説明
『I Know an Old Lady Who Swallowed a Fly』という歌の歌詞を生成しましょう。
歌詞をそのままコピー＆ペーストしたり、ファイルから読み込んだりしてもかまいませんが、アルゴリズム的に解いてみると、この問題はずっと面白くなります。
これは、作者不明の累積歌です。
よく知られている数あるバリエーションのうちのひとつです。
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!
Factor固有の内容
次のワードを実装します：
food-chain ( start end -- lines )
startとendは節番号（ハエが1、ウマが8まで）で、両端を含みます。要求された節を文字列のシーケンスとして返します。曲の1行につき1つの文字列です。
複数の節が要求された場合は、連続する節を1つの空文字列（""）で区切ります。こうすることで、節と節の間には空行が入って表示されます。最後の節のあとに空行は続きません。
1 2 food-chain .
! => {
! "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."
! }
