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SergiiVlasiuk's solution

to Food Chain in the Scala Track

Published at Aug 25 2019 · 0 comments
Instructions
Test suite
Solution

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!

The Scala exercises assume an SBT project scheme. The exercise solution source should be placed within the exercise directory/src/main/scala. The exercise unit tests can be found within the exercise directory/src/test/scala.

To run the tests simply run the command sbt test in the exercise directory.

For more detailed info about the Scala track see the help page.

Source

Wikipedia http://en.wikipedia.org/wiki/There_Was_an_Old_Lady_Who_Swallowed_a_Fly

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

FoodChainTest.scala

import org.scalatest.{Matchers, FunSuite}

/** @version 2.1.0 */
class FoodChainTest extends FunSuite with Matchers {

  test("fly") {
    FoodChain.recite(1, 1) should be ("""I know an old lady who swallowed a fly.
I don't know why she swallowed the fly. Perhaps she'll die.

""")
  }

  test("spider") {
    pending
    FoodChain.recite(2, 2) should be ("""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.

""")
  }

  test("bird") {
    pending
    FoodChain.recite(3, 3) should be ("""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.

""")
  }

  test("cat") {
    pending
    FoodChain.recite(4, 4) should be ("""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.

""")
  }

  test("dog") {
    pending
    FoodChain.recite(5, 5) should be ("""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.

""")
  }

  test("goat") {
    pending
    FoodChain.recite(6, 6) should be ("""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.

""")
  }

  test("cow") {
    pending
    FoodChain.recite(7, 7) should be ("""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.

""")
  }

  test("horse") {
    pending
    FoodChain.recite(8, 8) should be ("""I know an old lady who swallowed a horse.
She's dead, of course!

""")
  }

  test("multiple verses") {
    pending
    FoodChain.recite(1, 3) should be ("""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.

""")
  }

  test("full song") {
    pending
    FoodChain.recite(1, 8) should be ("""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!

""")
  }
}
object FoodChain {
  val parts = Array[(String, String, String, String)](
    ("fly", "", "", "I don't know why she swallowed the fly. Perhaps she'll die.\n"),
    ("spider", " that wriggled and jiggled and tickled inside her", "It wriggled and jiggled and tickled inside her.\n", ""),
    ("bird", "", "How absurd to swallow a bird!\n", ""),
    ("cat", "", "Imagine that, to swallow a cat!\n", ""),
    ("dog", "", "What a hog, to swallow a dog!\n", ""),
    ("goat", "", "Just opened her throat and swallowed a goat!\n", ""),
    ("cow", "", "I don't know how she swallowed a cow!\n", ""),
    ("horse", "", "", "She's dead, of course!\n"))

  def recite(from: Int, till: Int): String =
    (for (num <- from to till) yield recite(num - 1)).mkString

  private def recite(num: Int): String =
    s"I know an old lady who swallowed a ${parts(num)._1}.\n${parts(num)._3}${append(num)}\n"

  private def append(num: Int): String = parts(num)._4 match {
    case "" => swallow(parts(num)._1, parts(num - 1)._1 + parts(num - 1)._2) + append(num - 1)
    case x => x
  }

  private def swallow(x1: String, x2: String) = s"She swallowed the $x1 to catch the $x2.\n"
}

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