Walk the ops with a simple REPL. An interactive B::Concise.
Walk in main or exec order? main per default.

Inspect OP and SV/AV/HV/CV/GV vars and more by B::Concise et al methods.

Plan:

h    help
n    next op
s    step into kids
sib  step to next sibling
c<n> continue until state n (support also cop line number?)
b<n> break at state n (support also cop line number?)
u    up
o    B::Concise current op
f    B::Flags current op
d    B::Debug current op
a<n>  n-th argument var (by src name?)
sv<n> n-th global SV var (by src name?) (is a PV or IV a seperate SV here or 
     should we alias them?)
l<n> n-th lexvar on the current pad
t<var> typecheck var via Devel::TypeCheck

line => state

TODO: 
inspect op args (how many, which type?)

inspect var flags. What is a var? global, my (pad), local (temp), op args
  How to denote those vars? sv1, pv1, av1, av2, cv1, gv2, ... for global vars

Convenience:
.. skip BEGIN blocks
.. skip initial use modules