Ruby Training Notes

~/dev/ruby $ ruby ex1.rb

Hello World!
Hello Again
I like typing this.
This is fun.
Yay! Printing.
I'd much rather you 'not'.
I "said" do not touch this.
		

ex1.rb:

puts "Hello World!"
puts "Hello Again"
puts "I like typing this."
puts "This is fun."
puts 'Yay! Printing.'
puts "I'd much rather you 'not'."
puts 'I "said" do not touch this.'
		

~/dev/ruby $ ruby ex2.rb

I could have code like this.
This will run.
		

ex2.rb:

# A comment, this is so you can read your program later.
# Anything after the # is ignored by Ruby.

puts "I could have code like this." # and the comment after is ignored

# You can also use a comment to "disable" or comment out a piece of code:
# puts "This won't run."

puts "This will run."
		

~/dev/ruby $ ruby ex3.rb

I will now count my chickens:
Hens
30
Roosters
97
Now I will count the eggs:
7
Is it true that 3 + 2 < 5 - 7?
false
What is 3 + 2?
5
What is 5 - 7?
-2
Oh, that's why it's false.
How about some more.
Is it greater?
true
Is it greater or equal?
true
Is it less or equal?
false
		

ex3.rb:

puts "I will now count my chickens:"

puts "Hens", 25 + 30 / 6
puts "Roosters", 100 - 25 * 3 % 4

puts "Now I will count the eggs:"

puts 3 + 2 + 1 - 5 + 4 % 2 - 1 / 4 + 6

puts "Is it true that 3 + 2 < 5 - 7?"

puts 3 + 2 < 5 - 7

puts "What is 3 + 2?", 3 + 2
puts "What is 5 - 7?", 5 - 7

puts "Oh, that's why it's false."

puts "How about some more."

puts "Is it greater?", 5 > -2
puts "Is it greater or equal?", 5 >= -2
puts "Is it less or equal?", 5 <= -2
		

~/dev/ruby $ ruby ex4.rb

There are 100 cars available.
There are only 30 drivers available.
There will be 70 empty cars today.
We can transport 120.0 people today.
We have 90 passengers to carpool today.
We need to put about 3 in each car.
		

ex4.rb:

cars = 100
space_in_a_car = 4.0
drivers = 30
passengers = 90
cars_not_driven = cars - drivers
cars_driven = drivers
carpool_capacity = cars_driven * space_in_a_car
average_passengers_per_car = passengers / cars_driven

puts "There are #{cars} cars available."
puts "There are only #{drivers} drivers available."
puts "There will be #{cars_not_driven} empty cars today."
puts "We can transport #{carpool_capacity} people today."
puts "We have #{passengers} passengers to carpool today."
puts "We need to put about #{average_passengers_per_car} in each car."

~/dev/ruby $ ruby ex5.rb

Let's talk about Zed A. Shaw.
He's 74 inches tall.
He's 180 pounds heavy.
Actually that's not too heavy.
He's got Blue eyes and Brown hair.
His teeth are usually White depending on the coffee.
If I add 35, 74, and 180 I get 289.
		

ex5.rb:

my_name = 'Zed A. Shaw'
my_age = 35 # not a lie
my_height = 74 # inches
my_weight = 180 # lbs
my_eyes = 'Blue'
my_teeth = 'White'
my_hair = 'Brown'

puts "Let's talk about %s." % my_name
puts "He's %d inches tall." % my_height
puts "He's %d pounds heavy." % my_weight
puts "Actually that's not too heavy."
puts "He's got %s eyes and %s hair." % [my_eyes, my_hair]
puts "His teeth are usually %s depending on the coffee." % my_teeth

# this line is tricky, try to get it exactly right
puts "If I add %d, %d, and %d I get %d." % [
    my_age, my_height, my_weight, my_age + my_height + my_weight]
		

~/dev/ruby $ ruby ex6.rb

There are 10 types of people.
Those who know binary and those who don't.
I said: There are 10 types of people..
I also said: 'Those who know binary and those who don't.'.
Isn't that joke so funny?! false
This is the left side of...a string with a right side.
		

ex6.rb:

x = "There are #{10} types of people."
binary = "binary"
do_not = "don't"
y = "Those who know #{binary} and those who #{do_not}."

puts x
puts y

puts "I said: #{x}."
puts "I also said: '#{y}'."

hilarious = false
joke_evaluation = "Isn't that joke so funny?! #{hilarious}"

puts joke_evaluation

w = "This is the left side of..."
e = "a string with a right side."

puts w + e
		

~/dev/ruby $ ruby ex7.rb

Mary had a little lamb.
Its fleece was white as snow.
And everywhere that Mary went.
..........
CheeseBurger
		

ex7.rb:

puts "Mary had a little lamb."
puts "Its fleece was white as %s." % 'snow'
puts "And everywhere that Mary went."
puts "." * 10  # what'd that do?

end1 = "C"
end2 = "h"
end3 = "e"
end4 = "e"
end5 = "s"
end6 = "e"
end7 = "B"
end8 = "u"
end9 = "r"
end10 = "g"
end11 = "e"
end12 = "r"

# notice how we are using print instead of puts here. change it to puts
# and see what happens.
print end1 + end2 + end3 + end4 + end5 + end6
print end7 + end8 + end9 + end10 + end11 + end12

# this just is polite use of the terminal, try removing it
puts
		

~/dev/ruby $ ruby ex8.rb

1 2 3 4
one two three four
true false false true
%s %s %s %s %s %s %s %s %s %s %s %s %s %s %s %s
I had this thing. That you could type up right. But it didn't sing. So I said goodnight.
		

ex8.rb:

formatter = "%s %s %s %s"

puts formatter % [1, 2, 3, 4]
puts formatter % ["one", "two", "three", "four"]
puts formatter % [true, false, false, true]
puts formatter % [formatter, formatter, formatter, formatter]
puts formatter % [
    "I had this thing.",
    "That you could type up right.",
    "But it didn't sing.",
    "So I said goodnight."
]
		

~/dev/ruby $ ruby ex9.rb

Here are the days:
Mon Tue Wed Thu Fri Sat Sun
Here are the months:
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
There's something going on here.
With the PARAGRAPH thing
We'll be able to type as much as we like.
Even 4 lines if we want, or 5, or 6.
		

ex9.rb:

