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Table of Contents

• What is Erlang
  • Top of chapter
  • In a nutshell, what is Erlang?
  • What is OTP?
  • What sort of applications is Erlang particularly suitable for?
  • What sort of problems is Erlang not particularly suitable for?
  • Who uses Erlang for product development?
  • Who uses Erlang for research and teaching?
  • Can I get commercial support for Erlang?
• Questions about this FAQ
  • Top of chapter
  • Where can I get the latest version of the FAQ?
  • What's new?
  • Where do I ask questions which are not answered in this FAQ?
  • The answer to question 2.4 is wrong!
  • Disclaimer/Distribution
• Obtaining Erlang/OTP and books/articles about it
  • Top of chapter
  • Where can I get Erlang/OTP?
  • What's the current version of (Open Source) Erlang?
  • Which licence is Open Source Erlang shipped with?
  • What documentation is there for Erlang?
  • What advanced Erlang documentation is there?
  • What documentation is there in related subjects?
  • Is there public CVS/Git/your-favourite-vcs repository for the Erlang source?
  • How can I contribute to Erlang?
  • How can I propose changes to the language itself?
  • Where is Erlang discussed in the real world?
  • Where is Erlang discussed online?
  • Are there any websites apart from erlang.org?
  • Where can I find Erlang programmers/employers?
• Getting Started
  • Top of chapter
  • How long does it take to learn Erlang?
  • How can I learn Erlang?
  • What does "hello world" look like?
  • How do I quit the Erlang shell?
  • Why does Erlang print "ok" after my program's output?
• How do I...
  • Top of chapter
  • ...compare numbers?
  • ...represent a text-string?
  • ...convert a string to lower case?
  • ...convert a text string representation of a term to a term?
  • ...use unicode/UTF-8?
  • ...destructively update data, like in C
  • ...run an Erlang program directly from the unix shell?
  • ...communicate with non-Erlang programs?
  • ...write a unix pipe program in Erlang?
  • ...communicate with a DBMS?
  • ...decode binary Erlang terms
  • ...decode Erlang crash dumps
  • ...estimate performance of an Erlang system?
  • ...measure performance of an Erlang system?
  • ...measure memory consumption in an Erlang system?
  • ...estimate productivity in an Erlang project?
  • ...use multiple CPUs (or cores) in one server?
  • ...run distributed Erlang through a firewall?
  • ...find out which line my Erlang program crashed at?
  • ...distribute the Erlang programs I write to my friends/colleagues/users?
  • ...write to standard error (stderr)?
• Erlang Libraries
  • Top of chapter
  • What's in the OTP libraries?
  • Is there a collection of data structures, e.g. balanced trees?
  • Is there a serial port driver for Erlang?
  • Is there a toolkit for building GUIs?
  • I've written a library to handle XYZ. How do I get it into the standard Erlang distribution?
• Erlang Tools
  • Top of chapter
  • Is there a pretty printer for Erlang?
  • Where is the source for LEEX (the erlang lexer)?
  • Is there a diagram tool for Erlang?
  • What code testing tools and suites exist for and in Erlang/OTP?
  • Is there a way to benchmark an Erlang implementation?
  • Does anyone have a magic file for Erlang?
  • Is there an Erlang IDE?
  • Are there Erlang Coding Guidelines?
  • What refactoring tools are there for Erlang
  • What static code analysis tools are there?
  • Is there a "reverse compiler" for BEAM files?
• Implementation and Ports of Erlang
  • Top of chapter
  • What Production-quality implementations of Erlang are there?
  • What Experimental and Research Implementations are there?
  • Which version of Erlang am I running?
  • What operating systems does Erlang run on?
  • What implementations of the Erlang Virtual Machine are there?
  • Is there an unofficial port for...?
  • Can Erlang be compiled under Microsoft Windows?
  • Can Erlang be cross compiled?
  • Is Erlang small enough for Pocket PCs?
  • Is Erlang small enough for embedded systems?
• Troubleshooting, Problems and 'Gotchas'
  • Top of chapter
  • Why can't I write a = 3 (badmatch)?
  • Why can't I change the value of a variable?
  • Why do lists of numbers get printed incorrectly?
  • Why can't I call arbitrary functions in a guard?
  • Why can't I use "or" in a guard?
  • Why does 'catch' give me a syntax error?
  • What is a sticky directory?
  • Why won't my distributed Erlang nodes communicate?
  • When distribution won't work
  • Avoiding DNS
  • Why does my application die every second time I load new code into it?
  • Why can't I open devices (e.g. a serial port) like normal files?
  • Why doesn't the stack backtrace show the right functions for this code:
  • What do I do if I get an error when compiling Open Source Erlang?
  • Why do errors in the shell kill other processes?
• Academic and Historical Questions
  • Top of chapter
  • Why is Erlang called "Erlang"?
  • Who invented Erlang?
  • Where does Erlang syntax come from?
  • Why is Ericsson giving away Erlang?
  • What can I do for Open Source Erlang?
  • What does soft realtime mean?
  • How did the first Erlang compiler get written?
  • Erlang Syntax and Semantics Details
  • Is the order of message reception guaranteed?
  • If I send a message, is it guaranteed to reach the receiver?
  • What limits does Erlang have?
  • Do funs behave during a code change?
  • Examples of bound funs causing surprises
  • Is it just me, or are records ugly?
  • Can a process receive messages with varying priorities?
  • Flamewars
  • What's the history of static type checking in Erlang?
  • How does type checking in Erlang compare to Java/Python/C/C++/Haskell?
  • Why do we have to have yet another programming language; C++ (or Java, or Visual Basic) does everything.
  • Erlang should use a Just In Time compiler
  • Erlang should be object oriented
  • How are strings implemented and how can I speed up my string code?
  • How does the Garbage Collector work?
  • Can I exploit knowledge about my program to make the GC more efficient?
  • Could the Java Virtual Machine be used to run Erlang?
  • Is it possible to prove the correctness of Erlang programs?
  • I've heard it's a bad idea to program defensively in Erlang. Why?
• Mnesia Database Questions
  • Top of chapter
  • What is Mnesia good at?
  • What is Mnesia not so good at?
  • Is Mnesia good for storing blobs?
  • Is there an SQL interface for mnesia?
  • How much data can be stored in Mnesia?
  • Contributors

