. Am I missing the point? Perhaps Gödel's string is not something that can actually be printed, but rather a theoretical string that need not actually be defined? I thought it would be neat to write a computer program that actually prints Gödel's string, or Gödel's string encoded by Gödel numbering (yes, I realize it would have a gazillion digits) but it seems like doing so requires some kind of procedural language and a Gödel numbering system for that procedural language that isn't included in the book. Of course once you had that, you could write a program that plugs random numbers into variable "a" and run procedure PROOF-PAIR on it to test for theoromhood of Gödel's string. If you let it run for a trillion years you might find a derivation that proves Gödel's string.

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• On a queue, which end is the "head"?

  - by Aidan Cully

  I had always thought that the "head" of a queue as the next element to be read, and never really questioned that usage. So a linked-list library I wrote, which is used for maintaining queues, codified that terminology: we have a list1_head macro that retrieves the first element; when using this library in a queue, this will be the first element to be removed. But a new developer on the team was used to having queues implemented the other way around. He described a queue as behaving like a dog: you insert at the head, and remove at the tail. This is a clever enough description that I feel like his usage must be more widespread, and I don't have a similarly evocative description of my preferred usage. So, I guess, there are two related questions: 1, what does the "head" of a queue mean to you? and 2, why do we use the word "head" to describe that concept?

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• How to deal with social login

  - by Matteo Pagliazzi

  In my new web app I'm going to allow social login through Twitter (maybe), Facebook and Google and I'm in search of the best way to do it. Actually I'm using Rails with Devise + Omniauth and this is the problem: Should I ask the user to choose a password so that he can login without a social network? Or maybe the user should be able to set a password if he want (for example when editing his account?) The second way seems the best one but since Twitter doesn't provide user email and google doesn't provide an username I'll probably have to ask the user for username/email when he log in so in that case I may also ask for the password... waht do you think?

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• Exclusive use of a Jini server during long-running call

  - by Matthew Flint

  I'm trying to use Jini, in a "Masters/Workers" arrangement, but the Worker jobs may be long running. In addition, each worker needs to have exclusive access to a singleton resource on that machine. As it stands, if a Worker receives another request while a previous request is running, then the new request is accepted and executed in a second thread. Are there any best-practices to ensure that a Worker accepts no further jobs until the current job is complete? Things I've considered: synchronize the job on the server, with a lock on the singleton resource. This would work, but is far from ideal. A call from a Master would block until the current Worker thread completes, even if other Workers become free in the meantime unregister the Worker from the registry while the job is running, then re-register when it completes. Might work OK, but something doesn't smell right with this idea... Of course, I'm quite happy to be told that there are more appropriate technologies than Jini... but I wouldn't want anything too heavyweight, like rolling out EJB containers all over the place.

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• Good library for search text tokenization

  - by Chris Dutrow

  Looking to tokenize some text in the same or similar way in which a search engine would do it. The reason we are doing this is so that we can run some statistical analysis on the tokens. The language we are using is python, so would prefer a library in that language, but could probably set something up to use another language if necessary. Example Original token: We have some great burritos! More simplified: (remove plurals and punctuation) We have some great burrito Even more simplified: (remove superfluous words) great burrito Best: (recognize positive and negative meaning): burrito -positive-

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• Web framework able to handle many concurrent users [closed]

  - by Jonas

  Social networking sites needs to handle many concurrent users e.g. for chat functionality. What web frameworks scales well and are able to handle more than 10.000 concurrent users connected with Comet or WebSockets. The server is a Linux VPS with limited memory, e.g. 1GB-8GB. I have been looking for some Java frameworks but they consume much memory per connection. So I'm looking for other alternatives too. Are there any good frameworks that are able to handle more than 10.000 concurrent users with limited memory resources?

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• What are the arguments against parsing the Cthulhu way?

