Sharing Data Structures Introduction Converting an Existing Term Sending a Term in a Message Introduction On the list recently, the question of ensuring maximal sharing of an Erlang term came up. I've run into several cases where enforcing the sharing of data resulted in a significant memory savings. I'm talking about...

Mnesia Ordered By Queries Table of Contents Introduction Inefficient General Solution Efficient Solution: Primary Key Efficient General Solution: Secondary Sorted Index Introduction Mnesia is not a relational database engine; it's better described as a distributed transactional key-value store. Relational databases do...

Implementing a Counter in Erlang Table of Contents Introduction Slower but Ideologically Pure Faster Introduction Erlang, as a functional language, strives for a side-effect free sequential syntax.  Sometimes side-effects are desirable, the classic example being the collection of serving statistics . I want to add...

Welcome This is a site devoted to providing color commentary for erlang questions .  You can peruse the recently updated content indicated in the left bar, or you can check out the index of all content. I am also working on a searchable socialized Erlang Questions archive .  I'm slowly populating it with messages...

Mnesia Distributed Hello World Table of Contents Introduction Hello World Problem Solved Dynamic Maintenance Schema Other Tables Introduction One of the simultaneously coolest and most challenging features of Mnesia is distributed operation.  Before even tackling the complexities of managing failure cases, some...

Mnesia Schema Free Operation Introduction Most programmers are aware of the distinction between statically typed and dynamically typed programming languages, with respective advantages and disadvantages.  Analogously, databases can be schema driven or schema-free.  All relational database engines that I am familiar...

Mnesia Schema Maintenance Table of Contents Introduction Basics: Making Sure Tables are There Advanced: Schema Migrations Introduction Any database driven application faces the problem of initialization and maintenance of the data store in conjunction with the rest of the application, and Mnesia driven applications are...

About the Site The site consists of a document store written in Mnesia , a serving layer provided by inets httpd , a presentation layer which leverages Nitrogen , and an editing interface which leverages TinyMCE .  ( CouchDB looked like a good choice for the document store, but I am super familiar with Mnesia so that was...

Binding to a Privileged Port Table of Contents Introduction Do not do this: setuid beam as root Port forwarding Capabilities Reverse proxy Disable privileged ports Introduction Erlang is a natural fit for web applications and there are several webservers available for Erlang.  Since ports 80 and 443 are privileged...

Verifying a Facebook Connect Signature This site uses Facebook connect to authenticate.  Basically, Facebook javascript sets cookies in my domain (erlanganswers.com) which the server can read, and one of these cookies contains a user id.  In order to prevent malicious persons from faking authentication by setting...

Mnesia Equals Ignores Case Query Table of Contents Introduction Maintain the Data Canonicalized Match Specification Solution Secondary Index Solution Introduction Many more people know SQL than know Mnesia, so questions about how to translate a particular SQL construct into Mnesia arise frequently on the list, and in...

Complex Case Patterns Table of Contents Introduction Disjunctive Guards Universal Clause Transform Expression Introduction Erlang case statements have clauses that are guards, and since they can do pattern matching the case statement resembles conditional constructs from other languages.  However the correspondence...

Versioned Variables Table of Contents Introduction Numbered Variables Function Arguments Introduce New Scope Named Functions List Comprehensions Anonymous Functions Let Construct Folding Introduction Erlang doesn't have an assignment operator, but it has a pattern matching operator that looks like one.  The first...