Erlang/OTP for Rubyists

Erlang/OTP for Rubyists Sean Cribbs KC.rb - July 2009

Ruby Makes easy things trivial and hard things fun!

Erlang Makes easy things possible and impossible things trivial! Orion Henry and Blake Mizerany (Heroku)

What is Erlang? •Language, Runtime and Libraries (OTP) •Developed and maintained by Ericsson •Started mid 1980s, open-sourced 1998

Who uses it?

Object-oriented Programming

object object object object object object object object object object object object Object-oriented object Programming object object object object object object object object object

Object-oriented Programming

Concurrency-oriented Programming

process process process process process process process process process process process process Concurrency-oriented process Programming process process process process process process process process process

Concurrency-oriented Programming

Fault-tolerance IFF Concurrency

Error Handling Intra-process Inter-process Inter-machine

Sharing doesn’t scale •Deadlocks •Race Conditions •Starvation •Synchronization •Data Locality •Corruption

Message passing is the answer

Cool Features •Concurrent •Distributed •Share-nothing •Fault-tolerant •Hot upgrades •Highly available

Big Differences •Functional - no objects •Single assignment, few side-effects •Initially challenging syntax •Nothing like gems

Are you ready to be UNCOMFORTABLY PARALLEL?

Spawn Pid = spawn( fun()-> io:format("Hello, Joe.") end).

Send Messages Pid ! {greet, “Joe”}.

Receive Messages loop() -> receive {greet,S} -> io:format(“Hello, ~s”, [S]), loop(); stop -> ok; _ -> loop() end.

Syntax Overview

Numbers 1 -1 2501 3.14 12345678987654321.987654321

Atoms foo type true false ‘EXIT’

Lists [1,2,3] [“dog”, “cat”, “ﬁsh”] “hello, world”

Tuples {name, “Sean”} {address, “8700 State Line Rd”, “Leawood”, “KS”} {{line, 10},{column,30}} {{2009,7,14},{19,0,0}}

Binaries <<“chunk of bytes”>> <<131,108,0,0,0,2,100,0,3,111,110,101,100 ,0,3,116,119,111, 106>>

Some Weirdos “abc” == [97,98,99]. % lists of bytes true, false % atoms $a == 97. % characters (ASCII) P#person.name % compile-time struct

Assignment

Pattern Matching

Pattern Matching A = 5. B = 10. Group = “KC.rb”.

Pattern Matching {Type, Value} = {username, “sean”}. [{username, Value}, {orders, Orders}] = [{username, “sean”}, {orders, [1,2,3]}].

Single Assignment Really, this is just pattern matching. A = 5. A = A + 1. % error: badmatch (5 = 6)

Lists functional programming’s old friend

List Operations [First|Rest] = [1,2,3,4,5]. [H|T] = [1,2,3,4,5]. List1 ++ List2.

List Comprehensions Think select/ﬁlter + map. A = [1,2,3,4,5]. [X * 2 || X <- A]. % [2,4,6,8,10] [X || X <- A, X rem 2 == 0]. % [2,4]

Functions even_or_odd(Num) -> if Num rem 2 == 0 -> even; true -> odd end.

Functions even_or_odd(N) when N rem 2 == 0 -> even; even_or_odd(N) -> odd.

Functions even_or_odd(N) when is_number(N), N rem 2 == 0 -> even; even_or_odd(N) when is_number(N) -> odd.

Anonymous Functions like lambda/proc, block Double = fun(X) -> 2*X end. Double(2). % 4 lists:map(Double, [1,2,3,4,5]). % [2,4,6,8,10]

No Loops! use recursion

A Little CS Theorem iterative === recursive

List “iteration” print([]) -> ok; print([H|T]) -> io:format(“~p”, [H]), print(T).

List “iteration” print([]) -> ok; print([H|T]) -> io:format(“~p”, [H]), print(T). print(T).

Normal Recursion loop() loop() loop() loop()

Tail Recursion (aka tail-call optimization) loop()

Concurrent programs can be complicated.

Behaviors “patterns” •gen_server - client-server •gen_fsm - state machine •supervisor - fault-tolerance

How does it scale? •Micro-benchmarks, arithmetic slow •Best for network(ed) apps •Campﬁre just as fast as C, ~ 2-4ms •Near-linear speedup on multicores •GC per-process, generational

Sean ! Questions.

http://seancribbs.com	143
http://coderwall.com	31
http://www.slideshare.net	13
http://www.linkedin.com	4
http://www.apurva.com	1

Erlang/OTP for Rubyists

by Sean Cribbs

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