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  • Advice on improving programming skills, learning capabilities?

    - by anonymous-coward1234
    Hi all, After 2,5 years of professional Java programing, I still have problems that make my job difficult and, more importantly - more times that I would like to admit - not enjoyable. I would like to ask for advice by more experienced people on ways that would help me overcome them. These are the problems I have: I do not absorb new knowledge easily. Even when I understand something, after a couple of days I easily forget even basic stuff. Other co-workers, even with the same working experience, when reading new technologies put things easily into "context", and are able to compare in "real time| similar technologies they already have used. I always try to address all the issues to whatever I am doing at one go, which results in me trying to resolve too many problems at the same time, losing completely control. I find it difficult to make my mind on a single problem that I should address first, and even when I do, and find myself throwing away code that I wrote because I started addressing the wrong issue first. As far as architecture and data modeling is concerned, I have difficulty making decisions on what objects must be created, with what hierarchy, interfaces, abstraction etc. I imagine that - to a certain degree - these things come with experience. But after 2,5 years of Java programming, I would expect myself to have come much farther that I have come, both in terms of absorption and experience. Is there a way to improve my learning speed? Any books, methods, advice is welcome.

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  • Handling incremental Data Modeling Changes in Functional Programming

    - by Adam Gent
    Most of the problems I have to solve in my job as a developer have to do with data modeling. For example in a OOP Web Application world I often have to change the data properties that are in a object to meet new requirements. If I'm lucky I don't even need to programmatically add new "behavior" code (functions,methods). Instead I can declarative add validation and even UI options by annotating the property (Java). In Functional Programming it seems that adding new data properties requires lots of code changes because of pattern matching and data constructors (Haskell, ML). How do I minimize this problem? This seems to be a recognized problem as Xavier Leroy states nicely on page 24 of "Objects and Classes vs. Modules" - To summarize for those that don't have a PostScript viewer it basically says FP languages are better than OOP languages for adding new behavior over data objects but OOP languages are better for adding new data objects/properties. Are there any design pattern used in FP languages to help mitigate this problem? I have read Phillip Wadler's recommendation of using Monads to help this modularity problem but I'm not sure I understand how?

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  • Which linear programming package should I use for high numbers of constraints and "warm starts"

    - by davidsd
    I have a "continuous" linear programming problem that involves maximizing a linear function over a curved convex space. In typical LP problems, the convex space is a polytope, but in this case the convex space is piecewise curved -- that is, it has faces, edges, and vertices, but the edges aren't straight and the faces aren't flat. Instead of being specified by a finite number of linear inequalities, I have a continuously infinite number. I'm currently dealing with this by approximating the surface by a polytope, which means discretizing the continuously infinite constraints into a very large finite number of constraints. I'm also in the situation where I'd like to know how the answer changes under small perturbations to the underlying problem. Thus, I'd like to be able to supply an initial condition to the solver based on a nearby solution. I believe this capability is called a "warm start." Can someone help me distinguish between the various LP packages out there? I'm not so concerned with user-friendliness as speed (for large numbers of constraints), high-precision arithmetic, and warm starts. Thanks!

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  • Database Functional Programming in Clojure

    - by Ralph
    "It is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail." - Abraham Maslow I need to write a tool to dump a large hierarchical (SQL) database to XML. The hierarchy consists of a Person table with subsidiary Address, Phone, etc. tables. I have to dump thousands of rows, so I would like to do so incrementally and not keep the whole XML file in memory. I would like to isolate non-pure function code to a small portion of the application. I am thinking that this might be a good opportunity to explore FP and concurrency in Clojure. I can also show the benefits of immutable data and multi-core utilization to my skeptical co-workers. I'm not sure how the overall architecture of the application should be. I am thinking that I can use an impure function to retrieve the database rows and return a lazy sequence that can then be processed by a pure function that returns an XML fragment. For each Person row, I can create a Future and have several processed in parallel (the output order does not matter). As each Person is processed, the task will retrieve the appropriate rows from the Address, Phone, etc. tables and generate the nested XML. I can use a a generic function to process most of the tables, relying on database meta-data to get the column information, with special functions for the few tables that need custom processing. These functions could be listed in a map(table name -> function). Am I going about this in the right way? I can easily fall back to doing it in OO using Java, but that would be no fun. BTW, are there any good books on FP patterns or architecture? I have several good books on Clojure, Scala, and F#, but although each covers the language well, none look at the "big picture" of function programming design.

