Food Chain Example

food-chain.js

var ANIMALS = {
  1: { name: 'fly' },
  2: { name: 'spider', interjection: "It wriggled and jiggled and tickled inside her.\n",
       add: " that wriggled and jiggled and tickled inside her" },
  3: { name: 'bird', interjection: "How absurd to swallow a bird!\n" },
  4: { name: 'cat', interjection: "Imagine that, to swallow a cat!\n" },
  5: { name: 'dog', interjection: "What a hog, to swallow a dog!\n" },
  6: { name: 'goat', interjection: "Just opened her throat and swallowed a goat!\n" },
  7: { name: 'cow', interjection: "I don't know how she swallowed a cow!\n" },
  8: { name: 'horse', interjection: "She's dead, of course!\n" },
}

// Public functions -----------------------------------------------------------

exports.verse = verse
function verse(n) {
  if (n == 8) {
    return verseBeginning(n) + verseInterjection(n)
  } else {
    return verseBeginning(n) + verseInterjection(n) + verseBody(n) + verseEnding(n)
  }
}

exports.verses = verses
function verses(from, to) {
  return mapRange(from, to, verse).join('\n') + '\n'
}

// Verse generators -----------------------------------------------------------

function verseBeginning(n) { // :: number -> Lines
  return "I know an old lady who swallowed a " + animalName(n) + ".\n"
}

function verseInterjection(n) {
  return animal(n).interjection || ''
}

function verseBody(n) {
  if (n == 1) {
    return ""
  } else {
    return swallow(n) + verseBody(n - 1)
  }
}

function verseEnding(n) {
  return "I don't know why she swallowed the fly. Perhaps she'll die.\n"
}

// Helper functions -----------------------------------------------------------

function animal(n) {
  return ANIMALS[n]
}

function swallow(n) {
  return "She swallowed the " + animalName(n) +
    " to catch the " + animalDescription(n - 1) + ".\n"
}

function animalName(n) { // :: number -> String
  return animal(n).name
}

function animalDescription(n) {
  return animalName(n) + (animal(n).add || '')
}

function mapRange(from, to, f) {
  var out = []
  for (var i = from; i <= to; i ++) out.push(f(i))
  return out
}

food-chain_spec.js

var song = require('./food-chain');

describe('Food Chain', function () {

  it('fly', function () {
    var expected = "I know an old lady who swallowed a fly.\nI don't know why she swallowed the fly. Perhaps she'll die.\n";

    expect(song.verse(1)).toEqual(expected);
  });

  it('spider', function () {
    var expected = "I know an old lady who swallowed a spider.\nIt wriggled and jiggled and tickled inside her.\n" +
      "She swallowed the spider to catch the fly.\n" + "I don't know why she swallowed the fly. Perhaps she'll die.\n";

    expect(song.verse(2)).toEqual(expected);
  });

  it('bird', function () {
    var expected = "I know an old lady who swallowed a bird.\n" +
      "How absurd to swallow a bird!\n" +
      "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" +
      "She swallowed the spider to catch the fly.\n" +
      "I don't know why she swallowed the fly. Perhaps she'll die.\n";

    expect(song.verse(3)).toEqual(expected);
  });

  it('cat', function () {
    var expected = "I know an old lady who swallowed a cat.\n" +
      "Imagine that, to swallow a cat!\n" +
      "She swallowed the cat to catch the bird.\n" +
      "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" +
      "She swallowed the spider to catch the fly.\n" +
      "I don't know why she swallowed the fly. " +
      "Perhaps she'll die.\n";

    expect(song.verse(4)).toEqual(expected);
  });

  it('dog', function () {
    var expected = "I know an old lady who swallowed a dog.\n" +
      "What a hog, to swallow a dog!\n" +
      "She swallowed the dog to catch the cat.\n" +
      "She swallowed the cat to catch the bird.\n" +
      "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" +
      "She swallowed the spider to catch the fly.\n" +
      "I don't know why she swallowed the fly. " +
      "Perhaps she'll die.\n";

    expect(song.verse(5)).toEqual(expected);
  });

