Whenever the distinguished Broadway songwriter Stephen Sondheim is asked what comes first, the music or the lyrics, he always answers, "the book." All theater lovers know that Irving Berlin wrote the score for Annie Get Your Gun, that Rodgers and Hammerstein did the songs for The Sound of Music, and that Frank Loesser penned the musical numbers for Guys and Dolls. But who wrote the librettos for these Broadway classics? The libretto...