Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'.
While you could copy/paste the lyrics, or read them from a file, this problem is much more interesting if you approach it algorithmically.
This is a cumulative song of unknown origin.
This is one of many common variants.
I know an old lady who swallowed a fly.
I don't know why she swallowed the fly. Perhaps she'll die.
I know an old lady who swallowed a spider.
It wriggled and jiggled and tickled inside her.
She swallowed the spider to catch the fly.
I don't know why she swallowed the fly. Perhaps she'll die.
I know an old lady who swallowed a bird.
How absurd to swallow a bird!
She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
She swallowed the spider to catch the fly.
I don't know why she swallowed the fly. Perhaps she'll die.
I know an old lady who swallowed a cat.
Imagine that, to swallow a cat!
She swallowed the cat to catch the bird.
She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
She swallowed the spider to catch the fly.
I don't know why she swallowed the fly. Perhaps she'll die.
I know an old lady who swallowed a dog.
What a hog, to swallow a dog!
She swallowed the dog to catch the cat.
She swallowed the cat to catch the bird.
She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
She swallowed the spider to catch the fly.
I don't know why she swallowed the fly. Perhaps she'll die.
I know an old lady who swallowed a goat.
Just opened her throat and swallowed a goat!
She swallowed the goat to catch the dog.
She swallowed the dog to catch the cat.
She swallowed the cat to catch the bird.
She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
She swallowed the spider to catch the fly.
I don't know why she swallowed the fly. Perhaps she'll die.
I know an old lady who swallowed a cow.
I don't know how she swallowed a cow!
She swallowed the cow to catch the goat.
She swallowed the goat to catch the dog.
She swallowed the dog to catch the cat.
She swallowed the cat to catch the bird.
She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
She swallowed the spider to catch the fly.
I don't know why she swallowed the fly. Perhaps she'll die.
I know an old lady who swallowed a horse.
She's dead, of course!
For installation and learning resources, refer to the exercism help page.
For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:
gem install minitest
If you would like color output, you can require 'minitest/pride'
in
the test file, or note the alternative instruction, below, for running
the test file.
Run the tests from the exercise directory using the following command:
ruby food_chain_test.rb
To include color from the command line:
ruby -r minitest/pride food_chain_test.rb
Wikipedia http://en.wikipedia.org/wiki/There_Was_an_Old_Lady_Who_Swallowed_a_Fly
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
require 'minitest/autorun'
require_relative 'food_chain'
class NoCheating < IOError
def message
"The use of File.open and IO.read is restricted.\n" \
'This exercise intends to help you improve your ability to work ' \
'with data generated from your code. Your program must not read ' \
'the song.txt file.'
end
end
class FoodChainTest < Minitest::Test
# This test is an acceptance test.
#
# If you find it difficult to work the problem with so much
# output, go ahead and add a `skip`, and write whatever
# unit tests will help you. Then unskip it again
# to make sure you got it right.
# There's no need to submit the tests you write, unless you
# specifically want feedback on them.
def test_the_whole_song
song_file = File.expand_path('../song.txt', __FILE__)
expected = IO.read(song_file)
assert_equal expected, FoodChain.song
end
# Tests that an error is effectively raised when IO.read or
# File.open are used within FoodChain.
def test_read_guard
song_file = File.expand_path('../song.txt', __FILE__)
["IO.read '#{song_file}'", "File.open '#{song_file}'"].each do |trigger|
assert_raises(NoCheating) { FoodChain.send :class_eval, trigger }
end
end
# Problems in exercism evolve over time,
# as we find better ways to ask questions.
# The version number refers to the version of the problem you solved,
# not your solution.
#
# Define a constant named VERSION inside of BookKeeping.
# If you are curious, read more about constants on RubyDoc:
# http://ruby-doc.org/docs/ruby-doc-bundle/UsersGuide/rg/constants.html
def test_version
skip
assert_equal 2, BookKeeping::VERSION
end
end
module RestrictedClasses
class File
def self.open(*)
fail NoCheating
end
def self.read(*)
fail NoCheating
end
def open(*)
fail NoCheating
end
def read(*)
fail NoCheating
end
end
class IO
def self.read(*)
fail NoCheating
end
def read(*)
fail NoCheating
end
end
end
FoodChain.prepend RestrictedClasses
class Animal
ATTRS = %i(name comment reason catch_extra)
attr_accessor *ATTRS
def initialize(options)
options.each { |key, val| self.send("#{key}=".to_s, val) }
end
end
class FoodChain
VERSION = 2
def self.song
ANIMALS.map { |animal| stanza_for(animal) }.join("\n\n")
end
private
ANIMALS = [
Animal.new(name: "fly",
# note no comment, but a special reason!
reason: "I don't know why she swallowed the fly."\
" Perhaps she'll die."),
Animal.new(name: "spider",
comment:
"It wriggled and jiggled and tickled inside her.",
# note another special item here:
catch_extra:
" that wriggled and jiggled and tickled inside her"),
Animal.new(name: "bird",
comment: "How absurd to swallow a bird!"),
Animal.new(name: "cat",
comment: "Imagine that, to swallow a cat!"),
Animal.new(name: "dog",
comment: "What a hog, to swallow a dog!"),
Animal.new(name: "goat",
comment: "Just opened her throat and swallowed a goat!"),
Animal.new(name: "cow",
comment: "I don't know how she swallowed a cow!"),
Animal.new(name: "horse",
comment: "She's dead, of course!\n")
]
def self.reason_line_for_animal(animal)
animal.reason || begin
prev = ANIMALS[ANIMALS.index(animal) - 1]
"She swallowed the #{animal.name} to catch the #{prev.name}"\
"#{prev.catch_extra}."
end
end
def self.reason_lines_for_stanza(animal)
return [] if animal == ANIMALS.last # special case
# could also do take_while not stanza_animal, and also push that
ANIMALS[0, ANIMALS.index(animal) + 1].reverse.map { |a|
reason_line_for_animal(a) }
end
def self.stanza_for(animal)
# not worrying about "a" vs. "an"...
(["I know an old lady who swallowed a #{animal.name}.",
animal.comment].
compact +
reason_lines_for_stanza(animal)).join("\n")
end
end
A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.
Here are some questions to help you reflect on this solution and learn the most from it.
Level up your programming skills with 3,104 exercises across 52 languages, and insightful discussion with our volunteer team of welcoming mentors. Exercism is 100% free forever.
Sign up Learn More
Community comments
This is ten million percent more readable than what I came up with. Nice job.