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code-engine: sh

author: Colin MacDonald
email: colin@bluegraybox.com
title: Erlang Intro
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Erlang: Your New Favorite Scripting Language?

What’s cool about Erlang?

!SLIDE

Image by joguldi

Ok, but what do I do with it?

!SLIDE

Image by Stephen A. Wolfe

Procedural

Image from Pratham Books

Object-Oriented

Image from Frédéric Bisson

!SLIDE

Image from TheIguana

Functional

f(x)

What does that even mean?

!SLIDE

Image from Yun Huang Yong

Why?

Procedural

• 1 + 2 + 3 + 4 + 5 + … + n

Why?

Procedural

• 1 + 2 + 3 + 4 + 5 + … + n

Functional

• n(n+1)/2

Where are my curly braces?!

!SLIDE

• % comment

!SLIDE

• atom
• ‘atom’
• but not “atom”

!SLIDE

• Variable

!SLIDE

• [1, 2, 3] % list
• {1, 2, 3} % tuple

!SLIDE

• [X, Y, Z] = [1, 2, 3]

!SLIDE

• [First, Second | Rest] = [1, 2, 3, 4]
• [First, Second | Rest] = [1, 2]
• [First, Second] = [1, 2, 3, 4](error)
• [First, Second | _ ] = [1, 2, 3, 4]
• [First, Second | _Rest ] = [1, 2, 3, 4]

!SLIDE
{% code lang=erlang line_numbers=false }
my_func(Param1, … ) →
% intermediate stuff
Value.
{% end %}

!SLIDE
{% code lang=erlang line_numbers=false }
f(X) → X * 2.
{ end %}

!SLIDE

Image by Graeme Newcomb

!SLIDE

{% code lang=erlang line_numbers=false %}
my_func(Param1) →
my_func(Param1, “default”).

my_func(Param1, Param2) → %% actually do stuff…

{% end %}

!SLIDE
{% code lang=erlang line_numbers=false %}
my_func([]) → …

my_func([Only]) → … my_func([First, Second | Rest]) → …

{% end %}

!SLIDE
{% code lang=erlang line_numbers=false %}
my_func(0) → …

my_func(X) where X > 0 → … my_func(X) where X < 0 → …

{% end %}

!SLIDE
{% code lang=erlang line_numbers=false }
if
X >= 100 → 100;
X >= 0 → X;
true → 0
end
{ end %}

!SLIDE
{% code lang=erlang line_numbers=false }
case my_func(X) of
error → [];
List → List
end
{ end %}

!SLIDE
{% code lang=erlang line_numbers=false }
Output = case file:open(Filename, [read]) of
{ok, Handle} →
process_file(Handle);
{error, Reason} →
log_error(Reason, Filename),
[]
end.
{ end %}

• Output = process_file(Handle)
• Output = []

!SLIDE
{% code lang=erlang line_numbers=false %}
#!/usr/bin/escript

main(_Args) → io:format(“Hello World!~n”).

{% end %}

!SLIDE
{% code lang=erlang line_numbers=false %}
#!/usr/bin/escript

main(Args) → main(“World”, Args). main(_, [“-h” | _Args]) → io:format(“Help! Help!~n”); main(_, [“-n”, Name | Args]) → main(Name, Args); main(Name, []) → io:format(“Hello, ~s!~n”, [Name]).

{% end %}

!SLIDE

Image by chrisdlugosz

!SLIDE

       project
            action
            sub-project
                action
            action
        project
            sub-project
                sub-project
                    action

!SLIDE
p=. * work on presentation [computer, quiet] (2011-08-24) !!

!SLIDE

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Image from Wikimedia Commons

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!SLIDE

Image from O’Reilly Media

!SLIDE

Image from IMLS DCC

!SLIDE
{% code lang=java line_numbers=false }
String[] process(String[] input) {
String[] output = new String[input.length];
for (int i=0; i < input.length; i++) {
output[i] = do_stuff(input[i]);
}
return output;
}
{ end %}

!SLIDE
{% code lang=erlang line_numbers=false }
process([First|Rest], Output) →
NewFirst = do_stuff(First),
process(Rest, [NewFirst|Output]);
{ end %}

!SLIDE
{% code lang=erlang line_numbers=false %}
Output = process(Input, []).

process([First|Rest], Output) → NewFirst = do_stuff(First), process(Rest, [NewFirst|Output]); process([], Output) → lists:reverse(Output).

{% end %}

!SLIDE

Image by Brian Hillegas

!SLIDE

Image by Alex E. Proimos

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!SLIDE

Erlang: A kinder, gentler Lisp?

!SLIDE
{% code lang=erlang line_numbers=false %}
build_nodes([{Content, Indent}|Rest]) →
IsChild = fun({_C, I}) → I > Indent end,
{ChildLines, SiblingLines} = lists:splitwith(IsChild, Rest),
Children = build_nodes(ChildLines),
Siblings = build_nodes(SiblingLines),
[{Content, Children}|Siblings];

build_nodes([]) → [].

{% end %}

!SLIDE

Image by Sam Howzit

!SLIDE

Image from Wikipedia

!SLIDE
{% code lang=erlang line_numbers=false %}
score(Rolls) → frame(Rolls, 1, 0).

frame(_BonusRolls, 11, Score) → Score; frame([10|Rest], Frame, Score) → [Bonus1, Bonus2|_] = Rest, frame(Rest, Frame + 1, Score + 10 + Bonus1 + Bonus2); frame([First,Second|Rest], Frame, Score) when (First+Second==10)→ [Bonus1|_] = Rest, frame(Rest, Frame + 1, Score + 10 + Bonus1); frame([First,Second|Rest], Frame, Score) → frame(Rest, Frame + 1, Score + First + Second).

{% end %}

!SLIDE
{% code lang=erlang line_numbers=false %}
test() →
test(0, [0,0, 0,0, 0,0, 0,0, 0,0, 0,0, 0,0, 0,0, 0,0, 0,0]),
test(20, [1,1, 1,1, 1,1, 1,1, 1,1, 1,1, 1,1, 1,1, 1,1, 1,1]),
test(150, [5,5, 5,5, 5,5, 5,5, 5,5, 5,5, 5,5, 5,5, 5,5, 5,5, 5]),
test(47, [1,1, 1,1, 1,1, 1,1, 1,1, 1,1, 1,1, 1,1, 1,1, 10, 10 ,9]),
test(173, [7,3, 7,3, 7,3, 7,3, 7,3, 7,3, 7,3, 7,3, 7,3, 7,3, 10]),

test(Expected, Rolls) → case score(Rolls) of Expected → io:fwrite(“Pass~n”); Scored → io:fwrite(“Fail: expected=~p, scored=~p~n”, [Expected, Scored]) end.

{% end %}

!SLIDE

Image by Foxtongue

!SLIDE

Image by Cass Chin

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Image by orsocurioso

!SLIDE

Image by Shedking

!SLIDE

Image by dullhunk

!SLIDE

Image by somethingcommon

Colin MacDonald

• colin@bluegraybox.com
• http://bluegraybox.com
• https://github.com/bluegraybox/erlang_intro/
• http://bluegraybox.github.com/erlang_intro/