What is Erlang? Why it is important? Why should Python programmers learn Erlang? How is Erlang different? How is Erlang the same? These and other questions will be answered during this talk, as well as this one: Should Erlang be the new programming language you learn this year?

1. An Introduction to Erlang
for Python programmers
Paul Barry – Institute of Technology, Carlow in Ireland
PyCon Ireland 2011 - October 2011

2. Grab the slides:
http://paulbarry.itcarlow.ie/ErlangWebcast.pdf
2

3. Disclaimer
3

4. What exactly is Erlang?
4

5. “Erlang is a declarative,dynamically-typed,
functional, concurrent, distributed and
fault-tolerant programming language
with garbage collection and code
hot-swapping built into its runtime.”
Buzz-word city,
dude!
5

6. Scratching an itch in
the early '80s...
6

7. Why learn Erlang?
7

8. “Learn a new programming
language every year”
8

9. “Buy at least one new
programming book every year”
9

10. So, really, why learn Erlang?
10

11. A better programmer,
you will be...
11

12. Learn how others solve problems with a
different language, then apply these new
techniques to your current language
12

13. Learn what each language is good at,
then pick the right tool for the job
13

14. Works with a really big hammer!
14

15. What is Erlang good at?
15

16. What Erlang Wasn't Designed To Do
16

17. Erlang wasn't designed to...

Run in a browser

Process text efficiently

Be easy to teach

Be easy to learn

Build dynamic websites

Run on mobile phones

Allow non-programmers to program

Build GUIs
17

18. Erlang was designed to build
software systems that never stop
18

19. What exactly do you
mean by “never”?
19

20. “Never” at Ericsson means “no more
than 4 minutes downtime per year”...
http://www.infoq.com/presentations/Systems-that-Never-Stop-Joe-Armstrong 20

21. Wow! That's 5 nines
availability!*
21
* 99.999% uptime

22. Let's build software
that's 100% defect free!
22

23. Let's throw lots and lots
of code at the problem and
it'll go away, eh?
23

24. There has to be a better way
24

25. Let it crash!
Erlang programmers concentrate on
coding for the correct case
and crashing on failure
25

26. Robustness is achieved by having
programmers concentrate on processes and the
interactions (or messages) between them
26

27. Early error detection/recovery and the use
of concurrent programming techniques
lets you build fault tolerant systems
27

28. COP: Concurrency-Oriented Programming
28

29. The problem is...
29

30. The problem is...
Erlang is a little weird
30

31. Consider this code...
-module(hello_server).
-export([hello/0]).
hello() ->
receive
{FromPID, Who} ->
case Who of
robert -> FromPID ! "Hello Robert.";
mike -> FromPID ! "Hello Mike.";
joe -> FromPID ! "Hello Joe.";
_ -> FromPID ! "I don't know you."
end,
hello()
end.
31

32. Strange punctuation symbols . ; ,
-module(hello_server).
-export([hello/0]).
hello() ->
receive
{FromPID, Who} ->
case Who of
robert -> FromPID ! "Hello Robert.";
mike -> FromPID ! "Hello Mike.";
joe -> FromPID ! "Hello Joe.";
_ -> FromPID ! "I don't know you."
end,
hello()
end.
32

33. Lots of arrows -> in lots of places
-module(hello_server).
-export([hello/0]).
hello() ->
receive
{FromPID, Who} ->
case Who of
robert -> FromPID ! "Hello Robert.";
mike -> FromPID ! "Hello Mike.";
joe -> FromPID ! "Hello Joe.";
_ -> FromPID ! "I don't know you."
end,
hello()
end.
33

34. Even stranger symbols - _ !
-module(hello_server).
-export([hello/0]).
hello() ->
receive
{FromPID, Who} ->
case Who of
robert -> FromPID ! "Hello Robert.";
mike -> FromPID ! "Hello Mike.";
joe -> FromPID ! "Hello Joe.";
_ -> FromPID ! "I don't know you."
end,
hello()
end.
34

35. What's the deal with [] {} and () ?
-module(hello_server).
-export([hello/0]).
hello() ->
receive
{FromPID, Who} ->
case Who of
robert -> FromPID ! "Hello Robert.";
mike -> FromPID ! "Hello Mike.";
joe -> FromPID ! "Hello Joe.";
_ -> FromPID ! "I don't know you."
end,
hello()
end.
35

36. Functions that call themselves
-module(hello_server).
-export([hello/0]).
hello() ->
receive
{FromPID, Who} ->
case Who of
robert -> FromPID ! "Hello Robert.";
mike -> FromPID ! "Hello Mike.";
joe -> FromPID ! "Hello Joe.";
_ -> FromPID ! "I don't know you."
end,
hello()
end.
36

37. This is weird...
and there's even more
37

38. Erlang Culture Shock
38

39. Shock #1
Erlang's syntax is based on Prolog
-module(howdy).
-export([hi/1]).
hi(Name) ->
io:format('Hi there, ~p!~n', [Name]).
{person, First, Last} = {person, 'Paul', 'Barry'}.
howdy:hi(Last).
39

40. Shock #2
Erlang is not object-oriented
40

41. Shock #3
Everything in Erlang is immutable
Not just tuples and not just strings...
EVERYTHING
41

42. So... this doesn't work!
X = 10.
X = X + 1.
** exception error: no match of right hand side value 11
Y = X + 1.
42

43. Erlang's troublesome = operator
The “=” operator does not mean “assign”
It means “match” or “bind to”
43

44. No side effects here!
Destructive updates are forbidden
and (as an added twist)
Variables must start with an Uppercase letter:
X
Pid
Func
44

45. Shock #4
There are no built-in looping constructs
No for and no while
45

46. So... how do you loop?
46

47. List Comprehensions
Erlang:
Alist = [1, 2, 3, 4, 5].
Doubled = [X*2 || X <- Alist].
Python:
alist = [1, 2, 3, 4, 5]
doubled = [x*2 for x in alist]
Note: alist and doubled are mutable; Alist and Doubled are not
47

48. Shock #5
“Regular” looping is via recursion
48

49. Spot the loop?
-module(hello_server).
-export([hello/0]).
hello() ->
receive
{FromPID, Who} ->
case Who of
robert -> FromPID ! "Hello Robert.";
mike -> FromPID ! "Hello Mike.";
joe -> FromPID ! "Hello Joe.";
_ -> FromPID ! "I don't know you."
end,
hello()
49
end.

