\version "2.18.2"

#(define typewriter '((key default #f  0)
                      (cr default #f -2)
                      (bell default #f 2)))

drumPitchNames.key = #'key
drumPitchNames.cr = #'cr
drumPitchNames.bell = #'bell

% How can I append those bellow to the default list?
% (Instead of replacing the old list)
midiDrumPitches = #`(
                      (key . ,(ly:make-pitch 0 6  FLAT))
                      (cr . ,(ly:make-pitch 1 1 NATURAL))
                      (bell . ,(ly:make-pitch -2 0 DOUBLE-FLAT))
                      )

\header {
  title = \markup {\smallCaps "The Data Typewriter"}
  composer = \markup {\smallCaps "LaJoy Randallson"}
  instrument = \markup {
    \score {
      \new DrumStaff \with {
        \remove "Time_signature_engraver"
        %\remove "Clef_engraver"
        fontSize = -3
        \override StaffSymbol.staff-space = #(magstep -2)
      }
      \new DrumVoice \with {
        \consists "Balloon_engraver"
        \override BalloonTextItem.annotation-balloon = ##f
      }
      \drummode {
        \override Staff.StaffSymbol.line-positions = #'(0)
        \override Staff.BarLine.bar-extent = #'(-2 . 2)
        \set DrumStaff.drumStyleTable = #(alist->hash-table typewriter)
        \balloonLengthOff
        \balloonGrobText #'NoteHead #'(-1 . -1) \markup {\italic \bold "Key click" }
        key8
        \balloonGrobText #'NoteHead #'(-1 . .25) \markup {\italic \bold "Bell" }
        bell4\laissezVibrer
        \balloonGrobText #'NoteHead #'(1.5 . 1) \markup { \italic \bold"Carriage return" }
        cr4->
        \stopStaff
        s
      }
      \layout {indent = 0}
    }
  }
}

percussionI = \drummode {
  \override Staff.StaffSymbol.line-positions = #'(0)
  \override Staff.BarLine.bar-extent = #'(-2 . 2)
  \set DrumStaff.drumPitchTable = #(alist->hash-table midiDrumPitches)
  \set DrumStaff.drumStyleTable = #(alist->hash-table typewriter)
  \override BalloonTextItem.annotation-balloon = ##f

  \tempo 2=130
  \time 2/2

  \balloonGrobText #'NoteHead #'(2 . 2) \markup {
    \smaller \italic \bold "Typewriter key click" }
  key8\f key key key key key key key |
  key key key key key4 key8 key |
  key key key key key key key key |
  \balloonGrobText #'NoteHead #'(-2 . 2) \markup {
    \smaller \italic \bold "Bell" }
  bell4\laissezVibrer r
  \balloonGrobText #'NoteHead #'(3 . -3) \markup {
    \smaller \italic \bold \column {
      "Carriage return"
      \smaller "(UNIX: line feed)"}}
  cr->

  % Bellow is the "test" for normal midi output
  \balloonGrobText #'NoteHead #'(-2 . 3) \markup {
    \smaller \italic \bold "Typical snare" }
  sn |

}

percussionIPart =
\new DrumStaff
\new DrumVoice \with {
  \consists "Balloon_engraver"
} \percussionI



\score {
  \percussionIPart
  \layout {}
  \midi {}
}