# Here's some new strange stuff, remember type it exactly.

days = "Mon Tue Wed Thu Fri Sat Sun"
months = "Jan\nFeb\nMar\nApr\nMay\nJun\nJul\nAug"

puts "Here are the days: ", days
puts "Here are the months: ", months

puts <<PARAGRAPH
There's something going on here.
With the PARAGRAPH thing
We'll be able to type as much as we like.
Even 4 lines if we want, or 5, or 6.
PARAGRAPH
		

~/dev/ruby $ ruby ex10.rb

	I'm tabbed in.
I'm split
on a line.
I'm \ a \ cat.
I'll do a list:
	* Cat food
	* Fishies
	* Catnip
	* Grass
		

ex10.rb:

tabby_cat = "\tI'm tabbed in."
persian_cat = "I'm split\non a line."
backslash_cat = "I'm \\ a \\ cat."

fat_cat = <<MY_HEREDOC
I'll do a list:
\t* Cat food
\t* Fishies
\t* Catnip\n\t* Grass
MY_HEREDOC

puts tabby_cat
puts persian_cat
puts backslash_cat
puts fat_cat
		

~/dev/ruby $ ruby ex11.rb

How old are you? 35
How tall are you? 6'2"
How much do you weigh? 180lbs
So, you're 35 years old, 6'2" tall and 180lbs heavy.
		

ex11.rb:

print "How old are you? "
age = gets.chomp()
print "How tall are you? "
height = gets.chomp()
print "How much do you weigh? "
weight = gets.chomp()

puts "So, you're #{age} years old, #{height} tall and #{weight} heavy."
		

~/dev/ruby $ ruby ex12.rb

/usr/lib/ruby/1.9.1/net/http.rb:762:in `initialize': getaddrinfo: \
    Name or service not known (SocketError)
	from /usr/lib/ruby/1.9.1/net/http.rb:762:in `open'
	from /usr/lib/ruby/1.9.1/net/http.rb:762:in `block in connect'
	from /usr/lib/ruby/1.9.1/timeout.rb:54:in `timeout'
	from /usr/lib/ruby/1.9.1/timeout.rb:99:in `timeout'
	from /usr/lib/ruby/1.9.1/net/http.rb:762:in `connect'
	from /usr/lib/ruby/1.9.1/net/http.rb:755:in `do_start'
	from /usr/lib/ruby/1.9.1/net/http.rb:744:in `start'
	from /usr/lib/ruby/1.9.1/open-uri.rb:306:in `open_http'
	from /usr/lib/ruby/1.9.1/open-uri.rb:775:in `buffer_open'
	from /usr/lib/ruby/1.9.1/open-uri.rb:203:in `block in open_loop'
	from /usr/lib/ruby/1.9.1/open-uri.rb:201:in `catch'
	from /usr/lib/ruby/1.9.1/open-uri.rb:201:in `open_loop'
	from /usr/lib/ruby/1.9.1/open-uri.rb:146:in `open_uri'
	from /usr/lib/ruby/1.9.1/open-uri.rb:677:in `open'
	from /usr/lib/ruby/1.9.1/open-uri.rb:33:in `open'
	from ex12.rb:3:in `
'
		

ex12.rb:

require 'open-uri'

open("http://www.ruby-lang.org/en") do |f|
  f.each_line {|line| p line}
  puts f.base_uri         # <URI::HTTP:0x40e6ef2 URL:http://www.ruby-lang.org/en/>
  puts f.content_type     # "text/html"
  puts f.charset          # "iso-8859-1"
  puts f.content_encoding # []
  puts f.last_modified    # Thu Dec 05 02:45:02 UTC 2002
end
		

~/dev/ruby $ ruby ex13.rb first 2nd 3rd
~/dev/ruby $ ruby ex13.rb cheese apples bread
~/dev/ruby $ ruby ex13.rb Zed A. Shaw
~/dev/ruby $ ruby ex13.rb

The script is called: ex13.rb
Your first variable is: first
Your second variable is: 2nd
Your third variable is: 3rd

The script is called: ex13.rb
Your first variable is: cheese
Your second variable is: apples
Your third variable is: bread

The script is called: ex13.rb
Your first variable is: Zed
Your second variable is: A.
Your third variable is: Shaw

The script is called: ex13.rb
Your first variable is:
Your second variable is:
Your third variable is:
		

ex13.rb:

first, second, third = ARGV

puts "The script is called: #{$0}"
puts "Your first variable is: #{first}"
puts "Your second variable is: #{second}"
puts "Your third variable is: #{third}"
		

~/dev/ruby $ ruby ex14.rb Zed

Hi Zed, I'm the ex14.rb script.
I'd like to ask you a few questions.
Do you like me Zed?
> Yes, I wrote you
Where do you live Zed?
> The Rocky Mountains
What kind of computer do you have?
> I built it myself
Alright, so you said Yes, I wrote you about liking me.
You live in The Rocky Mountains.  Not sure where that is.
And you have a I built it myself computer.  Nice.
		

ex14.rb:

user = ARGV.first
prompt = '> '

puts "Hi #{user}, I'm the #{$0} script."
puts "I'd like to ask you a few questions."
puts "Do you like me #{user}?"
print prompt
likes = STDIN.gets.chomp()

puts "Where do you live #{user}?"
print prompt
lives = STDIN.gets.chomp()

puts "What kind of computer do you have?"
print prompt
computer = STDIN.gets.chomp()

puts <<MESSAGE
Alright, so you said #{likes} about liking me.
You live in #{lives}.  Not sure where that is.
And you have a #{computer} computer.  Nice.
MESSAGE
		

~/dev/ruby $ ruby ex15.rb ex15_sample.txt

Here's your file: ex15_sample.txt
This is stuff I typed into a file.
It is really cool stuff.
Lots and lots of fun to have in here.
I'll also ask you to type it again:
> ex15_sample.txt
This is stuff I typed into a file.
It is really cool stuff.
Lots and lots of fun to have in here.
		

ex15.rb:

filename = ARGV.first

prompt = "> "
txt = File.open(filename)

puts "Here's your file: #{filename}"
puts txt.read()
close()

puts "I'll also ask you to type it again:"
print prompt
file_again = STDIN.gets.chomp()

txt_again = File.open(file_again)

puts txt_again.read()
again.close()
		

File ex15_sample.txt:

This is stuff I typed into a file.
It is really cool stuff.
Lots and lots of fun to have in here.
		

~/dev/ruby $ touch test.txt
~/dev/ruby $ ruby ex16.rb test.txt

We're going to erase test.txt.
If you don't want that, hit CTRL-C (^C).
If you do want that, hit RETURN.
?
Opening the file...
Truncating the file.  Goodbye!
Now I'm going to ask you for three lines.
line 1: To all the people out there.
line 2: I say I don't like my hair.
line 3: I need to shave it off.
I'm going to write these to the file.
And finally, we close it.
		

