music = {
  \repeat unfold 8 c8
  c8 \repeat unfold 7 { c[ c] }  c
  \repeat unfold 8 c8
}

\relative c'' {
  <>^\markup { \typewriter Beam.breakable set to \typewriter "#t" }
  \override Beam.breakable = ##t
  \music
}

\relative c'' {
  <>^\markup { \typewriter Beam.breakable not set }
  \music
}

\paper {
  line-width = 100\mm
  tagline = ##f
}