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  • Are functional programming languages good for practical tasks?

    - by Clueless
    It seems to me from my experimenting with Haskell, Erlang and Scheme that functional programming languages are a fantastic way to answer scientific questions. For example, taking a small set of data and performing some extensive analysis on it to return a significant answer. It's great for working through some tough Project Euler questions or trying out the Google Code Jam in an original way. At the same time it seems that by their very nature, they are more suited to finding analytical solutions than actually performing practical tasks. I noticed this most strongly in Haskell, where everything is evaluated lazily and your whole program boils down to one giant analytical solution for some given data that you either hard-code into the program or tack on messily through Haskell's limited IO capabilities. Basically, the tasks I would call 'practical' such as Aceept a request, find and process requested data, and return it formatted as needed seem to translate much more directly into procedural languages. The most luck I have had finding a functional language that works like this is Factor, which I would liken to a reverse-polish-notation version of Python. So I am just curious whether I have missed something in these languages or I am just way off the ball in how I ask this question. Does anyone have examples of functional languages that are great at performing practical tasks or practical tasks that are best performed by functional languages?

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  • Programming style question on how to code functions

    - by shawnjan
    Hey all! So, I was just coding a bit today, and I realized that I don't have much consistency when it comes to a coding style when programming functions. One of my main concerns is whether or not its proper to code it so that you check that the input of the user is valid OUTSIDE of the function, or just throw the values passed by the user into the function and check if the values are valid in there. Let me sketch an example: I have a function that lists hosts based on an environment, and I want to be able to split the environment into chunks of hosts. So an example of the usage is this: listhosts -e testenv -s 2 1 This will get all the hosts from the "testenv", split it up into two parts, and it is displaying part one. In my code, I have a function that you pass it in a list, and it returns a list of lists based on you parameters for splitting. BUT, before I pass it a list, I first verify the parameters in my MAIN during the getops process, so in the main I check to make sure there are no negatives passed by the user, I make sure the user didnt request to split into say, 4 parts, but asking to display part 5 (which would not be valid), etc. tl;dr: Would you check the validity of a users input the flow of you're MAIN class, or would you do a check in your function itself, and either return a valid response in the case of valid input, or return NULL in the case of invalid input? Obviously both methods work, I'm just interested to hear from experts as to which approach is better :) Thanks for any comments and suggestions you guys have!

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  • Flowcharting functional programming languages

    - by Sadface
    Flowcharting. This ancient old practice that's been in use for over 1000 years now, being forced upon us poor students, without any usefulness (or so do I think). It might work well with imperative, sequentially running languages, but what about my beloved functional programming? Sadly, I'm forced to create a flow chart for my programm (that is written in Haskell). I imagine it being easy for something like this: main :: IO () main = do someInput <- getLine let upped = map toUpper someInput putStrLn upped Which is just 3 sequenced steps, fetching data, uppercasing it, outputting it. Things look worse this time: main :: IO () main = do someInput <- fmap toUpper getLine putStrLn someInput Or like this: main :: IO () main = interact (map toUpper) Okay, that was IO, you can handle that like an imperative language. What about pure functions? An actual example: onlyMatching :: String -> [FilePath] -> [FilePath] onlyMatching ext = filter f where f name = lower ('.' : ext) == (lower . takeExtension $ name) lower = map toLower How would you flowchart that last one?

