Lightweight library for parsing arbitrary anlytical function forms

[mattwthompson]

GMSO uses sympy, a stable and popular symbolic math library, to parse analytical expressions of arbitrary functional forms (i.e. everything between non-LJ non-bonded terms or whatever wild torsion form you feel like drawing up). I think GMSO has worked well with it, but it is a fairly heavy dependency to pull in and it is worth looking into alternatives.

Functionality I think we care about

• Parsing arbitrary analytical expressions into some useful internal representation
• Comparing expressions and individual variables to ensure an expression is fully described with parameters
• Equality-like comparisons between expressions for interfaces (see how it is done in GMSO here)

[mattwthompson]

Sire has a similar solution build-in (referred to as "general algebra" in their paper https://joss.theoj.org/papers/10.21105/joss.01831)

[mattwthompson]

No longer a priority