Removing dependency and use of parametric programs about grove HOT 3 CLOSED

@willzeng
I looked through the code and I think the problem has an upside and a downside.

• On the upside: VQE only has functions of the form f: list -> PyQuil.function which is exactly what we want. Hence there is no direct dependency on pyquil.ParametricFunction

• On the other hand pyqaoa.qaoa has a dependency on various parts od pyquil.Paulis, which hence indirectly introduces a dependency to ParametricFunctions through Paulis.exponential_map that returns a decorated program.

As far as I can tell from a first pass Paulis.exponential_map is the only point where we induce ParametricFunction into grove. There is no direct import of ParametricFunction in the grove library (except some ipynb) and the name of parametric_state_evolve is misleading. In this light it might be worthwhile to try and refactor Paulis to purge the dependency. What's our thought?

cc @ncrubin as he wrote most of qaoa.py according to the git annotate.

from grove.

Yep that's correct @jotterbach. As part of this issue exponential_map should be changed to return a python function rather than a parametric program. I also agree that changed should be made to make function behavior clear if their output type has changed

from grove.

this was fixed by #32

from grove.