Triskelion and Crapshoot

Triskelion
and
Crapshoot
Miami Ruby Brigade
January 17, 2010

Monday, January 17, 2011

Triskelion and Crapshoot
•Triskelion - Rails application
•UI Elements
•Crapshoot - Dice-rolling library
•Parsing with Ragel
•Inﬁx and Postﬁx Notation
•Random numbers


Pen and Paper Games
Pens
Paper Talking
Dice Snacks
Books

m p
sta
e
T im


m p e
sta am
e N
T im


m p e d e
sta am c o
e N rip
T im T


m p e d e n t
sta am c o n te
m e N Trip C o
T i


Colored Name
Easier to read than text-only nickname
Shift the ﬁrst few bytes of hash into LSBs of color

  def chat_color
    digest = Digest::SHA1.hexdigest(self.tripcode +
self.name)
    r = (digest[0..1].to_i(16) >> 1) + 127
    g = (digest[2..3].to_i(16) >> 1) + 127
    b = (digest[4..5].to_i(16) >> 1) + 127
    "##{r.to_s 16}#{g.to_s 16}#{b.to_s 16}"
  end

Tripcode
Identity without Password or Registration
Used on 4chan

  def tripcode_digest
    [Digest::SHA1.digest(self.tripcode)].
pack('m').
tr('+/','-_')[0..7]
  end


Chat
auto_link chat.content,
:html=>{:target=>'_blank'}


Chat
auto_link chat.content,
:html=>{:target=>'_blank'}

http://www.ﬂickr.com/photos/lostvegas/2214183472/


Roll

4d6v + 40 =57 ((3+5+6+6-3)+40)

<%=h roll.code %>

<%=h roll.result %>

<%=h roll.description %>

Dice Code
•2d4
•Two four-sided dice
•1d100 + 8
•One hundred-sided die plus eight
•4d6v
•Four six-sided dice, minus the lowest


Dice Language

A programming language is […] designed to
express computations, […] to express
algorithms precisely, or as a mode of human
communication.
http://en.wikipedia.org/wiki/Programming_language


Regular Language
In computer science, a regular language is a formal
language […] that satisﬁes the following equivalent
properties:
•it can be accepted by a deterministic ﬁnite state
machine
•it can be generated by a regular grammar
http://en.wikipedia.org/wiki/Regular_language


Dice Language
4d6v + 3d10^ – 2d6 - 300


Dice Language
4d6v + 3d10^ – 2d6 - 300
Expression


Dice Language
2d6 - 300


Dice Language
2d6 - 300
BinaryExpression


Dice Language
2d6
-
300

Dice Language
2d6 Series
-
300

Dice Language
2d6 Series
Arithmetic -
300

Dice Language
2d6 Series
Arithmetic -
Constant 300

Dice Language
0 % D
0 IE
1 F
Number = digit+; I
T AR
R L
E U
Constant = Number; C G G E
E UA
R G
Drop = ('^' | 'v'); N
Series = Number 'd' Number Drop?; LA
Arithmetic = ('+' | '-');

UnaryExpression = Series | Constant;
BinaryExpression = UnaryExpression (space* Arithmetic space* UnaryExpression)+;
Expression = UnaryExpression | BinaryExpression;


Ragel

Ragel compiles executable ﬁnite state machines from regular
languages. Ragel targets C, C++, Objective-C, D, Java and
Ruby.
http://www.complang.org/ragel/


scan.rl
%%{
 machine scanner;

 action _number { @mark_num = p }

Language Actions
 action number { @num_stack.push atos(data[@mark_num..p-1]) }

 action constant { @tokens << Tokens::Constant.new(@num_stack.pop) }
 action series {
 drop = @drop_current
 @drop_current = nil
 sides = @num_stack.pop
 count = @num_stack.pop
 @tokens << Tokens::Series.new(count, sides, drop)
 }
 action arithmetic { @tokens << Tokens::Arithmetic.new(data[p-1].chr) }

 action drop { @drop_current = data[p-1].chr }

 Number = digit+ >_number %number;

 Constant = Number %constant;

 Drop = ('^' | 'v') %drop;
 Series = Number 'd' Number Drop? %series;

 Arithmetic = ('+' | '-') %arithmetic;

