 There really was a Hamlet musical. And it really was a flop. It was  called "Rockabye Hamlet", starring Larry Marshall (I) (qv) as  Hamlet and Beverly DAngelo (qv) as Ophelia.  Cliff Jones (II) (qv) wrote book, lyrics and music;  Gower Champion (qv) directed and choreographed. It lasted for  seven performances at the Minskoff Theatre in 1976.