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  • Error using paho-mqtt in App Engine Python App

    - by calumb
    I am trying to right a Google Cloud Platform app in python with Flask that makes an MQTT connection. I have included the paho python library by doing pip install paho-mqtt -t libs/. However, when I try to run the app, even if I don't try to connect to MQTT. I get a weird error about IP address checking: RuntimeError: error('illegal IP address string passed to inet_pton',) It seems something in the remote_socket lib is causing a problem. Is this a security issue? Is there someway to disable it? Relevant code: from flask import Flask import paho.mqtt.client as mqtt import logging as logger app = Flask(__name__) # Note: We don't need to call run() since our application is embedded within # the App Engine WSGI application server. #callback to print out connection status def on_connect(mosq, obj, rc): logger.info('on_connect') if rc == 0: logger.info("Connected") mqttc.subscribe('test', 0) else: logger.info(rc) def on_message(mqttc, obj, msg): logger.info(msg.topic+" "+str(msg.qos)+" "+str(msg.payload)) mqttc = mqtt.Client("mqttpy") mqttc.on_message = on_message mqttc.on_connect = on_connect As well as full stack trace: ERROR 2014-06-03 15:14:57,285 wsgi.py:262] Traceback (most recent call last): File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/runtime/wsgi.py", line 239, in Handle handler = _config_handle.add_wsgi_middleware(self._LoadHandler()) File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/runtime/wsgi.py", line 298, in _LoadHandler handler, path, err = LoadObject(self._handler) File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/runtime/wsgi.py", line 84, in LoadObject obj = __import__(path[0]) File "/Users/cbarnes/code/ignite/tank-demo/appengine-flask-demo/main.py", line 24, in <module> mqttc = mqtt.Client("mqtthtpp") File "/Users/cbarnes/code/ignite/tank-demo/appengine-flask-demo/lib/paho/mqtt/client.py", line 403, in __init__ self._sockpairR, self._sockpairW = _socketpair_compat() File "/Users/cbarnes/code/ignite/tank-demo/appengine-flask-demo/lib/paho/mqtt/client.py", line 255, in _socketpair_compat listensock.bind(("localhost", 0)) File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/dist27/socket.py", line 222, in meth return getattr(self._sock,name)(*args) File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/api/remote_socket/_remote_socket.py", line 668, in bind self._SetProtoFromAddr(request.mutable_proxy_external_ip(), address) File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/api/remote_socket/_remote_socket.py", line 632, in _SetProtoFromAddr proto.set_packed_address(self._GetPackedAddr(address)) File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/api/remote_socket/_remote_socket.py", line 627, in _GetPackedAddr AI_NUMERICSERV|AI_PASSIVE): File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/api/remote_socket/_remote_socket.py", line 338, in getaddrinfo canonical=(flags & AI_CANONNAME)) File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/api/remote_socket/_remote_socket.py", line 211, in _Resolve canon, aliases, addresses = _ResolveName(name, families) File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/api/remote_socket/_remote_socket.py", line 229, in _ResolveName apiproxy_stub_map.MakeSyncCall('remote_socket', 'Resolve', request, reply) File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/api/apiproxy_stub_map.py", line 94, in MakeSyncCall return stubmap.MakeSyncCall(service, call, request, response) File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/api/apiproxy_stub_map.py", line 328, in MakeSyncCall rpc.CheckSuccess() File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/api/apiproxy_rpc.py", line 156, in _WaitImpl self.request, self.response) File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/ext/remote_api/remote_api_stub.py", line 200, in MakeSyncCall self._MakeRealSyncCall(service, call, request, response) File "/Users/cbarnes/google-cloud-sdk/platform/google_appengine/google/appengine/ext/remote_api/remote_api_stub.py", line 234, in _MakeRealSyncCall raise pickle.loads(response_pb.exception()) RuntimeError: error('illegal IP address string passed to inet_pton',) INFO 2014-06-03 15:14:57,291 module.py:639] default: "GET / HTTP/1.1" 500 - Thanks!