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  • Dynamic programming Approach- Knapsack Puzzle

    - by idalsin
    I'm trying to solve the Knapsack problem with the dynamical programming(DP) approach, with Python 3.x. My TA pointed us towards this code for a head start. I've tried to implement it, as below: def take_input(infile): f_open = open(infile, 'r') lines = [] for line in f_open: lines.append(line.strip()) f_open.close() return lines def create_list(jewel_lines): #turns the jewels into a list of lists jewels_list = [] for x in jewel_lines: weight = x.split()[0] value = x.split()[1] jewels_list.append((int(value), int(weight))) jewels_list = sorted(jewels_list, key = lambda x : (-x[0], x[1])) return jewels_list def dynamic_grab(items, max_weight): table = [[0 for weight in range(max_weight+1)] for j in range(len(items)+1)] for j in range(1,len(items)+1): val= items[j-1][0] wt= items[j-1][1] for weight in range(1, max_weight+1): if wt > weight: table[j][weight] = table[j-1][weight] else: table[j][weight] = max(table[j-1][weight],table[j-1][weight-wt] + val) result = [] weight = max_weight for j in range(len(items),0,-1): was_added = table[j][weight] != table[j-1][weight] if was_added: val = items[j-1][0] wt = items[j-1][1] result.append(items[j-1]) weight -= wt return result def totalvalue(comb): #total of a combo of items totwt = totval = 0 for val, wt in comb: totwt += wt totval += val return (totval, -totwt) if totwt <= max_weight else (0,0) #required setup of variables infile = "JT_test1.txt" given_input = take_input(infile) max_weight = int(given_input[0]) given_input.pop(0) jewels_list = create_list(given_input) #test lines print(jewels_list) print(greedy_grab(jewels_list, max_weight)) bagged = dynamic_grab(jewels_list, max_weight) print(totalvalue(bagged)) The sample case is below. It is in the format line[0] = bag_max, line[1:] is in form(weight, value): 575 125 3000 50 100 500 6000 25 30 I'm confused as to the logic of this code in that it returns me a tuple and I'm not sure what the output tuple represents. I've been looking at this for a while and just don't understand what the code is pointing me at. Any help would be appreciated.

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  • What is the best way to manage unix process from java?

    - by erotsppa
    I'm looking for some simple tasks like listing all the running process of a user, or kill a particular process by pid etc. Basic unix process management from Java. Is there a library out there that is relatively mature and documented? I could run a external command from the JVM and then parse the standard output/error but that seems like a lot of work and not robust at all. Any suggestions?

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  • Is there a way to close a Unix socket for only reading or writing?

    - by Sii
    Is there a way to only close "one end" of a TCP socket to cleanly indicate one side of a connection is done writing to the connection? (Just like you do with a pipe in every Unix pipe tutorial ever.) Or should I use some in-band solution like a sentinel value or some such? I only found shutdown() in the libc documentation and that doesn't seem like it does what I want.

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  • MySQL - Combine two fields to create a unix timestamp?

    - by Dan
    Hi, I'm trying to retrieve a UNIX timestamp from a query by combining a date and a time field in the table, however it keeps returning as zero. SELECT *, UNIX_TIMESTAMP(startdate starttime) AS start, UNIX_TIMESTAMP(enddate endtime) AS end FROM mytable; Can anyone help me out? Thanks.

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  • How can I extract a range of lines from a text file on unix?

    - by Adam J. Forster
    I have a ~23000 line sql dump containing several databases worth of data. I need to extract a certain section of this file (i.e. the data for a single database) and place it in a new file. I know both the start and end line numbers of the data that I want. Does anyone know a unix command (or series of commands) to extract all lines from a file between say line 16224 and 16482 and then redirect them into a new file?

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  • Why can't we have a single programming Language ? [closed]

    - by Kiran
    I am no expert in Programming Languages. But whenever I change the project, I am faced with Herculean challenge of learning the new programming language which takes weeks to master if not months.. With the previous experience of programming in different languages, I believe it takes few months of continuous programming to understand the amazing features the prog.language has to offer and to exploit. It makes me wonder, why cannot we have a single programming language which boasts all the amazing features from the existing programming language and make it mandatory for all the programmers to learn it.

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  • Is the Unix Philosophy still relevant in the Web 2.0 world?

