-- reversible polyphonic 
-- pattern instrument demo
--
-- 0.2.0 @andrew
--
-- grid: play notes
-- K2: record pattern
-- K3: play/pause pattern
-- E2: set direction

a reduction of ash/earthsea to demo a few proposed feature additions for lib/pattern_time:

• pattern:set_reverse()
• pattern:resume()
• a callback system, mirroring + extending lib/reflection:
  • start_callback
  • step_callback
  • end_of_loop_callback
  • end_of_rec_callback
  • end_callback
  • start_of_record_callback
  • clear_callback

compared to ash/earthsea, the demo'd pattern logic uses a simple immutable state system with a few advantages:

• ability to reverse playback direction
• notes held at the end of a recording are not stuck
• notes held at the beginning of a recording are included in the pattern

a possible con is performance – a new table copy is created for every grid input