content: print invalid
  print true
  print false
  
  print 5   ' a 32-bit integer
  print 6%  ' a 32-bit expicit integer
  print 7&  ' a 64-bit integer
  print 3e1 ' a float
  ? 4d1     ' a double
  ?"hello"  ' a string
  
  print &hff ' 255, in hex