    - by David Titarenco
    Introduction Hello, let me give you some background before I begin. I started programming when I was 5 or 6 on my dad's PSION II (some primitive BASIC-like language), then I learned more and more, eventually inching my way up to C, C++, Java, PHP, JS, etc. I think I'm a pretty decent coder. I think most people would agree. I'm not a complete social recluse, but I do stuff like write a virtual machine for fun. I've never taken a computer course in college because I've been in and out for the past couple of years and have only been taking core classes; never having been particularly amazing at school, perhaps I'm missing some basic tenet that most learn in CS101. I'm currently reading Coders at Work and this question is based on some ideas I read in there. A Brief (Fictionalized) Example So a certain sunny day I get an idea. I hire a designer and hammer away at some C/C++ code for a couple of months, soon thereafter releasing silvr.com, a website that transmutes lead into silver. Yep, I started my very own start-up and even gave it a clever web 2.0 name with a vowel missing. Mom and dad are proud. I come up with some numbers I should be seeing after 1, 2, 3, 6, 9, 12 months and set sail. Obviously, my transmuting server isn't perfect, sometimes it segfaults, sometimes it leaks memory. I fix it and keep truckin'. After all, gdb is my best friend. Eventually, I'm at a position where a very small community of people are happily transmuting lead into silver on a semi-regular basis, but they want to let their friends on MySpace know how many grams of lead they transmuted today. And they want to post images of their lead and silver nuggets on flickr. I'm losing out on potential traffic unless I let them log in with their Yahoo, Google, and Facebook accounts. They want webcam support and live cock fighting, merry-go-rounds and Jabberwockies. All these things seem necessary. The Aftermath Of course, I have to re-write the transmuting server! After all, I've been losing money all these months. I need OAuth libraries and OpenID libraries, JSON support, and the only stable Jabberwocky API is for Java. C++ isn't even an option anymore. I'm just one guy! The Java binary just grows and grows since I need some legacy Apache include for the JSON library, and some antiquated Sun dependency for OAuth support. Then I pick up a book like Coders at Work and read what people like jwz say about complexity... I think to myself.. Keep it simple, stupid. I like simple things. I've always loved the Unix Philosophy but even after trying to keep the new server source modular and sleek, I loathe having to write one more line of code. It feels that I'm just piling crap on top of other crap. Maybe I'm naive thinking every piece of software can be simple and clever. Maybe it's just a phase.. or is the Unix Philosophy basically dead when it comes to the current state of (web) development? I'm just kind of disheartened :(

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  • Book Review: Programming Windows Identity Foundation

    - by DigiMortal
    Programming Windows Identity Foundation by Vittorio Bertocci is right now the only serious book about Windows Identity Foundation available. I started using Windows Identity Foundation when I made my first experiments on Windows Azure AppFabric Access Control Service. I wanted to generalize the way how people authenticate theirselves to my systems and AppFabric ACS seemed to me like good point where to start. My first steps trying to get things work opened the door to whole new authentication world for me. As I went through different blog postings and articles to get more information I discovered that the thing I am trying to use is the one I am looking for. As best security API for .NET was found I wanted to know more about it and this is how I found Programming Windows Identity Foundation. What’s inside? Programming WIF focuses on architecture, design and implementation of WIF. I think Vittorio is very good at teaching people because you find no too complex topics from the book. You learn more and more as you read and as a good thing you will find that you can also try out your new knowledge on WIF immediately. After giving good overview about WIF author moves on and introduces how to use WIF in ASP.NET applications. You will get complete picture how WIF integrates to ASP.NET request processing pipeline and how you can control the process by yourself. There are two chapters about ASP.NET. First one is more like introduction and the second one goes deeper and deeper until you have very good idea about how to use ASP.NET and WIF together, what issues you may face and how you can configure and extend WIF. Other two chapters cover using WIF with Windows Communication Foundation (WCF) band   Windows Azure. WCF chapter expects that you know WCF very well. This is not introductory chapter for beginners, this is heavy reading if you are not familiar with WCF. The chapter about Windows Azure describes how to use WIF in cloud applications. Last chapter talks about some future developments of WIF and describer some problems and their solutions. Most interesting part of this chapter is section about Silverlight. Who should read this book? Programming WIF is targeted to developers. It does not matter if you are beginner or old bullet-proof professional – every developer should be able to be read this book with no difficulties. I don’t recommend this book to administrators and project managers because they find almost nothing that is related to their work. I strongly recommend this book to all developers who are interested in modern authentication methods on Microsoft platform. The book is written so well that I almost forgot all things around me when I was reading the book. All additional tools you need are free. There is also Azure AppFabric ACS test version available and you can try it out for free. Table of contents Foreword Acknowledgments Introduction Part I Windows Identity Foundation for Everybody 1 Claims-Based Identity 2 Core ASP.NET Programming Part II Windows Identity Foundation for Identity Developers 3 WIF Processing Pipeline in ASP.NET 4 Advanced ASP.NET Programming 5 WIF and WCF 6 WIF and Windows Azure 7 The Road Ahead Index

