Two generations of "Saturday Night Live" funnymen will soon collide when Steve Martin's "Shopgirl" hits theaters with Jimmy Fallon in a lead role.

The messy-haired "SNL" player is joining "SNL" veteran Martin and Claire Danes ("The Mod Squad") in the big-screen adaptation of Martin's popular novella, according to spokespeople for both actors. "Shopgirl" tells the story of a Neiman Marcus clerk torn between a well-off divorced man and a starving-artist musician.

In addition to writing the book and starring in the movie, Martin wrote the script and will serve as executive producer. Lakeshore Entertainment will also produce.

"Several producers came to me and wanted to turn [the book] into a movie," Martin joked while hosting the Academy Awards last year. "And I said, 'Look, if you think you're going to take this book and change it around and Hollywood-ize it and give it a new ending ... well, that's going to cost you.' "

Production is scheduled to begin on "Shopgirl" in January.

Fallon will next appear in Woody Allen's "Anything Else." Danes recently wrapped shooting on "Terminator 3," due next year.