1 # Things to Do in the future
5 - parser and code generator independent from `mrb_state` (picoruby?)
6 - variable sized AST node
8 - more peephole optimization (if possible)
10 # Things to do (Things we need to consider)
12 - `begin ... end while cond` to behave as CRuby
13 - special variables ($1,$2..)