~/dev/ruby $ cat test.txt

To all the people out there.
I say I don't like my hair.
I need to shave it off.
		

ex16.rb:

filename = ARGV.first
script = $0

puts "We're going to erase #{filename}."
puts "If you don't want that, hit CTRL-C (^C)."
puts "If you do want that, hit RETURN."

print "? "
STDIN.gets

puts "Opening the file..."
target = File.open(filename, 'w')

puts "Truncating the file.  Goodbye!"
target.truncate(target.size)

puts "Now I'm going to ask you for three lines."

print "line 1: "; line1 = STDIN.gets.chomp()
print "line 2: "; line2 = STDIN.gets.chomp()
print "line 3: "; line3 = STDIN.gets.chomp()

puts "I'm going to write these to the file."

target.write(line1)
target.write("\n")
target.write(line2)
target.write("\n")
target.write(line3)
target.write("\n")

puts "And finally, we close it."
target.close()
		

~/dev/ruby $ ruby ex17.rb test.txt copied.txt

Copying from test.txt to copied.txt
The input file is 81 bytes long
Does the output file exist? false
Ready, hit RETURN to continue, CTRL-C to abort.

Alright, all done.
		

~/dev/ruby $ cat copied.txt

To all the people out there.
I say I don't like my hair.
I need to shave it off.
		

ex17.rb:

from_file, to_file = ARGV
script = $0

puts "Copying from #{from_file} to #{to_file}"

# we could do these two on one line too, how?
input = File.open(from_file)
indata = input.read()

puts "The input file is #{indata.length} bytes long"

puts "Does the output file exist? #{File.exists? to_file}"
puts "Ready, hit RETURN to continue, CTRL-C to abort."
STDIN.gets

output = File.open(to_file, 'w')
output.write(indata)

puts "Alright, all done."

output.close()
input.close()
		

~/dev/ruby $ ruby ex18.rb

arg1: Zed, arg2: Shaw
arg1: Zed, arg2: Shaw
arg1: First!
I got nothin'.
		

ex18.rb:

# this one is like your scripts with argv
def puts_two(*args)
  arg1, arg2 = args
  puts "arg1: #{arg1}, arg2: #{arg2}"
end

# ok, that *args is actually pointless, we can just do this
def puts_two_again(arg1, arg2)
  puts "arg1: #{arg1}, arg2: #{arg2}"
end

# this just takes one argument
def puts_one(arg1)
  puts "arg1: #{arg1}"
end

# this one takes no arguments
def puts_none()
  puts "I got nothin'."
end

puts_two("Zed","Shaw")
puts_two_again("Zed","Shaw")
puts_one("First!")
puts_none()
		

~/dev/ruby $ ruby ex19.rb

We can just give the function numbers directly:
You have 20 cheeses!
You have 30 boxes of crackers!
Man that's enough for a party!
Get a blanket.

OR, we can use variables from our script:
You have 10 cheeses!
You have 50 boxes of crackers!
Man that's enough for a party!
Get a blanket.

We can even do math inside too:
You have 30 cheeses!
You have 11 boxes of crackers!
Man that's enough for a party!
Get a blanket.

And we can combine the two, variables and math:
You have 110 cheeses!
You have 1050 boxes of crackers!
Man that's enough for a party!
Get a blanket.
		

ex19.rb:

def cheese_and_crackers(cheese_count, boxes_of_crackers)
  puts "You have #{cheese_count} cheeses!"
  puts "You have #{boxes_of_crackers} boxes of crackers!"
  puts "Man that's enough for a party!"
  puts "Get a blanket."
  puts # a blank line
end

puts "We can just give the function numbers directly:"
cheese_and_crackers(20, 30)

puts "OR, we can use variables from our script:"
amount_of_cheese = 10
amount_of_crackers = 50
cheese_and_crackers(amount_of_cheese, amount_of_crackers)

puts "We can even do math inside too:"
cheese_and_crackers(10 + 20, 5 + 6)

puts "And we can combine the two, variables and math:"
cheese_and_crackers(amount_of_cheese + 100, amount_of_crackers + 1000)
		

~/dev/ruby $ ruby ex20.rb

First let's print the whole file:

To all the people out there.
I say I don't like my hair.
I need to shave it off.
Now let's rewind, kind of like a tape.
Let's print three lines:
1 To all the people out there.
2 I say I don't like my hair.
3 I need to shave it off.
		

ex20.rb:

input_file = ARGV[0]

def print_all(f)
  puts f.read()
end

def rewind(f)
  f.seek(0, IO::SEEK_SET)
end

def print_a_line(line_count, f)
  puts "#{line_count} #{f.readline()}"
end

current_file = File.open(input_file)

puts "First let's print the whole file:"
puts # a blank line

print_all(current_file)

puts "Now let's rewind, kind of like a tape."

rewind(current_file)

puts "Let's print three lines:"

current_line = 1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)
		

~/dev/ruby $ ruby ex21.rb

Let's do some math with just functions!
ADDING 30 + 5
SUBTRACTING 78 - 4
MULTIPLYING 90 * 2
DIVIDING 100 / 2
Age: 35, Height: 74, Weight: 180, IQ: 50
Here is a puzzle.
DIVIDING 50 / 2
MULTIPLYING 180 * 25
SUBTRACTING 74 - 4500
ADDING 35 + -4426
That becomes: -4391 Can you do it by hand?
		

ex21.rb:

def add(a, b)
  puts "ADDING #{a} + #{b}"
  a + b
end

def subtract(a, b)
  puts "SUBTRACTING #{a} - #{b}"
  a - b
end

def multiply(a, b)
  puts "MULTIPLYING #{a} * #{b}"
  a * b
end

def divide(a, b)
  puts "DIVIDING #{a} / #{b}"
  a / b
end

puts "Let's do some math with just functions!"

age = add(30, 5)
height = subtract(78,4)
weight = multiply(90, 2)
iq = divide(100, 2)

puts "Age: #{age}, Height: #{height}, Weight: #{weight}, IQ: #{iq}"

# A puzzle for the extra credit, type it in anyway.
puts "Here is a puzzle."

what = add(age, subtract(height, multiply(weight, divide(iq, 2))))

puts "That becomes: #{what} Can you do it by hand?"
		