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  • Platform Builder: Cloning – the Linker is your Friend

    - by Bruce Eitman
    I was tasked this week with making a minor change to NetMsgBox() behavior. NetMsgBox() is a little function in NETUI that handles MessageBox() for the Network User Interface.  The obvious solution is to clone the entire NETUI directory from Public\Common\Oak\Drivers (see Platform Builder: Clone Public Code for more on cloning). If you haven’t already, take a minute to look in that folder. There are a lot of files in the folder, but I only needed to modify one function in one of those files. There must be a better way. Enter the linker. Instead of cloning the entire folder, here is what I did: Create a new folder in my Platform named NETUI (but the name isn’t important) Copy the C file that I needed to modify to the new folder, in this case netui.c Copy a makefile from one of the other folder (really they are all the same) Run Sysgen_capture Open a build window (see Platform Builder: Build Tools, Opening a Build Window) Change directories to the new folder Run “Sysgen_capture netui” Rename sources.netui to sources Add the C file to sources as SOURCES=netui.c Modify the code Build the code Done That is it, the functions from my new folder now replace the functions from the Public code and link with the rest to create NETUI.dll. There is a catches. If you remove any of the functions from the C file, linking will fail because the remaining functions will be found twice.   Copyright © 2010 – Bruce Eitman All Rights Reserved

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  • Call for authors for new eBook on the Windows Azure Platform

    - by Eric Nelson
    I intend to pull together a FREE eBook on the Windows Azure Platform – but I need your help to make it rock! If you have detailed experience of any aspect of the Windows Azure Platform and can spare a few hours of time to turn that into a short article (400 to 800 words) then please get in touch. This is not a big commitment but my suspicion is the end result will make for a cracking good read. I am hoping for a mix – everything from lessons learnt from early adopters to introductions to elements of the platform to getting technologies such as Ruby up and running on Azure. 10 to 20 articles sound about right – which means I am after 10 to 20 authors :) All I need from you right now is: One or two suggestions of topics you would like to cover A pointer to any example of your previous work – which could be as simple as a blog post or a work document. For simplicity, just drop me an email direct to eric.nelson A@T microsoft.com. BIG THANKS! Eric The provisional dates are: Confirm authors and topics by 3rd May Get first draft from all authors by 10th May Complete reviews by 17th May Final versions by 24th May Published by 31st May And finally, an example: To give you an idea of what I have in mind, check out the eBook we pulled together last December which has had several thousand downloads. However I’m thinking of making this one a little bit more fun/informal. More on that later. UK MSDN Flash eBook Best Technical Articles #2 - ericnel Related Links: Spread the word – 6 Weeks of FREE Azure Training UK Azure Online Community – join today. UK Windows Azure Site Start working with Windows Azure

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  • Jung Meets the NetBeans Platform

    - by Geertjan
    Here's a small Jung diagram in a NetBeans Platform application: And the code, copied directly from the Jung 2.0 Tutorial:  public final class JungTopComponent extends TopComponent { public JungTopComponent() { initComponents(); setName(Bundle.CTL_JungTopComponent()); setToolTipText(Bundle.HINT_JungTopComponent()); setLayout(new BorderLayout()); Graph sgv = getGraph(); Layout<Integer, String> layout = new CircleLayout(sgv); layout.setSize(new Dimension(300, 300)); BasicVisualizationServer<Integer, String> vv = new BasicVisualizationServer<Integer, String>(layout); vv.setPreferredSize(new Dimension(350, 350)); add(vv, BorderLayout.CENTER); } public Graph getGraph() { Graph<Integer, String> g = new SparseMultigraph<Integer, String>(); g.addVertex((Integer) 1); g.addVertex((Integer) 2); g.addVertex((Integer) 3); g.addEdge("Edge-A", 1, 2); g.addEdge("Edge-B", 2, 3); Graph<Integer, String> g2 = new SparseMultigraph<Integer, String>(); g2.addVertex((Integer) 1); g2.addVertex((Integer) 2); g2.addVertex((Integer) 3); g2.addEdge("Edge-A", 1, 3); g2.addEdge("Edge-B", 2, 3, EdgeType.DIRECTED); g2.addEdge("Edge-C", 3, 2, EdgeType.DIRECTED); g2.addEdge("Edge-P", 2, 3); return g; } And here's what someone who attended a NetBeans Platform training course in Poland has done with Jung and the NetBeans Platform: The source code for the above is on Git: git://gitorious.org/j2t/j2t.git

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  • Your Experience Platform