  it('goat', function () {
    var expected = "I know an old lady who swallowed a goat.\n" +
      "Just opened her throat and swallowed a goat!\n" +
      "She swallowed the goat to catch the dog.\n" +
      "She swallowed the dog to catch the cat.\n" +
      "She swallowed the cat to catch the bird.\n" +
      "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" +
      "She swallowed the spider to catch the fly.\n" +
      "I don't know why she swallowed the fly. " +
      "Perhaps she'll die.\n";

    expect(song.verse(6)).toEqual(expected);
  });

  it('cow', function () {
    var expected = "I know an old lady who swallowed a cow.\n" +
      "I don't know how she swallowed a cow!\n" +
      "She swallowed the cow to catch the goat.\n" +
      "She swallowed the goat to catch the dog.\n" +
      "She swallowed the dog to catch the cat.\n" +
      "She swallowed the cat to catch the bird.\n" +
      "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" +
      "She swallowed the spider to catch the fly.\n" +
      "I don't know why she swallowed the fly. " +
      "Perhaps she'll die.\n";

    expect(song.verse(7)).toEqual(expected);
  });

  it('horse', function () {
    var expected = "I know an old lady who swallowed a horse.\n" + "She's dead, of course!\n";

    expect(song.verse(8)).toEqual(expected);
  });

  it('multiple verses', function () {
    var expected = "";

    expected += "I know an old lady who swallowed a fly.\nI don't know why she swallowed the fly. Perhaps she'll die.\n\n";
    expected += "I know an old lady who swallowed a spider.\nIt wriggled and jiggled and tickled inside her.\n" +
      "She swallowed the spider to catch the fly.\n" +
      "I don't know why she swallowed the fly. Perhaps she'll die.\n\n"

    expect(song.verses(1, 2)).toEqual(expected);
  });

  it('the whole song', function () {
    var expected = "";

    expected += "I know an old lady who swallowed a fly.\nI don't know why she swallowed the fly. Perhaps she'll die.\n\n";
    expected += "I know an old lady who swallowed a spider.\nIt wriggled and jiggled and tickled inside her.\n" +
    "She swallowed the spider to catch the fly.\n" +
    "I don't know why she swallowed the fly. Perhaps she'll die.\n\n"
    expected += "I know an old lady who swallowed a bird.\n" +
    "How absurd to swallow a bird!\n" +
    "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" +
    "She swallowed the spider to catch the fly.\n" +
    "I don't know why she swallowed the fly. Perhaps she'll die.\n\n";
     expected += "I know an old lady who swallowed a cat.\n" +
    "Imagine that, to swallow a cat!\n" +
    "She swallowed the cat to catch the bird.\n" +
    "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" +
    "She swallowed the spider to catch the fly.\n" +
    "I don't know why she swallowed the fly. " +
    "Perhaps she'll die.\n\n";
    expected += "I know an old lady who swallowed a dog.\n" +
    "What a hog, to swallow a dog!\n" +
    "She swallowed the dog to catch the cat.\n" +
    "She swallowed the cat to catch the bird.\n" +
    "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" +
    "She swallowed the spider to catch the fly.\n" +
    "I don't know why she swallowed the fly. " +
    "Perhaps she'll die.\n\n";
    expected += "I know an old lady who swallowed a goat.\n" +
    "Just opened her throat and swallowed a goat!\n" +
    "She swallowed the goat to catch the dog.\n" +
    "She swallowed the dog to catch the cat.\n" +
    "She swallowed the cat to catch the bird.\n" +
    "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" +
    "She swallowed the spider to catch the fly.\n" +
    "I don't know why she swallowed the fly. " +
    "Perhaps she'll die.\n\n";
    expected += "I know an old lady who swallowed a cow.\n" +
    "I don't know how she swallowed a cow!\n" +
    "She swallowed the cow to catch the goat.\n" +
    "She swallowed the goat to catch the dog.\n" +
    "She swallowed the dog to catch the cat.\n" +
    "She swallowed the cat to catch the bird.\n" +
    "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" +
    "She swallowed the spider to catch the fly.\n" +
    "I don't know why she swallowed the fly. " +
    "Perhaps she'll die.\n\n";
    expected += "I know an old lady who swallowed a horse.\n" + "She's dead, of course!\n\n";

    expect(song.verses(1, 8)).toEqual(expected);
  });

});