Re: rearrange music flow

[Antanas Budriūnas]

Sorry, I feel myself not yet ready for "froging" because such simple task makes me trouble.
Slightly modifying Carl's function I tend to include lyrics into parallel staves function. 
I can't understand what should be in place of 'ly:xxx?' as variable's type?

parallelStaffs = #(define-music-function (parser location firstStaff firstLyrics
secondStaff secondLyrics)
                     (ly:music? ly:xxx? ly:music? ly:xxx?)
#{ <<

    \context Staff = "StaffOne"  {
      \context Voice = "VoiceOne" {

        $firstStaff

      }

          \context Lyrics = "LyricsOne" \lyricmode {
             \set associatedVoice = #"VoiceOne"

             $firstLyrics
         }

    }
    \context Staff = "StaffTwo" {
      \context Voice = "VoiceTwo" {

        $secondStaff
      }

          \context Lyrics = "LyricsTwo" \lyricmode {
             \set associatedVoice = #"VoiceTwo"

             $secondLyrics
         }

    }
 >>
#})

intro = \parallelStaffs
 {c''4 c''}

{ ala ala }

 {c'4 c'}

{ alb alb } 

verse = \parallelStaffs
 {d''4 d''}

{ bla bla }

 {d'4 d'}

{ blb blb }

\score {
 {
   \intro
   \verse
  }
}

Thanks for tips.

Antanas Budriūnas