    - by David Dorf
    Crosstalk once again exceeded my expectations, improving upon last year's conference in terms of venue, knowledge sharing, and entertainment.  Its great to see the Oracle Retail family continues to grow, especially outside the US.  I had a great time talking to retailers, analysts, press, and colleagues from around the world. Because the economy, demographics, technology, etc. are constantly changing, retailers must always be evolving their business to capture the next market.  But it takes guts to change something that appears to be working, and it takes a bit of luck to get the timing right.  To a large extent, innovation is about "guts and luck." To help retailers innovate, Oracle Retail provides all the necessary software to create Your Experience Platform.  There is no "Oracle Experience Platform" as each retailer needs something different to deliver on their brand promise.  We provide the actionable insight, optimized operations, and connected interactions, but its still up to the retailer to make it theirs. One such retailer is Masters, a home improvement retailer in Australia formed through a partnership between Woolworths and Lowes.  Woolworths is an established retailer in Australia, so they are already close to their customers and able to understand their needs.  In Australia 74% of dwellings are detached houses and the population is continues to "move up" into bigger and bigger homes. Masters is using Oracle Retail's software to create their experience platform that will deliver on their brand promise, which includes everyday low prices, wide range of products, smarter self-service, and an inviting store environment.  The Oracle Retail software provides the foundation that allows them to rapidly deliver on this promise -- Masters is engineered for success.

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  • Gemalto Mobile Payment Platform on Oracle T4

    - by user938730
    Gemalto is the world leader in digital security, at the heart of our rapidly evolving digital society. Billions of people worldwide increasingly want the freedom to communicate, travel, shop, bank, entertain and work – anytime, everywhere – in ways that are convenient, enjoyable and secure. Gemalto delivers on their expanding needs for personal mobile services, payment security, identity protection, authenticated online services, cloud computing access, eHealthcare and eGovernment services, modern transportation solutions, and M2M communication. Gemalto’s solutions for Mobile Financial Services are deployed at over 70 customers worldwide, transforming the way people shop, pay and manage personal finance. In developing markets, Gemalto Mobile Money solutions are helping to remove the barriers to financial access for the unbanked and under-served, by turning any mobile device into a payment and banking instrument. In recent benchmarks by our Oracle ISVe Labs, the Gemalto Mobile Payment Platform demonstrated outstanding performance and scalability using the new T4-based Oracle Sun machines running Solaris 11. Using a clustered environment on a mid-range 2x2.85GHz T4-2 Server (16 cores total, 128GB memory) for the application tier, and an additional dedicated Intel-based (2x3.2GHz Intel-Xeon X4200) Oracle database server, the platform processed more than 1,000 transactions per second, limited only by database capacity --higher performance was easily achievable with a stronger database server. Near linear scalability was observed by increasing the number of application software components in the cluster. These results show an increase of nearly 300% in processing power and capacity on the new T4-based servers relative to the previous generation of Oracle Sun CMT servers, and for a comparable price. In the fast-evolving Mobile Payment market, it is crucial that the underlying technology seamlessly supports Service Providers as the customer-base ramps up, use cases evolve and new services are launched. These benchmark results demonstrate that the Gemalto Mobile Payment Platform is designed to meet the needs of any deployment scale, whether targeting 5 or 100 million subscribers. Oracle Solaris 11 DTrace technology helped to pinpoint performance issues and tune the system accordingly to achieve optimal computation resources utilization.

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  • Google+ Platform Office Hours for April 4th 2012: Open Q&A

    Google+ Platform Office Hours for April 4th 2012: Open Q&A We hold weekly Google+ Platform Office Hours using Hangouts On Air most Wednesdays from 11:30am until 12:15pm PST. This week we opened the session up to your questions about the Google+ platform. Here's a list of the topics we addressed: - 1:40 - HTTPS and hangout apps - 4:48 - The Google+ badge on Blogger - 6:51 - Warnings logged to the console by the +1 button - 7:57 - +1 button count discrepancies between the button, Google Analytics and Google Webmaster Tools - 11:04 - Using Google+ to identify users on an external website Our starter projects include this functionality. You can find them here: developers.google.com - 14:12 - When will the feature I want be released? - 16:05 - Redirecting your domain to your Google+ Page Jenny mentions a blog entry about redirecting to your Google+ profile: goo.gl - 17:30 - Pulling public Google+ activity from your Google+ Page into your website The starter projects also demonstrate this functionality: developers.google.com - 19:43 - Integrating the Google+ badge with Google Analytics tracking Oops! Jenny mentions callbacks. She was in error. The +1 button provides callbacks but the badge does not at this time. Sorry about that. Discuss this video on Google+: goo.gl Learn more about our Office Hours: developers.google.com From: GoogleDevelopers Views: 114 5 ratings Time: 21:28 More in Science & Technology

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  • Which platform to choose, Java or .NET?