~/dev/ruby $ ruby ex24.rb

Let's practice everything.
You'd need to know 'bout escapes with \ that do
 newlines and 	 tabs.
--------------

	The lovely world
with logic so firmly planted
cannot discern
 the needs of love
nor comprehend passion from intuition
and requires an explanation

		where there is none.

--------------
This should be five: 5
With a starting point of: 10000
We'd have 5000000 beans, 5000 jars, and 50 crates.
We can also do that this way:
We'd have 500000 beans, 500 jars, and 5 crates.
		

ex24.rb:

puts "Let's practice everything."
puts "You\'d need to know \'bout escapes with \\ that do \n newlines and \t tabs."

poem = <<MULTI_LINE_STRING

\tThe lovely world
with logic so firmly planted
cannot discern \n the needs of love
nor comprehend passion from intuition
and requires an explanation
\n\t\twhere there is none.

MULTI_LINE_STRING

puts "--------------"
puts poem
puts "--------------"

five = 10 - 2 + 3 - 6
puts "This should be five: #{five}"

def secret_formula(started)
  jelly_beans = started * 500
  jars = jelly_beans / 1000
  crates = jars / 100
  return jelly_beans, jars, crates
end

start_point = 10000
beans, jars, crates = secret_formula(start_point)

puts "With a starting point of: #{start_point}"
puts "We'd have #{beans} beans, #{jars} jars, and #{crates} crates."

start_point = start_point / 10

puts "We can also do that this way:"
puts "We'd have %s beans, %s jars, and %s crates." % secret_formula(start_point)
		

~/dev/ruby $ ruby ex25.rb

(nothing)
		

~/dev/ruby $ irb

irb(main):001:0> require './ex25.rb'
=> true
irb(main):002:0> sentence = "All good things come to those who wait."
=> "All good things come to those who wait."
irb(main):003:0> words = Ex25.break_words( sentence )
=> ["All", "good", "things", "come", "to", "those", "who", "wait."]
irb(main):004:0> sorted_words = Ex25.sort_words( words )
=> ["All", "come", "good", "things", "those", "to", "wait.", "who"]
irb(main):005:0> Ex25.print_first_word( words )
All
=> nil
irb(main):006:0> Ex25.print_last_word( words )
wait.
=> nil
irb(main):007:0> Ex25.wrods
NoMethodError: undefined method `wrods' for Ex25:Module
	from (irb):7
	from /usr/bin/irb:12:in `<main>'
irb(main):008:0> words
=> ["good", "things", "come", "to", "those", "who"]
irb(main):009:0> Ex25.print_first_word( sorted_words )
All
=> nil
irb(main):010:0> Ex25.print_last_word( sorted_words )
who
=> nil
irb(main):011:0> sorted_words
=> ["come", "good", "things", "those", "to", "wait."]
irb(main):012:0> Ex25.sort_sentence( sentence )
=> ["All", "come", "good", "things", "those", "to", "wait.", "who"]
irb(main):013:0> Ex25.print_first_and_last( sentence )
All
wait.
=> nil
irb(main):014:0> Ex25.print_first_and_last_sorted( sentence )
All
who
=> nil
irb(main):015:0>
		

ex25.rb:

module Ex25
  def self.break_words(stuff)
    # This function will break up words for us.
    words = stuff.split(' ')
    words
  end

  def self.sort_words(words)
    # Sorts the words.
    words.sort()
  end

  def self.print_first_word(words)
    # Prints the first word and shifts the others down by one.
    word = words.shift()
    puts word
  end

  def self.print_last_word(words)
    # Prints the last word after popping it off the end.
    word = words.pop()
    puts word
  end

  def self.sort_sentence(sentence)
    # Takes in a full sentence and returns the sorted words.
    words = break_words(sentence)
    sort_words(words)
  end

  def self.print_first_and_last(sentence)
    # Prints the first and last words of the sentence.
    words = break_words(sentence)
    print_first_word(words)
    print_last_word(words)
  end

  def self.print_first_and_last_sorted(sentence)
    # Sorts the words then prints the first and last one.
    words = sort_sentence(sentence)
    print_first_word(words)
    print_last_word(words)
  end
end
		

~/dev/ruby $ ruby ex29.rb

Too many cats! The world is doomed!
The world is dry!
People are greater than or equal to dogs.
People are less than or equal to dogs.
People are dogs.
My parens work.   
		

ex29.rb:

people = 20
cats = 30
dogs = 15

if people < cats
  puts "Too many cats! The world is doomed!"
end

if people > cats
  puts "Not many cats! The world is saved!"
end

if people < dogs
  puts "The world is drooled on!"
end

if people > dogs
  puts "The world is dry!"
end

dogs += 5

if people >= dogs
  puts "People are greater than or equal to dogs."
end

if people <= dogs
  puts "People are less than or equal to dogs."
end

if people == dogs
  puts "People are dogs."
end

if( people == dogs )             added this just to see if it works.)
  puts "My parens work."
end
		

~/dev/ruby $ ruby ex30.rb

We should take the cars.
Maybe we could take the buses.
Alright, let's just take the buses.
		

ex30.rb:

people = 30
cars = 40
buses = 15

if cars > people
  puts "We should take the cars."
elsif cars < people
  puts "We should not take the cars."
else
  puts "We can't decide."
end

if buses > cars
  puts "That's too many buses."
elsif buses < cars
  puts "Maybe we could take the buses."
else
  puts "We still can't decide."
end

if people > buses
  puts "Alright, let's just take the buses."
else
  puts "Fine, let's stay home then."
end
		

~/dev/ruby $ ruby ex31.rb

You enter a dark room with two doors.  Do you go through door #1 or door #2?
> 1
There's a giant bear here eating a cheese cake.  What do you do?
1. Take the cake.
2. Scream at the bear.
> 2
The bear eats your legs off.  Good job!
		

~/dev/ruby $ ruby ex31.rb

You enter a dark room with two doors.  Do you go through door #1 or door #2?
> 1
There's a giant bear here eating a cheese cake.  What do you do?
1. Take the cake.
2. Scream at the bear.
> 1
The bear eats your face off.  Good job!
		

~/dev/ruby $ ruby ex31.rb

You enter a dark room with two doors.  Do you go through door #1 or door #2?
> 2
You stare into the endless abyss at Cthuhlu's retina.
1. Blueberries.
2. Yellow jacket clothespins.
3. Understanding revolvers yelling melodies.
> 1
Your body survives powered by a mind of jello.  Good job!
		

