Thing to Do in the future

After mruby 3.0

multi-precision integer
NAN_BOXING: Allow MRB_INT64 along with NaN boxing
keyword arguments à la Ruby3.0 (update OP_SEND)
parser and code generator independent from mrb_state (picoruby?)
variable sized AST node

Things to do (Things that are not done yet)

begin ... end while cond to behave as CRuby
special variables ($1,$2..)