list of classes
{
  bpf [<num: time> <num: value> ...] - break point function
  dict [<any: key> <any: value> ...] - dictionary of arbitrary key/value pairs
  expr <sym: expression description> - expression
  fmat <num: # of rows> <num: # of columns> [<num: init values> ...] - matrix of floats
  fvec <num: vector size> [<num: init values> ...] | <fmat: base matrix> <'vec'|'col'|'row'|'diag'|'unwrap': type> <num: onset> - float vector or reference to an fmat row, column, diagonal or all (unwrapped) elements
  mat <num: # of rows> <num: # of columns> [<any: init values> ...] - matrix of arbitrary values
  midi <'note'|'poly'|'ctl'|'prg'|'touch'|'bend'|'sysex'|'mtc'|'spos'|'ssel'|'rt': type> [<num: MIDI bytes> ...] - MIDI message
  schema [<sym|tuple: elements> ...] - enumeration of names or pairs of names and default values (as tuples)
  scoob <'note'|'interval'|'rest'|'trill'|'unvoiced': type> <num: pitch> <num: interval> <num: duration> [<sym: opt. prop. name> <any: opt. prop. value> ...] - score object
  sequence [<sym: type (class name)>] - sequence of time tagged events
  track [<sym: type (class name)>] - sequence with metrics and tempo
  tuple [<any: value> ...] - immutable array of any values
}