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  • Error when reloading supervisord: unix:///tmp/supervisor.sock no such file

    - by Yarin
    I'm running supervisord on my CentOS 6 box like so, /usr/bin/supervisord -c /etc/supervisord.conf and when I launch supervisorctl all process status are fine, but if I try to reload using supervisorctl I get unix:///tmp/supervisor.sock no such file I'm using the same config file I've used successfully on other boxes, and im running everything as root. I can't undesrtand what the problem is... Config file: ; Sample supervisor config file. [unix_http_server] file=/tmp/supervisor.sock ; (the path to the socket file) ;chmod=0700 ; socket file mode (default 0700) ;chown=nobody:nogroup ; socket file uid:gid owner ;username=user ; (default is no username (open server)) ;password=123 ; (default is no password (open server)) ;[inet_http_server] ; inet (TCP) server disabled by default ;port=127.0.0.1:9001 ; (ip_address:port specifier, *:port for all iface) ;username=user ; (default is no username (open server)) ;password=123 ; (default is no password (open server)) [supervisord] logfile=/tmp/supervisord.log ; (main log file;default $CWD/supervisord.log) logfile_maxbytes=50MB ; (max main logfile bytes b4 rotation;default 50MB) logfile_backups=10 ; (num of main logfile rotation backups;default 10) loglevel=info ; (log level;default info; others: debug,warn,trace) pidfile=/tmp/supervisord.pid ; (supervisord pidfile;default supervisord.pid) nodaemon=false ; (start in foreground if true;default false) minfds=1024 ; (min. avail startup file descriptors;default 1024) minprocs=200 ; (min. avail process descriptors;default 200) ;umask=022 ; (process file creation umask;default 022) ;user=chrism ; (default is current user, required if root) ;identifier=supervisor ; (supervisord identifier, default is 'supervisor') ;directory=/tmp ; (default is not to cd during start) ;nocleanup=true ; (don't clean up tempfiles at start;default false) ;childlogdir=/tmp ; ('AUTO' child log dir, default $TEMP) ;environment=KEY=value ; (key value pairs to add to environment) ;strip_ansi=false ; (strip ansi escape codes in logs; def. false) ; the below section must remain in the config file for RPC ; (supervisorctl/web interface) to work, additional interfaces may be ; added by defining them in separate rpcinterface: sections [rpcinterface:supervisor] supervisor.rpcinterface_factory = supervisor.rpcinterface:make_main_rpcinterface [supervisorctl] serverurl=unix:///tmp/supervisor.sock ; use a unix:// URL for a unix socket ;serverurl=http://127.0.0.1:9001 ; use an http:// url to specify an inet socket ;username=chris ; should be same as http_username if set ;password=123 ; should be same as http_password if set ;prompt=mysupervisor ; cmd line prompt (default "supervisor") ;history_file=~/.sc_history ; use readline history if available ; The below sample program section shows all possible program subsection values, ; create one or more 'real' program: sections to be able to control them under ; supervisor. ;[program:foo] ;command=/bin/cat [program:embed_scheduler] command=/opt/web-apps/mywebsite/custom_process.py process_name=%(program_name)s_%(process_num)d numprocs=3 ;[program:theprogramname] ;command=/bin/cat ; the program (relative uses PATH, can take args) ;process_name=%(program_name)s ; process_name expr (default %(program_name)s) ;numprocs=1 ; number of processes copies to start (def 1) ;directory=/tmp ; directory to cwd to before exec (def no cwd) ;umask=022 ; umask for process (default None) ;priority=999 ; the relative start priority (default 999) ;autostart=true ; start at supervisord start (default: true) ;autorestart=unexpected ; whether/when to restart (default: unexpected) ;startsecs=1 ; number of secs prog must stay running (def. 1) ;startretries=3 ; max # of serial start failures (default 3) ;exitcodes=0,2 ; 'expected' exit codes for process (default 0,2) ;stopsignal=QUIT ; signal used to kill process (default TERM) ;stopwaitsecs=10 ; max num secs to wait b4 SIGKILL (default 10) ;killasgroup=false ; SIGKILL the UNIX process group (def false) ;user=chrism ; setuid to this UNIX account to run the program ;redirect_stderr=true ; redirect proc stderr to stdout (default false) ;stdout_logfile=/a/path ; stdout log path, NONE for none; default AUTO ;stdout_logfile_maxbytes=1MB ; max # logfile bytes b4 rotation (default 50MB) ;stdout_logfile_backups=10 ; # of stdout logfile backups (default 10) ;stdout_capture_maxbytes=1MB ; number of bytes in 'capturemode' (default 0) ;stdout_events_enabled=false ; emit events on stdout writes (default false) ;stderr_logfile=/a/path ; stderr log path, NONE for none; default AUTO ;stderr_logfile_maxbytes=1MB ; max # logfile bytes b4 rotation (default 50MB) ;stderr_logfile_backups=10 ; # of stderr logfile backups (default 10) ;stderr_capture_maxbytes=1MB ; number of bytes in 'capturemode' (default 0) ;stderr_events_enabled=false ; emit events on stderr writes (default false) ;environment=A=1,B=2 ; process environment additions (def no adds) ;serverurl=AUTO ; override serverurl computation (childutils) ; The below sample eventlistener section shows all possible ; eventlistener subsection values, create one or more 'real' ; eventlistener: sections to be able to handle event notifications ; sent by supervisor. ;[eventlistener:theeventlistenername] ;command=/bin/eventlistener ; the program (relative uses PATH, can take args) ;process_name=%(program_name)s ; process_name expr (default %(program_name)s) ;numprocs=1 ; number of processes copies to start (def 1) ;events=EVENT ; event notif. types to subscribe to (req'd) ;buffer_size=10 ; event buffer queue size (default 10) ;directory=/tmp ; directory to cwd to before exec (def no cwd) ;umask=022 ; umask for process (default None) ;priority=-1 ; the relative start priority (default -1) ;autostart=true ; start at supervisord start (default: true) ;autorestart=unexpected ; whether/when to restart (default: unexpected) ;startsecs=1 ; number of secs prog must stay running (def. 1) ;startretries=3 ; max # of serial start failures (default 3) ;exitcodes=0,2 ; 'expected' exit codes for process (default 0,2) ;stopsignal=QUIT ; signal used to kill process (default TERM) ;stopwaitsecs=10 ; max num secs to wait b4 SIGKILL (default 10) ;killasgroup=false ; SIGKILL the UNIX process group (def false) ;user=chrism ; setuid to this UNIX account to run the program ;redirect_stderr=true ; redirect proc stderr to stdout (default false) ;stdout_logfile=/a/path ; stdout log path, NONE for none; default AUTO ;stdout_logfile_maxbytes=1MB ; max # logfile bytes b4 rotation (default 50MB) ;stdout_logfile_backups=10 ; # of stdout logfile backups (default 10) ;stdout_events_enabled=false ; emit events on stdout writes (default false) ;stderr_logfile=/a/path ; stderr log path, NONE for none; default AUTO ;stderr_logfile_maxbytes=1MB ; max # logfile bytes b4 rotation (default 50MB) ;stderr_logfile_backups ; # of stderr logfile backups (default 10) ;stderr_events_enabled=false ; emit events on stderr writes (default false) ;environment=A=1,B=2 ; process environment additions ;serverurl=AUTO ; override serverurl computation (childutils) ; The below sample group section shows all possible group values, ; create one or more 'real' group: sections to create "heterogeneous" ; process groups. ;[group:thegroupname] ;programs=progname1,progname2 ; each refers to 'x' in [program:x] definitions ;priority=999 ; the relative start priority (default 999) ; The [include] section can just contain the "files" setting. This ; setting can list multiple files (separated by whitespace or ; newlines). It can also contain wildcards. The filenames are ; interpreted as relative to this file. Included files *cannot* ; include files themselves. ;[include] ;files = relative/directory/*.ini

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