    - by salman
    I am working in a private bank, a leading mid size bank in local market. We are going to create our core banking solution. Existing solution has been developed on Java using IBM Visual Age 4.0. It is very important to discuss architecture first, we have currently more than 350 branches working in standalone mode, and it means they are working in self contained environment. They have their own database server (IBM DB2 9.7) and they are communicating with other branches via sockets to send and receive data. Having experience of .NET for more than 5 years I am trying to convince my superiors to choose .NET platform, but they are reluctant and unwilling. It is my job to encourage them for choosing best available platform to create large scale enterprise application. In simple word, we are going to create a very large scale enterprise financial application, a centralize and integrated which connects all branch networks plus having scalable, solid architecture that easily evolve over time. I want professional people to comment on above scenarios. Which platform to choose .NET or Java? Our all resource is currently working in Java, we have homogeneous environment (no Linux, no Mac and no UNIX). Any idea, any thoughts, any points technical or non-technical i.e. administrative or management point of view will be really appreciated.

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  • Update 3 for "NetBeans Platform for Beginners"

    - by Geertjan
    The latest monthly update of NetBeans Platform for Beginners was released during the last few days. Without any question at all, this book is awesome. I love how it is a 'living book' and that on a monthly basis new updates are made available. In this particular update, as before, reader comments and questions have led to changes and enhancements in the book. In addition, there's now a tighter integration between the long list of samples on GitHub and the book, since wherever a sample relates to a text in the book, the book has a handy icon, so that you know when to hop over to GitHub to get a related sample. Do you have comments or questions about the book? That's what the feedback link is for: https://leanpub.com/nbp4beginners/feedback And there's also a free sample, just in case you'd like to get a feel for the book prior to buying it: http://samples.leanpub.com/nbp4beginners-sample.pdf If you're from a company where you're all sharing a single copy of the book, it would be great if you'd go back and support this great project (and hopefully encourage future books being written) by buying additional copies, ideally one for each developer. Let's show the authors that writing books on the NetBeans Platform is a really profitable thing to do (and I'm hoping they'll write one on Maven and the NetBeans Platform, as well)!

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  • Unit testing statically typed functional code

    - by back2dos
    I wanted to ask you people, in which cases it makes sense to unit test statically typed functional code, as written in haskell, scala, ocaml, nemerle, f# or haXe (the last is what I am really interested in, but I wanted to tap into the knowledge of the bigger communities). I ask this because from my understanding: One aspect of unit tests is to have the specs in runnable form. However when employing a declarative style, that directly maps the formalized specs to language semantics, is it even actually possible to express the specs in runnable form in a separate way, that adds value? The more obvious aspect of unit tests is to track down errors that cannot be revealed through static analysis. Given that type safe functional code is a good tool to code extremely close to what your static analyzer understands. However a simple mistake like using x instead of y (both being coordinates) in your code cannot be covered. However such a mistake could also arise while writing the test code, so I am not sure whether its worth the effort. Unit tests do introduce redundancy, which means that when requirements change, the code implementing them and the tests covering this code must both be changed. This overhead of course is about constant, so one could argue, that it doesn't really matter. In fact, in languages like Ruby it really doesn't compared to the benefits, but given how statically typed functional programming covers a lot of the ground unit tests are intended for, it feels like it's a constant overhead one can simply reduce without penalty. From this I'd deduce that unit tests are somewhat obsolete in this programming style. Of course such a claim can only lead to religious wars, so let me boil this down to a simple question: When you use such a programming style, to which extents do you use unit tests and why (what quality is it you hope to gain for your code)? Or the other way round: do you have criteria by which you can qualify a unit of statically typed functional code as covered by the static analyzer and hence needs no unit test coverage?

