Erlang (programming language)/Tutorials: Difference between revisions

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==Overview==
==Overview==


Erlang is language created to do parallel programming with message passing.  
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 [http://en.citizendium.org/wiki/Functional_programming])


Erlang is a functional language. 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
Print functions and message passing are side effects and are not part of the purely functional core of erlang.
(see Functional Programming [http://en.citizendium.org/wiki/Functional_programming])
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.


Erlang has been around for 20 years and has a large library of functions available,  especially for networking and the web.
Erlang has been around for 20 years and has a large library of functions available,  especially for networking and the web.

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Tutorials relating to the topic of Erlang (programming language).

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 C code. It is thought that erlang is short for "Ericsson Language", due to its place of birth.

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.

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
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 of values 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.
Advanced Syntax

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

math
gb_sets
lists
regexp: Regular Expressions

Nonstandard Modules

Eunit Unit Testing Module

Object Oriented Programming with erlang

Objects 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.

Advanced OTP

Databases

ETS programming
DETS programming
Mnesia database

Mnesia

Advanced Erlang

Making parsers with yecc
Evaluation

Projects using erlang

  • CouchDB - a scalable database for Apache
  • Wings3D - a 3-D editor

References

1 - Erlang Man Pages at Erlang,org