~/dev/ruby $ ruby ex31.rb

You enter a dark room with two doors.  Do you go through door #1 or door #2?
> 2
You stare into the endless abyss at Cthuhlu's retina.
1. Blueberries.
2. Yellow jacket clothespins.
3. Understanding revolvers yelling melodies.
> 3
The insanity rots your eyes into a pool of muck.  Good job!
		

~/dev/ruby $ ruby ex31.rb

You enter a dark room with two doors.  Do you go through door #1 or door #2?
> stuff
You stumble around and fall on a knife and die.  Good job!
		

~/dev/ruby $ ruby ex31.rb

You enter a dark room with two doors.  Do you go through door #1 or door #2?
> 1
There's a giant bear here eating a cheese cake.  What do you do?
1. Take the cake.
2. Scream at the bear.
> apples
Well, doing apples is probably better.  Bear runs away.
		

ex31.rb:

def prompt
  print "> "
end

puts "You enter a dark room with two doors.  Do you go through door #1 or door #2?"

prompt; door = gets.chomp

if door == "1"
  puts "There's a giant bear here eating a cheese cake.  What do you do?"
  puts "1. Take the cake."
  puts "2. Scream at the bear."

  prompt; bear = gets.chomp

  if bear == "1"
    puts "The bear eats your face off.  Good job!"
  elsif bear == "2"
    puts "The bear eats your legs off.  Good job!"
  else
    puts "Well, doing #{bear} is probably better.  Bear runs away."
  end

elsif door == "2"
  puts "You stare into the endless abyss at Cthuhlu's retina."
  puts "1. Blueberries."
  puts "2. Yellow jacket clothespins."
  puts "3. Understanding revolvers yelling melodies."

  prompt; insanity = gets.chomp

  if insanity == "1" or insanity == "2"
    puts "Your body survives powered by a mind of jello.  Good job!"
  else
    puts "The insanity rots your eyes into a pool of muck.  Good job!"
  end

else
  puts "You stumble around and fall on a knife and die.  Good job!"
end
		

~/dev/ruby $ ruby ex33.rb

At the top i is 0
Numbers now: [0]
At the bottom i is 1
At the top i is 1
Numbers now: [0, 1]
At the bottom i is 2
At the top i is 2
Numbers now: [0, 1, 2]
At the bottom i is 3
At the top i is 3
Numbers now: [0, 1, 2, 3]
At the bottom i is 4
At the top i is 4
Numbers now: [0, 1, 2, 3, 4]
At the bottom i is 5
At the top i is 5
Numbers now: [0, 1, 2, 3, 4, 5]
At the bottom i is 6
The numbers:
0
1
2
3
4
5
		

ex33.rb:

i = 0
numbers = []

while i < 6
  puts "At the top i is #{i}"
  numbers.push(i)

  i = i + 1
  puts "Numbers now: #{numbers}"
  puts "At the bottom i is #{i}"
end

puts "The numbers: "

for num in numbers
  puts num
end
		

~/dev/ruby $ ruby ex34.rb

bear
tiger
penguin
zebra
red
yellow
blue
green
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
a
b
c
d
e
f
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
		

ex34.rb:

animals    = ['bear', 'tiger', 'penguin', 'zebra']
colors     = [ "red", "yellow", "blue", "green" ]
digits     = [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
hexdigits  = [ '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' ]
hexnumbers = [ 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f ]

puts animals
puts colors
puts digits
puts hexdigits
puts hexnumbers
		

~/dev/ruby $ ruby ex35.rb

You are in a dark room.
There is a door to your right and left.
Which one do you take?
> left
There is a bear here.
The bear has a bunch of honey.
The fat bear is in front of another door.
How are you going to move the bear?
> taunt bear
The bear has moved from the door. You can go through it now.
> open door
This room is full of gold.  How much do you take?
> asf
Man, learn to type a number.  Good job!
		

ex35.rb:

def prompt()
  print "> "
end

def gold_room()
  puts "This room is full of gold.  How much do you take?"

  prompt; next_move = gets.chomp
  if next_move.include? "0" or next_move.include? "1"
    how_much = next_move.to_i()
  else
    dead("Man, learn to type a number.")
  end

  if how_much < 50
    puts "Nice, you're not greedy, you win!"
    Process.exit(0)
  else
    dead("You greedy bastard!")
  end
end


def bear_room()
  puts "There is a bear here."
  puts "The bear has a bunch of honey."
  puts "The fat bear is in front of another door."
  puts "How are you going to move the bear?"
  bear_moved = false

  while true
    prompt; next_move = gets.chomp

    if next_move == "take honey"
      dead("The bear looks at you then slaps your face off.")
    elsif next_move == "taunt bear" and not bear_moved
      puts "The bear has moved from the door. You can go through it now."
      bear_moved = true
    elsif next_move == "taunt bear" and bear_moved
      dead("The bear gets pissed off and chews your leg off.")
    elsif next_move == "open door" and bear_moved
      gold_room()
    else
      puts "I got no idea what that means."
    end
  end
end

def cthulhu_room()
  puts "Here you see the great evil Cthulhu."
  puts "He, it, whatever stares at you and you go insane."
  puts "Do you flee for your life or eat your head?"

  prompt; next_move = gets.chomp

  if next_move.include? "flee"
    start()
  elsif next_move.include? "head"
    dead("Well that was tasty!")
  else
    cthulhu_room()
  end
end

def dead(why)
  puts "#{why}  Good job!"
  Process.exit(0)
end

def start()
  puts "You are in a dark room."
  puts "There is a door to your right and left."
  puts "Which one do you take?"

  prompt; next_move = gets.chomp

  if next_move == "left"
    bear_room()
  elsif next_move == "right"
    cthulhu_room()
  else
    dead("You stumble around the room until you starve.")
  end
end

start()
		

~/dev/ruby $ ruby ex38.rb

Wait there's not 10 things in that list, let's fix that.
Adding: Boy
There's 7 items now.
Adding: Girl
There's 8 items now.
Adding: Banana
There's 9 items now.
Adding: Corn
There's 10 items now.
There we go: ["Apples", "Oranges", "Crows", "Telephone", "Light", "Sugar", "Boy", "Girl", "Banana", "Corn"]
Let's do some things with stuff.
Oranges
Corn
Corn
Apples Oranges Crows Telephone Light Sugar Boy Girl Banana
Telephone#Sugar
		

ex38.rb:

ten_things = "Apples Oranges Crows Telephone Light Sugar"

puts "Wait there's not 10 things in that list, let's fix that."

stuff = ten_things.split(' ')
more_stuff = %w(Day Night Song Frisbee Corn Banana Girl Boy)

while stuff.length != 10
  next_one = more_stuff.pop()
  puts "Adding: #{next_one}"
  stuff.push(next_one)
  puts "There's #{stuff.length} items now."
end

puts "There we go: #{stuff}"

puts "Let's do some things with stuff."

puts stuff[1]
puts stuff[-1] # whoa! fancy
puts stuff.pop()
puts stuff.join(' ') # what? cool!
puts stuff.values_at(3,5).join('#') # super stellar!
		