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  • Functional programming and stateful algorithms

    - by bigstones
    I'm learning functional programming with Haskell. In the meantime I'm studying Automata theory and as the two seem to fit well together I'm writing a small library to play with automata. Here's the problem that made me ask the question. While studying a way to evaluate a state's reachability I got the idea that a simple recursive algorithm would be quite inefficient, because some paths might share some states and I might end up evaluating them more than once. For example, here, evaluating reachability of g from a, I'd have to exclude f both while checking the path through d and c: So my idea is that an algorithm working in parallel on many paths and updating a shared record of excluded states might be great, but that's too much for me. I've seen that in some simple recursion cases one can pass state as an argument, and that's what I have to do here, because I pass forward the list of states I've gone through to avoid loops. But is there a way to pass that list also backwards, like returning it in a tuple together with the boolean result of my canReach function? (although this feels a bit forced) Besides the validity of my example case, what other techniques are available to solve this kind of problems? I feel like these must be common enough that there have to be solutions like what happens with fold* or map. So far, reading learnyouahaskell.com I didn't find any, but consider I haven't touched monads yet. (if interested, I posted my code on codereview)

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  • Is LINQ to objects a collection of combinators?

    - by Jimmy Hoffa
    I was just trying to explain the usefulness of combinators to a colleague and I told him LINQ to objects are like combinators as they exhibit the same value, the ability to combine small pieces to create a single large piece. Though I don't know that I can call LINQ to objects combinators. I've seen 2 levels of definition for combinator that I generalize as such: A combinator is a function which only uses things passed to it A combinator is a function which only uses things passed to it and other standard atomic functions but not state The first is very rigid and can be seen in the combinatory calculus systems and in haskell things like $ and . and various similar functions meet this rule. The second is less rigid and would allow something like sum as it uses the + function which was not passed in but is standard and not stateful. Though the LINQ extensions in C# use state in their iteration models, so I feel I can't say they're combinators. Can someone who understands the definition of a combinator more thoroughly and with more experience in these realms give a distinct ruling on this? Are my definitions of 'combinator' wrong to begin with?

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  • Performance of concurrent software on multicore processors

    - by Giorgio
    Recently I have often read that, since the trend is to build processors with multiple cores, it will be increasingly important to have programming languages that support concurrent programming in order to better exploit the parallelism offered by these processors. In this respect, certain programming paradigms or models are considered well-suited for writing robust concurrent software: Functional programming languages, e.g. Haskell, Scala, etc. The actor model: Erlang, but also available for Scala / Java (Akka), C++ (Theron, Casablanca, ...), and other programming languages. My questions: What is the state of the art regarding the development of concurrent applications (e.g. using multi-threading) using the above languages / models? Is this area still being explored or are there well-established practices already? Will it be more complex to program applications with a higher level of concurrency, or is it just a matter of learning new paradigms and practices? How does the performance of highly concurrent software compare to the performance of more traditional software when executed on multiple core processors? For example, has anyone implemented a desktop application using C++ / Theron, or Java / Akka? Was there a boost in performance on a multiple core processor due to higher parallelism?

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  • How do you encode Algebraic Data Types in a C#- or Java-like language?

    - by Jörg W Mittag
    There are some problems which are easily solved by Algebraic Data Types, for example a List type can be very succinctly expressed as: data ConsList a = Empty | ConsCell a (ConsList a) consmap f Empty = Empty consmap f (ConsCell a b) = ConsCell (f a) (consmap f b) l = ConsCell 1 (ConsCell 2 (ConsCell 3 Empty)) consmap (+1) l This particular example is in Haskell, but it would be similar in other languages with native support for Algebraic Data Types. It turns out that there is an obvious mapping to OO-style subtyping: the datatype becomes an abstract base class and every data constructor becomes a concrete subclass. Here's an example in Scala: sealed abstract class ConsList[+T] { def map[U](f: T => U): ConsList[U] } object Empty extends ConsList[Nothing] { override def map[U](f: Nothing => U) = this } final class ConsCell[T](first: T, rest: ConsList[T]) extends ConsList[T] { override def map[U](f: T => U) = new ConsCell(f(first), rest.map(f)) } val l = (new ConsCell(1, new ConsCell(2, new ConsCell(3, Empty))) l.map(1+) The only thing needed beyond naive subclassing is a way to seal classes, i.e. a way to make it impossible to add subclasses to a hierarchy. How would you approach this problem in a language like C# or Java? The two stumbling blocks I found when trying to use Algebraic Data Types in C# were: I couldn't figure out what the bottom type is called in C# (i.e. I couldn't figure out what to put into class Empty : ConsList< ??? >) I couldn't figure out a way to seal ConsList so that no subclasses can be added to the hierarchy What would be the most idiomatic way to implement Algebraic Data Types in C# and/or Java? Or, if it isn't possible, what would be the idiomatic replacement?

