Distributed Programming Language Sampler: Erlang
Table of Contents
1 Facts
- TBD Year, Ericsson
- http://www.erlang.org/ There is an Erlang PDF book legit free to download. Has examples.
2 Hype
- Buzz Words: concurrent real-time distributed fault-tolerant long-running
- "Erlang is a programming language which has many features more commonly associated with an operating system</a> than with a programming language: concurrent processes</a>, scheduling, garbage collection</a>, distribution, networking, etc." It permits only a single assignment of a value to any variable.</p>
- "Learn how to write truly concurrent programs – programs that run on … hundreds of local and remote processors. See how to write high reliability applications – even in the face of network and hardware failure"
- "" Erlang is a language that was designed to support distributed, fault-tolerant, soft-realtime applications with requirements for high availability and high concurrency.
- "" Erlang is a programming language used to build massively scalable soft real-time systems with requirements on high availability. Some of its uses are in telecoms, banking, e-commerce, computer telephony and instant messaging. Erlang's runtime system has built-in support for concurrency, distribution and fault tolerance.
- "" Erlang is a programming language created specifically to support long-running, concurrent, highly reliable distributed systems.
- "" OTP is a set of Erlang libraries and design principles providing middle-ware to develop these systems. It includes its own distributed database, applications to interface towards other languages, debugging and release handling tools.
3 Hello World
-module(hello).
-export([hello_world/0]).
hello_world() -> io:fwrite("Hello, World!\n").
4 Quick Sort
qsort([]) -> []; qsort([X|Xs]) -> qsort([ Y || Y <- Xs, Y < X]) ++ [X] ++ qsort([ Y || Y <- Xs, Y >= X]).
5 Concurrently Say "Enjoy" "Rosetta" "Code"
-module(hw).
-export([start/0]).
start() ->
[ spawn(fun() -> say(self(), X) end)
|| X <- ['Enjoy', 'Rosetta', 'Code'] ],
wait(2),
ok.
say(Pid,Str) ->
io:fwrite("~s~n",[Str]),
Pid ! done.
wait(N) ->
receive
done -> case N of
0 -> 0;
_N -> wait(N-1)
end
end.
6 A TCP/IP time server
% Author : Claes Wikstrom <klacke@erix.ericsson.se>
-module(time_server).
-author('klacke@erix.ericsson.se').
-export([start/0, loop0/1]).
-define(PORTNO, 2345).
start() ->
start(?PORTNO).
start(Pno) ->
spawn(?MODULE, loop0, [Pno]).
loop0(Port) ->
case gen_tcp:listen(Port, [binary, {packet, 0}, {active, false}]) of
{ok, LSock} ->
loop(LSock);
_ ->
stop
end.
loop(Listen) ->
case gen_tcp:accept(Listen) of
{ok, S} ->
gen_tcp:send(S, io_lib:format("~p~n", [{date(), time()}])),
gen_tcp:close(S),
loop(Listen);
_ ->
loop(Listen)
end.
7 Compute the Digits of Pi
% http://shootout.alioth.debian.org/ contributed by Mark Scandariato
% erl -noshell -noinput -run pidigits main 7
-module(pidigits).
-export([main/1]).
is_safe(Z, N) -> N == extr(Z, 4).
next(Z) -> extr(Z, 3).
prod(Z, N) -> comp({10, -10*N, 0, 1}, Z).
cons(Z, Zp) -> comp(Z, Zp).
-define(unit, {1,0,0,1}).
comp({Q,R,S,T}, {Qp, Rp, Sp, Tp}) ->
{Q*Qp + R*Sp, Q*Rp + R*Tp, S*Qp + T*Sp, S*Rp + T*Tp}.
extr({Q,R,S,T}, X) -> (Q * X + R) div (S * X + T).
lft(K) -> {K, 4*K+2, 0, 2*K+1}.
stream(N) -> stream(N, 0, 1, ?unit, []).
stream(N, N, _, _, P) -> print(N,P);
stream(N, C, K, Z, P) ->
Y = next(Z),
case is_safe(Z, Y) of
true ->
stream(N, C+1, K, prod(Z,Y), update(C,Y,P));
false ->
stream(N, C, K+1, cons(Z, lft(K)), P)
end.
update(C, D, P) when C rem 10 == 0, C > 0 ->
print(C, P),
[D];
update(_, D, P) -> [D|P].
print(C, P) -> do_print(C, lists:reverse(P)).
do_print(C, []) when C rem 10 == 0 -> io:fwrite("\t:~p~n", [C]);
do_print(C, []) -> io:fwrite("~*.1c:~p~n", [10 - C rem 10, $\t, C]);
do_print(C, [H|T]) -> io:fwrite("~p", [H]), do_print(C, T).
main([Arg]) ->
N = list_to_integer(Arg),
main(N),
erlang:halt(0);
main(N) when N > 1 -> stream(N).
8 RESTful Services with Erlang and Yaws
- Yaws "Yet Another Web Server". Written in Erlang. For serving dynamic RESTful web.
- REST = Representational State Transfer. An architecture for large-scale distributed systems, like the web.
- Static web page servers: lighttpd, nginx
9 Erlang References
- http://www.erlang.org/ Download, etc. http://www.erlang.org/download/erlang-book-part1.pdf Legit download. This manuscript contains the complete text of Part I of "Concurrent programming in Erlang" (ISBN 0-13-508301-X). 2015
- http://www.infoq.com/articles/vinoski-erlang-rest
- http://rosettacode.org/ "Rosetta Code is a programming chrestomathy site. The idea is to present solutions to the same task in as many different languages as possible, to demonstrate how languages are similar and different, and to aid a person with a grounding in one approach to a problem in learning another. Rosetta Code currently has 766 tasks, 144 draft tasks, and is aware of 567 languages, though we do not (and cannot) have solutions to every task in every language." 2015