Dealing with terms and formulaes

[gvegayon]

Dealing with terms should be more general. In the current design, terms in C++ receive a vector. This should change to a list, and more over, using C++ classes:

typedef std::vector< int > v_int;

class term_args;

class ergmito_term {
public:
  ...
  // Calculation
  std::function<void(v_int&, term_args*) fun;
  // Checker
  std::function<void(v_int&, term_args*) check_args;
}

This way terms can be generated with a set of arbitrary arguments. Moreover, this could be ported to a C++ header-only library for computing sufficient statistics on networks (represented as list of source/target).

On the R side, functions with the same name of the term should be defined such that those can be called within R and set up all the requirements.

Formulas need to be more regeneral. Here is a proposed set of steps:

1. Extract the RHS of the formula
2. Match terms by using something like "(edge|ctriad|triad|...)(\(.*\))?"
3. If only the first part matched, then add () and make a call, otherwise make the call.