~/dev/ruby $ ruby ex39.rb

----------
NY State has:
New York
OR State has:
Portland
----------
Michigan's abbreviation is:
MI
Florida's abbreviation is:
FL
----------
Michigan has:
Detroit
Florida has:
Jacksonville
----------
Oregon is abbreviated OR
Florida is abbreviated FL
California is abbreviated CA
New York is abbreviated NY
Michigan is abbreviated MI
----------
CA has the city San Francisco
MI has the city Detroit
FL has the city Jacksonville
NY has the city New York
OR has the city Portland
----------
Oregon state is abbreviated OR and has city Portland
Florida state is abbreviated FL and has city Jacksonville
California state is abbreviated CA and has city San Francisco
New York state is abbreviated NY and has city New York
Michigan state is abbreviated MI and has city Detroit
----------
Sorry, no Texas.
The city for the state 'TX' is: Does Not Exist
		

ex39.rb:

# create a mapping of state to abbreviation
states = {
    'Oregon' => 'OR',
    'Florida' => 'FL',
    'California' => 'CA',
    'New York' => 'NY',
    'Michigan' => 'MI'
}

# create a basic set of states and some cities in them
cities = {
    'CA' => 'San Francisco',
    'MI' => 'Detroit',
    'FL' => 'Jacksonville'
}

# add some more cities
cities['NY'] = 'New York'
cities['OR'] = 'Portland'

# puts out some cities
puts '-' * 10
puts "NY State has: ", cities['NY']
puts "OR State has: ", cities['OR']

# puts some states
puts '-' * 10
puts "Michigan's abbreviation is: ", states['Michigan']
puts "Florida's abbreviation is: ", states['Florida']

# do it by using the state then cities dict
puts '-' * 10
puts "Michigan has: ", cities[states['Michigan']]
puts "Florida has: ", cities[states['Florida']]

# puts every state abbreviation
puts '-' * 10
for state, abbrev in states
    puts "%s is abbreviated %s" % [state, abbrev]
end

# puts every city in state
puts '-' * 10
for abbrev, city in cities
    puts "%s has the city %s" % [abbrev, city]
end

# now do both at the same time
puts '-' * 10
for state, abbrev in states
    puts "%s state is abbreviated %s and has city %s" % [
        state, abbrev, cities[abbrev]]
end

puts '-' * 10
# if it's not there you get nil
state = states['Texas']

if not state
    puts "Sorry, no Texas."
end

# get a city with a default value
city = cities['TX'] || 'Does Not Exist'
puts "The city for the state 'TX' is: %s" % city
		

~/dev/ruby $ ruby ex40.rb

Happy birthday to you
I don't want to get sued
So I'll stop right there
They rally around the family
With pockets full of shells
		

ex40.rb:

class Song
    def initialize(lyrics)
        @lyrics = lyrics
    end

    def sing_me_a_song()
        for line in @lyrics
            puts line
        end
    end
end

happy_bday = Song.new(["Happy birthday to you",
                   "I don't want to get sued",
                   "So I'll stop right there"])

bulls_on_parade = Song.new(["They rally around the family",
                        "With pockets full of shells"])

happy_bday.sing_me_a_song()

bulls_on_parade.sing_me_a_song()
		

~/dev/ruby $ ruby ex41.rb

class Boot
	def initialize(cup)
	end
end

> class Boot has-a initialize that takes cup as a parameter.

ANSWER:  class Boot has-a initialize that takes cup parameters.

border = Cap.new()

> border gets a new Cap.

ANSWER:  Set border to an instance of class Cap.

cord.appliance = 'account'

> Set cord's appliance to the string "account".

ANSWER:  From cord get the appliance attribute and set it to 'account'.

chicken.doctor(bridge, beef)

> Call chicken's doctor passing bridge and beef as parameters.

ANSWER:  From chicken get the doctor function, and call it with parameters bridge, beef.

class Arch < Beetle
end

> Class Arch inherits class Beetle's attributes.

ANSWER:  Make a class named Arch that is-a Beetle.

class Cry
	def celery(drawer)
	end
end
^D
		

~/dev/ruby $ ruby ex41.rb english

From church get the cart attribute and set it to 'cord'.

> church.cart = 'cord'

ANSWER:  church.cart = 'cord'

class Bubble has-a function named crush that takes drug parameters.

> class Bubble def crush( drug ) end end

ANSWER:  class Bubble
	def crush(drug)
	end
end

Set channel to an instance of class Advertisement.

> channel = Advertisement.new()

ANSWER:  channel = Advertisement.new()

From door get the arithmetic function, and call it with parameters curtain, basketball.

> door.arithmetic( curtain, basketball )

ANSWER:  door.arithmetic(curtain, basketball)

Make a class named Cactus that is-a Aftermath.
^D
		

ex41.rb:

require 'open-uri'

WORD_URL = "http://learncodethehardway.org/words.txt"
WORDS = []

PHRASES = {
  "class ### < ###\nend" => "Make a class named ### that is-a ###.",
  "class ###\n\tdef initialize(@@@)\n\tend\nend"  => "class ### has-a initialize that takes @@@ parameters.",
  "class ###\n\tdef ***(@@@)\n\tend\nend" => "class ### has-a function named *** that takes @@@ parameters.",
  "*** = ###.new()"  => "Set *** to an instance of class ###.",
  "***.***(@@@)"  => "From *** get the *** function, and call it with parameters @@@.",
  "***.*** = '***'" => "From *** get the *** attribute and set it to '***'."
}

PHRASE_FIRST = ARGV[0] == "english"

open(WORD_URL) {|f|
  f.each_line {|word| WORDS.push(word.chomp)}
}

def craft_names(rand_words, snippet, pattern, caps=false)
  names = snippet.scan(pattern).map do
    word = rand_words.pop()
    caps ? word.capitalize : word
  end

  return names * 2
end

def craft_params(rand_words, snippet, pattern)
  names = (0...snippet.scan(pattern).length).map do
    param_count = rand(3) + 1
    params = (0...param_count).map {|x| rand_words.pop() }
    params.join(', ')
  end

  return names * 2
end

def convert(snippet, phrase)
  rand_words = WORDS.sort_by {rand}
  class_names = craft_names(rand_words, snippet, /###/, caps=true)
  other_names = craft_names(rand_words, snippet, /\*\*\*/)
  param_names = craft_params(rand_words, snippet, /@@@/)

  results = []

  for sentence in [snippet, phrase]
    # fake class names, also copies sentence
    result = sentence.gsub(/###/) {|x| class_names.pop }