  - by smarmy53

  I have been assigned the task of implementing a Domain Specific Language for a tool that may become quite important for the company. The language is simple but not trivial, it already allows nested loops, string concatenation, etc. and it is practically sure that other constructs will be added as the project advances. I know by experience that writing a lexer/parser by hand -unless the grammar is trivial- is a time consuming and error prone process. So I was left with two options: a parser generator à la yacc or a combinator library like Parsec. The former was good as well but I picked the latter for various reasons, and implemented the solution in a functional language. The result is pretty spectacular to my eyes, the code is very concise, elegant and readable/fluent. I concede it may look a bit weird if you never programmed in anything other than java/c#, but then this would be true of anything not written in java/c#. At some point however, I've been literally attacked by a co-worker. After a quick glance at my screen he declared that the code is uncomprehensible and that I should not reinvent parsing but just use a stack and String.Split like everybody does. He made a lot of noise, and I could not convince him, partially because I've been taken by surprise and had no clear explanation, partially because his opinion was immutable (no pun intended). I even offered to explain him the language, but to no avail. I'm positive the discussion is going to re-surface in front of management, so I'm preparing some solid arguments. These are the first few reasons that come to my mind to avoid a String.Split-based solution: you need lot of ifs to handle special cases and things quickly spiral out of control lots of hardcoded array indexes makes maintenance painful extremely difficult to handle things like a function call as a method argument (ex. add( (add a, b), c) very difficult to provide meaningful error messages in case of syntax errors (very likely to happen) I'm all for simplicity, clarity and avoiding unnecessary smart-cryptic stuff, but I also believe it's a mistake to dumb down every part of the codebase so that even a burger flipper can understand it. It's the same argument I hear for not using interfaces, not adopting separation of concerns, copying-pasting code around, etc. A minimum of technical competence and willingness to learn is required to work on a software project after all. (I won't use this argument as it will probably sound offensive, and starting a war is not going to help anybody) What are your favorite arguments against parsing the Cthulhu way?* *of course if you can convince me he's right I'll be perfectly happy as well

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• Need help in using hadoop in a Spring-Hibernate-JPA based web application [closed]

  - by John Varghese

  Possible Duplicate: Need help in using hadoop framework in a Spring-Hibernate-JPA based web application We are developing a Spring-Hibernate-JPA based web application which uses MySql as the database for storage and retrieval. We need to store and compute huge amounts of data, for that we need to use hadoop framework. How hadoop framework can be used in our web application to store and compute huge amounts of data?

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• Is an 'if password == XXXXXXX' enough for minimum security?

  - by Morgan Herlocker

  If I create a login for an app that has middle to low security risk (in other words, its not a banking app or anything), is it acceptable for me to verify a password entered by the user by just saying something like: if(enteredPassword == verifiedPassword) SendToRestrictedArea(); else DisplayPasswordUnknownMessage(); It seems to easy to be effective, but I certainly would not mind if that was all that was required. Is a simple check on username/password combo enough? Update: The particular project happens to be a web service, the verification is entirely server side, and it is not open-source. Does the domain change how you would deal with this?

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• What are basic programming directions? [closed]

  - by Goward Gerald

  What are basic programming directions? Can you please list them and give a brief review of each? Would be nice to have a list for each direction (web-development/*enterprise*/standalone/*mobile*/etc, correct me if I skipped something) like this: 1). Most popular languages of this direction (php for web, objective C for iOS mobile development etc) 2). It's demand on market (from 0 to 5, subjective) 3). How much tasks differ (do you always create same-of-a-kind programs which are like clones of each oother or projects change and you often get to create something interesting, new and fresh?) 4). Freelance demand (from 0 to 5) 5). Fun factor (from 0 to 5, totally subjective but still write it please) Thanks!

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• What php programmer should know?

  - by emchinee

  I've dig the database here and didn't found any answer for my question. What is a standard for a php programmer to know? I mean, literally, what group of language functions, mechanisms, variables should person know to consider oneself a (good) php programmer? (I know 'being good' is beyond language syntax, still I'm considering syntax of plain php only) To give an example what I mean: functions to control http sessions, cookies functions to control connection with databases functions to control file handling functions to control xml etc.. I omit phrases like 'security' or 'patterns' or 'framework' intentionally as it applies to every programming language. Hope I made myself clear, any input appreciated :) Note: Michael J.V. is right claiming that databases are independent from language, so to put my question more precisely and emphasise differences: Practises or security, are some ideas to implement (there is no 'Pattern' object with 'Decorator()' method, is there?) while using databases means knowing a mysqli and a set of its methods.