50. Shock #6
Strings are stored as a
list of integers
50

51. Sweet mother of all
things Erlang! Whose bright
idea was that?
51

52. Shock #7
There is no
if... then... else...
statement
52

53. There are if and case expressions
but... they're kinda weird
53

54. 54

55. With enough pig-headed persistence,
weirdness can be overcome
55

56. So... who do I call to
help me learn Erlang?
56

57. 57

58. 58

59. Erlang is a language you study
as getting up-to-speed with
Erlang takes time
59

60. Web Resources

http://www.erlang.org

Try Erlang:

http://www.tryerlang.org/

“Learn Some Erlang For Great Good!”:

http://learnyousomeerlang.com/

The Erlang Factory:

http://erlang-factory.com/

InfoQ:

http://www.infoq.com
60

61. Some Unique “Characteristics”
61

62. Banned by Ericsson in 1998 for
“not being open enough”
62

63. 63
http://video.google.com/videoplay?docid=-5830318882717959520

64. 64

65. This is all great, but...
how exactly do I use
Erlang to build a
fault-tolerant system?
65

66. Learn Three Things

Create an Erlang process with spawn()

Send a message to a process with !

Process a message with receive
66

67. Remember this code?
%% Saved in 'hello_server.erl'.
-module(hello_server).
-export([hello/0]).
hello() ->
receive
{FromPID, Who} ->
case Who of
robert -> FromPID ! "Hello Robert.";
mike -> FromPID ! "Hello Mike.";
joe -> FromPID ! "Hello Joe.";
_ -> FromPID ! "I don't know you."
end,
hello()
end. 67

68. Create the hello() process
Pid = spawn(fun hello_server:hello/0).
<0.38.0>
68

69. Send a message to a process with !
Pid ! robert.
robert
69

70. A little twist
Pid ! {self(), robert}.
{<0.31.0>,robert}
70

71. Messages sent to a process with !
are received by receive
71

72. Can you spot the pattern match?
%% Saved in 'hello_server.erl'.
-module(hello_server).
-export([hello/0]).
hello() ->
receive
{FromPID, Who} ->
case Who of
robert -> FromPID ! "Hello Robert.";
mike -> FromPID ! "Hello Mike.";
joe -> FromPID ! "Hello Joe.";
_ -> FromPID ! "I don't know you."
end,
hello()
end. 72

73. The {FromPID, Who} tuple matches
%% Saved in 'hello_server.erl'.
-module(hello_server).
-export([hello/0]).
hello() ->
receive
{FromPID, Who} ->
case Who of
robert -> FromPID ! "Hello Robert.";
mike -> FromPID ! "Hello Mike.";
joe -> FromPID ! "Hello Joe.";
_ -> FromPID ! "I don't know you."
end,
hello()
end. 73

74. Send a message back...
%% Saved in 'hello_server.erl'.
-module(hello_server).
-export([hello/0]).
hello() ->
receive
{FromPID, Who} ->
case Who of
robert -> FromPID ! "Hello Robert.";
mike -> FromPID ! "Hello Mike.";
joe -> FromPID ! "Hello Joe.";
_ -> FromPID ! "I don't know you."
end,
hello()
end. 74

75. spawn, send (!) then receive
Pid = spawn(fun hello_server:hello/0),
Pid ! {self(), robert},
receive
Response ->
Response
end.
"Hello Robert."
75

76. Things get really interesting
when the processes are
linked together with spawn_link()
and the trap_exit signal
76

77. Processes that are linked together can
react appropriately to EXIT messages from
each other... and what happens next is
controlled by the programmer
77

78. Distributed Erlang
I need to spawn
hello/0 hello/0 is
on glasnost... registered
pbmac.itcarlow.ie as 'hr'
78
glasnost.itcarlow.ie

79. Pid = spawn(fun hello_server:hello/0),
becomes
Pid = spawn(‘hr@glasnost.itcarlow.ie’, hello_server, hello, []),
79

80. Over time, you'll end up repeating
a lot of your process management code...
80

81. 81

82. OTP is the jewel in Erlang's crown
82

83. So... if Erlang's so
cool, how come no one
is using it?
83

84. The TIOBE Index
84

85. 85

86. Erlang in Telecoms
86

87. Erlang in Data
87

88. Erlang on the Web
88

89. Erlang in Gaming
“…Mochi Media is the world's
largest browser-based games
network, with more than 140 million
monthly active users and 15,000
games on nearly 40,000 publisher
websites…”
89
Check out Bob Ippolito’s Erlang-Factory talks!

90. More Erlang in Gaming
90
Thanks to Malcolm Dowse (of DemonWare, Dublin) for permission to use these
images, which were first delivered as part of Malcolm's talk to Erlang Factory London 2011.

91. So... is Erlang
worth learning?
91

92. Yes
92

93. Lots more to discover...

Fun with fun

Bit-strings and bit syntax

ETS and DETS

“Live” code updating

The Mnesia Distributed Database

The Standard Library

CEAN
93

94. Friendly Community
erlang-questions mailing list
94

95. Questions?
95