Sondheim and Lapine have collaborated on several musicals, including "Sunday in the Park With George" and "Into the Woods, " both full of popular songs and plentiful humor.
Anastasio, who was obsessed with "West Side Story" as a kid, joked that he used to love poring over old photos of Stephen Sondheim and Leonard Bernstein lounging on couches as they collaborated on last-minute songs.