Enums
Captures the output from a steppable function. In the future, this should become an associated type.
Traits
A trait capturing the essence of a steppable computation. We can
take a single step on a computation with a given state S which
either produces an updated state S or a terminal state T.
A trait capturing the essence of a steppable computation over
mutable state. We can take a single step on a computation with
a given state S which either produces an updated state S or a
terminal state T.