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  • Erlang: What are the pros and cons of different methods for avoiding intermediate variables?

    - by erlacher
    At one point while traveling the web, I came across a great page which contrasted the clarity and terseness of different methods of doing a sequence of operations without having to make a bunch of throwaway variables, e.g., Var1, Var2, Var3. It tried list comprehensions, folds, maps, etc. For some reason, now matter what I google, I can't find it again. Anyone have any idea what I'm talking about? Or want to explore the topic anyway?

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  • Erlang: What's a good way to automatically assign node names?

    - by mwt
    I want to have an EC2 based cluster that can grow and shrink at will. No node will be special in any way nor do I want them to have to coordinate their names with any other nodes. I don't want to hard code the names since I want to use one image and spin them up as needed. I understand nodes have to have names to communicate, though. What's a good strategy for automatically and dynamically coming up with a name at start script time?

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  • Erlang: How do you reload an application env configuration?

    - by mwt
    How do you reload an application's configuration? Or, what are good strategies for managing dynamic application configuration? For example, let's say I had log levels and I wanted to change them at runtime. Also, let's assume this is one of many such options. Does it make sense to have a "configuration server" that holds configuration state for other parts of the application to query? Do people do that or did I just make it up?

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  • how to read the contents of a file In Erlang ?

    - by Zubair
    I know you can do something like this: readlines(FileName) -> {ok, Device} = file:open(FileName, [read]), get_all_lines(Device, []). get_all_lines(Device, Accum) -> case io:get_line(Device, "") of eof -> file:close(Device), Accum; Line -> get_all_lines(Device, Accum ++ [Line]) end. : Is there a one liner BIF that can do this too?

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  • Rabbitmq 2.2 not working on Snow Leopard (SSL errors)

    - by ebeland
    When I start rabbitmq, I see the following message. I have Activating RabbitMQ plugins ... WARNING Undefined function crypto:des3_cbc_decrypt/5 WARNING Undefined function crypto:start/0 WARNING Undefined function ssl:close/1 WARNING Undefined function ssl:controlling_process/2 WARNING Undefined function ssl:peercert/1 WARNING Undefined function ssl:peername/1 WARNING Undefined function ssl:recv/3 WARNING Undefined function ssl:send/2 WARNING Undefined function ssl:sockname/1 WARNING Undefined function ssl:ssl_accept/3 0 plugins activated: I followed the advice here to install openssl and recompile erlang with a --with-ssl path set: http://old.nabble.com/2.1.1%3A-no-such-file-or-directory-crypto.app-message-prevents-broker-from-starting-td30011026.html When I recompiled erlang, I used the following .configure: ./configure \ --prefix=/usr/local/erlang/R13B04 \ --enable-smp-support \ --enable-threads \ --enable-darwin-64bit \ --with-ssl=/usr/include/openssl It compiled fine. Then, just in case, I reinstalled rabbit from macports. I still get the error. Am I using the wrong path for --with-ssl? Help?

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  • Distribute CouchDB as part of a Rails app?

    - by AaronThomson
    I am working on a Rails project and the Architect has asked me to investigate bundling CouchDB into to application so that it can be deployed by Capistrano across multiple platforms and managed by Rake. My expectation was that I could set up the Erlang VM on the various environments and then distribute the CouchDB application with Capistrano. However I can't find any option to download CouchDB without the Erlang runtime. I can, however see an option to build CouchDB from source which I assume is platform dependent. I am new to Erlang and CouchBD, am I missing something? Is there a way to bundle CouchDB into a Rails app and distribute it across multiple platforms?

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  • Time order of messages

    - by Aiden Bell
    Read (skimmed enough to get coding) through Erlang Programming and Programming Erlang. One question, which is as simple as it sounds: If you have a process Pid1 on machine m1 and a billion million messages are sent to Pid1, are messages handled in parallel by that process (I get the impression no) and(answered below) is there any guarantee of order when processing messages? ie. Received in order sent? If so, how is clock skew handled in high traffic situations for ordering? Coming from the whole C/Thread pools/Shared State background ... I want to get this concrete. I understand distributing an application, but want to ensure the 'raw bones' are what I expect before building processes and distributing workload. Also, am I right in thinking the whole world is currently flicking through Erlang texts ;)

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  • Nginx's speed, and how to replicate it [migrated]

    - by Mediocre Gopher
    I'm interested in this from more than an academic standpoint rather than a practical standpoint; I don't plan on creating a production webserver to compete with nginx. What I'm wondering is how exactly nginx is so fast. The top google response for this is this thread, but it merely links to a cryptic slideshow and a general covering of different io strategies. All other results seem to simply describe how fast nginx is, rather then the reason. I tried building a simple erlang server to try to compete with nginx, but to no avail; nginx won out. All my server does is spawn a new process for each request, uses that process to read the file to a socket, then closes the file and kills the thread. It's not complicated, but given erlang's lightweight processes and underlying aio structure I thought it would compete, but nginx still wins out by a consistent 300 ms average under a heavy stress test. What is nginx doing that my simple server isn't? My first thought would be keeping files in main memory instead of tossing them between requests, but the filesystem cache does this already so I didn't think it would make that great of difference. Am I wrong? Or is there something else that I'm missing?