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• Is there any site which tells or highlights by zone developer income source? I think i am getting less yearly [closed]

  - by YumYumYum

  http://www.itjobswatch.co.uk/ Thats the only one good site i have found, but missing for Belgium and for other European countries. I was searching a site which can tell the income source details for European developer (specially for Belgium). But mostly not a single website exist who tells the true. My situation: As a programmer myself in one company i use all my knowledge, 20++ hours a day (office , home, office, home) because every-time its challenge/complex/stress/over-time feature-requests, at the end of the year in Europe i was getting in total not even the lowest amount shown here (UK pound vs Euro + high-tech most of the time they use + speed in development): http://www.itjobswatch.co.uk/ In one company i have to use my best performance knowledge for whole year with: C, Java, PHP (Zend Framework, Cakephp), BASH, MySQL/DB2, Linux/Unix, Javascript, Dojo, JQuery, Css, Html, Xml. Company wants to pay lesser but always it has to be perfect and it has to be solid gold and diamond like quality. And the total amount in Europe is not sufficient for me if i compare with other countries and living cost in Europe including taxes. Is there any developers/community site where we can see by country, zone what is minimum to maximum income source getting offered to the developers? So that some developers who is in troubles, they can shout and speak up louder with those references?

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• I need advice on laptop purchase for university [closed]

  - by Systemic33

  I'm currently in University studying Computer Science/IT/Information Technology. And this first year i've managed to do with the laptop I had; an ASUS Eee PC 1000H with a 10.1" screen. But this is getting way too underpowered and small for programming more than just quick programming introduction excercises. So I'm looking to buy a more suitable laptop. It's not supposed to be a desktop replacement though, since I've got a pretty good desktop already with a 24" monitor. So the kinda laptop I want to buy is one suited for university. If this bears any significance, I'm working in Java atm, but I will likely work with lots of other things incl. web development. I'm looking to spend about $1700 plus/minus. And it should be powerful/big enough for working on programming projects as well as the usual university stuff like MATLAB, Maple, etc out "in the field", and sometimes for maybe a week when visiting my parents. What I'm looking at right now is the ASUS Zenbook UX31A with the 1920 x 1080 resolution on 13.3" IPS display. But I'm kinda nervous that this will be too petite for programming. In essence i'm looking for a powerfull computer, that has good enough battery, and looks good. I would love suggestions or any type of feedback, either with maybe a better choice, or input on how its like programming on 13" laptops. Very much thanks in advance for anyone who even went through all that! PS. I don't want a mac, or my inner karma would commit Seppuku xD But experiences from working on the 13" Macbook Air would kinda be equivalent to the Zenbook i'm considering, so I would love to hear that. tl;dr The quick brown fox jumps over the lazy dog ;)

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• Using an actor model versus a producer-consumer model?

  - by hewhocutsdown

  I'm doing some early-stage research towards architecting a new software application. Concurrency and multithreading will likely play a significant part, so I've been reading up on the various topics. The producer-consumer model, at least how it is expressed in Java, has some surface similarities but appears to be deeply dissimilar to the actor model in use with languages such as Erlang and Scala. I'm having trouble finding any good comparative data, or specific reasons to use or avoid the one or the other. Is the actor model even possible with Java or C#, or do you have do use one of the languages built for the purpose? Is there a third way?

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• Pirate Problem In Interview Question

  - by Hafiz

  Some one asked me this question in an interview, so I want to know that what can be technical or algorithmic or strategical solution can we provide? If I am a leader of Pirates who looted 100kg gold, now every pirate has 1 bullet in gun and every pirate wants to get each other's share. They are 5 in number including me. So what strategy I will use to get to kill others while being safe or is there way to decrease probability?

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