Defining pitches in variables

[address@hidden]

Hey all,

I am writing a percussion part that shadows a vocal part one-on-one and I'd 
like to do something like:

vocal = #(define-music-function (parser location) ()
#{
  foo = { a' }
  bar = { a'' }
#})

percu = #(define-music-function (parser location) ()
#{
  foo = { snare }
  bar = { tomh }
#})

music = {
foo8 bar8 foo8 bar8
}

<<
\new Staff { \vocal \music }
\new DrumStaff { \percu \music }
>>

Obviously the above doesn't get the desired effect but I hope people get the 
idea.  Is there a way to do this?

Cheers,
MS