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  • Mochiweb's Scalability Features

    - by ErJab
    From all the articles I've read so far about Mochiweb, I've heard this over and over again that Mochiweb provides very good scalability. My question is, how exactly does Mochiweb get its scalability property? Is it from Erlang's inherent scalability properties or does Mochiweb have any additional code that explicitly enables it to scale well? Put another way, if I were to write a simple HTTP server in Erlang myself, with a simple 'loop' (recursive function) to handle requests, would it have the same level scalability as a simple web server built using the Mochiweb framework?

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  • Concept of GUI's - Centralized or decentralized

    - by wvd
    Hello all, Since a few months I've been learning Erlang, and now it was time to do some basic GUI. After some quick research I saw there was an interesting library called 'wxi' (based on Fudgets of Haskell) which uses a different approach on GUI's. No central loop, every widget processes it's own events and handles it's own data. What do you guys think about this? It looks like it kind of can be efficient in languages such as Erlang, and it's an interesting approach. William van Doorn

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  • Could CouchDB benefit significantly from the use of BERT instead of JSON?

    - by Victor Rodrigues
    I appreciate a lot CouchDB attempt to use universal web formats in everything it does: RESTFUL HTTP methods in every interaction, JSON objects, javascript code to customize database and documents. CouchDB seems to scale pretty well, but the individual cost to make a request usually makes 'relational' people afraid of. Many small business applications should deal with only one machine and that's all. In this case the scalability talk doesn't say too much, we need more performance per request, or people will not use it. BERT (Binary ERlang Term http://bert-rpc.org/ ) has proven to be a faster and lighter format than JSON and it is native for Erlang, the language in which CouchDB is written. Could we benefit from that, using BERT documents instead of JSON ones? I'm not saying just for retrieving in views, but for everything CouchDB does, including syncing. And, as a consequence of it, use Erlang functions instead of javascript ones. This would modify some original CouchDB principles, because today it is very web oriented. Considering I imagine few people would make their database API public and usually its data is accessed by the users through an application, it would be a good deal to have the ability to configure CouchDB for working faster. HTTP+JSON calls could still be handled by CouchDB, considering an extra cost in these cases because of parsing.

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  • Couchdb failing test suite on Linux

    - by user52674
    Hi I've been trying to install CouchDB on my webfusion virtual server. I followed the latest instructions from the webfusion forum (see: http://forum.webfaction.com/viewtopic.php?id=2355 ) and it runs (just) Futon is very sluggish and I get 502 errors. Anyway when I run the test suite it fails on multiple tests. Webfaction support have been great but don't have erlang experience to interpret the error logs. Can anyone help me know what might be wrong? Test suite result: basics, all_docs, attachments, attachments_multipart, attachment_names, compact, config, conflicts, delayed_commits, design_docs, design_options all the errors are: Exception raised: {"error":"unknown","reason":"\u000d\u000a502 Bad Gateway\u000d\u000a\u000d\u000a<\h1502 Bad Gateway\u000d\u000a nginx\u000d\u000a\u000d\u000a\u000d\u000a"} except for 'compact; which also has: Assertion failed: xhr.responseText == "This is a base64 encoded text" Assertion failed: xhr.getResponseHeader("Content-Type") == "text/plain" I'm stumped. Anybody know what these indicate? AL

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  • who uses a TCP port?

    - by dijxtra
    One of gen_servers in my app call gen_tcp:listen(Port, [{active, true}]). First time I run unit test, it returns {ok, Socket}, but second time I run the same unit test, it returns an {error, eaddrinuse}, but lsof -i TCP returns nothing. Also, when the same unit_test is run twice on another machine (WinXP), it works as expected (that is, returns {ok, Socket} both times). Therefore, my gen_server obviously releases the port, but Erlang somehow doesn't know that. So, how can I figure out who does Erlang think uses this address?

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  • AMQP 'connection.open' reserved parameters

    - by jldupont
    I am writing an AMQP Client Library in Erlang. For the 'connection.open' method, there are 2 reserved parameters "documented" in AMQP 0.9.1 out of a total of 3. When I send the method in question without the "reserved parameters", I get "unable to decode method" in the error log. What should I be sending as value for those "reserved parameters" ?? Update: It seems the server still expects some parameters even if the parameters are deprecated (see source code for code generator).

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  • Passing local variables to Erlydtl block

    - by Justin
    Hi, I've got a block of erlydtl code which I use repeatedly and would like to abstract to some kind of block / partial template. The issue is that I need to pass the block a local variable. This is possible with Rails partial templates; it looks like it's possible with Django's blocks [albeit with some kind of Python hackery]; I'm wondering if it's possible with Erlydtl [Erlang implementation of Django templates] Ideas ? Thanks you.

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  • Log errors in a file

    - by Konstantin
    How do I log all process crashes into a file instead of a tty ? I've read in the documentation that there are some standard Erlang modules that can do it (SASL, error_logger), but unfortunately haven't found any clean examples.

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  • How to connect Nitrogen with Couchdb using Ecouch

    - by maryjanne
    I don't understand how to make a connection with nitrogen and couchdb using ecouch, because I have a error on this connection CAUGHT ERROR: error-undef [{ecouch,db_info,["test_suite_db"]} I put ecouch in my erlang library path and I create a symlink to support/include.mk (even I don't know if it has necessary). Or if anyone know a database how can connect with nitrogen and who to make this connection.

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