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  • why are transaction monitors on decline? or are they?

    - by mrkafk
    http://www.itjobswatch.co.uk/jobs/uk/cics.do http://www.itjobswatch.co.uk/jobs/uk/tuxedo.do Look at the demand for programmers (% of job ads that the keyword appears), first graph under the table. It seems like demand for CICS, Tuxedo has fallen from 2.5%/1% respectively to almost zero. To me, it seems bizarre: now we have more networked and internet enabled machines than ever before. And most of them are talking to some kind of database. So it would seem that use of products whose developers spent last 20-30 years working on distributing and coordinating and optimizing transactions should be on the rise. And it appears they're not. I can see a few causes but can't tell whether they are true: we forgot that concurrency and distribution are really hard, and redoing it all by ourselves, in Java, badly. Erlang killed them all. Projects nowadays have changed character, like most business software has already been built and we're all doing internet services, using stuff like Node.js, Erlang, Haskell. (I've used RabbitMQ which is written in Erlang, "but it was small specialized side project" kind of thing). BigData is the emphasis now and BigData doesn't need transactions very much (?). None of those explanations seem particularly convincing to me, which is why I'm looking for better one. Anyone?

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  • How to write Haskell function to verify parentheses matching?

    - by Rizo
    I need to write a function par :: String -> Bool to verify if a given string with parentheses is matching using stack module. Ex: par "(((()[()])))" = True par "((]())" = False Here's my stack module implementation: module Stack (Stack, push, pop, top, empty, isEmpty) where data Stack a = Stk [a] deriving (Show) push :: a -> Stack a -> Stack a push x (Stk xs) = Stk (x:xs) pop :: Stack a -> Stack a pop (Stk (_:xs)) = Stk xs pop _ = error "Stack.pop: empty stack" top :: Stack a -> a top (Stk (x:_)) = x top _ = error "Stack.top: empty stack" empty :: Stack a empty = Stk [] isEmpty :: Stack a -> Bool isEmpty (Stk [])= True isEmpty (Stk _) = False So I need to implement a 'par' function that would test a string of parentheses and say if parentheses in it matches or not. How can I do that using a stack?

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  • Why is Haskell used so little in the industry?

    - by bugspy.net
    It is a wonderful, very fast, mature and complete language. It exists for a very long time and has a big set of libraries. Yet, it appears not to be widely used. Why ? I suspect it is because it is pretty rough and unforgiving for beginners, and maybe because its lazy execution makes it even harder

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  • In Haskell, what does it mean if a binding "shadows an existing binding"?

    - by Alistair
    I'm getting a warning from GHC when I compile: Warning: This binding for 'pats' shadows an existing binding in the definition of 'match_ignore_ancs' Here's the function: match_ignore_ancs (TextPat _ c) (Text t) = c t match_ignore_ancs (TextPat _ _) (Element _ _ _) = False match_ignore_ancs (ElemPat _ _ _) (Text t) = False match_ignore_ancs (ElemPat _ c pats) (Element t avs xs) = c t avs && match_pats pats xs Any idea what this means and how I can fix it? Cheers.

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  • In Haskell, will calling length on a Lazy ByteString force the entire string into memory?

    - by me2
    I am reading a large data stream using lazy bytestrings, and want to know if at least X more bytes is available while parsing it. That is, I want to know if the bytestring is at least X bytes long. Will calling length on it result in the entire stream getting loaded, hence defeating the purpose of using the lazy bytestring? If yes, then the followup would be: How to tell if it has at least X bytes without loading the entire stream? EDIT: Originally I asked in the context of reading files but understand that there are better ways to determine filesize. Te ultimate solution I need however should not depend on the lazy bytestring source.

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  • What is wrong with my definition of Zip in Haskell?

    - by kunjaan
    -- eg. myzip [’a’, ’b’, ’c’] [1, 2, 3, 4] -> [(’a’, 1), (’b’, 2), (’c’, 3)] myzip :: Ord a => [a] -> [a] -> [(a,a)] myzip list1 list2 = [(x,y) | [x, _] <-list1, [y,_] <-list2 ] I get this error message: Occurs check: cannot construct the infinite type: a = [a] When generalising the type(s) for `myzip' Failed, modules loaded: none.