    # fake other names
    result.gsub!(/\*\*\*/) {|x| other_names.pop }

    # fake parameter lists
    result.gsub!(/@@@/) {|x| param_names.pop }

    results.push(result)
  end

  return results
end

# keep going until they hit CTRL-D
loop do
  snippets = PHRASES.keys().sort_by {rand}

  for snippet in snippets
    phrase = PHRASES[snippet]
    question, answer = convert(snippet, phrase)

    if PHRASE_FIRST
      question, answer = answer, question
    end

    print question, "\n\n> "

    exit(0) unless STDIN.gets

    puts "\nANSWER:  %s\n\n" % answer
  end
end
		

~/dev/ruby $ ruby ex42.rb

ex42.rb:

## Animal is-a object look at the extra credit
class Animal
end

## ??
class Dog < Animal

    def initialize(name)
        ## ??
        @name = name
    end
end

## ??
class Cat < Animal

    def initialize(name)
        ## ??
        @name = name
    end
end

## ??
class Person

    def initialize(name)
        ## ??
        @name = name

        ## Person has-a pet of some kind
        @pet = nil
    end

    attr_accessor :pet
end

## ??
class Employee < Person

    def initialize(name, salary)
        ## ?? hmm what is this strange magic?
        super(name)
        ## ??
        @salary = salary
    end

end

## ??
class Fish
end

## ??
class Salmon < Fish
end

## ??
class Halibut < Fish
end


## rover is-a Dog
rover = Dog.new("Rover")

## ??
satan = Cat.new("Satan")

## ??
mary = Person.new("Mary")

## ??
mary.pet = satan

## ??
frank = Employee.new("Frank", 120000)

## ??
frank.pet = rover

## ??
flipper = Fish.new()

## ??
crouse = Salmon.new()

## ??
harry = Halibut.new()
		

~/dev/ruby $ ruby ex44-1.rb

PARENT implicit()
PARENT implicit()
		

ex44-1.rb:

class Parent
    def implicit()
        puts "PARENT implicit()"
    end
end

class Child < Parent
end

dad = Parent.new()
son = Child.new()

dad.implicit()
son.implicit()
		

~/dev/ruby $ ruby ex44-2.rb

PARENT override()
CHILD override()
		

ex44-2.rb:

class Parent
    def override()
        puts "PARENT override()"
    end
end

class Child < Parent
    def override()
        puts "CHILD override()"
    end
end

dad = Parent.new()
son = Child.new()

dad.override()
son.override()
		

~/dev/ruby $ ruby ex44-3.rb

PARENT altered()
CHILD, BEFORE PARENT altered()
PARENT altered()
CHILD, AFTER PARENT altered()
		

ex44-3.rb:

class Parent
    def altered()
        puts "PARENT altered()"
    end
end

class Child < Parent
    def altered()
        puts "CHILD, BEFORE PARENT altered()"
        super()
        puts "CHILD, AFTER PARENT altered()"
    end

end

dad = Parent.new()
son = Child.new()

dad.altered()
son.altered()
		

~/dev/ruby $ ruby ex44-4.rb

PARENT implicit()
PARENT implicit()
PARENT override()
CHILD override()
PARENT altered()
CHILD, BEFORE PARENT altered()
PARENT altered()
CHILD, AFTER PARENT altered()
		

ex44-4.rb:

class Parent
    def override()
        puts "PARENT override()"
    end

    def implicit()
        puts "PARENT implicit()"
    end

    def altered()
        puts "PARENT altered()"
    end
end

class Child < Parent
    def override()
        puts "CHILD override()"
    end

    def altered()
        puts "CHILD, BEFORE PARENT altered()"
        super()
        puts "CHILD, AFTER PARENT altered()"
    end
end

dad = Parent.new()
son = Child.new()

dad.implicit()
son.implicit()

dad.override()
son.override()

dad.altered()
son.altered()
		

~/dev/ruby $ ruby ex44-5.rb

OTHER implicit()
CHILD override()
CHILD, BEFORE OTHER altered()
OTHER altered()
CHILD, AFTER OTHER altered()
		

ex44-5.rb:

class Other
    def override()
        puts "OTHER override()"
    end

    def implicit()
        puts "OTHER implicit()"
    end

    def altered()
        puts "OTHER altered()"
    end
end

class Child
    def initialize()
        @other = Other.new()
    end

    def implicit()
        @other.implicit()
    end

    def override()
        puts "CHILD override()"
    end

    def altered()
        puts "CHILD, BEFORE OTHER altered()"
        @other.altered()
        puts "CHILD, AFTER OTHER altered()"
    end
end

son = Child.new()

son.implicit()
son.override()
son.altered()
		

~/dev/ruby $ ruby ex44-6.rb

OTHER implicit()
CHILD override()
CHILD, BEFORE OTHER altered()
OTHER altered()
CHILD, AFTER OTHER altered()
		

ex44-6.rb:

module Other
    def Other.override()
        puts "OTHER override()"
    end

    def Other.implicit()
        puts "OTHER implicit()"
    end

    def Other.altered()
        puts "OTHER altered()"
    end
end

class Child
    def implicit()
        Other.implicit()
    end

    def override()
        puts "CHILD override()"
    end

    def altered()
        puts "CHILD, BEFORE OTHER altered()"
        Other.altered()
        puts "CHILD, AFTER OTHER altered()"
    end
end

son = Child.new()

son.implicit()
son.override()
son.altered()
		

~/dev/ruby $ cd ruby/projects/ex47/test ; ruby test_ex47.rb

Run options:

# Running tests:

...

Finished tests in 0.000732s, 4100.5566 tests/s, 9567.9654 assertions/s.

