DB<135> sub ctx {print wantarray ? 'list' : defined wantarray ? 'scalar' : 'void'; return}

  DB<136> @a= do {ctx();ctx()}   # list-do
voidlist
  DB<137> do {ctx();ctx()};1     # void-do
voidvoid
  DB<138> $a=do {ctx();ctx()}    # scalar-do
voidscalar

  DB<140> scalar (ctx(),ctx())   # scalar comma
voidscalar
  DB<141> 1 while (ctx(),ctx())  # scalar (boolean) comma
voidscalar