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=Erlang Language Programming 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, [http://www.erlang.se/publications/icfp97.ps.gz]) 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==
==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 [http://en.citizendium.org/wiki/Functional_programming])
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==
:[[/Command Line|Get to know the Command Line]]
:[[/Quick_tips|Quick tips]]
:[[/Terms|Terms]]
:[[/Pattern Matching|Pattern Matching]]
:[[/Expressions|Expressions]]
:[[/Functions|Functions]]
:[[/guards|Guards]]
:[[/Modules|Modules]]
:[[/Errors|Errors]] - working with exceptions
:[[/Processes|Processes and Messages]]
:[[/Trap_exit|Trapping Exit Signals]]
:[[/Timeouts|Timeouts]]
:[[/Macros|Macros]]
:[[/Techniques of Recursion|Techniques of Recursion]]
:[[/List Comprehensions|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.
:[[Erlang_programming_language/Tutorials/Advanced_syntax|Advanced Syntax]]
==Simple Types==
==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==
==Advanced Types==
==Examples==
*binary - a binary data block, <<42>>
===Hello World (serial)===
*function - a function, F = fun(X) -> X*X end.
===Hello World (parallel)===
*port - a path for data to flow to the outside world
===Prime Sieve (parallel with linda type coordination)===
*reference - a unique id over all processes
*record - the standard erlang data structure


    -module(primes).
==Modules==


    % This is a simple linda tuplespace. Here we use it to find primes numbers.
===Adding/Replacing Modules===
    % This tuple-space can not have duplicate tuples, but with a prime sieve it does
Erlang is picky about updating or replacing modules of the same name.
    %  not matter.
You should completely remove the old module code from the directory tree,  
not just rename the containing directory.


    -compile(export_all).
===Popular Modules===
:[[Erlang_programming_language/Tutorials/Math|math]]
:[[Erlang_programming_language/Tutorials/gb_sets|gb_sets]]
:[[Erlang_programming_language/Tutorials/Lists|lists]]
:[[Erlang_programming_language/Tutorials/regexp|regexp: Regular Expressions]]


    start() -> start(100).  % defualt value for max is 100
===Nonstandard Modules===
    start(Max) ->
:[[Erlang_programming_language/Tutorials/eunit|Eunit]] Unit Testing Module
        io:format("  Loading ~w numbers into matrix (+N) \n ", [ Max ] ),
        Lid = spawn_link( primes, linda, [Max, [], [] ]),
        Sqrt = round(math:sqrt(Max)+0.5), 
        io:format(" Sqrt(~w) + 1 = ~w \n " , [Max,Sqrt] ), 
        io:format(" Tuple space is started ~n ",[]), 
        io:format(" ~w sieves are spawning (+PN) ~n ", [Sqrt] ),
        io:format(" Non prime sieves are being halted (-PN) ~n ", [] ),
        % load numbers into tuplespace
        % and spawn seive process
        spawn( primes, put_it, [Max, Max, Lid] ).


    sleep(N) ->
==Object Oriented Programming with erlang==
        receive
        after N -> time_is_up 
        end.


    start_sieves(Lid) ->
Behaviours
        Lid ! {self(), get, all, pids}, 
:[[Erlang_programming_language/Tutorials/behaviours|Behaviours]]
        receive
            {lindagram, pids, Pids} -> done
        end,
        start_sieve_loop(Pids).


    start_sieve_loop([]) -> done;
Nonstandard OOP with erlang
    start_sieve_loop([Pid|Pids]) ->
:[[Erlang_programming_language/Tutorials/erlangOOP|Objects with erlang]]
        receive
        after 100 -> done
        end,
        Pid ! {start},
        start_sieve_loop(Pids).


    spawn_sieves( _Max, Sqrt, _Lid, Sqrt ) -> done; 
==Functional Programming with erlang==
    spawn_sieves( Max, Inc, Lid, Sqrt ) ->
        T = 1000,
        Pid = spawn( primes, sieve, [ Max, Inc+Inc, Inc, Lid, T ]),
        Name = list_to_atom("P" ++ integer_to_list(Inc)),
        Lid ! {put, pid, Name},
        register( Name, Pid),
        io:format(" +~s ", [atom_to_list(Name)]),
        spawn_sieves( Max, Inc+1, Lid, Sqrt ).


    put_it(Max, N, Lid) when N =< 1 ->
:[[Erlang_programming_language/Tutorials/Folding|Fun with folding]]
        Sqrt = round(math:sqrt(Max)+0.5),
:[[Erlang_programming_language/Tutorials/Iterator|Iterator]]
        spawn_sieves( Max, 2, Lid, Sqrt ); 
:[[Erlang_programming_language/Tutorials/Simplify|Simplify Numeric Types]] (auto-demotion of numerical types)


    put_it(Max, N,Lid) when N > 1 ->
==Example programs==
        receive
        after 0 ->
:[[Erlang_programming_language/Tutorials/Hello|Hello World (Serial)]]
            Lid ! {put, N, N},
:[[Erlang_programming_language/Tutorials/Tree_Hello|Hello World (parallel) ]]
            if
:[[Erlang_programming_language/Tutorials/Linda_Sieve|Prime Sieve with Linda]]
                N rem 1000 == 0 ->
:[[Erlang_programming_language/Tutorials/Agents|Autonomous Agents in Erlang]] -- def: [[Autonomous Agent]].
                    io:format(" +~w ", [N]);
                true -> done
            end,
            put_it(Max, N-1,Lid)
        end.