3 tests, 7 assertions, 0 failures, 0 errors, 0 skips
		

ruby/projects/ex47/lib/ex47.rb:

class Room
  attr_accessor :name, :description, :paths

  def initialize(name, description)
    @name = name
    @description = description
    @paths = {}
  end

  def go(direction)
    @paths[direction]
  end

  def add_paths(paths)
    @paths.update(paths)
  end
end
		

ruby/projects/ex47/test/test_ex47.rb:

require 'test/unit'
require_relative '../lib/ex47'

class MyUnitTests < Test::Unit::TestCase

  def test_room()
    gold = Room.new("GoldRoom",
                    """This room has gold in it you can grab. There's a
                door to the north.""")
    assert_equal(gold.name, "GoldRoom")
    assert_equal(gold.paths, {})
  end

  def test_room_paths()
    center = Room.new("Center", "Test room in the center.")
    north = Room.new("North", "Test room in the north.")
    south = Room.new("South", "Test room in the south.")

    center.add_paths({:north => north, :south => south})
    assert_equal(center.go(:north), north)
    assert_equal(center.go(:south), south)
  end

  def test_map()
    start = Room.new("Start", "You can go west and down a hole.")
    west = Room.new("Trees", "There are trees here, you can go east.")
    down = Room.new("Dungeon", "It's dark down here, you can go up.")

    start.add_paths({:west => west, :down => down})
    west.add_paths({:east => start})
    down.add_paths({:up => start})

    assert_equal(start.go(:west), west)
    assert_equal(start.go(:west).go(:east), start)
    assert_equal(start.go(:down).go(:up), start)
  end
end
		

~/dev/ruby/projects/lexicon/test $ ruby test_lexicon.rb

ruby test_lexicon.rb
Run options:

# Running tests:

north
north
south
east
.ASDFADFASDF
bear
IAS
princess
.bear
bear
princess
.1234
3
91234
.the
the
in
of
.go
go
kill
eat
.

Finished tests in 0.000892s, 6725.6506 tests/s, 13451.3012 assertions/s.

6 tests, 12 assertions, 0 failures, 0 errors, 0 skips
		

projects/lexicon/lib/lexicon.rb:

class Lexicon
  attr_accessor :lexicon, :dict

  def initialize()
    @dict = {
      :north => :direction,
      :south => :direction,
      :east  => :direction,
      :west  => :direction,
      :go    => :verb,
      :kill  => :verb,
      :eat   => :verb,
      :bear     => :noun,
      :princess => :noun,
      :the   => :stop,
      :in    => :stop,
      :of    => :stop,
    }
  end

  Pair = Struct.new(:qualifier, :value)

  def scan(list)
    pairs = []
    list.split.map do | value |
      puts value
      if value.match( /^[0-9]+$/ )
        pairs.push( Pair.new(:number, value.to_i) )
      elsif qualifier = @dict[value.intern]
        pairs.push( Pair.new(qualifier, value) )
      else
        pairs.push( Pair.new(:error, value.to_s) )
      end
    end
    pairs
  end
end
		

projects/lexicon/test/test_lexicon.rb:

require 'test/unit'
require_relative "../lib/lexicon/lexicon"

class LexiconTests < Test::Unit::TestCase

  Pair = Lexicon::Pair
  @@lexicon = Lexicon.new()

  def test_directions()
    assert_equal([Pair.new(:direction, 'north')], @@lexicon.scan("north"))
    result = @@lexicon.scan("north south east")
    assert_equal(result, [Pair.new(:direction, 'north'),
                 Pair.new(:direction, 'south'),
                 Pair.new(:direction, 'east')])
  end

  def test_verbs()
    assert_equal(@@lexicon.scan("go"), [Pair.new(:verb, 'go')])
    result = @@lexicon.scan("go kill eat")
    assert_equal(result, [Pair.new(:verb, 'go'),
                 Pair.new(:verb, 'kill'),
                 Pair.new(:verb, 'eat')])
  end

  def test_stops()
    assert_equal(@@lexicon.scan("the"), [Pair.new(:stop, 'the')])
    result = @@lexicon.scan("the in of")
    assert_equal(result, [Pair.new(:stop, 'the'),
                 Pair.new(:stop, 'in'),
                 Pair.new(:stop, 'of')])
  end

  def test_nouns()
    assert_equal(@@lexicon.scan("bear"), [Pair.new(:noun, 'bear')])
    result = @@lexicon.scan("bear princess")
    assert_equal(result, [Pair.new(:noun, 'bear'),
                 Pair.new(:noun, 'princess')])
  end

  def test_numbers()
    assert_equal(@@lexicon.scan("1234"), [Pair.new(:number, 1234)])
    result = @@lexicon.scan("3 91234")
    assert_equal(result, [Pair.new(:number, 3),
                 Pair.new(:number, 91234)])
  end

  def test_errors()
    assert_equal(@@lexicon.scan("ASDFADFASDF"), [Pair.new(:error, 'ASDFADFASDF')])
    result = @@lexicon.scan("bear IAS princess")
    assert_equal(result, [Pair.new(:noun, 'bear'),
                 Pair.new(:error, 'IAS'),
                 Pair.new(:noun, 'princess')])
  end
end
		

parsererror.rb:

		class ParserError < Exception

end

class Sentence

  def initialize(subject, verb, object)
    # remember we take Pair.new(:noun, "princess") structs and convert them
    @subject = subject.word
    @verb = verb.word
    @object = object.word
  end

end

module Parser

  def self.peek(word_list)
    begin
      word_list.first.token
    rescue
      nil
    end
  end

  def self.match(word_list, expecting)
    begin
      word = word_list.shift
      if word.token == expecting
        word
      else
        nil
      end
    rescue
      nil
    end
  end

  def self.skip(word_list, token)
    while peek(word_list) == token
      match(word_list, token)
    end
  end

  def self.parse_verb(word_list)
    skip(word_list, :stop)

    if peek(word_list) == :verb
      return match(word_list, :verb)
    else
      raise ParserError.new("Expected a verb next.")
    end
  end

  def self.parse_object(word_list)
    skip(word_list, :stop)
    next_word = peek(word_list)

    if next_word == :noun
      return match(word_list, :noun)
    end
    if next_word == :direction
      return match(word_list, :direction)
    else
      raise ParserError.new("Expected a noun or direction next.")
    end
  end

  def self.parse_subject(word_list, subj)
    verb = parse_verb(word_list)
    obj = parse_object(word_list)

    return Sentence.new(subj, verb, obj)
  end

  def self.parse_sentence(word_list)
    skip(word_list, :stop)

    start = peek(word_list)

    if start == :noun
      subj = match(word_list, :noun)
      return parse_subject(word_list, subj)
    elsif start == :verb
      # assume the subject is the player then
      return parse_subject(word_list, Pair.new(:noun, "player"))
    else
      raise ParserError.new("Must start with subject, object, or verb not: #{start}")
    end
  end
end