 UnaryExpression = Series | Constant;
 BinaryExpression = UnaryExpression (space* Arithmetic space* UnaryExpression)+;
 Expression = UnaryExpression | BinaryExpression;

 main := Expression;
}%%

Ragel


Ragel
scan.rl: 62 lines


Ragel
scan.rl: 62 lines
scan.rb: 330 lines


Ragel
scan.rl: 62 lines
scan.rb: 330 lines
scan.pdf: priceless


scan.rl
Transform constant, series, and arithmetic elements into
Token objects

 action constant { @tokens << Tokens::Constant.new(@num_stack.pop) }
 action series {
 drop = @drop_current
 @drop_current = nil
 sides = @num_stack.pop
 count = @num_stack.pop
 @tokens << Tokens::Series.new(count, sides, drop)
 }
 action arithmetic { @tokens << Tokens::Arithmetic.new(data[p-1].chr) }

Tokens
Token#eval
Turn token into result during evaluation

Token#independent
Determine if token needs the next token during postﬁxing

Token#inspect
<Crapshoot::Tokens::Series dice=4d6 drop=nothing>

Parsed Dice
4d6v + 3d10^ - 2d6 - 300
count: 4 count: 3 count: 2 value: 300
sides: 6 sides: 10 sides: 6
drop: ‘v’ drop: ‘^’ drop: nil


Inﬁx & Postﬁx


Infix & Postfix

Infix
1+2+3+4
Used for centuries
Hard for computers


Infix & Postfix

Infix Postfix
1+2+3+4 12+3+4+
Used for centuries Easy for computers
Hard for computers Convertible from infix


Postﬁxed Dice
4d6v 3d10^ + 2d6 - 300 -


Postﬁx Evaluation


Postﬁx Evaluation

•Series


Postﬁx Evaluation

•Series
•Roll dice


Postﬁx Evaluation

•Series
•Roll dice
•Do drop


Postﬁx Evaluation

•Series
•Roll dice
•Do drop
•Push result to stack


Postﬁx Evaluation

•Constant
•Series
•Roll dice
•Do drop


Postﬁx Evaluation

•Constant
•Series
•Push value to stack
•Roll dice
•Do drop


Postﬁx Evaluation

•Constant
•Series
•Roll dice
•Arithmetic
•Do drop


Postﬁx Evaluation

•Constant
•Series
•Roll dice
•Arithmetic
•Do drop
•Pop twice


Postﬁx Evaluation

•Constant
•Series
•Roll dice
•Arithmetic
•Do drop
•Pop twice
•Push result


Postﬁx Evaluation
4d6v 3d10^ + 2d6 - 300 -

Stack


Postﬁx Evaluation
15 3d10^ + 2d6 - 300 -
count: 3 count: 2 value: 300
sides: 10 sides: 6
drop: ‘^’ drop: nil

Stack


Postﬁx Evaluation
3d10^ + 2d6 - 300 -
count: 3 count: 2 value: 300
sides: 10 sides: 6
drop: ‘^’ drop: nil

Stack

15

Postﬁx Evaluation
5 + 2d6 - 300 -
count: 2 value: 300
sides: 6
drop: nil

Stack

15

Postﬁx Evaluation
+ 2d6 - 300 -
count: 2 value: 300
sides: 6
drop: nil

Stack

15 5

Postﬁx Evaluation
2d6 - 300 -
count: 2 value: 300
sides: 6
drop: nil

Stack

15 + 5

Postﬁx Evaluation
2d6 - 300 -
count: 2 value: 300
sides: 6
drop: nil

Stack

20

Postﬁx Evaluation
9 - 300 -
value: 300

Stack

20

Postﬁx Evaluation
- 300 -
value: 300

Stack

20 9

Postﬁx Evaluation
300 -
value: 300

Stack

20 - 9

Postﬁx Evaluation
300 -
value: 300

Stack

11

Postﬁx Evaluation
300 -

Stack

11

Postﬁx Evaluation
-

Stack

11 300

Postﬁx Evaluation

Stack

11 - 300

Postﬁx Evaluation

Stack

-289

Result

-289


Randomness

Computers are deterministic
Gather and store entropy where
possible
Use secure hashes to disburse entropy


Randomness

Just use
OpenSSL

SecureRandom

Ruby 1.9 and ActiveSupport
random_number
random_bytes
hex


Triskelion and Crapshoot

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