Erlang (programming language)/Tutorials
Erlang Language Programming Tutorials
History
The erlang language was first written in prolog by Joe Armstrong. Ref:audio interview with Joe Armstrong from (http://www.se-radio.net). Joe is a known fan of prolog and borrowed much syntax from prolog in the design of erlang. This first prolog version of erlang was slow and motivated the creation of a virtual machine. Later an emulator called the BEAM(Bogdans's Erlang Abstract Machine, [1]) was written in C and is about 200,000 lines of code. The language name erlang was most likey used because it is also a (unit of phone connection); because of its original use in the phone company Ericsson.
Overview
Erlang is a language created to do parallel programming with only message passing. Pure message passing makes MIMD (Parallel_computation) programming almost easy once you get friendy with it. No memory is shared. Erlang is a concurency oriented language and the primary programming building block is a process. In erlang, processes are allowed to fail and are simply restarted.
Erlang has a purely functional core. A functional language is one that is based on Lambda_calculus. In lambda calculus variables have single assignment and behave like mathematical functions and functions are stateless. The advantages of referential transparency(single assignment) are many. Single assignment makes debugging easier(Joe Armstrong http://www.se-radio.net). Statelessness makes hot code swapping easy in erlang(Joe Armstrong). Referential transparency makes editing and code transformation easier(via find and replace). Functional languages have the advantage that syntax and semantics are unified. This unification makes it easier for code to modify itself safely, which facilitates meta-programming. Added benefits of functional programming include the ability to prove things like the correctness and equivalence between programs (see Functional Programming [2])
Print functions and message passing are side effects and are not part of the purely functional core of erlang. One of the main ideas in erlang is to make as much of a program purely functional as possible and isolate the functions that include side effects to improve stability. The theory is that the purely functional part is naturally well behaved.
Erlang has been around for 20 years and has a large library of functions available, especially for networking and the web.
Basic Erlang
- Get to know the Command Line
- Quick tips
- Terms
- Pattern Matching
- Expressions
- Functions
- Guards
- Modules
- Errors - working with exceptions
- Processes and Messages
- Trapping Exit Signals
- Timeouts
- Macros
- Techniques of Recursion
- List Comprehensions
- List Comments
Syntax
Functions are defined by the domain of the arguments and the number of arguemnts. A function ends with a period. A function over a particular domain(set of inputs) is separated by a semicolon. The arrow shows how a particular function of a particular value or variable maps to an output.
fact(0) -> 1;
fact(N) when is_integer(N) ->
fact(N-1)*N.
Simple Types
Basic types in erlang include:
- atom - alice
- integer - 3
- float - 3.1415
- pid - a process id number <0.42.0>
- list - [ things in square brackets ]
- tuple - { things in curly braces }
Advanced Types
- binary - a binary data block, <<42>>
- function - a function, F = fun(X) -> X*X end.
- port - a path for data to flow to the outside world
- reference - a unique id over all processes
- record - the standard erlang data structure
Modules
Adding/Replacing Modules
Erlang is picky about updating or replacing modules of the same name. You should completely remove the old module code from the directory tree, not just rename the containing directory.
Popular Modules
Nonstandard Modules
- Eunit Unit Testing Module
Object Oriented Programming with erlang
Behaviours
Nonstandard OOP with erlang
Functional Programming with erlang
- Fun with folding
- Iterator
- Simplify Numeric Types (auto-demotion of numerical types)
Example programs
- Hello World (Serial)
- Hello World (parallel)
- Prime Sieve with Linda
- Autonomous Agents in Erlang -- def: Autonomous Agent.
OTP
Design of OTP programs
OTP Behaviours
client-server event-handler :gen_server hot-standby keep-me-alive supervision-tree upgrade-handler worker-supervisor
Databases
Advanced Erlang
Glossary of Erlang Terms
Call: a Synchronous message between processes
Cast: an Asynchronous message between processes
Reference: an data type that provides a unique mark of identification
you can generate an id with the command:
erlang:make_ref()
Projects using erlang
- CouchDB - a scalable database for Apache
- Wings3D - a 3-D editor