    % the 2 sieve starts last and has the most to do so it finishes last
==OTP==
    sieve(Max, N, 2, Lid, _T) when N > Max ->
Design of OTP programs
        io:format("final sieve ~w done, ~n", [2] ),
:[[Erlang_programming_language/Tutorials/otp_design|otp_design]]
        Lid ! {dump,output};
OTP Behaviours
  client-server
  event-handler
  :[[Erlang_programming_language/Tutorials/gen_server|gen_server]]  
  hot-standby
  keep-me-alive
  supervision-tree
  upgrade-handler
  worker-supervisor


    sieve(Max, N, Inc, _Lid, _T) when N > Max ->   
        io:format("sieve ~w done ", [Inc] );


    sieve(Max, N, Inc, Lid, T) when N =< Max -> 
==Databases==
        receive
        after
            T -> NT = 0 
        end,
        receive
            {lindagram,Number} when Number =/= undefined ->
                clearing_the_queue;
            {exit} -> exit(normal)
        after
            1 -> done
        end,


        % remove multiple of number from tuple-space
:[[Erlang_programming_language/Tutorials/ETS|ETS programming]]
        Lid ! {self(), get, N},
:[[Erlang_programming_language/Tutorials/DETS|DETS programming]]
        Some_time = (N rem 1000)==0,
:[[Erlang_programming_language/Tutorials/Mnesia|Mnesia database]]
        if Some_time -> io:format("."); true -> done end,


        % remove (multiple of Inc) from sieve-process space
==Advanced Erlang==
        Name = list_to_atom("P" ++ integer_to_list(N)),
:[[Erlang_programming_language/Tutorials/Yecc|Making parsers with yecc]]
        Exists = lists:member( Name, registered()),
:[[Erlang_programming_language/Tutorials/Evaluation|Evaluation]]
        if
            Exists ->
                Name ! {exit},
                io:format(" -~s ", [atom_to_list(Name)] );
            true -> done
        end,
        sieve(Max, N+Inc, Inc, Lid, NT).        % next multiple
       
    %% linda is a simple tutple space
    %%    if it receives no messages for 2 whole seconds it dumps its contents
    %%    as output and halts


    linda(Max, Keys, Pids) ->
==Glossary of Erlang Terms==
        receive
  Call:      a Synchronous message between processes
        {put, pid, Pid} ->
  Cast:      an Asynchronous message between processes
            linda(Max, Keys, Pids++[Pid]);
  Reference: an data type that provides a unique mark of identification
        {put, Name, Value} ->
            you can generate an id with the command:
            put( Name, Value),
            erlang:make_ref()
            linda(Max, Keys++[Name], Pids);
 
        {From, get, Name} ->
==Projects using erlang==
            From ! {lindagram, get( Name)},
*CouchDB - a scalable database for Apache
            erase( Name ),                          % get is a desructive read 
*Wings3D - a 3-D editor
            linda(Max, Keys--[Name],Pids);
        {From, get, all, pids} ->
            From ! {lindagram, pids, Pids},
            linda(Max, Keys, Pids );
        {From, get, pid, Pid} ->
            L1 = length( Pids ),
            L2 = length( Pids -- [Pid]),
            if
                L1 > L2 ->  % if it exists
                    From ! {lindagram, pid, Pid};
                true ->
                    From ! {lindagram, pid, undefined}
            end,
            linda(Max, Keys, Pids );
        {dump,output} ->
            io:format(" ~w final primes remain: ~w ~n ", [length(Keys),  lists:sort(Keys) ])
        after (100*Max) -> % if there is not tuple action after some time then print the results
            io:format(" ~w primes remain: ~w ~n ", [length(Keys),  lists:sort(Keys) ])
        end.


==References==
==References==
[http://www.erlang.org/doc/man/| 1 - Erlang Man Pages at Erlang,org]

Latest revision as of 14:28, 24 August 2009

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https://en.citizendium.org/wiki/index.php?title=Erlang_(programming_language)/Tutorials&printable=yes
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 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.
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

Behaviours

Behaviours

Nonstandard OOP 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.

OTP

Design of OTP programs

otp_design

OTP Behaviours 

 client-server 
 event-handler 
 :gen_server 
 hot-standby 
 keep-me-alive 
 supervision-tree 
 upgrade-handler 
 worker-supervisor


Databases

ETS programming
DETS programming
Mnesia database

Advanced Erlang

Making parsers with yecc
Evaluation

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

References

1 - Erlang Man Pages at Erlang,org

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