2 Questions about this FAQ

2.1  Where can I get the latest version of the FAQ?

The open source Erlang website .

2.2  What's new?

April 2010

Migrated the FAQ to the new OTP documentation build

May 2009

Updated for R13B-1, fixed broken links

Updated the sections related to type checking to focus on or mention dialyzer.

Added to the list of known high-profile commercial and academic users.

Updated the conference section to cover the Erlang exchange conferences in SF and London.

Mentioned the #erlang IRC channel.

January 2009

Updated for R12B-5, fixed broken links

Erlang now has public GIT, Bazaar and CVS repositories

March 2008

Updated for R12B-1, fixed broken links

November 2007

Migrated the FAQ source from docbook to OTP's own docbuilder

Updated for R11B-5, fixed broken links

New question: How do I write to standard error on a unix system?

May 2007

Updated for R11B-4

Added a link to the new Joe Armstrong book.

New question: How can I propose changes to the language itself?

New question: Can a process receive messages with varying priorities?

Added CEAN (cean.process-one.net) to the 'obtaining' section.

Removed the "why is the release so big?" question. Given the bandwidth available to most people nowadays, the question is no longer of general interest.

2.3  Where do I ask questions which are not answered in this FAQ?

In most cases, the best place is the erlang-questions mailing list at erlang-questions@erlang.org. Anyone can subscribe.

2.4  The answer to question 2.4 is wrong!

If you've found an editorial error in the FAQ (broken link, an addition to a list of links, typo, ambiguity, badly expressed answer, etc.), send some mail to matthias@corelatus.com and I'll fix it.

Problems along the lines of "the advice about the importance of type checking is complete drivel" might be of general interest on the erlang-questions mailing list at erlang-questions@erlang.org.

2.5  Disclaimer/Distribution

The information in this document is available free of charge in the hope that it will be of use. However, the author specifically disclaims any liability for any direct, indirect, or consequential damages arising out of its use. The author grants permission to distribute this FAQ in unmodified form on any medium.

Opinions in this FAQ do not necessarily agree with Ericsson's official opinions. The maintainer no longer works for Ericsson and this FAQ is not an Ericsson product.