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  • what's the way to determine if an Int a perfect square in Haskell?

    - by valya
    I need a simple function is_square :: Int -> Bool which determines if an Int N a perfect square (is there an integer x such that x*x = N). Of course I can just write something like is_square n = sq * sq == n where sq = floor $ sqrt $ (fromIntegral n::Double) but it looks terrible! Maybe there is a common simple way to implement such predicate?

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  • Why do compiled Haskell libraries see invalid static FFI storage?

    - by John Millikin
    I am using GHC 6.12.1, in Ubuntu 10.04 When I try to use the FFI syntax for static storage, only modules running in interpreted mode (ie GHCI) work properly. Compiled modules have invalid pointers, and do not work. I'd like to know whether anybody can reproduce the problem, whether this an error in my code or GHC, and (if the latter) whether it's a known issue. Given the following three modules: -- A.hs {-# LANGUAGE ForeignFunctionInterface #-} module A where import Foreign import Foreign.C foreign import ccall "&sys_siglist" siglist_a :: Ptr CString -- -- B.hs {-# LANGUAGE ForeignFunctionInterface #-} module B where import Foreign import Foreign.C foreign import ccall "&sys_siglist" siglist_b :: Ptr CString -- -- Main.hs {-# LANGUAGE ForeignFunctionInterface #-} module Main where import Foreign import Foreign.C import A import B foreign import ccall "&sys_siglist" siglist_main :: Ptr CString main = do putStrLn $ "siglist_a = " ++ show siglist_a putStrLn $ "siglist_b = " ++ show siglist_b putStrLn $ "siglist_main = " ++ show siglist_main peekSiglist "a " siglist_a peekSiglist "b " siglist_b peekSiglist "main" siglist_main peekSiglist name siglist = do ptr <- peekElemOff siglist 2 str <- maybePeek peekCString ptr putStrLn $ "siglist_" ++ name ++ "[2] = " ++ show str I would expect something like this output, where all pointer values identical and valid: $ runhaskell Main.hs siglist_a = 0x00007f53a948fe00 siglist_b = 0x00007f53a948fe00 siglist_main = 0x00007f53a948fe00 siglist_a [2] = Just "Interrupt" siglist_b [2] = Just "Interrupt" siglist_main[2] = Just "Interrupt" However, if I compile A.hs (with ghc -c A.hs), then the output changes to: $ runhaskell Main.hs siglist_a = 0x0000000040378918 siglist_b = 0x00007fe7c029ce00 siglist_main = 0x00007fe7c029ce00 siglist_a [2] = Nothing siglist_b [2] = Just "Interrupt" siglist_main[2] = Just "Interrupt"

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  • Haskell: "how much" of a type should functions receive? and avoiding complete "reconstruction"

    - by L01man
    I've got these data types: data PointPlus = PointPlus { coords :: Point , velocity :: Vector } deriving (Eq) data BodyGeo = BodyGeo { pointPlus :: PointPlus , size :: Point } deriving (Eq) data Body = Body { geo :: BodyGeo , pict :: Color } deriving (Eq) It's the base datatype for characters, enemies, objects, etc. in my game (well, I just have two rectangles as the player and the ground right now :p). When a key, the characters moves right, left or jumps by changing its velocity. Moving is done by adding the velocity to the coords. Currently, it's written as follows: move (PointPlus (x, y) (xi, yi)) = PointPlus (x + xi, y + yi) (xi, yi) I'm just taking the PointPlus part of my Body and not the entire Body, otherwise it would be: move (Body (BodyGeo (PointPlus (x, y) (xi, yi)) wh) col) = (Body (BodyGeo (PointPlus (x + xi, y + yi) (xi, yi)) wh) col) Is the first version of move better? Anyway, if move only changes PointPlus, there must be another function that calls it inside a new Body. I explain: there's a function update which is called to update the game state; it is passed the current game state, a single Body for now, and returns the updated Body. update (Body (BodyGeo (PointPlus xy (xi, yi)) wh) pict) = (Body (BodyGeo (move (PointPlus xy (xi, yi))) wh) pict) That tickles me. Everything is kept the same within Body except the PointPlus. Is there a way to avoid this complete "reconstruction" by hand? Like in: update body = backInBody $ move $ pointPlus body Without having to define backInBody, of course.

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